Archive for the ‘Female Genetics’ Category
Triple X syndrome, also known as trisomy X and 47 XXX, is characterized by the presence of an extra X chromosome in each cell of a female. Those affected are often taller than average. Usually there is no other physical differences and normal fertility. Occasionally there are learning difficulties, decreased muscle tone, seizures, or kidney problems.
Triple X is due to a random event. Triple X can result either during the division of the mother’s reproductive cells or during division of cells during early development. It is not typically inherited from one generation to the next. A form where only a percentage of the body cells contain XXX can also occur. Diagnosis is by chromosomal analysis.
Treatment may include speech therapy, physical therapy, and counseling. It occurs in about one in every 1,000 female births. It is estimated that 90% of those affected are not diagnosed as they either have no or only few symptoms. It was first identified in 1959.
Because the vast majority of triple X females are never diagnosed, it may be very difficult to make generalizations about the effects of this syndrome. The samples that were studied were small and may be nonrepresentative. Because of the lyonization, inactivation, and formation of Barr bodies in all female cells, only one X chromosome is active at any time. Thus, triple X syndrome most often has only mild effects or has no effects. The symptoms vary from person to person, with some women being more affected than others.
Symptoms may include tall stature, vertical skin folds that may cover the inner corners of the eyes (epicanthal folds), poor muscle tone, and a curve in the 5th finger towards the 4th. There may also be a small head (microcephaly). There are seldom any observable physical anomalies in triple X females, other than being taller than average.
Poor coordination may be present. Those affected appear to have higher rates of scoliosis.
Epicanthal folds and increased distance between the eyes in 2-year-old girl with trisomy X
The type of finger curvature frequently seen in triple X syndrome
Females with triple X syndrome often have delayed language development. On average those affected have IQs that are 20 points lower. Poor self-esteem, anxiety, and depression are also common.
Triple X syndrome is not inherited, but usually, occurs as an event during the formation of reproductive cells (ovum and sperm). An error in cell division called nondisjunction can result in reproductive cells with additional chromosomes. For example, an oocyte or sperm cell may gain an extra copy of the X chromosome as a result of the non-disjunction. If one of these cells contributes to the genetic makeup of a child, the child will have an extra X chromosome in each of her cells. In some cases, trisomy X occurs during cell division in early embryonic development.
Some females with triple X syndrome have an extra X chromosome in only some of their cells. These cases are called 46,XX/47,XXX mosaics.
The vast majority of triple X women are never diagnosed, unless they undergo tests for other medical reasons later in life. Triple X can be diagnosed by a blood test which is able to look at a persons chromosomes (karyotype). Abnormalities on the electroencephalography may be present.
Triple X syndrome can be diagnosed prenatally through amniocentesis or chorionic villus sampling. In Denmark, between 1970 and 1984, 76% of the prenatally diagnosed fetuses with triple-X were aborted. Between 1985-1987, this figure dropped to 56%. With improved information, the number of abortions diminished. In the Netherlands, between 1991 and 2000, 33% (18/54) of the couples that were confronted with a prenatal diagnosis of 47, XXX elected to abort. If balanced information is provided to prospective parents, prenatally, the incidence of voluntary termination (abortion) is reduced.
A stable home environment can improve some of the symptoms.
Triple X syndrome occurs in around 1 in 1,000 girls. On average, five to ten girls with triple X syndrome are born in the United States each day.
The first published report of a woman with a 47,XXX karyotype was by Patricia A. Jacobs, et al. at Western General Hospital in Edinburgh, Scotland, in 1959. It was found in a 35year-old, 5ft. 9 in. (176cm) tall, 128lb. (58.2kg) woman who had premature ovarian failure at age 19; her mother was age 41 and her father was 40 at the time of her conception. Jacobs, et al. called the 47,XXX woman a “superfemale”, a term which was immediately criticized, did not gain acceptance, and was based on the incorrect assumption that the sex-determination system in mammals was the same as in the fruit fly Drosophila. British pathologist and geneticist Bernard Lennox, the principal consultant on medical terms for the Oxford English Dictionary, suggested the term “XXX syndrome”.
Read more here:
Triple X syndrome – Wikipedia
The XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects (Drosophila), and some plants (Ginkgo). In this system, the sex of an individual is determined by a pair of sex chromosomes (gonosomes). Females have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Males have two distinct sex chromosomes (XY), and are called the heterogametic sex.
This system is in contrast with the ZW sex-determination system found in birds, some insects, many reptiles, and other animals, in which the heterogametic sex is female.
A temperature-dependent sex determination system is found in some reptiles.
All animals have a set of DNA coding for genes present on chromosomes. In humans, most mammals, and some other species, two of the chromosomes, called the X chromosome and Y chromosome, code for sex. In these species, one or more genes are present on their Y-chromosome that determine maleness. In this process, an X chromosome and a Y chromosome act to determine the sex of offspring, often due to genes located on the Y chromosome that code for maleness. Offspring have two sex chromosomes: an offspring with two X chromosomes will develop female characteristics, and an offspring with an X and a Y chromosome will develop male characteristics.
In humans, half of spermatozoons carry X chromosome and the other half Y chromosome. A single gene (SRY) present on the Y chromosome acts as a signal to set the developmental pathway towards maleness. Presence of this gene starts off the process of virilization. This and other factors result in the sex differences in humans. The cells in females, with two X chromosomes, undergo X-inactivation, in which one of the two X chromosomes is inactivated. The inactivated X chromosome remains within a cell as a Barr body.
Humans, as well as some other organisms, can have a chromosomal arrangement that is contrary to their phenotypic sex; for example, XX males or XY females (see androgen insensitivity syndrome). Additionally, an abnormal number of sex chromosomes (aneuploidy) may be present, such as Turner’s syndrome, in which a single X chromosome is present, and Klinefelter’s syndrome, in which two X chromosomes and a Y chromosome are present, XYY syndrome and XXYY syndrome. Other less common chromosomal arrangements include: triple X syndrome, 48, XXXX, and 49, XXXXX.
In most mammals, sex is determined by presence of Y. “Female” is the default sex; due to the absence of the Y. In the 1930s, Alfred Jost determined that the presence of testosterone was required for Wolffian duct development in the male rabbit.
SRY is a sex-determining gene on the Y chromosome in the therians (placental mammals and marsupials). Non-human mammals use several genes on the Y-chromosome. Not all male-specific genes are located on the Y-chromosome. Other species (including most Drosophila species) use the presence of two X chromosomes to determine femaleness. One X chromosome gives putative maleness. The presence of Y-chromosome genes is required for normal male development.
Birds and many insects have a similar system of sex determination (ZW sex-determination system), in which it is the females that are heterogametic (ZW), while males are homogametic (ZZ).
Many insects of the order Hymenoptera instead have a system (the haplo-diploid sex-determination system), where the males are haploid individuals (which have just one chromosome of each type), while the females are diploid (with chromosomes appearing in pairs). Some other insects have the X0 sex-determination system, where just one chromosome type appears in pairs for the female but alone in the males, while all other chromosomes appear in pairs in both sexes.
For a long time, biologists believed that the female form was the default template for the mammalian fetuses of both sexes. After the discovery of the testis-determining gene SRY, many scientists shifted to the theory that the genetic mechanism that determines a fetus to develop into a male form was initiated by the SRY gene, which was thought to be responsible for the production of testosterone and its overall effects on body and brain development. This perspective still shared the classical way of thinking; that in order to produce two sexes, nature has developed a default female pathway and an active pathway by which male genes would initiate the process of determining a male sex, as something that is developed in addition to and based on the default female form. This view is no longer considered accurate by most scientists who study the genetics of sex. In an interview for the Rediscovering Biology website, researcher Eric Vilain described how the paradigm changed since the discovery of the SRY gene:
For a long time we thought that SRY would activate a cascade of male genes. It turns out that the sex determination pathway is probably more complicated and SRY may in fact inhibit some anti-male genes.
The idea is instead of having a simplistic mechanism by which you have pro-male genes going all the way to make a male, in fact there is a solid balance between pro-male genes and anti-male genes and if there is a little too much of anti-male genes, there may be a female born and if there is a little too much of pro-male genes then there will be a male born.
We [are] entering this new era in molecular biology of sex determination where it’s a more subtle dosage of genes, some pro-males, some pro-females, some anti-males, some anti-females that all interplay with each other rather than a simple linear pathway of genes going one after the other, which makes it very fascinating but very complicated to study.
In mammals, including humans, the SRY gene is responsible with triggering the development of non-differentiated gonads into testes, rather than ovaries. However, there are cases in which testes can develop in the absence of an SRY gene (see sex reversal). In these cases, the SOX9 gene, involved in the development of testes, can induce their development without the aid of SRY. In the absence of SRY and SOX9, no testes can develop and the path is clear for the development of ovaries. Even so, the absence of the SRY gene or the silencing of the SOX9 gene are not enough to trigger sexual differentiation of a fetus in the female direction. A recent finding indicates that ovary development and maintenance is an active process, regulated by the expression of a “pro-female” gene, FOXL2. In an interview for the TimesOnline edition, study co-author Robin Lovell-Badge explained the significance of the discovery:
We take it for granted that we maintain the sex we are born with, including whether we have testes or ovaries. But this work shows that the activity of a single gene, FOXL2, is all that prevents adult ovary cells turning into cells found in testes.
Looking into the genetic determinants of human sex can have wide-ranging consequences. Scientists have been studying different sex determination systems in fruit flies and animal models to attempt an understanding of how the genetics of sexual differentiation can influence biological processes like reproduction, ageing and disease.
In humans and many other species of animals, the father determines the sex of the child. In the XY sex-determination system, the female-provided ovum contributes an X chromosome and the male-provided sperm contributes either an X chromosome or a Y chromosome, resulting in female (XX) or male (XY) offspring, respectively.
Hormone levels in the male parent affect the sex ratio of sperm in humans. Maternal influences also impact which sperm are more likely to achieve conception.
Human ova, like those of other mammals, are covered with a thick translucent layer called the zona pellucida, which the sperm must penetrate to fertilize the egg. Once viewed simply as an impediment to fertilization, recent research indicates the zona pellucida may instead function as a sophisticated biological security system that chemically controls the entry of the sperm into the egg and protects the fertilized egg from additional sperm.
Recent research indicates that human ova may produce a chemical which appears to attract sperm and influence their swimming motion. However, not all sperm are positively impacted; some appear to remain uninfluenced and some actually move away from the egg.
Maternal influences may also be possible that affect sex determination in such a way as to produce fraternal twins equally weighted between one male and one female.
The time at which insemination occurs during the oestrus cycle has been found to affect the sex ratio of the offspring of humans, cattle, hamsters, and other mammals. Hormonal and pH conditions within the female reproductive tract vary with time, and this affects the sex ratio of the sperm that reach the egg.
Sex-specific mortality of embryos also occurs.
Since ancient times, people have believed that the sex of an infant is determined by how much heat a man’s sperm had during insemination. Aristotle wrote that:
…the semen of the male differs from the corresponding secretion of the female in that it contains a principle within itself of such a kind as to set up movements also in the embryo and to concoct thoroughly the ultimate nourishment, whereas the secretion of the female contains material alone. If, then, the male element prevails it draws the female element into itself, but if it is prevailed over it changes into the opposite or is destroyed.
Aristotle claimed that the male principle was the driver behind sex determination, such that if the male principle was insufficiently expressed during reproduction, the fetus would develop as a female.
Nettie Stevens and Edmund Beecher Wilson are credited with independently discovering, in 1905, the chromosomal XY sex-determination system, i.e. the fact that males have XY sex chromosomes and females have XX sex chromosomes.
The first clues to the existence of a factor that determines the development of testis in mammals came from experiments carried out by Alfred Jost, who castrated embryonic rabbits in utero and noticed that they all developed as female.
In 1959, C. E. Ford and his team, in the wake of Jost’s experiments, discovered that the Y chromosome was needed for a fetus to develop as male when they examined patients with Turner’s syndrome, who grew up as phenotypic females, and found them to be X0 (hemizygous for X and no Y). At the same time, Jacob & Strong described a case of a patient with Klinefelter syndrome (XXY), which implicated the presence of a Y chromosome in development of maleness.
All these observations lead to a consensus that a dominant gene that determines testis development (TDF) must exist on the human Y chromosome. The search for this testis-determining factor (TDF) led a team of scientists in 1990 to discover a region of the Y chromosome that is necessary for the male sex determination, which was named SRY (sex-determining region of the Y chromosome).
XY sex-determination system – Wikipedia
Venus de Milo at the Louvre has been described as a “classical vision of beauty”. However, one expert claimed her “almost matronly representation” was meant to convey an “impressive appearance” rather than “ideal female beauty”.
Physical attractiveness is the degree to which a person’s physical features are considered aesthetically pleasing or beautiful. The term often implies sexual attractiveness or desirability, but can also be distinct from either. There are many factors which influence one person’s attraction to another, with physical aspects being one of them. Physical attraction itself includes universal perceptions common to all human cultures, as well as aspects that are culturally and socially dependent, along with individual subjective preferences.
In many cases, humans subconsciously attribute positive characteristics, such as intelligence and honesty, to physically attractive people. From research done in the United States and United Kingdom, it was found that the association between intelligence and physical attractiveness is stronger among men than among women.Evolutionary psychologists have tried to answer why individuals who are more physically attractive should also, on average, be more intelligent, and have put forward the notion that both general intelligence and physical attractiveness may be indicators of underlying genetic fitness. A person’s physical characteristics can signal cues to fertility and health. Attending to these factors increases reproductive success, furthering the representation of one’s genes in the population.
Men, on average, tend to be attracted to women who are shorter than they are, have a youthful appearance, and exhibit features such as a symmetrical face, full breasts, full lips, and a low waist-hip ratio. Women, on average, tend to be attracted to men who are taller than they are, display a high degree of facial symmetry, masculine facial dimorphism, and who have broad shoulders, a relatively narrow waist, and a V-shaped torso.
Generally, physical attractiveness can be viewed from a number of perspectives; with universal perceptions being common to all human cultures, cultural and social aspects, and individual subjective preferences. The perception of attractiveness can have a significant effect on how people are judged in terms of employment or social opportunities, friendship, sexual behavior, and marriage.
Some physical features are attractive in both men and women, particularly bodily and facial symmetry, although one contrary report suggests that “absolute flawlessness” with perfect symmetry can be “disturbing”. Symmetry may be evolutionarily beneficial as a sign of health because asymmetry “signals past illness or injury”. One study suggested people were able to “gauge beauty at a subliminal level” by seeing only a glimpse of a picture for one-hundredth of a second. Other important factors include youthfulness, skin clarity and smoothness of skin; and “vivid color” in the eyes and hair. However, there are numerous differences based on gender.
A 1921 study, of the reports of college students regarding those traits in individuals which make for attractiveness and repulsiveness argued that static traits, such as beauty or ugliness of features, hold a position subordinate to groups of physical elements like expressive behavior, affectionate disposition, grace of manner, aristocratic bearing, social accomplishments, and personal habits.
Grammer and colleagues have identified eight “pillars” of beauty: youthfulness, symmetry, averageness, sex-hormone markers, body odor, motion, skin complexion and hair texture.
Most studies of the brain activations associated with the perception of attractiveness show photographs of faces to their participants and let them or a comparable group of people rate the attractiveness of these faces. Such studies consistently find that activity in certain parts of the orbitofrontal cortex increases with increasing attractiveness of faces. This neural response has been interpreted as a reaction on the rewarding nature of attractiveness, as similar increases in activation in the medial orbitofrontal cortex can be seen in response to smiling faces and to statements of morally good actions. While most of these studies have not assessed participants of both genders or homosexual individuals, evidence from one study including male and female hetero- and homosexual individuals indicate that some of the aforementioned increases in brain activity are restricted to images of faces of the gender participants feel sexually attracted to.
With regard to brain activation related to the perception of attractive bodies, one study with heterosexual participants suggests that activity in the nucleus accumbens and the anterior cingulate cortex increases with increasing attractiveness. The same study finds that for faces and bodies alike, the medial part of the orbitofrontal cortex responds with greater activity to both very attractive and very unattractive pictures.
Women, on average, tend to be more attracted to men who have a relatively narrow waist, a V-shaped torso, and broad shoulders. Women also tend to be more attracted to men who are taller than they are, and display a high degree of facial symmetry, as well as relatively masculine facial dimorphism. With regard to male-male-attractiveness, one source reports that the most important factor that attracts gay men to other males is the man’s physical attractiveness.
Studies have shown that ovulating heterosexual women prefer faces with masculine traits associated with increased exposure to testosterone during key developmental stages, such as a broad forehead, relatively longer lower face, prominent chin and brow, chiseled jaw and defined cheekbones. The degree of differences between male and female anatomical traits is called sexual dimorphism. Female respondents in the follicular phase of their menstrual cycle were significantly more likely to choose a masculine face than those in menses and luteal phases, (or in those taking hormonal contraception). This distinction supports the sexy son hypothesis, which posits that it is evolutionarily advantageous for women to select potential fathers who are more genetically attractive, rather than the best caregivers. However, women’s likeliness to exert effort to view male faces does not seem to depend on their masculinity, but to a general increase with women’s testosterone levels.
It is suggested that the masculinity of facial features is a reliable indication of good health, or, alternatively, that masculine-looking males are more likely to achieve high status. However, the correlation between attractive facial features and health has been questioned. Sociocultural factors, such as self-perceived attractiveness, status in a relationship and degree of gender-conformity, have been reported to play a role in female preferences for male faces. Studies have found that women who perceive themselves as physically attractive are more likely to choose men with masculine facial dimorphism, than are women who perceive themselves as physically unattractive. In men, facial masculinity significantly correlates with facial symmetryit has been suggested that both are signals of developmental stability and genetic health. One study called into question the importance of facial masculinity in physical attractiveness in men arguing that when perceived health, which is factored into facial masculinity, is discounted it makes little difference in physical attractiveness. In a cross-country study involving 4,794 women in their early twenties, a difference was found in women’s average “masculinity preference” between countries.
A study found that the same genetic factors cause facial masculinity in both males and females such that a male with a more masculine face would likely have a sister with a more masculine face due to the siblings having shared genes. The study also found that, although female faces that were more feminine were judged to be more attractive, there was no association between male facial masculinity and male facial attractiveness for female judges. With these findings, the study reasoned that if a woman were to reproduce with a man with a more masculine face, then her daughters would also inherit a more masculine face, making the daughters less attractive. The study concluded that there must be other factors that advantage the genetics for masculine male faces to offset their reproductive disadvantage in terms of “health”, “fertility” and “facial attractiveness” when the same genetics are present in females. The study reasoned that the “selective advantage” for masculine male faces must “have (or had)” been due to some factor that is not directly tied to female perceptions of male facial attractiveness.
In a study of 447 gay men in China, researchers said that tops preferred feminized male faces, bottoms preferred masculinized male faces and versatiles had no preference for either feminized or masculinized male faces.
In pre-modern Chinese literature, the ideal man in caizi jiaren romances was said to have “rosy lips, sparkling white teeth” and a “jasper-like face” (Chinese: ).
In Middle English literature, a beautiful man should have a long, broad and strong face.
A study that used Chinese, Malay and Indian judges said that Chinese men with orthognathism where the mouth is flat and in-line with the rest of the face were judged to be the most attractive and Chinese men with a protruding mandible where the jaw projects outward were judged to be the least attractive.
Symmetrical faces and bodies may be signs of good inheritance to women of child-bearing age seeking to create healthy offspring. Studies suggest women are less attracted to men with asymmetrical faces, and symmetrical faces correlate with long term mental performance and are an indication that a man has experienced “fewer genetic and environmental disturbances such as diseases, toxins, malnutrition or genetic mutations” while growing. Since achieving symmetry is a difficult task during human growth, requiring billions of cell reproductions while maintaining a parallel structure, achieving symmetry is a visible signal of genetic health.
Studies have also suggested that women at peak fertility were more likely to fantasize about men with greater facial symmetry, and other studies have found that male symmetry was the only factor that could significantly predict the likelihood of a woman experiencing orgasm during sex. Women with partners possessing greater symmetry reported significantly more copulatory female orgasms than were reported by women with partners possessing low symmetry, even with many potential confounding variables controlled. This finding has been found to hold across different cultures. It has been argued that masculine facial dimorphism (in men) and symmetry in faces are signals advertising genetic quality in potential mates. Low facial and body fluctuating asymmetry may indicate good health and intelligence, which are desirable features. Studies have found that women who perceive themselves as being more physically attractive are more likely to favor men with a higher degree of facial symmetry, than are women who perceive themselves as being less physically attractive. It has been found that symmetrical men (and women) have a tendency to begin to have sexual intercourse at an earlier age, to have more sexual partners, and to have more one-night stands. They are also more likely to be prone to infidelity. A study of quarterbacks in the American National Football League found a positive correlation between facial symmetry and salaries.
Double-blind studies found that women prefer the scent of men who are rated as facially attractive. For example, both males and females were more attracted to the natural scent of individuals who had been rated by consensus as facially attractive. Additionally, it has also been shown that women have a preference for the scent of men with more symmetrical faces, and that women’s preference for the scent of more symmetrical men is strongest during the most fertile period of their menstrual cycle. Within the set of normally cycling women, individual women’s preference for the scent of men with high facial symmetry correlated with their probability of conception.
Studies have explored the genetic basis behind such issues as facial symmetry and body scent and how they influence physical attraction. In one study in which women wore men’s T-shirts, researchers found that women were more attracted to the bodily scents in shirts of men who had a different type of gene section within the DNA called Major histocompatibility complex (MHC). MHC is a large gene area within the DNA of vertebrates which encodes proteins dealing with the immune system and which influences individual bodily odors. One hypothesis is that humans are naturally attracted by the sense of smell and taste to others with dissimilar MHC sections, perhaps to avoid subsequent inbreeding while increasing the genetic diversity of offspring. Further, there are studies showing that women’s natural attraction for men with dissimilar immune profiles can be distorted with use of birth control pills. Other research findings involving the genetic foundations of attraction suggest that MHC heterozygosity positively correlates with male facial attractiveness. Women judge the faces of men who are heterozygous at all three MHC loci to be more attractive than the faces of men who are homozygous at one or more of these loci. Additionally, a second experiment with genotyped women raters, found these preferences were independent of the degree of MHC similarity between the men and the female rater. With MHC heterozygosity independently seen as a genetic advantage, the results suggest that facial attractiveness in men may be a measure of genetic quality.
A 2010 OkCupid study on 200,000 of its male and female dating site users found that women are, except those during their early to mid-twenties, open to relationships with both somewhat older and somewhat younger men; they have a larger potential dating pool than men until age 26. At age 20, women, in a “dramatic change”, begin sending private messages to significantly older men. At age 29 they become “even more open to older men”. Male desirability to women peaks in the late 20s and does not fall below the average for all men until 36. Other research indicates that women, irrespective of their own age, are attracted to men who are the same age or older.
For the Romans especially, “beardlessness” and “smooth young bodies” were considered beautiful to both men and women. For Greek and Roman men, the most desirable traits of boys were their “youth” and “hairlessness”. Pubescent boys were considered a socially appropriate object of male desire, while post-pubescent boys were considered to be “” or “past the prime”. This was largely in the context of pederasty (adult male interest in adolescent boys). Today, men and women’s attitudes towards male beauty has changed. For example, body hair on men may even be preferred (see below).
A 1984 study said that gay men tend to prefer gay men of the same age as ideal partners, but there was a statistically significant effect (p
The physique of a slim waist, broad shoulders and muscular chest are often found to be attractive to females. Further research has shown that, when choosing a mate, the traits females look for indicate higher social status, such as dominance, resources, and protection. An indicator of health in males (a contributing factor to physical attractiveness) is the android fat distribution pattern which is categorized as more fat distributed on the upper body and abdomen, commonly referred to as the “V shape.” When asked to rate other men, both heterosexual and homosexual men found low waist-to-chest ratios (WCR) to be more attractive on other men, with the gay men showing a preference for lower WCR (more V-shaped) than the straight men.
Other researchers found waist-to-chest ratio the largest determinant of male attractiveness, with body mass index and waist-to-hip ratio not as significant.
Women focus primarily on the ratio waist to chest or more specifically waist to shoulder. This is analogous to the waist to hip ratio (WHR) that men prefer. Key body image for a man in the eyes of a woman would include big shoulders, chest, and upper back, and a slim waist area. Research has additionally shown that college males had a better satisfaction with their body than college females. The research also found that when a college female’s waist to hip ratio went up, their body image satisfaction decreased. The results indicate that males had significantly greater body image satisfaction than did females.
Some research has shown that body weight may have a stronger effect than WHR when it comes to perceiving attractiveness of the opposite sex. It was found that waist to hip ratio played a smaller role in body preference than body weight in regards to both sexes.
Psychologists Viren Swami and Martin J. Tovee compared female preference for male attractiveness cross culturally, between Britain and Malaysia. They found that females placed more importance on WCR (and therefore body shape) in urban areas of Britain and Malaysia, while females in rural areas placed more importance on BMI (therefore weight and body size). Both WCR and BMI are indicative of male status and ability to provide for offspring, as noted by evolutionary theory.
Females have been found to desire males that are normal weight and have the average WHR for a male. Females view these males as attractive and healthy. Males who had the average WHR but were overweight or underweight are not perceived as attractive to females. This suggests that WHR is not a major factor in male attractiveness, but a combination of body weight and a typical male WHR seem to be the most attractive. Research has shown that men who have a higher waist to hip ratio and a higher salary are perceived as more attractive to women.
A 1982 study, found that an abdomen that protrudes was the “least attractive” trait for men.
In Middle English literature, a beautiful man should have a flat abdomen.
Men’s bodies portrayed in magazines marketed to men are more muscular than the men’s bodies portrayed in magazines marketed to women. From this, some have concluded that men perceive a more muscular male body to be ideal, as distinct from a woman’s ideal male, which is less muscular than what men perceive to be ideal. This is due to the within-gender prestige granted by increased muscularity and within-gender competition for increased muscularity. Men perceive the attractiveness of their own musculature by how closely their bodies resemble the “muscle man.” This “muscle man” ideal is characterized by large muscular arms, especially biceps, a large muscular chest that tapers to their waist and broad shoulders.
In a study of stated profile preferences on Match.com, a greater percentage of gay men than lesbians selected their ideal partner’s body type as “Athletic and Toned” as opposed to the other two options of “Average” or “Overweight”.
In pre-modern Chinese literature, such as in The Story of the Western Wing, a type of masculinity called “scholar masculinity” is depicted wherein the “ideal male lover” is “weak, vulnerable, feminine, and pedantic”.
In Middle English literature, a beautiful man should have thick, broad shoulders, a square and muscular chest, a muscular back, strong sides that taper to a small waist, large hands and arms and legs with huge muscles.
A 2006 study, of 25,594 heterosexual men found that men who perceived themselves as having a large penis were more satisfied with their own appearance.
A 2014 study, criticized previous studies based on the fact that they relied on images and used terms such as “small”, “medium”, and “large” when asking for female preference. The new study used 3D models of penises from sizes of 4 inches (10cm) long and 2.5 inches (6.4cm) in circumference to 8.5 inches (22cm) long and 7 inches (18cm) in circumference and let the women “view and handle” them. It was found that women overestimated the actual size of the penises they have experimented with when asked in a follow-up survey. The study concluded that women on average preferred the 6.5-inch (17cm) penis in length both for long-term and for one-time partners. Penises with larger girth were preferred for one-time partners.
Females’ sexual attraction towards males may be determined by the height of the man. Height in men is associated with status or wealth in many cultures (in particular those where malnutrition is common), which is beneficial to women romantically involved with them. One study conducted of women’s personal ads support the existence of this preference; the study found that in ads requesting height in a mate, 80% requested a height of 6 feet (1.83m) or taller. The online dating Website eHarmony only matches women with taller men because of complaints from women matched with shorter men.
Other studies have shown that heterosexual women often prefer men taller than they are rather than a man with above average height. While women usually desire men to be at least the same height as themselves or taller, several other factors also determine male attractiveness, and the male-taller norm is not universal. For example, taller women are more likely to relax the “taller male” norm than shorter women. Furthermore, professor Adam Eyre-Walker, from the University of Sussex, has stated that there is, as of yet, no evidence that these preferences are evolutionary preferences, as opposed to merely cultural preferences. In a double-blind study by Graziano et al., it was found that, in person, using a sample of women of normal size, they were on average most attracted to men who were of medium height (5’9″ 5’11”, 1.75m 1.80m) and less attracted to both men of shorter height (5’5″ 5’7″, 1.65m 1.70m) and men of tallest height (6’2″ 6’4″, 1.88m 1.93m).
Additionally, women seem more receptive to an erect posture than men, though both prefer it as an element within beauty. According to one study (Yee N., 2002), gay men who identify as “only tops” tend to prefer shorter men, while gay men who identify as “only bottoms” tend to prefer taller men.
In romances in Middle English literature, all of the “ideal” male heroes are tall, and the vast majority of the “valiant” male heroes are tall too.
Studies based in the United States, New Zealand, and China have shown that women rate men with no trunk (chest and abdominal) hair as most attractive, and that attractiveness ratings decline as hairiness increases. Another study, however, found that moderate amounts of trunk hair on men was most attractive, to the sample of British and Sri Lankan women. Further, a degree of hirsuteness (hairiness) and a waist-to-shoulder ratio of 0.6 is often preferred when combined with a muscular physique.
In a study using Finnish women, women with hairy fathers were more likely to prefer hairy men, suggesting that preference for hairy men is the result of either genetics or imprinting. Among gay men, another study (Yee N., 2002) reported gay males who identify as “only tops” prefer less hairy men, while gay males who identify as “only bottoms” prefer hairier men.
