Sure, and you spent how much of that time looking out for predators, unfamiliar terrain, only on animal trails, other non-friendly groups of people etc? We all

Sure, and you spent how much of that time looking out for predators, unfamiliar terrain, only on animal trails, other non-friendly groups of people etc? We all know humans can run all day long, but the point is that it wasn't as easy then, and if it wasn't necessary then they probably wouldn't have taken the risk.