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Origin Of Bipedalism Closely Tied To Environmental Changes
Space Daily ^ | 05-01-2002 | staff writer at Space Daily

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."

TOPICS: Culture/Society; Extended News; Philosophy
KEYWORDS: godsgravesglyphs; humanevolution; origins; thelatesttheory
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I am not a "young earth" creationist. I don't say God created the universe. I say God is creating the universe. God is outside of time in any case.

Nevertheless, I remain skeptical of stuff like this. Still a good read, and possibly true, IMO.

1 posted on 05/29/2002 2:11:47 PM PDT by Salman
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To: Salman
I see the picture but these people are on foot. What happened to the bikes?
2 posted on 05/29/2002 2:17:32 PM PDT by A Vast RightWing Conspirator
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To: Salman
If global warming hits, do you think people will switch to unipedalism?
3 posted on 05/29/2002 2:18:10 PM PDT by Atlas Sneezed
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To: Salman
On the other hand, the origin of motorcyclism is likely tied to age, which makes bipedalism seem like too much effort ;)
4 posted on 05/29/2002 2:18:57 PM PDT by Sender
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To: Salman
It's obvious the humans started to walk upright because the can of beer kept geting spilled by dragging the knuckles.
5 posted on 05/29/2002 2:19:03 PM PDT by brooklin
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To: Salman
Adam and Eve were created walking and talking. All this junk science is good for is to try to keep you from knowing your creator. And they are probably using taxpayers dollars to study this nonsense.
6 posted on 05/29/2002 2:21:53 PM PDT by Russell Scott
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To: Russell Scott
I suppose your computer is preventing you from knowing your computer as well.
7 posted on 05/29/2002 2:24:52 PM PDT by psychoknk
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To: Salman
Does being a commie lib reverse the process -- i.e., one reverts to knuckle-dragging?

Witness: Hillary Rodham. Q.E.D.

8 posted on 05/29/2002 2:24:52 PM PDT by quark
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To: psychoknk
doh! Redo:

I suppose your computer is prenting you from knowing your creator as well.

9 posted on 05/29/2002 2:25:50 PM PDT by psychoknk
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To: Russell Scott
As Popeye would say, "It's faskinating!"
BTW, did you know your dog makes his own Vitamin C, and yet you cannot?
Why would God create humans to be inferior to dogs?
The answer has to do with "use it or lose it" and
is a powerful indicator that early hominids ate fruit so
exclusively that the need to make C was selected out and didn't come back.
Else, God is a lousy craftsman.
10 posted on 05/29/2002 2:30:17 PM PDT by gcruse
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To: Salman
the growing incidence of open spaces

That fails the smell test. There aren't many four-legged things that are slower than the two-legged thing. How would being slower be an advantage in crossing open spaces? It not only takes you longer to get to the food, it makes you an easy mark for the things that want to turn you into food.

My hunch is that the "tool thing" came first, and bipedalism arose because there was a higher valued use for hands.

11 posted on 05/29/2002 2:35:10 PM PDT by Nick Danger
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To: Salman
I believe that the Aquatic Ape Theory is by far the most logical evolutionary explanation of the development of the human species.

Sea Shepherd International is an IRS fully certified 501(c)(3) non-profit organization. All donations are tax-deductible

The Aquatic Ape

By Captain Paul Watson

This article appeared in the Spring 2001  issue of Ocean Realm magazine and appears here by permission.

Sometimes scientific beliefs can be as rigidly dogmatic as religious beliefs. For the inquiring scientist who dares to challenge the "facts," the punishment is usually ridicule, and the deterrent is usually pressure to desist, or else one's career might suffer as a consequence.

One piece of scientific dogmas that has troubled me for years is the premise that modern humans descended from some savanna-hunting ape. I remember questioning this in an undergraduate anthropology class, only to have the professor silence me with that "don't be ridiculous" look.

The savanna hypothesis holds that humans left the trees and strode out upon the plains. WE became bipedal because we stood up like meerkats to peruse the horizon in search of prey. We lost our body hair as a means of regulating temperature because we began to run in pursuit of our prey under the open sun. We developed our large brains as a result of hunting in packs on the plains.

It just never seemed to click. The same theory holds that man was the hunter, and woman the gatherer, yet if body hair was lost due to running after prey, then why do women have even less body hair than men? Why do all other grassy plains predators have thick body hair and walk on four legs?

