In search of "Precision grips, hand morphology, and tools"

By Mary W. Marzke, American Journal of Physical Anthropology 102 (1997)

1. http://www3.interscience.wiley.com/journal/39772/abstract?CRETRY=1&SRETRY=0

ABSTRACT

This study asks whether there are discernable links between precision gripping, tool behaviors,[Note ] [The term tool behavior has been variously used in the literature, in some cases implying exclusively tool making distinctive of humans (Susman, 1991) and in others referring variably to tool using and/or tool-making abilities, some shared with us by other animals (Susman, 1988a,b, 1994). In this paper the term is used to include both tool using and tool making behaviors of humans and non-humans; the term tool makingis used in place of tool behavior whenever the discussion is focused upon distinguishing a capacity for removing flakes from stone preforms from a more general capacity to manipulate stone tools.] and hand morphology in modern hominoids, which may guide functional interpretation of early hominid hand morphology. 

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 distinctive human precision grips and effective tool making. (A connection is not 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 distinguished by the greater force with which objects may be secured by the thumb and fingers of one hand (precision pinching) and the ability to adjust the orientation of gripped objects through movements at joints distal to the wrist (precision handling). 

(3) Morphological studies reveal eight features distinctive of modern humans which facilitate use of these grips. Among these features are substantially larger moment arms for intrinsic muscles that stabilize the proximal thumb joints. Examination of evidence for these reveals that three of the eight features occur in Australopithecus afarensis, but limited thumb mobility would have compromised tool making. Also, Olduvai hand morphology strongly suggests a capacity for stone tool making. However, functional and behavioral implications of Sterkfontein and Swartkrans hand morphology are less clear. At present, no single skeletal feature can be safely relied upon as an indicator of distinctively human capabilities for precision gripping or tool making in fossil hominids. Am J Phys Anthropol 102:91-110, 1997. © 1997 Wiley-Liss, Inc.