Homosexuality in animals
Encyclopedia
Homosexual behavior in animals refers to the documented evidence of homosexual
and bisexual behavior in non-human species. Such behaviors include sex
, courtship
, affection
, pair bond
ing, and parenting
among same sex animals. A 1999 review by researcher Bruce Bagemihl
shows that homosexual behavior has been observed in close to 1,500 species, ranging from primates to gut worms
, and is well documented for 500 of them. Animal sexual behavior takes many different forms, even within the same species
. The motivations for and implications of these behaviors have yet to be fully understood, since most species have yet to be fully studied.
According to Bagemihl, "the animal kingdom[does] it with much greater sexual diversity — including homosexual, bisexual and nonreproductive sex — than the scientific community and society at large have previously been willing to accept." Current research indicates that various forms of same-sex sexual behavior are found throughout the animal kingdom. A new review made in 2009 of existing research showed that same-sex behavior is a nearly universal phenomenon in the animal kingdom, common across species. Homosexual behavior is best known from social species. According to geneticist Simon Levay in 1996, "Although homosexual behavior is very common in the animal world, it seems to be very uncommon that individual animals have a long-lasting predisposition to engage in such behavior to the exclusion of heterosexual activities. Thus, a homosexual orientation, if one can speak of such thing in animals, seems to be a rarity. One species in which exclusive homosexual orientation occurs, however, is that of domesticated sheep (Ovis aries). "About 10% of rams (males) refuse to mate with ewes (females) but do readily mate with other rams."
The observation of homosexual behavior in animals can be seen as both an argument for and against the acceptance of homosexuality in humans
, and has been used especially against the claim that it is a peccatum contra naturam ('sin against nature'). For instance, homosexuality in animals was cited in the United States Supreme Court's decision in Lawrence v. Texas
which struck down the sodomy laws of 14 states. Whether animal sexuality has logical, ethical, or moral implications in human sexuality is also a source of debate (see appeal to nature
).
in 1868 to describe same-sex sexual attraction and sexual behavior in humans. Its use in animal studies has been controversial for two main reasons: animal sexuality and motivating factors have been and remain poorly understood, and the term has strong cultural implications in western society that are irrelevant for species other than human
s. Thus homosexual behavior has been given a number of terms over the years. When describing animals, the term "homosexual" is preferred over "gay", "lesbian" and other terms currently in use, as these are seen as even more bound to human homosexuality.
Animal preference and motivation is always inferred from behavior. In wild animals, researchers will as a rule not be able to map the entire life of an individual, and must infer from frequency of single observations of behavior. The correct usage of the term homosexual is that an animal exhibits homosexual behavior or even same-sex sexual behavior; however, this article conforms to the usage by modern research
applying the term homosexuality to all sexual behavior (copulation, genital stimulation, mating games and sexual display behavior
) between animals of the same sex. In most instances, it is presumed that the homosexual behavior is but part of the animal's overall sexual behavioral repertoire, making the animal "bisexual" rather than "homosexual" as the terms are commonly understood in humans, but cases of homosexual preference and exclusive homosexual pairs are known.
caused by social attitudes to same-sex sexual behavior, innocent confusion, or even from a fear of "being ridiculed by their colleagues." Georgetown University biologist
Janet Mann states "Scientists who study the topic are often accused of trying to forward an agenda, and their work can come under greater scrutiny than that of their colleagues who study other topics." They also noted "Not every sexual act has a reproductive function ... that's true of humans and non-humans." It appears to be widespread amongst social bird
s and mammal
s, particularly the sea mammals and the primates. The true extent of homosexuality in animals is not known. While studies have demonstrated homosexual behavior in a number of species, Petter Bøckman, the scientific advisor of the exhibition Against Nature?
in 2007, speculated that the true extent of the phenomenon may be much larger than was then recognized:
An example of overlooking homosexual behavior is noted by Bruce Bagemihl
describing mating giraffes where nine out of ten pairings occur between males.
Some researchers believe this behavior to have its origin in male social organization and social dominance, similar to the dominance traits shown in prison sexuality
. Others, particularly Joan Roughgarden
, Bruce Bagemihl
, Thierry Lodé
and Paul Vasey suggest the social function of sex (both homosexual and heterosexual) is not necessarily connected to dominance, but serves to strengthen alliances and social ties within a flock. Others have argued that social organization theory is inadequate because it cannot account for some homosexual behaviors, for example, penguin
species where same-sex individuals mate for life and refuse to pair with females when given the chance. While reports on many such mating scenarios are still only anecdotal, a growing body of scientific work confirms that permanent homosexuality occurs not only in species with permanent pair bonds, but also in non-monogamous species like sheep.
One report on sheep cited below states:
In fact, apparent homosexual individuals are known from all of the traditional domestic species, from sheep, cattle and horses to cats, dogs and budgerigars.
underwent a slightly altered developmental programme in the brain to resemble the male brain in terms of sexual preference" said Professor Chankyu Park of the Korea Advanced Institute of Science and Technology in Daejon, South Korea, who led the research. His most recent findings have been published in the BMC Genetics journal
on July 7, 2010.
In March 2011, research shows that serotonin
is involved in the mechanism of sexual orientation of mice.
An estimated one-quarter of all black swans
pairings are homosexual and they steal nests, or form temporary threesomes with females to obtain eggs, driving away the female after she lays the eggs. More of their cygnet
s survive to adulthood than those of different-sex pairs, possibly due to their superior ability to defend large portions of land. The same reasoning has been applied to male flamingo
pairs raising chicks.
s in some populations in the wild exhibit homosexual behavior.
can increase the prevalence of homosexual behavior in male American White Ibis
. The study involved exposing chicks in varying dosages to the chemical and measuring the degree of homosexual behavior in adulthood. The results discovered was that as the dosage was increased the likelihood of homosexual behavior also increased. The endocrine blocking feature of mercury has been suggested as a possible cause of sexual disruption in other bird species.
Mallard
s form male-female pairs only until the female lays eggs, at which time the male leaves the female. Mallards have rates of male-male sexual activity that are unusually high for birds, in some cases, as high as 19% of all pairs in a population.
, a male pair of chinstrap penguin
s in the Central Park Zoo
in New York City
had successfully hatched and fostered a female chick from a fertile egg they had been given to incubate. Other penguin
s in New York zoos have also been reported to have formed same-sex pairs.
Zoos in Japan
and Germany
have also documented homosexual male penguin couples. The couples have been shown to build nests together and use a stone as a substitute for an egg. Researchers at Rikkyo University
in Tokyo
found 20 homosexual pairs at 16 major aquariums and zoos in Japan.
Bremerhaven Zoo in Germany attempted to encourage reproduction of endangered Humbolt penguins by importing females from Sweden and separating three male pairs, but this was unsuccessful. The zoo's director said that the relationships were "too strong" between the homosexual pairs. German gay groups protested at this attempt to break up the male-male pairs but the zoo's director was reported as saying "We don't know whether the three male pairs are really homosexual or whether they have just bonded because of a shortage of females... nobody here wants to forcibly separate homosexual couples."
A pair of male Magellanic penguin
s who had shared a burrow for six years at the San Francisco Zoo
and raised a surrogate chick, split when the male of a pair in the next burrow died and the female sought a new mate.
