PRECISION GRIPS IN YOUNG CHIMPANZEES

A precision grip, thumb-finger opposition, has been regarded as an uni quely human trait. Napier's conclusion that chimpanzees were incapable of precision grip was based on two subjects and prehension of a singl e object (i.e., a grape). The purpose of the present study was to spec ify grip type and hand use by 13 young chimpanzees to prehend three di fferent-sized food objects. The subjects were laboratory raised (eight males and five females) and ranged in age from 27 to 58 months. An et hogram was devised that comprised 43 different grip types: ten configu rations of precision grips were found, in addition to imprecise or ine fficient grip types (nine types), thumb-to-finger opposition (10 types ), power grips (two types), and a variety of other grips (12 types). S ubjects most often prehended were very small-sized (5 mm x 5 mm x 3 mm ) or small-sized (10 mm x 10 mm x 3 mm) food objects with precision an d imprecise grips. An analysis of latency to prehend, i.e., efficiency , revealed (1) precision grips were equally efficient for all object s izes; (2) power grips were most efficient with the largest object (a g rape); (3) with imprecise grips, the left hand was more efficient than the right with small objects, and with power grips the right hand was more efficient than the left for medium-sized objects. No population handedness was observed, but individual handedness was seen in nine su bjects for some grip types and some object sizes. This study provides evidence that young chimpanzees preferentially use a true precision gr ip to prehend small and very small objects. (C) 1996 Wiley-Liss, Inc.