19 - On which side of the apes? Ethological study of laterality of hand use  pp. 255-272

On which side of the apes? Ethological study of laterality of hand use

By William C. McGrew and Linda F. Marchant

Image View Previous Chapter Next Chapter



Of particular interest is the study of Shafer (1987) in which, for the first time in other primates, a significant humanlike pattern consisting of a greater number of animals [i.e. Gorilla gorilla] which preferred the right hand for all acts was observed.

MacNeilage, Studdert-Kennedy & Lindblom, 1991, p. 344

Overall, our findings suggest that functional motor asymmetries are present in great apes. A left-hand population preference was found for carrying, while right-hand population preferences were found for object manipulation and leading limbs in locomotion.

Hopkins & Morris, 1993, p. 20

INTRODUCTION

Until 1987, the received wisdom in psychobiology was that laterality of function in Homo sapiens was unique, and so qualitatively different from all other species, including even our nearest relations, the great apes. Humans were said to be overwhelmingly right-handed at species (or population) level, that is, about 90% of persons show right-hand dominance for virtually all kinds of hand-use. In contrast, other hominoids were said to be randomly lateralized, either showing no consistent, overall preference for left or right, or being individually lateralized to either the left or right side in about equal numbers.

The published data available on apes at the time seemed to support these views of 50 : 50 randomness, but findings were sparse. Finch's (1941) benchmark study showed a population of 30 chimpanzees in which all but one were lateralized, but to an equal extent for left and right.