"Hot Tub Monkeys" Offer Eye on Nonhuman "Culture"

Bijal P. Trivedi
National Geographic Channel

February 6, 2004

When Japanese macaques (Macaca fuscata) began receiving food handouts more than 50 years ago— freeing them from the daily grind of foraging for food—they invented "cultural activities" to fill their newly acquired leisure time, researchers say.

Stone-play, hot-tubbing in volcanic springs, and potato and wheat washings have all become mainstay behaviors within various troops of macaques around Japan that are still given daily food provisions at research stations. Half a century later many of these behaviors persist and are the subject of studies exploring nonhuman primate culture.

In 1979, during a 14-month stay at the Arashiyama macaque study site, Michael Huffman, a primatologist at the Primate Research Institute (PRI) at Kyoto University, noticed one female monkey playing with stones. "I had never seen, or heard about, anything like it. It was like a child playing with building blocks."

When Huffman returned to the site a few years later in 1983 he was astounded by what he saw. "Half the group was playing with stones, banging them on nearby roofs and making a total racquet," said Huffman. "I couldn't understand why a behavior that seemed to have no adaptive significance—it didn't provide an edge for survival or reproduction—could spread through a group and be maintained in a society for so long."

New Monkey Traditions

Japanese macaque studies began in 1948 when scientists visiting the southern Japanese island of Koshima, encountered a troop of wild monkeys. To facilitate observation they lured the creatures out of the forest with rations of sweet potatoes and wheat.

With these daily handouts, and more free time, the macaques began to invent new behaviors.

The great innovator within the Koshima troop was a one-and-a-half year old infant female named Imo. In 1953, Imo was the first to begin washing the sweet potatoes. She passed the behavior to her mother and it slowly began to spread. A decade later, potato washing had become a fixed behavior in the troop. Most newborns picked up the skill quickly. By 1962, about three quarters of Koshima monkeys over two years old washed their food.

Imo's second feat of genius was to develop a method for sorting wheat from sand. Imo discovered that rather than eat the wheat handouts grain by grain, a mixture of wheat and sand could be dropped in water allowing the wheat to float and the sand to sink. Within several years many of the younger monkeys practiced this behavior.

When behaviors or innovations are adopted by other members of the group, passing from parent to offspring, infant to parent, or adult-to-adult, a "culture" or tradition is born, said Satoshi Hirata, a primatologist and a colleague of Huffmans at PRI.

"Culture and innovation are often ways of adapting to environmental changes, or a response to a change in lifestyle," said Huffman, who studies both chimpanzee and macaque behavior.

Hot Tub Monkeys

In the 1950s, Japanese macaques of the mountainous Shiga Heights region, also known as snow monkeys, took advantage of a beneficial environmental change: humans altered the temperature of some volcanic hot springs to make the water more comfortable for bathers. The snow monkeys, taking a cue from their human cousins, began to partake in the hot tub experience.

"Humans could survive with fur around their waist, but it is a lot nicer with a fire and a couch," said Huffman. So, too, the macaques adapted to the change, making the harsh winters a little more tolerable by sitting in the hot tub.

Many cultural differences, independent of human interference, have been observed between monkey troops living around Japan. The troops differ in eating habits; for instance, monkeys in some regions eat bird's eggs. Social behaviors between macaques from disparate regions also vary; only in some troops do males engage in paternal care for infants. In other troops social rank is sharply defined; males behave more aggressively towards one another.

After 50 years of observation, primatologists believe that macaques have an established culture: invented behaviors passed from one monkey to another.

Huffman, and his posse of graduate and post-graduate students, have been studying stone handling behavior at three sites in Japan since 1979. The macaques, according to Huffman, seem fascinated by the sounds that the stones make when the rocks are hit together.

"People smoke or fiddle with prayer or worry beads in their leisure time," said Huffman. "Stone handling is a similar situation." Stone handling suggests that animals, other than humans, can have activities that just make them feel good and keep their hands busy, he added.

Monkey Culture—A Basis For Human Culture?

"Stone handling is particularly fascinating because it doesn't seem to have any function, it doesn't seem like a useful thing to do, so it is more convincing that this behavior is being passed on through social learning," said Andrew Whiten, an evolutionary psychologist at the University of St. Andrews in Scotland. Whiten is co-leader of an international effort to compare variation in chimpanzee cultures across a dozen study sites in Africa.

Activities like potato and wheat washing could have a potential nutritional benefit, and hot-tubbing could be said to confer survival advantage because it helps the animals stay warm. But stone play seems just recreational.

The behavior only appears to emerge when the monkeys are given regular handouts. When the provisions stopped at the Takagoyama, for example, leisure time diminished, and so did the stone handling.

Currently Huffman is investigating stone handling in wild monkeys and comparing their cultures with those of captive macaques at the PRI. Already he has observed that the captive group has a much broader range of stone handling behaviors—40 distinct activities compared with 17 in the Arashiyama group.

Some of the richest cultural variation, in nonhuman species, has been observed in chimpanzee populations. Chimps seem to have about 40 distinct traditions spanning tool use, social grooming, courtship, food choice and handling, and sexual behavior—which seem to mirror the range of cultural differences in humans. Orangutans have been documented to have about 25 traditions, said Whiten.

In the last 30 years these results have challenged the idea that culture is a unique hallmark of human society, said Whiten. "It will be very interesting to get similar data for macaques and other monkeys."

Human culture is transmitted through language and the written word; individuals are taught in detail how to do something through teaching and imitation. With nonhuman primates like macaques, the learning process occurs through observation.

Monkey culture is definitely not the same as human culture, said Hirata. But by studying the monkeys "we see an evolutionary basis for our culture," he said. "These monkeys are similar to humans because they take an interest in the behavior of other individuals—which is vital for the development of a culture."

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