Do Japanese monkeys season their food?

Let's say you're dining with friends at a pizzeria, and one person orders a pie with anchovies. You've never tried anchovies, but you turn up your nose at the odorous fish. When the pizza comes, your friends devour the anchovy slices. Observing their positive reactions, you decide to live a little and take a bite. The next time you eat pizza, you take yours with anchovies as well.

A similar type of behavioral learning through social interaction happened in a group of Japanese monkeys on the island of Koshima in the 1950s. Researchers were studying the macaques and to lure them into the open to better observe their behavior, the researchers gave them sweet potatoes.

Usually, the monkeys would brush excess dirt off the potatoes with their hands before eating them because the grit hurt their teeth. But one day in September 1953, a female the researchers named Imo took the rudimentary potato cleaning a step further by washing hers in a freshwater stream. Five years later, six out of nine members of Imo's family practiced the same potato-washing habit [source: Carpenter]. By 1965, not only had the washing habit been passed to new generations of the macaques, but they also had started rinsing with saltwater instead of freshwater. The monkeys would repeatedly dip their potatoes in the water, then take a bite, implying that they enjoyed the salty flavor. For that reason, researchers suspected that the purpose behind the saltwater habit had evolved from merely cleaning the potatoes to actually seasoning them.

Lead researcher Masao Kawai published the findings in 1965 in the journal "Primates," under the title "Newly-acquired pre-cultural behavior of the natural troop of Japanese monkeys on Koshima islet." Notice there's nothing in that heading about food. That's because the monkeys' acquisition of a taste for salt was merely a byproduct of what had unfolded. Rather, the social learning in macaque troops garnered attention because it implied that monkeys are capable of creating basic cultural practices.

Taking a closer look at how the saltwater-dipping custom caught on throughout the macaque family uncovers other clues at the development of the novel habits. Read on to learn the details of how the potato seasoning spread in the macaque troop.

Imo's mother Eba was the first to mimic the potato washing. Females in the troop were more likely to wash their sweet potatoes than older males. Remember that when they become old enough to mate, male macaques leave the troop, meaning they have less social interaction with their original troop members. Without that integral social interaction and exposure to the new behavioral patterns in a group setting, the older males didn't pick up the habit [source: Carpenter].

Age also played an important role in whether monkeys would wash their potatoes. In general, monkeys younger than the age of two were quicker to try something new. This is because of the inverse relationship between age and brain plasticity -- the brain's ability to create new neural connections required for learning -- which allows us to acquire new skills. Additional behavioral studies with macaques correlated with this age gradient, as the youngest members show the most innovation and least conservatism.

A similar adaptation pattern occurred when testing if the monkeys would try caramel candy. The juvenile and infant macaques paved the way as they were the first ones to eat the candy that researchers gave them. Adults followed suit, as an example of observational learning in monkeys.

The sweet potato washing remained confined to the one macaque troop on the island of Koshima [source: Baumeister]. Nevertheless, Imo's clever idea sparked a novel way of thinking about how animals interact. For more information about monkeys, visit the links on the next page.