George Murray Levick, an explorer with the Scott Antarctic expedition, spent the summer of 1911-12 taking detailed notes on the breeding cycle of Adélie penguins. Male penguins, he was surprised to discover, frequently had sex with other males, but this fact was deemed too shocking for inclusion in the official expedition report and it was another 50 years before it was noted in the scientific literature.
Today, same-sex sexual behaviours have been reported in a wide variety of species, but a new analysis suggests a gulf remains between how often it happens and how often we hear about it. A survey of animal scientists found they widely observe, yet seldom publish about, same-sex sexual behaviour in primates and other mammals.
Karyn Anderson, the first author of the survey and a graduate student in anthropology at the University of Toronto, said: “This appears to be due to a perception of researchers that same-sex sexual behaviour is very rare. We found, however, that it was commonly observed by our survey participants.”
Of 65 researchers working on 52 different species, 77% had observed same-sex sexual behaviour, such as mounting or genital stimulation, but only 48% had collected data and just 19% had published their findings, according to the study in PLOS One.
Certain species, such as penguins and Japanese macaque monkeys, have become poster animals for same-sex couplings, but tend to be presented as outliers. The latest analysis highlighted observations of same-sex couplings in many species with no previous reports, including mole-rats, squirrels, mongoose, ring-tailed coatis and various monkeys.
Anderson said the perception that same-sex sexual behaviour was rare in animals had fed into a narrative that it was “unnatural” in humans. “I think that record should be corrected,” she said. “One thing I think we can say for certain is that same-sex sexual behaviour is widespread and natural in the animal kingdom.”
Respondents said they were not influenced by sociopolitical concerns, but many remarked that journals appeared biased against publishing anecdotal reports compared with systematic studies.
Josh Davis, of the Natural History Museum in London and author of A Little Gay Natural History, said: “Around 1,500 species have been observed showing homosexual behaviours, but this is certainly an underestimate because it’s seen in almost every branch of the evolutionary tree – spiders, squids, monkeys.
“There’s a growing suggestion it’s normal and natural to almost every species,” he added. “It’s probably more rare to be a purely heterosexual species.”
Prof Paul Vasey, a psychologist at the University of Lethbridge in Alberta, has been studying female homosexual behaviour in Japanese macaques for more than three decades. “I can say with certainty that in some populations, such as the one I study, female homosexual behaviour occurs relatively frequently,” he said, adding that in many species it is probably less common and hard to study quantitatively.
In the past, same-sex sexual behaviours were often framed as a “Darwinian paradox” – apparently contradicting the evolutionary pressure to survive and reproduce. There is growing evidence, however, that some same-sex sexual behaviours can have evolutionary advantages. In black swans, male-male couples frequently court each other, steal eggs, raise chicks together and are more successful in ensuring these chicks’ survival than heterosexual swan pairs.
Julia Monk, an ecologist at the University of California, Berkeley, said animal behaviour can become a prism through which humans attempt to make sense of their own natures. “I don’t believe we should be bound by what animals do or don’t do to set norms for human behaviour,” she said. “But I do think it’s important to better investigate how animals live, and question how much our understanding of the natural world has been limited by our own social imaginations.”