Doctoral Dissertation Research: Evolutionary biomechanics of the human hyolingual apparatus

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The human tongue and hyoid bone have been extensively studied for their role in the evolution of speech. Some researchers hypothesize that our unique tongue and hyoid morphology also makes us more prone to choking. This research uses advanced imaging techniques and computational modeling to test whether human hyolingual morphology is beneficial or detrimental for swallowing. While this research focuses on swallowing function in an evolutionary context, the findings of this research will also advance our understanding of normal swallowing mechanisms and therefore may have clinical applications. The software for the computational model generated by this project will be made freely available upon completion. This project provides mentored research not only to a woman in science but specifically one studying biomechanics, a field in which women are underrepresented. Furthermore, the project will support undergraduate research and training for a diverse group of students at the University of Chicago.The short faces and low tongue, hyoid, and larynx of humans have been argued to be adapted for speech and maladapted for swallowing. Recent studies cast doubt on both of these claims, prompting further exploration of alternative hypotheses to explain the origin of the uniquely human hyolingual apparatus. This project tests the hypothesis that hyolingual biomechanics constrain morphology, specifically that a low hyolingual apparatus is necessary to maintain swallowing performance as the face becomes shorter. X-ray Reconstruction of Moving Morphology (XROMM), diffusible iodine-based contrast-enhanced CT (diceCT), and electromyography (EMG) will be used to obtain high spatiotemporal resolution in vivo measurements of bone, tongue, and muscle biomechanics, including hyolingual muscle length, velocity, and activity in a primate model system. These data will then be used to validate a computational model of the impacts on swallowing biomechanics and performance of variation in hyolingual position, and craniofacial morphology. Falsification of the constraint hypothesis would provide indirect support for the hypothesis that the morphology of the human vocal tract is the result of natural selection for speech performance. This project will inform future research on how the functional requirements of the hyolingual apparatus may have influenced the morphology of surrounding structures, e.g., the mandibular symphysis, in both extant and extinct taxa.