Approaches for assessing whether the human hand evolved by natural selection in adaptation to stone tool use

Identifier:  TDX:3062

Handle: https://hdl.handle.net/20.500.11797/TDX3062

Authors:  Bucchi Morales, Ana

Abstract:
Studies in hand morphology have generally concluded that derived traits in humans facilitated stone tool-related behaviors and made us a highly dexterous primate. How humans acquired this unique configuration of musculoskeletal traits has profound implications for our understanding of human evolution overall, considering that stone technology is a key element defining culture in our species. The aim of this thesis was to evaluate whether the human hand evolved by natural selection in adaptation to stone tool use, which is the most widespread hypothesis for the evolution of the human hand. For this purpose, a comparative sample of hands of extant primates, mainly humans, chimpanzees and gorillas, were analyzed under different methods that relate biological form and function. The first objective of this thesis was to evaluate the performance of the thumb during simulated hammerstone use through a finite element analysis. The results that stress distribution in hand bones was unlikely to be a selective pressure strong enough to shape the hand of humans. The second objective was to evaluate whether humans have a different covariation structure at the wrist than that of chimpanzees and gorillas. Results indicate that different covariation patterns may be shaping the evolution of the wrist in these primates, which might be related to different functional demands of locomotion and manipulation. The last objective was to test whether entheseal size of ligaments and muscles are reliable for inferring activity patterns in the hand. The results indicate that stone tool use may be inferred in hominins by analyzing hand regions where tendons (with fibrocartilaginous entheses) and ligaments attach. This serves to discuss since when and to which extent hominins were using stone tools.