Three main stresses that human body learn to deal with during the course of evolution trigger development of brain (and nervous system in general).<p>These stresses are endurance activity (walk long hours), strength activity (fight or flight response) and famine.<p>The agent responsible for development of nervous system in these cases is brain-derived neurotrophic factor. It is responsible for creation of new neurons and branching of old ones and directly related to intellectual performance.<p>So your link to high level machine intelligence is wrong, I believe. I also think I explained above why do you feel smarter after a day of physical activity.