We should also consider the importance of changes to our vocal apparatus, that allowed us to become more articulate social creatures (which in turn lead to more effective group activities such as hunting and warfare). And eventually lead to reading, writing, and arithmetic... and advanced musical abilities, which, most importantly, eventually, lead to twerking.I remember reading an article, ages ago, that since humans are the only primates who's palms are lighter than the rest of our bodies, this aided in communication, as it was easier to see hand gestures in poor light. This would have been important when our ancestors were gathered around fires and talking. We first controlled fire roughly 2 million years ago, so it might have been that gestures were the sole means of communication, or the primary form of communication, at this time. ETA: I heard an interview with an anthropologist who one day noticed that her young daughter was taking rocks and chipping them into the shape of arrowheads. The anthropologist thought that this was interesting because she'd never taught her daughter how to do such a thing, and her daughter had never been anywhere that she might have picked up the skill, but the arrowheads were exceedingly well-made. The anthropologist thought that there might be some kind of genetic component which "compelled" her daughter to try her hand at it, much the same way its been shown that New Caledonia corvids have a genetic component which "programs" them towards the use of tools in order to get food.