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Orangutan cultures? Tool use, social transmission and population differences

Orangutan cultures? Tool use, social transmission and population differences
Michelle Yvonne Merrill


Department of Biological Anthropology and Anatomy, Duke University, Durham, NC 27708, UNITED STATES OF AMERICA.


This dissertation considers the evidence for orangutan (Pongo pygmaeus) cultures. Eight long-term orangutan research sites were compared using the geographic approach. Correlation between rare behavior count and observation intensity showed innovation is fairly consistent across sites. Lack of correlation between observation intensity and number of cultural behaviors indicates that something else explains this variation. Cultural behaviors were classified into subsistence skills, weal skills, reference variants, display variants and those whose function remains unknown. Types of behaviors that vary culturally in orangutans were similar to those reported for chimpanzees (Pan troglodytes).

Further evidence for the role of social learning and proximity is based on data from focal animal follows of wild orangutans at Ketambe and Suaq Balimbing on Sumatra. Suaq Balimbing had more cultural variants requiring close proximity for observational learning, including tool use. Adult female orangutans at Suaq Balimbing (particularly in the sub-group with greater tree-hole tool-use specialization) spent more time with independent conspecifics and had more diverse social partners at close proximity.

Behaviors related to nest building were examined in detail. Data from nests built with or without the nest raspberry (ubiquitous at Suaq Balimbing, absent at Ketambe) were investigated. Duration of nest-building activities is related to nest raspberry production. Nest raspberries were not related to nearest neighbor proximity or nest position; their adaptive function is not apparent. Adult females at both sites tended to be alone (no independent conspecifics within 50m) more often when building a night nest than during the rest of the active day, but this trend was stronger at Ketambe.

Evidence for vertical social transmission of a limited traditional behavior was based on published work, interviews with previous field researchers, and videotape and data collected during fieldwork at Ketambe. The persistence of unusual behaviors within rehabiltant matrilines, and the failure of these behaviors to spread throughout the wild population, may result from selectivity in social learning.

The presence of complex cultural variation in orangutans and chimpanzees suggests that the capacity for such behavior was present over 12 million years ago, in the last common ancestor of the great apes.