Exploding stars put humans in upright positions

We are the only primates walking exclusively on two legs. Doing so leaves our hands free to make and use tools.

This, the experts claim, was a crucial development in the evolution of early humans. But there is little consensus as to how the radical change from walking on all fours to standing upright came about. In a Journal of Geology paper just published, Kansas-based physicists Adrian Melot and Brian Thomas put forward a novel theory.