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Snarlio t1_iwr1yja wrote

Reply to comment by Notorious_Rug in I saw in a video that chimpanzees and gorillas do not knuckle-walk in the same way, but they didn't explain what the difference is. Could someone elaborate on the physiological/anatomical differences? by [deleted]

I think it's also worth noting that the clavicle (collar bone) of arboreal apes is different than that of terrestrial apes. Gorillas have a more "C" shaped collar bone, which allows for a lot more force to be applied to the sternum and rib cage without the bone breaking. This lets them put a lot more weight on their arms safely.

Chimpanzees have an "S" shaped clavicle, which is not nearly as efficient in transferring force, but allows for a lot more mobility for brachiation (swinging through trees). It's the same reason that people can break their collarbones when they fall face first and use an outstretched arm to break their fall - we also have "S" shaped clavicles.

Found this after a quick search: https://doi.org/10.1002/ar.a.20354 Figure 2 shows the bones in question

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FillRevolutionary900 t1_iwr5n7n wrote

But then humans are terrestrial apes, not arboreal apes. So why do we have S shaped clavicles like chimpanzees?

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waterslidelobbyist t1_iwr9rvz wrote

We share a common ancestor with chimpanzees more recently than with gorillas. Either the mutation to a more gorilla-like clavicle hadn't happened or was not enough of an advantage to be selected for as we evolved away from proto-chimps.

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FillRevolutionary900 t1_iwrab2v wrote

But that makes the statement distinguishing the terrestrial apes and arboreal apes in terms of the shape of their clavicles meaningless. Because there are really only two terrestrial apes (gorillas and humans), and one of those two doesn't fit what the statement claims. So why make that distinction in the first place.

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waterslidelobbyist t1_iwrkjyx wrote

I'm honestly not smart enough to explain the distinction but I'll try. We're one of the two terrestrial apes now, but in the Miocene we've got a whole grip of weird apes running around Africa and Eurasia on the ground, and they're all more closely related to gorillas and have similar adaptations.

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Norwester77 t1_iwt0whv wrote

We don’t seem to have gone through a knuckle-walking stage (the ancestors of gorillas, chimps, and humans became terrestrial independently of one another), so our clavicles never had to support much body weight.

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