Posted on 05/29/2002 2:11:46 PM PDT by Salman
Origin Of Bipedalism Closely Tied To Environmental Changes
Champaign - May 01, 2002
During the past 100 years, scientists have tossed around a great many hypotheses about the evolutionary route to bipedalism, to what inspired our prehuman ancestors to stand up straight and amble off on two feet.
Now, after an extensive study of evolutionary, anatomical and fossil evidence, a team of paleoanthropologists has narrowed down the number of tenable hypotheses to explain bipedalism and our prehuman ancestors' method of navigating their world before they began walking upright.
The hypothesis they found the most support for regarding the origin of bipedalism is the one that says our ancestors began walking upright largely in response to environmental changes in particular, to the growing incidence of open spaces and the way that changed the distribution of food.
In response to periods of cooling and drying, which thinned out dense forests and produced "mosaics" of forests, woodlands and grasslands, it seems likely that "some apes maintained a
forest-oriented adaptation, while others may have begun to exploit forest margins and grassy woodlands," said paleoanthropologist Brian Richmond, lead author in the new study. The process of increasing commitment to bipediality probably involved "an extended and complex opening of habitats, rather than a single, abrupt transition from dense forest to open savanna," he said.
Richmond, from the University of Illinois, with anthropologist David Begun from the University of Toronto and David Strait from the department of anatomy at the New York College of Osteopathic Medicine, describe their findings, which involved a comprehensive review and analyses of the five leading hypotheses on the origin of bipedalism, in a recent issue of the Yearbook of Physical Anthropology. Other hypotheses that remain viable, according to the team: "freeing" the hands for carrying or for some kind of tool use, and an increased emphasis on foraging from branches of small fruit trees, which is the context in which modern chimpanzees spend the most time on two legs.
For their study, the researchers combined data from biomechanics movement and posture, pressure distributions and strain gauge and from finger-shape growth and development. They found that our prehuman ancestors had terrestrial features in the hands and feet, climbing features throughout the skeleton, and knuckle-walking features in the wrist and hand; that finger curvature is responsive to changes in arboreal activity during growth. Evidence from the wrist joint, in particular, "suggests that the earliest humans evolved bipedalism from an ancestor adapted for knuckle-walking on the ground and climbing in trees."
The YPA article, according to Richmond, is "the first attempt in decades to bring together all of the available evidence for the argument that the earliest human biped evolved from ancestors that both knuckle-walked and climbed trees, rather than from ancestors living exclusively in trees and 'coming down from the trees,' or walking on the ground in ways similar to modern baboons."
Good question, I don't know. However, I imagine that the earliest campfires were probably indistinguishable from natural fires. In a real sense, according to my hypothesis, the earliest campfires were natural fires.
If I may re-direct your attention to some comments from Dr. Odent's article, which I recently posted for your benefit:
It appears that the emergence of the savannah occurred after the origin of the human family. Furthermore, we must bear in mind that the bones of our ancestor, the famous Lucy (Australopithecus Afarensis) were found eroding from the sand, lying among turtle and crocodile eggs and crab claws. And the bones of an older Australopithecus, found near Lake Rudolph in Kenya in 1995 were surrounded by many fossil vertebrates including fish and aquatic reptiles.
We must also keep in mind that even though the human family emerged several million years ago, Homo Sapiens - the modern human being - is a young species. It is worth noticing that the oldest known footprints of a modern human being - dating back 117,000 years ago - have been found on the shore of a South African lagoon.
A meandering reply...
How rude can the hammer be?
(I'm trying to remember the anthropological name for clearly artificially fashioned stone tools... something-liths.)
I might be recalling incorrectly, but when Jane Goodall observed the Chimp Wars in N'Goro N'Goro in the 70s, weren't rocks (and branches) used?
I think I've seen reports of chimps using rocks, but if you happened across one, you wouldn't know it was a "tool" of any kind. Seems to me the artificial fashioning of sticks would certainly predate the artificial fashioning of rocks.
