If you’ve ever been separated from the opposite sex, you’ve experienced something that nearly no other primate species has. For a long time, humans were the only primate species we knew of that ever systematically separates society along sex lines. But now we have a companion in the “boys/girls are gross” world: the spider monkey.
According to Carole Jahme at New Scientist, researchers tracked groups of spider monkeys for nearly two years to try and figure out whether they were really separating their societies by sex. The study they published found that “males and females were significantly segregated in 15 out of the 23 months of the study, and that periods of nonsegregation coincided with months of low food availability.”
In other words, the monkeys only hung out with one another when resources were scarce. When food was plentiful, the males and females wanted nothing to do with one another.
“Males are friendly to each other, spending hours mutually grooming and falling asleep hugging. But they are aggressive towards females and attempt to dominate them,” Jahme writes. Unlike humans, who are just mean to each other out of anger and spite, Jahme says that the monkeys might have other reasons to separate themselves:
Hartwell suggests that males need to expend a lot of energy patrolling their territory and driving off rival males. To keep up their strength, they eat more ripe fruits than females, often chasing the females away from fruiting trees. The females mostly eat less nutritious leaves and travel far less, spending most of their time tending their infants. They may accept the situation because they need the males' protection. "If they are going to have to eat leaves they might as well do so segregated and free of aggression," says Hartwell.
Think of it like this: spider monkey females are basically living together in a feminist commune to escape the aggressive, greedy males.