Buddy and Pedro, a pair of male African Penguin
s, will be separated by the Toronto Zoo
to mate with female penguins.
s named Dashik and Yehuda, at the Jerusalem Biblical Zoo, engaged in "open and energetic sex" and built a nest. The keepers provided the couple with an artificial egg, which the two parents took turns incubating; and 45 days later, the zoo replaced the egg with a baby vulture. The two male vultures raised the chick together. A few years later, however, Yehuda became interested in a female vulture that was brought into the aviary. Dashik became depressed, and was eventually moved to the zoological research garden at Tel Aviv University
where he too set up a nest with a female vulture.
Two homosexual male vultures at the Allwetter Zoo in Muenster built a nest together, although they were picked on and often had their nest materials stolen by other vultures. They were eventually separated to try to promote breeding by placing one of them with female vultures, despite the protests of German homosexual groups.
Some pigeons also display fetish
behavior and attempt to mate with specific inanimate objects.
or boto has been reported to form up in bands of 3–5 individuals enjoying group sex. The groups usually comprise young males and sometimes one or two females. Sex is often performed in non-reproductive ways, using snout, flippers and genital rubbing, without regards to gender. In captivity, they have been observed to sometimes perform homosexual and heterosexual penetration of the blowhole
, a hole homologous with the nostril
of other mammals, making this the only known example of nasal sex in the animal kingdom. The males will sometimes also perform sex with tucuxi
males, a small porpoise
.
Courtship, mounting, and full anal penetration
between bulls has been noted to occur among American Bison
. The Mandan nation Okipa festival concludes with a ceremonial enactment of this behavior, to "ensure the return of the buffalo in the coming season." Also, mounting of one female by another is common among cattle
.
The Bonobo
, which has a matriarchal
society, unusual amongst ape
s, is a fully bisexual species—both males and females engage in heterosexual and homosexual behavior, being noted for female-female homosexuality in particular. About 60% of all sexual activity in this species is between two or more females. While the homosexual bonding system in Bonobos represents the highest frequency of homosexuality known in any species, homosexuality has been reported for all great apes
(a group which includes human
s), as well as a number of other primate
species. Dutch primatologist Frans de Waal
on observing and filming bonobos noted that there were two reasons to believe sexual activity is the bonobo's answer to avoiding conflict.
Anything that arouses the interest of more than one bonobo at a time, not just food, tends to result in sexual contact. If two bonobos approach a cardboard box thrown into their enclosure, they will briefly mount each other before playing with the box. Such situations lead to squabbles in most other species. But bonobos are quite tolerant, perhaps because they use sex to divert attention and to defuse tension.
Bonobo sex often occurs in aggressive contexts totally unrelated to food. A jealous male might chase another away from a female, after which the two males reunite and engage in scrotal
rubbing. Or after a female hits a juvenile, the latter's mother may lunge at the aggressor, an action that is immediately followed by genital rubbing between the two adults.
s. Sexual encounters between females take the shape of "beak-genital propulsion", where one female insert her beak in the genital opening of the other while swimming gently forward. Between males, homosexual behaviour include rubbing of genitals against each other, which sometimes lead to the males swimming belly to belly, inserting the penis in the others genital slit and sometimes anus.
Janet Mann, Georgetown University
professor of biology and psychology, argues that the strong personal behavior among male dolphin calves is about bond formation and benefits the species in an evolutionary context. She cites studies showing that these dolphins later in life as adults are in a sense bisexual, and the male bonds forged earlier in life work together for protection as well as locating females to reproduce with. Confrontations between flocks of bottlenose dolphins and the related species Atlantic spotted dolphin
will sometimes lead to cross-species homosexual behaviour between the males rather than combat.
males will engage in same-sex bonding and mounting. Such encounters are often associated with affectionate interactions, such as kissing, trunk intertwining, and placing trunks in each other's mouths. Male elephants, who often live apart from the general herd, often form "companionships", consisting of an older individual and one or sometimes two younger, attendant males with sexual behavior being an important part of the social dynamic. Unlike heterosexual relations, which are always of a fleeting nature, the relationships between males may last for years. The encounters are analogous to heterosexual bouts, one male often extending his trunk along the other's back and pushing forward with his tusks to signify his intention to mount. Same-sex relations are common and frequent in both sexes, with Asiatic elephants in captivity devoting roughly 45% of sexual encounters to same-sex activity.
s have been observed to engage in remarkably high frequencies of homosexual behavior. After aggressive "necking", it is common for two male giraffes to caress and court each other, leading up to mounting and climax. Such interactions between males have been found to be more frequent than heterosexual coupling. In one study, up to 94% of observed mounting incidents took place between two males. The proportion of same sex activities varied between 30 and 75%, and at any given time one in twenty males were engaged in non-combative necking behavior with another male. Only 1% of same-sex mounting incidents occurred between females.
and Robin Fox
conducted a study on how Depo-Provera contraceptives lead to decreased male attractiveness to females and eventually to male homosexuality. Janet E. Smith
summarizes the findings as follows:
, also known as the "snow monkey
", same-sex relations
are frequent, though rates vary between troops. Females will form "consort
ships" characterized by affectionate social and sexual activities. In some troops up to one quarter of the females form such bonds, which vary in duration from a few days to a few weeks. Often, strong and lasting friendships result from such pairings. Males also have same-sex relations, typically with multiple partners of the same age. Affectionate and playful activities are associated with such relations.
. Male lions pair-bond for a number of days and initiate homosexual activity with affectionate nuzzling and caressing, leading to mounting and thrusting. About 8% of mountings have been observed to occur with other males. Pairings between females are held to be fairly common in captivity but have not been observed in the wild.
s Mustela putorius were found to engage homosexually with non-sibling animals. Exclusive homosexuality with mounting and anal penetration in this solitary species serves no apparent adaptive function.
An October 2003 study by Dr. Charles E. Roselli et al. (Oregon Health and Science University) states that homosexuality in male sheep (found in 8% of rams) is associated with a region in the rams' brains which the authors call the "ovine Sexually Dimorphic Nucleus" (oSDN) which is half the size of the corresponding region in heterosexual male sheep.
Scientists found that, "The oSDN in rams that preferred females was significantly larger and contained more neurons than in male-oriented rams and ewes. In addition, the oSDN of the female-oriented rams expressed higher levels of aromatase
, a substance that converts testosterone
to estradiol
, a form of estrogen
which is believed to facilitate typical male sexual behaviors. Aromatase expression was no different between male-oriented rams and ewes."
"The dense cluster of neurons that comprise the oSDN express cytochrome
P450 aromatase. Aromatase mRNA levels in the oSDN were significantly greater in female-oriented rams than in ewes, whereas male-oriented rams exhibited intermediate levels of expression." These results suggest that "...naturally occurring variations in sexual partner preferences may be related to differences in brain anatomy and its capacity for estrogen synthesis." As noted prior, given the potential unagressiveness of the male population in question, the differing aromatase levels may also have been evidence of aggression levels, not sexuality. It should also be noted that the results of this study have not been confirmed by other studies.
The Merck Manual of Veterinary Medicine
appears to consider homosexuality among sheep as a routine occurrence and an issue to be dealt with as a problem of animal husbandry.
The family structure of the Spotted Hyena is matriarchal, and dominance relationships with strong sexual elements are routinely observed between related females. Due largely to the female spotted hyena's unique urogenital system, which looks more like a penis rather than a vagina, early naturalists thought hyenas were hermaphroditic
males who commonly practiced homosexuality
. Early writings such as Ovid
's Metamorphoses and the Physiologus suggested that the hyena continually changed its sex and nature from male to female and back again. In Paedagogus
, Clement of Alexandria noted that the hyena
(along with the hare
) was "quite obsessed with sexual intercourse." Many Europeans associated the hyena with sexual deformity, prostitution, deviant sexual behavior, and even witchcraft.
