Origin Of Bipedalism Closely Tied To Environmental Changes

Space Daily ^ | 05-01-2002 | staff writer at Space Daily

[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."

[Physicist]

I think that bones are much more obvious fossils than stone tools, even to a trained eye.

That's entirely possible, but presumably the same trained eyes are looking at strata from two million years ago and four million years ago, and they do see a remarkable change in the number of tools.

Not to be overglib, but I've lost track... is this a hypothetical?

Perhaps I misunderstood. I thought your "small group" idea was to explain the paucity of noticably stone tools. That may have been true, but it would predate (or be contemporaneous with) the evolution of bipedalism; all of the seed stock of proto-humanity must have been doing it, or we wouldn't have developed this way. But in the fossil record, we see that the paucity of noticably worn stone tools continued for millions of years after the emergence of bipedalism. So most of them must have stopped carrying stone tools around as their forefathers did, for awhile.

[mamelukesabre]

Bipedal walking is faster?? I don't think I buy that.

Here's a trivia question for everyone, and sorry, I don't have a link or a source.

Q. If a perfect example of every species were lined up at a starting line for a race and at the signal each individual is to begin running(or walking) at his/her desired pace untill dead due to total exaustion....which one would traverse the greatest distance before dying? The rules being that swimming and flying are disqualified, and no resting, sleeping, eating, or stopping is allowed. Also, the race is not to take place in extreme climate or weather conditions or harsh terrain. Assume this race takes place in a garden of eden like environment.

A. the human being would win this contest.

It is due to a combination of unique physical features of the human body. Bipedalism is a big one. Also the fat reserves contribute. But there are two more that people are not often aware of. A healthy human foot has two arches that make for extremely efficient locomotion, the most efficient in all the animal kingdom in fact. And the human nose and nasal cavities are very good at capturing and recycling moisture from exhaled breath...of course, you need to breath through your nose for it to work properly...so all you mouth breathers out there would lose the race, hehe.

There was a tribe of africans that hunted in this way. They did not have projectile weapons, so they captured game by being expert trackers and having superior endurance. Equipped with only a club, they would choose their prey and persue it for days and nights on end without stopping. They would literally chase the animal untill it was totally exausted, and then club it to death. It didn't matter how fast this animal was, the animal always lost in the long run.(pun intended)

[Physicist]

Bipedal walking is faster?? I don't think I buy that.

I specified long-distance travel. You might outrun a chimp in a sprint, or you might not. You will outrun a chimp in a marathon.

For the purposes of survival, fast sprinting is a much more immediate advantage than fast migration, so I don't think speed was the issue that drove our evolution towards bipedalism. That transition happens quickly or not at all, so it requires a very strong and immediate selector. Thus, fast migration is probably more of a fringe benefit of bipedalism than a cause of it. Still, it is an advantage.

[mamelukesabre]

Oh, I see. THe english language is sometimes not clear.

"...is faster and more efficient for long distance travel..."

That sentence has two interpretations. "for long distance travel" could apply only to "efficient", or to both "efficient" and "faster".

[Vinnie]

The females were the first bipedal. Down on all fours put them in an 'exposed' position. They got tired of being continously mounted. ( The headache hadn't been invented yet).
The females decided to try two feet only as a defense against the males.

[gore3000]

Another evolutionist hypothesis without any evidence for it. Aside from ability to carry weapons, it does not help much. Speedwise four footeds are faster. There is also a lot more to changing from four leggedness to two than just wishing it. Lots of structural changes, muscular changes, etc. need to accompany such a change and wishing it does not do it. Of course, the fossils showing that this happened will be found, in another 150, 300, 1,000, 10,000, 1,000,000 years or so.

Only thing that this article shows is that evolution is the anti-science. With real science the evidence comes first and then the explanation. With evo-science, the explanation comes first and then they make up the evidence.

[Bob J]

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[sarasmom]

As to a human infants comfort and/or affinity to water, it is easily explained by the dynamics of the human womb and the large, water filled embryonic sac.Sara kicked hard enough sometimes, I can believe she thought she was swimming in a very small pool.LOL

[U S Army EOD]

Actually, it was the transition from the Marine Corp to the Army. The Army learned to walked upright due to more sohpistcated weapons. The Jarheads still spill their beer.

[paulklenk]

your dog makes his own Vitamin C

But if he sells it on eBay, he's not allowed to make any claims about its ability to cure or prevent illness.

[U S Army EOD]

A crocodile can run much faster on his hind legs than on four. They can run for quite a distance like that and faster than a horse.

Also, if you have ever been mugged in a big city, it happens a lot like you mention when you try to run.

[hosepipe]

[ 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. ]

Damn they were smart.... HEY Og!.... its a long way over there....
Why don't we, like, just stand up and walk!... ?

BWAHAHAHAHAHAHA

[hosepipe]

I never really liked walking on my knuckles anyway....

BWAHAHAHAA

[U S Army EOD]

The question of the day is, "Where are the kangaroos hiding all of their tools"?

[RightWhale]

Bipedalism and the development of the new, larger, and improved brain allowed new food-gathering techniques. In particular, man could see over the tall grass constantly rather than intermittently and thereby spot game. The larger brain allowed improved rock-throwing skills so small animals once spotted could be killed from a distance thereby imnproving the diet. When rabbits were added to the traditional diet of bugs and berries, man grew strong and multiplied.

Whether moving from the forest to the savannah cause such physical changes is a different question, but there is little question that the modifications enhanced hunting ability.

[U S Army EOD]

Are you saying we had to watch rabbits to learn how to reproduce on a grand scale? I guess that finally explains why there are so many people. We were always a little perverted I guess.

[<1/1,000,000th%]

Good post!

[<1/1,000,000th%]

Where are the aquatic ape fossils?

Now you're getting serious and spoiling all the fun. ;)

[U S Army EOD]

You must have seen "Quest for Fire". As a result of that movie, I at times wonder what certain young ladies would look like bent over at the waterhole.

[chilepepper]

the shorelines have moved: also, we would need to be very lucky since

shoreline == waves

and those would make mincemeat of bones.

a cave near an ancient shore might be the best bet, or a rock formation near an ancient volcano...