Recent evident has cast even greater doubts on the savanna theory. It appears that the conditions that created the great African grasslands did not occur until after our ancestors had already evolved to walk upright.

In 1995, South African paleontologist Phillip Tobias delivered a lecture at the University of London. He reported that foot bones found in Sterkfontein, South Africa, Demonstrated an "arboreal element" in the environment of the hominids whose fossils were found there. He concluded that Australopithecines were not plains dwellers at all. New findings of fossil animals, plants, and pollen indicate that the large brain was already well developed before any hominid set foot on the savanna. Molecular dating places the hominid/chimpanzee split somewhere between four and six million years ago.

The climate at this time was warm. Much of East Africa was inundated by a sea-level rise at the end of the Miocene period and the beginning of the Pliocene. This meant that much of the jungle was literally swamped, similar to the great salt estuaries of modern-day East Africa. The early hominid ancestors did not go to the water. The water came to them. AS a result, hominids, after the split with the chimp, literally returned to the sea.

Marine biologist Alistair Hardy first gave voice to this theory in 960. He called it the Aquatic Ape hypothesis. Hardy noticed that modern humans shared certain characteristics with marine mammals that we did not share with other primates.

Unfortunately, Hardy was advised by his academic colleagues not to pursue the theory for fear of damaging his career. Until recently, a very lonely Elaine Morgan, the author of The Descent of Woman, championed the theory. Since she gave a presentation at the 1968 Dual Congress on Paleontology and Human Biology, there has been more attention given to the idea, especially in the light of the emerging data refuting the once sacred savanna theory of human development.

The Aquatic Ape theory postulates that during a period of a million or two years after hominids broke away from chimpanzees, human ancestors spent a considerable time living and evolving in estuaries, marshy jungles and along coastal shorelines.

We share 99 percent of our DNA with the chimpanzee and we share many pliesiomorphies with chimps and other primates, the shared characteristics of species with a common ancestor. An example is that both chimps and humans have four fingers and an opposable thumb.

Apomorphies are the characteristics that separate us from our cousins. An example of this is our relative hairlessness. The fascinating thing is that most of our apomorphic characteristics are shared with marine mammals. There are physiological traits that humans and dolphins share that chimps, monkeys and gorillas do not. In fact, these characteristics are completely lacking in most land mammals.

How is it that humans can have these traits yet all other primates and most other land mammals do not? Looking at the human body and comparing it to a chimpanzee, we quite readily see both the similarities and the differences. Looking at a human body and comparing it to a seal or a dolphin, we can see the similarities that we share with both the chimps and the dolphins that differentiate the species Homo sapiens from the other primates.

Hairlessness is a characteristics shared by humans, dolphins, whales, manatees, and hippos. All are mammals, and all have hair that is extremely sparse compared to land mammals. Perceived hairlessness is a trait that has developed in tropical and subtropical marine mammal species. Elephants spend a great deal of time in the water, and there is evidence suggesting that ancestors of today's modern elephants were even more aquatic-oriented, and that the trunk may have first evolved as a snorkel.

If we look at the characteristics that we share with dolphins and do not share with chimpanzees, we find conscious breath control, greatly reduced body hair, subcutaneous body fat, and greater brain size and complexity.

Dolphins, however, became fully aquatic, whereas humans evolved to be semi aquatic.

The ability to walk upright carries great advantages in a watery environment. Two legs allow for the primate to wade into deeper water than four legs, thus expanding forage range. Over time, wading, swimming, and diving would greatly expand the range of food sources. It is interesting that the Bonobo and the Proboscis monkeys have longer legs than chimps and other monkeys respectively, and both these species do spend time in watery habitats.

Bipedalism on the grasslands would have slowed the species down, as species that run on four legs are much faster than species that run on two. Only an aquatic or arboreal-aquatic lifestyles would give a two-legged primate an advantage.

Probably the best way to examine this theory is to ask what specific features an aquatic animals would be expected to have. The next question would be: do we have these features?

Strangely, we actually have more hair follicles than our cousin, the chimpanzee. The difference is that human hair is very fine and short, giving us a hairless appearance. What we do have is ten times more adipocytes (fat cells) than the chimp.

Human babies are born fat, whereas all other primate babies are born lean. Human babies can swim from the moment of birth. Other primate babies cannot. Human babies not only float but also, after being born submerged, can swim under their own power, holding their breath until reaching the surface. In the water, the human baby is not helpless. From the moment of birth on, the human baby can swim alongside its mother.

