Comment by coenhyde

I like the water ape theory. ie we had a period of time in our history where we spent a lot of time in low lying water that encouraged us to stand upright. There's a few things which point in this direction. iirc we're the only primate which can control its breath; good for swimming under water. Our fingers wrinkle when we spend time in water; good for picking things up in water. And we lost our hair; hair may have gotten caught on underwater objects drowning the hairiest amongst of us.