What Fossils Can and Can't Tell Us about Hominin Locomotor Evolution: Insights from Experimental Skeletal Biomechanics
Authors: Wallace Ian J. , Holowka Nicholas B. 
Published: June 2021

Lacking a time machine, the best way to glean information about hominin locomotor evolution is by making inferences about the behavior of our ancient ancestors from the anatomy of their fossilized remains. Such inferences are only credible, however, if underlying assumptions about links between skeletal form and function are valid. In order to faithfully translate the static fossil record into a behaviorally dynamic picture, experiments are required to test and validate these assumptions. This talk provides an overview of the critical role that experimental skeletal biomechanics plays in the epistemology of paleoanthropology and highlights examples of research that have been especially influential for our understanding of what fossils can and cannot tell us about the locomotor behavior of ancient hominins.

Experimental biomechanics in paleoanthropology has generally proceeded on two fronts. First, comparative biomechanical studies of living primates have been carried out within phylogenetic frameworks to explicitly test hypotheses of evolutionary change in various skeletal structures and their functions. Some of the most significant advances in interpreting hominin fossil anatomy have come from studies comparing the skeletal biomechanics of humans and those of our closest living relatives, chimpanzees. Two key lines of evidence from these studies are kinematics, or the measurement of motion of the body, and electromyography, the measurement of the neuromuscular control of motion. Application of these techniques has allowed researchers to relate skeletal anatomy to muscle activity patterns and the body movements they produce, rather than just infer function based on differences in skeletal morphology between species. Key studies have illuminated the relationship between pelvis and lower limb anatomy and the evolution of bipedalism.

Second, experiments with animal models such as rodents, sheep, pigs and fowl have been conducted to establish basic principles about how bone structure changes throughout life in response to loads sustained during locomotion. The responsiveness of the skeleton to loading is of interest because if bones are shaped by locomotor activity during life, then it might be possible to infer the lifetime locomotor patterns of hominins based on fossil morphology. Although many experiments have shown that loads produced by locomotion can indeed affect bone structure, the process has often been observed to be complex in ways that would seem to greatly undermine the accuracy of inferences about lifetime physical activity from fossil structure. Important issues raised by these studies include the weak correspondence between bone structure and its in vivo loading environment, the large influence of genetics on bone structure independent of loading and the age‐dependency of bone's responsiveness to loading.

While paleoanthropological investigations of hominin locomotor evolution once relied primarily on speculation about the functional significance of fossil anatomy, today researchers are equipped with a variety of experimental models and tools to empirically evaluate their ideas. Experimental biomechanics provides a means of testing hypotheses about skeletal form and function that cannot be determined from fossil anatomy alone.

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.