Linking brains and brawn: exercise and the evolution of human neurobiology. Raichlen DA, Polk JD. Proc Biol Sci. 2013 Jan 7;280(1750):20122250. Here is the abstract: http://www.ncbi.nlm.nih.gov/pubmed/23173208 A short precis: endurance running provided access to a high protein diet, altering human body shape and the human brain over generations. This change is assumed to be due to increased neurotrophin levels. These levels are increased with this kind of exercise in mammals and humans. In turn the elevated neurotrophin stimulates brain function. There is a literature review supporting this position. Very interesting paper.