sigh I should go and get my evolution notes to make sure i'm not making stuff up but basically becoming bipedal gave one really significant evolutionary advantage... use of our hands. Being able to use our hands, well... is pretty huge haha... can protect from predators from afar by throwing things, communication, using tools, etc... Mind you bipedal locomotion has quite a few flaws in itself but nontheless we're still better off by having the use of our hands.
As an aside, because of bipedal locomotion humans are born several months premature compaired to other animals (think about it.... newborn babies are pretty useless and don't even move) because the shape of our pelvis was adapted to bipedal locomotion and human head would not be able to fit through. :)
I could explain this much better but I don't feel like finding my notes :)