The reality behind the confusing reports is the sexually aggressive behavior between the females, including mounting between females. Research has shown that "in contrast to most other female mammals, female Crocuta are male-like in appearance, larger than males, and substantially more aggressive," and they have "been masculinized
without being defeminized
.”
Study of this unique genitalia and aggressive behavior in the female hyena has led to the understanding that more aggressive females are better able to compete for resources, including food and mating partners. Research has shown that "elevated levels of testosterone
in utero
" contribute to extra aggressiveness; both males and females mount members of the same sex, who in turn are possibly acting more submissive because of lower levels of testosterone in utero.
genus) females have the ability to reproduce through parthenogenesis
and as such males are rare and sexual breeding non-standard. Females engage in sexual behavior to stimulate ovulation
, with their behavior following their hormonal cycles; during low levels of estrogen, these (female) lizards engage in "masculine" sexual roles. Those animals with currently high estrogen levels assume "feminine" sexual roles.
Lizards that perform the courtship ritual have greater fertility than those kept in isolation due to an increase in hormones triggered by the sexual behaviors. So, even though asexual whiptail lizards populations lack males, sexual stimuli still increase reproductive success.
From an evolutionary standpoint, these females are passing their full genetic code to all of their offspring (rather than the 50% of genes that would be passed in sexual reproduction). Certain species of gecko
also reproduce by parthenogenesis.
Male homosexuality has been inferred in several species of dragonflies (the order
Odonata
). The cloacal pinchers of male damselflies and dragonflies inflict characteristic head damage to females during sex. A survey of 11 species of damsel and dragonflies has revealed such mating damages in 20 to 80 % of the males too, indicating a fairly high occurrence of sexual coupling between males.
flies bearing two copies of a mutant allele in the fruitless
gene court and attempt to mate exclusively with other males. The genetic basis of animal homosexuality has been studied in the fly Drosophila melanogaster
. Here, multiple genes have been identified that can cause homosexual courtship and mating. These genes are thought to control behavior through pheromone
s as well as altering the structure of the animal's brains. These studies have also investigated the influence of environment on the likelihood of flies displaying homosexual behavior.
in which the male pierces the female abdomen with his needle-like penis. In homosexual mating this risks abdominal injuries as males lack the female counteradaptive spermalege
structure. Males produce alarm pheromone
s to reduce such homosexual matings.
Homosexuality
Homosexuality is romantic or sexual attraction or behavior between members of the same sex or gender. As a sexual orientation, homosexuality refers to "an enduring pattern of or disposition to experience sexual, affectional, or romantic attractions" primarily or exclusively to people of the same...
and bisexual behavior in non-human species. Such behaviors include sex
Sexual intercourse
Sexual intercourse, also known as copulation or coitus, commonly refers to the act in which a male's penis enters a female's vagina for the purposes of sexual pleasure or reproduction. The entities may be of opposite sexes, or they may be hermaphroditic, as is the case with snails...
, courtship
Courtship
Courtship is the period in a couple's relationship which precedes their engagement and marriage, or establishment of an agreed relationship of a more enduring kind. In courtship, a couple get to know each other and decide if there will be an engagement or other such agreement...
, affection
Affection
Affection or fondness is a "disposition or rare state of mind or body" that is often associated with a feeling or type of love. It has given rise to a number of branches of philosophy and psychology concerning: emotion ; disease; influence; state of being ; and state of mind...
, pair bond
Pair bond
In biology, a pair bond is the strong affinity that develops in some species between the males and females in a pair, potentially leading to breeding. Pair-bonding is a term coined in the 1940s that is frequently used in sociobiology and evolutionary psychology circles...
ing, and parenting
Parenting
Parenting is the process of promoting and supporting the physical, emotional, social, and intellectual development of a child from infancy to adulthood...
among same sex animals. A 1999 review by researcher Bruce Bagemihl
Bruce Bagemihl
Bruce Bagemihl is a Canadian biologist, linguist, and author of the book Biological Exuberance: Animal Homosexuality and Natural Diversity.-Life and career:He served on the faculty of University of British Columbia, and he earned a Ph.D...
shows that homosexual behavior has been observed in close to 1,500 species, ranging from primates to gut worms
Acanthocephala
Acanthocephala is a phylum of parasitic worms known as acanthocephales, thorny-headed worms, or spiny-headed worms, characterized by the presence of an evertable proboscis, armed with spines, which it uses to pierce and hold the gut wall of its host...
, and is well documented for 500 of them. Animal sexual behavior takes many different forms, even within the same species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
. The motivations for and implications of these behaviors have yet to be fully understood, since most species have yet to be fully studied.
According to Bagemihl, "the animal kingdom
The observation of homosexual behavior in animals can be seen as both an argument for and against the acceptance of homosexuality in humans
Human sexuality
Human sexuality is the awareness of gender differences, and the capacity to have erotic experiences and responses. Human sexuality can also be described as the way someone is sexually attracted to another person whether it is to opposite sexes , to the same sex , to either sexes , or not being...
, and has been used especially against the claim that it is a peccatum contra naturam ('sin against nature'). For instance, homosexuality in animals was cited in the United States Supreme Court's decision in Lawrence v. Texas
Lawrence v. Texas
Lawrence v. Texas, 539 U.S. 558 , is a landmark United States Supreme Court case. In the 6-3 ruling, the Court struck down the sodomy law in Texas and, by proxy, invalidated sodomy laws in the thirteen other states where they remained in existence, thereby making same-sex sexual activity legal in...
which struck down the sodomy laws of 14 states. Whether animal sexuality has logical, ethical, or moral implications in human sexuality is also a source of debate (see appeal to nature
Appeal to nature
An appeal to nature is a type of argument that depends on an understanding of nature as a source of intelligibility for its claims, and which relies on that understanding for its outcome...
).
Applying the term "homosexual" to animals
The term homosexual was coined by Karl-Maria KertbenyKarl-Maria Kertbeny
Karl-Maria Kertbeny or Károly Mária Kertbeny was an Austrian-born Hungarian journalist, memoirist, and human rights campaigner...
in 1868 to describe same-sex sexual attraction and sexual behavior in humans. Its use in animal studies has been controversial for two main reasons: animal sexuality and motivating factors have been and remain poorly understood, and the term has strong cultural implications in western society that are irrelevant for species other than human
Human
Humans are the only living species in the Homo genus...
s. Thus homosexual behavior has been given a number of terms over the years. When describing animals, the term "homosexual" is preferred over "gay", "lesbian" and other terms currently in use, as these are seen as even more bound to human homosexuality.
Animal preference and motivation is always inferred from behavior. In wild animals, researchers will as a rule not be able to map the entire life of an individual, and must infer from frequency of single observations of behavior. The correct usage of the term homosexual is that an animal exhibits homosexual behavior or even same-sex sexual behavior; however, this article conforms to the usage by modern research
applying the term homosexuality to all sexual behavior (copulation, genital stimulation, mating games and sexual display behavior
Display (zoology)
Display is a form of animal behaviour, linked to survival of the species in various ways. One example of display used by some species can be found in the form of courtship, with the male usually having a striking feature that is distinguished by colour, shape or size, used to attract a female...