Testosterone has been shown to darken skin color in laboratory experiments. In his foreword to Peter Frost’s 2005 Fair Women, Dark Men, University of Washington sociologist Pierre L. van den Berghe writes: “Although virtually all cultures express a marked preference for fair female skin, even those with little or no exposure to European imperialism, and even those whose members are heavily pigmented, many are indifferent to male pigmentation or even prefer men to be darker.” Despite this, the aesthetics of skin tone varies from culture to culture. Manual laborers who spent extended periods of time outside developed a darker skin tone due to exposure to the sun. As a consequence, an association between dark skin and the lower classes developed. Light skin became an aesthetic ideal because it symbolized wealth. “Over time society attached various meanings to these colored differences. Including assumptions about a person’s race, socioeconomic class, intelligence, and physical attractiveness.”
A scientific review published in 2011, identified from a vast body of empirical research that skin colour as well as skin tone tend to be preferred as they act as indicators of good health. More specifically, these indicators are thought to suggest to potential mates that the beholder has strong or good genes capable of fighting off disease.
According to one study (Yee N., 2002), gay men who identify as “only tops” tend to prefer lighter-skinned men while gay men who identify as “only bottoms” tend to prefer darker-skinned men.
More recent research has suggested that redder and yellower skin tones, reflecting higher levels of oxygenated blood, carotenoid and to a lesser extent melanin pigment, and net dietary intakes of fruit and vegetables, appears healthier, and therefore more attractive.
Research indicates that heterosexual men tend to be attracted to young and beautiful women with bodily symmetry. Rather than decreasing it, modernity has only increased the emphasis men place on women’s looks.Evolutionary psychologists attribute such attraction to an evaluation of the fertility potential in a prospective mate.
Research has attempted to determine which facial features communicate attractiveness. Facial symmetry has been shown to be considered attractive in women, and men have been found to prefer full lips, high forehead, broad face, small chin, small nose, short and narrow jaw, high cheekbones, clear and smooth skin, and wide-set eyes. The shape of the face in terms of “how everything hangs together” is an important determinant of beauty. A University of Toronto study found correlations between facial measurements and attractiveness; researchers varied the distance between eyes, and between eyes and mouth, in different drawings of the same female face, and had the drawings evaluated; they found there were ideal proportions perceived as attractive (see photo). These proportions (46% and 36%) were close to the average of all female profiles. Women with thick, dark limbal rings in their eyes have also been found to be more attractive. The explanation given is that because the ring tends to fade with age and medical problems, a prominent limbal ring gives an honest indicator of youth.
In a cross-cultural study, more neotenized (i.e., youthful looking) female faces were found to be most attractive to men while less neotenized female faces were found to be less attractive to men, regardless of the females’ actual age. One of these desired traits was a small jaw. In a study of Italian women who have won beauty competitions, it was found that their faces had more “babyish” (pedomorphic) traits than those of the “normal” women used as a reference.
In a cross-cultural study, Marcinkowska et al. said that 18- to 45-year-old heterosexual men in all 28 countries surveyed preferred photographs of 18- to 24-year-old Caucasian women whose faces were feminized using Psychomorph software over faces of 18- to 24-year-old Caucasian women that were masculinized using that software, but there were differences in preferences for femininity across countries. The higher the National Health Index of a country, the more were the feminized faces preferred over the masculinized faces. Among the countries surveyed, Japan had the highest femininity preference and Nepal had the lowest femininity preference.
Michael R. Cunningham of the Department of Psychology at the University of Louisville found, using a panel of East Asian, Hispanic and White judges, that the Asian, Hispanic and White female faces found most attractive were those that had “neonate large eyes, greater distance between eyes, and small noses” and his study led him to conclude that “large eyes” were the most “effective” of the “neonate cues”. Cunningham also said that “shiny” hair may be indicative of “neonate vitality”. Using a panel of blacks and whites as judges, Cunningham found more neotenous faces were perceived as having both higher “femininity” and “sociability”. In contrast, Cunningham found that faces that were “low in neoteny” were judged as “intimidating”. Cunningham noted a “difference” in the preferences of Asian and white judges with Asian judges preferring women with “less mature faces” and smaller mouths than the White judges. Cunningham hypothesized that this difference in preference may stem from “ethnocentrism” since “Asian faces possess those qualities”, so Cunningham re-analyzed the data with “11 Asian targets excluded” and concluded that “ethnocentrism was not a primary determinant of Asian preferences.” Rather than finding evidence for purely “neonate” faces being most appealing, Cunningham found faces with “sexually-mature” features at the “periphery” of the face combined with “neonate” features in the “center of the face” most appealing in men and women. Upon analyzing the results of his study, Cunningham concluded that preference for “neonate features may display the least cross-cultural variability” in terms of “attractiveness ratings” and, in another study, Cunningham concluded that there exists a large agreement on the characteristics of an attractive face.
In computer face averaging tests, women with averaged faces have been shown to be considered more attractive. This is possibly due to average features being more familiar and, therefore, more comfortable.
Commenting on the prevalence of whiteness in supposed beauty ideals in his book White Lies: Race and the Myth of Whiteness, Maurice Berger states that the schematic rendering in the idealized face of a study conducted with American subjects had “straight hair,” “light skin,” “almond-shaped eyes,” “thin, arched eyebrows,” “a long, thin nose, closely set and tiny nostrils” and “a large mouth and thin lips”, though the author of the study stated that there was consistency between his results and those conducted on other races. Scholar Liu Jieyu says in the article White Collar Beauties, “The criterion of beauty is both arbitrary and gendered. The implicit consensus is that women who have fair skin and a slim figure with symmetrical facial features are pretty.” He says that all of these requirements are socially constructed and force people to change themselves to fit these criteria.
One psychologist speculated there were two opposing principles of female beauty: prettiness and rarity. So on average, symmetrical features are one ideal, while unusual, stand-out features are another. A study performed by the University of Toronto found that the most attractive facial dimensions were those found in the average female face. However, that particular University of Toronto study looked only at white women.
A study that used Chinese, Malay and Indian judges said that Chinese women with orthognathism where the mouth is flat and in-line with the rest of the face were judged to be the most attractive and Chinese women with a protruding mandible where the jaw projects outward were judged to be the least attractive.
A 2011 study, by Wilkins, Chan and Kaiser found correlations between perceived femininity and attractiveness, that is, women’s faces which were seen as more feminine were judged by both men and women to be more attractive.
A component of the female beauty ideal in Persian literature is for women to have faces like a full moon.
In Arabian society in the Middle Ages, a component of the female beauty ideal was for women to have round faces which were like a “full moon”.
In Japan, during the Edo period, a component of the female beauty ideal was for women to have long and narrow faces which were shaped like ovals.
In Jewish Rabbinic literature, the Rabbis considered full lips to be the ideal type of lips for women.
Historically, in Chinese and Japanese literature, the feminine ideal was said to include small lips. Women would paint their lips thinner and narrower to align with this ideal.
Classical Persian literature, paintings, and miniatures portrayed traits such as long black curly hair, a small mouth, long arched eyebrows, large almond shaped eyes, a small nose, and beauty spots as being beautiful for women.
Evidence from various cultures suggests that heterosexual men tend to find the sight of women’s genitalia to be sexually arousing.
Cross-cultural data shows that the reproductive success of women is tied to their youth and physical attractiveness such as the pre-industrial Sami where the most reproductively successful women were 15 years younger than their man. One study covering 37 cultures showed that, on average, a woman was 2.5 years younger than her male partner, with the age difference in Nigeria and Zambia being at the far extreme of 6.5 to 7.5 years. As men age, they tend to seek a mate who is ever younger.
25% of eHarmony’s male customers over the age of 50 request to only be matched with women younger than 40. A 2010 OkCupid study, of 200,000 users found that female desirability to its male users peaks at age 21, and falls below the average for all women at 31. After age 26, men have a larger potential dating pool than women on the site; and by age 48, their pool is almost twice as large. The median 31-year-old male user searches for women aged 22 to 35, while the median 42-year-old male searches for women 27 to 45. The age skew is even greater with messages to other users; the median 30-year-old male messages teenage girls as often as women his own age, while mostly ignoring women a few years older than him. Excluding the 10% most and 10% least beautiful of women, however, women’s attractiveness does not change between 18 and 40, but if extremes are not excluded “There’s no doubt that younger [women] are more physically attractiveindeed in many ways beauty and youth are inextricable. That’s why most of the models you see in magazines are teenagers”.
Pheromones (detected by female hormone markers) reflects female fertility and the reproductive value mean. As females age, the estrogen-to-androgen production ratio changes and results in female faces to appear more and more masculine (thus appearing less “attractive”). In a small (n=148) study performed in the United States, using male college students at one university, the mean age expressed as ideal for a wife was found to be 16.87 years old, while 17.76 was the mean ideal age for a brief sexual encounter. However, the study sets up a framework where “taboos against sex with young girls” are purposely diminished, and biased their sample by removing any participant over the age of 30, with a mean participant age of 19.83. In a study of penile tumescence, men were found most aroused by pictures of young adult females.
Signals of fertility in women are often also seen as signals of youth. The evolutionary perspective proposes the idea that when it comes to sexual reproduction, the minimal parental investment required by men gives them the ability and want to simply reproduce ‘as much as possible.' It therefore makes sense that men are attracted to the features in women which signal youthfulness, and thus fertility. Their chances of reproductive success are much higher than they would be should they pick someone olderand therefore less fertile.
This may explain why combating age declines in attractiveness occurs from a younger age in women than in men. For example, the removal of one’s body hair is considered a very feminine thing to do. This can be explained by the fact that aging results in raised levels of testosterone and thus, body hair growth. Shaving reverts one’s appearance to a more youthful stage and although this may not be an honest signal, men will interpret this as a reflection of increased fertile value. Research supports this, showing hairlessness to considered sexually attractive by men.
Research has shown that most heterosexual men enjoy the sight of female breasts, with a preference for large, firm breasts. However, a contradictory study of British undergraduates found younger men preferred small breasts on women. Smaller breasts were widely associated with youthfulness. Cross-culturally, another study found “high variability” regarding the ideal breast size. Some researchers in the United Kingdom have speculated that a preference for larger breasts may have developed in Western societies because women with larger breasts tend to have higher levels of the hormones estradiol and progesterone, which both promote fertility.
A study showed that men prefer symmetrical breasts. Breast symmetry may be particularly sensitive to developmental disturbances and the symmetry differences for breasts are large compared to other body parts. Women who have more symmetrical breasts tend to have more children.
Historical literature often includes specific features of individuals or a gender that are considered desirable. These have often become a matter of convention, and should be interpreted with caution. In Arabian society in the Middle Ages, a component of the female beauty ideal was for women to have small breasts. In Persian literature, beautiful women are said to have breasts like pomegranates or lemons. In the Chinese text “Jeweled Chamber Secrets” (Chinese: ) from the Six Dynasties period, the ideal woman was described as having firm breasts. In Sanskrit literature, beautiful women are often said to have breasts so large that they cause the women to bend a little bit from their weight. In Middle English literature, beautiful women should have small breasts that are round like an apple or a pear.
Biological anthropologist Helen E. Fisher of the Center for Human Evolution Studies in the Department of Anthropology of Rutgers University said that, “perhaps, the fleshy, rounded buttocks… attracted males during rear-entry intercourse.” Bobbi S. Low et al. of the School of Natural Resources and Environment at the University of Michigan, said the female “buttocks evolved in the context of females competing for the attention and parental commitment of powerful resource-controlling males” as an “honest display of fat reserves” that could not be confused with another type of tissue, although T. M. Caro, professor in the Center for Population Biology and the Department of Wildlife, Fish, and Conservation Biology, at University of California, Davis, rejected that as being a necessary conclusion, stating that female fatty deposits on the hips improve “individual fitness of the female”, regardless of sexual selection.
In a 1995 study, black men were more likely than white men to use the words “big” or “large” to describe their conception of an attractive woman’s posterior.
Body Mass Index (BMI) is an important determinant to the perception of beauty. Even though the Western ideal is for a thin woman, some cultures prefer plumper women, which has been argued to support that attraction for a particular BMI merely is a cultural artifact. The attraction for a proportionate body also influences an appeal for erect posture. One cross-cultural survey comparing body-mass preferences among 300 of the most thoroughly studied cultures in the world showed that 81% of cultures preferred a female body size that in English would be described as “plump”.
Availability of food influences which female body size is attractive which may have evolutionary reasons. Societies with food scarcities prefer larger female body size than societies that have plenty of food. In Western society males who are hungry prefer a larger female body size than they do when not hungry.
In the United States, women overestimate men’s preferences for thinness in a mate. In one study, American women were asked to choose what their ideal build was and what they thought the build most attractive to men was. Women chose slimmer than average figures for both choices. When American men were independently asked to choose the female build most attractive to them, the men chose figures of average build. This indicates that women may be misled as to how thin men prefer women to be. Some speculate that thinness as a beauty standard is one way in which women judge each other and that thinness is viewed as prestigious for within-gender evaluations of other women. A reporter surmised that thinness is prized among women as a “sign of independence, strength and achievement.” Some implicated the fashion industry for the promulgation of the notion of thinness as attractive.
East Asians have historically preferred women whose bodies had small features. For example, during the Spring and Autumn period of Chinese history, women in Chinese harems wanted to have a thin body in order to be attractive for the Chinese emperor. Later, during the Tang Dynasty, a less thin body type was seen as most attractive for Chinese women. In Arabian society in the Middle Ages, a component of the female beauty ideal was for women to be slender like a “cane” or a “twig”. In the Chinese text “Jeweled Chamber Secrets” (Chinese: ) from the Six Dynasties period, the ideal woman was described as not being “large-boned”.
In the Victorian era, women who adhered to Victorian ideals were expected to limit their food consumption to attain the ideal slim figure. In Middle English literature, “slender” women are considered beautiful.
A WHR of 0.7 for women has been shown to correlate strongly with general health and fertility. Women within the 0.7 range have optimal levels of estrogen and are less susceptible to major diseases such as diabetes, heart disease, and ovarian cancers. Women with high WHR (0.80 or higher) have significantly lower pregnancy rates than women with lower WHRs (0.700.79), independent of their BMIs. Female waist-to-hip ratio (WHR) has been proposed by evolutionary psychologists to be an important component of human male mate choice, because this trait is thought to provide a reliable cue to a woman’s reproductive value.
Both men and women judge women with smaller waist-to-hip ratios more attractive. Ethnic groups vary with regard to their ideal waist-to-hip ratio for women, ranging from 0.6 in China, to 0.8 or 0.9 in parts of South America and Africa, and divergent preferences based on ethnicity, rather than nationality, have also been noted. A study found the Machiguenga people, an isolated indigenous South American ethnic group, prefer women with high WHR (0.9). The preference for heavier women, has been interpreted to belong to societies where there is no risk of obesity.
In Chinese, the phrase “willow waist” (Chinese: ) is used to denote a beautiful woman by describing her waist as being slender like a willow branch.
In the Victorian era, a small waist was considered the main trait of a beautiful woman.
Most men tend to be taller than their female partner. It has been found that, in Western societies, most men prefer shorter women. Having said this, height is a more important factor for a woman when choosing a man than it is for a man choosing a woman. Men tend to view taller women as less attractive, and people view heterosexual couples where the woman is taller to be less ideal. Women who are 0.7 to 1.7 standard deviations below the mean female height have been reported to be the most reproductively successful, since fewer tall women get married compared to shorter women. However, in other ethnic groups, such as the Hadza, study has found that height is irrelevant in choosing a mate.
In Middle English literature, ‘tallness’ is a characteristic of ideally beautiful women.
A study using Polish participants by Sorokowski found 5% longer legs than average person leg to body ratio for both on man and woman was considered most attractive. The study concluded this preference might stem from the influence of leggy runway models. Another study using British and American participants, found “mid-ranging” leg-to-body ratios to be most ideal.
A study by Swami et al. of British male and female undergraduates showed a preference for men with legs as long as the rest of their body and women with 40% longer legs than the rest of their body. The researcher concluded that this preference might be influenced by American culture where long legged women are portrayed as more attractive.
Marco Bertamini criticized the Swami et al. study for using a picture of the same person with digitally altered leg lengths which he felt would make the modified image appear unrealistic. Bertamini also criticized the Swami study for only changing the leg length while keeping the arm length constant. After accounting for these concerns in his own study, Bertamini’s study which used stick figures also found a preference for women with proportionately longer legs than men. When Bertamini investigated the issue of possible sexual dimorphism of leg length, he found two sources that indicated that men usually have slightly proportionately longer legs than women or that differences in leg length proportion may not exist between men and women. Following this review of existing literature on the subject, he conducted his own calculations using data from 1774 men and 2208 women. Using this data, he similarly found that men usually have slightly proportionately longer legs than women or that differences in leg length proportion may not exist between men and women. These findings made him rule out the possibility that a preference for women with proportionately longer legs than men is due proportionately longer legs being a secondary sex characteristic of women.
According to some studies, most men prefer women with small feet, such as in ancient China where foot binding was practiced.
In Jewish Rabbinic literature, the Rabbis considered small feet to be the ideal type of feet for women.
Men have been found to prefer long-haired women. An evolutionary psychology explanation for this is that malnutrition and deficiencies in minerals and vitamins causes loss of hair or hair changes. Hair therefore indicates health and nutrition during the last 23 years. Lustrous hair is also often a cross-cultural preference. One study reported non-Asian men to prefer blondes and Asian men to prefer black-haired women.
A component of the female beauty ideal in Persian literature is for women to have black hair, which was also preferred in Arabian society in the Middle Ages. In Middle English literature, curly hair is a necessary component of a beautiful woman.
The way an individual moves can indicate health and even age and influence attractiveness. A study reflecting the views of 700 individuals and that involved animated representations of people walking, found that the physical attractiveness of women increased by about 50 percent when they walked with a hip sway. Similarly, the perceived attractiveness of males doubled when they moved with a swagger in their shoulders.
A preference for lighter-skinned women has remained prevalent over time, even in cultures without European contact, though exceptions have been found. Anthropologist Peter Frost stated that since higher-ranking men were allowed to marry the perceived more attractive women, who tended to have fair skin, the upper classes of a society generally tended to develop a lighter complexion than the lower classes by sexual selection (see also Fisherian runaway). In contrast, one study on men of the Bikosso tribe in Cameroon found no preference for attractiveness of females based on lighter skin color, bringing into question the universality of earlier studies that had exclusively focused on skin color preferences among non-African populations.
Today, skin bleaching is not uncommon in parts of the world such as Africa, and a preference for lighter-skinned women generally holds true for African Americans, Latin Americans, and Asians. One exception to this has been in contemporary Western culture, where tanned skin used to be associated with the sun-exposed manual labor of the lower-class, but has generally been considered more attractive and healthier since the mid-20th century.
More recent work has extended skin color research beyond preferences for lightness, arguing that redder (higher a* in the CIELab colour space) and yellower (higher b*) skin has healthier appearance. These preferences have been attributed to higher levels of red oxygenated blood in the skin, which is associated with aerobic fitness and lack of cardiac and respiratory illnesses, and to higher levels of yellow-red antioxidant carotenoids in the skin, indicative of more fruit and vegetables in the diet and, possibly more efficient immune and reproductive systems.
Research has additionally shown that skin radiance or glowing skin indicates health, thus skin radiance influences perception of beauty and physical attractiveness.
In Persian literature, beautiful women are said to have noses like hazelnuts.
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Physical attractiveness – Wikipedia
Some people believe that calico cats are a breed, or that calico refers to a color of a cat. Since all cats are colored, calico refers to the pattern of how the coloring appears on the cat’s coat.
According to a leading expert in Feline Genetics, Dr. Elizabeth A. Oltenacu of the Department of Animal Science at Cornell University:
“Early in its inception, a calico/tortie kitty is formed by a gene known as the white spotting factor. The white spotting factor effectively slows down the migration of cells across the kitten’s body. One X-chromosome in every cell is switched off.
This is a random happenstance, and when a tortoiseshell kitten appears in the litter, you will see a mix of two colors of hair on the kitten.
In a calico kitten, the white spotting factor being present allows patches of cells with the same X chromosome shut-off to develop.
The results are patches of white, orange, and non-orange in the kitten. The more white in a calico, the larger the patches of white, orange and non-orange because the migration of cells in the embryo is slowed. Once the color is in patches, you can see the effect of the tabby genes in the orange patches.”
Calico cats are overwhelmingly female. According to The Cat Fancier’s Association Complete Cat Book; Persian calico cats have been accepted by CFA for years and calico Persians are always female and give birth to black-and-white or red and white bi-colored sons.
Genetically, two X chromosomes are needed to produce a calico coat, which is why the majority of calico cats are females. If the colors are black/orange upon the coat, then the cat is a calico cat. If the colors are blue/cream instead of the standard black/orange, then the cat is a muted calico.
Dr. Oltenacu further explains: “There’s a gene on the X-chromosome that controls orange/non-orange color. One form (allele) determines orange, the other allele non-orange (usually black, but the actual color is determined by other genes on the autosomes). Neither form is dominant to the other, so a cat with one of each is a tortie.
It has to be female, as this requires 2 X-chromosomes. Sometimes an abnormal male is born XXY instead of the usual XY, so can be tortie.
Clearly, this male is the result of inaccurate separation of the chromosomes during egg or sperm formation. Usually, males are orange or non-orange, but not tortie as they have just one X-chromosome.
Now, if the cat also has the white-spotting gene (again autosomal, not on the sex chromosome). This will cause the color to be in patches, rather than the diffuse mix of orange and black in the tortie. Hence the calico.”
If the majority of calico cats are female, then does this make male calicos valuable? For cat lovers, a calico cat, regardless of gender is valuable to the owner. Calico cats are quirky, independent, a tad stubborn and fun to be around.
It is clear that calico cats have captivated hearts of cat fanciers around the world. On October 1, 2001 the state of Maryland was so enamored with this delightful cat that they declared the calico cat as their official state cat.
The author wishes to acknowledge her great appreciation for Dr. Oltenacu’s assistance in preparing this article.
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Calico Cats – TheCatSite.com Community
In genetics, a mosaic (or mosaicism) means the presence of two different genotypes in an individual which developed from a single fertilized egg. As a result, the individual has two or more genetically different cell lines derived from a single zygote.
Mosaicism may result from:
The phenomenon was discovered by Curt Stern. In 1936, he demonstrated that recombination, normal in meiosis, can also take place in mitosis. When it does, it results in somatic (body) mosaics. These are organisms which contain two or more genetically distinct types of tissue.
A genetic chimera is an organism composed of two or more sets of genetically distinct cells. Dispermic chimeras happen when two fertilized eggs fuse together. Mosaics are a different kind of chimerism: they originate from a single fertilized egg.
This is easiest to see with eye colours. When eye colours vary between the two eyes, or within one or both eyes, the condition is called heterochromia iridis (= ‘different coloured iris’). It can have many different causes, both genetic and accidental. For example, David Bowie has the appearance of different eye colours due to an injury that caused one pupil to be permanently dilated.
On this page, only genetic mosaicism is discussed.
The most common cause of mosaicism in mammalian females is X-inactivation. Females have two X chromosomes (and males have only one). The two X chromosomes in a female are rarely identical. They have the same genes, but at some loci (positions) they may have different alleles (versions of the same gene).
In the early embryo, each cell independently and randomly inactivates one copy of the X chromosome. This inactivation lasts the lifetime of the cell, and all the descendants of the cell inactivate that same chromosome.
This phenomenon shows in the colouration of calico cats and tortoiseshell cats. These females are heterozygous for the X-linked colour genes: the genes for their coat colours are carried on the X chromosome. X-inactivation causes groups of cells to carry either one or the other X-chromosome in an active state.
X-inactivation is reversed in the female germline, so that all egg cells contain an active X chromosome.
Mosaicism refers to differences in the genotype of various cell populations in the same individual, but X-inactivation is an epigenetic change, a switching off of genes on one chromosome. It is not a change in the genotype. Descendent cells of the embryo carry the same X-inactivation as the original cells. This may give rise to mild symptoms in female ‘carriers’ of X-linked genetic disorders.
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Mosaic (genetics) – Simple English Wikipedia, the free …
Calico cats are domestic cats with a spotted or particolored coat that is predominantly white, with patches of two other colors (often, the two other colors are orange and black). Outside North America, the pattern is more usually called tortoiseshell-and-white. In the province of Quebec, Canada, they are sometimes called chatte d’Espagne (French for ‘(female) cat of Spain’). Other names include brindle, tricolor cat, tobi mi-ke (Japanese for ‘triple fur’), and lapjeskat (Dutch for ‘patches cat’); calicoes with diluted coloration have been called calimanco or clouded tiger. Occasionally, the tri-color calico coloration is combined with a tabby patterning. This calico patched tabby is called a caliby.
“Calico” refers only to a color pattern on the fur, not to a breed. Among the breeds whose standards allow calico coloration are the Manx, American Shorthair, British Shorthair, Persian, Japanese Bobtail, Exotic Shorthair, Siberian, Turkish Van, Turkish Angora and Norwegian Forest Cat.
Because genetic determination of coat colors in calico cats is linked to the X chromosome, calicoes are nearly always female, with one color linked to the maternal X chromosome and a second color linked to the paternal X chromosome. Because males only have one X chromosome, a male calico would have to have a rare condition where they have three sex chromosomes (two X chromosomes and one Y chromosome) in order to be calico. In addition to other symptoms caused by the condition, these male calicos are often sterile.
There is also a calico cat referred to as a Dilute Calico. Dilute Calicos are not necessarily rare. They are recognized by their grey, silver, and gold colors instead if the traditional white, black, brown or red patched coat of a calico. Dilute calicos are also called light calicos; because they usually have no dark colored fur.
The coat pattern of calico cats does not define any breed, but occurs incidentally in cats that express a range of color patterns; accordingly the effect has no definitive historical background. However, the existence of patches in calico cats was traced to a certain degree by Neil Todd in a study determining the migration of domesticated cats along trade routes in Europe and Northern Africa. The proportion of cats having the orange mutant gene found in calicoes was traced to the port cities along the Mediterranean in Greece, France, Spain and Italy, originating from Egypt.
In genetic terms, calico cats are tortoiseshells in every way, except that in addition they express a white spotting gene. There is however one anomaly: as a rule of thumb the larger the areas of white, the fewer and larger the patches of ginger and dark or tabby coat. In contrast a non-white-spotted tortoiseshell usually has small patches of color or even something like a salt-and-pepper sprinkling. This reflects the genetic effects on relative speeds of migration of melanocytes and X-inactivation in the embryo.
Serious study of calico cats seems to have begun about 1948 when Murray Barr and his graduate student E.G. Bertram noticed dark, drumstick-shaped masses inside the nuclei of nerve cells of female cats, but not in male cats. These dark masses became known as Barr bodies. In 1959, Japanese cell biologist Susumu Ohno determined the Barr bodies were X chromosomes. In 1961, Mary Lyon proposed the concept of X-inactivation: one of the two X chromosomes inside a female mammal shuts off. She observed this in the coat color patterns in mice.
Calico cats are almost always female because the locus of the gene for the orange/non-orange coloring is on the X chromosome. In the absence of other influences, such as color inhibition that causes white fur, the alleles present in those orange loci determine whether the fur is orange or not. Female cats like all female placental mammals normally have two X chromosomes. In contrast, male placental mammals, including chromosomally stable male cats, have one X and one Y chromosome. Since the Y chromosome does not have any locus for the orange gene, there is no chance that an XY male could have both orange and non-orange genes together, which is what it takes to create tortoiseshell or calico coloring.
One exception is that in rare cases faulty cell division may leave an extra X chromosome in one of the gametes that produced the male cat. That extra X then is reproduced in each of his cells, a condition referred to as XXY, or Klinefelter syndrome. Such a combination of chromosomes could produce tortoiseshell or calico markings in the male, in the same way as XX chromosomes produce them in the female.
All but about one in three thousand of the rare calico or tortoiseshell male cats are sterile because of the chromosome abnormality, and breeders reject any exceptions for stud purposes because they generally are of poor physical quality and fertility. In any event, because the genetic conditions for calico coloring are X linked, a fertile male calico’s coloring would not have any determination in the coloring of any male offspring (who would receive the Y, not the X chromosome from their father).
As Sue Hubble stated in her book Shrinking the Cat: Genetic Engineering before We Knew about Genes,
The mutation that gives male cats a ginger-colored coat and females ginger, tortoiseshell, or calico coats produced a particularly telling map. The orange mutant gene is found only on the X, or female, chromosome. As with humans, female cats have paired sex chromosomes, XX, and male cats have XY sex chromosomes. The female cat, therefore, can have the orange mutant gene on one X chromosome and the gene for a black coat on the other. The piebald gene is on a different chromosome. If expressed, this gene codes for white, or no color, and is dominant over the alleles that code for a certain color (i.e. orange or black), making the white spots on calico cats. If that is the case, those several genes will be expressed in a blotchy coat of the tortoiseshell or calico kind. But the male, with his single X chromosome, has only one of that particular coat-color gene: he can be not-ginger or he can be ginger (although some modifier genes can add a bit of white here and there), but unless he has a chromosomal abnormality he cannot be a calico cat.
It is currently impossible to reproduce the fur patterns of calico cats by cloning. Penelope Tsernoglou wrote “This is due to an effect called x-linked inactivation which involves the random inactivation of one of the X chromosomes. Since all female mammals have two X chromosomes, one might wonder if this phenomenon could have a more widespread impact on cloning in the future.”
Calico cats may have already provided findings relating to physiological differences between male and female mammals. This insight may be one day broadened to the fields of psychology, psychiatry, sociology, biology and medicine as more information becomes available regarding the complete effect of random X-inactivation in female mammals.
Cats of this coloration are believed to bring good luck in the folklore of many cultures. In the United States, these are sometimes referred to as money cats. A cat of the calico coloration is also the state cat of Maryland in the United States. In the late nineteenth century, Eugene Field published “The Duel”, a beloved poem for children also known as “The Gingham Dog and the Calico Cat.” In Japan, the Maneki-Neko figures depict Calico cats, bringing good luck.
