This one dips a bit hard into the ev psych world, so take it with a grain or two of salt, but reportedly, homosexuality in mammals may have evolved to reduce group conflict. Given that same-sex sexual behavior has been seen in non-mammalian animals as evolutionarily ancient as crickets, that's part of why I'm skeptical.
This:
Dieter Lukas, an evolutionary biologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who was not involved in the new study, was skeptical of this conclusion. “Taken together, the findings in this study have not convinced me that there is a single explanation for the occurrence of same-sex behavior,” he said.
His skepticism came in part from the data on which the scientists based their study. The challenges of observing animals in the wild may mean that same-sex behavior in some species goes overlooked. “It will be much easier to observe whether the behavior occurs if individuals are on open ground and active during daytime,” Dr. Lukas said.
Is a good starting point.
And, per others, those crickets may suggest another answer:
Marlene Zuk, an evolutionary biologist at the University of Minnesota who was not involved in the study, commended the researchers for focusing their study on mammals alone, rather than the entire animal kingdom. “We’re trying to steer way from one explanation to rule them all,” she said.
In April, Dr. Zuk and Jon Richardson, a postdoctoral researcher in her lab, put forward a different explanation for same-sex behavior based on an experiment on crickets. They showed that male crickets will sometimes produce courtship songs and try to mate with other males and with juveniles.
Since the crickets don’t live in social groups, that can’t explain the behavior Dr. Zuk and Dr. Richardson documented. Instead, crickets and perhaps many other species may engage in same-sex sexual behavior as part of a strategy to take advantage of as many opportunities to mate as possible.
Dr. Zuk likened the strategy to a smoke detector. “You want a smoke detector that is sensitive enough to detect all fires,” she said. “And if it does that, occasionally it’s going to go off when you burn your toast.”
Or at least, per Lukas, that there is no single answer.
Another reason to be skeptical? It's a meta-study. They can be good, but overall, no better than the weakest of the individual studies.
Yet one more reason for skepticism? Dean Hamer. Yes, I went there.
In addition, males of many of the species involved generally do NOT form social groups much of the year. Only in winter, for example, do wild ungulates become part of herds, and they're going to be more socialized at that point because they're testosterone-exhausted after the end of their rut.
At a minimum, I think we should say that already existing homosexuality perhaps underwent cultural evolution in some eusocial mammals.