Fat is a characteristic of marine mammals. It encourages buoyancy. It is an excellent insulator in the water. No other primates have it all over their bodies. The fat on aquatic mammals adheres to the skin, whereas on terrestrial animals it is attached to the muscle. In humans it is attached to the skin.

Human beings do not have a layer of cutaneous muscle. This layer of "panniculus carnosus" is found in most terrestrial mammals, including every primate except ourselves. This is the muscle that allows for twitching of the skin and thus allows for the twitching away of insects.

No other terrestrial animal has ever exchanged fur or thick hair for body fat as a form of thermoregulation. Rhinos, pigs, elephants and hippos all have done so, and all have been aquatic. One other group that does accumulate great amounts of fat, although retaining fur, is the hibernators like the bears. Humans are not hibernators and thus our accumulation of body fat can only be aquatic.

Another difference is that compared to all other primates, humans are notorious for wasting water. We sweat and lose great amounts of salt and water, and we expel urine much more frequently than other primates do. This kind of waste makes sense only if water is readily available to the species at all times. Add to this the fact that humans have more and larger sebaceous glands than any other primate. The role of sebum is simply to waterproof the hair and skin.

When swimming, the aquatic apes would have kept one part of their anatomy above the water more than any other part, and that of course is the head. Thus hair remained on the head to insulate the body by preventing heat loss and preventing sunstroke. L But hair also had another functional use. We are the only primate whose head hair grows to great lengths. In the water, without fur to cling to, a baby hominid needed to cling to something, and long hair provides the most practical way for the child to attach itself to the parent. It is well-researched that women's hair grows faster and thicker during pregnancy.

The development of the human female breast can also be explained by this theory. A female breast is primarily fat, and fat floats, thus the child in the water would have access to the nipple at the surface.

The most fascinating aspect of this theory however is the fact that humans possess the "diving reflex." The diving reflex, or bradycardia, is a condition which occurs in aquatic and semi aquatic animals. It involves a decrease in the heart rate and the redistribution of blood to the brain and the oranges. This process is called vasoconstriction. This ability is natural in humans. Blow on a baby's face and submerge the baby and the baby will hold its breath until it resurfaces. This ability is both voluntary and involuntary. When we choose to dives, we can hold our breath for up to two minutes, and with training up to seven minutes. Humans can dive to depths of one hundred meters at the extreme, but most humans in fair health can certainly dive to ten meters. No other primate would choose to do this.

In involuntary situations, especially in colder waters, the body can shut down, and people have survived over thirty minutes of submersion without physical or mental damage. Studies on dolphins, seals, and sea lions demonstrates that they can willfully hold their breath for long periods, but when forced to submerge without knowing when they will resurface, heart rates plummet to as low as eight beats a minute from the forty of a normal dive, and they can remain submerged for three to four times as long as they would voluntarily.

It is interesting that the diving reflex of an ex-aquatic, the pig, when trained to dive is equal to that of an untrained human being. This ability to hold and control our breath also led to a skill that we share with marine mammals and not shared by our primate cousins: the ability to form complex speech. Although we share the ability to communicate through body language and facial expressions with other primates, we depend upon complex vocalization as our primary method of communication-just as whales and dolphins do.

Complex speech is dependent upon the ability to hold and control breath. Other primates are unable to voluntarily hold their breath. Additionally, the more advanced range of sounds that humans can emit is due to a descended larynx. In humans, the larynx is deep in the throat, and unlike other apes, is no longer in contact with the uvula. This allows humans to take in air not only through the nose but also through the mouth. The larynx descended so that we could take in air through our mouths. The ability to take in air through the mouth allowed us to take deep breaths prior to diving. Thus our ability to speak the way we do is a direct result of adaptations meant for diving. A descended larynx is not found in other primates, but it is found in sea lions, walrus, and in manatees.

Let's look at our teeth. If we were predators on the plains, we should have developed baboon like canines. The fact is we do not have teeth that can tear and rip animal flesh. Yet our teeth are ideally adapted to eat practically anything in a marine environment. We can crack crustacean shells, we can eat live fish raw, and we can chew seaweed. By chewing raw fish, fresh water can also be extracted, sufficient to support a hominid for long periods without access to fresh water. Early Australopithecine teeth most closely resemble those of the sea otter. Today we possess relatively weak jaws and teeth suited for softer aquatic foods, more so than rough plant fiber and animal flesh. I once sat on the bottom in thirty feet of water and ate oysters. I was able to open them, put them in my mouth, expel the seawater and swallow them without the use of any tool or scuba equipment. I think our ancestors may have done that easily.