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Calico cat – Wikipedia
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Female () is the sex of an organism, or a part of an organism, that produces non-mobile ova (egg cells). Most female mammals, including female humans, have two X chromosomes.
The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male. A female individual cannot reproduce sexually without access to the gametes of a male (an exception is parthenogenesis). Some organisms can reproduce both sexually and asexually.
There is no single genetic mechanism behind sex differences in different species and the existence of two sexes seems to have evolved multiple times independently in different evolutionary lineages. Patterns of sexual reproduction include
Other than the defining difference in the type of gamete produced, differences between males and females in one lineage cannot always be predicted by differences in another. The concept is not limited to animals; egg cells are produced by chytrids, diatoms, water moulds and land plants, among others. In land plants, female and male designate not only the egg- and sperm-producing organisms and structures, but also the structures of the sporophytes that give rise to male and female plants.
The word female comes from the Latin femella, the diminutive form of femina, meaning “woman”. It is not etymologically related to the word male, but in the late 14th century the spelling was altered in English to parallel the spelling of male.
A distinguishing characteristic of the class Mammalia is the presence of mammary glands. The mammary glands are modified sweat glands that produce milk, which is used to feed the young for some time after birth. Only mammals produce milk. Mammary glands are most obvious in humans, as the female human body stores large amounts of fatty tissue near the nipples, resulting in prominent breasts. Mammary glands are present in all mammals, although they are vestigial in the male of the species.
Most mammalian females have two copies of the X chromosome as opposed to the male which carries only one X and one smaller Y chromosome (but some mammals, such as the Platypus, have different combinations). To compensate for the difference in size, one of the female’s X chromosomes is randomly inactivated in each cell of placental mammals while the paternally derived X is inactived in marsupials. In birds and some reptiles, by contrast, it is the female which is heterozygous and carries a Z and a W chromosome whilst the male carries two Z chromosomes. Intersex conditions can also give rise to other combinations, such as XO or XXX in mammals, which are still considered as female so long as they do not contain a Y-chromosome. However, these conditions frequently result in sterility.
Mammalian females bear live young (with the rare exception of monotremes, which lay eggs). Some non-mammalian species, such as guppies, have analogous reproductive structures; and some other non-mammals, such as sharks, whose eggs hatch inside their bodies, also have the appearance of bearing live young.
A common symbol used to represent the female sex is (Unicode: U+2640 Alt codes: Alt+12), a circle with a small cross underneath. According to Schott, the most established view is that the male and female symbols “are derived from contractions in Greek script of the Greek names of these planets, namely Thouros (Mars) and Phosphoros (Venus). These derivations have been traced by Renkama who illustrated how Greek letters can be transformed into the graphic male and female symbols still recognised today.” Thouros was abbreviated by , and Phosphoros by , both in the handwriting of alchemists so somewhat different from the Greek symbols we know. These abbreviations were contracted into the modern symbols.
The sex of a particular organism may be determined by a number of factors. These may be genetic or environmental, or may naturally change during the course of an organism’s life. Although most species with male and female sexes have individuals that are either male or female, hermaphroditic animals have both male and female reproductive organs.
The sex of most mammals, including humans, is genetically determined by the XY sex-determination system where males have X and Y (as opposed to X and X) sex chromosomes. During reproduction, the male contributes either an X sperm or a Y sperm, while the female always contributes an X egg. A Y sperm and an X egg produce a male, while an X sperm and an X egg produce a female. The ZW sex-determination system, where males have ZZ (as opposed to ZW) sex chromosomes, is found in birds, reptiles and some insects and other organisms. Members of Hymenoptera, such as ants and bees, are determined by haplodiploidy, where most males are haploid and females and some sterile males are diploid.
The young of some species develop into one sex or the other depending on local environmental conditions, e.g. many crocodilians’ sex is influenced by the temperature of their eggs. Other species (such as the goby) can transform, as adults, from one sex to the other in response to local reproductive conditions (such as a shortage of males).
Ayers, Donald M. English Words from Latin and Greek Elements. Second Edition. 1986. University of Arizona Press. United States.
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Female – Wikipedia
A male () organism is the physiological sex that produces sperm. Each spermatozoon can fuse with a larger female gamete, or ovum, in the process of fertilization. A male cannot reproduce sexually without access to at least one ovum from a female, but some organisms can reproduce both sexually and asexually. Most male mammals, including male humans, have a Y chromosome, which codes for the production of larger amounts of testosterone to develop male reproductive organs.
Not all species share a common sex-determination system. In most animals, including humans, sex (as opposed to gender) is determined genetically, but in some species it can be determined due to social, environmental or other factors. For example, Cymothoa exigua changes sex depending on the number of females present in the vicinity.
The existence of two sexes seems to have been selected independently across different evolutionary lineages (see convergent evolution). The repeated pattern is sexual reproduction in isogamous species with two or more mating types with gametes of identical form and behavior (but different at the molecular level) to anisogamous species with gametes of male and female types to oogamous species in which the female gamete is very much larger than the male and has no ability to move. There is a good argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction.
Accordingly, sex is defined operationally across species by the type of gametes produced (i.e.: spermatozoa vs. ova) and differences between males and females in one lineage are not always predictive of differences in another.
Male/female dimorphism between organisms or reproductive organs of different sexes is not limited to animals; male gametes are produced by chytrids, diatoms and land plants, among others. In land plants, female and male designate not only the female and male gamete-producing organisms and structures but also the structures of the sporophytes that give rise to male and female plants. As of the year 2012, the United Arab Emirates has the highest ratio of human males in the world, followed by Qatar.
A common symbol used to represent the male sex is the Mars symbol, (Unicode: U+2642 Alt codes: Alt+11)a circle with an arrow pointing northeast. The symbol is identical to the planetary symbol of Mars. It was first used to denote sex by Carl Linnaeus in 1751. The symbol is often called a stylized representation of the Roman god Mars’ shield and spear. According to Stearn, however, all the historical evidence favours that it is derived from , the contraction of the Greek name for the planet, Thouros.
The sex of a particular organism may be determined by a number of factors. These may be genetic or environmental, or may naturally change during the course of an organism’s life. Although most species with male and female sexes have individuals that are either male or female, hermaphroditic animals, such as worms, have both male and female reproductive organs.
Most mammals, including humans, are genetically determined as such by the XY sex-determination system where males have an XY (as opposed to XX) sex chromosome. It is also possible in a variety of species, including human beings, to be XXY or have other intersex/hermaphroditic qualities, though one would still be considered genotypically (if not necessarily phenotypically) male so long as one has a Y-chromosome. During reproduction, a male can give either an X sperm or a Y sperm, while a female can only give an X egg. A Y sperm and an X egg produce a male, while an X sperm and an X egg produce a female.
The part of the Y-chromosome which is responsible for maleness is the sex-determining region of the Y-chromosome, the SRY. The SRY activates Sox9, which forms feedforward loops with FGF9 and PGD2 in the gonads, allowing the levels of these genes to stay high enough in order to cause male development; for example, Fgf9 is responsible for development of the spermatic cords and the multiplication of Sertoli cells, both of which are crucial to male sexual development.
The ZW sex-determination system, where males have a ZZ (as opposed to ZW) sex chromosome may be found in birds and some insects (mostly butterflies and moths) and other organisms. Members of the insect order Hymenoptera, such as ants and bees, are often determined by haplodiploidy, where most males are haploid and females and some sterile males are diploid.
In some species of reptiles, including alligators, sex is determined by the temperature at which the egg is incubated. Other species, such as some snails, practice sex change: adults start out male, then become female. In tropical clown fish, the dominant individual in a group becomes female while the other ones are male.
In some arthropods, sex is determined by infection. Bacteria of the genus Wolbachia alter their sexuality; some species consist entirely of ZZ individuals, with sex determined by the presence of Wolbachia.
In those species with two sexes, males may differ from females in ways other than production of spermatozoa. In many insects and fish the male is smaller than the female. In seed plants, which exhibit alternation of generations, the female and male parts are both included within the sporophyte sex organ of a single organism. In mammals, including humans, males are typically larger than females. In birds, the male often exhibits a colorful plumage that attracts females.
Male – Wikipedia
acquired trait: A phenotypic characteristic, acquired during growth and development, that is not genetically based and therefore cannot be passed on to the next generation (for example, the large muscles of a weightlifter).
adaptation: Any heritable characteristic of an organism that improves its ability to survive and reproduce in its environment. Also used to describe the process of genetic change within a population, as influenced by natural selection.
adaptive landscape: A graph of the average fitness of a population in relation to the frequencies of genotypes in it. Peaks on the landscape correspond to genotypic frequencies at which the average fitness is high, valleys to genotypic frequencies at which the average fitness is low. Also called a fitness surface.
adaptive logic: A behavior has adaptive logic if it tends to increase the number of offspring that an individual contributes to the next and following generations. If such a behavior is even partly genetically determined, it will tend to become widespread in the population. Then, even if circumstances change such that it no longer provides any survival or reproductive advantage, the behavior will still tend to be exhibited — unless it becomes positively disadvantageous in the new environment.
adaptive radiation: The diversification, over evolutionary time, of a species or group of species into several different species or subspecies that are typically adapted to different ecological niches (for example, Darwin’s finches). The term can also be applied to larger groups of organisms, as in “the adaptive radiation of mammals.”
adaptive strategies: A mode of coping with competition or environmental conditions on an evolutionary time scale. Species adapt when succeeding generations emphasize beneficial characteristics.
agnostic: A person who believes that the existence of a god or creator and the nature of the universe is unknowable.
algae: An umbrella term for various simple organisms that contain chlorophyll (and can therefore carry out photosynthesis) and live in aquatic habitats and in moist situations on land. The term has no direct taxonomic significance. Algae range from macroscopic seaweeds such as giant kelp, which frequently exceeds 30 m in length, to microscopic filamentous and single-celled forms such as Spirogyra and Chlorella.
allele: One of the alternative forms of a gene. For example, if a gene determines the seed color of peas, one allele of that gene may produce green seeds and another allele produce yellow seeds. In a diploid cell there are usually two alleles of any one gene (one from each parent). Within a population there may be many different alleles of a gene; each has a unique nucleotide sequence.
allometry: The relation between the size of an organism and the size of any of its parts. For example, an allometric relation exists between brain size and body size, such that (in this case) animals with bigger bodies tend to have bigger brains. Allometric relations can be studied during the growth of a single organism, between different organisms within a species, or between organisms in different species.
allopatric speciation: Speciation that occurs when two or more populations of a species are geographically isolated from one another sufficiently that they do not interbreed.
allopatry: Living in separate places. Compare with sympatry.
amino acid: The unit molecular building block of proteins, which are chains of amino acids in a certain sequence. There are 20 main amino acids in the proteins of living things, and the properties of a protein are determined by its particular amino acid sequence.
amino acid sequence: A series of amino acids, the building blocks of proteins, usually coded for by DNA. Exceptions are those coded for by the RNA of certain viruses, such as HIV.
ammonoid: Extinct relatives of cephalopods (squid, octopi, and chambered nautiluses), these mollusks had coiled shells and are found in the fossil record of the Cretaceous period.
amniotes: The group of reptiles, birds, and mammals. These all develop through an embryo that is enclosed within a membrane called an amnion. The amnion surrounds the embryo with a watery substance, and is probably an adaptation for breeding on land.
amphibians: The class of vertebrates that contains the frogs, toads, newts, and salamanders. The amphibians evolved in the Devonian period (about 370 million years ago) as the first vertebrates to occupy the land. They have moist scaleless skin which is used to supplement the lungs in gas exchange. The eggs are soft and vulnerable to drying, therefore reproduction commonly occurs in water. Amphibian larvae are aquatic, and have gills for respiration; they undergo metamorphosis to the adult form. Most amphibians are found in damp environments and they occur on all continents except Antarctica.
analogous structures: Structures in different species that look alike or perform similar functions (e.g., the wings of butterflies and the wings of birds) that have evolved convergently but do not develop from similar groups of embryological tissues, and that have not evolved from similar structures known to be shared by common ancestors. Contrast with homologous structures. Note: The recent discovery of deep genetic homologies has brought new interest, new information, and discussion to the classical concepts of analogous and homologous structures.
anatomy: (1) The structure of an organism or one of its parts. (2) The science that studies those structures.
ancestral homology: Homology that evolved before the common ancestor of a set of species, and which is present in other species outside that set of species. Compare with derived homology.
anthropoid: A member of the group of primates made up of monkeys, apes, and humans.
antibacterial: Having the ability to kill bacteria.
antibiotics: Substances that destroy or inhibit the growth of microorganisms, particularly disease-causing bacteria.
antibiotic resistance: A heritable trait in microorganisms that enables them to survive in the presence of an antibiotic.
aperture: Of a camera, the adjustable opening through which light passes to reach the film. The diameter of the aperture determines the intensity of light admitted. The pupil of a human eye is a self-adjusting aperture.
aquatic: Living underwater.
arboreal: Living in trees.
archeology: The study of human history and prehistory through the excavation of sites and the analysis of physical remains, such as graves, tools, pottery, and other artifacts.
archetype: The original form or body plan from which a group of organisms develops.
artifact: An object made by humans that has been preserved and can be studied to learn about a particular time period.
artificial selection: The process by which humans breed animals and cultivate crops to ensure that future generations have specific desirable characteristics. In artificial selection, breeders select the most desirable variants in a plant or animal population and selectively breed them with other desirable individuals. The forms of most domesticated and agricultural species have been produced by artificial selection; it is also an important experimental technique for studying evolution.
asexual reproduction: A type of reproduction involving only one parent that ususally produces genetically identical offspring. Asexual reproduction occurs without fertilization or genetic recombination, and may occur by budding, by division of a single cell, or by the breakup of a whole organism into two or more new individuals.
assortative mating: The tendency of like to mate with like. Mating can be assortative for a certain genotype (e.g., individuals with genotype AA tend to mate with other individuals of genotype AA) or phenotype (e.g., tall individuals mate with other tall individuals).
asteroid: A small rocky or metallic body orbitting the Sun. About 20,000 have been observed, ranging in size from several hundred kilometers across down to dust particles.
atheism: The doctrine or belief that there is no god.
atomistic: (as applied to theory of inheritance) Inheritance in which the entities controlling heredity are relatively distinct, permanent, and capable of independent action. Mendelian inheritance is an atomistic theory because in it, inheritance is controlled by distinct genes.
australopithecine: A group of bipedal hominid species belonging to the genus Australopithecus that lived between 4.2 and 1.4 mya.
Australopithecus afarensis: An early australopithecine species that was bipedal; known fossils date between 3.6 and 2.9 mya (for example, Lucy).
autosome: Any chromosome other than a sex chromosome.
avian: Of, relating to, or characteristic of birds (members of the class Aves).
bacteria: Tiny, single-celled, prokaryotic organisms that can survive in a wide variety of environments. Some cause serious infectious diseases in humans, other animals, and plants.
base: The DNA molecule is a chain of nucleotide units; each unit consists of a backbone made of a sugar and a phosphate group, with a nitrogenous base attached. The base in a unit is one of adenine (A), guanine (G), cytosine (C), or thymine (T). In RNA, uracil (U) is used instead of thymine. A and G belong to the chemical class called purines; C, T, and U are pyrimidines.
Batesian mimicry: A kind of mimicry in which one non-poisonous species (the Batesian mimic) mimics another poisonous species.
belemnite: An extinct marine invertebrate that was related to squid, octopi, and chambered nautiluses. We know from the fossil record that belemnites were common in the Jurassic period and had bullet-shaped internal skeletons.
big bang theory: The theory that states that the universe began in a state of compression to infinite density, and that in one instant all matter and energy began expanding and have continued expanding ever since.
biodiversity (or biological diversity): A measure of the variety of life, biodiversity is often described on three levels. Ecosystem diversity describes the variety of habitats present; species diversity is a measure of the number of species and the number of individuals of each species present; genetic diversity refers to the total amount of genetic variability present.
bioengineered food: Food that has been produced through genetic modification using techniques of genetic engineering.
biogenetic law: Name given by Haeckel to recapitulation.
biogeography: The study of patterns of geographical distribution of plants and animals across Earth, and the changes in those distributions over time.
biological species concept: The concept of species, according to which a species is a set of organisms that can interbreed among each other. Compare with cladistic species concept, ecological species concept, phenetic species concept, and recognition species concept.
biometrics: The quantitative study of characters of organisms.
biosphere: The part of Earth and its atmosphere capable of sustaining life.
bipedalism: Of hominids, walking upright on two hind legs; more generally, using two legs for locomotion.
bivalve: A mollusk that has a two-part hinged shell. Bivalves include clams, oysters, scallops, mussels, and other shellfish.
Blackmore, Susan: A psychologist interested in memes and the theory of memetics, evolutionary theory, consciousness, the effects of meditation, and why people believe in the paranormal. A recent book, The Meme Machine, offers an introduction to the subject of memes.
blending inheritance: The historically influential but factually erroneous theory that organisms contain a blend of their parents’ hereditary factors and pass that blend on to their offspring. Compare with Mendelian inheritance.
botanist: A scientist who studies plants.
brachiopod: Commonly known as “lamp shells,” these marine invertebrates resemble bivalve mollusks because of their hinged shells. Brachiopods were at their greatest abundance during the Paleozoic and Mesozoic eras.
Brodie, Edmund D., III: A biologist who studies the causes and evolutionary implications of interactions among traits in predators and their prey. Much of his work concentrates on the coevolutionary arms race between newts that posess tetrodotoxin, one of the most potent known toxins, and the resistant garter snakes who prey on them.
Brodie, Edmund D., Jr.: A biologist recognized internationally for his work on the evolution of mechanisms in amphibians that allow them to avoid predators. These mechanisms include toxins carried in skin secretions, coloration, and behavior.
Bruner, Jerome: A psychologist and professor at Harvard and Oxford Universities, and a prolific author whose book, The Process of Education, encouraged curriculum innovation based on theories of cognitive development.
bryozoan: A tiny marine invertebrate that forms a crust-like colony; colonies of bryozoans may look like scaly sheets on seaweed.
Burney, David: A biologist whose research has focused on endangered species, paleoenvironmental studies, and causes of extinction in North America, Africa, Madagascar, Hawaii, and the West Indies.
carbon isotope ratio: A measure of the proportion of the carbon-14 isotope to the carbon-12 isotope. Living material contains carbon-14 and carbon-12 in the same proportions as exists in the atmosphere. When an organism dies, however, it no longer takes up carbon from the atmosphere, and the carbon-14 it contains decays to nitrogen-14 at a constant rate. By measuring the carbon-14-to-carbon-12 ratio in a fossil or organic artifact, its age can be determined, a method called radiocarbon dating. Because most carbon-14 will have decayed after 50,000 years, the carbon isotope ratio is mainly useful for dating fossils and artifacts younger than this. It cannot be used to determine the age of Earth, for example.
carnivorous: Feeding largely or exclusively on meat or other animal tissue.
Carroll, Sean: Developmental geneticist with the Howard Hughes Medical Institute and professor at the University of Wisconsin-Madison. From the large-scale changes that distinguish major animal groups to the finely detailed color patterns on butterfly wings, Dr. Carroll’s research has centered on those genes that create the “molecular blueprint” for body pattern and play major roles in the origin of new features. Coauthor, with Jennifer Grenier and Scott Weatherbee, of From DNA to Diversity: Molecular Genetics and the Evolution of Animal Design.
Carson, Rachel: A scientist and writer fascinated with the workings of nature. Her best-known publication, Silent Spring, was written over the years 1958 to 1962. The book looks at the effects of insecticides and pesticides on songbird populations throughout the United States. The publication helped set off a wave of environmental legislation and galvanized the emerging ecological movement.
Castle, W.E.: An early experimental geneticist, his 1901 paper was the first on Mendelism in America. His Genetics of Domestic Rabbits, published in 1930 by Harvard University Press, covers such topics as the genes involved in determining the coat colors of rabbits and associated mutations.
cell: The basic structural and functional unit of most living organisms. Cell size varies, but most cells are microscopic. Cells may exist as independent units of life, as in bacteria and protozoans, or they may form colonies or tissues, as in all plants and animals. Each cell consists of a mass of protein material that is differentiated into cytoplasm and nucleoplasm, which contains DNA. The cell is enclosed by a cell membrane, which in the cells of plants, fungi, algae, and bacteria is surrounded by a cell wall. There are two main types of cell, prokaryotic and eukaryotic.
Cenozoic: The era of geologic time from 65 mya to the present, a time when the modern continents formed and modern animals and plants evolved.
centromere: A point on a chromosome that is involved in separating the copies of the chromosome produced during cell division. During this division, paired chromosomes look somewhat like an X, and the centromere is the constriction in the center.
cephalopod: Cephalopods include squid, octopi, cuttlefish, and chambered nautiluses. They are mollusks with tentacles and move by forcing water through their bodies like a jet.
character: Any recognizable trait, feature, or property of an organism. In phylogenetic studies, a character is a feature that is thought to vary independantly of other features, and to be derived from a corresponding feature in a common ancestor of the organisms being studied. A “character state” is one of the possible alternative conditions of the character. For example, “present” and “absent” are two states of the character “hair” in mammals. Similarly, a particular position in a DNA sequence is a character, and A, T, C, and G are its possible states (see bases.)
character displacement: The increased difference between two closely related species where they live in the same geographic region (sympatry) as compared with where they live in different geographic regions (allopatry). Explained by the relative influences of intra- and inter-specific competition in sympatry and allopatry.
chloroplast: A structure (or organelle) found in some cells of plants; its function is photosynthesis.
cholera: An acute infectious disease of the small intestine, caused by the bacterium Vibrio cholerae which is transmitted in drinking water contaminated by feces of a patient. After an incubation period of 1-5 days, cholera causes severe vomiting and diarrhea, which, if untreated, leads to dehydration that can be fatal.
chordate: A member of the phylum Chordata, which includes the tunicates, lancelets, and vertebrates. They are animals with a hollow dorsal nerve cord; a rodlike notochord that forms the basis of the internal skeleton; and paired gill slits in the wall of the pharynx behind the head, although in some chordates these are apparent only in early embryonic stages. All vertebrates are chordates, but the phylum also contains simpler types, such as sea-squirts, in which only the free-swimming larva has a notochord.
chromosomal inversion: See inversion.
chromosome: A structure in the cell nucleus that carries DNA. At certain times in the cell cycle, chromosomes are visible as string-like entities. Chromosomes consist of the DNA with various proteins, particularly histones, bound to it.
chronology: The order of events according to time.
Clack, Jenny: A paleontologist at Cambridge University in the U.K., Dr. Clack studies the origin, phylogeny, and radiation of early tetrapods and their relatives among the lobe-finned fish. She is interested in the timing and sequence of skeletal and other changes which occurred during the transition, and the origin and relationships of the diverse tetrapods of the late Paleozoic.
clade: A set of species descended from a common ancestral species. Synonym of monophyletic group.
cladism: Phylogenetic classification. The members of a group in a cladistic classification share a more recent common ancestor with one another than with the members of any other group. A group at any level in the classificatory hierarchy, such as a family, is formed by combining a subgroup at the next lowest level (the genus, in this case) with the subgroup or subgroups with which it shares its most recent common ancestor. Compare with evolutionary classification and phenetic classification.
cladistic species concept: The concept of species, according to which a species is a lineage of populations between two phylogenetic branch points (or speciation events). Compare with biological species concept, ecological species concept, phenetic species concept, and recognition species concept.
cladists: Evolutionary biologists who seek to classify Earth’s life forms according to their evolutionary relationships, not just overall similarity.
cladogram: A branching diagram that illustrates hypotheses about the evolutionary relationships among groups of organisms. Cladograms can be considered as a special type of phylogenetic tree that concentrates on the order in which different groups branched off from their common ancestors. A cladogram branches like a family tree, with the most closely related species on adjacent branches.
class: A category of taxonomic classification between order and phylum, a class comprises members of similar orders. See taxon.
classification: The arrangement of organisms into hierarchical groups. Modern biological classifications are Linnaean and classify organisms into species, genus, family, order, class, phylum, kingdom, and certain intermediate categoric levels. Cladism, evolutionary classification, and phenetic classification are three methods of classification.
cline: A geographic gradient in the frequency of a gene, or in the average value of a character.
clock: See molecular clock.
clone: A set of genetically identical organisms asexually reproduced from one ancestral organism.
coadaptation: Beneficial interaction between (1) a number of genes at different loci within an organism, (2) different parts of an organism, or (3) organisms belonging to different species.
codon: A triplet of bases (or nucleotides) in the DNA coding for one amino acid. The relation between codons and amino acids is given by the genetic code. The triplet of bases that is complementary to a condon is called an anticodon; conventionally, the triplet in the mRNA is called the codon and the triplet in the tRNA is called the anticodon.
coelacanth: Although long thought to have gone extinct about 65 million years ago, one of these deep-water, lungless fish was caught in the 1930s. Others have since been caught and filmed in their natural habitat.
coevolution: Evolution in two or more species, such as predator and its prey or a parasite and its host, in which evolutionary changes in one species influence the evolution of the other species.
cognitive: Relating to cognition, the mental processes involved in the gathering, organization, and use of knowledge, including such aspects as awareness, perception, reasoning, and judgement. The term refers to any mental “behaviors” where the underlying characteristics are abstract in nature and involve insight, expectancy, complex rule use, imagery, use of symbols, belief, intentionality, problem-solving, and so forth.
common ancestor: The most recent ancestral form or species from which two different species evolved.
comparative biology: The study of patterns among more than one species.
comparative method: The study of adaptation by comparing many species.
concerted evolution: The tendency of the different genes in a gene family to evolve in concert; that is, each gene locus in the family comes to have the same genetic variant.
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Elephants are large mammals of the family Elephantidae and the order Proboscidea. Two species are traditionally recognised, the African elephant (Loxodonta africana) and the Asian elephant (Elephas maximus), although some evidence suggests that African bush elephants and African forest elephants are separate species (L.africana and L.cyclotis respectively). Elephants are scattered throughout sub-Saharan Africa, South Asia, and Southeast Asia. Elephantidae is the only surviving family of the order Proboscidea; other, now extinct, members of the order include deinotheres, gomphotheres, mammoths, and mastodons. Male African elephants are the largest extant terrestrial animals and can reach a height of 4m (13ft) and weigh 7,000kg (15,000lb). All elephants have several distinctive features, the most notable of which is a long trunk or proboscis, used for many purposes, particularly breathing, lifting water and grasping objects. Their incisors grow into tusks, which can serve as weapons and as tools for moving objects and digging. Elephants’ large ear flaps help to control their body temperature. Their pillar-like legs can carry their great weight. African elephants have larger ears and concave backs while Asian elephants have smaller ears and convex or level backs.
Elephants are herbivorous and can be found in different habitats including savannahs, forests, deserts and marshes. They prefer to stay near water. They are considered to be keystone species due to their impact on their environments. Other animals tend to keep their distance where predators such as lions, tigers, hyenas, and wild dogs usually target only the young elephants (or “calves”). Females (“cows”) tend to live in family groups, which can consist of one female with her calves or several related females with offspring. The groups are led by an individual known as the matriarch, often the oldest cow. Elephants have a fissionfusion society in which multiple family groups come together to socialise. Males (“bulls”) leave their family groups when they reach puberty, and may live alone or with other males. Adult bulls mostly interact with family groups when looking for a mate and enter a state of increased testosterone and aggression known as musth, which helps them gain dominance and reproductive success. Calves are the centre of attention in their family groups and rely on their mothers for as long as three years. Elephants can live up to 70 years in the wild. They communicate by touch, sight, smell and sound; elephants use infrasound, and seismic communication over long distances. Elephant intelligence has been compared with that of primates and cetaceans. They appear to have self-awareness and show empathy for dying or dead individuals of their kind.
African elephants are listed as vulnerable by the International Union for Conservation of Nature (IUCN), while the Asian elephant is classed as endangered. One of the biggest threats to elephant populations is the ivory trade, as the animals are poached for their ivory tusks. Other threats to wild elephants include habitat destruction and conflicts with local people. Elephants are used as working animals in Asia. In the past they were used in war; today, they are often controversially put on display in zoos, or exploited for entertainment in circuses. Elephants are highly recognisable and have been featured in art, folklore, religion, literature and popular culture.
The word “elephant” is based on the Latin elephas (genitive elephantis) (“elephant”), which is the Latinised form of the Greek (elephas) (genitive (elephantos)), probably from a non-Indo-European language, likely Phoenician. It is attested in Mycenaean Greek as e-re-pa (genitive e-re-pa-to) in Linear B syllabic script. As in Mycenaean Greek, Homer used the Greek word to mean ivory, but after the time of Herodotus, it also referred to the animal. The word “elephant” appears in Middle English as olyfaunt (c.1300) and was borrowed from Old French oliphant (12th century).Loxodonta, the generic name for the African elephants, is Greek for “oblique-sided tooth”.
Elephants belong to the family Elephantidae, the sole remaining family within the order Proboscidea. Their closest extant relatives are the sirenians (dugongs and manatees) and the hyraxes, with which they share the clade Paenungulata within the superorder Afrotheria. Elephants and sirenians are further grouped in the clade Tethytheria. Traditionally, two species of elephants are recognised; the African elephant (Loxodonta africana) of sub-Saharan Africa, and the Asian elephant (Elephas maximus) of South and Southeast Asia. African elephants have larger ears, a concave back, more wrinkled skin, a sloping abdomen and two finger-like extensions at the tip of the trunk. Asian elephants have smaller ears, a convex or level back, smoother skin, a horizontal abdomen that occasionally sags in the middle and one extension at the tip of the trunk. The looped ridges on the molars are narrower in the Asian elephant while those of the African are more diamond-shaped. The Asian elephant also has dorsal bumps on its head and some patches of depigmentation on its skin. In general, African elephants are larger than their Asian cousins.
