It is hard for us to imagine now, but our earliest human ancestors who ventured out onto the grasslands of East Africa some six million years ago were remarkably weak and vulnerable creatures. They stood less than five feet tall. They walked upright and could run on their two legs, but nowhere near as fast as the swift predators on four legs that pursued them. They were skinny—their arms could not provide much defense. They had no claws or fangs or poison to resort to if under attack. To gather fruits, nuts, and insects, or to scavenge dead meat, they had to move out into the open savanna where they became easy prey to leopards or packs of hyenas. So weak and small in number, they might have easily become extinct.And yet within the space of a few million years (remarkably short on the time scale of evolution), these rather physically unimpressive ancestors of ours transformed themselves into the most formidable hunters on the planet. What could possibly account for such a miraculous turnaround?
