Do Primates have culture?

Based on.... the Japan Monkey Center reports in Primates, vol. 2, vol. 5 and vol. 6, here is how the real story seems to have gone.

Up until 1958, Keyes' description follows the research quite closely, although not all the young monkeys in the troop learned to wash the potatoes. By March, 1958, 15 of the 19 young monkeys (aged two to seven years} and 2 of the 11 adults were washing sweet potatoes. Up to this time, the propagation of the innovative behavior was on an individual basis, along family lines and playmate relationships. Most of the young monkeys began to wash the potatoes when they were one to two and a half years old. Males older than 4 years, who had little contact with the young monkeys, did not acquire the behavior.

By 1959, the sweet potato washing was no longer a new behavior to the group. Monkeys that had acquired the behavior as juveniles were growing up and having their own babies. This new generation of babies learned sweet potato washing behavior through the normal cultural pattern of the young imitating their mothers. By January, 1962, almost all the monkeys in the Koshima troop, excepting those adults born before 1950, were observed to be washing their sweet potatoes. If an individual monkey had not started to wash sweet potatoes by the time he was an adult, he was unlikely to learn it later, regardless of how widespread it became among the younger members of the troop.

In the original reports, there was no mention of the group passing a critical threshold that would impart the idea to the entire troop. The older monkeys remained steadfastly ignorant of the new behavior. Likewise, there was no mention of widespread sweet potato washing in other monkey troops. There was mention of occasional sweet potato washing by individual monkeys in other troops, but I think there are other simpler explanations for such occurrences. If there was an Imo in one troop, there could be other Imo-like monkeys in other troops.

Instead of an example of the spontaneous transmission of ideas, I think the story of the Japanese monkeys is a good example of the propagation of a paradigm shift, as in Thomas Kuhn's The Structure of Scientific Revolutions. The truly innovative points of view tend to come from those on the edge between youth and adulthood. The older generation continues to cling to the world view they grew up with. The new idea does not become universal until the older generation withdraws from power, and a younger generation matures within the new point of view.

It is also an example of the way that simple innovations can lead to extensive cultural change. By using the water in connection with their food, the Koshima monkeys began to exploit the sea as a resource in their environment. Sweet potato washing led to wheat washing, and then to bathing behavior and swimming, and the utilization of sea plants and animals for food. "Therefore, provisioned monkeys suffered changes in their attitude and value system and were given foundations on which pre-cultural phenomena developed." (M Kawai, Primates, Vol 6, #1, 1965).

One smart monkey

Perry and her colleague Joseph Manson, a cultural primatologist at the University of California, Los Angeles, decided to study capuchins in part because these feisty creatures have the highest brain-to-body-size ratio of any primate other than people. "I was interested in finding out what they were doing with these big brains," says Perry, who also has a position at the University of California, Los Angeles.
Their study is the first detailed observation of capuchins' social lives. In the April 2003 Current Anthropology, Perry, Manson, and their colleagues published their analysis of the monkeys' social behaviors. It's based on data collected over 13 years.
They had tracked 13 capuchin troops in four nature reserves, including Lomas Barbudal. Each troop contained 15 to 38 monkeys and had more females than males. More than half of each group was made up of juveniles. "Because they live in multimale, multifemale groups, they have a lot of potential for politics," Perry explains.
The groups selected were geographically close enough to each other to ensure only limited genetic variation from group to group, but they were far enough away so that they didn't ordinarily mix. By comparing notes, the researchers following different troops could check which behaviors were unique to their group. And within groups, they could trace the rise and fall of different behaviors. "The most important aspect of a tradition is that it's transmitted to new practitioners via social learning," Perry explains.

In all, she and her colleagues nominated five conspicuous, lasting behaviors to be considered as social traditions in the monkeys. All of them were playful activities: the hair-in-mouth game; the fingers-in-noses pastime, which the scientists call hand-sniffing; the sucking of a companion's body parts, such as fingers, tails, or ears; a finger-in-mouth game; and a game in which a pair of monkeys use their teeth to pass an object, such as a stick or pebble, back and forth.

"We arbitrarily set a 6-month minimum for a behavior to be considered a tradition," Manson says. "This was a conservative cutoff to be sure that we didn't count as traditions behaviors that were tried only once or twice by a very small number of individuals."
When Perry started following her group, some of the capuchins were already practicing hand-sniffing. After grooming each other, the monkeys would stick their fingers up each other's nose, sometimes poking each other in the eye while doing so. They would then sit together, swaying gently, in what appears to some observers to be a trancelike state. The capuchins "have very long fingernails, and it's probably not very comfortable," Perry says. And having a finger in its nose can make a monkey sneeze. When that happens and a finger is ejected, the partner puts its finger back in place, and the pair continues swaying.

The researchers noticed the hand-sniffing behavior in different monkey groups and often with different practitioners. In some groups, all pairs were females; in others, all were males. "In one group, hand-sniffing faded out and then years later came back in, being performed by different individuals," Manson says.

In another type of behavior, monkeys lie side by side and suck on each other's tail. In a novel iteration of this social convention, one monkey would sit on another's head, and the monkey underneath would suck the top monkey's tail while giving the partner a foot massage. Once a pair of capuchins figured out a configuration they liked, the behavior became routine. Various monkeys have independently invented "funny little mutations of these behaviors," Perry says. Finally, there's the game in which one monkey keeps another monkey's finger firmly gripped in its mouth. The trapped monkey uses its feet and other hand to pry open the captor-monkey's mouth and free the finger. "It's a very slow, methodical, relaxed interaction," Perry says. "They're working hard at getting the mouth open, but not in a frantic way. It's more like they're solving a puzzle."