Which macaque species is famous for washing sweet potatoes?

The Japanese macaque is the macaque species famous for washing sweet potatoes. At Koshima Island in Japan, researchers observed a young female macaque washing sandy sweet potatoes in water before eating them.

The female, named Imo—which means “potato” or “yam” in Japanese—was first observed performing the behavior in 1953. Other members of her troop gradually copied the technique, and the behavior spread through the group. Some macaques even dipped cleaned potatoes into seawater, producing a salty food that observers sometimes describe as “seasoned.”

This episode became a classic example of social learning and animal culture: a behavior was invented by one individual and transmitted through observation rather than inherited biologically. The story is sometimes connected to the “hundredth monkey” claim, which suggests that a behavior suddenly spreads once enough animals learn it. That dramatic version is not supported by the original Koshima observations, which showed gradual social diffusion.