I couldn’t imagine how chimps managed this evolutionary leap. But then, I couldn’t imagine what they were actually doing. Using blades of grass to tickle one another? Building heart-shaped beds of moss? Using stones for massages, or vines for bondage, or — well, I really had no idea, so I called Dr. McGrew, who is a professor at the University of Cambridge.
The tool for sex, he explained, is a leaf. Ideally a dead leaf, because that makes the most noise when the chimp clips it with his hand or his mouth.
“Males basically have to attract and maintain the attention of females,” Dr. McGrew said. “One way to do this is leaf clipping. It makes a rasping sound. Imagine tearing a piece of paper that’s brittle or dry. The sound is nothing spectacular, but it’s distinctive.”
O.K., a distinctive sound. Where does the sex come in?
“The male will pluck a leaf, or a set of leaves, and sit so the female can see him. He spreads his legs so the female sees the erection, and he tears the leaf bit by bit down the midvein of the leaf, dropping the pieces as he detaches them. Sometimes he’ll do half a dozen leaves until she notices.”
And then?
“Presumably she sees the erection and puts two and two together, and if she’s interested, she’ll typically approach and present her back side, and then they’ll mate.”
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