Strong selection on brain size, but not body size, dominates hominin evolution
CEES Extra seminar by Mark Grabowski
Abstract (updated 29 April)
The evolution of relatively large brains in hominins has been the subject of intense study for over 100 years, but few hypotheses have accounted for the implications of brain-body integration. Integration between brain and body size may lead to a correlated response in one trait when selection acts on the other. Thus, integration could potentially impede evolutionary transitions that significantly change brain-body proportions such as those that occurred during the evolution of our relatively large brains. As integration can evolve in response to selection, and a number of findings suggest that changes in patterns and/or a reduction in magnitudes of integration may have played a major role in the evolution of our lineage, a reduction in evolutionary constraints imposed by brain-body integration might have been the key to hominin brain expansion. This study demonstrates that brain-body integration levels did not relax during human evolution, and changes in brain and body size were the result of the interplay between selection and integration. Results show that brain evolution in the hominin clade was the result of strong selection pressures to increase brain size, coupled with relatively weak selection to reduce body size. The exception to this pattern was the evolutionary transition to Homo ergaster where integration facilitated increases in both brain and body size, changes that had wide ranging implications for the biology and behavior of our genus.
Center for the Advanced Study of Hominid Paleobiology
The Department of Anthropology
The George Washington University