Doctoral Dissertation Research: Dissecting the effect of encephalization on skull morphogenesis

Dramatic increases in cranial capacity have occurred in hominins. These shifts in relative brain size are hypothesized to have caused (1) alterations to the modern human skull and (2) delays or reductions in somatic growth that may affect skull development. While prior studies have used fossil or comparative primate data to understand the relationship between the brain and skull, this project utilizes an experimental approach to link the process of encephalization with specific changes in skull morphology. The results of this project will be incorporated into multiple educational and outreach activities designed to stimulate interest in younger students pursuing STEM fields and careers, particularly young women, and foster awareness of the interdisciplinary potential for biological anthropology. Through the Penn State Expanding Your Horizons STEM Career Day for Women and the ScienceU Pre-Med Expo, the researchers will help students understand the morphological changes that have occurred in the human skull over time, including the specific impact of encephalization.

This project uses the BAF170 murine model with a known genetic variant that results in an enlarged brain phenotype. The BAF170 gene is knocked-out only in cortical tissue resulting in an enlarged cortex, such that any changes in the skull can only be attributed to the effect of the larger cortex. Using high-resolution micro-computed tomography data of prenatal and early postnatal skull development, this research will test whether an increase in relative brain size affects somatic growth of the skull or causes changes in cranial development or eventual morphology. Experiments are designed to determine whether the change in brain size causes changes in: (1) the timing of the appearance/formation of cranial ossification centers during embryological development; (2) cranial bone quality, evaluated by quantifying bone volume and bone density; or (3) morphology of the cranial base, cranial vault, or facial skeleton that can be compared with similar changes seen through time in hominins. These experiments will test the spatial packing hypothesis and the expensive brain hypothesis, by examining the relationship between brain size and cranial base angle and between changes in brain size and somatic ontogenetic trajectories. The resulting data will provide experimental evidence pertaining to the relationship between encephalization in hominins and changes in skull morphology and growth producing the unique human skull phenotype.