I wonder... have any experiments ever been attempted at teaching chimps to make spears and stone tools? Could this learned info be passed on to other chimps?
I've read of a breakthrough among the Japanese snow monkeys which live on the coast. Within the last several decades, one female was observed tossing sandy seeds into shallow pools of water. The sand sank, the seeds floated, and she had a clean meal. Other monkeys learned the technique, and now the whole clan apes the practice (couldn't resist).
I'm guessing that some of the development of toolmaking is going to be cultural like this, awaiting that "eureka" moment when some ape figrued out how to make a rock or stick a little sharper, and the others learned by example.
Part of the problem with labor intensive tools would be having a practical place to keep them... either in a relatively permanent residence (which I don't think chimps generally have), or in some sort of bag, which would likely have come later.
An unfashioned rock off the ground. When someone picks up a rock in his hand and strikes it repeatedly against an anvil of some kind (another rock, typically), it acquires an identifiable pattern of pits and scratches that remain indefinitely. At some point in the fossil record, you start finding rocks that exhibit this wear pattern, but before that, nothing. Apparently these things are common; after all, the "fossilization" rate is near 100%.
I'm a former swim coach and have taught babies to "swim." They've got a breathholding reflex which enables them to float and can pump their limbs a little, but they don't have a natural instinct or capacity for swimming.
The key word being "repeatedly," meaning the same favored rock gets used. That means some practical place to keep it.
But stone tools can be much cruder than that, if the rocks are used once and then discarded. And no consistent wear pattern would result.
I could be wrong, but I believe the threshold for "repeatedly" is only a few whacks in one spot, enough to distinguish it from the natural bumping and grinding of stones. A couple of nuts should do it.
But stone tools can be much cruder than that, if the rocks are used once and then discarded. And no consistent wear pattern would result.
That's true, but then, there's no need to carry those. If tools are the key to bipedalism, "favored" rocks (as opposed to single-use rocks) would appear around the same time as bipedalism.
I don't know either, but let's assume this is the case.
First, I still believe the earliest stone tools would be used once and disposed. Once you got to the point where a particular stone was used repetedly, that would suggest some way to keep track of it, probably at least a semi-permanent residence.
Such a clan of apes would by definition be isolated to a degree from others... who knows for how long? Toolmaking could have developed for a while before being learned by others of the species.
So I don't think it's a given that we've discovered the earliest stone tools, or even any that are necessarily close to the earliest.
So, any archaeologists lurking out there, start sifting the pebbles!
Perhaps not, but we've probably discovered the earliest stone tools worth carrying. And if we're postulating that carried tools prompted us to evolve bipedalism, then we'd expect tools worth carrying to be as widespread as walking hominids throughout the fossil record. Since they manifestly aren't, we'd also have to postulate that the carrying of at least stone tools fell out of fashion, for a few thousand millenia, with the descendants of the apes who were bootstrapped (a singularly appropriate term) to bipedalism by the process of carrying them. But why would it cease to be an advantage?
It seems a pretty complicated adaptation for that use. A very long neck would require much fewer genetic changes.
Here's another advantage: bipedal walking is faster and more efficient for long-distance travel. But again, partial bipedalism doesn't cut it.
Since they manifestly aren't, we'd also have to postulate that the carrying of at least stone tools fell out of fashion, for a few thousand millenia, with the descendants of the apes who were bootstrapped (a singularly appropriate term) to bipedalism by the process of carrying them. But why would it cease to be an advantage?First, if you'll recall, I'm backing the shadow-puppet postulate. I actually don't have a hard opinion on why bipedalism evolved.
Second, I think that bones are much more obvious fossils than stone tools, even to a trained eye.
Not to be overglib, but I've lost track... is this a hypothetical?
That would presume asexual reprodution in said apes, as women never stop at two shoes.
Ah, but our knuckle-walking ancestors had opposable big toes, so they would have worn four gloves, and gloves are cheaper than shoes. (Just ask O.J.)
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