In late May, I shared with you a paper that introduced us to the hypothesis of bipedalism originating in Orangutans. I thought it was a rather foolish hypothesis to make considering the wealth of comparative anatomical and physiological research done with chimpanzee to human gaits. Chimpanzees have more similar anatomy to us than Orangutans and Gorillas, and they walk bipedally a bit more than Gorillas and Orangutans. I was surprised that Science published it despite these well established facts.

Now, a new paper published in PNAS last week vindicates some of my concerns from the above publication. It is tilted, “Chimpanzee Locomotor Energetics and the Origin of Human Bipedalism” and comes from Herman Pontzer, from Washington University in St. Louis who collaborated with several other colleagues in studying energetics and biomecanics of adult chimpanzees and humans, using treadmills. A similar publication was conducted in 1973, but it was flawed in that it used juvenile chimps, which have a different gait compared to their adults. So this study is significant because it retests the same experiments done before, but under new conditions.

The team also took their analysis a step further, from EurekAlert,

“[they] also examined the early hominin fossil record, which they found to include predicted changes consistent with lower energy cost- longer hind legs compared to body mass and structural changes to the pelvic bone allowing for more upright walking.

Analysis of these features in early fossil hominins, coupled with with analysis of bipedal walking in chimpanzees, indicate that bipedalism in early, ape-like hominins could indeed have been less costly than quadrupedal knucklewalking.”

I’ve plucked one of the more enlightening figures from the PNAS paper, which clearly shows how human bipedalism exerts less tension than the chimpanzee form of bipedalism.

Comparison of walking mechanics in chimpanzees and humans.

So, I consider this study more analytical than the several orangutans that swayed back and forth in trees. To end this post, if you aren’t convinced on what I’ve been arguing for then the following video should surely convince you: