Chimpanzees Stick to Gender Stereotypes

The nature vs nurture debate is one of science’s longer-running questions, and it doesn’t seem likely it will be settled any time soon. But a newly-published study shows the issue isn’t confined to the human race.

Sonya Kahlenberg of Bates College, Maine, and Richard Wrangham of Harvard University have published an article in Current Biology showing evidence of a gender divide among young chimpanzees. It’s the first time such a study has been carried out involving chimps in the wild rather than in captivity.

The study, which was carried out over 14 years, considered the way chimps in Kibale National Park in Uganda used sticks for four main activities: to probe holes that might contain water or honey; as a weapon (either thrown, used to strike, or simply brandished); for play; and as a simple object to carry around.

The study found that young females (data shown below with circles) were much more likely to simply carry a stick than males (shown with triangles), but that the divide largely disappeared once the chimpanzees reached their teens.

The researchers’ theory is that the stick carrying is the equivalent to human children carrying dolls. One point backing that idea is that those chimpanzees that simply carried sticks were much more likely to keep hold of them in day-nests than those who used sticks for other purposes. Another was that among females who carried sticks, the practice consistently ceased when they gave birth for the first time.

That latter point may be the most important. Other case studies have shown that young female chimpanzees are much more likely to ape (sorry…) their mother’s behavior than males are, but by definition that can’t be the explanation here. That suggests that young chimps may be learning the action — and that it should be a female action — purely from social norms among their peers, a practice that has normally only been associated with humans.

Male chimps did have their own use for natural resources: as well as being slightly more likely to use sticks as weapons, they were considerably more likely to use leaves to wipe their genitals after copulation.

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