When and why did masturbation evolve in primates? A new study provides clues

The behavior may help males be fertile and disease-free. But data on females are lacking

A photo of a male Japanese macaque sitting on a rock with a blurry forest in the background.

Low-ranking male Japanese macaques (Macaca fuscata) masturbate more frequently than dominant males to ensure their sperm are fresh and healthy when they get the rare chance to mate. A new study looks at the evolution of masturbation across primate species.

mochida1970/Moment/getty images

Though masturbation is common across the animal kingdom, it seems, at its face, to be an evolutionary paradox: Why would an animal waste time, energy and reproductive resources on self-pleasure instead of copulating with a partner?

Studies on individual species have found some explanations.