Coll.4 journal club: Bigger brains led to bigger bodies in humans?

Abstract:

Most investigations of hominin brain and body size evolution assume that different selection pressures acted on each trait or that brain and body size are linked physiologically via the energetic demands of large brains. However, evidence from model organisms suggests that some genes cause variation in both brain and body size, with the result that selection on either trait can lead to a correlated response in the unselected trait. If brain and body size covariation exists in our lineage, correlated evolution could mean that changes observed in the fossil record are poor predictors of past selection pressures that produced those changes. This study shows that modern humans, chimpanzees, and all primates included here have significant and roughly similar levels of evolutionary constraints from brain and body size covariance, arguing that similar levels were present in earlier hominins. Building on these findings, results suggest that strong selection to increase brain size alone played a large role in both brain and body size increases throughout human evolution and may have been solely responsible for the major increase in both traits that occurred during the transition toHomo erectus. This switch in emphasis has major implications for adaptive hypotheses on the origins of our genus.