The misunderstood monkey; primates, potatoes and cultural evolution

The Misunderstood Monkey Primates, Potatoes, & Cultural Evolution

THE STORY OF THE HUNDREDTH MONEKY originates from Lyall Watson's non-scientific interpretation of "potato washing," a cultural behavior discovered in the Japanese macaque monkey. There is nothing mysterious about what happened in the transmission of potato washing behavior among Japanese monkeys, despite what Watson leads people to believe in his book, Lifetide. On the other hand, much that may prove to be genuinely applicable to human cultural evolution has been learned from the study of Japanese macaques.

The true significance of potato washing is that it was the first evidence for the existence of culture in nonhuman primates. Rubbing off dirt or snow from roots and other soiled foods is common behavior among all Japanese monkeys and most other terrestrial primates. Such behavior is identical to potato washing, only without the water. The potatoes used in the early days of provisioning (from which the Hundredth Monkey story arises) usually came directly from the field and were still quite soiled when given to the monkeys. Before attempting to eat these potatoes, the monkeys brushed off the dirt. All it took was for some young, curious, and inventive individual to take the potato to water (perhaps initially only in play) to see that the dirt fell off easier when wet than when simply rubbed.

Koshima Island was an exceptional site for this because the troop of monkeys was provisioned on a beach with enough room for each to have access to the water while feeding, thus more chances to observe and imitate one another, and to apply what they had learned. The necessary condition of water in the feeding area was also present in study area other than Koshima (see map), thus allowing the opportunity for other monkey populations to innovate potato washing. However, these sites were on mountain slopes and the sources of water (ponds and streams) near the feeding areas were considerably smaller than the beach at Koshima. This is one of the obvious reasons why the behavior never spread to many individuals in these other troops -- the chances of potato handling occurring near a body of water were much less than at Koshima.

Watson appears to have been impressed by the fact that the potato washing behavior was observed in places geographically isolated from each other. But the occurrence of novel behaviors like food washing in populations completely isolated from each other has been repeated time and time again. In 1985, J. Scheurer and B. Thierry reported the food washing tradition of a group of Japanese monkeys in the Burgers' Zoo in Holland. The making of snowballs by young monkeys to use as play objects can be seen at Shiga-kogen in Nagano prefecture, and the same behavior was also reported by G. Eaton in 1972 for a group of Japanese monkeys at the Oregon Primate Research Institute. The Oregon troop was imported from a site outside Hiroshima.

In my own field research here in Japan, I came across (and reported in The Journal of Human Evolution) another example of this manipulation of objects for play, a behavior I call stone-play. This behavior has been observed at Arashiyama, Takasakiyama and Takagoyama (see map). Like potato washing, it has become a cultural behavior passed down from older to younger individuals as a form of tradition.

Until December 1979, monkeys were not seen to play with stones at Arashiyama. Apparently the behavior started at Takasakiyama in 1978 or 1979, as I first recorded the behavior there the same month I first saw it at Arashiyama, and the park employees responsible for feeding the monkeys at Takasakiyama said they had seen the behavior occasionally that year, but not much earlier. Stone carrying had been observed at Takagoyama in 1974 and reported by M. Hiraiwa in 1975. Members of the group of Japanese monkeys in Oregon have also been reported to carry stones.

At Arashiyama, the first individual I saw stone-playing was a three-year-old female named Glance-6476. By 1983, stone-play was a common behavior among the young monkeys of the group. The stones could be easily found around the feeding area. During this time 115 (49 percent) of 263 monkeys were seen to exhibit the behavior of stone-playing. Of these individuals, 80 percent were born between 1980 and 1983, after the behavior was first innovated. The remaining 20 percent were slightly older individuals that learned stone-play while they were younger, shortly after it had been innovated.

Among these were female relatives of Glance-6476 and their childhood playmates. Unlike other previously studied cultural behaviors, stone-play was never transmitted to adults. This is likely due to the fact that it is a play behavior, and adults are rarely seen to play.

Initially, the behavior was transmitted between young females of the same family and then on to playmates of the same age from other families. The speed of diffusion increased greatly when younger playmates, siblings, and one's own offspring began to acquire the behavior. The youngest monkeys I have seen play with stones at Arashiyama were 40 days old.

In the spring of 1984, I classified stone-play into a number of basic types of behavior: gathering, picking up, rolling in hands, clacking, carrying, and cuddling. Some behavioral types involve making noise by clacking stones together, rubbing them on top of larger stones, or scraping them on the tin roof of the research station. As long as the stimulus to perform the behavior is present, it will continue to be passed on from generation to generation through the normal process of imitation and social facilitation.

It is interesting to note that not only can the same behavior appear simultaneously in geographically isolated areas as a response to the same environmental stimuli, but the same behavior can reappear in the same group after having been lost. Stone-play is an example of this. Eiji Ohta, an educator and naturalist in kyoto, was one of the first people to observe the troop of monkeys at Arashiyama before they were provisioned. At this time the monkeys were still hard to observe for long periods of time as they were not yet used to humans. In the troop's old range were several citrus trees of the species Poncirus trifoliata. The small four-centimeter-in-diameter fruit was not eaten by the monkeys, but on a few occasions, Ohta saw some monkeys collecting, carrying, and scattering about the fruits as they now do with stones. AFter the troop was successfully provisioned, their range shifted and they no longer frequented the area containing these trees. Prior to 1979, when stone-play was first observed, such play behavior had not been reported.

When I first visited Koshima in 1979, potato washing appeared to be dying out, as chances for the young to observe and imitate the behavior were few, and the potatoes were no longer as dirty as they were, apparently, in the early days. Since 1972, provisioning at Koshima has been gradually discontinued, occurring only occasionally during the summer months. Potatoes are frequently replaced by wheat and soy beans.

What is the possible significance of such phenomena? Stone-play and potato washing are similar in that they both originate from behavior already present in the behavioral repertoire of the monkeys as a species. That is, monkeys have the propensity to brush off and manipulate objects. While potato washing had an immediate practical application (i.e., to clean off dirt), stone-play appears to be a means to no end. Or is it? Dr. Duane Quiatt, of the University of Colorado, and I think this may be of significance in understanding the evolution of stone tool use. Environmental opportunity brought about the right circumstances for potato washing to emerge and then to fade away. Stone-play in its present state is at most a form of play behavior. In its earlier form, the behavior was performed in the forest with soft fruits. Now, with stones in a new setting, the behavior has reappeared and spread. As the monkeys become more familiar with stone and its properties, the chances for it to be used as some form of tool increase. We propose that stone-tool use depends on a foundation of free, noninstrumental manipulation of stones. That is, play with stones is a prerequisite for stone-tool use. Through the mechanisms of innovation, diffusion, and tradition, the use of stone as a tool becomes possible. We are not implying that these monkeys will start making stone tools. We simply suggest that this model can provide an approach to understanding the selective events we must keep in mind when considering the evolution of stone-tool use and stone-tool manufacture when applied to early hominids, or even chimpanzees.

Since the behavior first started at Arashiyama, six years have passed, and stone-play is still quite popular. With each birth season comes a new group of "stone-play initiates," and the behavioral repertoire of stone-play has increased. With approximately 20 variations on the old behaviors, the creative and playful young monkeys are continuously experimenting with the properties of stone. To date I have seen stone-play remotely resemble tool use only once, and that may not have been intentional. The shell of an acorn was partially removed after rubbing it together with a stone, and the nut inside was then eaten. Let us hope the monkeys continue their progress in stone-play toward peaceful purposes only!

COPYRIGHT 1986 Point Foundation
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