Culture in nonhuman primates

In 1953 a young Japanese monkey named Imo did something remarkable. Her troop lived on Koshima Island in Japan, and was provisioned by Japanese researchers who studied them. Provisioning involves providing additional food to sustain the population in areas of limited resources or to encourage animals to remain in a particular locale for observation. Imo's group was provided with sweet potatoes placed on the sand at the edge of the water. Imo began to use the nearby water to wash sand from the sweet potatoes. This behavior spread through the group, with younger animals adopting it first and some older animals never adopting it. Four years later, Imo introduced another novel behavior. The monkeys were provided with grains of wheat scattered on the sand that were difficult to eat because they mixed with the sand. Imo placed handfuls of this mixture of wheat grains and sand into standing pools of water. The wheat grain floated to the top and could be scooped up and eaten, free of sand. Years and generations later the monkeys of Koshima Island continue to wash sweet potatoes and to place sandy wheat grains in water. The spread of these novel behaviors through individuals in the group appeared to be an instance of social transmission of a novel behavior. This interpretation began a discussion of culture in nonhuman primate groups.

Recent analyses of behaviors shown by communities of chimpanzees and of orangutans suggest the presence of cultural variations across groups within each species living in different geographical areas. Behaviors that varied included instances of tool use, social behaviors related to grooming or

communicative signals, and food-related behaviors. For example, some chimpanzee communities crack nuts with hammer and anvil tools, but others do not, despite the availability in their environment of hard-shelled nuts and objects that could serve as tools for nutcracking. The absence of a behavior pattern in the presence of all necessary components (e.g., nuts and potential tools) rules out ecological factors to explain these differences. Similarly, genetic factors do not play a role in the variability of such behavior patterns. That is, a similar pattern of tool use may be shown by two groups who are genetically isolated from one another, or it may be present in one community but missing in another community of the same genetic background. Some form of social learning is thought to have promoted the spread and maintenance of these specific behavior patterns within certain communities.

Even in a species that is not typically group living, cultural differences are found across geographical areas. Orangutans observed in Sumatra use tools constructed from sticks to pry the seeds from Neesia fruits, a fruit with a very tough husk that also has spiny hairs protecting the seeds. Bornean orangutans do not use tools to acquire the seeds; rather, they tear a piece of the husk open to expose seeds. Only adult males can perform this latter method because of the strength required to force open the fruit. Otherwise, females and juveniles must wait until the husk opens and older, less desirable seeds are naturally available. Geographic isolation leading to a genetic basis for these differences in technique is not a sufficient explanation. At a second Sumatran site orangutans do not use tools, ruling out the genetic explanation. Neesia is available to and eaten by orangutans in both Sumatra and Borneo, eliminating an ecological explanation. Social transmission through social learning is the most likely explanation for this phenomenon, through mother-offspring transmission and/or through social encounters among animals inhabiting the same area.

Social learning can occur at several levels, from simple to complex, all based on observation of one animal by another. Most simple is social facilitation in which one animal's interest in an object elicits interest in that object from another animal. By drawing another's interest to an object that the other then explores, the first animal has influenced the behavior of the second but has not explicitly transferred information. In observational learning, the observer learns something specific about stimuli and responses from watching another animal. Imitation is the most cognitively complex form of social learning and involves the observer copying the form and intent of a novel behavior demonstrated by another animal. Imitation is distinguished from a similar form of social learning termed emulation, in which an animal performs actions similar to another, with the same intent, but without mimicking the spe cific actions of the model. Great apes do show imitation but that capacity may be limited to great apes.

Whether the transmission of cultural variations within a group is based on imitation or some simpler form of social learning remains unresolved. However, ongoing investigations of nonhuman primate behavior in the laboratory and in the wild will provide better understanding about the origin and transmission of novel behaviors through social groups.

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