Something similar may be happening with what we perceive to be homosexual sex in an array of animal species: we may be grouping together a big grab bag of behaviors based on only a superficial similarity. Within the logic of each species, or group of species, many of these behaviors appear to have their own causes and consequences — their own evolutionary meanings, so to speak. The Stanford biologist Joan Roughgarden told me to think of all these animals as “multitasking” with their private parts.
It’s also possible that some homosexual behaviors don’t provide a conventional evolutionary advantage; but neither do they upend everything we know about biology. For the last 15 years, for example, Paul Vasey has been studying Japanese macaques, a species of two-and-a-half-foot-tall, pink-faced monkey. He has looked almost exclusively at why female macaques mount one another during the mating season. Vasey now says he is on to the answer: “It isn’t functional,” he told me; the behavior has no discernible purpose, adaptationally speaking. Instead, it’s a byproduct of a behavior that does, and the supposedly streamlining force of evolution just never flushed that byproduct from the gene pool. Female macaques regularly mount males too, Vasey explained, probably to focus their attention and reinforce their bond as mates. The females are physically capable of mounting any gender of macaque. They’ve just never developed an instinct to limit themselves to one. “Evolution doesn’t create perfect adaptations,” Vasey said. As Zuk put it, “There’s a lot of slop in the system — which,” she was sure to add, “is not the same as saying homosexuality is a mistake.”
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