View source for Animal sexual behaviour

[[Animal]] [[sexual behavior]] takes many different forms; even within the same [[species]], researchers have drawn parallels between this and [[homosexuality]], [[bisexuality]], [[intersex]]uality and [[transgender]] behavior in humans.  Homosexual behavior has been [http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2004/02/07/MNG3N4RAV41.DTL documented] in 450 species.

==Homosexual behavior==

The presence of [[same-sex sexual behavior]] was not 'officially' observed on a large scale until recent times, possibly due to [[Observer effect|observer bias]] caused by social attitudes to [[same-sex sexual behavior]]. It appears to be widespread amongst [[bird]]s, [[mammal]]s and the [[ape]]s. Some researchers believe it to have its origin in male social organization and social dominance, similar to the dominance traits shown in [[prison sexuality]].  However others cast doubt on this male social organization theory [http://www.365gay.com/newscon05/02/021105penguins.htm citing] gay Penguins that mate for life and refuse to pair with females when given the chance. However these permanent mating scenarios are still only anecdotal and yet to be proven by scientific study.

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..."''

==Cross species sex==
Although most people believe animals sexuality is instinctive and therefore (implied) almost mechanistic, in fact research regularly records that many animals are sexual opportunists, and may show an interest in other partners than their own or related species. This is more visible in domesticated species, as domestication commonly selects for increased breeding rate (and so an accelerated breeding cycle has commonly arisen in domesticated species over the centuries), and also because these species are easier to witness by humans. Nevertheless non-domesticated animals have been observed to attempt sexual activity with other species, or indeed inanimate objects. This form of cross-species sex, however, has been observed with animals in captivity (such as the zoo), rather than in the wild

Examples: 
* [http://nacho.princeton.edu/fowler/joshua/year2/dec1_zoo/antelope_humping_zebra.jpg Antelope and Zebra] 
* [http://img.lj.com.ua/dashing/1218_cat_dog.jpg Dog and Cat]

If the pair are a male and a female, [[hybrid]] offspring can result if the two species are related. However, this offspring may not be able to breed itself. The mule, for example (horse/donkey cross) is normally sterile, whilst the [[liger]] (lion/tiger cross) is sometimes fertile. Novosibirsk zoo director Rostislav Shilo says on the liger (born in its zoo); &#8220;It&#8217;s just that the lion and the tiger live in neighboring caves in the Novosibirsk zoo, and got used to each other. It&#8217;s practically impossible in the wild.&#8221;

==Specific species ==
===Bonobo apes===
The [[bonobo]], which has a [[matriarchal]] society (unusual amongst apes), is a fully [[bisexual]] species -- both males and females engage in heterosexual and homosexual behavior, being noted for [[lesbianism]] in particular.

===Birds===
[[Image:Gay penguins NY Zoo.jpg|right|frame|'''Squawk and Milou'''<br> Male chinstrap penguins,
one of several homosexual pairs at the Central Park Zoo
in Manhattan. <br>(Picture:Nicole Bengiveno/The New York Times)]]
Some black swans of Australia form sexually active male-male mated pairs and steal nests, or form temporary threesomes with females to obtain eggs, driving away the female after she lays the eggs. More of their cygnets survive to adulthood than those of different-sex pairs possibly due to their superior ability to defend large portions of land.

In early February [[2004]] the ''[[New York Times]]'' [http://query.nytimes.com/gst/abstract.html?res=FA0C1EF83A5F0C748CDDAB0894DC404482 reported] a male pair of [[chinstrap penguin]]s in the [[Central Park Zoo]] in [[New York City]] were partnered and even successfully hatched a female chick from an egg. Other penguins in New York have also been [http://www.jrn.columbia.edu/studentwork/cns/2002-06-10/591.asp reported] to be forming same-sex pairs.

Zoos in [[Japan]] and [[Germany]] have also [http://www.365gay.com/newscon05/02/021105penguins.htm documented] gay male penguin couples.  The couples have been shown to build nests together and use a stone to replace an egg in the nest.  Researchers at [[Rikkyo University]] in [[Tokyo]], found 20 gay pairs at 16 major aquariums and zoos in Japan.  Bremerhaven Zoo in Germany attempted to break up the gay male couples by importing female penguins from [[Sweden]] and separating the male couples, they were unsuccessful.  The zoo director stated the relationships were too strong between the gay couples.  

[http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2004/02/07/MNG3N4RAV41.DTL Studies have shown] that 10 to 15 percent of female western gulls in some populations in the wild are [[lesbian]].

===Lizards===
Whip-tailed lizard 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 fecundity 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.

===Sheep===
An [[October]] [[2003]] [http://endo.endojournals.org/cgi/content/abstract/145/2/478 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 two times smaller than the corresponding region in heterosexual male sheep.

It should be noted however that some view this study to be flawed in that the determination of homosexuality within the sheep (sample population of 27 for the study) was to have animals who were unable to mount female ewes placed in a cage with two stanchioned males and two unstanchioned females (i.e. the males could not move or struggle while the females could). Given the agressive nature of sheep copulation, the uneven treatment of males and females, many see this as simply evidence that the sheep in question were unable to be aggressive enough to mount females. As with most animal homosexuality, the results were situational sexuality, unlike the bonds seen in human homosexuality.
The 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]] so that the [[androgen]] [[hormone]] can 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." [http://endo.endojournals.org/cgi/content/abstract/145/2/478 Read the abstract of the study.] 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.

===Spotted Hyena===
The female [[Spotted Hyena]] has a unique urinary-genital system, closely resembling the penis of the male. The family structure is matriarchal and dominance relationships with strong sexual elements are routinely observed between related females.

===Bottlenose Dolphins===
[[Bottlenose Dolphin]] males have been observed working in pairs to follow and/or restrict the movement of a female for weeks at a time, waiting for her to become sexually receptive. The same pairs have also been observed engaging in intense sexual play with each other. 

[[Georgetown University]] [http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2004/02/07/MNG3N4RAV41.DTL argues] that the common same-sex behavior among male dolphin calves is about bond formation and benefits the species evolutionarily.  They cite studies that have shown the dolphins later in life are bisexual and the male bonds forged from homosexuality work for protection as well as locating females to reproduce with.

== References ==

* [[Bruce Bagemihl]]: ''Biological Exuberance: Animal Homosexuality and Natural Diversity''. St. Martin's Press, [[1999]]. ISBN 0312192398


==Related articles==
*[[Freemartin]]

==External Links==

*[http://www.salon.com/it/feature/1999/03/cov_15featurea.html biologists' view]
*[http://news.nationalgeographic.com/news/2004/07/0722_040722_gayanimal.html National Geographic]
[[Category:Sexual orientation and science]]