The world already has quite enough evolutionary "just so" stories. Our ancestors lived in trees, which presumably is safe from most predators, and standing upri

The world already has quite enough evolutionary "just so" stories. Our ancestors lived in trees, which presumably is safe from most predators, and standing upright isn't much of an advantage. Gathering would have been off the ground (no advantage to standing) or from bushes / trees (where climbing is better than standing). Most African predators (such as the many big cats, but also some crocodiles) easily outrun humans, we are in no way evolved to outrun them. They will sneak up and then do a short sprint. Remember we're not running a marathon against them - we're playing tag and when they tag you, you lose. We're almost certainly not evolved to run to avoid predators.