Well, I guess I'll be a monkey's uncle after all!

[Uthgar the Brazen]

Walking upright (http://news.yahoo.com/s/livescience/20071010/sc_livescience/humanancestorswalkeduprightstudyclaims) may not be as "new" to humans as previously thought. With apes possibly being the move evolved in terms of ambulation, that would make Planet of the Apes...

:gasp:

[JoeP]

I can't view the article ...
dc:title="Human Ancestors Walked Upright, Study Claims" trackback:ping="http://labs.news.yahoo.com/trackback/livescience/humanancestorswalkeduprightstudyclaims" /> --> <link rel="stylesheet" type="text

In fact I don't think I've been able to see news.yahoo.com pages for days. Is everyone else getting it OK? Tried different browsers and different network connections.

[Uthgar the Brazen]

Still shows for me okay. :shrug:

Here's a wee bit of it, anyway.

The ancestors of humanity are often depicted as knuckle-draggers, making humans seem unusual in our family tree as "upright apes."

Controversial research now suggests the ancestors of humans and the other great apes might have actually walked upright too, making knuckle-walking chimpanzees and gorillas the exceptions and not the rule.

In other words, "the other great apes we see now, such as chimps or gorillas or orangutans, might have descended from human-like ancestors," researcher Aaron Filler, a Harvard-trained evolutionary biologist and medical director at Cedars-Sinai Institute for Spinal Disorders in Los Angeles, told LiveScience.

[Dingfod]

I've seen some devolution like that among some of the homo "sapiens" I've known.

[Sock Puppet]

And where the HELL is The Lone Ranger with his commentary on this subject? What am I paying that guy for?

Oh yeah, I'm not paying him. But that's no excuse, dammit! :shakeshaker:

[Uthgar the Brazen]

He's probably off somewhere "teaching." Jesus, what a shiftless bum.

[The Lone Ranger]

My apologies! I've been absolutely swamped the past few weeks!


Actually, it wouldn't surprise me at all if it were to turn out that an upright stance is the ancestral condition in the ape lineage, and that the "knuckle-walking" quadrupedalism of modern non-human apes is a derived trait.


You have to keep in mind that forest-dwelling animals very rarely fossilize. By contrast, animals that live in plains (especially floodplains) environments are far more likely to leave fossils behind. So, as it happens, we know a lot more about human evolution from the fossil record than we do about the evolution of chimps, gorillas, or orang-utans -- that's because our immediate ancestors lived on the African plains and left us lots of nice fossils, while the ancestors of the other Great Apes presumably lived in forests and left few -- if any -- fossils for us to discover.

So far as I'm aware, there have been no fossils discovered so far that are universally agreed to be ancestors of gorillas or chimpanzees. That's unsurprising (though disappointing) if all the various species in question were forest-dwellers.


Or is it that we had some of the fossils all along and we were mis-interpreting them?

You see, the earliest fossils that are universally agreed to be part of the human lineage are various species in the genus Australopithecus. These fossils go back to about 5 million years ago or thereabouts. The weird thing is that even the oldest fossils in the genus Australopithecus had hips and legs that were well-adapted for walking upright.

The usual assumption is that the Australopithecines represent an ape lineage that came out of the forest and onto the plains, and that selection for life on the plains led to the rapid evolution of an upright stance. Okay, but if that's the case, why were the earliest-known Australopithecines already well-adapted for walking upright?

If Australopithecines had evolved an upright stance (allowing for more efficient locomotion in the trees) before moving onto the plains, the mystery is neatly solved. It just so happens that an upright stance is also useful for a plains-dwelling species, and so was preserved in those Australopithecines that eventually gave rise to the genus Homo.


A bipedal stance can be an effective means of locomotion for a forest-dwelling animal, and many monkey species and smaller ape species (notably gibbons) are effectively bipedal. But for larger apes, bipedalism isn't so efficient, perhaps because they're too heavy for brachiation to be an efficient means of locomotion. This might help explain why chimps and especially gorillas spend so much time on the ground and tend to walk on all fours.


But what about the ancestors of non-human apes? Where did they come from?


The fossil record shows clearly that there were at least 2 different lineages among the early Australopithecines. The "Robust" Australopithecines were much larger and more heavily built. The "Gracile" Australopithecines were smaller-bodied and much more lightly built. The usual assumption is that the Robust Australopithecines went extinct, with no modern descendants, while the Gracile Australopithecines gave rise to the genus Homo and, ultimately, to us.


It has been recently suggested, however, that this was not the case. Some paleoanthropologists think that the Robust Australopithecines went back to the forest and ultimately gave rise to the Gorillas. (This would explain why they disappeared from the fossil record -- not because they went extinct, but because they went back to the forest and so left us no fossils.) Similarly, it may be that some of the Gracile Australopithecines went back to the forest as well, and gave rise to the Chimpanzees. This would neatly explain the close morphological and genetic similarities between Gorillas, Chimpanzees, and Humans, and it would also fit neatly with the fact that genetic analyses clearly indicate that Chimpanzees are more closely related to Humans than they are to Gorillas.


So, it wouldn't surprise me in the least to find that bipedalism arose very early in the ape lineage, and that "knuckle-walking" in modern non-human apes is a "derived" state whereas human bipedalism is actually a "primitive" state. It would neatly explain a number of puzzling things about human/ape evolution.



I'm not so sure I buy their argument about the horizontal septum, though. I've dissected lots of vertebrates, and the horizontal septum is very clearly evident in fishes, for example, but it isn't a prominent feature in any mammals, so far as I can see. It would be interesting if our bipedalism was the result of a macromutation that happened to make walking on all fours uncomfortable, but I don't buy it.


Cheers,

Michael