Homosexual behavior in animals

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Two male mallards

As homosexual behavior in animals behavior is referred to as the homo- or bisexual can be interpreted. This is expressed, among other things, through courtship behavior , the expression of affection and the couple bond to / towards same-sex conspecifics, as well as same-sex brood care. Scientific research shows that homosexual behavior in animals occurs in different forms in the animal kingdom. Same-sex behavior (SSB) has been identified in over 1,500 animal species.

Application of the term homosexual to animals

The term homosexual was first used by Karl-Maria Kertbeny in 1868 to describe same-sex attraction and sexual behavior in people. (See in the article, Writings on Homosexuality ) The use of this term in animal studies has been controversial for two reasons: The sexuality of animals and the underlying motivating factors are poorly understood, and the term has many strong cultural connotations in Western societies, which are irrelevant to non-human species. Therefore, over the years, homosexual behavior in animals has been given different terms, with the term “homosexual” being given preference over words such as gay , lesbian and other terms, as these refer even more to human homosexuality.

In the case of wild animals, researchers often cannot generally study and record the entire life of an animal, so that their behavior has to be interpreted through individual observations. The correct use of the term “homosexual” must therefore be that an animal exhibits “homosexual behavior” or “same sex behavior”. However, in this article, the term is used in accordance with the conventions of modern research, applying homosexuality to any sexual behavior in animals where copulation, genital stimulation, mating games and courtship between same-sex animals occur. In most cases it is believed that homosexual behavior is only part of the animal's complete sexual behavior, with the result that most of these animals are "bisexual" rather than "homosexual". However, cases of homosexual preference as well as exclusively homosexual couples are known.

According to Bruce Bagemihl , the animal kingdom shows a far greater sexual diversity than the scientific community has hitherto been ready to accept - with a homosexual, bisexual and non-reproductive orientation. Bagemihl adds that this is nonetheless a concession to the human interpretation of this phenomenon. Simon LeVay adds that despite the frequency of homosexual behavior in the animal kingdom, it is rather unusual for individual animals to persist for a long time to the exclusion of heterosexuality. “Therefore a homosexual orientation in animals, if one can speak of it, seems to be rather a rarity.” However, one species in which an exclusively homosexual orientation occurs is the domestic sheep , in which around 10% of the goats refuse to to mate with females but willingly do so with other males.

The sexual behavior of animals takes many different forms in the same animal species, but homosexual behavior is best known from social species. The causes of this behavior need to be better understood, especially since many species need further study.

Observing homosexual behavior in animals can be used as an argument both for and against the acceptance of homosexual behavior in humans, but in particular it is used against the argument that homosexuality is a "sin against nature". For example, homosexual behavior in animals has been promoted by the American Psychiatric Association and other groups as an argument in the United States Supreme Court in the Lawrence v. Texas , which eventually led to 14 states abolishing sodomy laws.

research

Much of the research available does not specify more precisely between exclusively homosexual animals and those that display equally homosexual and heterosexual behavior. As a result, there are different opinions and conflicting interpretations among researchers about the data they have collected. For example, Bruce Bagemihl emphasizes that there are no anatomical or endocrinological differences between exclusively homosexual and exclusively heterosexual pairs of animals. Nevertheless, differences in the hormonal composition of key sexual hormones such as testosterone and estradiol were found when exclusively heterosexual animals were compared with animals exhibiting both homosexual and heterosexual courtship behavior.

Many animals used in laboratory studies that display homosexual behavior do not necessarily do so in the wild. Such behavior is often induced by scientists during the experiment, among other things by destroying part of the brain tissue or by exposing them to high amounts of steroid hormones prenatally. The information obtained from such experiments is therefore only of limited use and can only be applied to wild animals to a limited extent.

The presence of same-sex behavior was not "officially" observed until recently. This is most likely due to observer-related bias due to social attitudes towards same-sex behavior, unintentional mix-ups or fear of being "ridiculed" by colleagues. Janet Mann of Georgetown University says, "Scientists working in this area are often accused of having a particular agenda and their work is often scrutinized more than that of their peers working in other fields." it was noted, "Not every sexual act has a reproductive function ... this is true of both humans and animals." This appears to be widespread among social birds and mammals, particularly marine mammals and primates. However, the real level of homosexuality in animals is not known. While studies show homosexual behavior for a certain number of species, Petter Bøckman, the scientific supervisor of the exhibition Against Nature? that the full extent of this phenomenon is significantly greater than previously assumed:

“So far, no species has been found that does not show homosexual behavior , with the exception of species that do not reproduce sexually, such as sea ​​cucumbers or aphids . Furthermore, part of the animal kingdom is hermaphrodite , which means really bisexual. There is practically no homosexuality for them. "

An example where homosexual behavior has been overlooked: Nine out of ten pairings in giraffes occur between males.