Look at our hands-squared compared to the elongated hands of other primates. More paddle like, and between the fingers and toes, there is evidence of webbing. Some people have more than others do. There is no doubt that we are the swimming ape. We know how to move through water and our bodies seem to be designed for it. When you pour a pail of water onto a chimp or a monkey, the hair follicles on the body actually resist the flow of water, whereas on the human, the hair follicles flow with the water.

When we pull our heads from the water, the water streams down and is diverted from the eyes by our eyebrows. This is a very functional use for this strange pattern of hair growth. Consider the nose. It also is ideally suited for submergence in water. Because we have a sinus cavity, we can equalize pressure simply by holding the nose and breathing out. Many young children have the ability to completely close their nostrils at will just like seals and dolphins do. Usually this ability is lost as the child grows, but quite possibly it is lost due to the lack of use and is a carry-through of our once-aquatic past.

Recent research (S. C. Cunnane 1999) has shown that the overall development of brain size has actually decreased in mammals and primates evolving on African savanna ecosystems. This has been linked to the deficiency in the savanna food chain of Docosahexanoic acid. This molecule is essential for brain growth and is deficient in terrestrial ecosystems although very abundant in marine ecosystems.

It is not accident that the most highly developed brains are found in the oceans among the aquatic and semi aquatic species. The best source of nutrients for a developing brain is the marine or lake habitats where essential elements like iodine, zinc, and long=chained fatty acids are plentiful.

Look at the human foot. It is an ideal structure for walking on mud and sand.

In a hostile world with jungle and grasslands literally crawling with predators, what safer place would there be than the area between the shore and deep-water? Food is plentiful, the habitat comfortable. We still all love the beach, many love to swim, enjoy the feeling of mud between our toes and like sushi. Most importantly, our physiology suggests that at some point we spent a considerable amount of time in the water.

How long? It is interesting that our fossil record is very sparse from that period when we diverged from the chimps until about a million and a half years ago. This gives a period of between two and three million years for our ancestors to have been beach bums. That's plenty of time for physiological evolution to allow for the adaptation of physical changes that would allow us to utilize the aquatic environment more efficiently.

I think the fossils exist. We've just been looking for them in the wrong places. Look instead to where the shores of Africa once were, some two million years ago, places that today are deep beneath the sea. There in the benthic muck, alongside the fossilized shells and fish bones, I am of the opinion we could find the skulls and bones of those water-loving ancestors whose chosen habitat has made us what we are today-the naked, swimming, dive-reflex-equipped, vocalizing and intelligent primates that we are.

12 posted on 05/29/2002 2:37:25 PM PDT by Maceman
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To: Salman
And I thought it was mainly because you can have quickie behind a tree far easier standing up than on all fours.
13 posted on 05/29/2002 2:37:39 PM PDT by VRWC_minion
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To: Maceman
Interesting, but I don't think it holds water.
14 posted on 05/29/2002 2:44:23 PM PDT by stanz
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To: Nick Danger
My hunch is that the "tool thing" came first, and bipedalism arose because there was a higher valued use for hands.

Your "hunch" is the most widely accepted notion today. Traditionally, it was believed that bipedalism was the result of a larger brain-to-body size---that walking upright was a singularly human trait because humans had the largest brains. The fossil record changed that thinking. Early forms, including Australopithecus were totally bipedal yet, possessed a cranial capacity not much larger than the chimpanzee.

15 posted on 05/29/2002 2:53:43 PM PDT by stanz
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To: Salman
I still like the theory of "The Naked Ape", the ancestors of homo sapiens spent time in water and lost the fur and turn upright.
16 posted on 05/29/2002 3:11:47 PM PDT by Kermit
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To: Beelzebubba
No, silly, we'll go back to swimming. Don't you know that global warming is going to cause sea level to rise by several hundred feet, leaving most of what's now land underwater? /s
17 posted on 05/29/2002 3:41:15 PM PDT by GovernmentShrinker
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Comment #18 Removed by Moderator

To: Maceman
Do you have a link?
19 posted on 05/29/2002 4:46:41 PM PDT by rmlew
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To: Salman
Its simply impossible to tiptoe through the tulips gracefully on four feet.
20 posted on 05/29/2002 6:03:01 PM PDT by jwalsh07
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