More 'gay' animals - and why they exist

Homosexual behavior has been documented in so many species that many scientists believe it is universal within the animal kingdom.

Last year a post of mine '11 'Gay' Animals' for Care2.com was my most viewed ever, being the most read for six weeks and attracting nearly 500 comments. When the site did a rejig last year I got dropped with many other writers so this follow up was never published. A friend picking up on the original inspired me to drag it out. So here's another 11 for you, starting with the most familiar: Homo Sapiens.

Homosexuality in humans has been documented for thousands of years, but we still have no final explanation as to why it occurs and how it develops.

We know that there are a number of features which distinguish homosexual human beings from heterosexuals. Studies have discovered some very odd distinctions -- like finger-length and hair swirl and even penis thickness. The existence of young children who are apparently gay or lesbian has come much more to the fore in recent years, as have transgendered children, suggesting that a "born this way" theory is on the right track.

Research has pointed at a number of possible biological causes with immunology currently a favorite because such traits are known to be influenced in utero. In any family, the second-born son is 33 percent more likely than the first to be gay, and the third is 33 percent more likely than the second, and so on, as though there is some sort of “maternal memory.”

Hypothetical mechanisms include an alteration in the flow of male hormones in the formation of boys and female hormones in the gestation of girls. Why? It could be germs, genes, maternal stress, and even allergy.

In this interview with the renowned evolutionist Richard Dawkins, Dawkins explains how evolutionists have a few theories for why human homosexual behavior would be favored in natural selection, they includes the 'gay uncle theory'. Here, gay members of a group help look after children, increasing the group's survival chances. This is also the case with many other species where non breeding members of a group help raise, for example, pups or other bees. Anthropologist Sarah B. Hrdy argues that for much of human history children were raised by groups, not just their parents alone.

Another is that a 'gay gene' we find now may have operated differently in another environment. An analogy would be how in hunter-gatherer times a gene that stores energy as fat quickly and efficiently during the rare times of abundant food may have been advantageous; genes that helped people fatten quickly would have been favored by selection. But now those same genes aren't so useful, because food is always abundant -- at least in the wealthy parts of the world -- and so people with these 'thrifty' genes are especially prone to diabetes and obesity.

Another theory is that a 'gay gene' could have a double function, just as the gene variant for sickle-cell anemia is maintained because it reduces the severity of malaria. It could be that the gene that causes men to become homosexual also makes women better at reproducing. Women with that gene would have more children than other women, and even though some of their sons become homosexuals who do not reproduce, they would still have enough heterosexual daughters to carry the genes on.

Studies of twins strongly suggest that such a gene does exist, but we are still to definitively idetify it.

Many societies, such as Polynesia's, have clear and approved roles for 'gay' sons and 'lesbian' daughters and throughout history priests and shamans have often been 'gay'. Richard Lippa, a psychologist from California State University, has found cross-cultural confirmation that gay men and lesbians tend to take up certain sorts of job and have common other stereotypes. This suggests that homosexuality evolved and persists in humans because it benefits groups or relatives, rather than individuals, like how in bonobo chimpanzee society, homosexual behavior has benefits at a group level by promoting social cohesion.

Biologists looking at the rest of the animal kingdom are trying to explain the apparent evolutionary advantages of homosexual behaviour. Researchers Nathan Bailey and Marlene Zuk provide a variety of possible answers in their short paper Same-Sex Sexual Behavior and Evolution (pdf). They give numerous examples of how same-sex sexuality appears to benefit various species.

After the jump read more about dolphins, elephants, flamingos, koalas and orang-utans.