@article{bacd167ab9484d1f9f37bda5997ea5b4,
title = "A simple rule governs the evolution and development of hominin tooth size",
abstract = "The variation in molar tooth size in humans and our closest relatives (hominins) has strongly influenced our view of human evolution. The reduction in overall size and disproportionate decrease in third molar size have been noted for over a century, and have been attributed to reduced selection for large dentitions owing to changes in diet or the acquisition of cooking. The systematic pattern of size variation along the tooth row has been described as a 'morphogenetic gradienta' in mammal, and more specifically hominin, teeth since Butler and Dahlberg. However, the underlying controls of tooth size have not been well understood, with hypotheses ranging from morphogenetic fields to the clone theory. In this study we address the following question: are there rules that govern how hominin tooth size evolves? Here we propose that the inhibitory cascade, an activator-inhibitor mechanism that affects relative tooth size in mammals, produces the default pattern of tooth sizes for all lower primary postcanine teeth (deciduous premolars and permanent molars) in hominins. This configuration is also equivalent to a morphogenetic gradient, finally pointing to a mechanism that can generate this gradient. The pattern of tooth size remains constant with absolute size in australopiths (including Ardipithecus, Australopithecus and Paranthropus). However, in species of Homo, including modern humans, there is a tight link between tooth proportions and absolute size such that a single developmental parameter can explain both the relative and absolute sizes of primary postcanine teeth. On the basis of the relationship of inhibitory cascade patterning with size, we can use the size at one tooth position to predict the sizes of the remaining four primary postcanine teeth in the row for hominins. Our study provides a development-based expectation to examine the evolution of the unique proportions of human teeth.",
author = "Evans, {Alistair R.} and Daly, {E. Susanne} and Catlett, {Kierstin K.} and Paul, {Kathleen S.} and King, {Stephen J.} and Skinner, {Matthew M.} and Nesse, {Hans P.} and Hublin, {Jean Jacques} and Townsend, {Grant C.} and Gary Schwartz and Jukka Jernvall",
note = "Funding Information: Acknowledgements This contribution is dedicated to the late Professor Percy Butler, the inspiration for much of this work and discoverer of the morphogenetic gradient in teeth, who unfortunately did not see this work completed. We thank M. Fortelius, G. Evans, A.-L. Khoo, F. Grine, P. Trusler, J. Adams, J. Clutterbuck, L. Chieu, D. Hocking, M. McCurry, Q. Nasrullah, T. Park and the Evans EvoMorph Laboratory for discussions and criticism of the manuscript. Thanks to M. Collard for supplementary information on the hominin phylogeny. We thank the Powell-Cotton Museum (M. Harman), American Museum of Natural History, Cleveland Museum of Natural History (L. Jellema), Museum of Comparative Zoology (J. Chupasko), Royal Belgian Institute of Natural Sciences (G. Lenglet), Royal Museum for Central Africa (E. Gilissen and W. Wendelen), National Museum of Natural History (USA), The Bavarian State Collection of Zoology (M. Hiermeier and C. Lang) and Anthropological Institute and Museum (Switzerland) (M. Ponce de Le{\'o}n and C. Zollikofer) for access to great ape material. For access to computed tomography scans of fossil hominin material we thank the following individuals and institutions: National Museums of Kenya (E. Mbua), Ditsong National Museum of Natural History (S. Potze), University of Witwatersrand (C. Menter and B. Zipfel), Senckenberg Natural History Museum (F. Schrenk and O. Kullmer) and the Royal Belgian Institute of Natural Sciences (M. Toussaint). This study was made possible by use of material from the Burlington Growth Centre, Faculty of Dentistry, University of Toronto, which was supported by funds provided by grant (1) (number 605-7-299) National Health Grant (Canada), (data collection); (2) Province of Ontario Grant PR 33 (duplicating); and (3) the Varsity Fund (for housing and collection). All research protocols were reviewed and granted exemption by Arizona State University{\textquoteright}s (ASU) Institutional Review Board and the Burlington Growth Centre, and informed consent was obtained for all human subjects. This research was financially supported by grants from the Australian Research Council Future Fellowship (A.R.E., FT130100968), Academy of Finland (J.J.), National Science Foundation (GRFP number 2011121784; K.S.P.), Max Planck Society (M.M.S.), Wenner-Gren Foundation (K.K.C.), Graduate and Professional Student Association at ASU (E.S.D., K.K.C.), and ASU Sigma XI chapter (E.S.D., K.K.C.). This research was also facilitated in part by a grant (48952) from the John Templeton Foundation (G.T.S.). The opinions expressed in this publication do not necessarily reflect the views of the John Templeton Foundation. Publisher Copyright: {\textcopyright} 2016 Macmillan Publishers Limited. All rights reserved.",
year = "2016",
month = feb,
day = "24",
doi = "10.1038/nature16972",
language = "English (US)",
volume = "530",
pages = "477--480",
journal = "Nature",
issn = "0028-0836",
publisher = "Nature Publishing Group",
number = "7591",
}