According to Darwin, the sexual impulses of animals are designed to cause reproduction, and are therefore necessarily heterosexual.
But recent research suggests that homosexual animals – often dismissed by biologists as the exceptions that prove the rule – may be more common than previously thought.
Some biologists claim 'gay' animal behaviour has been spotted in 1,500 different species, and reliably recorded in a third of these cases – roughly 450 species.
Animals that have displayed homosexual behavior include emus, chickens, koalas, salmon, cats, owls and dolphins. According to research, about a fifth of captive king penguins are gay and it is common for male black swans to raise cygnets as a couple – possibly to provide better protection.
Zoologist Petter Bockman, an expert on the subject at the University of Oslo, dismisses those who draw political implications from the scientific findings. He says: “If you ask: ‘Can animals be gay?’ The short answer is: ‘Yes.’ ‘Gay’ is a human word, however, so we prefer to use the word 'homosexual' for animals. Sexuality is not just about making babies, it is also about making the flock work. For some animals, homosexuality is normal flock behaviour.”
He says the issue has long been taboo for researchers who are “fearful of being ridiculed by their colleagues.”
Farmers often come across bulls and rams that simply refuse to mate with females, he claims, and, in 2004, Charles Roselli at the Ohio Health and Science University reported that about eight percent of domestic rams prefer other males.
Bockman curated an exhibition, Against Nature's Order, for the Norwegian Natural History Museum. One Pentecostal minister told him he would 'burn in hell' for his work. Another said the money would be better spent 'curing gay animals'.
Why do animals indulge in homosexuality?
There are many reasons. In tribal animals, homosexuality sometimes takes on a social role – occupying unwanted males or bonding male members of the pack.
In other species, the reasons are less clear.
“Birds are really complicated,” says Bockman. “What goes on in birds' brains is anyone's guess.”
Male black swans will often bring up cygnets together, involving females only in the initial breeding process. This could be because males are better able to protect the young.