You guys ever check out one of the earliest hominids - ardipithecus? Pretty cool stuff. She lived about 4.5 mya predating lucy by 1 million years, was bipedal, but also had grasping fingers on her feet. Brain about the same size as a chimp.
It was always assumed that bipedalism developed in African savannahs, but apparently this view has been overturned b/c the areas in which this hominid are found were all covered by forest. So basically bipedalism first developed in the forest as opposed to the grasslands. Paleontologists speculate a number of reasons. Hands to carry: foraged food back to women/kids, tools, babies. There are other advantages that probably refined our bipedal nature as climate and our location changed, but it looks like these were the original stimuli for bipedalism.
And on a side note, I would guess that we began using tools at least as early. 2 reasons - first chimps have demonstrated ability to use tools, and two, it appears to be part of the reason why bipedalism developed. Kind of cool to think we've been using tools for over 4.5 millions years. Who knows if this particular line of hominids actually developed in to modern humans, but no doubt this still gives all kind of insight into our development.
