PRECISION GRIPS, HAND MORPHOLOGY, AND TOOLS

This study asks whether there are discernable links between precision gripping, tool behaviors,(1) and hand morphology in modern hominoids, which may guide functional interpretation of early hominid hand morpho logy. Findings from a three-pronged investigation answer this question in the affirmative, as follows. (1) Experimental manufacture of early prehistoric tools provides evidence of connections between distinctiv e human precision grips and effective tool making. (A connection is no t found between the ''fine'' thumb/index finger pad precision grip and early tool making.) (2) Manipulative behavior studies of chimpanzees, hamadryas baboons, and humans show that human precision grips are dis tinguished by the greater force with which objects may be secured by t he thumb and fingers of one hand (precision pinching) and the ability to adjust the orientation of gripped objects through movements at join ts distal to the wrist (precision handling). (3) Morphological studies reveal eight features distinctive of modern humans which facilitate u se of these grips. Among these features are substantially larger momen t arms for intrinsic muscles that stabilize the proximal thumb joints. Examination of evidence for these reveals that three of the eight fea tures occur in Australopithecus afarensis, but limited thumb mobility would have compromised tool making. Also, Olduvai hand morphology stro ngly suggests a capacity for stone tool making. However, functional an d behavioral implications of Sterkfontein and Swartkrans hand morpholo gy are less clear. At present, no single skeletal feature can be safel y relied upon as an indicator of distinctively human capabilities for precision gripping or tool making in fossil hominids. (C) 1997 Wiley-L iss, Inc.