Anyone whose resolve to exercise in 2013 is a bit shaky might want to consider an emerging scientific view of human evolution. It suggests that we are clever today in part because a million years ago, we could outrun and outwalk most other mammals over long distances.
Our brains were shaped and sharpened by movement, the idea goes, and we continue to require physical activity for our brains to function optimally.
The role of physical endurance in shaping humankind has intrigued anthropologists for some time. In 2004, evolutionary biologists Daniel E. Lieberman of Harvard and Dennis M. Bramble of the University of Utah published a seminal article in the journal Nature titled “Endurance Running and the Evolution of Homo,” positing that our bipedal ancestors survived by becoming endurance athletes, able to bring down swifter prey through sheer doggedness, jogging and plodding along behind them until the animals dropped.
Endurance produced meals, which provided energy for mating, which meant that adept early joggers passed along their genes. In this way, natural selection drove early humans to become even more athletic, their bodies developing longer legs, shorter toes, less hair and complicated inner-ear mechanisms to maintain balance and stability during upright ambulation.
But simultaneously, in a development that until recently many scientists viewed as unrelated, humans were becoming smarter. Their brains were increasing rapidly in size.
To explain those outsize brains, evolutionary scientists have pointed to such occurrences as meat eating and our early ancestors’ need for social interaction. Early humans had to plan and execute hunts as a group, which required complicated thinking patterns and, it’s been thought, rewarded the social and brainy with evolutionary success.
But now some scientists are suggesting that physical activity also played a critical role in making our brains larger.
Anthropologists began by looking at existing data about brain size and endurance capacity in a variety of mammals, including dogs, guinea pigs, foxes and wolves. They found a notable pattern. Species like dogs and rats that have a high innate endurance capacity also have large brain volumes relative to their body size.
The researchers also looked at recent experiments in which mice and rats were bred for marathon running.
Lab animals that willingly put in the most miles on running wheels were interbred. After multiple generations, these animals began to develop innately high levels of substances that promote tissue growth and health, including a protein called brain-derived neurotrophic factor. These substances are important for endurance. They also are known to drive brain growth.
What all of this means, said David A. Raichlen, an anthropologist at the University of Arizona, is that physical activity may have helped to make early humans smarter.