All primates - Japanese macaques included - have a unique culture. Here, culture is taken to mean behaviour which is copied, not genetically prescribed. The Japanese macaque culture dictates that the monkeys wash their food.
In 1953, one single Japanese macaque (Macaca fuscata) was seen washing his food before eating it. This one monkey rinsed a sand-covered potato in the sea, and within a few months others in his group had taken on the behaviour. In ten years’ time, all members of the group were washing their food. The Japanese Macaques in Artis Royal Zoo also wash their food even when it is not sandy: this behaviour has become a habit – a tradition of the Japanese macaque culture.