The goal of this project is to find the genes involved in human skull development and evolution. We will bring together data and methods from paleontology, genetics, quantitative morphology, and bioinformatics.
Overview
Relative to other apes, humans have evolved skulls with short faces and reduced jaws tucked under an enlarged braincase. To better understand the genetics underlying our unique skull shape, we look in closely related primate species for genes involved in skull development. To this end, we are measuring the skulls of a large sample of captive baboons with a detailed pedigree. Physical features measured from computed tomography (CT) scans of the baboon skulls can be tested for heritability.
Anterior and lateral views of a CT reconstruction of a baboon skull
Heritable features then can be associated with certain regions of the baboons’ chromosomes. Once we have identified those regions associated with physical features, we can turn to bioinformatic methods, knowing that developmental genes are often conserved between species. Whole genome sequences are now available for humans, in addition to the chimpanzee, rhesus macaque, and mouse. Comparison between them makes it possible to identify evolutionary changes that have occurred at the molecular level in humans.
In addition to baboons, we have a large sample of mice that have been specially bred for 34 generations to provide detailed genetic information about skull shape.
Anterior and lateral views of a micro-CT reconstruction of a mouse skull
These have a high density of genetic markers that make it possible to identify fairly narrow chromosomal regions that contain potential candidate genes. Candidate genes—genes that we suspect are involved in skull shape—from both the baboon and mouse populations can be the subject of experiments, including looking at gene expression in mouse embryos.
Example of a mouse embryo used for gene expression studies. The location of expression (function) of a particular gene is marked by dark purple in this experiment.
This will give us a fuller understanding of the function of genes involved in mammalian and especially human skull development.
As a final step, with this genetic information in hand, we can examine the fossil record of humans and baboons to estimate from changes in skull shape when and in what sequence the major genetic changes occurred that have produced the uniquely human skull.
Lateral view of a skull of the extinct baboon Theropithecus oswaldi