I think the answer is to be found in natural selection. We have not evolved to be healthy, or to have a nice experience on this earth. Evolution is only really interested in the human body staying alive long enough to procreate. From that point on, natural selection is more or less disinterested in our well-being. When we look at these cognitive rewards in this way what do they tell us about ourselves and the human body?
Outrunning Your Knowledge
The human body has been around for about 2m years, and only in the last few thousand of these have we become literate – map-makers that can walk, make notes, and record journeys. For most of our history we have not had the technology that allows us to outsource this heavy cognitive work to a piece of paper, or a GPS.
As a child, the 19th-century poet, John Clare, desired to walk to the edge of the horizon to find new worlds beyond. He wanted, he said, to walk all the way out of his knowledge. I think that what these discoveries about running and improving cognitive abilities tell us is that the hunter-gatherers of prehistory had to have the ability to outrun theirs.
The many tweaks to the human body that make it possible for us to run for 10km on a hot day (standing on two feet, with the ability to sweat to keep cool) mean that even though we are slow in a sprint, we can chase down almost any animal on the planet to the point of exhaustion over longer distances. This is called persistence hunting, and it was a risky activity because it required hunters to leave behind the places they knew in the determined pursuit of prey. With no map-making technologies, the navigational skills of the brain had to step up and do all the work. So those people who adapted this brain cell growth response to distance running were more likely to find their way back to their tribe, and consequently, to survive.
The growth of new brain cells in the hippocampus and the enhancement of spatial memory that is brought on by endurance running is basically an evolutionary safety net for when you have outrun your knowledge, when you have run so far that you no longer know where you are and you need to learn, fast. It is a mechanism that makes information uptake easiest when historically you might have been tired, lost, and at your most vulnerable.
So lace up, step out the door, and prepare yourself for the rewards of an out of knowledge experience.