) between animals of the same sex. In most instances, it is presumed that the homosexual behavior is but part of the animal's overall sexual behavioral repertoire, making the animal "bisexual" rather than "homosexual" as the terms are commonly understood in humans, but cases of homosexual preference and exclusive homosexual pairs are known.
Research on homosexual behavior in animals
The presence of same-sex sexual behavior was not 'officially' observed on a large scale until recent times, possibly due to observer biasObserver effect
Observer effect may refer to:* Observer effect , the impact of observing a process while it is running* Observer effect , the impact of observing a physical system...
caused by social attitudes to same-sex sexual behavior, innocent confusion, or even from a fear of "being ridiculed by their colleagues." Georgetown University biologist
Biologist
A biologist is a scientist devoted to and producing results in biology through the study of life. Typically biologists study organisms and their relationship to their environment. Biologists involved in basic research attempt to discover underlying mechanisms that govern how organisms work...
Janet Mann states "Scientists who study the topic are often accused of trying to forward an agenda, and their work can come under greater scrutiny than that of their colleagues who study other topics." They also noted "Not every sexual act has a reproductive function ... that's true of humans and non-humans." It appears to be widespread amongst social bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s and mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, particularly the sea mammals and the primates. The true extent of homosexuality in animals is not known. While studies have demonstrated homosexual behavior in a number of species, Petter Bøckman, the scientific advisor of the exhibition Against Nature?
Against Nature?
Against Nature? is an exhibition on homosexuality in animals made by the Natural History Museum, University of Oslo, Norway. The exhibition focuses on occurrence and function of homosexuality in animals, and is the first of its kind....
in 2007, speculated that the true extent of the phenomenon may be much larger than was then recognized:
No species has been found in which homosexual behaviour has not been shown to exist, with the exception of species that never have sex at all, such as sea urchinSea urchinSea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull...
s and aphisAphisAphis may refer to:* Aphis, a genus of aphid species* Animal and Plant Health Inspection Service , organizational unit of the USDA* HMS Aphis , Royal Navy insect class gunboat...
. Moreover, a part of the animal kingdom is hermaphroditicHermaphroditeIn biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...
, truly bisexual. For them, homosexuality is not an issue.
Bruce Bagemihl
Bruce Bagemihl is a Canadian biologist, linguist, and author of the book Biological Exuberance: Animal Homosexuality and Natural Diversity.-Life and career:He served on the faculty of University of British Columbia, and he earned a Ph.D...
describing mating giraffes where nine out of ten pairings occur between males.
Every male that sniffed a female was reported as sex, while anal intercourse with orgasm between males was only "revolving around" dominanceDominanceDominance may refer to:* Dominance , an aspect of virtual inheritance in the C++ programming language* Dominance , in economics, the degree of inequality in market share distribution...
, competition or greetingGreetingGreeting is an act of communication in which human beings intentionally make their presence known to each other, to show attention to, and to suggest a type of relationship or social status between individuals or groups of people coming in contact with each other...
s.
Some researchers believe this behavior to have its origin in male social organization and social dominance, similar to the dominance traits shown in prison sexuality
Prison sexuality
Prison sexuality deals with sexual relationships between confined individuals or those between a prisoner and a prison employee . Since prisons are separated by gender, most sexual activity is conducted with a same-sex partner, often in contradiction to a person's normal social sexual orientation...
. Others, particularly Joan Roughgarden
Joan Roughgarden
Joan E. Roughgarden is an American evolutionary biologist.- Biography :...
, Bruce Bagemihl
Bruce Bagemihl
Bruce Bagemihl is a Canadian biologist, linguist, and author of the book Biological Exuberance: Animal Homosexuality and Natural Diversity.-Life and career:He served on the faculty of University of British Columbia, and he earned a Ph.D...
, Thierry Lodé
Thierry Lodé
Thierry Lodé is a French biologist and professor who teaches evolutionary ecology in the CNRS Units ETHOS...
and Paul Vasey suggest the social function of sex (both homosexual and heterosexual) is not necessarily connected to dominance, but serves to strengthen alliances and social ties within a flock. Others have argued that social organization theory is inadequate because it cannot account for some homosexual behaviors, for example, penguin
Penguin
Penguins are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have become flippers...
species where same-sex individuals mate for life and refuse to pair with females when given the chance. While reports on many such mating scenarios are still only anecdotal, a growing body of scientific work confirms that permanent homosexuality occurs not only in species with permanent pair bonds, but also in non-monogamous species like sheep.
One report on sheep cited below states:
Approximately 8% of rams exhibit sexual preferences [that is, even when given a choice] for male partners (male-oriented rams) in contrast to most rams, which prefer female partners (female-oriented rams). We identified a cell group within the medial preoptic area/anterior hypothalamus of age-matched adult sheep that was significantly larger in adult rams than in ewes...
In fact, apparent homosexual individuals are known from all of the traditional domestic species, from sheep, cattle and horses to cats, dogs and budgerigars.
Genetic and physiological basis for homosexual animal behavior
Researchers found that disabling the (fucose mutarotase) FucM gene in laboratory mice – which influences the levels of estrogen to which the brain is exposed – caused the female mice to behave as if they were male as they grew up. "The mutant female mouseKnockout mouse
A knockout mouse is a genetically engineered mouse in which researchers have inactivated, or "knocked out," an existing gene by replacing it or disrupting it with an artificial piece of DNA...
underwent a slightly altered developmental programme in the brain to resemble the male brain in terms of sexual preference" said Professor Chankyu Park of the Korea Advanced Institute of Science and Technology in Daejon, South Korea, who led the research. His most recent findings have been published in the BMC Genetics journal
BioMed Central
BioMed Central is a UK-based, for-profit scientific publisher specialising in open access journal publication. BMC, and its sister companies Chemistry Central and PhysMath Central, publish over 200 scientific journals. Most BMC journals are now published only online. BMC describes itself as the...
on July 7, 2010.
In March 2011, research shows that serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
is involved in the mechanism of sexual orientation of mice.
Some selected species and groups
Black swans
Black Swans
Black Swans is a 2005 Dutch drama film.The film won a Golden Calf for best sound at the Netherlands Film Festival in 2005.-Plot:Marleen works as a volunteer in a rest home in Spain. When she meets Vince they are attracted to each other. Their passionate relationship has its ups and downs, and...
pairings are homosexual and they steal nests, or form temporary threesomes with females to obtain eggs, driving away the female after she lays the eggs. More of their cygnet
Swan
Swans, genus Cygnus, are birds of the family Anatidae, which also includes geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form the tribe Cygnini. Sometimes, they are considered a distinct subfamily, Cygninae...
s survive to adulthood than those of different-sex pairs, possibly due to their superior ability to defend large portions of land. The same reasoning has been applied to male flamingo
Flamingo
Flamingos or flamingoes are gregarious wading birds in the genus Phoenicopterus , the only genus in the family Phoenicopteridae...
pairs raising chicks.
Gulls
Studies have shown that 10 to 15 percent of female western gullWestern Gull
The Western Gull, Larus occidentalis, is a large white-headed gull that lives on the western coast of North America. It was previously considered conspecific, the same species, with the Yellow-footed Gull of the Gulf of California...
s in some populations in the wild exhibit homosexual behavior.
