The development, acquisition and transmission of a tool-use skill in wild chimpanzees.

摘要

By the age of 5.5 years, all of the young chimpanzees (Pan troglodytes schweinfurthi) of Gombe National Park, Tanzania have acquired a culturally transmitted behavior known as “termite-fishing”. Termite-fishing involves inserting flexible tools made from vegetation into a termite mound and extracting the termites that attack and cling to the tool. I performed a four-year longitudinal field study during which I observed and videotaped young chimpanzees' development of the termite-fishing behavior. I found sex differences in the speed of development, with females successfully termite-fishing an average of 19 months earlier than males. Both gender and mothers' time spent alone or with maternal family were positively correlated to measures of acquisition speed. This suggests that having greater opportunities to watch maternal relatives model the behavior may accelerate acquisition of the skill. However, none of these maternal characteristics predicted an offspring's proficiency at the skill once acquired. Only age and gender were significantly correlated to proficiency, with older individuals and females gathering more termites per dip. In addition, I found that chimpanzee mothers have individual differences in technique as measured by preferred insertion depth of tools used. Female offspring resemble their mothers in termite-fishing technique, whereas male offspring do not. These results suggest that male and female offspring differ in the social learning processes used to acquire the termite-fishing skill. The general result from all three chapters is that (1) female offspring learn to termite-fish more quickly than males, (2) are more successful than males once they have acquired the skill and (3) each use a technique similar to their mother's, while males do not. As a result, I propose that sex differences must be taken into account in studies of socially learned behaviors. As this thesis was a first attempt to study the sex differences in development of a cultural behavior, I suggest that there are many potential avenues for future research in this field.