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The Japanese macaque is an intelligent species. Researchers studying this species at Koshima Island in Japan left sweet potatoes out on the beach for them to eat, then witnessed one female, named Imo (Japanese for yam or potato), washing the food off with river water rather than brushing it off as the others were doing, and later even dipping her clean food into salty sea water. After a while, other members of her troop started to copy her behavior. This trait was then passed on from generation to generation, until eventually all except the oldest members of the troop were washing their food and even seasoning it in the sea. Similarly, she was the first observed balling up wheat with air pockets and soil, throwing it all into the water, and waiting for the wheat to float back up free from the soil in order to consume it. An altered misaccount of this incident is the basis for the “hundredth monkey” effect. That behavior also spread among her troop members.
⇒ Imo
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In 1948 three Japanese scientists initiated long term research into wild Japanese macaques (Macaca fuscata) on Koshima Island. They began leaving food on the sandy beaches for the monkeys to draw them out of the forest in an attempt to study behavior. Some of these prizes were sweet potatoes. The macaques would wipe the sand off the potatoes and eat them readily. In September of 1953, an 18 month old macaque the scientists named Imo washed her potato in a river instead of wiping the sand off with her hand. Imo must not have liked the taste or texture of the sand and her intelligent approach to solving a problem impressed the scientists.
Then something amazing happened.
Imo taught her siblings how to do the same thing. Imo also taught her parents how to wash the potatoes. For offspring to teach behavior to their parents is highly unusual in nature. But Imo did just that. Imo even began taking her washed sweet potatoes to the ocean and dipping them into the water before each bite. Apparently Imo liked the taste of salty potatoes even better than simply clean ones.
Soon the behavior spread and a community changed forever.
Over time, the troop adopted this behavior and all but the oldest monkeys washed their food before they ate. In 1958, only 18.1%of adults had adopted the behavior but the younger macaques adopted it across 78.9%of the population (Hirata, Watanabe, Kawai, 2001, p490). By 1962, the vast majority, 73.4% of ALL monkeys in the troop over 2 years old washed their potatoes. Only a very few of the oldest monkeys had not adopted the behavior. Now, all of the macaques on Koshima Island wash their potatoes.