Ibises
Research has shown that the environmental pollutant methylmercuryMethylmercury
Methylmercury is an organometallic cation with the formula . It is a bioaccumulative environmental toxicant.-Structure:...
can increase the prevalence of homosexual behavior in male American White Ibis
American White Ibis
The American White Ibis is a species of wading bird in the ibis family Threskiornithidae. It occurs from the mid-Atlantic and Gulf coast of the United States south through most of the New World tropics...
. The study involved exposing chicks in varying dosages to the chemical and measuring the degree of homosexual behavior in adulthood. The results discovered was that as the dosage was increased the likelihood of homosexual behavior also increased. The endocrine blocking feature of mercury has been suggested as a possible cause of sexual disruption in other bird species.
Mallards
Mallard
The Mallard , or Wild Duck , is a dabbling duck which breeds throughout the temperate and subtropical Americas, Europe, Asia, and North Africa, and has been introduced to New Zealand and Australia....
s form male-female pairs only until the female lays eggs, at which time the male leaves the female. Mallards have rates of male-male sexual activity that are unusually high for birds, in some cases, as high as 19% of all pairs in a population.
Penguins
In early February 2004 the New York Times reported that Roy and SiloRoy and Silo
Roy and Silo are Chinstrap Penguins who were a male-male pair in New York City's Central Park Zoo.Roy and Silo met at the zoo and they began their relationship in 2004. The pair were observed trying to hatch a rock as if it were an egg. They also attempted to steal eggs from other penguin couples...
, a male pair of chinstrap penguin
Chinstrap Penguin
The Chinstrap Penguin is a species of penguin which is found in the South Sandwich Islands, Antarctica, the South Orkneys, South Shetland, South Georgia, Bouvet Island and Balleny...
s in the Central Park Zoo
Central Park Zoo
The Central Park Zoo is a small zoo located in Central Park in New York City. It is part of an integrated system of four zoos and the New York Aquarium managed by the Wildlife Conservation Society , and is accredited by the Association of Zoos and Aquariums .The zoo began in the 1860s as a...
in New York City
New York City
New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...
had successfully hatched and fostered a female chick from a fertile egg they had been given to incubate. Other penguin
Penguin
Penguins are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have become flippers...
s in New York zoos have also been reported to have formed same-sex pairs.
Zoos in Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
and Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
have also documented homosexual male penguin couples. The couples have been shown to build nests together and use a stone as a substitute for an egg. Researchers at Rikkyo University
Rikkyo University
, also known as Saint Paul's University, is a private university, based on Christian precepts, in Ikebukuro, Tokyo. There is a suburban campus in Niiza in nearby Saitama.It is known for its liberal climate symbolized by the motto -History:...
in Tokyo
Tokyo
, ; officially , is one of the 47 prefectures of Japan. Tokyo is the capital of Japan, the center of the Greater Tokyo Area, and the largest metropolitan area of Japan. It is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family...
found 20 homosexual pairs at 16 major aquariums and zoos in Japan.
Bremerhaven Zoo in Germany attempted to encourage reproduction of endangered Humbolt penguins by importing females from Sweden and separating three male pairs, but this was unsuccessful. The zoo's director said that the relationships were "too strong" between the homosexual pairs. German gay groups protested at this attempt to break up the male-male pairs but the zoo's director was reported as saying "We don't know whether the three male pairs are really homosexual or whether they have just bonded because of a shortage of females... nobody here wants to forcibly separate homosexual couples."
A pair of male Magellanic penguin
Magellanic Penguin
The Magellanic Penguin, Spheniscus magellanicus, is a South American penguin, breeding in coastal Argentina, Chile and the Falkland Islands, with some migrating to Brazil where they are occasionally seen as far north as Rio de Janeiro. It is the most numerous of the Spheniscus penguins. Its nearest...
s who had shared a burrow for six years at the San Francisco Zoo
San Francisco Zoo
The San Francisco Zoo, housing more than 260 animal species, is a zoo located in the southwestern corner of San Francisco, California, between Lake Merced and the Pacific Ocean along the Great Highway...
and raised a surrogate chick, split when the male of a pair in the next burrow died and the female sought a new mate.
Buddy and Pedro, a pair of male African Penguin
African Penguin
The African Penguin , also known as the Black-footed Penguin is a species of penguin, confined to southern African waters. It is known as Brilpikkewyn in Afrikaans, Inguza or Unombombiya in Xhosa, Manchot Du Cap in French and Pingüino Del Cabo in Spanish...
s, will be separated by the Toronto Zoo
Toronto Zoo
The Toronto Zoo is a zoo located in Toronto, Ontario, Canada. It opened August 15, 1974 as the Metropolitan Toronto Zoo and is owned by the City of Toronto; the word "Metropolitan" was dropped from its name when the cities of the Municipality of Metropolitan Toronto were amalgamated to form the...
to mate with female penguins.
Vultures
In 1998 two male Griffon vultureGriffon Vulture
The Griffon Vulture is a large Old World vulture in the bird of prey family Accipitridae.The Griffon Vulture is long with a wingspan. In the nominate race the males weigh and females typically weigh , while in the Indian subspecies the vultures average...
s named Dashik and Yehuda, at the Jerusalem Biblical Zoo, engaged in "open and energetic sex" and built a nest. The keepers provided the couple with an artificial egg, which the two parents took turns incubating; and 45 days later, the zoo replaced the egg with a baby vulture. The two male vultures raised the chick together. A few years later, however, Yehuda became interested in a female vulture that was brought into the aviary. Dashik became depressed, and was eventually moved to the zoological research garden at Tel Aviv University
Tel Aviv University
Tel Aviv University is a public university located in Ramat Aviv, Tel Aviv, Israel. With nearly 30,000 students, TAU is Israel's largest university.-History:...
where he too set up a nest with a female vulture.
Two homosexual male vultures at the Allwetter Zoo in Muenster built a nest together, although they were picked on and often had their nest materials stolen by other vultures. They were eventually separated to try to promote breeding by placing one of them with female vultures, despite the protests of German homosexual groups.
Pigeons
Both male and female pigeons sometimes exhibit homosexual behavior. As well as sexual behavior same-sex pigeon pairs will build nests, and hens will lay (infertile) eggs and attempt to incubate them.Some pigeons also display fetish
Fetish
Fetish may refer to:* Fetishism, the attribution of religious or mystical qualities to inanimate objects* Sexual fetishism, sexual attraction to objects, body parts, or situations not conventionally viewed as being sexual in nature....
behavior and attempt to mate with specific inanimate objects.
Amazon Dolphin
The Amazon River dolphinBoto
The Amazon river dolphin, alternatively Bufeo, Bufeo Colorado, Boto Cor de Rosa, Boutu, Nay, Tonina, or Pink Dolphin , is a freshwater river dolphin endemic to the Orinoco, Amazon and Araguaia/Tocantins River systems of Brazil, Bolivia, Peru, Ecuador, Colombia and Venezuela...
or boto has been reported to form up in bands of 3–5 individuals enjoying group sex. The groups usually comprise young males and sometimes one or two females. Sex is often performed in non-reproductive ways, using snout, flippers and genital rubbing, without regards to gender. In captivity, they have been observed to sometimes perform homosexual and heterosexual penetration of the blowhole
Blowhole (biology)
In biology, a blowhole is the hole at the top of a cetacean's head through which the animal breathes air. It is homologous with the nostril of other mammals. As whales reach the water surface to breathe, they will forcefully expel air through the blowhole. Not only is air expelled, but mucus and...
