Walking upright is a grassland thing, and Humans are in no way adapted to arboreal life. If you look back at something like an Australopithecus (and maybe even

Walking upright is a grassland thing, and Humans are in no way adapted to arboreal life. If you look back at something like an Australopithecus (and maybe even as far back as Sahelanthropus - fossils are far from complete) they basically look like a chimp with a human set of legs. So it's been awhile.