To fathom just how advantageous it is to walk upright instead of knuckle walk like an ape, let’s return to that morning I spent with Bagayo and Hasani. That 7.4-mile walk likely cost me a respectable 325 calories. However, if I were as inefficient as a chimpanzee, the walk would have cost me roughly 700 calories. By walking upright instead of knuckle walking, hunter-gatherers like Bagayo and Hasani save more than 2,400 calories per week, adding up to 125,000 calories a year. That’s roughly enough energy to run about forty-five marathons.