, a hole homologous with the nostril
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
of other mammals, making this the only known example of nasal sex in the animal kingdom. The males will sometimes also perform sex with tucuxi
Tucuxi
The Tucuxi , alternately bufeo gris or bufeo negro is a dolphin found in the rivers of the Amazon Basin. The word "tucuxi" is derived from the Tupi language word tuchuchi-ana and has now been adopted as the species' common name...
males, a small porpoise
Porpoise
Porpoises are small cetaceans of the family Phocoenidae; they are related to whales and dolphins. They are distinct from dolphins, although the word "porpoise" has been used to refer to any small dolphin, especially by sailors and fishermen...
.
American Bison
Anal sex
Anal sex is the sex act in which the penis is inserted into the anus of a sexual partner. The term can also include other sexual acts involving the anus, including pegging, anilingus , fingering, and object insertion.Common misconception describes anal sex as practiced almost exclusively by gay men...
between bulls has been noted to occur among American Bison
American Bison
The American bison , also commonly known as the American buffalo, is a North American species of bison that once roamed the grasslands of North America in massive herds...
. The Mandan nation Okipa festival concludes with a ceremonial enactment of this behavior, to "ensure the return of the buffalo in the coming season." Also, mounting of one female by another is common among cattle
Cattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
.
Bonobo and other apes
Bonobo
The bonobo , Pan paniscus, previously called the pygmy chimpanzee and less often, the dwarf or gracile chimpanzee, is a great ape and one of the two species making up the genus Pan. The other species in genus Pan is Pan troglodytes, or the common chimpanzee...
, which has a matriarchal
Matriarchy
A matriarchy is a society in which females, especially mothers, have the central roles of political leadership and moral authority. It is also sometimes called a gynocratic or gynocentric society....
society, unusual amongst ape
Ape
Apes are Old World anthropoid mammals, more specifically a clade of tailless catarrhine primates, belonging to the biological superfamily Hominoidea. The apes are native to Africa and South-east Asia, although in relatively recent times humans have spread all over the world...
s, is a fully bisexual species—both males and females engage in heterosexual and homosexual behavior, being noted for female-female homosexuality in particular. About 60% of all sexual activity in this species is between two or more females. While the homosexual bonding system in Bonobos represents the highest frequency of homosexuality known in any species, homosexuality has been reported for all great apes
Great Apes
Great Apes may refer to*Great apes, species in the biological family Hominidae, including humans, chimpanzees, gorillas, and orangutans*Great Apes , a 1997 novel by Will Self...
(a group which includes human
Human
Humans are the only living species in the Homo genus...
s), as well as a number of other primate
Primate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
species. Dutch primatologist Frans de Waal
Frans de Waal
Fransiscus Bernardus Maria de Waal, PhD , is a Dutch primatologist and ethologist. He is the Charles Howard Candler professor of Primate Behavior in the Emory University psychology department in Atlanta, Georgia, and director of the Living Links Center at the Yerkes National Primate Research...
on observing and filming bonobos noted that there were two reasons to believe sexual activity is the bonobo's answer to avoiding conflict.
Anything that arouses the interest of more than one bonobo at a time, not just food, tends to result in sexual contact. If two bonobos approach a cardboard box thrown into their enclosure, they will briefly mount each other before playing with the box. Such situations lead to squabbles in most other species. But bonobos are quite tolerant, perhaps because they use sex to divert attention and to defuse tension.
Bonobo sex often occurs in aggressive contexts totally unrelated to food. A jealous male might chase another away from a female, after which the two males reunite and engage in scrotal
Scrotum
In some male mammals the scrotum is a dual-chambered protuberance of skin and muscle containing the testicles and divided by a septum. It is an extension of the perineum, and is located between the penis and anus. In humans and some other mammals, the base of the scrotum becomes covered with curly...
rubbing. Or after a female hits a juvenile, the latter's mother may lunge at the aggressor, an action that is immediately followed by genital rubbing between the two adults.
Bottlenose dolphins
Dolphins of several species engage in homosexual acts, though it is best studied in the bottlenose dolphinBottlenose Dolphin
Bottlenose dolphins, the genus Tursiops, are the most common and well-known members of the family Delphinidae, the family of oceanic dolphins. Recent molecular studies show the genus contains two species, the common bottlenose dolphin and the Indo-Pacific bottlenose dolphin , instead of one...
s. Sexual encounters between females take the shape of "beak-genital propulsion", where one female insert her beak in the genital opening of the other while swimming gently forward. Between males, homosexual behaviour include rubbing of genitals against each other, which sometimes lead to the males swimming belly to belly, inserting the penis in the others genital slit and sometimes anus.
Janet Mann, Georgetown University
Georgetown University
Georgetown University is a private, Jesuit, research university whose main campus is in the Georgetown neighborhood of Washington, D.C. Founded in 1789, it is the oldest Catholic university in the United States...
professor of biology and psychology, argues that the strong personal behavior among male dolphin calves is about bond formation and benefits the species in an evolutionary context. She cites studies showing that these dolphins later in life as adults are in a sense bisexual, and the male bonds forged earlier in life work together for protection as well as locating females to reproduce with. Confrontations between flocks of bottlenose dolphins and the related species Atlantic spotted dolphin
Atlantic Spotted Dolphin
The Atlantic Spotted Dolphin is a dolphin found in the Gulf Stream of the North Atlantic Ocean. Older members of the species have a very distinctive spotted coloration all over their body.-Taxonomy:...
will sometimes lead to cross-species homosexual behaviour between the males rather than combat.
Elephants
African and AsianAsian Elephant
The Asian or Asiatic elephant is the only living species of the genus Elephas and distributed in Southeast Asia from India in the west to Borneo in the east. Three subspecies are recognized — Elephas maximus maximus from Sri Lanka, the Indian elephant or E. m. indicus from mainland Asia, and E. m....
males will engage in same-sex bonding and mounting. Such encounters are often associated with affectionate interactions, such as kissing, trunk intertwining, and placing trunks in each other's mouths. Male elephants, who often live apart from the general herd, often form "companionships", consisting of an older individual and one or sometimes two younger, attendant males with sexual behavior being an important part of the social dynamic. Unlike heterosexual relations, which are always of a fleeting nature, the relationships between males may last for years. The encounters are analogous to heterosexual bouts, one male often extending his trunk along the other's back and pushing forward with his tusks to signify his intention to mount. Same-sex relations are common and frequent in both sexes, with Asiatic elephants in captivity devoting roughly 45% of sexual encounters to same-sex activity.
Giraffes
Male giraffeGiraffe
The giraffe is an African even-toed ungulate mammal, the tallest of all extant land-living animal species, and the largest ruminant...
s have been observed to engage in remarkably high frequencies of homosexual behavior. After aggressive "necking", it is common for two male giraffes to caress and court each other, leading up to mounting and climax. Such interactions between males have been found to be more frequent than heterosexual coupling. In one study, up to 94% of observed mounting incidents took place between two males. The proportion of same sex activities varied between 30 and 75%, and at any given time one in twenty males were engaged in non-combative necking behavior with another male. Only 1% of same-sex mounting incidents occurred between females.
