Humans are far from the only primates engaging in same-sex sexual activity.
A new study found instances in which 59 nonhuman primate species, including bonobos, chimpanzees and macaques, have taken part in same-sex behaviors.
Researchers observed repeated occurrences of the behavior in 23 species. The study, published Monday in the journal Nature Ecology & Evolution, is the most comprehensive review of same-sex behavior in primates to date (though humans are not included). The findings challenge some common assumptions about the purpose of sex in the animal world, suggesting it plays a broader social role.