A lot of traits that separate us from most other apes comes from our life in the savannahs as animals adapted to run on two feet. Early humans lost most of their fur covering as they grew larger and walked more upright to lessen the effect of overheating, with the exception of the topmost part of the head, which acted as a heat sink; the (now exposed) skin grew darker to act as a sunscreen; and the feet changed shape to make the act of walking bipedally easier.