Walking on two legs uses up a quarter of the energy it takes to walk on all fours, according to a study that could explain why early human ancestors adopted bipedalism rather than the knuckle-walking of chimpanzees and gorillas. Explaining why humans went from a four-legged gait to a two-legged, upright posture has proven to be one of the most difficult and contentious issues in evolution. The study suggests that it all comes down to energy expenditure and how costly it is to move around in terms of the food required. Scientists compared the amount of energy expended by humans and chimps when walking on a treadmill and found that a two-legged gait is about 75 per cent less costly compared with walking on all fours. The results provide powerful evidence in support of the idea that the bipedal gait of humans became established because it was more energy efficient and so required less food. David Raichlen, professor of anthropology at the University of Arizona, said that although in the past scholars have suggested that bipedalism may have something do to with saving energy, there was little hard evidence to support of it. ‘For […]