Doctoral Dissertation Improvement: Primate Cranial Morphology in a Comparative Context

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This project by doctoral student Jessica Joganic, under the supervision of Dr. James Cheverud at Washington University, St. Louis, brings together the fields of genetics, anatomy, and evolutionary biology in a comparative examination of primate cranial morphology. The research examines the genetic variants contributing to normal variation in primate skulls, as well as the molecular evolution and human population variation of genes responsible for the dramatic changes in the size and shape of the skull in human and primate evolution. The organization of the human skull represents a unique departure from the typical mammalian pattern. It has an enlarged neural vault, a short upright face, and a flexed cranial base. Genes contributing to variation in these traits that may have been modified in the human lineage will be identified using a primate model, the baboon. This will be accomplished by: 1) measuring craniofacial size and shape variation in a population of pedigreed baboons, 2) identifying genetic variants contributing to this variation, and 3) characterizing the molecular evolution of these genetic variants, both across a broad sample of primates, as well as within human populations. To achieve these goals, three-dimensional landmark coordinates will be obtained from the surface and interior of skulls from a large population of pedigreed baboons using a 3D digitizer and CT scans. These traits will be tested against variation in the baboon's genomes to identify regions where molecular variation contributes to craniofacial variation. These regions will be investigated for signatures of selection and evolutionary rate heterogeneity across primates as well as within human populations. As genetic variation is the basis for evolutionary change, identifying the genetic loci underlying trait variation is a necessary step in studying the evolution of complex morphologies like the human cranium. Knowledge of a trait's genetic basis and evolutionary history also informs our ability to manage, treat, and study the origin of skull abnormalities and diseases that have clinical and biomedical relevance.