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Simian improvement

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Recently - well, in 2007, which is recently given how far behind I am on my reading - some scientists examined the spines of a 21 million year old fossil monkey, Morotopithicus bishopi, and concluded that it was adapted to an upright posture. This conclusion was based on a lack of the bracing against the sagging that would happen if the creature had walked on all fours, with spine horizontal; in an upright posture, the stresses are different and that bracing is not required. Since humans branched from chimpanzees only about 5 million years ago, the earlier upright fossil suggests that our common ancestor with chimps also walked upright - and in that sense was more human than chimp.

More details can be found in the article at:
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0001019

One might consider it evidence against this theory that humans' three closest living relatives - chimpanzees, gorillas, and orangutans - all tend to walk on back legs and front knuckles, rather than fully upright. They also all have bracing against spinal sag. However, it turns out that the bracing is different in each of these: vertebral facet locks - basically locking bumps in the vertebrae - in orangutans, laminar blocks - a different set of vertebral bumps - in gorillas, and ligaments in chimpanzees. Having three distinctly different mechanisms for accomplishing the same goal suggests strongly that knuckle walking evolved independently in each of these lineages, again supporting the theory that they all branched from a line with an upright posture.

One is tempted to conclude that, instead of humans evolving as an improvement on chimpanzees, chimps devolved from humans. But is it really devolution? Another experiment now indicates that chimpanzees may be smarter than humans based on a task that involves memory, spatial perception, and numerical ordering with arabic numbers:

http://news.nationalgeographic.com/news/2007/12/071204-chimps-video-ap.html

Maybe the branch was better than the basic form after all; it's just that chimps are the improvement, and humans are the older and less effective model.
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On May 29th, 2009 05:33 pm (UTC), kirisutogomen commented:
Maybe the branch was better than the basic form after all; it's just that chimps are the improvement, and humans are the older and less effective model.

Well, let's see. 6,000,000,000 humans, 200,000 chimps, and chimps are pretty much guaranteed to be extinct in the wild within 50 years. Nope, humans are not the less effective model.

One is tempted to conclude that, instead of humans evolving as an improvement on chimpanzees, chimps devolved from humans.

Are we discussing which cousin evolved from which other cousin? In my family tree, cousins don't descend from one another, so neither of us is either evolved or "devolved" (whatever that means) from the other. We have common ancestors.

Since humans branched from chimpanzees only about 5 million years ago, the earlier upright fossil suggests that our common ancestor with chimps also walked upright - and in that sense was more human than chimp.

Sure, in that sense. But in that sense a wallaby is more human than a chimp is, which isn't very informative.

Besides, the innovation that Morotopithecus hypothetically represents is not walking around bipedally, but climbing trees and swinging from branches, so in that sense we aren't any more like Morotopithecus than chimps or gorillas are.
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On May 29th, 2009 05:55 pm (UTC), psychohist replied:
Okay, most of my wording was tongue in cheek, though the articles are valid science.

Do you have a link or reference for Morotopithecus being a tree swinger rather than a walker? As best I can tell from the article, the latter is being claimed.
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On May 29th, 2009 07:23 pm (UTC), kirisutogomen replied:
Yeah, I'm probably over-sensitive to this. I volunteer at the Museum of Science in the biology area, and we focus especially on (a) evolution and (b) human biology, so I spend a lot of time dealing with misconceptions about either or both.

Sadly, my journal access is severely limited this week, but this abstract indicates that they think it was arboreal.
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On January 10th, 2011 06:01 am (UTC), psychohist replied:
My understanding was that Morotopithecus was both arboreal and a walker, with walking along branches as the primary mode of locomotion.
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On June 1st, 2009 10:38 pm (UTC), (Anonymous) commented:
Thanks for dropping by the site on Friday and leaving a comment.
Love the 'Simian' post.
-Mahmee
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