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Edited by Gary T. Schwartz, Arizona State University, Tempe, AZ, and accepted by Editorial Board Member C. O. Lovejoy September 9, 2020 (received for review April 24, 2020)
Significance
Of the skeleton, teeth preserve well in the fossil record and have the strongest genetic signature and thus great potential for reconstructing evolutionary processes involved in human origins. The enamel–dentine junction (EDJ) is especially important, because it is more frequently preserved and somewhat decoupled from dietary function. Researchers have used the EDJ to test hypotheses of human evolution, but this trait has not yet been comprehensively studied across human populations. This study is the largest investigation of EDJ morphology to date, spanning 161 archaeological individuals from six continents. These data demonstrate that the EDJ evolves neutrally, and biomedical imaging of EDJ morphology can therefore be used as a noninvasive method to investigate ancient population movement and human genetic structure.
Abstract
Teeth have been studied for decades and continue to reveal information relevant to human evolution. Studies have shown that many traits of the outer enamel surface evolve neutrally and can be used to infer human population structure. However, many of these traits are unavailable in archaeological and fossil individuals due to processes of wear and taphonomy. Enamel–dentine junction (EDJ) morphology, the shape of the junction between the enamel and the dentine within a tooth, captures important information about tooth development and vertebrate evolution and is informative because it is subject to less wear and thus preserves more anatomy in worn or damaged specimens, particularly in mammals with relatively thick enamel like hominids. This study looks at the molar EDJ across a large sample of human populations. We assessed EDJ morphological variation in a sample of late Holocene modern humans (n = 161) from archaeological populations using μ-CT biomedical imaging and geometric morphometric analyses. Global variation in human EDJ morphology was compared to the statistical expectations of neutral evolution and “Out of Africa” dispersal modeling of trait evolution. Significant correlations between phenetic variation and neutral genetic variation indicate that EDJ morphology has evolved neutrally in humans. While EDJ morphology reflects population history, its global distribution does not follow expectations of the Out of Africa dispersal model. This study increases our knowledge of human dental variation and contributes to our understanding of dental development more broadly, with important applications to the investigation of population history and human genetic structure.
Footnotes
- ↵1To whom correspondence may be addressed. Email: tesla.monson{at}wwu.edu.
Author contributions: T.A.M., D.F., and M.S. performed research; T.A.M. analyzed data; and T.A.M., D.F., and M.S. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission. G.T.S. is a guest editor invited by the Editorial Board.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2008037117/-/DCSupplemental.
Data Availability.
All data and code for this study are available on GitHub (https://github.com/teslamonson/EDJ) (91).
Published under the PNAS license.
References
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Neutral evolution of human enamel–dentine junction morphology
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Article Classifications
- Biological Sciences
- Anthropology
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