Study: Walking Upright Tied to Energy Conservation

A new study published in the Proceedings of the National Academy of Science suggests that walking upright (bipedalism) was likely an attempt by early hominins to conserve energy.

The study was conducted by Michael D. Sockol, Academic from the Department of Anthropology at the University of California at Davis, David A. Raichlen, Assistant Professor in the Department of Anthropology at the University of Arizona in Tucson and Herman Pontzer from the Anthropology Department at Washington University in St. Louis, Missouri.

The research was in response to questions of why early hominins developed an exclusive approach to movement that involved two legs.

The researchers evaluated the energy conversion and biomechanical features in adult chimpanzees and humans to assess if bipedalism actually lessened energy expenditure. To accomplish this, the team collected metabolic and kinematic (motion) information from five chimpanzees that were trained to walk on a treadmill using two (bipedal) and four (quadrupedal) extremities at a time, and subsequently compared it to data from four adult humans also walking on a treadmill.

As shown by previous studies, the research team was able to confirm that there was no difference in the energy expenses incurred by bipedal and quadrupedal chimpanzee locomotion.

When they conducted a more detailed analysis however, the team found that in most individuals, there was a significant variation in bipedal and quadrupedal energy expenditure. The investigators realized that these differences were hidden when the groups were analyzed collectively.

An examination of the anatomical and gait data, revealed that human walking is approximately 75% more energy efficient than quadrupedal or bipedal walking in chimpanzees. The biomechanical differences that conferred this advantage were specifically related to humans having an enhanced extended hip and a longer posterior limb.