Monkeys
Among monkeys, Lionel TigerLionel Tiger
Lionel Tiger is a Canadian-born, American-based anthropologist. He is the Charles Darwin Professor of Anthropology at Rutgers University and co-Research Director of the Harry Frank Guggenheim Foundation. He is a graduate of McGill University, and the London School of Economics at the University of...
and Robin Fox
Robin Fox
Robin Fox is an Anglo-American anthropologist who has written on the topics of marriage, human and primate kinship systems, and evolutionary anthropology and sociology. He was born in Yorkshire. He founded the department of anthropology at Rutgers University in 1967 and remained a professor there...
conducted a study on how Depo-Provera contraceptives lead to decreased male attractiveness to females and eventually to male homosexuality. Janet E. Smith
Janet E. Smith
Janet E. Smith is a professor of moral theology and the Fr. Michael J. McGivney Chair of Life Issues at the Sacred Heart Major Seminary in Detroit, Michigan. She previously taught at the University of Notre Dame, and the University of Dallas...
summarizes the findings as follows:
[The] study in the early 70s [...] involved a tribe of monkeys. The alpha monkey of this tribe, named Austin, chose three female monkeys to be his exclusive sexual partners. Austin had a grand time with these three female monkeys. Then the researchers injected Austin's three females with the contraceptive Depo-Provera. Austin stopped having sex with them and chose other female monkeys to be his sexual partners. Then they contracepted all of the females in the tribe. The males stopped have sex with the females and started behaving in a turbulent and confused manner.
Japanese macaque
With the Japanese macaqueJapanese Macaque
The Japanese macaque , historically known as saru , but now known as Nihonzaru to distinguish it from other primates, is a terrestrial Old World monkey species native to Japan....
, also known as the "snow monkey
Monkey
A monkey is a primate, either an Old World monkey or a New World monkey. There are about 260 known living species of monkey. Many are arboreal, although there are species that live primarily on the ground, such as baboons. Monkeys are generally considered to be intelligent. Unlike apes, monkeys...
", same-sex relations
Homosexuality
Homosexuality is romantic or sexual attraction or behavior between members of the same sex or gender. As a sexual orientation, homosexuality refers to "an enduring pattern of or disposition to experience sexual, affectional, or romantic attractions" primarily or exclusively to people of the same...
are frequent, though rates vary between troops. Females will form "consort
Consort
Consort may refer to:Titles:* Queen consort, wife of a reigning king* Prince consort, husband of a reigning queen* King consort, rarely used alternative title for husband of a reigning queen...
ships" characterized by affectionate social and sexual activities. In some troops up to one quarter of the females form such bonds, which vary in duration from a few days to a few weeks. Often, strong and lasting friendships result from such pairings. Males also have same-sex relations, typically with multiple partners of the same age. Affectionate and playful activities are associated with such relations.
Lions
Both male and female lions have been seen to interact homosexuallyAnimal sexuality
Animal sexual behaviour takes many different forms, even within the same species. Among animals other than humans, researchers have observed monogamy, promiscuity, sex between species, sexual arousal from objects or places, sex apparently via duress or coercion, copulation with dead animals,...
. Male lions pair-bond for a number of days and initiate homosexual activity with affectionate nuzzling and caressing, leading to mounting and thrusting. About 8% of mountings have been observed to occur with other males. Pairings between females are held to be fairly common in captivity but have not been observed in the wild.
Polecat
European polecatEuropean polecat
The European polecat , also known as the black or forest polecat , is a species of Mustelid native to western Eurasia and North Africa, which is classed by the IUCN as Least Concern due to its wide range and large numbers. It is of a generally dark brown colour, with a pale underbelly and a dark...
s Mustela putorius were found to engage homosexually with non-sibling animals. Exclusive homosexuality with mounting and anal penetration in this solitary species serves no apparent adaptive function.
Sheep
The reason why Ovis aries has attracted so much attention is that some rams seem to have an exclusive homosexual orientation.An October 2003 study by Dr. Charles E. Roselli et al. (Oregon Health and Science University) states that homosexuality in male sheep (found in 8% of rams) is associated with a region in the rams' brains which the authors call the "ovine Sexually Dimorphic Nucleus" (oSDN) which is half the size of the corresponding region in heterosexual male sheep.
Scientists found that, "The oSDN in rams that preferred females was significantly larger and contained more neurons than in male-oriented rams and ewes. In addition, the oSDN of the female-oriented rams expressed higher levels of aromatase
Aromatase
Aromatase is an enzyme responsible for a key step in the biosynthesis of estrogens. It is a member of the cytochrome P450 superfamily , which are monooxygenases that catalyze many reactions involved in steroidogenesis. In particular, aromatase is responsible for the aromatization of androgens into...
, a substance that converts testosterone
Testosterone
Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...
to estradiol
Estradiol
Estradiol is a sex hormone. Estradiol is abbreviated E2 as it has 2 hydroxyl groups in its molecular structure. Estrone has 1 and estriol has 3 . Estradiol is about 10 times as potent as estrone and about 80 times as potent as estriol in its estrogenic effect...
, a form of estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
which is believed to facilitate typical male sexual behaviors. Aromatase expression was no different between male-oriented rams and ewes."
"The dense cluster of neurons that comprise the oSDN express cytochrome
Cytochrome
Cytochromes are, in general, membrane-bound hemoproteins that contain heme groups and carry out electron transport.They are found either as monomeric proteins or as subunits of bigger enzymatic complexes that catalyze redox reactions....
P450 aromatase. Aromatase mRNA levels in the oSDN were significantly greater in female-oriented rams than in ewes, whereas male-oriented rams exhibited intermediate levels of expression." These results suggest that "...naturally occurring variations in sexual partner preferences may be related to differences in brain anatomy and its capacity for estrogen synthesis." As noted prior, given the potential unagressiveness of the male population in question, the differing aromatase levels may also have been evidence of aggression levels, not sexuality. It should also be noted that the results of this study have not been confirmed by other studies.
The Merck Manual of Veterinary Medicine
Merck Veterinary Manual
The Merck Veterinary Manual is a reference manual of animal health care. It is published by Merck & Co., Inc. and Merial Limited. The Merck Veterinary Manual is available as a reference manual or as an online resource for veterinarians, veterinary students, and others involved in animal health...
appears to consider homosexuality among sheep as a routine occurrence and an issue to be dealt with as a problem of animal husbandry.
Spotted Hyena
Hermaphrodite
In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...
males who commonly practiced homosexuality
Homosexuality
Homosexuality is romantic or sexual attraction or behavior between members of the same sex or gender. As a sexual orientation, homosexuality refers to "an enduring pattern of or disposition to experience sexual, affectional, or romantic attractions" primarily or exclusively to people of the same...
. Early writings such as Ovid
Ovid
Publius Ovidius Naso , known as Ovid in the English-speaking world, was a Roman poet who is best known as the author of the three major collections of erotic poetry: Heroides, Amores, and Ars Amatoria...
's Metamorphoses and the Physiologus suggested that the hyena continually changed its sex and nature from male to female and back again. In Paedagogus
Paedagogus
Paedagogus , second in the great trilogy of Clement of Alexandria.Having laid a foundation in the knowledge of divine truth in the first book, he goes on in the Paedagogus to develop a Christian ethic...
, Clement of Alexandria noted that the hyena
Hyena
Hyenas or Hyaenas are the animals of the family Hyaenidae of suborder feliforms of the Carnivora. It is the fourth smallest biological family in the Carnivora , and one of the smallest in the mammalia...
(along with the hare
Hare
Hares and jackrabbits are leporids belonging to the genus Lepus. Hares less than one year old are called leverets. Four species commonly known as types of hare are classified outside of Lepus: the hispid hare , and three species known as red rock hares .Hares are very fast-moving...
