The Evolution Of Man
It seems scientists studying the behaviour of chimpanzees have stumbled upon what they believe to be the reason that man first stood on two legs and began to walk. They observed that during times of limited food availability chimpanzees spent markedly more time upright as they gathered food and carried it away rather than staying to eat it where it was found. This behaviour was seen to be particularly prevalent when competition for a favourite food source was involved as individuals would carefully gather armfuls and carry food to a safe area away from their rivals, successfully increasing their personal food intake.
Scientists now believe this could be what drove early hominid man to stand and that increased competition forced him to become more expert at standing upright, walking and carrying until it became the preferred method and the body adapted accordingly.