Why Are Baboons But Red?

February 15, 2024

The red bottom of the baboon is a sign that it’s time for mating. But that doesn’t mean it’s all about sex, scientists say.

The bottoms of female monkeys and other primates, including chimpanzees, experience sexual swellings—enlarged red butts—which indicate fertility. The swellings occur during a period of ovulation that lasts for 32 to 37 days, when the female’s estrogen levels are at their highest.

Until recently, it was believed that the size of a female’s swollen buttocks would affect her ability to reproduce and successfully rear offspring through infancy—that is, bigger buttocks meant healthier babies. However, the latest research involving baboons shows that this is not necessarily true.

In a 2105 study published in Animal Behaviour, researchers found that swollen rumps didn’t have much of an effect on infant survival once other factors were taken into account. For instance, baboon males seem to be more interested in how long it’s been since a female had her last baby than she has in her top size—even though the latter is also an important indicator of pregnancy potential.

Like other primates, baboons live in social groups called troops. Unlike human families, which typically live together all the time, baboon troops are organized into hierarchies of dominance and rank. In addition to competing for resources, troop members also spend endless hours grooming each other to remove ticks and parasites, which can cause disease. Males use shows of physical strength to establish their status and control troop members, including females, but they rarely physically fight each other.


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