Swedish zoologist Carl Linnaeus first described the genus Elephas and an elephant from Sri Lanka (then known as Ceylon) under the binomial Elephas maximus in 1758. In 1798, Georges Cuvier classified the Indian elephant under the binomial Elephas indicus. Dutch zoologist Coenraad Jacob Temminck described the Sumatran elephant in 1847 under the binomial Elephas sumatranus. English zoologist Frederick Nutter Chasen classified all three as subspecies of the Asian elephant in 1940. Asian elephants vary geographically in their colour and amount of depigmentation. The Sri Lankan elephant (Elephas maximus maximus) inhabits Sri Lanka, the Indian elephant (E.m.indicus) is native to mainland Asia (on the Indian subcontinent and Indochina), and the Sumatran elephant (E.m.sumatranus) is found in Sumatra. One disputed subspecies, the Borneo elephant, lives in northern Borneo and is smaller than all the other subspecies. It has larger ears, a longer tail, and straighter tusks than the typical elephant. Sri Lankan zoologist Paules Edward Pieris Deraniyagala described it in 1950 under the trinomial Elephas maximus borneensis, taking as his type an illustration in National Geographic. It was subsequently subsumed under either E.m.indicus or E.m.sumatranus. Results of a 2003 genetic analysis indicate its ancestors separated from the mainland population about 300,000years ago. A 2008 study found that Borneo elephants are not indigenous to the island but were brought there before 1521 by the Sultan of Sulu from Java, where elephants are now extinct.
The African elephant was first named by German naturalist Johann Friedrich Blumenbach in 1797 as Elephas africana. The genus Loxodonta was commonly believed to have been named by Georges Cuvier in 1825. Cuvier spelled it Loxodonte and an anonymous author romanised the spelling to Loxodonta; the International Code of Zoological Nomenclature recognises this as the proper authority. In 1942, 18 subspecies of African elephant were recognised by Henry Fairfield Osborn, but further morphological data has reduced the number of classified subspecies, and by the 1990s, only two were recognised, the savannah or bush elephant (L.a.africana) and the forest elephant (L.a.cyclotis); the latter has smaller and more rounded ears and thinner and straighter tusks, and is limited to the forested areas of western and Central Africa. A 2000 study argued for the elevation of the two forms into separate species (L.africana and L.cyclotis respectively) based on differences in skull morphology. DNA studies published in 2001 and 2007 also suggested they were distinct species, while studies in 2002 and 2005 concluded that they were the same species. Further studies (2010, 2011, 2015) have supported African savannah and forest elephants’ status as separate species. The two species are believed to have diverged 6 million years ago. The third edition of Mammal Species of the World lists the two forms as full species and does not list any subspecies in its entry for Loxodonta africana. This approach is not taken by the United Nations Environment Programme’s World Conservation Monitoring Centre nor by the IUCN, both of which list L.cyclotis as a synonym of L.africana. Some evidence suggests that elephants of western Africa are a separate species, although this is disputed. The pygmy elephants of the Congo Basin, which have been suggested to be a separate species (Loxodonta pumilio) are probably forest elephants whose small size and/or early maturity are due to environmental conditions.
Over 161 extinct members and three major evolutionary radiations of the order Proboscidea have been recorded. The earliest proboscids, the African Eritherium and Phosphatherium of the late Paleocene, heralded the first radiation. The Eocene included Numidotherium, Moeritherium and Barytherium from Africa. These animals were relatively small and aquatic. Later on, genera such as Phiomia and Palaeomastodon arose; the latter likely inhabited forests and open woodlands. Proboscidean diversity declined during the Oligocene. One notable species of this epoch was Eritreum melakeghebrekristosi of the Horn of Africa, which may have been an ancestor to several later species. The beginning of the Miocene saw the second diversification, with the appearance of the deinotheres and the mammutids. The former were related to Barytherium, lived in Africa and Eurasia, while the latter may have descended from Eritreum and spread to North America.
The second radiation was represented by the emergence of the gomphotheres in the Miocene, which likely evolved from Eritreum and originated in Africa, spreading to every continent except Australia and Antarctica. Members of this group included Gomphotherium and Platybelodon. The third radiation started in the late Miocene and led to the arrival of the elephantids, which descended from, and slowly replaced, the gomphotheres. The African Primelephas gomphotheroides gave rise to Loxodonta, Mammuthus and Elephas. Loxodonta branched off earliest, around the Miocene and Pliocene boundary, while Mammuthus and Elephas diverged later during the early Pliocene. Loxodonta remained in Africa, while Mammuthus and Elephas spread to Eurasia, and the former reached North America. At the same time, the stegodontids, another proboscidean group descended from gomphotheres, spread throughout Asia, including the Indian subcontinent, China, southeast Asia and Japan. Mammutids continued to evolve into new species, such as the American mastodon.
At the beginning of the Pleistocene, elephantids experienced a high rate of speciation. Loxodonta atlantica became the most common species in northern and southern Africa but was replaced by Elephas iolensis later in the Pleistocene. Only when Elephas disappeared from Africa did Loxodonta become dominant once again, this time in the form of the modern species. Elephas diversified into new species in Asia, such as E.hysudricus and E.platycephus; the latter the likely ancestor of the modern Asian elephant.Mammuthus evolved into several species, including the well-known woolly mammoth. In the Late Pleistocene, most proboscidean species vanished during the Quaternary glaciation which killed off 50% of genera weighing over 5kg (11lb) worldwide. The Pleistocene also saw the arrival of Palaeoloxodon namadicus, the largest terrestrial mammal of all time.
Proboscideans experienced several evolutionary trends, such as an increase in size, which led to many giant species that stood up to 5m (16ft) tall. As with other megaherbivores, including the extinct sauropod dinosaurs, the large size of elephants likely developed to allow them to survive on vegetation with low nutritional value. Their limbs grew longer and the feet shorter and broader. Early proboscideans developed longer mandibles and smaller craniums, while more advanced ones developed shorter mandibles, which shifted the head’s centre of gravity. The skull grew larger, especially the cranium, while the neck shortened to provide better support for the skull. The increase in size led to the development and elongation of the mobile trunk to provide reach. The number of premolars, incisors and canines decreased. The cheek teeth (molars and premolars) became larger and more specialized, especially after elephants started to switch from C3-plants to C4-grasses, which caused their teeth to undergo a three-fold increase in teeth height as well as substantial multiplication of lamellae after about five million years ago. Only in the last million year or so did they return to a diet mainly consisting of C3 trees and shrubs. The upper second incisors grew into tusks, which varied in shape from straight, to curved (either upward or downward), to spiralled, depending on the species. Some proboscideans developed tusks from their lower incisors. Elephants retain certain features from their aquatic ancestry such as their middle ear anatomy and the internal testes of the males.
There has been some debate over the relationship of Mammuthus to Loxodonta or Elephas. Some DNA studies suggest Mammuthus is more closely related to the former, while others point to the latter. However, analysis of the complete mitochondrial genome profile of the woolly mammoth (sequenced in 2005) supports Mammuthus being more closely related to Elephas.Morphological evidence supports Mammuthus and Elephas as sister taxa, while comparisons of protein albumin and collagen have concluded that all three genera are equally related to each other. Some scientists believe a cloned mammoth embryo could one day be implanted in an Asian elephant’s womb.
Several species of proboscideans lived on islands and experienced insular dwarfism. This occurred primarily during the Pleistocene, when some elephant populations became isolated by fluctuating sea levels, although dwarf elephants did exist earlier in the Pliocene. These elephants likely grew smaller on islands due to a lack of large or viable predator populations and limited resources. By contrast, small mammals such as rodents develop gigantism in these conditions. Dwarf proboscideans are known to have lived in Indonesia, the Channel Islands of California, and several islands of the Mediterranean.
Elephas celebensis of Sulawesi is believed to have descended from Elephas planifrons. Elephas falconeri of Malta and Sicily was only 1m (3ft), and had probably evolved from the straight-tusked elephant. Other descendants of the straight-tusked elephant existed in Cyprus. Dwarf elephants of uncertain descent lived in Crete, Cyclades and Dodecanese, while dwarf mammoths are known to have lived in Sardinia. The Columbian mammoth colonised the Channel Islands and evolved into the pygmy mammoth. This species reached a height of 1.21.8m (46ft) and weighed 2002,000kg (4404,410lb). A population of small woolly mammoths survived on Wrangel Island, now 140km (87mi) north of the Siberian coast, as recently as 4,000 years ago. After their discovery in 1993, they were considered dwarf mammoths. This classification has been re-evaluated and since the Second International Mammoth Conference in 1999, these animals are no longer considered to be true “dwarf mammoths”.
Elephants are the largest living terrestrial animals. African elephants stand 34m (1013ft) and weigh 4,0007,000kg (8,80015,400lb) while Asian elephants stand 23.5m (711ft) and weigh 3,0005,000kg (6,60011,000lb). In both cases, males are larger than females. Among African elephants, the forest form is smaller than the savannah form. The skeleton of the elephant is made up of 326351 bones. The vertebrae are connected by tight joints, which limit the backbone’s flexibility. African elephants have 21 pairs of ribs, while Asian elephants have 19 or 20 pairs.
An elephant’s skull is resilient enough to withstand the forces generated by the leverage of the tusks and head-to-head collisions. The back of the skull is flattened and spread out, creating arches that protect the brain in every direction. The skull contains air cavities (sinuses) that reduce the weight of the skull while maintaining overall strength. These cavities give the inside of the skull a honeycomb-like appearance. The cranium is particularly large and provides enough room for the attachment of muscles to support the entire head. The lower jaw is solid and heavy. Because of the size of the head, the neck is relatively short to provide better support. Lacking a lacrimal apparatus, the eye relies on the harderian gland to keep it moist. A durable nictitating membrane protects the eye globe. The animal’s field of vision is compromised by the location and limited mobility of the eyes. Elephants are considered dichromats and they can see well in dim light but not in bright light. The core body temperature averages 35.9C (97F), similar to a human. Like all mammals, an elephant can raise or lower its temperature a few degrees from the average in response to extreme environmental conditions.
Elephant ears have thick bases with thin tips. The ear flaps, or pinnae, contain numerous blood vessels called capillaries. Warm blood flows into the capillaries, helping to release excess body heat into the environment. This occurs when the pinnae are still, and the animal can enhance the effect by flapping them. Larger ear surfaces contain more capillaries, and more heat can be released. Of all the elephants, African bush elephants live in the hottest climates, and have the largest ear flaps. Elephants are capable of hearing at low frequencies and are most sensitive at 1 kHz.
The trunk, or proboscis, is a fusion of the nose and upper lip, although in early fetal life, the upper lip and trunk are separated. The trunk is elongated and specialised to become the elephant’s most important and versatile appendage. It contains up to 150,000 separate muscle fascicles, with no bone and little fat. These paired muscles consist of two major types: superficial (surface) and internal. The former are divided into dorsals, ventrals and laterals, while the latter are divided into transverse and radiating muscles. The muscles of the trunk connect to a bony opening in the skull. The nasal septum is composed of tiny muscle units that stretch horizontally between the nostrils. Cartilage divides the nostrils at the base. As a muscular hydrostat, the trunk moves by precisely coordinated muscle contractions. The muscles work both with and against each other. A unique proboscis nerve formed by the maxillary and facial nerves runs along both sides of the trunk.
Elephant trunks have multiple functions, including breathing, olfaction, touching, grasping, and sound production. The animal’s sense of smell may be four times as sensitive as that of a bloodhound. The trunk’s ability to make powerful twisting and coiling movements allows it to collect food, wrestle with conspecifics, and lift up to 350kg (770lb). It can be used for delicate tasks, such as wiping an eye and checking an orifice, and is capable of cracking a peanut shell without breaking the seed. With its trunk, an elephant can reach items at heights of up to 7m (23ft) and dig for water under mud or sand. Individuals may show lateral preference when grasping with their trunks: some prefer to twist them to the left, others to the right. Elephants can suck up water both to drink and to spray on their bodies. An adult Asian elephant is capable of holding 8.5L (2.2USgal) of water in its trunk. They will also spray dust or grass on themselves. When underwater, the elephant uses its trunk as a snorkel.
The African elephant has two finger-like extensions at the tip of the trunk that allow it to grasp and bring food to its mouth. The Asian elephant has only one, and relies more on wrapping around a food item and squeezing it into its mouth. Asian elephants have more muscle coordination and can perform more complex tasks. Losing the trunk would be detrimental to an elephant’s survival, although in rare cases individuals have survived with shortened ones. One elephant has been observed to graze by kneeling on its front legs, raising on its hind legs and taking in grass with its lips.Floppy trunk syndrome is a condition of trunk paralysis in African bush elephants caused by the degradation of the peripheral nerves and muscles beginning at the tip.
Elephants usually have 26 teeth: the incisors, known as the tusks, 12 deciduous premolars, and 12 molars. Unlike most mammals, which grow baby teeth and then replace them with a single permanent set of adult teeth, elephants are polyphyodonts that have cycles of tooth rotation throughout their lives. The chewing teeth are replaced six times in a typical elephant’s lifetime. Teeth are not replaced by new ones emerging from the jaws vertically as in most mammals. Instead, new teeth grow in at the back of the mouth and move forward to push out the old ones. The first chewing tooth on each side of the jaw falls out when the elephant is two to three years old. The second set of chewing teeth falls out when the elephant is four to six years old. The third set is lost at 915 years of age, and set four lasts until 1828 years of age. The fifth set of teeth lasts until the elephant is in its early 40s. The sixth (and usually final) set must last the elephant the rest of its life. Elephant teeth have loop-shaped dental ridges, which are thicker and more diamond-shaped in African elephants.
The tusks of an elephant are modified incisors in the upper jaw. They replace deciduous milk teeth when the animal reaches 612 months of age and grow continuously at about 17cm (7in) a year. A newly developed tusk has a smooth enamel cap that eventually wears off. The dentine is known as ivory and its cross-section consists of crisscrossing line patterns, known as “engine turning”, which create diamond-shaped areas. As a piece of living tissue, a tusk is relatively soft; it is as hard as the mineral calcite. Much of the incisor can be seen externally, while the rest is fastened to a socket in the skull. At least one-third of the tusk contains the pulp and some have nerves stretching to the tip. Thus it would be difficult to remove it without harming the animal. When removed, ivory begins to dry up and crack if not kept cool and moist. Tusks serve multiple purposes. They are used for digging for water, salt, and roots; debarking or marking trees; and for moving trees and branches when clearing a path. When fighting, they are used to attack and defend, and to protect the trunk.
Like humans, who are typically right- or left-handed, elephants are usually right- or left-tusked. The dominant tusk, called the master tusk, is generally more worn down, as it is shorter with a rounder tip. For the African elephants, tusks are present in both males and females, and are around the same length in both sexes, reaching up to 3m (10ft), but those of males tend to be thicker. In earlier times elephant tusks weighing over 200 pounds (more than 90kg) were not uncommon, though it is rare today to see any over 100 pounds (45kg).
In the Asian species, only the males have large tusks. Female Asians have very small ones, or none at all. Tuskless males exist and are particularly common among Sri Lankan elephants. Asian males can have tusks as long as Africans’, but they are usually slimmer and lighter; the largest recorded was 3.02m (10ft) long and weighed 39kg (86lb). Hunting for elephant ivory in Africa and Asia has led to natural selection for shorter tusks and tusklessness.
An elephant’s skin is generally very tough, at 2.5cm (1in) thick on the back and parts of the head. The skin around the mouth, anus and inside of the ear is considerably thinner. Elephants typically have grey skin, but African elephants look brown or reddish after wallowing in coloured mud. Asian elephants have some patches of depigmentation, particularly on the forehead and ears and the areas around them. Calves have brownish or reddish hair, especially on the head and back. As elephants mature, their hair darkens and becomes sparser, but dense concentrations of hair and bristles remain on the end of the tail as well as the chin, genitals and the areas around the eyes and ear openings. Normally the skin of an Asian elephant is covered with more hair than its African counterpart.
An elephant uses mud as a sunscreen, protecting its skin from ultraviolet light. Although tough, an elephant’s skin is very sensitive. Without regular mud baths to protect it from burning, insect bites, and moisture loss, an elephant’s skin suffers serious damage. After bathing, the elephant will usually use its trunk to blow dust onto its body and this dries into a protective crust. Elephants have difficulty releasing heat through the skin because of their low surface-area-to-volume ratio, which is many times smaller than that of a human. They have even been observed lifting up their legs, presumably in an effort to expose their soles to the air.
To support the animal’s weight, an elephant’s limbs are positioned more vertically under the body than in most other mammals. The long bones of the limbs have cancellous bone in place of medullary cavities. This strengthens the bones while still allowing haematopoiesis. Both the front and hind limbs can support an elephant’s weight, although 60% is borne by the front. Since the limb bones are placed on top of each other and under the body, an elephant can stand still for long periods of time without using much energy. Elephants are incapable of rotating their front legs, as the ulna and radius are fixed in pronation; the “palm” of the manus faces backward. The pronator quadratus and the pronator teres are either reduced or absent. The circular feet of an elephant have soft tissues or “cushion pads” beneath the manus or pes, which distribute the weight of the animal. They appear to have a sesamoid, an extra “toe” similar in placement to a giant panda’s extra “thumb”, that also helps in weight distribution. As many as five toenails can be found on both the front and hind feet.
Elephants can move both forwards and backwards, but cannot trot, jump, or gallop. They use only two gaits when moving on land, the walk and a faster gait similar to running. In walking, the legs act as pendulums, with the hips and shoulders rising and falling while the foot is planted on the ground. With no “aerial phase”, the fast gait does not meet all the criteria of running, although the elephant uses its legs much like other running animals, with the hips and shoulders falling and then rising while the feet are on the ground. Fast-moving elephants appear to ‘run’ with their front legs, but ‘walk’ with their hind legs and can reach a top speed of 18km/h (11mph). At this speed, most other quadrupeds are well into a gallop, even accounting for leg length. Spring-like kinetics could explain the difference between the motion of elephants and other animals. During locomotion, the cushion pads expand and contract, and reduce both the pain and noise that would come from a very heavy animal moving. Elephants are capable swimmers. They have been recorded swimming for up to six hours without touching the bottom, and have travelled as far as 48km (30mi) at a stretch and at speeds of up to 2.1km/h (1mph).
The brain of an elephant weighs 4.55.5kg (1012lb) compared to 1.6kg (4lb) for a human brain. While the elephant brain is larger overall, it is proportionally smaller. At birth, an elephant’s brain already weighs 3040% of its adult weight. The cerebrum and cerebellum are well developed, and the temporal lobes are so large that they bulge out laterally. The throat of an elephant appears to contain a pouch where it can store water for later use.
The heart of an elephant weighs 1221kg (2646lb). It has a double-pointed apex, an unusual trait among mammals. When standing, the elephant’s heart beats approximately 30 times per minute. Unlike many other animals, the heart rate speeds up by 8 to 10 beats per minute when the elephant is lying down. The lungs are attached to the diaphragm, and breathing relies mainly on the diaphragm rather than the expansion of the ribcage.Connective tissue exists in place of the pleural cavity. This may allow the animal to deal with the pressure differences when its body is underwater and its trunk is breaking the surface for air, although this explanation has been questioned. Another possible function for this adaptation is that it helps the animal suck up water through the trunk. Elephants inhale mostly through the trunk, although some air goes through the mouth. They have a hindgut fermentation system, and their large and small intestines together reach 35m (115ft) in length. The majority of an elephant’s food intake goes undigested despite the process lasting up to a day.
A male elephant’s testes are located internally near the kidneys. The elephant’s penis can reach a length of 100cm (39in) and a diameter of 16cm (6in) at the base. It is S-shaped when fully erect and has a Y-shaped orifice. The female has a well-developed clitoris at up to 40cm (16in). The vulva is located between the hind legs instead of near the tail as in most mammals. Determining pregnancy status can be difficult due to the animal’s large abdominal cavity. The female’s mammary glands occupy the space between the front legs, which puts the suckling calf within reach of the female’s trunk. Elephants have a unique organ, the temporal gland, located in both sides of the head. This organ is associated with sexual behaviour, and males secrete a fluid from it when in musth. Females have also been observed with secretions from the temporal glands.
The African bush elephant can be found in habitats as diverse as dry savannahs, deserts, marshes, and lake shores, and in elevations from sea level to mountain areas above the snow line. Forest elephants mainly live in equatorial forests, but will enter gallery forests and ecotones between forests and savannahs. Asian elephants prefer areas with a mix of grasses, low woody plants and trees, primarily inhabiting dry thorn-scrub forests in southern India and Sri Lanka and evergreen forests in Malaya. Elephants are herbivorous and will eat leaves, twigs, fruit, bark, grass and roots. They are born with sterile intestines, and require bacteria obtained from their mothers feces to digest vegetation. African elephants are mostly browsers while Asian elephants are mainly grazers. They can consume as much as 150kg (330lb) of food and 40L (11USgal) of water in a day. Elephants tend to stay near water sources. Major feeding bouts take place in the morning, afternoon and night. At midday, elephants rest under trees and may doze off while standing. Sleeping occurs at night while the animal is lying down. Elephants average 34 hours of sleep per day. Both males and family groups typically move 1020km (612mi) a day, but distances as far as 90180km (56112mi) have been recorded in the Etosha region of Namibia. Elephants go on seasonal migrations in search of food, water and mates. At Chobe National Park, Botswana, herds travel 325km (202mi) to visit the river when the local waterholes dry up.
Because of their large size, elephants have a huge impact on their environments and are considered keystone species. Their habit of uprooting trees and undergrowth can transform savannah into grasslands; when they dig for water during drought, they create waterholes that can be used by other animals. They can enlarge waterholes when they bathe and wallow in them. At Mount Elgon, elephants excavate caves that are used by ungulates, hyraxes, bats, birds and insects. Elephants are important seed dispersers; African forest elephants ingest and defecate seeds, with either no effect or a positive effect on germination. The seeds are typically dispersed in large amounts over great distances. In Asian forests, large seeds require giant herbivores like elephants and rhinoceros for transport and dispersal. This ecological niche cannot be filled by the next largest herbivore, the tapir. Because most of the food elephants eat goes undigested, their dung can provide food for other animals, such as dung beetles and monkeys. Elephants can have a negative impact on ecosystems. At Murchison Falls National Park in Uganda, the overabundance of elephants has threatened several species of small birds that depend on woodlands. Their weight can compact the soil, which causes the rain to run off, leading to erosion.
Elephants typically coexist peacefully with other herbivores, which will usually stay out of their way. Some aggressive interactions between elephants and rhinoceros have been recorded. At Aberdare National Park, Kenya, a rhino attacked an elephant calf and was killed by the other elephants in the group. At HluhluweUmfolozi Game Reserve, South Africa, introduced young orphan elephants went on a killing spree that claimed the lives of 36 rhinos during the 1990s, but ended with the introduction of older males. The size of adult elephants makes them nearly invulnerable to predators, though there are rare reports of adult elephants falling prey to tigers. Calves may be preyed on by lions, spotted hyenas, and wild dogs in Africa and tigers in Asia. The lions of Savuti, Botswana, have adapted to hunting juvenile elephants during the dry season, and a pride of 30 lions has been recorded killing juvenile individuals between the ages of four and eleven years. Elephants appear to distinguish between the growls of larger predators like tigers and smaller ones like leopards (which have not been recorded killing calves); the latter they react less fearfully and more aggressively to. Elephants tend to have high numbers of parasites, particularly nematodes, compared to other herbivores. This is due to lower predation pressures that would otherwise kill off many of the individuals with significant parasite loads.
Female elephants spend their entire lives in tight-knit matrilineal family groups, some of which are made up of more than ten members, including three pairs of mothers with offspring, and are led by the matriarch which is often the eldest female. She remains leader of the group until death or if she no longer has the energy for the role; a study on zoo elephants showed that when the matriarch died, the levels of faecal corticosterone (‘stress hormone’) dramatically increased in the surviving elephants. When her tenure is over, the matriarch’s eldest daughter takes her place; this occurs even if her sister is present. The older matriarchs tend to be more effective decision-makers.
The social circle of the female elephant does not necessarily end with the small family unit. In the case of elephants in Amboseli National Park, Kenya, a female’s life involves interaction with other families, clans, and subpopulations. Families may associate and bond with each other, forming what are known as bond groups. These are typically made of two family groups. During the dry season, elephant families may cluster together and form another level of social organisation known as the clan. Groups within these clans do not form strong bonds, but they defend their dry-season ranges against other clans. There are typically nine groups in a clan. The Amboseli elephant population is further divided into the “central” and “peripheral” subpopulations.
Some elephant populations in India and Sri Lanka have similar basic social organisations. There appear to be cohesive family units and loose aggregations. They have been observed to have “nursing units” and “juvenile-care units”. In southern India, elephant populations may contain family groups, bond groups and possibly clans. Family groups tend to be small, consisting of one or two adult females and their offspring. A group containing more than two adult females plus offspring is known as a “joint family”. Malay elephant populations have even smaller family units, and do not have any social organisation higher than a family or bond group. Groups of African forest elephants typically consist of one adult female with one to three offspring. These groups appear to interact with each other, especially at forest clearings.
The social life of the adult male is very different. As he matures, a male spends more time at the edge of his group and associates with outside males or even other families. At Amboseli, young males spend over 80% of their time away from their families when they are 1415. The adult females of the group start to show aggression towards the male, which encourages him to permanently leave. When males do leave, they either live alone or with other males. The former is typical of bulls in dense forests. Asian males are usually solitary, but occasionally form groups of two or more individuals; the largest consisted of seven bulls. Larger bull groups consisting of over 10 members occur only among African bush elephants, the largest of which numbered up to 144 individuals. A dominance hierarchy exists among males, whether they range socially or solitarily. Dominance depends on the age, size and sexual condition. Old bulls appear to control the aggression of younger ones and prevent them from forming “gangs”. Adult males and females come together for reproduction. Bulls appear to associate with family groups if an oestrous cow is present.
Adult males enter a state of increased testosterone known as musth. In a population in southern India, males first enter musth at the age of 15, but it is not very intense until they are older than 25. At Amboseli, bulls under 24 do not go into musth, while half of those aged 2535 and all those over 35 do. Young bulls appear to enter musth during the dry season (JanuaryMay), while older bulls go through it during the wet season (JuneDecember). The main characteristic of a bull’s musth is a fluid secreted from the temporal gland that runs down the side of his face. He may urinate with his penis still in his sheath, which causes the urine to spray on his hind legs. Behaviours associated with musth include walking with the head held high and swinging, picking at the ground with the tusks, marking, rumbling and waving only one ear at a time. This can last from a day to four months.
Males become extremely aggressive during musth. Size is the determining factor in agonistic encounters when the individuals have the same condition. In contests between musth and non-musth individuals, musth bulls win the majority of the time, even when the non-musth bull is larger. A male may stop showing signs of musth when he encounters a musth male of higher rank. Those of equal rank tend to avoid each other. Agonistic encounters typically consist of threat displays, chases and minor sparring with the tusks. Serious fights are rare.
Elephants are polygynous breeders, and copulations are most frequent during the peak of the wet season. A cow in oestrus releases chemical signals (pheromones) in her urine and vaginal secretions to signal her readiness to mate. A bull will follow a potential mate and assess her condition with the flehmen response, which requires the male to collect a chemical sample with his trunk and bring it to the vomeronasal organ. The oestrous cycle of a cow lasts 1416 weeks with a 46-week follicular phase and an 810-week luteal phase. While most mammals have one surge of luteinizing hormone during the follicular phase, elephants have two. The first (or anovulatory) surge, could signal to males that the female is in oestrus by changing her scent, but ovulation does not occur until the second (or ovulatory) surge. Fertility rates in cows decline around 4550 years of age.
Bulls engage in a behaviour known as mate-guarding, where they follow oestrous females and defend them from other males. Most mate-guarding is done by musth males, and females actively seek to be guarded by them, particularly older ones. Thus these bulls have more reproductive success. Musth appears to signal to females the condition of the male, as weak or injured males do not have normal musths. For young females, the approach of an older bull can be intimidating, so her relatives stay nearby to provide support and reassurance. During copulation, the male lays his trunk over the female’s back. The penis is very mobile, being able to move independently of the pelvis. Prior to mounting, it curves forward and upward. Copulation lasts about 45 seconds and does not involve pelvic thrusting or ejaculatory pause.
Homosexual behaviour is frequent in both sexes. As in heterosexual interactions, this involves mounting. Male elephants sometimes stimulate each other by playfighting and “championships” may form between old bulls and younger males. Female same-sex behaviours have been documented only in captivity where they are known to masturbate one another with their trunks.
Gestation in elephants typically lasts around two years with interbirth intervals usually lasting four to five years. Births tend to take place during the wet season. Calves are born 85cm (33in) tall and weigh around 120kg (260lb). Typically, only a single young is born, but twins sometimes occur. The relatively long pregnancy is maintained by five corpus luteums (as opposed to one in most mammals) and gives the foetus more time to develop, particularly the brain and trunk. As such, newborn elephants are precocial and quickly stand and walk to follow their mother and family herd. A new calf is usually the centre of attention for herd members. Adults and most of the other young will gather around the newborn, touching and caressing it with their trunks. For the first few days, the mother is intolerant of other herd members near her young. Alloparenting where a calf is cared for by someone other than its mother takes place in some family groups. Allomothers are typically two to twelve years old. When a predator is near, the family group gathers together with the calves in the centre.
For the first few days, the newborn is unsteady on its feet, and needs the support of its mother. It relies on touch, smell and hearing, as its eyesight is poor. It has little precise control over its trunk, which wiggles around and may cause it to trip. By its second week of life, the calf can walk more firmly and has more control over its trunk. After its first month, a calf can pick up, hold and put objects in its mouth, but cannot suck water through the trunk and must drink directly through the mouth. It is still dependent on its mother and keeps close to her.