) was "quite obsessed with sexual intercourse." Many Europeans associated the hyena with sexual deformity, prostitution, deviant sexual behavior, and even witchcraft.
The reality behind the confusing reports is the sexually aggressive behavior between the females, including mounting between females. Research has shown that "in contrast to most other female mammals, female Crocuta are male-like in appearance, larger than males, and substantially more aggressive," and they have "been masculinized
Masculine
Masculine or masculinity, normally refer to qualities positively associated with men.Masculine may also refer to:*Masculine , a grammatical gender*Masculine cadence, a final chord occurring on a strong beat in music...
without being defeminized
Femininity
Femininity is a set of attributes, behaviors, and roles generally associated with girls and women. Though socially constructed, femininity is made up of both socially defined and biologically created factors...
.”
Study of this unique genitalia and aggressive behavior in the female hyena has led to the understanding that more aggressive females are better able to compete for resources, including food and mating partners. Research has shown that "elevated levels of testosterone
Testosterone
Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...
in utero
In utero
In utero is a Latin term literally meaning "in the womb". In biology, the phrase describes the state of an embryo or fetus. In legal contexts, the phrase is used to refer to unborn children. Under common law, unborn children are still considered to exist for property transfer purposes.-See also:*...
" contribute to extra aggressiveness; both males and females mount members of the same sex, who in turn are possibly acting more submissive because of lower levels of testosterone in utero.
Lizards
Whiptail lizard (TeiidaeTeiidae
Teiidae is a family of lizards native to the Americas, generally known as whiptails. The group includes the parthenogenic genera Cnemidophorus and Aspidoscelis, and the non-parthenogenic Tupinambis. It has over 230 member species in ten genera...
genus) females have the ability to reproduce through parthenogenesis
Parthenogenesis
Parthenogenesis is a form of asexual reproduction found in females, where growth and development of embryos occur without fertilization by a male...
and as such males are rare and sexual breeding non-standard. Females engage in sexual behavior to stimulate ovulation
Ovulation
Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...
, with their behavior following their hormonal cycles; during low levels of estrogen, these (female) lizards engage in "masculine" sexual roles. Those animals with currently high estrogen levels assume "feminine" sexual roles.
Lizards that perform the courtship ritual have greater fertility than those kept in isolation due to an increase in hormones triggered by the sexual behaviors. So, even though asexual whiptail lizards populations lack males, sexual stimuli still increase reproductive success.
From an evolutionary standpoint, these females are passing their full genetic code to all of their offspring (rather than the 50% of genes that would be passed in sexual reproduction). Certain species of gecko
Gecko
Geckos are lizards belonging to the infraorder Gekkota, found in warm climates throughout the world. They range from 1.6 cm to 60 cm....
also reproduce by parthenogenesis.
Dragonflies
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Odonata
Odonata
Odonata is an order of insects, encompassing dragonflies and damselflies . The word dragonfly is also sometimes used to refer to all Odonata, but the back-formation odonate is a more correct English name for the group as a whole...
). The cloacal pinchers of male damselflies and dragonflies inflict characteristic head damage to females during sex. A survey of 11 species of damsel and dragonflies has revealed such mating damages in 20 to 80 % of the males too, indicating a fairly high occurrence of sexual coupling between males.
Fruit flies
Male Drosophila melanogasterDrosophila melanogaster
Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...
flies bearing two copies of a mutant allele in the fruitless
Fruitless (gene)
The fruitless gene is a Drosophila melanogaster gene that encodes several variants of a putative transcription factor protein. Normal fruitless function is required for proper development of several anatomical structures necessary for courtship, including motor neurons which innervate muscles...
gene court and attempt to mate exclusively with other males. The genetic basis of animal homosexuality has been studied in the fly Drosophila melanogaster
Drosophila melanogaster
Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...
. Here, multiple genes have been identified that can cause homosexual courtship and mating. These genes are thought to control behavior through pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
s as well as altering the structure of the animal's brains. These studies have also investigated the influence of environment on the likelihood of flies displaying homosexual behavior.
Bed bugs
Male bed bugs (Cimex lectularius) are sexually attracted to any newly fed individual and this results in homosexual mounting. This occurs in heterosexual mounting by the traumatic inseminationTraumatic insemination
Traumatic insemination, also known as hypodermic insemination, is the mating practice in some species of invertebrates in which the male pierces the female's abdomen with his penis and injects his sperm through the wound into her abdominal cavity . The sperm diffuse through the female's hemolymph,...
in which the male pierces the female abdomen with his needle-like penis. In homosexual mating this risks abdominal injuries as males lack the female counteradaptive spermalege
Spermalege
The spermalege is a special-purpose organ found in bed bugs that appears to have evolved to mitigate the effects of traumatic insemination. The spermalege has two embryologically distinct parts, known as the ectospermalege and mesospermalege...
structure. Males produce alarm pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
s to reduce such homosexual matings.
See also
- Animal sexual behavior
- Xq28Xq28Xq28 is a genetic marker on the X chromosome found by Dean Hamer and others in 1993. Hamer's study led to his belief that they found a link between the Xq28 marker and male homosexuality, but the original study's results have been disputed.-1993 study:...
- Against Nature?Against Nature?Against Nature? is an exhibition on homosexuality in animals made by the Natural History Museum, University of Oslo, Norway. The exhibition focuses on occurrence and function of homosexuality in animals, and is the first of its kind....
- Biology and sexual orientationBiology and sexual orientationBiology and sexual orientation is the subject of research into the role of biology in the development of human sexual orientation. No simple, single cause for sexual orientation has been conclusively demonstrated, but research suggests that it is by a combination of genetic, hormonal, and...
- FreemartinFreemartinA freemartin or free-martin is an infertile female mammal which has masculinized behavior and non-functioning ovaries. Genetically and externally the animal is female, but it is sterilized in the womb by hormones from a male twin, becoming an infertile partial intersex...
- Homosexuality and psychologyHomosexuality and psychologyPsychology was one of the first disciplines to study homosexuality as a discrete phenomenon. Prior to and throughout most of the 20th century, common standard psychology viewed homosexuality in terms of pathological models as a mental illness...
- Hermaphroditism in animals
- Innate bisexualityInnate bisexualityInnate bisexuality is a term introduced by Sigmund Freud , that expounds all humans are born bisexual but through psychological development become monosexual while the bisexuality remains in a latent state.There is no modern scientific consensus as to...
- Non-human primate experiments
- Norms of reactionNorms of reactionIn ecology and genetics, a norm of reaction describes the pattern of phenotypic expression of a single genotype across a range of environments. One use of norms of reaction is in describing how different species—especially related species—respond to varying environments...
- Plant sexualityPlant sexualityPlant sexuality covers the wide variety of sexual reproduction systems found across the plant kingdom. This article describes morphological aspects of sexual reproduction of plants....
- Sexual orientationSexual orientationSexual orientation describes a pattern of emotional, romantic, or sexual attractions to the opposite sex, the same sex, both, or neither, and the genders that accompany them. By the convention of organized researchers, these attractions are subsumed under heterosexuality, homosexuality,...
- Sexual orientation and medicineSexual orientation and medicineSexual orientation and medicine may refer to:*Medical association positions and policy regarding sexual orientation or homosexuality*Timeline of sexual orientation and medicine*Homosexuality and psychology...
- Cross species sex
- List of animals displaying homosexual behavior