Girl Monkeys Throw Rocks at Boy Monkeys to Flirt

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In Serra da Capivara National Park in Brazil, she who casts the first stone gets laid: Researchers have observed that female capuchin monkeys throw rocks at their desired males to communicate their readiness to procreate.

First, the female will stalk about the male, looking all nervy and excited and checking in with her girlfriends. Then she's like screw it and she just flings the rock at her favorite cutie. After she throws the rock, she scurries the hell out of there! So, embarrassed, but also a little self-satisfied? Some of these lady-monkeys even run up trees — and the male monkeys follow them.

Researchers reported that the stone doesn't usually make contact with the male, but the two times that they did see the male monkey get hit, he mated with the female that threw the rock at him.

Capuchins (like humans) must perform some sort of mating ritual, since they don't display physical indicators of fertility. But this sort of behavior has never been witnessed in the wild before, say the scientists observing the monkeys. Previously, they reported, females would pout or whine loudly or touch males and run away in order to show their affections. But, as every dating book tells the girl monkeys, the game has changed. If these girl monkeys really want to snag a suitable monkey-mate, they're going to have to pick up the rock.