For its first three months, a calf relies entirely on milk from its mother for nutrition after which it begins to forage for vegetation and can use its trunk to collect water. At the same time, improvements in lip and leg coordination occur. Calves continue to suckle at the same rate as before until their sixth month, after which they become more independent when feeding. By nine months, mouth, trunk and foot coordination is perfected. After a year, a calf’s abilities to groom, drink, and feed itself are fully developed. It still needs its mother for nutrition and protection from predators for at least another year. Suckling bouts tend to last 24 min/hr for a calf younger than a year and it continues to suckle until it reaches three years of age or older. Suckling after two years may serve to maintain growth rate, body condition and reproductive ability. Play behaviour in calves differs between the sexes; females run or chase each other, while males play-fight. The former are sexually mature by the age of nine years while the latter become mature around 1415 years. Adulthood starts at about 18 years of age in both sexes. Elephants have long lifespans, reaching 6070 years of age.Lin Wang, a captive male Asian elephant, lived for 86 years.
Touching is an important form of communication among elephants. Individuals greet each other by stroking or wrapping their trunks; the latter also occurs during mild competition. Older elephants use trunk-slaps, kicks and shoves to discipline younger ones. Individuals of any age and sex will touch each other’s mouths, temporal glands and genitals, particularly during meetings or when excited. This allows individuals to pick up chemical cues. Touching is especially important for mothercalf communication. When moving, elephant mothers will touch their calves with their trunks or feet when side-by-side or with their tails if the calf is behind them. If a calf wants to rest, it will press against its mother’s front legs and when it wants to suckle, it will touch her breast or leg.
Visual displays mostly occur in agonistic situations. Elephants will try to appear more threatening by raising their heads and spreading their ears. They may add to the display by shaking their heads and snapping their ears, as well as throwing dust and vegetation. They are usually bluffing when performing these actions. Excited elephants may raise their trunks. Submissive ones will lower their heads and trunks, as well as flatten their ears against their necks, while those that accept a challenge will position their ears in a V shape.
Elephants produce several sounds, usually through the larynx, though some may be modified by the trunk. Perhaps the most well known is the trumpet, which is made during excitement, distress or aggression. Fighting elephants may roar or squeal, and wounded ones may bellow.Rumbles are produced during mild arousal and some appear to be infrasonic. Infrasonic calls are important, particularly for long-distance communication, in both Asian and African elephants. For Asian elephants, these calls have a frequency of 1424Hz, with sound pressure levels of 8590dB and last 1015 seconds. For African elephants, calls range from 1535Hz with sound pressure levels as high as 117dB, allowing communication for many kilometres, with a possible maximum range of around 10km (6mi).
At Amboseli, several different infrasonic calls have been identified. A greeting rumble is emitted by members of a family group after having been separated for several hours. Contact calls are soft, unmodulated sounds made by individuals that have been separated from their group and may be responded to with a “contact answer” call that starts out loud, but becomes softer. A “let’s go” soft rumble is emitted by the matriarch to signal to the other herd members that it is time to move to another spot. Bulls in musth emit a distinctive, low-frequency pulsated rumble nicknamed the “motorcycle”. Musth rumbles may be answered by the “female chorus”, a low-frequency, modulated chorus produced by several cows. A loud postcopulatory call may be made by an oestrous cow after mating. When a cow has mated, her family may produce calls of excitement known as the “mating pandemonium”.
Elephants are known to communicate with seismics, vibrations produced by impacts on the earth’s surface or acoustical waves that travel through it. They appear to rely on their leg and shoulder bones to transmit the signals to the middle ear. When detecting seismic signals, the animals lean forward and put more weight on their larger front feet; this is known as the “freezing behaviour”. Elephants possess several adaptations suited for seismic communication. The cushion pads of the feet contain cartilaginous nodes and have similarities to the acoustic fat found in marine mammals like toothed whales and sirenians. A unique sphincter-like muscle around the ear canal constricts the passageway, thereby dampening acoustic signals and allowing the animal to hear more seismic signals. Elephants appear to use seismics for a number of purposes. An individual running or mock charging can create seismic signals that can be heard at great distances. When detecting the seismics of an alarm call signalling danger from predators, elephants enter a defensive posture and family groups will pack together. Seismic waveforms produced by locomotion appear to travel distances of up to 32km (20mi) while those from vocalisations travel 16km (10mi).
Elephants exhibit mirror self-recognition, an indication of self-awareness and cognition that has also been demonstrated in some apes and dolphins. One study of a captive female Asian elephant suggested the animal was capable of learning and distinguishing between several visual and some acoustic discrimination pairs. This individual was even able to score a high accuracy rating when re-tested with the same visual pairs a year later. Elephants are among the species known to use tools. An Asian elephant has been observed modifying branches and using them as flyswatters. Tool modification by these animals is not as advanced as that of chimpanzees. Elephants are popularly thought of as having an excellent memory. This could have a factual basis; they possibly have cognitive maps to allow them to remember large-scale spaces over long periods of time. Individuals appear to be able to keep track of the current location of their family members.
Scientists debate the extent to which elephants feel emotion. They appear to show interest in the bones of their own kind, regardless of whether they are related. As with chimps and dolphins, a dying or dead elephant may elicit attention and aid from others, including those from other groups. This has been interpreted as expressing “concern”, however, others would dispute such an interpretation as being anthropomorphic; the Oxford Companion to Animal Behaviour (1987) advised that “one is well advised to study the behaviour rather than attempting to get at any underlying emotion”.
Distribution of elephants
African elephants were listed as vulnerable by the International Union for Conservation of Nature (IUCN) in 2008, with no independent assessment of the conservation status of the two forms. In 1979, Africa had an estimated minimum population of 1.3million elephants, with a possible upper limit of 3.0million. By 1989, the population was estimated to be 609,000; with 277,000 in Central Africa, 110,000 in eastern Africa, 204,000 in southern Africa, and 19,000 in western Africa. About 214,000 elephants were estimated to live in the rainforests, fewer than had previously been thought. From 1977 to 1989, elephant populations declined by 74% in East Africa. After 1987, losses in elephant numbers accelerated, and savannah populations from Cameroon to Somalia experienced a decline of 80%. African forest elephants had a total loss of 43%. Population trends in southern Africa were mixed, with anecdotal reports of losses in Zambia, Mozambique and Angola, while populations grew in Botswana and Zimbabwe and were stable in South Africa. Conversely, studies in 2005 and 2007 found populations in eastern and southern Africa were increasing by an average annual rate of 4.0%. Due to the vast areas involved, assessing the total African elephant population remains difficult and involves an element of guesswork. The IUCN estimates a total of around 440,000 individuals for 2012.
African elephants receive at least some legal protection in every country where they are found, but 70% of their range exists outside protected areas. Successful conservation efforts in certain areas have led to high population densities. As of 2008, local numbers were controlled by contraception or translocation. Large-scale cullings ceased in 1988, when Zimbabwe abandoned the practice. In 1989, the African elephant was listed under Appendix I by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), making trade illegal. Appendix II status (which allows restricted trade) was given to elephants in Botswana, Namibia and Zimbabwe in 1997 and South Africa in 2000. In some countries, sport hunting of the animals is legal; Botswana, Cameroon, Gabon, Mozambique, Namibia, South Africa, Tanzania, Zambia, and Zimbabwe have CITES export quotas for elephant trophies. In June 2016 the First Lady of Kenya, Margaret Kenyatta, helped launch the East Africa Grass-Root Elephant Education Campaign Walk, organised by elephant conservationist Jim Nyamu. The event was conducted to raise awareness of the value of elephants and rhinos, to help mitigate human-elephant conflicts, and to promote anti-poaching activities.
In 2008, the IUCN listed the Asian elephant as endangered due to a 50% population decline over the past 6075 years, while CITES lists the species under Appendix I. Asian elephants once ranged from Syria and Iraq (the subspecies Elephas maximus asurus), to China (up to the Yellow River) and Java. It is now extinct in these areas, and the current range of Asian elephants is highly fragmented. The total population of Asian elephants is estimated to be around 40,00050,000, although this may be a loose estimate. It is likely that around half of the population is in India. Although Asian elephants are declining in numbers overall, particularly in Southeast Asia, the population in the Western Ghats appears to be increasing.
The poaching of elephants for their ivory, meat and hides has been one of the major threats to their existence. Historically, numerous cultures made ornaments and other works of art from elephant ivory, and its use rivalled that of gold. The ivory trade contributed to the African elephant population decline in the late 20th century. This prompted international bans on ivory imports, starting with the United States in June 1989, and followed by bans in other North American countries, western European countries, and Japan. Around the same time, Kenya destroyed all its ivory stocks. CITES approved an international ban on ivory that went into effect in January 1990. Following the bans, unemployment rose in India and China, where the ivory industry was important economically. By contrast, Japan and Hong Kong, which were also part of the industry, were able to adapt and were not badly affected. Zimbabwe, Botswana, Namibia, Zambia, and Malawi wanted to continue the ivory trade and were allowed to, since their local elephant populations were healthy, but only if their supplies were from elephants that had been culled or died of natural causes.
The ban allowed the elephant to recover in parts of Africa. In January 2012, 650 elephants in Bouba Njida National Park, Cameroon, were killed by Chadian raiders. This has been called “one of the worst concentrated killings” since the ivory ban. Asian elephants are potentially less vulnerable to the ivory trade, as females usually lack tusks. Still, members of the species have been killed for their ivory in some areas, such as Periyar National Park in India. China was the biggest market for poached ivory but announced they would phase out the legal domestic manufacture and sale of ivory products in May, 2015, and in September 2015 China and the United States “said they would enact a nearly complete ban on the import and export of ivory.”
Other threats to elephants include habitat destruction and fragmentation. The Asian elephant lives in areas with some of the highest human populations. Because they need larger amounts of land than other sympatric terrestrial mammals, they are the first to be affected by human encroachment. In extreme cases, elephants may be confined to small islands of forest among human-dominated landscapes. Elephants cannot coexist with humans in agricultural areas due to their size and food requirements. Elephants commonly trample and consume crops, which contributes to conflicts with humans, and both elephants and humans have died by the hundreds as a result. Mitigating these conflicts is important for conservation. One proposed solution is the provision of urban corridors which allow the animals access to key areas.
Elephants have been working animals since at least the Indus Valley Civilization and continue to be used in modern times. There were 13,00016,500 working elephants employed in Asia as of 2000. These animals are typically captured from the wild when they are 1020 years old, when they can be trained quickly and easily, and will have a longer working life. They were traditionally captured with traps and lassos, but since 1950, tranquillisers have been used. Individuals of the Asian species are more commonly trained to be working animals, although the practice has also been attempted in Africa. The taming of African elephants in the Belgian Congo began by decree of Leopold II of Belgium during the 19th century and continues to the present with the Api Elephant Domestication Centre.
Asian elephants perform tasks such as hauling loads into remote areas, moving logs into trucks, transporting tourists around national parks, pulling wagons and leading religious processions. In northern Thailand, the animals are used to digest coffee beans for Black Ivory coffee. They are valued over mechanised tools because they can work in relatively deep water, require relatively little maintenance, need only vegetation and water as fuel and can be trained to memorise specific tasks. Elephants can be trained to respond to over 30 commands. Musth bulls can be difficult and dangerous to work with and are chained until the condition passes. In India, many working elephants are alleged to have been subject to abuse. They and other captive elephants are thus protected under the The Prevention of Cruelty to Animals Act of 1960.
In both Myanmar and Thailand, deforestation and other economic factors have resulted in sizable populations of unemployed elephants resulting in health problems for the elephants themselves as well as economic and safety problems for the people amongst whom they live.
Historically, elephants were considered formidable instruments of war. They were equipped with armour to protect their sides, and their tusks were given sharp points of iron or brass if they were large enough. War elephants were trained to grasp an enemy soldier and toss him to the person riding on them or to pin the soldier to the ground and impale him.
One of the earliest references to war elephants is in the Indian epic Mahabharata (written in the 4th century BCE, but said to describe events between the 11th and 8th centuries BCE). They were not used as much as horse-drawn chariots by either the Pandavas or Kauravas. During the Magadha Kingdom (which began in the 6th century BCE), elephants began to achieve greater cultural importance than horses, and later Indian kingdoms used war elephants extensively; 3,000 of them were used in the Nandas (5th and 4th centuries BCE) army, while 9,000 may have been used in the Mauryan army (between the 4th and 2nd centuries BCE). The Arthashastra (written around 300 BCE) advised the Mauryan government to reserve some forests for wild elephants for use in the army, and to execute anyone who killed them. From South Asia, the use of elephants in warfare spread west to Persia and east to Southeast Asia. The Persians used them during the Achaemenid Empire (between the 6th and 4th centuries BCE), while Southeast Asian states first used war elephants possibly as early as the 5th century BCE and continued to the 20th century.
Alexander the Great trained his foot soldiers to injure the animals and cause them to panic during wars with both the Persians and Indians. Ptolemy, who was one of Alexander’s generals, used corps of Asian elephants during his reign as the ruler of Egypt (which began in 323 BCE). His son and successor Ptolemy II (who began his rule in 285 BCE) obtained his supply of elephants further south in Nubia. From then on, war elephants were employed in the Mediterranean and North Africa throughout the classical period. The Greek king Pyrrhus used elephants in his attempted invasion of Rome in 280 BCE. While they frightened the Roman horses, they were not decisive and Pyrrhus ultimately lost the battle. The Carthaginian general Hannibal took elephants across the Alps during his war with the Romans and reached the Po Valley in 217 BCE with all of them alive, but they later succumbed to disease.
Elephants were historically kept for display in the menageries of Ancient Egypt, China, Greece and Rome. The Romans in particular pitted them against humans and other animals in gladiator events. In the modern era, elephants have traditionally been a major part of zoos and circuses around the world. In circuses, they are trained to perform tricks. The most famous circus elephant was probably Jumbo (1861 15 September 1885), who was a major attraction in the Barnum & Bailey Circus. These animals do not reproduce well in captivity, due to the difficulty of handling musth bulls and limited understanding of female oestrous cycles. Asian elephants were always more common than their African counterparts in modern zoos and circuses. After CITES listed the Asian elephant under Appendix I in 1975, the number of African elephants in zoos increased in the 1980s, although the import of Asians continued. Subsequently, the US received many of its captive African elephants from Zimbabwe, which had an overabundance of the animals. As of 2000, around 1,200 Asian and 700 African elephants were kept in zoos and circuses. The largest captive population is in North America, which has an estimated 370 Asian and 350 African elephants. About 380 Asians and 190 Africans are known to exist in Europe, and Japan has around 70 Asians and 67 Africans.
Keeping elephants in zoos has met with some controversy. Proponents of zoos argue that they offer researchers easy access to the animals and provide money and expertise for preserving their natural habitats, as well as safekeeping for the species. Critics claim that the animals in zoos are under physical and mental stress. Elephants have been recorded displaying stereotypical behaviours in the form of swaying back and forth, trunk swaying or route tracing. This has been observed in 54% of individuals in UK zoos. Elephants in European zoos appear to have shorter lifespans than their wild counterparts at only 17 years, although other studies suggest that zoo elephants live as long those in the wild.
The use of elephants in circuses has also been controversial; the Humane Society of the United States has accused circuses of mistreating and distressing their animals. In testimony to a US federal court in 2009, Barnum & Bailey Circus CEO Kenneth Feld acknowledged that circus elephants are struck behind their ears, under their chins and on their legs with metal-tipped prods, called bull hooks or ankus. Feld stated that these practices are necessary to protect circus workers and acknowledged that an elephant trainer was reprimanded for using an electric shock device, known as a hot shot or electric prod, on an elephant. Despite this, he denied that any of these practices harm elephants. Some trainers have tried to train elephants without the use of physical punishment. Ralph Helfer is known to have relied on gentleness and reward when training his animals, including elephants and lions. In January 2016 Ringling Bros. and Barnum and Bailey circus announced it would retire its touring elephants in May 2016.
Like many mammals, elephants can contract and transmit diseases to humans, one of which is tuberculosis. In 2012, two elephants in Tete dOr zoo, Lyon were diagnosed with the disease. Due to the threat of transmitting tuberculosis to other animals or visitors to the zoo, their euthanasia was initially ordered by city authorities but a court later overturned this decision. At an elephant sanctuary in Tennessee, a 54-year-old African elephant was considered to be the source of tuberculosis infections among eight workers.
As of 2015[update], tuberculosis appears to be widespread among captive elephants in the US. It is believed that the animals originally acquired the disease from humans, a process called reverse zoonosis. Because the disease can spread through the air to infect both humans and other animals, it is a public health concern affecting circuses and zoos.
Elephants can exhibit bouts of aggressive behaviour and engage in destructive actions against humans. In Africa, groups of adolescent elephants damaged homes in villages after cullings in the 1970s and 1980s. Because of the timing, these attacks have been interpreted as vindictive. In India, male elephants regularly enter villages at night, destroying homes and killing people. Elephants killed around 300 people between 2000 and 2004 in Jharkhand, while in Assam 239 people were reportedly killed between 2001 and 2006. Local people have reported their belief that some elephants were drunk during their attacks, although officials have disputed this explanation. Purportedly drunk elephants attacked an Indian village a second time in December 2002, killing six people, which led to the killing of about 200 elephants by locals.
Elephants have been represented in art since Paleolithic times. Africa in particular contains many rock paintings and engravings of the animals, especially in the Sahara and southern Africa. In the Far East, the animals are depicted as motifs in Hindu and Buddhist shrines and temples. Elephants were often difficult to portray by people with no first-hand experience with them. The ancient Romans, who kept the animals in captivity, depicted anatomically accurate elephants on mosaics in Tunisia and Sicily. At the beginning of the Middle Ages, when Europeans had little to no access to the animals, elephants were portrayed more like fantasy creatures. They were often depicted with horse- or bovine-like bodies with trumpet-like trunks and tusks like a boar; some were even given hooves. Elephants were commonly featured in motifs by the stonemasons of the Gothic churches. As more elephants began to be sent to European kings as gifts during the 15th century, depictions of them became more accurate, including one made by Leonardo da Vinci. Despite this, some Europeans continued to portray them in a more stylised fashion.Max Ernst’s 1921 surrealist painting The Elephant Celebes depicts an elephant as a silo with a trunk-like hose protruding from it.
Elephants have been the subject of religious beliefs. The Mbuti people believe that the souls of their dead ancestors resided in elephants. Similar ideas existed among other African tribes, who believed that their chiefs would be reincarnated as elephants. During the 10th century AD, the people of Igbo-Ukwu buried their leaders with elephant tusks. The animals’ religious importance is only totemic in Africa but is much more significant in Asia. In Sumatra, elephants have been associated with lightning. Likewise in Hinduism, they are linked with thunderstorms as Airavata, the father of all elephants, represents both lightning and rainbows. One of the most important Hindu deities, the elephant-headed Ganesha, is ranked equal with the supreme gods Shiva, Vishnu, and Brahma. Ganesha is associated with writers and merchants and it is believed that he can give people success as well as grant them their desires. In Buddhism, Buddha is said to have been a white elephant reincarnated as a human. In Islamic tradition, the year 570, when Muhammad was born, is known as the Year of the Elephant. Elephants were thought to be religious themselves by the Romans, who believed that they worshipped the sun and stars. The ‘Land of a Million Elephants’ was the name of the ancient kingdom of Lan Xang and later the Lan Chang Province and it is now a nickname for Laos.
Elephants are ubiquitous in Western popular culture as emblems of the exotic, especially since as with the giraffe, hippopotamus and rhinoceros there are no similar animals familiar to Western audiences. The use of the elephant as a symbol of the US Republican Party began with an 1874 cartoon by Thomas Nast. As characters, elephants are most common in children’s stories, in which they are generally cast as models of exemplary behaviour. They are typically surrogates for humans with ideal human values. Many stories tell of isolated young elephants returning to a close-knit community, such as “The Elephant’s Child” from Rudyard Kipling’s Just So Stories, Disney’s Dumbo and Kathryn and Byron Jackson’s The Saggy Baggy Elephant. Other elephant heroes given human qualities include Jean de Brunhoff’s Babar, David McKee’s Elmer and Dr. Seuss’s Horton.
Several cultural references emphasise the elephant’s size and exotic uniqueness. For instance, a “white elephant” is a byword for something expensive, useless and bizarre. The expression “elephant in the room” refers to an obvious truth that is ignored or otherwise unaddressed. The story of the blind men and an elephant teaches that reality may be viewed by different perspectives.
Elephant – Wikipedia, the free encyclopedia
The mission of the Department of Science and Health Department at UC Clermont is to provide outstanding, comprehensive undergraduate programs for careers in the biological and chemical sciences and in allied health professions. We strive to nurture a classroom environment which demonstrates and inculcates in our students the understanding and ability to acquire and critically interpret knowledge of basic facts and theories of the basic and clinical sciences, strive to add to the body of scientific knowledge through research, and encourage our students to communicate their understanding to others.We use every opportunity in our classrooms to encourage curiosity, propose hypotheses, construct scientifically valid tests for hypotheses, and nurture critical thinking skills. We teach our students the tools needed to create hypothetical answers to new questions, to make an educated guess.
Our laboratories emphasize hands-on experiments or manipulations which demonstrate principles presented in lecture. Each student will be taught the use of specialized scientific or clinical equipment and the performance of important lab or clinical techniques.
We provide a classroom environment which favors the learning process through small class size and lively classroom discussions. We test in a manner which enhances student improvement to more effectively engage them in their learning process. We believe that all of the material we teach should relate directly or indirectly to a students life or professional interests. Our curriculum is organized around these shared values.
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Science & Health, Colleges Around Cincinnati, University …
Homosexuality is the condition of “sexual desire or behavior directed toward a person or persons of one’s own sex.”
Homosexuality has a number of causal factors that influence its ultimate origination in individuals; these factors will be addressed shortly. In addition, homosexuality has a variety of effects on individuals and society. Next, some of the historical events, religious matters, and legal matters relating to homosexuality will be covered. Finally, the latter part of the 20th century has seen a large body of research on the causes and effects of homosexuality.
For more information please see: Homosexuality and biblical interpretation and Homosexuality and the Bible and Atheism and homosexuality and Atheism and the persecution of homosexuals
Below are several Bible verses that condemn homosexuality:
In addition, there are numerous other references that also condemn the lifestyle, such as 1 Kings 22:46 (NASB): “The remnant of the sodomites who remained in the days of his father Asa, he expelled from the land.”
For more information please see: Causes of Homosexuality
Homosexuality is sometimes also defined in terms of an attraction, preference, orientation, or identity. The term “orientation” is particularly favored by those who are promoting public acceptance of homosexuality.
For more information please see: Homosexuality and Genetics
A common argument is that an inclination to homosexuality is inborn and immutable. It is widely believed that the public will become more accepting of homosexuality if they are convinced that it is inborn and immutable. For example, neuroscientist and homosexual Simon Levay stated: “…people who think that gays and lesbians are born that way are also more likely to support gay rights.”
Eight major studies of identical twins in the United States, Australia and Scandinavia during the last two decades indicate that homosexuals were not born that way.Research into the issue of the origins of homosexuality suggests that adoptive brothers are more likely to both be homosexuals than the biological brothers, who share half their genes which suggests that homosexuality is not genetically caused.  This data prompted the journal Science to report “this . . . suggests that there is no genetic component, but rather an environmental component shared in families”. However, in regards to psychosocial and biological theories in regards to the origin of homosexuality, Columbia University psychiatry professors Drs. William Byrne and Bruce Parsons stated in 1994: “There is no evidence that at present to substantiate a biological theory. [T]he appeal of current biological explanations for sexual orientation may derive more from dissatisfaction with the present status of psychosocial explanations than from a substantiating body of experimental data”.
Dr. Tahir I. Jaz, M.D., Winnipeg, Canada states: “The increasing claims of being “born that way” parallels the rising political activism of homosexual organizations, who politicize the issue of homosexual origins. In the 1970s, approximately ten percent of homosexuals claimed to be “born homosexual” according to a large scale survey….However, in a survey in the 1980s, with the homosexual rights movement increasingly becoming active, thirty-five percent claimed to be born that way.
For more information please see: Religious Upbringing and Culture Affects Rates of Homosexuality
Dr. Neil Whitehead is a research scientist and biochemist from New Zealand and his wife Briar Whitehead is a writer. Dr. Whitehead coauthored a book with with his wife entitled My Genes Made Me Do it – a scientific look at sexual orientation which argues that there is no genetic determinism in regards to homosexuality (homosexuals are “not born that way”) and that there is abundant documentation that individuals are able to leave homosexuality and become heterosexuals.
Dr. Whitehead and Briar Whitehead declared:
This evidence comes from missionaries who commonly spend 25 years of their lives living in one culture, far more than almost any anthropologist….Overall they can be considered as reliable witnesses. For example, in contrast to groups like the Sambia in the New Guinea highlands, where homosexuality was compulsory, only about 2-3 percent of Western Dani (also in the New Guinea highlands) practiced it. However, in another group of Dani who were genetically related, homosexuality was totally unknown. Missionaries report that when they were translating the Bible into Dani for this group, their tribal assistants, who knew their own culture intimately, were nonplused by references to homosexuality in Romans 1; they did not understand the concept. Another missionary, with the same group for 25 years, overheard many jests and sexually ribald exchanges among the men, but never a single mention of homosexuality in all that time. When Dani went to help with missionary work among the Sambia, they were astounded at some of the homosexual practices they saw for the first time. Although it is always difficult for a foreigner to be completely sure whether a rare and stigmatized behavior exists, it is certainly true that if three such different experiences of homosexuality can occur in groups of people so closely related genetically, genetically enforced homosexuality is an impossibility.
The religious leader and civil rights leader Martin Luther King (MLK) never championed the homosexual agenda. In fact, MLK saw homosexuality as probably a culturally induced “problem” and he believed that homosexuals could become ex-homosexuals. (see: Overcoming homosexuality).
King wrote in a 1958 column: The type of feeling that you have toward boys is probably not an innate tendency, but something that has been culturally acquired, . You are already on the right road toward a solution, since you honestly recognize the problem and have a desire to solve it.
In 1994, the book Sex in America: A definitive survey by Robert T. Michael, John H. Gagnon, Edward O. Laumann, and Gina Kolata stated the following:
The aforementioned authors Dr. Whitehead and Briar Whitehead similarly wrote:
For more information please see: Failure of Experiments to Show Genetic Determinism For Homosexuality
Dr. Dean Hamer is a researcher often cited to show that there is empirical data supporting the notion of genetic determinism in regards to homosexuality. News organizations like National Public Radio and Newsweek have done news stories regarding his work. In respect to the press trumpeting various findings genetics-of-behavior research uncritically the science journal Science stated the following in 1994:
The Gallup Organization reported: “The Family Research Report says ‘around 2-3% of men, and 2% of women, are homosexual or bisexual.'” The U.S Department of Health and Human Services reported: “While the percentage of women and men aged 18-44 years who reported they were either heterosexual or homosexual was similar (94% of women and 96% of men said they were heterosexual while 1.1% of women and 1.7% of men said they were homosexual or gay), the percentage of women who reported they were bisexual was more than 3 times as high as men (3.5% of women vs. 1.1% of men).”
In regards to the issue of homosexuality and choice, given the existence of ex-homosexuals and given the existence of human cultures where homosexuality has apparently not existed, the position that homosexuality is ultimately a choice in individuals or at the very least can be a choice in individuals has strong evidential support. In short, there is a strong argument that one can leave homosexuality.
Also, in 2012 ABC News reported concerning actress Cynthia Nixon: “Cynthia Nixon stands by her statement that she is gay by choice, despite the backlash shes received from members of the gay community.” In addition, given that the homosexual population has significantly higher rates of many diseases and the homosexual population also has significantly lower rates of various measures of mental health it can be strongly argued that engaging in homosexual acts is a bad choice for individuals. Another other factor that makes engaging in homosexual acts a bad choice for individuals is the significantly higher rates of domestic violence in homosexual couples. In addition, according to experts homosexual murders are relatively or quite common and often homosexual murders are very brutal. Also, the homosexual population has a greater propensity to engage in illegal drug use.
A 2003 poll done by Ellison Research of Phoenix, Arizona stated that 82% of all American Protestant ministers agreed with the statement homosexuality is a choice people make”.
Immutability is the inability of a thing to be changed. For example, it is impossible to change a dog into a cat. Likewise, it is impossible to change one’s race, although with makeup or plastic surgery has made it possible to alter one’s racial appearance. The immutability of membership in a group is an important consideration in determining the level of scrutiny given to a law against that group under the Equal Protection Clause.
There has been much debate over whether homosexuality is immutable despite the existence of ex-homosexuals. Often the argument is made that it’s either genetically determined (and thus immutable), or that it is entirely a matter of choice. Given this dichotomy, the premise that “I didn’t choose to be gay” yields the conclusion that it must be genetically determined. However, the search for a “gay gene” has proved elusive. Many others, including most scientists, have a much less ‘black and white’ view. They propose that it is determined by a complex interaction of many factors, some of which could be genetic, but probably also include psychological, environmental and cognitive factors, and is shaped at a very early age.
Simon LeVay wrote: “It’s important to stress what I didn’t find. I did not prove that homosexuality is genetic, or find a genetic cause for being gay. I didn’t show that gay men are born that way, the most common mistake people make in interpreting my work. Nor did I locate a gay center in the brain. … Since I look at adult brains, we don’t know if the differences I found were there at birth or if they appeared later.”
See also: Homosexuality and frontal lobe injury and Religiosity and larger frontal lobes and Atheism and brain function
The frontal lobe plays a role in controlling sexual behavior.
According to the 2007 medical journal article (and its abstract) entitled Neurological control of human sexual behaviour: insights from lesion studies which was published in the Journal of Neurology, Neurosurgery, and Psychiatry:
Disinhibited sexual behaviour has been reported following damage to the frontal lobes, particularly the orbitofrontal region of the limbic system.
Kolarsky and colleagues54 examined the relationships between sexual deviation, age of lesion onset and localisation of lesion (temporal vs extratemporal). The authors defined two diagnostic categories: (1) sexual deviation, involving a deviation of sexual object (for example, paedophilia). Homosexuality was included in this category, which would now be considered inappropriate, and (2) sexual disturbances other than deviations, including orgasm in response to stimuli unrelated to the subject’s sexual preference, hypersexuality and hyposexuality…
An association between temporal lobe abnormalities and paedophilia has been reported by Mendez and colleagues.