In this regard, Bagemihl quotes:

"Every male who smelled a female was assumed to have a sexual motive, while anal intercourse between males with orgasm was about dominance, competition or greeting."

Some researchers believe that this behavior stems from male social organization and dominance, similar to the dominance traits found in prison sexuality. Researchers like Bagemihl, Joan Roughgarden , Thierry Lodé and Paul Vasey suggest that the social function of sex (both homosexual and heterosexual) is not necessarily linked to dominance, but rather serves to strengthen social communities and connections in a group. Others argue that social organization theory is inappropriate because it fails to describe some aspects of homosexual behavior. For example, in penguins males enter into a lifelong partnership and refuse to mate with females when given the opportunity. Although some of such reports are initially only anecdotal, there is growing scientific contribution to confirm that permanent homosexuality occurs not only in species with permanent pairing, but also in non-monogamous species, such as sheep. According to a report on sheep, approximately 8% of the bucks, when given the opportunity, show sexual preferences for male partners (male-oriented bucks). In contrast, most other bucks prefer female partners (female-oriented bucks). The researchers found a group of cells in the medial preoptic area of the anterior hypothalamus of adult sheep of the corresponding age that was significantly larger in adult male goats than in female sheep.

In fact, apparently homosexual individuals are known from all traditional domesticated animals, from sheep to cattle and horses to cats, dogs and budgies.

basis

Physiological basis

A clear physiological explanation or cause for homosexual activities in animals has not yet been found by researchers. Many scientists believe that fluctuating levels (either higher or lower) of the animals' sex hormones, in addition to the size of the gonads, play a direct role in the animal's sexual behavior and the resulting benefits. Others consistently argue that there is no evidence to support this thesis when comparing animals of a particular species that exhibit exclusively homosexual behavior with those that do not. Finally, there is evidence from extensive endocrinological studies that support both the one and the other thesis. Researchers have found no evidence of a difference in the size of the gonads or the amount of sex hormones between exclusively homosexual western gulls and ring-billed gulls . However, bisexual bucks were found to have lower levels of testosterone and estradiol in the blood and smaller gonads than the corresponding heterosexual animals.

Additional studies regarding hormone involvement in homosexual behavior show that when testosterone or estradiol is given to female animals, it increases the likelihood of homosexual behavior. In addition, increasing hormone levels during pregnancy increases the likelihood of homosexual offspring being born.

Genetic basis

Researchers have found that inactivating the fucose mutarotase gene, which regulates estrogen levels, causes female laboratory mice to behave like males as they grow up. Another study found that manipulating genes in fruit flies ( Drosophila ) can apparently induce homosexual behavior. However, in addition to homosexual behavior, other behaviors that were triggered by this mutation were also observed.

Neurobiological basis

In March 2011 it was shown that serotonin is involved in the mechanism of sexual orientation in mice. A study was conducted on fruit flies showed that the inhibition of dopamine - the neurotransmitter inhibits labor induced homosexual behavior.

Some selected species and groups

Birds

Black Swan

Black Swan

It is estimated that a quarter of all Black Swan takes place pairings between homosexual males. They steal nests or form temporary communities of three (two males, one female) to obtain eggs, evicting the female after she has laid the eggs. Of the young swans of homosexual couples, more are reaching adulthood than of heterosexual couples, possibly due to better ability to defend larger territories. The same conclusion can also be drawn for male flamingo pairs when rearing young birds.

Seagulls

Studies have shown that 10 to 15 percent of female western gulls exhibit homosexual behavior in some wild populations.

Ibises

Research has shown that the environmental pollutant methylmercury increases the prevalence of homosexual behavior in the snow ibis. In the study, chicks were exposed to different doses of the chemical and the extent of homosexual behavior in adulthood was measured. The study concluded that the higher the dose of methylmercury, the greater the likelihood of homosexual behavior occurring. It is believed that the blockage of endocrine functions by mercury is a possible cause of sexual dysfunction in other bird species as well.

