Gretchen Reynolds reviews work suggesting that our advanced cleverness and big brains may have come not from the need to think but becoming endurance athletes, able to bring down swifter prey through sheer doggedness, jogging and plodding along behind them until the animals dropped. It turns out our larger brain size with respect to body size is also shown to some extent by species like dogs and rats that have a high innate endurance capacity, presumably evolved over millennia. it is also seen in mice and rats systematically bred to be marathon runners. After multiple generations, these animals begin to develop innately higher levels of tissue growth and health promoters, including the protein brain-derived neurotrophic factor, or BDNF. These substances are important for endurance performance. They also are known to drive brain growth. Such observations have led Raichlen and Polk to suggest that physical activity may have helped to make early humans smarter:
The hunting and gathering lifestyle adopted by human ancestors around 2 Ma required a large increase in aerobic activity. High levels of physical activity altered the shape of the human body, enabling access to new food resources (e.g. animal protein) in a changing environment. Recent experimental work provides strong evidence that both acute bouts of exercise and long-term exercise training increase the size of brain components and improve cognitive performance in humans and other taxa. However, to date, researchers have not explored the possibility that the increases in aerobic capacity and physical activity that occurred during human evolution directly influenced the human brain. Here, we hypothesize that proximate mechanisms linking physical activity and neurobiology in living species may help to explain changes in brain size and cognitive function during human evolution. We review evidence that selection acting on endurance increased baseline neurotrophin and growth factor signalling (compounds responsible for both brain growth and for metabolic regulation during exercise) in some mammals, which in turn led to increased overall brain growth and development. This hypothesis suggests that a significant portion of human neurobiology evolved due to selection acting on features unrelated to cognitive performance.