For more information please see: Ex-Homosexuals and Overcoming Homosexuality and Resources on becoming a Christian
In regards to the question of whether or not homosexuality is a permanent condition, one of the earliest historical records regarding of the existence of ex-homosexuals is a letter of the Apostle Paul to the Corinthian Christian church.
The Apostle Paul taught that homosexuality is a sin when he wrote the following:
Today people still report leaving homosexuality and becoming heterosexual through their Christian faith.
Peter LaBarbera is the President of Americans for Truth which is a organization which counters the homosexual agenda. Peter LaBarbera stated the following regarding Christian ex-homosexuals who reported being transformed by the power of God:
In respect to Peter LaBarbera’s statement above regarding homosexuals overcoming homosexuality through the power of God, in 1980 a study was published in the American Journal of Psychiatry and eleven men participated in this study. The aforementioned study in the American Journal of Psychiatry stated that eleven homosexual men became heterosexuals “without explicit treatment and/or long-term psychotherapy” through their participation in a Pentecostal church. The Apostle Paul in a letter to the church of Corinth indicated that Christians were able to overcome being drunkards through the power of Jesus Christ (I Corinthians 6:9-11).
Dr. Whitehead and Briar Whitehead state in their aforementioned book the following regarding ex-homosexuals overcoming homosexuality:
West mentions one man who was exclusively homosexual for eight years, then became heterosexual…
Another well known author in the field, Hatterer, who believes in sexual orientation change, said, Ive heard of hundreds of … men who went from a homosexual to a heterosexual adjustment on their own.
See: Hate Crime Law Misapplied to Ex-homosexual
See also: Denials that ex-homosexuals exist
Commonly homosexual activists fallaciously argue that ex-homosexuals must never have been really gay at all (see: No true Scotsman fallacy) or is just deluding himself.  For example, when the alleged homosexual, male penguin “Harry” mated with a female penguin (see: Homosexuality in animals myth), the homosexual activist Wayne Besen angrily exclaimed “There is no ex-gay sexual orientation. Harry is simply in denial. Hes living what I call the big lie. In Madison, Wisconsin an ex-homosexual was forced to do 50 hours of community service and undergo “tolerance training” (or face jail time and fines) due to a discussion he had with a homosexual (see: Hate Crime Law Misapplied to Ex-homosexual).
The denial that homosexuality is a choice by homosexual activists and liberals is similar to the behavior of fat acceptance movement activists who insist that being overweight is never a choice and ostracize ex-overweight people (see: fat acceptance movement for details).
Two of the more popular anti-homosexuality blogs are Americans For Truth and Gay Christian Movement Watch. The blog Americans For Truth is run by Peter LaBarbera and the blog Gay Christian Movement Watch is run by Pastor D.L. Foster.
A 2006 survey finds homosexual men seek to leave homosexual lifestyle to heal emotional pain and for spiritual reasons rather than outside pressure. In addition, there is other data that supports the above 2006 survey findings.
For additional information please see: Homosexuality and biblical interpretation and Homosexuality and the Bible and Atheism and homosexuality
In respect to homosexuality and the Bible, sound Bible exegesis and Bible exposition demonstrates that the Bible condemns homosexuality. In addition, Christian apologist JP Holding refutes various arguments that assert that the Bible does not condemn homosexuality. In his essay which examines the biblical passages regarding homosexuality, Pastor and Associate Professor of Pastoral Ministries at The Master’s Seminary Dr. Alex D. Montoya states that “The Christian needs to befriend and witness to the homosexual with such love, compassion, and wisdom that such will respond to the saving grace of God.”
The Bible clearly associates the city of Sodom with homosexuality (Genesis 19:4-9), although the Bible associates with Sodom other sins as well. Claims that the primary reason for Sodom’s judgment was inhospitality are not supported by sound Bible exegesis.
The Bible states regarding Sodom:
…the LORD rained on Sodom and Gomorrah brimstone and fire from the LORD out of heaven, and He overthrew those cities, and all the valley, and all the inhabitants of the cities, and what grew on the ground. Genesis 19:24-25
The following was reported in respect to Dr. Bryant Wood’s archaeological work in relating to the biblical city of Sodom:
Dr. Bryant Wood, in describing these charnel houses, stated that a fire began on the roofs of these buildings. Eventually the burning roof collapsed into the interior and spread inside the building. This was the case in every house they excavated. Such a massive fiery destruction would match the biblical account that the city was destroyed by fire that rained down from heaven. Wood states, “The evidence would suggest that this site of Bab edh-Drha is the biblical city of Sodom.”
Dr. Wood provides some additional material in relation to the find being the biblical city of Sodom.
For related information see: Homosexuality and promiscuity and Homosexuality Statistics
A 2004 article by Michael Foust states:
According to the researchers, 42.9 percent of homosexual men in Chicago’s Shoreland area have had more than 60 sexual partners, while an additional 18.4 percent have had between 31 and 60 partners. All total, 61.3 percent of the area’s homosexual men have had more than 30 partners, and 87.8 percent have had more than 15, the research found.
As a result, 55.1 percent of homosexual males in Shoreland — known as Chicago’s “gay center” — have at least one sexually transmitted disease, researchers said.
The three-year study on the sexual habits of Chicago’s citizens will appear in the upcoming book, “The Sexual Organization of The City” (University of Chicago Press), due out this spring.
For more information please see: Homosexual Couples and Domestic Violence and Gay bashing
Studies report that homosexual couples have significantly higher incidences of violent behavior. For example, a recent study by the Canadian government states that “violence was twice as common among homosexual couples compared with heterosexual couples”. According the American College of Pediatricians who cite several studies, “Violence among homosexual partners is two to three times more common than among married heterosexual couples.” In addition, the American College of Pediatricians states the following: “Homosexual partnerships are significantly more prone to dissolution than heterosexual marriages with the average homosexual relationship lasting only two to three years.”
In June of 2004, the journal Nursing Clinics of North America reported the following regarding homosexuality and domestic violence:
Male-on-male same-sex domestic violence also has been reported in couples where one or both persons are HIV-positive. Intimate partner abuse and violence include humilation, threatening to disclose HIV status, withholding HIV therapy, and harming family members or pets.
For more information please see: Homosexuality and Murders
Vernon J. Geberth, M.S., M.P.S. who is a former commander of Bronx homicide for the New York City Police Department stated in 1995 concerning homosexuality and murders that homosexual murders are relatively common and these murders may involve male victims murdered by other males or may involve female victims who are in some type of lesbian relationship and they are murdered by another female. In 2005, Dr. Harnam Singh, Dr. Luv Sharma, and Dr. Dhattarwal reported in the Journal of Indian Academy of Forensic Medicine in respect to homosexuality and murders that homosexual murders are quite common and that these murders may involve both sexes either as victims or as assailants.
There have been a number of forensic journal articles on the issue of homosexual homicides and overkill. In 1996, the forensic journal The American Journal of Forensic Medicine and Pathology published an article entitled Homicide in homosexual victims: a study of 67 cases from the Broward County, Florida, Medical Examiner’s office (1982-1992), with special emphasis on “overkill”. The abstract for the journal article states:
According to the New York Times, Dr. William Eckert was a world-renowned authority in the field of pathology and he worked on major murder cases including the assassination of Senator Robert F. Kennedy and the Charles Manson murders. Dr. Eckert founded the American Journal of Forensic Medicine and Pathology. According to Time magazine, Dr. Eckert was a pioneer who encouraged collaborative effort between law-enforcement and forensics teams.
Dr. Eckert wrote concerning homosexual murders:
The Encyclopedia of Serial Killers by Michael Newton reports:
The previously cited pathology textbook by Knight and Saukko stated the following: “In addition, quite a number of fatal altercations arise because a heterosexual man becomes violent when importuned by a homosexual.”
Women who engage in homosexuality are called lesbians (after the ancient Greek island of Lesbos). Recently, the former lesbian activist Charlene Cothran left homosexuality and converted her pro-homosexuality magazine to one that helps homosexuals find freedom and deliverance through faith in Jesus Christ. Lesbian activist Yvette Cantu Schneider also became a Christian and left homosexuality.
In 2007, WorldNetDaily published the following regarding a lesbian woman:
For more information please see: Homosexuality and health and Gay bathhouses
A review of the history of homosexuality and AIDS, indicates the original spread of AIDS is generally attributed to the aforementioned promiscuity of homosexual men. Originally the syndrome was called the “gay disease” because the overwhelming majority of patients were homosexual men.
In September of 2010, Reuters reported: “Nearly one in five gay and bisexual men in 21 major U.S. cities are infected with HIV, and nearly half of them do not know it”. A September 2010 report of the Centers for Disease Control and Prevention (CDC) reported: “Gay, bisexual, and other men who have sex with men (MSM) represent approximately 2% of the US population, yet are the population most severely affected by HIV and are the only risk group in which new HIV infections have been increasing steadily since the early 1990s. In 2006, MSM accounted for more than half (53%) of all new HIV infections in the United States…”
In August of 2009, LifeSiteNews reported: “An official with the Centers for Disease Control and Prevention (CDC) announced the CDC’s estimate Monday that in the United States AIDS is fifty times more prevalent among men who have sex with men (‘MSM’) than the rest of the population.” This is a dramatic recent increase. In June of 2004, the journal Nursing Clinics of North America reported that homosexual men and men who have sex with men “are nine times more likely to become infected with HIV than their heterosexual counterparts”. Of newly diagnosed HIV infections in the United States during the year 2003, the Centers for Disease Control and Prevention (CDC) estimated that about 63% were among men who were infected through sexual contact with other men. As of 1998, fifty-four percent of all AIDS cases in the United States were homosexual men, and the CDC stated that nearly ninety percent of these men acquired HIV through sexual activity with other men.
In 2004, Jeffrey D. Klausner, Robert Kohn, and Charlotte Kent reported in the journal Clinical Infectious Diseases the following: “Proctitis, or inflammation of the rectum, is a condition that is not uncommon among men who have sex with men (MSM), and, in HIV-negative men, greatly increases the risk of acquiring HIV infection. With the recent increases in bacterial sexually transmitted diseases (STDs) among MSM in the United States and Europe, there has been a concomitant increase in the number of cases of clinical proctitis.” On March 15, 2004 Medscape published an article by John G. Bartlett, M.D. entitled New Look at “Gay Bowel Syndrome” in which they commented on the aforementioned 2004 journal article Etiology of clinical proctitis among men who have sex with men published by JD Klausner and C. Kent in the journal Clinical Infectious Diseases. The article in Medscape stated the following:
Johns Hopkins HIV Guide website has a duplicate of the aforementioned article by John G. Bartlett, M.D. at Medscape which was entitled New Look at “Gay Bowel Syndrome”.
In 2004, the prominent medical website, WebMD, stated the following: “Men who have sex with men and women are a “significant bridge for HIV to women,” the CDC’s new data suggest.”
See: Teenage homosexuality and Teenage AIDS
In relation to homosexuality and MRSA, on January 15, 2008 the newspaper San Francisco Chronicle had a news article entitled San Francisco gay community an epicenter for new strain of virulent staph. The San Francisco Chronicle news article stated the following in regards to homosexuality and MRSA:
On February 19, 2008 the Annals of Internal Medicine published a study regarding antiobiotic resistant staph infection in relation to men who have sex with men and the abstract for the article states the following in relation to homosexuality and MRSA:
Syphilis is an infection caused by the bacteria Treponema pallidum. An early publication to propose the link between homosexuality contributing to the spread of sexually transmitted disease was the English publication Proceedings of the Royal Society of Medicine in 1962. The Proceedings of the Royal Society of Medicine made the following statement: “The importance of homosexual practices in the spread of venereal diseases has attracted particular attention recently. It almost seems that these practices are keeping syphilis alive in this country.” 
The news organization Cybercast News Service reported the following about homosexuality and syphilis:
In a report on sexually transmitted diseases (STDs) issued Tuesday, the government said syphilis, a disease that was almost eliminated as a public health threat less than 10 years ago, is on the rise — with cases increasing each year since 2000.
In relation to homosexuality and gonorrhea, in 2006, the American Association of Family Physicians reported: “Men who have sex with men (MSM) have high rates of gonococcal infection. In San Francisco, more than one half of these infections occur in MSM, and previous cross-sectional studies have reported a prevalence of up to 15.3 percent in this group.”
In 2007, the medical journal Sexually Transmitted Diseases published an article entitled Sexually Transmitted Infections in Western Europe Among HIV-Positive Men Who Have Sex With Men which stated the following regarding homosexuality and gonorrhea:
In Denmark (19941999), gonorrhea incidence was 6 times higher among known HIV-positive MSM [men who have sex with men]… A study in a Parisian clinic showed that at least one-third (30/92) of MSM diagnosed with gonorrhea between January 1999 and May 2001 were HIV-positive… In Sweden, 5.4% (4/74) of gonorrhea cases were in HIV-positive MSM in 2000. By comparison, at sentinel sites in England and Wales, 32% (123/381) of MSM with gonorrhea were HIV-positive in 2004.
Lymphogranuloma venereum is a sexually transmitted disease that mainly infects the lymphatics. According to the recent medical literature, there have been recent outbreaks of lymphogranuloma venereum in Europe and North America and the outbreaks have been limited to the homosexual community.
In 2006, the The Medical Journal of Australia reported the following:
Amoebiasis has become endemic in MSM in Japan and causes significant morbidity and mortality; complications such as colitis and liver abscesses occur more frequently in homosexual and bisexual men than in heterosexual men. Similar findings on amoebiasis are reported from Taiwan, with MSM at increased risk for invasive amoebiasis and intestinal colonisation with E. histolytica.
In 2001, The journal Internal Medicine (Tokyo, Japan) published an article entitled Amebiasis in acquired immunodeficiency syndrome in which they stated the following the following:
Sexually transmitted diseases that cause proctitis include syphilis, gonorrhea, lymphogranuloma venereum, and amebiasis and as noted earlier the homosexual community has significant problems in regards to these illnesses. In addition, as mentioned earlier proctitis significant risk factor in respect to HIV infection. According to the Mayo Clinic, “proctitis in general mainly affects adult males”.Proctitis, syphilis, gonorrhea, lymphogranuloma venereum, and amebiasis are all maladies that are associated with gay bowel syndrome which why John G. Bartlett, M.D. stated at the Johns Hopkins HIV Guide website and at Medscape that gay bowel syndrome is still currently an issue.
For more information please see: Homosexuality and Hepatitis
In relation to homosexuality and hepatitis, according to the Centers for Disease Control and Prevention (CDC) both Hepatitis A and Hepatitis B disproportionately affects men who have sex with men (MSM).
In a 2007 article entitled Advances in the Management of Viral Hepatitis B and Hepatitis C Infection in HIV-Coinfected Patients Vincent V. Soriano, MD, PhD reported in Medscape the following regarding homosexuality and Hepatitis C viral infections:
Viral hepatitis is one of the illnesses of gay bowel syndrome.
Go here to read the rest:
Homosexuality – Conservapedia
The genetics of cat coat coloration, pattern, length, and texture is a complex subject, and many different genes are involved.
Cat coat genetics can produce a variety of colors and coat patterns. These are physical properties and should not be confused with a breed of cat. Furthermore, cats may show the color and/or pattern particular to a certain breed without actually being of that breed. For example, cats may have point coloration, but not be Siamese.
A cat with Oo and white spotting genes is commonly called a calico. The reason for the patchwork effect in female cats heterozygous for the O gene (Oo) is X-inactivation one or the other X chromosome in every cell in the embryo is randomly inactivated (see Barr body), and the gene in the other X chromosome is expressed.
For a cat to be tortoiseshell, calico, or one of the variants such as blue-cream or chocolate tortoiseshell, the cat must simultaneously express two alleles, O and o, which are located on the X chromosome. Males normally cannot do this, as they have only one X chromosome, and therefore only one allele, and so calico cats are normally only female. Male tortoiseshell or calico cats occur only if they have chromosomal abnormalities such as the genotype XXY (in which case they are sterile), chromosomal mosaicism (only portions of their cells have the genotype XXY, so these cats may be fertile), or chimerism (a single individual formed from two fused embryos, at least one of which was male). Approximately 1 in 3,000 calico/tortoiseshell cats are male. Chimericism (which may result in fertile male cats) appears to be the most common mechanism.
One can deduce that a grey male cat with a white bib and paws, but showing no tabby pattern:
Tabby cats (AA or Aa), normally have:
Most or all striping disappears in the chinchilla or shaded cat, but it is still possible to identify the cat as a tabby from these other features.
The genetics involved in producing the ideal tabby, tipped, shaded, or smoke cat is complex. Not only are there many interacting genes, but genes sometimes do not express themselves fully, or conflict with one another. For example, the melanin inhibitor gene sometimes does a poor job blocking pigment, resulting in an excessively gray undercoat, or in tarnishing (yellowish or rusty fur).
Likewise, poorly-expressed non-agouti or over-expression of melanin inhibitor will cause a pale, washed out black smoke. Various polygenes (sets of related genes), epigenetic factors, or modifier genes, as yet unidentified, are believed to result in different phenotypes of coloration, some deemed more desirable than others by fanciers.
Here are the genetic influences on tipped or shaded cats:
Cat fur length is governed by the Long hair gene in which the dominant form, L, codes for short hair, and the recessive l codes for long hair. In the longhaired cat, the transition from anagen (hair growth) to catagen (cessation of hair growth) is delayed due to this mutation. A rare recessive shorthair gene has been observed in some lines of Persian cat (silvers) where two longhaired parents have produced shorthaired offspring.
There have been many genes identified that result in unusual cat fur. These genes were discovered in random-bred cats and selected for. Some of the genes are in danger of going extinct because the cats are not sold beyond the region where the mutation originated or there is simply not enough demand for cats expressing the mutation.
In many breeds, coat gene mutations are unwelcome. An example is the rex allele which appeared in Maine Coons in the early 1990s. Rexes appeared in America, Germany and the UK, where one breeder caused consternation by calling them “Maine Waves”. Two UK breeders did test mating which indicated that this was probably a new rex mutation and that it was recessive. The density of the hair was similar to normally coated Maine Coons, but consisted only of down type hairs with a normal down type helical curl, which varied as in normal down hairs. Whiskers were more curved, but not curly. Maine Coons do not have awn hairs, and after moulting, the rexes had a very thin coat.
There are various genes producing curly coated or “rex” cats. New types of rex pop up spontaneously in random-bred cats now and then. Here are some of the rex genes that breeders have selected for:
There are also genes for hairlessness:
Some rex cats are prone to temporary hairlessness, known as baldness, during moulting.
Here are a few other genes resulting in unusual fur:
What is Cloning?
Learn the basics about cloning and see how its done.
Evaluate the reasons for using cloning technologies.
The History of Cloning
Explore the history of cloning technologies.
Here we help you separate the facts from the fiction.
Click and Clone
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Is it Cloning? Or Not?
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Genetic Science Learning Center. (2014, July 10) Cloning. Retrieved August 24, 2016, from http://learn.genetics.utah.edu/content/cloning/
Cloning [Internet]. Salt Lake City (UT): Genetic Science Learning Center; 2014 [cited 2016 Aug 24] Available from http://learn.genetics.utah.edu/content/cloning/
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Cloning – Learn Genetics
Historians of homosexuality will judge much twentieth-century “science” harshly when they come to reflect on the prejudice, myth, and downright dishonesty that litter modern academic research on sexuality. Take, for example, the lugubrious statements of-once respected investigators. Here is Sandor Feldman, a well-known psychotherapist, in 1956:
Or consider the remarks of the respected criminologist Herbert Hendin:
The notion of the homosexual as a deeply disturbed deviant in need of treatment was the orthodoxy until only recently. Bernard Oliver, Jr., a psychiatrist specializing in sexual medicine, wrote in 1967 that Dr. Edmond Bergler feels that the homosexual’s real enemy is not so much his perversion but [sic] ignorance of the possibility that he can be helped, plus his psychic masochism which leads him to shun treatment….
There is good reason to believe now, more than ever before, that many homosexuals can be successfully treated by psychotherapy, and we should encourage homosexuals to seek this help.
Such views about the origin of homosexual preferences have become part of American political culture as well. When, in 1992, Vice-President Dan Quayle offered the view that homosexuality “is more of a choice than a biological situation…. It is a wrong choice,” he merely reasserted the belief that homosexuality reflected psychological conditioning with little biological basis, and certainly without being influenced by a person’s biological inheritance.
And now we have the much publicized spectacle–Time magazine has taken up the story in a dramatic feature entitled “Search for a Gay Gene” –of homosexuality’s origins being revealed in the lowly fruit fly, Drosophila. Males and females of this, one has to admit, rather distant relation adopt courtship behavior that has led two researchers at the US National Institutes of Health to draw extravagant parallels with human beings.
Shang-Ding Zhang and Ward F. Odenwald found that what they took to be homosexual behavior among male fruit flies–touching male partners with forelegs, licking their genitalia, and curling their bodies to allow genital contact–could be induced by techniques that abnormally activated a gene called w (for “white,” so called because of its effect on eye color). Widespread activation (or “expression”) of the white gene in Drosophila produced male-to-male rituals that took place in chains or circles of five or more flies. If female fruit flies lurked nearby, male flies would only rarely be tempted away from their male companions. These findings, which have apparently been reproduced by others, have led the investigators to conclude that “w misexpression has a profound effect on male sexual behavior.”
Zhang and Odenwald go on to speculate that the expression of w could lead to severe shortages of serotonin, an important chemical signal that enables nerve cells to communicate with one another. The authors conjecture that mass activation of w diminishes brain serotonin by promoting its use elsewhere in the body. Indeed, cats, rabbits, and rats all show some elements of “gay” behavior when their brain serotonin concentrations fall. Intriguing and, you might think, convincing evidence.
Yet, although w is found in modified form in human beings, it is a huge (and, it seems to me, a dangerous) leap to extrapolate observations from fruit flies to humans. In truth, when the recent data are interpreted literally we find that (a) the w gene induces male group sex behavior in highly ritualized linear or circular configurations, and (b) while these tend more toward homosexual than straight preferences, they are truly bisexual (as pointed out by Larry Thompson in Time). Zhang and Odenwald force their experimental results with fruit flies to fit their preconceived notions of homosexuality. How simplistic it seems to equate genital licking in Drosophila with complex individual and social homosexual behavior patterns in humans. Can notions of homosexuality apply uniformly across the biological gulf that divides human beings and insects? Such arguments by analogy seem hopelessly inadequate.
By contrast, the work of Simon LeVay, Dean Hamer, and a small group of researchers concerned to distinguish biological and genetic influences on sexual behavior has discredited much of the loose rhetoric that has been used about homosexuality. In August 1991, LeVay, a neuroscientist who now directs the Institute of Gay and Lesbian Education in southern California, published in the magazine Science findings from autopsies of men and women of known sexual preference. He found that a tiny region in the center of the brain–the interstitial nucleus of the anterior hypothalamus (INAH) 3–was, on average, substantially smaller in nineteen gay men who died from AIDS than among sixteen heterosexual men.
The observation that the male brain could take two different forms, depending on one’s sexual preference, was a stunning discovery. The hypothalamus-a small, intricate mass of cells lying at the base of the brain-was long believed to have a role in sexual behavior, but direct evidence that it did so was weak. Yet LeVay expressed caution. Although his data showed that human sexual preference “is amenable to study at the biological level,” he noted that it was impossible to be certain whether the anatomical differences between the brains of gay and straight men were a cause or a consequence of their preference.
In the thirteen persuasive essays that make up The Sexual Brain, LeVay takes account of the current bio-behavioral controversy over the science of sex. From the union of wiry sperm and bloated ovum to the child-rearing practices of mammals and humans, for which mothers are largely responsible, he writes (metaphorically), the “male is little more than a parasite who takes advantage of [the female’s] dedication to reproduction.” He goes on to draw from a wide range of sources to support his contentious assertion that “there are separate centers within the hypothalamus for the generation of male-typical and female-typical sexual behavior and feelings.” He argues that a connection–the details of which remain mysterious–between brain and behavior exists through hormones such as testosterone.
The most convincing evidence he puts forward to support his view comes from women with congenital adrenal hyperplasia. This condition, in which masculine characteristics, such as androgenized genitalia, including clitoral enlargement and partially fused labia, become pronounced in women, is caused by excessive testosterone production and leads, in adulthood, to an increased frequency of lesbianism affecting up to half of all the women who have the condition. The theory, still unproven, that is proposed to explain these behavioral effects of hormones is that one or more chemical signals act during a brief early critical period in the development of most males to alter permanently both the brain and the pattern of their later adult behavior. Unless this hormonal influence is switched on, a female pattern of development will follow automatically.
What might be the origin of biological differences underlying male sexual preference? In 1993 Dean Hamer and his colleagues at the National Cancer Institute discovered a preliminary but nevertheless tantalizing clue. Hamer began his painstaking search for a genetic contribution to sexual behavior by studying the rates of homosexuality among male relatives of seventy-six known gay men. He found that the incidence of homosexual preference in these family members was strikingly higher (13.5 percent) than the rate of homosexuality among the whole sample (2 percent). When he looked at the patterns of sexual orientation among these families, he discovered more gay relatives on the maternal side. Homosexuality seemed, at least, to be passed from generation to generation through women.
Maternal inheritance could be explained if there was a gene influencing sexual orientation on the X chromosome, one of the two human sex chromosomes that bear genes determining the sex of offspring. Men have both X and Y chromosomes, while women have two X chromosomes. A male sex-determining gene, called SRY, is found on the Y chromosome. Indeed, the Y chromosome is the most obvious site for defining male sexuality since it is the only one of the forty-six human chromosomes to be found in men alone. The SRY gene is the most likely candidate both to turn on a gene that prevents female development and to trigger testosterone production. Since the female has no Y chromosome, she lacks this masculinizing gene. In forty pairs of homosexual brothers, Hamer and his team looked for associations between the DNA on the X chromosome and the homosexual trait. They found that thirty-three pairs of brothers shared the same five X chromosomal DNA “markers,” or genetic signatures, at a region near the end of the long arm of the X chromosome designated Xq28. The possibility that this observation could have occurred by chance was only 1 in 10,000.
LeVay takes a broad philosophical perspective in his discussion of human sexuality by placing his research in the context of animal evolution. Hamer, on the other hand, has written, with the assistance of the journalist Peter Copeland, a more focused popular account of his research. He conceived his project after reflecting on a decade of laborious research on yeast genes. Although the project was approved by the National Institutes of Health after navigating a labyrinthine course through government agencies, it remained rather meagerly funded.
Taken together, the scientific papers of both LeVay and Hamer and the books that their first reports have now spawned make a forceful but by no means definitive case for the view that biological and genetic influences have an important–perhaps even decisive–part in determining sexual preference among males. LeVay writes, for example, that “…the scientific evidence presently available points to a strong influence of nature, and only a modest influence of nurture.” But there is no broad scientific agreement on these findings. They have become mired in a quasi-scientific debate that threatens to let obscurantism triumph over inquiry. What happened?
To begin with, we must ask what LeVay and Hamer have not shown. LeVay has found no proof of any direct link between the size of INAH 3 and sexual behavior. Size differences alone prove nothing. He was also unable to exclude the possibility that AIDS has an influence on brain structure, although this seemed unlikely, since six of the heterosexual men he studied also had AIDS. Moreover, Hamer did not find a gene for homosexuality; what he discovered was data suggesting some influence of one or more genes on one particular type of sexual preference in one group of people. Seven pairs of brothers did not have the Xq28 genetic marker, yet these brothers were all gay. Xq28 is clearly not a sine qua non for homosexuality; it is neither a necessary nor a sufficient cause by itself.
And what about women? Although the genitalia of women as well as men are clearly biologically determined, no data exist to prove a genetic link, or a link based on brain structure, with female sexual preferences, whether heterosexual or homosexual. Finally, neither study has been replicated by other researchers, the necessary standard of scientific proof. Indeed, there is every reason to suppose that the INAH 3 data will be extremely difficult to confirm. Only a few years ago INAH 1 (located close to INAH 3) was also thought to be larger in men than in women. Two groups, including LeVay’s, have failed to reproduce this result.
Most of these limitations are clearly acknowledged by both LeVay and Hamer in their original scientific papers and are reinforced at length in their books. But reactions to their findings have nevertheless been harshly critical. For instance, after pointing out several potential weaknesses in Hamer’s study and criticizing his decision to publish in Science at a time when gay “lives are at stake,” two biologists, Anne Fausto-Sterling and Evan Balaban, asked “whether it might not have been prudent for the authors and the editors of Science to have waited until more of the holes in the study had been plugged….” Fortunately, their somewhat hysterical reaction has been followed by more careful comment by other scientists.
Lack of prudence also characterized the response in the press. In London, the conservative Daily Telegraph ran the clumsy headline, “Claim that homosexuality is inherited prompts fears that science could be used to eradicate it.” Another story began, “A lot of mothers are going to feel guilty,” while another was entitled “Genetic tyranny.”
These headlines are part of the popular rhetoric about DNA, which supposes that a gene represents an irreducible and immutable unit of the human self. The correlation between a potentially active gene and a behavior pattern is assumed to indicate cause and effect. Was Hamer himself guilty of over-interpretation? In his original paper, he went to extraordinary lengths to qualify his findings. He and his co-authors offer no fewer than ten statements advising a cautious reading of their data, and they note that “replication and confirmation of our results are essential.” Neither the hyperbolic press response with its relentless message of genetic determinism nor the ill-judged scientific criticism was appropriate.
Nevertheless, there are three conceptual issues raised by these reports –namely, heritability, sexual categorization, and the meaning of the phrase “biological basis of behavior” –which have been largely ignored in the scramble to publish instant analyses of the findings of LeVay and Hamer, among others.