Ducks

Two male mallards

Mallards form heterosexual couples only until the female lays eggs, at which point the male then leaves the female. Mallards have an unusually high rate of male-male sexual behavior for birds; in some populations this can affect up to 19 percent of couples. Kees Moeliker from the Natural History Museum Rotterdam observed a male mallard who showed homosexual necrophilia .

Penguins

It has been known since 1911 that penguins show homosexual behavior. George Murray Levick documented this behavior in Adelie penguins at Cape Adare and described it as "depraved". This report was considered too shocking for the public at the time and its publication was suppressed. The report was rediscovered over 100 years later and published in June 2012.

In February 2004, the New York Times reported that Roy and Silo, a pair of male chinstrap penguins, successfully hatched and raised a female chick from a fertilized and given egg at New York City's Central Park Zoo . Other penguins in the New York Zoo have also been reported to form same-sex pairs.

Zoos in Japan and Germany have also documented male gay penguin pairs. It was found that these couples build nests together and use a stone as a substitute for an egg. Researchers from Rikkyo University in Tokyo found a total of 20 homosexual couples in 16 large aquariums and zoos in Japan.

The Zoo am Meer in Bremerhaven tried to breed the endangered Humboldt penguin by importing female animals from Sweden and separating three male pairs. However, this was unsuccessful because the relationships between the homosexual couples were too strong. German homosexual groups protested against this attempt to break the male-male couple bond, whereas the zoo director is said to have said: "We do not know whether the three male couples are actually homosexual or whether they only got together for lack of females" and on : "Nobody here wants to use violence to separate same-sex couples."

A pair of male Magellanic penguins who shared a burrow at the San Francisco Zoo for six years and raised a chick as surrogate fathers separated when the male of a heterosexual couple died in the neighboring cave and the female sought a new mate.

Buddy and Pedro, a male pair of African penguins , were separated at the Toronto Zoo to mate with females. Buddy has since mated with a female.

Suki and Chupchikoni are two female African penguins who met on the Ramat Gan Safari in Israel . Chupchikoni was initially thought to be a male until the animal's blood was tested.

In 2014, Jumbs and Kermit, two Humboldt penguins at Wingham Wildlife Park in Kent , received international media attention when, after living as a homosexual couple for several years, they successfully hatched an egg and raised the chick as surrogate parents, after mother and father left it halfway through the breeding season.

vulture

In 1998 two male griffon vultures named Dashik and Yehuda were involved in "open and energetic sex" at the Jerusalem Biblical Zoo and built a nest. The zookeepers gave them an artificial egg, which the two of them hatched together, whereupon the keepers replaced it with a young bird after 45 days. The chick was raised by both vultures together. However, a few years later, Yehuda became interested in a female that was brought into the aviary. Dashik became depressed and was ultimately taken to the Tel Aviv University zoological research garden , where he too built a nest with a female.

Two homosexual male vultures in the all-weather zoo in Münster built a nest together, although they were harassed by other vultures and their nesting material was stolen. They were eventually separated and attempts were made to induce them to breed by joining them with female vultures. This was accompanied by protests by groups of homosexual people.

Pigeons

Both male and female pigeons sometimes exhibit homosexual behavior. In addition, same-sex pairs of pigeons build nests and hens lay (unfertilized) eggs and try to hatch them.

Mammals

Bottlenose dolphin

Dolphins of different species exhibit homosexual behavior; it is best studied in the bottlenose dolphin . Sexual encounters between females take the form of snout-genital propulsion, with one female sticking its snout into another's genital opening while gently swimming forward. Between males, homosexual behavior involves the rubbing of genitals together that sometimes causes males to swim belly to belly, with the penis inserted into the other's genital orifice or anus.

Janet Mann of Georgetown University argues that the strong personal behaviors between male dolphin calves create strong bonds and are beneficial to the entire species in an evolutionary context. She cites studies that show that later in life these dolphins are broadly bisexual, the male bonds have protective functions, and also result in females being found to reproduce. Confrontations between herds of bottlenose dolphins and the rein dolphin , a related species, sometimes result in homosexual behavior between species rather than fighting.

