Gebo, Daniel Lee, 1955-
M.A. (Master of Arts)
Department of Anthropology
Physical anthropology; Paleontology
Prehensility is a hand activity that applies forces while grasping an object. In the crudest sense, prehensile movements of the hand can be divided into two types based on an actor needing a precision or a power grip. To analyze prehensility more specifically, I suggest that the movements of the hand can be divided into three categories including power, modified precision, and true precision grips. A power grip is when an object is held in one hand with the aid of the palm with fingers buttressing the object, while a true precision grip is when an object is picked up using only the tips of the first and second digit in similar fashion as tweezers. The in-between category, a modified precision grip, is defined when using an anatomically restricted hand posture that mimics the forceful pinch biomechanics of true precision grips. In this project, I study human hand anatomy by assessing hand proportions, finger curvature, and fourth metacarpal articulation in African apes ( Pan troglodytes, Gorilla gorilla), other living primates ( Papio anubis, Papio papio, Macaca fascicularis, and Cebus apella), and several fossil humans (Australopithecus sediba, Homo naledi, and Homo neanderthalensis). I assess the evolution of the human hand in association with our evolutionary ability to grasp tools using a true precision grip. Non-human primates with a more generalized functional hand may show enhanced dexterity capabilities that could be quite informative about the evolution of true precision grip in the human fossil record. To compare all of the living primates, humans, and fossils, I expressed averages for inner hand proportions and hand proportions including geometric means. This study also the included angle of phalangeal curvature and the radius of phalangeal curvature for measured specimens. Using a principal component analysis (PCA), this project showed significant similarities between extant and fossil primates to modern day humans analyzed. My overall assessment is that a precision grip is possible in other non-human primates and this result suggests that tool-use could have been possible before the appearance of stone tools in the human fossil record.
Bemis, Caitlin Marie, "Anatomy of a precision grip in human and non-human primates" (2018). Graduate Research Theses & Dissertations. 1477.
Northern Illinois University
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