Big brained humans
We humans have the largest brain relative to body weight, compared to all other animals. On average the human brain is three times the size that of our nearest primate relative, the chimpanzee. Why is this so? In a think piece in last week’s edition of the journal Science, Michael Balter summarizes some of the hypotheses.
In his article the author examines the “social brain hypothesis” and other competing explanations for our large brain size. He mentions a significant aspect of this discussion: the amount of energy needed to keep the brain functioning. That reference takes us back to a paper written in 1995 by Aiello and Wheeler in which they proposed the “expensive tissue hypothesis”. This postulated brain use and digestion were in competition with each other. The fossil record reveals anatomical changes occurring around two million years ago gave rise to Homo erectus and indicate a shift toward smaller digestive systems and larger brains. In the years since, scientists have hypothesized a shift in diet to include meat (easier to digest than the grasses which comprised a large part of the australopithecine diet),whether scavenged or hunted, marked the beginning of significant brain expansion.
This Science article offers a good introduction to the question of human brain size and provides references for further reading.