Teeth dominate the fossil and bioarchaeological records because they consist mostly of inorganic material. Consequently, dental anthropology has long been essential in our investigation of the human past. Variation in the anatomy of teeth is instrumental for differentiating species, identifying biological affinities between populations, making inferences about dietary adaptations, and timing key developmental life stages. Recent advances in genetics, genomics, and developmental biology have revealed that this variation in tooth size and shape is underlain by extensive pleiotropy—when one gene influences more than one anatomical structure simultaneously. In the Tied2Teeth project, we investigate these pleiotropic relationships in order to improve and expand the information about human biological evolution that can be learned from the dentition.
This project consists of three major aims, or approaches. In the first, we use quantitative genetic analyses to identify shared genetic effects between the skull and dentition. Our study population is comprised of 985 deceased and skeletonized baboons from the Southwest National Primate Research Center in Texas. These animals are all part of one large extended family for which all relationships are know. This pedigree information enables us to investigate how variation is inherited through the population. We utilize CT scans of the skulls that were made after death alongside high-resolution surface scans of the dentitions that we collected using a laser scanner. In the first two years of the project, we made the dental 3-d scans and semi-automated the data collection from the crania CT and the oral scans. We have begun to collect data from both types of scans. These genetic analyses will help us understand how the cranium and face evolve relative to the dentition, and whether or not the evolution of these different anatomical regions is intertwined. As humans have a unique combination of small faces, very large brains, and reduced dentitions, we anticipate that our forthcoming analyses will elucidate human evolutionary history.
The second major aim of the Tied2Teeth project focuses on dental variation within and across human populations. For decades, dental anthropologists have applied a scoring system to quantify minor shape variation on human teeth. In particular, three anthropologists amassed dental scores for tens of thousands of individuals from around the world (Christy G. Turner II, G. Richard Scott, and Tsunehiko Hanihara). Although the data were collected individual-by-individual, these data have been aggregated in various ways prior to analyses and are generally always published as population averages. The recent advances in genetic analyses raise a number of hypotheses about the genetic interrelationships between these various dental traits. However, these hypotheses can only be tested with the original data reported for each individual. The Tied2Teeth project has constructed an online database that will provide open access to these historical, original, individual data, enabling modern analytical approaches. In addition to constructing the database and beginning to populate it with data from Christy G. Turner II, G. Richard Scott, and Tsunehiko Hanihara, we formed an Advisory Committee of twelve experts in dental anthropology from across four continents to develop the policies and protocols for how the database will be accessed and what will be publicly available, keeping in mind F.A.I.R. principles and current ethical standards. We anticipate that this database and the analyses that it will facilitate could lead to new insights about the genetic structure of human dental variation.
The third and final aim of Tied2Teeth applies the knowledge gained through genetic analyses to fossil assemblages. Over the first two years of the project, we innovated methods for taxonomically identifying isolated hominid teeth dating between 1 and 3 million years in age, begun an investigation of the dietary habits of cercopithecid monkeys over the last 500.000 years to pair with the microevolution of genetically-defined traits, and conducted a range of smaller, related projects that span from odd enamel defects in a population of macaques to the application of artificial intelligence to reconstruct missing dental tissue. As the project progresses, we anticipate being able to tie many of these smaller studies together into a more cohesive, and new understanding of primate dental evolution.
