The truth about why we walk on two legs: it saves energy

The truth about why we walk on two legs: it saves energy:

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.

Rival Theories:

• Tree walking: A recent theory suggests that our tree-living ancestors walked upright on branches, using their arms for balance. The idea is based on observing modern-day orang-utans, which often move around in trees by walking on two legs, gripping the branches with their hands.
• A cooling effect: Another idea is that it was cooler to walk upright in savannah grasslands because by doing so there was less surface area of the body exposed to the Sun.
• Wading in water: If our ancestors had to wade through water, they would have learned to walk on two legs. Modern-day chimps often adopt a two-legged gait when walking through water.