The connection between exercise and brain health has now been super conclusively and astonishingly shown, but what are some possible evolutionary reasons for this connection? Maybe the extra energetic investment in brain health is only justified when there is an energetic surplus, and doing exercise correlates with having extra energy available? (As opposed to starving and thus needing to conserve energy.) But that d…
Prehistoric humans likely exercised as a matter of course. They weren't sedentary. The brain evolved assuming the condition of exercise. naturally occurring byproducts of exercise were just always there for the brain to use.
Physical activity levels were also within a standard deviation of one another (between western and h/g populations).
The brain evolved in similar conditions to modern man. I would argue current conditions are far better for the brain in terms of good nutrition and low disease.
The effect in the OP was not selected for, it is likely a serendipitous biochemical interaction. Repair enzymes from one part of they also effecting another.