Doctoral Dissertation Research: Skull Growth and Biomechanical Constraints on Molar Emergence in Primates

Project: Research project

Description

Life history theory describes how species use limited energetic resources to schedule growth and reproduction in a manner that minimizes mortality risks and increase fitness. Modern humans possess an unusual pattern of life history among primates. Humans have long lifespans and grow slowly but possess short inter-birth intervals resulting in fast reproductive rates. This life history profile likely evolved as a response to low mortality rates and allocare and current research suggests that it is unique to modern humans. Much of this work is inferred in the fossil record from M1 emergence age, yet we lack an understanding of how variation in molar emergence age arises and why it is closely associated with life history. This proposed study aims to determine whether or not the biomechanics of the growing masticatory system constrain the position and timing of molar emergence in primates. Molars are part of an integrated system in which they function, together with the jaws and masticatory muscles, to break down food during mastication. Developmental coordination among parts of the masticatory system is key to proper food ingestion throughout life. In adult anthropoids, the biomechanics of mastication constrain where molars can be situated along the maxillary and mandibular arches to avoid damage to the temporomandibular joint (TMJ) during chewing. Using three-dimensional coordinate data from cross-sectional ontogenetic samples of primate skulls, representing 18 species, this research will test the hypothesis that the location and timing of molar emergence is constrained to avoid damage to the TMJ throughout ontogeny. Support of this hypothesis will indicate that variation in molar emergence schedules among primates is driven by ontogenetic changes in the biomechanical configuration of the masticatory system, suggesting that life history is closely associated with molar emergence ages vis--vis its influence on growth rate.
Intellectual Merit
Ages at molar emergence are important indicators of life history and are commonly used to reconstruct the life history attributes of fossil primates. The proposed research will investigate the underlying mechanism of molar emergence times in primates. Identifying the mechanism that operates to modulate coordinated growth of the masticatory system, including the position and timing of molar emergence, will provide a model for contextualizing variation in the timing of molar emergence among primates, and will contribute to understanding the reason for the close association between molar emergence and life history. The results of this research will have implications for interpreting observed changes in the timing of molar emergence across the primate fossil record. An ontogenetic as well as a cross-taxonomic approach will not only aid in unraveling the link between molar emergence and life history, but will provide a new dimension to studying coordinated growth and development of the primate masticatory system. The raw landmark data collected for this project will be submitted to permanent online data repositories for public use (e.g., GitHub, and Dryad) and the R code written will be submitted to GitHub and included as supplementary information in publications of project results. The results of the study will be disseminated to the scientific community through peer-reviewed publications and as presentations at national and international conferences.
Broader Impacts
The novel approach taken by this research will be introduced to the public as a new way to learn about human evolution. The Co-PI participates in a science outreach program run by the Institute of Human Origins (IHO) at Arizona State University (ASU). She will develop an outreach module that summarizes this research and the insights that it provides on human evolution, which will be presented at a series of science outreach events (e.g., Night of the Open Door) that are held annually at ASU. As further public outreach, during her data collection travels, the Co-PI will contribute to IHOs Notes from the Field blog, which publicizes the research and field work experiences of IHO graduate students. This research is an instrumental component of the dissertation work and overall graduate training of Co-PI Glowacka, who is a female graduate student working in a STEM field. The proposed research will result in the training of undergraduate students, recruited through the School of Human Evolution and Social Changes Research Apprenticeship Program, who will help in the data-analysis process of the proposed project.
StatusFinished
Effective start/end date9/1/158/31/16

Funding

  • National Science Foundation (NSF): $10,100.00

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earning a doctorate
graduate
damages
mortality
food
student
apprenticeship
integrated system
scientific community
life-span
science
weblog
fitness
social change
data analysis
travel