Chimpanzees Gait Energetics & The Origin of Human Bipedalism

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:

5 thoughts on “Chimpanzees Gait Energetics & The Origin of Human Bipedalism

  1. “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.”

    Is it “new”, right? Because as far as I know (or knew), humans were first considered to be “at the other end” of the “apes” group, having split before or right after babboons, and it was based on larger morphological similarity with orangutans and babboons (I believe that in earlier times gorillas were proposed as an alternative of the closest living relative too).

    Then somewhat later, but just with molecular data that we were revealed as more closely related with chimps than they are with gorillas. And even then, people like Schwartz will still say that it’s “only genetics” that bring humans and chimps closer to humans than to orangutans, and that (unbearably cranky proposition if you ask me) we’re really more closely related with orangutans.

    So, even despite the anti-genetics crankyness, humans are not even more similar anatomically to orangutans, babboons and gorillas “anymore”?

    I think I’ve read about non-cranky human-orangutan proximity in things as “new” as Pilbeam’s “the ascent of man”, which is from the 70s. But it was not the supported view, the molecular data was known and accepted already. I think it was mentioned as relevant though, as if the (more common) anatomical similarities between orangutans and babbons and humans suggested that we evolved from brachiators (or “not so good brachiators”, whatever orangutans are), not from knuckle-walkers or fist-walkers. So we’d be retaining an improved secondary bipedality, whereas gorillas and chimpanzees evolved independently as faster “quadrupeds”.

    At least from the perspective of someone who is not trained on that, their skeleton looks more similar to ours . The rounded shape of the ribcage, rather than somewhat like a funnel (but oddly enough, gorillas and chimps are more like neanderthal’s in this sense, which I think that maybe would be the best support against it being a plesiomorphy), and the shoulders, most obviously. But I think that even the hips, somewhat.

    It’s very surprising to me that only relatively recently that we’d be found to be more similar in “adaptive” traits like these, rather than some subtle details that may be more relevant to infer relatedness.

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