Amazon dolphin

When Amazon river dolphin from the family of Amazon river dolphins showed that this operates in groups of three to five individuals Group. The groups usually consist of young males and sometimes one or two females. Sex is often practiced in a non-reproductive manner, using the snouts and fins and rubbing the genitals together, regardless of gender. In captivity, the Amazon dolphins have sometimes been seen making both homosexual and heterosexual penetrations of the breathing hole. Since the breathing hole is homologous to the nostril, this observation is the only one of nasal sex in the animal kingdom. The males sometimes have sex with tucuxi -Männchen, a small dolphin from the family of dolphins .

American bison

American bison

Courtship, jumping up, and full anal penetration between bulls have been observed in the American bison . The Mandan people's Okipa ceremony ends with a spectacle of this behavior to ensure the buffalo return for the next year. Furthermore, climbing one female by another is very common. This behavior is hormone-controlled and synchronized with the onset of oestrus, especially in the presence of a bull.

Bonobo and other great apes

Bonobo

Bonobos , thrown in for great apes unusual matriarchal life society are completely bisexual, with both males and females homosexual and heterosexual behavior show. In particular, the females show pronounced homosexual behavior. Approximately 60% of all bonobo sexual activity occurs between two or more females. While homosexual behavior is the largest percentage of any species in bonobos, it has been observed in all great apes (which includes humans) as well as some other primates .

Frans de Waal noticed during the bonobo observation that homosexual behavior is a reason to avoid conflict. If there is anything that piques the interest of several bonobos at the same time, it often leads to sexual contact. If a cardboard box is thrown into a bonobo enclosure and two bonobos approach, one observes that they first climb on before they play with the box. Such situations often lead to quarrels. Still, the bonobos are quite tolerant, possibly because sexual activity distracts attention and reduces tension. Sex between bonobos often arises from an aggressive, unrelated context of food. A jealous male may scare another away from a female, and the two then come together again and rub their scrotas together. Another example: a female hits a strange young animal, the mother then rushes at the aggressor, whereupon both of them rub their genitals together.

Monkeys

A study between monkeys by Lionel Tiger and Robin Fox has been carried out on how Depo-Provera, a contraceptive , leads to decreased sexual attraction between males and females.

Japanese macaque

The Japanese macaques homosexual relationships often occur with the frequency may be different in different groups. Females form partnerships that are characterized by social affection and sexual activity. In some groups, up to a quarter of the females do, and these relationships can last from a few days to several weeks. Often this results in strong and lasting friendships. Males also have same-sex partnerships, typically with multiple males of the same age group, in which affection and playful activities occur.

Elephants

Males of African elephants as well as Asian elephants show same-sex bonds and jumping behavior. This is often related to affection, kissing, devouring the trunk, and putting the trunk in the other's mouth. Male elephants who live away from the actual herd form partnerships that often consist of one older and one or two younger animals, with sexual behavior often being an important part of social dynamics. Unlike heterosexual partnerships, which are often of a temporary nature, homosexual partnerships between males last for several years. Homosexual encounters are similar to heterosexual encounters, with a male often guiding his trunk along the partner's back and pushing his tusks forward to signal the opening. Same-sex relationships are common and common among both sexes, with Asiatic elephants in captivity about 45% of their sexual activities being same-sex in nature.

Giraffes

Male giraffes were observed to be homosexually active with an above-average frequency. After aggressive “necking” (“necking”) two males, the exchange of tenderness and courtship occur more frequently, which often leads to jumping up and climax . Such interactions between males were observed more frequently than heterosexual matings. In one study, up to 94% of jumps were between males. The ratio of same-sex activities varies between 30% and 75%, and at any one time one in 20 males was involved in non-combative necking with another male. Only 1% of same-sex jumps occurred among females.

Lions

Male lions in mating

Both male and female lions have been observed to be homosexually active. Male lions bond for a few days and begin homosexual activities by inclined rubbing their snouts that causes them to pop open. Approximately 8% of all matings take place between males. Mating between females is known from captivity, but has not yet been observed in the wild.

Polecats

The European polecat has been observed to behave homosexually. Exclusive homosexuality with jumping up and anal penetration has no apparent function in this solitary species.

Sheep

So far, the sheep have received a great deal of attention, as approx. 8–10% of the goats show exclusively homosexual behavior. Furthermore, around 18–22% of all bucks are bisexual.

A study by Oregon Health and Science University found that homosexuality in male sheep (found in 8% of all bucks) is associated with a region in the sheep's brain that the authors of the study call "oSDN" ("ovine Sexually Dimorphic Nucleus") which is twice as large in heterosexual sheep as in homosexual sheep.

The researchers report that the oSDN region in heterosexual rams is significantly larger and more pronounced than in homosexual rams and females. In addition, this region releases more aromatase in heterosexual bucks , an enzyme that converts testosterone into estradiol , which is a form of estrogen and is believed to aid typical male sexual behavior. The aromatase expression was not different between homosexual bucks and females. Due to the given non-aggressiveness of the observed male sheep population, the different aromatase levels can also be an expression of the level of aggression and less of sexuality. The results of this study have not yet been confirmed by other studies.

The Merck Veterinary Manual regards homosexuality between sheep as a regular occurrence and a problem in relation to livestock.

Spotted hyena

Spotted hyena

The spotted hyena's family structure is matriarchal and relationships with strong sexual elements are regularly observed between related females. Due to the hyena's clitoris , which is more like a penis , it was previously assumed that hyenas were hermaphrodites who occasionally engage in homosexuality. Early writings such as Physiologus and Ovid's Metamorphoses claimed that the hyena was constantly changing sex from male to female. In Pedagogus , Clement of Alexandria notes that the hyena (together with the hare) is "obsessed" with sexual intercourse. Many Europeans associated the hyena with sexual depravity, prostitution, abnormal sexual behavior, and even witchcraft.

In fact, behind these reports lies the sexually aggressive behavior between female animals, which includes jumping up. Research has shown that, unlike other female mammals, females of the genus Crocuta have a male appearance, are larger than the males, and are much more aggressive.

Examination of the hyena's unusual and unique genital tract and aggressive behavior suggests that more aggressive females are better able to fight for resources, food and mating partners. Research has shown that increased testosterone levels in utero contribute to increased aggressiveness; Both males and females mount partners of the same or the opposite sex, who in turn are more submissive due to the lower amount of testosterone.

Other

Lizards

Females of some species of rail lizard are able to reproduce by parthenogenesis (virgin generation), which is why males are rare and sexual reproduction does not usually occur. The females display sexual behavior that stimulates ovulation and is based on their normal hormonal cycle. Females with low levels of estrogen take the male role. Females who are high in estrogen at the time take on the female roles. Lizards that practice this courtship behavior show greater fertility than those that are kept in isolation due to the increase in hormones generated in this way. Sexual activity thus increases the chances of successful reproduction, even if the full genome is passed on to the offspring and not just 50%, as is the case with sexual reproduction. Some gecko species can also reproduce through parthenogenesis.

Insects and arachnids

There is evidence that at least 110 species of insects and spiders exhibit homosexual behavior. Homosexual behavior in insects has been the subject of much debate among scientists. Although various theories have been proposed, the leading claim is that male homosexuality, which is believed to be as high as 85% in some insect species, is the result of incorrectly assigned sexes. By refusing to reproduce with a female, the male loses more than he gains in return from homosexual acts with another male.

Dragonflies
Basiaeschna janata

Male homosexuality was in some species of dragonflies from the order of dragonflies accepted. The copulation apparatus of the dragonflies and dragonflies inflicts characteristic damage on the head of the females during mating. An examination of 11 species of small and large dragonflies has shown that this head damage is found in 20–80% of the males, which suggests a high proportion of male matings.

Fruit flies

Male animals of the black-bellied fruit fly Drosophila melanogaster carry two copies of a mutant allele in the fruitless gene and only mate with other males. The genetic basis of animal homosexuality was investigated in D. melanogaster . Several genes that cause homosexual courtship and homosexual mating have been identified. It is believed that these genes control behavior through pheromones as well as by changing brain structure. These studies also looked at the likelihood of environmental influences producing homosexual behavior.

Bed bug

Male bed bugs are attracted to any newly fed individual, resulting in homosexual matings. This also happens in heterosexual pairings, where traumatic insemination occurs by drilling the needle-like penis into the female's abdomen. In homosexual pairings, this leads to injuries to the abdomen, as males lack the corresponding female counterpart, the sperm gene . Males therefore produce an alarm pheromone to reduce the likelihood of such homosexual pairings.

Individual evidence

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