PhD project: It's all in the wrist: understanding the evolution of Homo tool-making through internal bone structure
The aim of this study is to gain a better understanding of wrist function and evolution through holistic analyses of the internal trabecular and cortical bone structure in humans, great apes (e.g., chimpanzees, orangutans), and fossil hominins using two novel methods.
The wrist is the link between the hand and the forelimb and thus plays a critical role in the stability, flexibility, and dexterity of the upper limb. As such, the morphology of the wrist has played a pivotal role in fundamental questions of human evolution, including the origin of bipedalism, development of tool use, and the extraordinary manipulative abilities that characterise the human hand. In particular, there is a suite of derived features of the human wrist and hand that is shared with Neanderthals and considered to be an adaptive requirement for the forceful loading of the hand that occurs during intense tool making and use. Some, but not all, of these features appear in earlier fossil humans (hominins), bringing into question how their wrist and hands functioned and if these features can be considered an adaptive response to tool-related behaviours.
This study will quantify, for the first time, the variation in cortical and trabecular bone of the human and great ape wrist, to test whether it is consistent with:
- the distinctive shapes to the radial bones (scaphoid, trapezium, trapezoid, capitate) of the human wrist and the hypothesised greater transverse loading across the wrist and palm, or
- the greater use of power grips and ulnar loading of the hand during arboreal climbing and suspension.
Within this comparative context, including additional earlier (Australopithecus) and later (Neanderthal) fossil hominins, Emma will investigate the cortical and trabecular structure of the more human-like wrist of H. naledi and the more ape-like wrist of H. floresiensis to reconstruct wrist function. Ultimately, this objective will help determine if H. naledi was using its hand for both locomotion and tool-use and how H. floresiensis was able to make and use tools with such a primitive wrist morphology, and better inform our understanding of human hand evolution and what morphology is required for stone tool-making.
Vice-Chancellor's Scholarship, University of Kent