Animal sexual behavior takes many different forms; even within the same species, researchers have drawn parallels between this and homosexuality, bisexuality, intersexuality and transgender behavior in humans.

Contents

1 Homosexuality 2 Cross species sex 3 Specific species 3.1 Bonobo apes 3.2 Birds 3.3 Lizards 3.4 Sheep 3.5 Spotted Hyena 3.6 Bottlenose Dolphins 4 References 5 Related articles 6 External Links

Homosexuality

The presence of same-sex sexual behavior was not 'officially' observed on a large scale until recent times, possibly due to observer bias caused by social attitudes to same-sex sexual behavior. It appears to be widespread amongst birds, mammals and the apes. Some researchers believe it to have its origin in male social organization and social dominance, similar to the dominance traits shown in prison sexuality.

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. However, this from of cross-species sex only occurs with animals in captivity (such as the zoo), and does not occur in the wild

Examples:

• Antelope and Zebra [1] (http://nacho.princeton.edu/fowler/joshua/year2/dec1_zoo/antelope_humping_zebra.jpg) (however, this takes place in a zoo and thus may not be an accurate representation of natural behavior)
• Dog and Cat [2] (http://img.lj.com.ua/dashing/1218_cat_dog.jpg)

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 normally fertile. Novosibirsk zoo director Rostislav Shilo says on the liger (born in its zoo); “It’s just that the lion and the tiger live in neighboring caves in the Novosibirsk zoo, and got used to each other. It’s practically impossible in the wild.”

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

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 reported a male pair of chinstrap penguins in the Central Park Zoo in New York City were partnered and even successfully hatched a female chick from an egg.[3] (http://query.nytimes.com/gst/abstract.html?res=FA0C1EF83A5F0C748CDDAB0894DC404482) Other penguins in New York have also been reported to be forming same-sex pairs.[4] (http://www.jrn.columbia.edu/studentwork/cns/2002-06-10/591.asp)

Lizards

Whip-tailed lizard females have the ability to reproduce through parthenogenesis and as such males are rare and generally disdained (from a Darwinian standpoint the females are passing their full genetic code to all of their offspring and do not want it compromised by sexual reproduction), the females engage in sexual behavior to stimulate ovulation. Certain species of gecko also reproduce by parthenogenesis.

Sheep

In October 2003 a study [5] (http://endo.endojournals.org/cgi/content/abstract/145/2/478) 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 their brain which they called the "ovine Sexually Dimorphic Nucleus" (oSDN) which is two times smaller than the corresponding region in heterosexual male sheep.

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." Read the abstract of the study. (http://endo.endojournals.org/cgi/content/abstract/145/2/478) It is possible but unproven that this hypothesis could apply also to humans.

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. This has generally been described as being "highly sexual", rather than bi-sexual.

References

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

Related articles

• Freemartin

External Links

• biologists view (http://www.salon.com/it/feature/1999/03/cov_15featurea.html)
• [6] (http://news.nationalgeographic.com/news/2004/07/0722_040722_gayanimal.html) National Geographic