Opposable Thumb

by Pamela J. Hines (Science  23 Apr 2021:
Vol. 372, Issue 6540, pp. 357)

Hand bones of australopithecine hominid fossils dated to over 2 million years ago have a long, slender thumb that may have added dexterity. Karakostis et al. add muscle to the story of hand evolution with their analysis of torque at the thumb joint. A model validated on the hand movements of modern humans and chimpanzees was used to estimate the opposable thumb strength of fossil hominins. Torque at the thumb joint of early australopithecines, reflecting biomechanical efficiency, was comparatively low, but around 2 million years ago, the efficiency of the thumb joint began to increase. Further dexterity and thumb strength may have facilitated greater complexity in tool use and food acquisition as the genus Homo evolved. Tool-using skills could have evolved not so much in conjunction with big brains as much as with stronger, more dexterous hands.

Curr. Biol. 31, 1317 (2021)