Heritability is a measure of the resemblance between relatives; it is expressed as the proportion of variability in an observable characteristic that can be attributed to genetic factors. Eye color, for example, is 100 percent heritable, whereas we know that most behavioral traits have genetic contributions of well below 50 percent. Heritability is a quarrelsome issue among geneticists, and its proportional value is often quoted without the necessary qualifications. Variation in any trait is accounted for by the influence of genes (including, importantly, the interaction among genes), environment (the family and one’s wider life experience), and the interaction between one or more genes and one or more environmental variables. The standard measure of heritability is the sum of all genetic influences, and it ignores potentially complex interactions–for example, the influence of the family milieu on the behavioral expression of a gene influencing sexual preference. The most common error made by those who discuss genetic contributions to behavior is to forget that heritability is a property only of the population under study at one particular time. It cannot be generalized to characterize the behavior itself.
When we apply these considerations to Hamer’s data, we make a surprising discovery. If we accept his own hypothesis of the relation between the Xq28 marker and the behavioral trait, the maximum heritability of homosexuality in the group he studied is 67 percent, which may seem a remarkably high figure. Yet this group was a particularly selected one: the seventy-six study participants openly acknowledged being gay, and had volunteered for the study. What Hamer’s results do not tell us is what the influence of the Xq28 marker in the general population might be. He infers from various mathematical calculations “that Xq28 plays some role in about 5 to 30 percent of gay men.” But he admits that this is merely a preliminary estimate and that accurate measuring of Xq28 heritability in the general population remains to be done. In fact, a frequent criticism of Hamer’s Science paper was that he did not measure the incidence of Xq28 markers among heterosexual brothers of gay sibling pairs. Without this information, it is impossible to guess the influence of any genes that might be located at Xq28. Their effects will be unpredictable at best, and any interaction with the environment will assume critical importance.
At this point, science inches uneasily toward dogma and diatribe. Hamer cites Richard Lewontin’s Not in Our Genes as one of his early inspirations to change the direction of his research. Hamer writes that he
knew that [Lewontin] had criticized the idea that behavior is genetic, arguing instead that it is a product of class-based social structures….Why was Lewontin, a formidable geneticist, so determined not to believe that behavior could be inherited? He couldn’t disprove the genetics of behavior in a lab, so he wrote a political polemic against it.
Indeed, Lewontin has frequently provided cogent arguments against the view that heritability can help delineate the effects of genes on human behavior. He has described the separation of behavioral variation into genetic and environmental contributions and the interaction between the two as “illusory.” For him and his co-writers, such a model “cannot produce information about causes of phenotypic difference,” i.e., differences in observable physical and mental traits. The precise meaning of heritability forces the inevitable conclusion, Lewontin has written, that whatever proportion is quoted, it “is nearly equivalent to no information at all for any serious problem in human genetics.”
Imagine Dean Hamer’s astonishment, therefore, when he received a letter from Richard Lewontin in 1992. A Harvard professor teaching genetics and behavior had invited Hamer to submit a pamphlet describing his research as an example of “conceptual advances” in “modern behavior genetic studies.” He had willingly complied, but only later discovered that it had been ruled “scientifically unacceptable” by Ruth Hubbard, an emeritus professor at the Harvard Biological Laboratories deeply skeptical about determinism. In his letter, Hamer writes, Lewontin
went on to theorize that human behaviors must be “very, very far from the genes” because “there are some at least that we know for sure are not influenced by genes as, for example, the particular language one speaks.” That made about as much sense as saying that since some people eat tacos and some eat hamburgers, there is no biological drive to eat.
Hamer, tongue firmly in cheek, offered to give Lewontin’s students a lecture on how good research into behavior genetics is done. Lewontin accepted. On the day of his scheduled talk, Hamer faced not only Lewontin but also Ruth Hubbard and Evan Balaban (a co-author of the hostile letter later published in Science). Hamer described his methods carefully and stressed that his research could identify only potential genetic influences and not isolate specific genetic causes of behavior. At the end of the lecture, Lewontin indicated that he had no dispute with Hamer after all, and left the classroom without further comment. One wonders from this if Lewontin has modified his views on studying genetic contributions to human behavior.
Although it is true that heritability is only a crude measure of genetic influence, it remains a valuable research tool if, as one scientist has said, the researchers realize that
genetic influence on behavior appears to involve multiple genes rather than one or two major genes, and nongenetic sources of variance are at least as important as genetic factors….This should not be interpreted to mean that genes do not affect human behavior; it only demonstrates that genetic influence on behavior is not due to major-gene effects.
More importantly, one can move beyond the “lump sum” theory of genetic influences to study the way in which genes affect behavior over time, or to discover how a gene influences different but possibly related behaviors, for instance both sexual preference and aggression.
Lewontin also cited the “terrible mischief” that could result from a research program based on heritability as his reason to suggest stopping “the endless search for better methods of estimating useless quantities.”” Hamer agrees that precise genetic determinacy is an impossible goal; his 1993 article for Science on DNA markers also ended with an unusual admonition:
We believe that it would be fundamentally unethical to use [this] information to try to assess or alter a person’s current or future sexual orientation, either heterosexual or homosexual, or other normal attributes of human behavior. Rather, scientists, educators, policy-makers, and the public should work together to ensure that such research is used to benefit all members of society.
If scientists who have opposed research on heritability would accept that it can have, when it is carried out in this spirit, an important place in the study of behavior, that would add much-needed weight to calls to expand, and improve, research on human sexuality.
Although Hamer and LeVay have both expressed cautious confidence in their results, they are evidently uneasy about their own categorizations of men as either gay or straight. Hamer writes that,
In truth, I don’t think that there is such a thing as “the” rate of homosexuality in the population at large. It all depends on the definition, how it’s measured, and who is measured.
Classifying sexuality into homosexual and heterosexual categories may have benefits of simplicity for researchers, but how closely does this division fit the real world? Poorly is the answer. Sexual behavior and styles of life among men and women vary from day to day and year to year, and a conclusion about whether or not sexual experience is characterized as homosexual frequently depends on the definition one uses. The slippery nature of our crude categories should alert us to beware of conclusions about groups labeled as “homosexual” or “heterosexual.”
Moreover, the concept of sexuality itself cannot easily be analyzed. It exists at several levels–chromosomal, genital, brain, preference, gender self-image, gender role, and a range of subtle influences on behavior (hair color, eye color, and many more). Each of these can be grouped together with the others to produce a single measurable component on a scale, devised by Alfred Kinsey in the 1940s, that allegedly shows a person’s degree of homosexual preference. Hamer used this scale somewhat uncritically to categorize his volunteers. Stephen Levine, a medical expert on sexual behavior, has noted that the conflated and crude Kinsey scale “does not do justice to the diversity among homosexual women and men.”
One of Hamer’s severest critics, Anne Fausto-Sterling, a developmental geneticist at Brown University, has tried to extend sexual categories beyond the binary divisions of male and female[(22] She suggests adding three more groups based on “intersex” humans: herms (true hermaphrodites who possess one testis and one ovary), merms (individuals who have testes, no ovaries, but some female genitalia), and ferms (who have ovaries, no testes, but some male characteristics). This attempt to create multiple categories is, however, futile. It tries to systematize the un-systematizable by proposing a neatly divided-up continuum of sexuality, while, in fact, very different and mutually exclusive factors may be at work in particular cases. It is an impossible and intellectually misguided task.
Two major studies examining the historical origins of modern sexual categories show how social groupings that evolve over time can mislead one into supposing that inherent biological classes exist in some unchangeable sense. Michel Foucault chronicled the history of sexual norms by concentrating on the fluid notion of “homosexuality.” He denounced what he called “Freud’s conformism” in taking heterosexuality to be the normal standard in psychoanalysis. He concluded:
We must not forget that the psychological, psychiatric, medical category of homosexuality was constituted from the moment it was characterized–Westphal’s famous article of 1870 on “contrary sexual sensations” can stand as its date of birth–less by a type of sexual relations than by a certain quality of sexual sensibility…. The sodomite had been a temporary aberration; the homosexual was now a species.
This analysis, it seems to me, points to a critical error in the research of both Hamer and LeVay. Both, in spite of their qualifications, adopt the idea of the homosexual as a physical “species” different from the heterosexual. But there are no convincing historical grounds for this view. As Foucault points out, at the time of Plato,
People did not have the notion of two distinct appetites allotted to different individuals or at odds with each other in the same soul; rather, they saw two ways of enjoying one’s pleasure…
The cultural historian Jonathan Katz has recently attacked the naive partitioning of sexual orientation by tracing the dominance of the norm–heterosexuality –throughout history. He provides a convincing argument that the “just-is hypothesis” of heterosexuality–i.e., that the word corresponds to a true behavioral norm–is an “invented tradition.” He shows that the categories of gay and straight are gradually dissolving as notions of the family become more various. Basing his view more on intuition than on sociological evidence, he predicts “the declining significance of sexual orientation.”
The final issue that has confused the interpretation of research into sexuality is the meaning of “biological influence.” Unfortunately, both LeVay and Hamer, in their effort to popularize their findings, ignore the subtlety of this question. As has been noted, LeVay is unambiguous about his own position on biological determinism,
The most promising area for exploration is the identification of genes that influence sexual behavior and the study of when, where, and how these genes exert their effects.
Both researchers ignore the central issue in the debate over nature and nurture. The question is: How do genes get you from a biochemical program that instructs cells to make proteins to an unpredictable interplay of behavioral impulses–fantasy, courtship, arousal, sexual selection–that constitutes “sexuality”? The question remains unresolved. The classic fall-back position is to claim that genes merely provide a basis, at most a predisposition, to a particular behavior. But such statements lack a precise or testable meaning.
Perhaps we are asking the wrong question when we set out to find whether there is a gene for sexual orientation. We know that genes are responsible for the development of our lungs, larynx, mouth, and the speech areas of our brain. And we understand that this complexity cannot be collapsed into the notion of a gene for “talking.” Similarly, what possible basis can there be for concluding that there is a single gene for sexuality, even though we accept that there are genes that direct the development of our penises, vaginas, and brains? This analogy is not to deny the importance of genes, but merely to recast their role in a different conceptual setting, one devoid of dualist prejudice.
The search for a single dominant gene–the “O-GOD” (one gene, one disorder) hypothesis–that would influence a behavioral variant is likely to be fruitless. Many different genes, together with many different environmental factors, will interact in unpredictable ways to guide behavioral preferences. Each component will contribute small quanta of influence. One result of such a quantum theory of behavior is that it makes irrelevant the overstretched speculations of both Hamer and LeVay about why a gene for homosexuality still exists when it apparently has little apparent survival value in evolutionary terms. The quest for a teleological explanation to identify a reason for the existence of a “gay gene” becomes pointless when one understands that there is not now, and never was, a single and final reason for being gay or straight, or having any other identity along the continuum of sexual preference.
Does this complexity, together with an adverse and polarized social milieu, preclude successful research efforts concerning human sexuality? In 1974, Lewontin wrote that reconstruction of man’s genetic past is “an activity of leisure rather than of necessity.” Perhaps so. But, as Robert Plomin argues, the value of studying inheritance in behavior lies in its importance
per se rather than in its usefulness for revealing how genes work. Some of society’s most pressing problems, such as drug abuse, mental illness, and mental retardation, are behavioral problems. Behavior is also a key in health as well as illness, in abilities as well as disabilities, and in the personal pluses of life, such as sense of well-being and the ability to love and work.
What research into human sexuality, then, lies ahead? Dean Hamer has repeated his initial work among male homosexuals in an entirely new group of families and has included a much-needed analysis of women. He has also compared the frequency of the Xq28 marker among pairs of gay siblings and their heterosexual brothers, important control data that he did not acquire the first time around. This work has been submitted to the journal Nature Genetics. Two other teams–one recently formed at the National Institutes of Health and a Canadian group that has reached some preliminary results–are attempting to replicate Hamer’s initial findings. All Hamer will say about his latest data is that they have not discouraged him from continuing with his project.
To track down and sequence the DNA from one or more relevant genes at Xq28, from a total of about two hundred candidates, seems an almost insuperable task. To read the molecular script of DNA involves deciphering millions of constituent elements. Moreover, each gene will have to be studied individually and many more pairs of gay brothers will be needed to achieve this goal. The work will be extremely difficult for a single laboratory to undertake on its own. Hamer’s request for a federally funded center for research into sexuality–a National Institute of Sexual Health–is therefore timely, for the study of differences between the sexes has reached a critical, though admittedly fragmented, stage and a coordinated research program would be valuable.
The concerns of such an institute should be broad. For example, it might have included the recent work reported from Yale which overturns the conventional view that language function is identical for both men and women. By studying which brain areas were activated during various linguistic tasks, the Yale scientists found that women used regions in both their right and left brain cortices in certain instances, while men used only the left side of their brains. If functional brain differences for sophisticated behaviors exist between the sexes, the task for the future would be to link function to structure and to describe how both evolve from a background of genetic and environmental influence.
Inevitably, the idea of biological determinism carries with it the threat of manipulating the genes or the brain in order to adapt to the prevailing norm. As I have noted, Hamer was acutely aware of this possibility when he wrote his paper. But the prospects for pinpointing genetic risk have moved rapidly and worryingly forward with the recent availability of genetic screening techniques for, among other diseases, several cancers, including a small proportion of cancers of the breast, colon, and thyroid. Most such techniques are used without any current prospect for gene therapy or for any other effective treatment of the conditions identified. Geneticists such as Francis Collins, director of the Human Genome Project, have opposed unrestricted and unregulated screening techniques, describing their recent uses as “alarming” because we are “treading into a territory which the genetics community has felt rather strongly is still [in the stage of] research.” Hamer’s fine words opposing genetic manipulation are likely to mean little in the marketplace if his work eventually leads to the isolation of a gene that has an effect on sexual preference, even if it has only a small effect that is present in only a limited number of people. US state legislatures are slowly responding to these issues. Colorado recently became the eleventh state to enact a law preventing information derived from genetic testing to be used in a discriminatory fashion.
In recognition of the emerging risks from dubious applications of preliminary discoveries, NIH launched a Task Force on Genetic Testing in April. The twenty-member committee includes representatives from industry, managed-care organizations, and patient-advocacy groups, and is chaired by Neil A. Holtzman, a professor of pediatrics and health policy at Johns Hopkins University. Far from being a friend to the hyperbolists, Holtzman has written that “physicians should be at the forefront of decrying florid genetic determinism and its dire implications for health and welfare reform.” His committee is charged with performing a two-year study of genetic technologies, which will look specifically at the accuracy, safety, reliability, and social implications of new testing procedures. This move is not without self-interest on the part of the geneticists at the NIH. Members of the US Congressional House Appropriations Committee, which closely monitors NIH spending, have said that they may freeze the Human Genome Project’s $153 million grant if ethics issues are not given close attention.
But sex-based research has already run into political trouble. The Council for Citizens Against Government Waste has charged that some NIMH research is a misuse of taxpayer’s money. Tom Schatz, CCAGW’s president, has criticized twenty such studies, including one involving research into sex offenders. Rex Cowdry, acting director of the National Institute of Mental Health, argues that “for these grants, I think first you have to believe that the factors that motivate and control sexual behavior are worth knowing about…you have to believe that knowing more about how men and women are both similar and different is important.”
With such partisan pressures dominating the future of the research agenda, the circulation of uninformed opinions couched in scholarly prose is a cause for anxiety. In an otherwise superb and iconoclastic critique of the history of heterosexuality, Jonathan Katz ends with a sweeping and badly informed declaration:
Biological determinism is misconceived intellectually, as well as politically loathsome…Contrary to today’s bio-belief, the heterosexual/homosexual binary is not in nature, but is socially constructed, therefore deconstructable.
LeVay and Hamer on the one hand, and Katz, on the other, evidently have taken completely antithetical positions. But Katz’s extreme intellectual reductionism makes him as guilty as the more simplistic biologists and journalists who inflate claims about every new genetic discovery. After convincingly undermining the distinction between gay and straight, he then accepts the naive dualism of nature vs. nurture. It is such attempts as Katz’s to put into opposition forces that are not in opposition which argue so strongly for planned research free from the ideological temptations that he succumbs to. Biological research into sexuality will indeed be misconceived if we assume that we already understand the differences between the sexes. In part the results of that research often contradict any such assumption. Katz demands that “we need to look less to oracles [presumably biological], and trust more in our desires, visions, and political organizing.” But to take this path risks perpetuating a debate based on ignorance rather than one based on evidence.
It is true that the research of Hamer and LeVay presents technical and conceptual difficulties and that their preliminary findings obviously need replication or refutation. Yet their work represents a genuine epistemological break away from the past’s rigid and withered conceptions of sexual preference. The pursuit of understanding about the origins of human sexuality –the quest to find an answer to the question, What does it mean to be gay and/or straight?–offers the possibility of eliminating what can be the most oppressive of cultural forces, the prejudiced social norm.
1 See Perversions: Psychodynamics and Therapy, edited by Sandor Lorand and Michael Balint (Ortolan Press, 1965; first edition, Random House, 1956), p. 75.
2 Quoted in Kenneth Lewes, The Psychoanalytic Theory of Male Homosexuality (Simon and Schuster, 1988), p. 188.
3 See Bernard J. Oliver, Jr., Sexual Deviation in American Society (College and University Press, 1967), p. 146.
4 See Karen de Witt, “Quayle Contends Homosexuality Is a Matter of Choice, Not Biology,” The New York Times, September 14, 1992, p. A17.
5 See Larry Thompson, “Search for a Gay Gene,” Time (June 12, 1995), pp. 60-61.
6 See Shang-Ding Zhang and Ward F. Odenwald, “Misexpression of the White (w) Gene Triggers Male-male Courtship in Drosophila,” Proceedings of the National Academy of Sciences, USA, Vol. 92 (June 6, 1995), pp. 5525-5529.
7 See Simon LeVay, “A Difference in Hypothalamic Structure Between Heterosexual and Homosexual Men,” Science (August 30, 1991), pp. 1034-1037.
8 The suprachiasmatic nucleus, also located in the hypothalamus, is larger in homosexual men than in either heterosexual men or women. The anterior commissure of the corpus callosum (a band of tissue that connects the right and left hemispheres of the brain) is also larger in gay men.
9 See Dean H. Hamer et al., “A Linkage Between DNA Markers on the X Chromosome and Male Sexual Orientation,” Science (July 16, 1993), pp. 321-327.
10. The normal complement of human chromosomes is forty-six per individual, two of which are designated sex chromosomes. In the male, the sex chromosomal makeup is XY, while in the female it is XX. If a gene for homosexuality (Xh) was transmitted through the maternal line, one can see how the subsequent offspring would be affected.
Suppose the unaffected female carrier for homosexuality (XXh) produced offspring with a non-Xh male (XY). Half of all female children would be carriers of Xh (like their mothers), while half of all male offspring would carry Xh unopposed by another X. The Xh trait — homosexuality — would then be able to express itself.
11 By chance, one would expect each pair of brothers to share half their DNA. So, assuming that there was no gene for homosexuality, one would expect twenty of the forty pairs of brothers to share the X chromosome marker.
12 LeVay has recently completed a second book in collaboration with Elisabeth Nonas–City of Friends–that surveys gay and lesbian culture; it will be published by MIT Press in November. He is currently working on Queer Science, a study of how scientific research has affected the lives of gays and lesbians.
13 See Anne Fausto-Sterling and Evan Balaban, “Genetics and Male Sexual Orientation,” Science (September 3, 1993), p. 1257.
14 For example, see David Weatherall, Science and the Quiet Art (Norton, 1995) who notes that “these findings should not surprise us. Almost every condition…reveals a complex mixture of nature and nurture,” p. 287.
15 See R.C. Lewontin, S. Rose, and L. J. Kamin, Not in Our Genes (Pantheon, 1984).
16 Lewontin is not a total skeptic about the importance of molecular genetics research in medicine. For instance, he accepts “that some fraction of cancers arise on a background of genetic predisposition.” See R.C. Lewontin, “The Dream of the Human Genome,” The New York Review (May 28, 1992), pp. 31-40.
17 See M. W. Feldman and R. C. Lewontin, “The Heritability Hang-up,” Science (December 19, 1975), pp. 1163-1168.
18 See Robert Plomin, “The Role of Inheritance in Behavior,” Science (April 13, 1990), pp. 183-188.
19 See R.C. Lewontin, “The Analysis of Variance and the Analysis of Causes,” The American Journal of Human Genetics, Vol. 26 (1974), pp. 400-411.
20 For example, in a UK study (see Anne M. Johnson, “Sexual lifestyles and HIV risks,” Nature [December 3, 1992], pp. 410-412), although only 1.4 percent of men reported a male partner during the past five years, 6.1 percent of men reported having experienced some same-gender behavior.
21 See Stephen B Levine, Sexual Life: A Clinician’s Guide (Plenum, 1992). The Kinsey scale has seven levels ranging from exclusively heterosexual (0) to exclusively gay (6). Hamer applied this scale to four aspects of sexuality: self-identification, attraction, fantasy, and behavior.
22 See Anne Fausto-Sterling, “The Five Sexes: Why Male and Female Are Not Enough,” The Sciences (March/April, 1993), pp. 20-24.
23 See Michel Foucault, The History of Sexuality, Vols. One and Two (Vintage, 1990).
24 Dr. K.F.O. Westphal became the first modern author to publish an account of what he described as a “contrary sexual feeling” (Die contrare Sexualempfindung), although the word homosexual was first used in a private letter written by Karl Maria Kertbeny on May 6, 1868. This linguistic history is described in detail by Jonathan Katz (see note 25).
25 See Jonathan Ned Katz, The Invention of Heterosexuality (Dutton, 1995).
26 R.C. Lewontin, “The Analysis of Variance and the Analysis of Causes,” The American Journal of Human Genetics, Vol. 26 (1974), pp. 400-411.
27. Robert Plomin, “The Role of Inheritance in Behavior,” Science (April 13, 1990), pp. 183-188.
28. See Bennett A. Shaywitz et al., “Sex differences in the functional organization of the brain for language,” Nature (February 16, 1995), pp. 607-609.
29 See Gina Kolata, “Tests to Assess Risks for Cancer Raising Questions,” The New York Times (March 27, 1995), p. A1.
30 See Neil A. Holtzman, “Genetics,” Journal of the American Medical Association (April 26, 1995), pp. 1304-1306.
31 See “NIMH’s Cowdry Defends Institute’s Research Against Appropriations Committee, Watchdog Group Criticism,” The Blue Sheet (March 29, 1995), pp. 5-6.
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A gay Gene – Is Homosexuality Inherited Assault On Gay …
Nicole Kush is the first new cannabis strain to be released by DNA Genetics in collaboration with Marimberos.
The sativa-dominant strain, Nicole, can trace it’s lineage back to a carefully bred plant in Mexico’s Durango desert almost ten years ago. With a pedigree that includes such classic strains as MK Ultra, Shiskaberry and Blueberry, Nicole was then crossed with DNA Genetics legendary Kosher Kush to create this exciting new strain – Nicole Kush.
DNA and Marimberos’ test grows of Nicole Kush, conducted in a legal environment, showed insane, over-the-top resin production. A blanket of sticky trichomes coats the plants; Nicole Kush is ideal for extractions. Flavours and aromas are fruity like blueberries and wine or even grape jam.
A lovely new strain from DNA and Marimberos that is a certainty to be popular with connoisseur cannabis seed collectors everywhere.
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All our descriptions and images have come direct from the breeders who operate in a legal climate much different to that within the United Kingdom. Take note, you should NEVER try cultivating any cannabis plants within ANY jurisdiction where such cultivation is illegal. Our seeds are sold purely for souvenirs and should be treated as a curio or novelty item and should never be germinated. PLEASE DO NOT BREAK THE LAW!
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Nicole Kush Female Cannabis Seeds by DNA Genetics and …
**In fruit flies, eye color is a sex linked trait. Red is dominant to white.**
1. What are the sexes and eye colors of flies with the following genotypes?
X R X r _________ X R Y __________ X r X r __________
X R X R ____________ X r Y ____________
2. What are the genotypes of these flies:
white eyed, male ____________ red eyed female (heterozygous) ________
white eyed, female ___________ red eyed, male ___________
3. Show the cross of a white eyed female X r X r with a red-eyed male X R Y .
4. Show a cross between a pure red eyed female and a white eyed male. What are the genotypes of the parents:
___________ and _______________
How many are:
white eyed, male ____ white eyed, female ____ red eyed, male ____ red eyed, female ____
5. Show the cross of a red eyed female (heterozygous) and a red eyed male.
What are the genotypes of the parents?
___________ & ________________
How many are:
white eyed, male ____ white eyed, female ____ red eyed, male ____ red eyed, female ____
Math: What if in the above cross, 100 males were produced and 200 females. How many total red-eyed flies would there be? ________
6. In humans, hemophilia is a sex linked trait. Females can be normal, carriers, or have the disease. Males will either have the disease or not (but they wont ever be carriers)
X h Y= male, hemophiliac
Show the cross of a man who has hemophilia with a woman who is a carrier.
What is the probability that their children will have the disease? __________
7. A woman who is a carrier marries a normal man. Show the cross. What is the probability that their children will have hemophilia? What sex will a child in the family with hemophilia be?
8. A woman who has hemophilia marries a normal man. How many of their children will have hemophilia, and what is their sex?
9. In cats, the gene for calico (multicolored) cats is codominant. Females that receive a B and an R gene have black and oRange splotches on white coats. Males can only be black or orange, but never calico.
Heres what a calico females genotype would look like: X B X R
Show the cross of a female calico cat with a black male?
What percentage of the kittens will be black and male? _________ What percentage of the kittens will be calico and male? _________ What percentage of the kittens will be calico and female? _________
10. Show the cross of a female black cat, with a male orange cat.
What percentage of the kittens will be calico and female? _____What color will all the male cats be? ______
What Are Chromosomes?
Our bodies are made up of about 60 trillion cells. Each one of those cells manufactures proteins. The kinds of proteins any given cell makes determine its particular characteristics, which in turn create the characteristics of the entire body.
The instructions for making these proteins are stored in chemicals or molecules called DNA, which is organized into chromosomes. Chromosomes are found in the center, or nucleus, of all of our cells, including the eggs and sperm.
Chromosomes are passed down from generation to generation through the egg and sperm. Typically, we all have 46 chromosomes in our cells, two of which are sex chromosomes. In females, these are two Xs; in males they are an X and a Y.
Genes are sections of DNA that are passed from generation to generation and perform one function. If we think of DNA as letters in the alphabet, the genes are words and the chromosome is a full sentence. All 46 chromosomes then make up the whole book.
There are many genes on each chromosome; we all have tens of thousands of genes that instruct our bodies on how to develop.
Genes are given names to identify them and the gene responsible for fragile X syndrome is called FMR1. The FMR1 Gene is on the X chromosome.
The FMR1 gene appears in four forms that are defined by the number of repeats of a pattern of DNA called CGG repeats.
Individuals with less than 45 CGG repeats have a normal FMR1 gene. Those with 45-54 CGG repeats have what is called an intermediate or grey zone allele, which does not cause any of the known fragile X associated disorders.
Individuals with 55-200 CGG repeats have a premutation, which means they carry an unstable mutation of the gene that can expand in future generations and thus cause fragile X syndrome in their children or grandchildren. Individuals with a premutation can also develop FXTAS or FXPOI themselves.
Individuals with over 200 CGG repeats have a full mutation of the FMR1 gene, which causes fragile X syndrome.
The full mutation causes the FMR1 gene to shut down or methylate in one region. Normally, the FMR1 gene produces an important protein called FMRP. When the gene is turned off, the individual does not make this protein. The lack of this specific protein is what causes fragile X syndrome.
Fragile X-associated Disorders are a group of conditions called trinucleotide repeat disorders. A common feature of these conditions is that the gene can change sizes over generations, becoming more unstable, and thus the conditions may occur more frequently or severely in subsequent generations. These conditions are often caused by a gene change that begins with a premutation and then expands to a full mutation in subsequent generations.
Approximately 1 in 151 females and 1 in 468 males carry the FMR1 premutation. They are thus carriers of the premutation.
Premutations are defined as having 55-200 CGG repeats and can occur in both males and females. When a father passes the premutation on to his daughters, it usually does not expand to a full mutation. A man never passes the fragile X gene to his sons, since he passes only his Y chromosome to them, which does not contain a fragile X gene.
A female with the FMR1 premutation will often pass on a larger version of the mutation to her children (more on this point below). She also has a 50 percent chance of passing on her normal X chromosome in each pregnancy, since usually only one of her X chromosomes has the FMR1 mutation.
The chance of the premutation expanding to a full mutation is related to the size of the mothers premutation. The larger the mothers CGG repeat number, the higher the chance that it will expand to a full mutation if it is passed on.
Typically, the premutation has no immediate and observable impact on a persons appearance or health. However, some females with a premutation will experience fragile X-associated primary ovarian insufficiency (FXPOI), which causes infertility, irregular or missed menstrual cycles, and/or early menopause.
Additionally, some older adults with a premutation may develop a neurological condition called FXTAS, (fragile X-associated tremor/ataxia syndrome), an adult onset neurodegenerative disorder.
FXTAS and FXPOI are part of the family of conditions called Fragile X-associated Disorders.
A full mutation is defined as having over 200 CGG repeats and causes that indicate the presence of fragile X syndrome in males and some females. Most full mutation expansions have some degree of Methylation (the process which turns off the gene). Males with a full mutation will have Fragile X Syndrome, though with varying degrees of severity
About 65-70 percent of females with a full mutation exhibit some difficulties with cognitive, learning, behavioral, or social functioning, and may also have some of the physical features of FXS (such as large ears or a long face). The remaining 30-35 percent are at risk to develop mental health issues such as anxiety or depression, or they may have no observable effects of the full mutation.
Fragile X in an X-linked condition, which means that the gene is on the X chromosome.
