When it comes to same-sex sexual behaviour, scientists need to keep an open mind.
It’s widely recognised that the animal kingdom is full of male-on-male and female-on-female action, from fruit flies to bottlenose dolphins and, of course, Homo sapiens. But though the origins and evolutionary consequences of homosexuality are varied, biologists tend to oversimplify such behaviour, according to University of California at Riverside biologists Nathan Bailey and Marlene Zuk.
Beyond searching for mechanistic explanations in simple creatures like fruit flies — who rely on smell to recognise each other, and aren’t very good at it — biologists have focused on homosexuality as a paradox, write Bailey and Zuk. They’ve tended to explain homosexuality as an adaptation that serves to strengthen social bonds, reduce sexual competition and refine mating technique.
(A few particularly arresting examples: male dung flies are believed to mate with other males simply to occupy their time, thus denying them a chance to reproduce; small male Goodeid fishes camouflage themselves as female, and mate with females while males pursue them. And young fruit flies seem to do better at heterosexual mating once they’ve had some same-sex practice.)
Such explanations are sometimes useful, but only to a point. In the Laysan albatross, for example, where monogamy is common but females outnumber males, nearly one-third of all couples are female-female pairs. They’re better at rearing chicks than single females, and their coupling reduces the likelihood of single females luring married males from the nest.
Homosexuality benefits the Laysan albatross community at large. That’s also one possible consequence, albeit unmentioned in this study, for human homosexuality. Perhaps communities in which some non-reproducing, same-sex-preferring members devoted their energies to caring for unrelated individuals have historically been healthier than those in which heterosexuality was absolute.
Citation: “Same-sex sexual behavior and evolution.” By Nathan W. Bailey and Marlene Zuk. Trends in Ecology & Evolution, Vol. 24, Iss. 7, July 2009.