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A study found that, our ancestors evolved to walk upright for the simple reason that doing so saves energy. But for decades some scientists have suggested we evolved to walk upright because doing so helped our ancestors conserve precious calories under harsh environmental conditions, when food was scarce.

A mask worn by human volunteers and the chimps as they walked on the treadmill enabled the researchers to calculate the number of calories burned, based on oxygen consumption. Researchers also used non-toxic paint and reflective badges to mark the leg joints of both groups. This allowed a machine to track the subjects’ joints as they walked on the treadmill and to characterise their gait. A complex algorithm also revealed the muscle force exerted on the joints in each step.

The results of the experiment revealed that while a 50 kilogram (110 pound) human uses roughly 13 kilocalories to walk a kilometre (above and beyond the energy needed to keep sustain the body at rest), a similarly-sized chimp uses about 50 kcal to walk the same distance on two feet. And when chimps move on all fours they require slightly less energy – 46 kcal, on average – to cover the same distance.

Future fossil findings will tell us for sure if it energy efficiency was the key advantage and, if so, shed light on exactly which changes in anatomy allowed early hominins to conserve calories by walking upright.

Journal reference: Proceedings of the National Academy of Science (DOI: 10.1073/pnas.0703267104)

Topik: Habits