Since a woman has two X chromosomes a woman with a premutation or full mutation has a 50% chance of passing on the X with the mutation in each pregnancy, and a 50% chance of passing on her normal X.
If she has a premutation, and it is passed on (to either males or females), it can remain a premutation or it can expand to a full mutation. If she has a full mutation and it is passed on (to either males or females), it will remain a full mutation.
Because males have only one X chromosome, fathers who carry the premutation will pass it on to all their daughters and none of their sons (they pass their Y chromosome on to their sons). There have been no reports of premutations that are passed from a father to his daughter expanding to a full mutation. This appears to only occur when passed from a mother to her children.
In many X-linked conditions only males who inherit the abnormal gene are affected. Fragile X syndrome is one of the X-linked conditions that can also affect females.
Additionally, in other X-linked conditions all males who carry the abnormal form of the gene are affected. In fragile X syndrome, unaffected males can carry the gene in the premutation form while themselves having no symptoms of the condition.
Follow this link:
Genetics and Inheritance – National Fragile X Foundation
The long-term objectives of our research team are:
a. to understand the molecular etiology in the development of human cancer, and b. to identify and characterize cancer molecules for cancer detection, diagnosis, and therapy.
We use ovarian carcinoma as a disease model because it is one of the most aggressive neoplastic diseases in women. For the first research direction, we aim to identify and characterize the molecular alterations during initiation and progression of ovarian carcinomas. Previous genome-wide analyses from our team have identified molecular alterations in several new cancer-associated genes including Rsf-1, NAC-1, and Notch3 among several others. We have demonstrated the essential roles of these gene products in sustaining tumor growth and survival. Current projects are focusing on elucidating the mechanisms by which these genes function in cancer cells and delineating the cross-talks between those genes and other signaling pathways. Specifically, we are identifying their downstream targets and pathways, and are determining their roles in maintaining cancer stem cell-like features, invasion and drug resistance. The second research direction is a translation-based study. We are assessing the clinical significance of an array of new cancer-associated genes in predicting clinical outcome and in the developing potential target-based therapy in mouse preclinical models. We are also establishing innovative assays for cancer detection and diagnosis by identifying new tumor-associated genetic and protein biomarkers through serial analysis of gene expression, gene expression arrays, proteomics and methylation profiling. The purpose is to develop new tools in detecting human cancer using body fluid samples. In collaboration with several investigators, we are integrating new technologic platforms such as microfluidics, nanotechnology and systems biology in our studies.
In addition to ovarian cancer genetics, we are interested in the diagnostic pathology and basic research of gestational trophoblastic diseases. Please visit “Pathology of Trophoblastic Lesions” for details.
Click here for the Ovarian Cancer Prevention Website
Click here for the Ovarian Cancer Research Program
“What we observe is not nature itself, but nature exposed to our method of questioning.” — Werner Heisenberg, Physics and Philosophy, 1958
Tian-Li Wang, PhD email@example.com
Professor Departments of Pathology, Oncology, and Gynecology & Obstetrics Faculty in Pathobiology Graduate Program Johns Hopkins Medical Institutions
National Taiwan University, BS Johns Hopkins University School of Medicine, PhD University of Pennsylvania, School of Medicine, Post-doc fellow (Neuroscience) Howard Hughes Medical Institutions, Associate (Cancer Genetics)
Ie-Ming Shih, MD, PhD Co-director, Breast & Ovarian Cancer Program Sidney Kimmel Comprehensive Cancer Center firstname.lastname@example.org
Richard W. TeLinde Professor Department of Gynecology & Obstetrics Departments of Pathology and Oncology Faculty in Pathobiology Graduate Program Johns Hopkins University School of Medicine
Taipei Medical University, MD University of Pennsylvania, PhD Johns Hopkins University, Residency (Pathology) Johns Hopkins University, Fellowships (Gynecologic Pathology and Cancer Genetics)
The Y chromosome is one of two sex chromosomes (allosomes) in mammals, including humans, and many other animals. The other is the X chromosome. Y is the sex-determining chromosome in many species, since it is the presence or absence of Y that determines the male or female sex of offspring produced in sexual reproduction. In mammals, the Y chromosome contains the gene SRY, which triggers testis development. The DNA in the human Y chromosome is composed of about 59 million base pairs. The Y chromosome is passed only from father to son. With a 30% difference between humans and chimpanzees, the Y chromosome is one of the fastest evolving parts of the human genome. To date, over 200 Y-linked genes have been identified. All Y-linked genes are expressed and (apart from duplicated genes) hemizygous (present on only one chromosome) except in the cases of aneuploidy such as XYY syndrome or XXYY syndrome. (See Y linkage.)
The Y chromosome was identified as a sex-determining chromosome by Nettie Stevens at Bryn Mawr College in 1905 during a study of the mealworm Tenebrio molitor. Edmund Beecher Wilson independently discovered the same mechanisms the same year. Stevens proposed that chromosomes always existed in pairs and that the Y chromosome was the pair of the X chromosome discovered in 1890 by Hermann Henking. She realized that the previous idea of Clarence Erwin McClung, that the X chromosome determines sex, was wrong and that sex determination is, in fact, due to the presence or absence of the Y chromosome. Stevens named the chromosome “Y” simply to follow on from Henking’s “X” alphabetically.
The idea that the Y chromosome was named after its similarity in appearance to the letter “Y” is mistaken. All chromosomes normally appear as an amorphous blob under the microscope and only take on a well-defined shape during mitosis. This shape is vaguely X-shaped for all chromosomes. It is entirely coincidental that the Y chromosome, during mitosis, has two very short branches which can look merged under the microscope and appear as the descender of a Y-shape.
Most mammals have only one pair of sex chromosomes in each cell. Males have one Y chromosome and one X chromosome, while females have two X chromosomes. In mammals, the Y chromosome contains a gene, SRY, which triggers embryonic development as a male. The Y chromosomes of humans and other mammals also contain other genes needed for normal sperm production.
There are exceptions, however. For example, the platypus relies on an XY sex-determination system based on five pairs of chromosomes. Platypus sex chromosomes in fact appear to bear a much stronger homology (similarity) with the avian Z chromosome, and the SRY gene so central to sex-determination in most other mammals is apparently not involved in platypus sex-determination. Among humans, some men have two Xs and a Y (“XXY”, see Klinefelter syndrome), or one X and two Ys (see XYY syndrome), and some women have three Xs or a single X instead of a double X (“X0”, see Turner syndrome). There are other exceptions in which SRY is damaged (leading to an XY female), or copied to the X (leading to an XX male). For related phenomena, see Androgen insensitivity syndrome and Intersex.
Many ectothermic vertebrates have no sex chromosomes. If they have different sexes, sex is determined environmentally rather than genetically. For some of them, especially reptiles, sex depends on the incubation temperature; others are hermaphroditic (meaning they contain both male and female gametes in the same individual).
The X and Y chromosomes are thought to have evolved from a pair of identical chromosomes, termed autosomes, when an ancestral mammal developed an allelic variation, a so-called ‘sex locus’ simply possessing this allele caused the organism to be male. The chromosome with this allele became the Y chromosome, while the other member of the pair became the X chromosome. Over time, genes which were beneficial for males and harmful to (or had no effect on) females either developed on the Y chromosome, or were acquired through the process of translocation.
Until recently, the X and Y chromosomes were thought to have diverged around 300 million years ago. However, research published in 2010, and particularly research published in 2008 documenting the sequencing of the platypus genome, has suggested that the XY sex-determination system would not have been present more than 166 million years ago, at the split of the monotremes from other mammals. This re-estimation of the age of the therian XY system is based on the finding that sequences that are on the X chromosomes of marsupials and eutherian mammals are present on the autosomes of platypus and birds. The older estimate was based on erroneous reports that the platypus X chromosomes contained these sequences.
Recombination between the X and Y chromosomes proved harmfulit resulted in males without necessary genes formerly found on the Y chromosome, and females with unnecessary or even harmful genes previously only found on the Y chromosome. As a result, genes beneficial to males accumulated near the sex-determining genes, and recombination in this region was suppressed in order to preserve this male specific region. Over time, the Y chromosome changed in such a way as to inhibit the areas around the sex determining genes from recombining at all with the X chromosome. As a result of this process, 95% of the human Y chromosome is unable to recombine. Only the tips of the Y and X chromosomes recombine. The tips of the Y chromosome that could recombine with the X chromosome are referred to as the pseudoautosomal region. The rest of the Y chromosome is passed on to the next generation intact. It is because of this disregard for the rules that the Y chromosome is such a superb tool for investigating recent human evolution from a male perspective.
By one estimate, the human Y chromosome has lost 1,393 of its 1,438 original genes over the course of its existence, and linear extrapolation of this 1,393-gene loss over 300 million years gives a rate of genetic loss of 4.6 genes per million years. Continued loss of genes at the 4.6 genes per million year rate would result in a Y chromosome with no functional genes that is the Y chromosome would lose complete function within the next 10 million years, or half that time with the current age estimate of 160 million years. Comparative genomic analysis reveals that many mammalian species are experiencing a similar loss of function in their heterozygous sex chromosome. Degeneration may simply be the fate of all non-recombining sex chromosomes, due to three common evolutionary forces: high mutation rate, inefficient selection, and genetic drift.
However, comparisons of the human and chimpanzee Y chromosomes (first published in 2005) show that the human Y chromosome has not lost any genes since the divergence of humans and chimpanzees between 67 million years ago, and a scientific report in 2012 stated that only one gene had been lost since humans diverged from the rhesus macaque 25 million years ago. These facts provide direct evidence that the linear extrapolation model is flawed and suggest that the current human Y chromosome is either no longer shrinking or is shrinking at a much slower rate than the 4.6 genes per million years estimated by the linear extrapolation model.
The human Y chromosome is particularly exposed to high mutation rates due to the environment in which it is housed. The Y chromosome is passed exclusively through sperm, which undergo multiple cell divisions during gametogenesis. Each cellular division provides further opportunity to accumulate base pair mutations. Additionally, sperm are stored in the highly oxidative environment of the testis, which encourages further mutation. These two conditions combined put the Y chromosome at a greater risk of mutation than the rest of the genome. The increased mutation risk for the Y chromosome is reported by Graves as a factor 4.8. However, her original reference obtains this number for the relative mutation rates in male and female germ lines for the lineage leading to humans.
Without the ability to recombine during meiosis, the Y chromosome is unable to expose individual alleles to natural selection. Deleterious alleles are allowed to “hitchhike” with beneficial neighbors, thus propagating maladapted alleles in to the next generation. Conversely, advantageous alleles may be selected against if they are surrounded by harmful alleles (background selection). Due to this inability to sort through its gene content, the Y chromosome is particularly prone to the accumulation of “junk” DNA. Massive accumulations of retrotransposable elements are scattered throughout the Y. The random insertion of DNA segments often disrupts encoded gene sequences and renders them nonfunctional. However, the Y chromosome has no way of weeding out these “jumping genes”. Without the ability to isolate alleles, selection cannot effectively act upon them.
A clear, quantitative indication of this inefficiency is the entropy rate of the Y chromosome. Whereas all other chromosomes in the human genome have entropy rates of 1.51.9 bits per nucleotide (compared to the theoretical maximum of exactly 2 for no redundancy), the Y chromosome’s entropy rate is only 0.84. This means the Y chromosome has a much lower information content relative to its overall length; it is more redundant.
Even if a well adapted Y chromosome manages to maintain genetic activity by avoiding mutation accumulation, there is no guarantee it will be passed down to the next generation. The population size of the Y chromosome is inherently limited to 1/4 that of autosomes: diploid organisms contain two copies of autosomal chromosomes while only half the population contains 1 Y chromosome. Thus, genetic drift is an exceptionally strong force acting upon the Y chromosome. Through sheer random assortment, an adult male may never pass on his Y chromosome if he only has female offspring. Thus, although a male may have a well adapted Y chromosome free of excessive mutation, it may never make it in to the next gene pool. The repeat random loss of well-adapted Y chromosomes, coupled with the tendency of the Y chromosome to evolve to have more deleterious mutations rather than less for reasons described above, contributes to the species-wide degeneration of Y chromosomes through Muller’s ratchet.
As it has been already mentioned, the Y chromosome is unable to recombine during meiosis like the other human chromosomes; however, in 2003, researchers from MIT discovered a process which may slow down the process of degradation. They found that human Y chromosome is able to “recombine” with itself, using palindrome base pair sequences. Such a “recombination” is called gene conversion.
In the case of the Y chromosomes, the palindromes are not noncoding DNA; these strings of bases contain functioning genes important for male fertility. Most of the sequence pairs are greater than 99.97% identical. The extensive use of gene conversion may play a role in the ability of the Y chromosome to edit out genetic mistakes and maintain the integrity of the relatively few genes it carries. In other words, since the Y chromosome is single, it has duplicates of its genes on itself instead of having a second, homologous, chromosome. When errors occur, it can use other parts of itself as a template to correct them.
Findings were confirmed by comparing similar regions of the Y chromosome in humans to the Y chromosomes of chimpanzees, bonobos and gorillas. The comparison demonstrated that the same phenomenon of gene conversion appeared to be at work more than 5 million years ago, when humans and the non-human primates diverged from each other.
In the terminal stages of the degeneration of the Y chromosome, other chromosomes increasingly take over genes and functions formerly associated with it. Finally, the Y chromosome disappears entirely, and a new sex-determining system arises. Several species of rodent in the sister families Muridae and Cricetidae have reached these stages, in the following ways:
Outside of the rodent family, the black muntjac, Muntiacus crinifrons, evolved new X and Y chromosomes through fusions of the ancestral sex chromosomes and autosomes.
Fisher’s principle outlines why almost all species using sexual reproduction have a sex ratio of 1:1, meaning that 50% of offspring will receive a Y chromosome, and 50% will not. W.D. Hamilton gave the following basic explanation in his 1967 paper on “Extraordinary sex ratios”, given the condition that males and females cost equal amounts to produce:
In humans, the Y chromosome spans about 58 million base pairs (the building blocks of DNA) and represents approximately 1% of the total DNA in a male cell. The human Y chromosome contains over 200 genes, at least 72 of which code for proteins. Traits that are inherited via the Y chromosome are called holandric traits (although biologists will usually just say ‘Y-linked’).
Some cells, especially in older men and smokers, lack a Y-chromosome. It has been found that men with a higher percentage of hematopoietic stem cells in blood lacking the Y-chromosome (and perhaps a higher percentage of other cells lacking it) have a higher risk of certain cancers and have a shorter life expectancy. Men with “loss of Y” (which was defined as no Y in at least 18% of their hematopoietic cells) have been found to die 5.5 years earlier on average than others. This has been interpreted as a sign that the Y-chromosome plays a role going beyond sex determination and reproduction (although the loss of Y may be an effect rather than a cause). And yet women, who have no Y-chromosome, have lower rates of cancer. Male smokers have between 1.5 and 2 times the risk of non-respiratory cancers as female smokers.
The human Y chromosome is normally unable to recombine with the X chromosome, except for small pieces of pseudoautosomal regions at the telomeres (which comprise about 5% of the chromosome’s length). These regions are relics of ancient homology between the X and Y chromosomes. The bulk of the Y chromosome, which does not recombine, is called the “NRY” or non-recombining region of the Y chromosome. It is the SNPs (single-nucleotide polymorphism) in this region that are used to trace direct paternal ancestral lines.
Not including pseudoautosomal genes, genes include:
Y-Chromosome-linked diseases can be of more common types, or very rare ones. Yet, the rare ones still have importance in understanding the function of the Y-chromosome in the normal case.
No vital genes reside only on the Y chromosome, since roughly half of humans (females) do not have a Y chromosome. The only well-defined human disease linked to a defect on the Y chromosome is defective testicular development (due to deletion or deleterious mutation of SRY). However, having two X chromosomes and one Y chromosome has similar effects. On the other hand, having Y chromosome polysomy has other effects than masculinization.
Y chromosome microdeletion (YCM) is a family of genetic disorders caused by missing genes in the Y chromosome. Many affected men exhibit no symptoms and lead normal lives. However, YCM is also known to be present in a significant number of men with reduced fertility or reduced sperm count.
This results in the person presenting a female phenotype (i.e., is born with female-like genitalia) even though that person possesses an XY karyotype. The lack of the second X results in infertility. In other words, viewed from the opposite direction, the person goes through defeminization but fails to complete masculinization.
The cause can be seen as an incomplete Y chromosome: the usual karyotype in these cases is 44X, plus a fragment of Y. This usually results in defective testicular development, such that the infant may or may not have fully formed male genitalia internally or externally. The full range of ambiguity of structure may occur, especially if mosaicism is present. When the Y fragment is minimal and nonfunctional, the child is usually a girl with the features of Turner syndrome or mixed gonadal dysgenesis.
Klinefelter syndrome (47, XXY) is not an aneuploidy of the Y chromosome, but a condition of having an extra X chromosome, which usually results in defective postnatal testicular function. The mechanism is not fully understood; the extra X does not seem to be due to direct interference with expression of Y genes.
47,XYY syndrome (simply known as XYY syndrome) is caused by the presence of a single extra copy of the Y chromosome in each of a male’s cells. 47, XYY males have one X chromosome and two Y chromosomes, for a total of 47 chromosomes per cell. Researchers have found that an extra copy of the Y chromosome is associated with increased stature and an increased incidence of learning problems in some boys and men, but the effects are variable, often minimal, and the vast majority do not know their karyotype. When chromosome surveys were done in the mid-1960s in British secure hospitals for the developmentally disabled, a higher than expected number of patients were found to have an extra Y chromosome. The patients were mischaracterized as aggressive and criminal, so that for a while an extra Y chromosome was believed to predispose a boy to antisocial behavior (and was dubbed the ‘criminal karyotype’). Subsequently, in 1968 in Scotland the only ever comprehensive nationwide chromosome survey of prisons found no over-representation of 47,XYY men, and later studies found 47,XYY boys and men had the same rate of criminal convictions as 46,XY boys and men of equal intelligence. Thus, the “criminal karyotype” concept is inaccurate and obsolete.
The following Y chromosome-linked diseases are rare, but notable because of their elucidating of the nature of the Y chromosome.
Greater degrees of Y chromosome polysomy (having more than one extra copy of the Y chromosome in every cell, e.g., XYYY) are rare. The extra genetic material in these cases can lead to skeletal abnormalities, decreased IQ, and delayed development, but the severity features of these conditions are variable.
XX male syndrome occurs when there has been a recombination in the formation of the male gametes, causing the SRY-portion of the Y chromosome to move to the X chromosome. When such an X chromosome contributes to the child, the development will lead to a male, because of the SRY gene.
In human genetic genealogy (the application of genetics to traditional genealogy), use of the information contained in the Y chromosome is of particular interest because, unlike other chromosomes, the Y chromosome is passed exclusively from father to son, on the patrilineal line. Mitochondrial DNA, maternally inherited to both sons and daughters, is used in an analogous way to trace the matrilineal line.
Research is currently investigating whether male-pattern neural development is a direct consequence of Y chromosome-related gene expression or an indirect result of Y chromosome-related androgenic hormone production.
The presence of male chromosomes in fetal cells in the blood circulation of women was discovered in 1974. In 1996, it was found that male fetal progenitor cells could persist postpartum in the maternal blood stream for as long as 27 years.
A 2004 study at the Fred Hutchinson Cancer Research Center, Seattle investigated the origin of male chromosomes found in the peripheral blood of women who had not had male progeny. A total of 120 subjects (women who had never had sons) were investigated and it was found that 21% of them had male DNA. The subjects were categorised into four groups based on their case histories:
The study noted that 10% of the women had never been pregnant before, raising the question where the Y Chromosomes in their blood could have come from? The study suggests that possible reasons for occurrence of male chromosome microchimerism could be one of the following:
A 2012 study, at the same institute, has detected cells with the Y chromosome in multiple areas of the brains of dead women.
Many groups of organisms in addition to mammals have Y chromosomes, but these Y chromosomes do not share common ancestry with mammalian Y chromosomes. Such groups include Drosophila, some other insects, some fish, some reptiles, and some plants. In Drosophila melanogaster, the Y chromosome does not trigger male development. Instead, sex is determined by the number of X chromosomes. The D. melanogaster Y chromosome does contain genes necessary for male fertility. So XXY D. melanogaster are female, and D. melanogaster with a single X (X0), are male but sterile. There are some species of Drosophila in which X0 males are both viable and fertile.
Other organisms have mirror image sex chromosomes: the female is “XY” and the male is “XX”, but by convention biologists call a “female Y” a W chromosome and the other a Z chromosome. For example, female birds, snakes, and butterflies have ZW sex chromosomes, and males have ZZ sex chromosomes.
There are some species, such as the Japanese rice fish, where the Y chromosome is not inverted and can still swap genes with the X. Because the Y does not have male-specific genes and can interact with the X, XX males can be formed as well as XY and YY females.
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Y chromosome – Wikipedia, the free encyclopedia
Value Genetics Bull & Female Sale
Saturday March 5, 2016 12:30 p.m. Clinton Livestock Auction, Clinton, OK View Sale Book View Videos
Davis Angus began in 1973 when Bud Davis, Jim’s father purchased ten registered Angus cows from Al Rutledge. Jim and wife Debbie, later added cattle from the UT, Allen Greer and Pat O’Brian, and B&L dispersals. The first AI sires were introduced in 1995; Davis Angus chose BR New Design 323 and TC Dividend 963. Through the technological advances of breeding and the use of artificial insemination inspiration developed, a dream that cattle could be produced that had all the desired carcass traits with the show ring appeal. This idea led Davis Angus to produce the cattle you see today. Cattle that have Carcass and Conformation without Compromise.
The 2007 Davis Angus calf crop was very successful with 100% of the steers grading choice, 60% went CAB and prime, producing a 46% yield grade 1 and 2, this allowed Davis Angus to receive a premium of $106.95 per head above the market while costing only $0.78 per pound with corn costing $6.00 per bushel.
Davis Angus was very successful in the show ring with several champions; we encourage you to view our “Hall of Champions” page and view the results!
In the past decade we have become very successful in the show ring as well as winning several carcass competitions.
We encourage you to come visit us at Davis Angus, let us put you in the winner’s circle!
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Davis Angus Foss, Oklahoma
The X chromosome is one of the two sex-determining chromosomes (allosomes) in many animal species, including mammals (the other is the Y chromosome), and is found in both males and females. It is a part of the XY sex-determination system and X0 sex-determination system. The X chromosome was named for its unique properties by early researchers, which resulted in the naming of its counterpart Y chromosome, for the next letter in the alphabet, after it was discovered later.
The X chromosome in humans spans more than 153 million base pairs (the building material of DNA). It represents about 2000 out of 20,000 – 25,000 genes. Each person normally has one pair of sex chromosomes in each cell. Females have two X chromosomes, whereas males have one X and one Y chromosome. Both males and females retain one of their mother’s X chromosomes, and females retain their second X chromosome from their father. Since the father retains his X chromosome from his mother, a human female has one X chromosome from her paternal grandmother (father’s side), and one X chromosome from her mother.
Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. The X chromosome contains about 2000 genes compared to the Y chromosome containing 78 genes, out of the estimated 20,000 to 25,000 total genes in the human genome. Genetic disorders that are due to mutations in genes on the X chromosome are described as X linked.
The X chromosome carries a couple of thousand genes but few, if any, of these have anything to do directly with sex determination. Early in embryonic development in females, one of the two X chromosomes is randomly and permanently inactivated in nearly all somatic cells (cells other than egg and sperm cells). This phenomenon is called X-inactivation or Lyonization, and creates a Barr body. If X-inactivation in the somatic cell meant a complete de-functionalizing of one of the X-chromosomes, it would ensure that females, like males, had only one functional copy of the X chromosome in each somatic cell. This was previously assumed to be the case. However, recent research suggests that the Barr body may be more biologically active than was previously supposed.
It is theorized by Ross et al. 2005 and Ohno 1967 that the X chromosome is at least partially derived from the autosomal (non-sex-related) genome of other mammals, evidenced from interspecies genomic sequence alignments.
The X chromosome is notably larger and has a more active euchromatin region than its Y chromosome counterpart. Further comparison of the X and Y reveal regions of homology between the two. However, the corresponding region in the Y appears far shorter and lacks regions that are conserved in the X throughout primate species, implying a genetic degeneration for Y in that region. Because males have only one X chromosome, they are more likely to have an X chromosome-related disease.
It is estimated that about 10% of the genes encoded by the X chromosome are associated with a family of “CT” genes, so named because they encode for markers found in both tumor cells (in cancer patients) as well as in the human testis (in healthy patients).
Triple X syndrome (also called 47,XXX or trisomy X):
XX male syndrome is a rare disorder, where the SRY region of the Y chromosome has recombined to be located on one of the X chromosomes. As a result, the XX combination after fertilization has the same effect as a XY combination, resulting in a male. However, the other genes of the X chromosome cause feminization as well.
X-linked endothelial corneal dystrophy is an extremely rare disease of cornea associated with Xq25 region. Lisch epithelial corneal dystrophy is associated with Xp22.3.
Megalocornea 1 is associated with Xq21.3-q22[medical citation needed]
The X-chromosome has played a crucial role in the development of sexually selected characteristics for over 300 million years. During that time it has accumulated a disproportionate number of genes concerned with mental functions. For reasons that are not yet understood, there is an excess proportion of genes on the X-chromosome that are associated with the development of intelligence, with no obvious links to other significant biological functions. There has also been interest in the possibility that haploin sufficiency for one or more X-linked genes has a specific impact on development of the Amygdala and its connections with cortical centres involved in socialcognition processing or the social brain’.[clarification needed]
It was first noted that the X chromosome was special in 1890 by Hermann Henking in Leipzig. Henking was studying the testicles of Pyrrhocoris and noticed that one chromosome did not take part in meiosis. Chromosomes are so named because of their ability to take up staining. Although the X chromosome could be stained just as well as the others, Henking was unsure whether it was a different class of object and consequently named it X element, which later became X chromosome after it was established that it was indeed a chromosome.
The idea that the X chromosome was named after its similarity to the letter “X” is mistaken. All chromosomes normally appear as an amorphous blob under the microscope and only take on a well defined shape during mitosis. This shape is vaguely X-shaped for all chromosomes. It is entirely coincidental that the Y chromosome, during mitosis, has two very short branches which can look merged under the microscope and appear as the descender of a Y-shape.
It was first suggested that the X chromosome was involved in sex determination by Clarence Erwin McClung in 1901 after comparing his work on locusts with Henking’s and others. McClung noted that only half the sperm received an X chromosome. He called this chromosome an accessory chromosome and insisted, correctly, that it was a proper chromosome, and theorized, incorrectly, that it was the male determining chromosome.
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X chromosome – Wikipedia, the free encyclopedia
for 1st YEAR STUDENTS X-LINKED INHERITANCE
hen the locus for a gene for a particular trait or disease lies on the X chromosome, the disease is said to be X-linked. The inheritance pattern for X-linked inheritance differs from autosomal inheritance only because the X chromosome has no homologous chromosome in the male, the male has an X and a Y chromosome. Very few genes have been discovered on the Y chromosome.
The inheritance pattern follows the pattern of segregation of the X and Y chromosomes in meiosis and fertilization. A male child always gets his X from one of his mother’s two X’s and his Y chromosome from his father. X-linked genes are never passed from father to son. A female child always gets the father’s X chromosome and one of the two X’s of the mother. An affected female must have an affected father. Males are always hemizygous for X linked traits, that is, they can never be heterozygoses or homozygotes. They are never carriers. A single dose of a mutant allele will produce a mutant phenotype in the male, whether the mutation is dominant or recessive. On the other hand, females must be either homozygous for the normal allele, heterozygous, or homozygous for the mutant allele, just as they are for autosomal loci.
When an X-linked gene is said to express dominant inheritance, it means that a single dose of the mutant allele will affect the phenotype of the female. A recessive X-linked gene requires two doses of the mutant allele to affect the female phenotype. The following are the hallmarks of X-linked dominant inheritance:
The following Punnett Squares explain the first three hallmarks of X-linked dominant inheritance. X represents the X chromosome with the normal allele, XA represents the X chromosome with the mutant dominant allele, and Y represents the Y chromosome. Note that the affected father never passes the trait to his sons but passes it to all of his daughters, since the heterozygote is affected for dominant traits. On the other hand, an affected female passes the disease to half of her daughters and half of her sons.
Males are usually more severely affected than females because in each affected female there is one normal allele producing a normal gene product and one mutant allele producing the non-functioning product, while in each affected male there is only the mutant allele with its non-functioning product and the Y chromosome, no normal gene product at all. Affected females are more prevalent in the general population because the female has two X chromosomes, either of which could carry the mutant allele, while the male only has one X chromosome as a target for the mutant allele. When the disease is no more deleterious in males than it is in females, females are about twice as likely to be affected as males. As shown in Pedigree 5 below, X-linked dominant inheritance has a unique heritability pattern.
The key for determining if a dominant trait is X-linked or autosomal is to look at the offspring of the mating of an affected male and a normal female. If the affected male has an affected son, then the disease is not X-linked. All of his daughters must also be affected if the disease is X-linked. In Pedigree 5, both of these conditions are met.
What happens when males are so severely affected that they can’t reproduce? Suppose they are so severely affected they never survive to term, then what happens? This is not uncommon in X-linked dominant diseases. There are no affected males to test for X-linked dominant inheritance to see if the produce all affected daughters and no affected sons. Pedigree 6 shows the effects of such a disease in a family. There are no affected males, only affected females, in the population. Living females outnumber living males two to one when the mother is affected. The ratio in the offspring of affected females is: 1 affected female: 1 normal female: 1 normal male.
You will note that in Pedigree 6 there have also been several spontaneous abortions in the offspring of affected females. Normally, in the general population of us normal couples, one in six recognized pregnancies results in a spontaneous abortion. Here the ratio is much higher. Presumably many of the spontaneous abortions shown in Pedigree 6 are males that would have been affected had they survived to term.
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Human Genetics – Mendelian Inheritance 5