July 23, 2007 1:27 PM PDT

Why do humans walk on two legs? To save energy

Why do humans walk on two legs? To save energy
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Four legs are good--but two legs are more energy-efficient, theorizes a researcher at the University of California at Davis.

For some, walking on two legs consumes less energy than walking on all fours, according to a paper from UC Davis. The findings may help explain why human ancestors evolved into bipeds 10 million years ago.

The study--which compared data from humans and specially trained chimps on treadmills--found that humans used about 75 percent less energy and burned 75 percent fewer calories than walking on all fours or two legs for chimpanzees, according to the report.

Interestingly enough, some of the chimps in the experiment--who were taught to walk on two legs and to "knucklewalk"--also did better on two legs.

Images: Humans vs. chimps at the gym

For three chimps, bipedalism consumed more energy than walking on all fours. One chimp, however, expended as much energy walking on four legs as two legs, and one other chimp consumed less energy walking upright.

"We were prepared to find that all of the chimps used more energy walking on two legs--but that finding wouldn't have been as interesting. What we found was much more telling," Andrew Sockol, a Ph.D. candidate in anthropology at UC Davis, said in a statement. "This isn't the complete answer, but it's a good piece of a puzzle humans have always wondered about: How and why did we become human? And why do we alone walk on two legs?"

The researchers also found that, for some of the chimps, walking on two legs required no more energy than knucklewalking.

These two chimps also had different gaits and anatomy than the others. Their anatomy and skeletal characteristics, in fact, were similar to early hominid fossils that allowed for greater extension of the hind limb.

Sockol studied the biomechanics and oxygen consumption of specially trained chimps on a treadmill. While the chimps worked out, the scientists collected metabolic and kinetic data as well as information on oxygen consumption. The same data was gathered for human subjects.

One of the more difficult parts of the project was getting the chimps to walk on two legs and knucklewalk. It took two years to find a trainer--for the chimps, that is.

Fossil and molecular evidence suggests that climate changes in equatorial Africa some 8 million to 10 million years ago prompted a change in human evolution. The area had been forested, but began to become drier. This may have increased the distance between food patches. This would have forced early hominids to travel longer distances. Those that used less energy had an advantage.

The research appears this week in the online early edition of the Proceedings of the National Academy of Sciences of the United States of America.

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18 comments

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4 legged animals don't need to save evergy...
Maybe we missed a trick 10 million years ago.

Other 4 legged predators discovered that they didn't need to save energy for those long food forages; they just needed to expend a short burst of intense energy, just enough to catch some slow moving 2 legged prey.

The great human development was not our evolution to 2 legged walking (that made us weaker, for crying out loud). The pivotal human development was speech. Our close relatives, the apes, also developed dexterous hands (4 of them as a matter of fact) and nearly made it to 2 legs, but failed to capitalise on what should have been an evolutionary advantage over early man due to the failure to develop the ability to retain and pass on knowledge through the power of verbal communication.
Posted by Flytrap (82 comments )
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very true
i agree
Posted by dondarko (261 comments )
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2 legs is better
Bipedalism made us stronger, in that we can use weapons more effectively. Once we learned to throw rocks and spears and use other weapons we made, we became the most effective killers on the planet. Also, once we were bipedal that allowed us to learn to ride and tame 4 legged creatures. You don't ever see 4 legged creatures learning to ride humans. 2 legs is much better than 4 legs. We are the most versatile creatures.

I agree with this article because bipedalism is like leverage. It allowed us to use our environment more effectively, less work more results.

Other creatures have been shown to possess speech or language abilities, like prairie dogs for instance, yet they do not rule the world. Speech and language develop most likely to support social structure and behaviors and then only aid in survival.

Also much more important is probably our ability to eat everything. Thus we became skilled at killing everything. Our sense of taste or lack thereof probably help to promote our rise to the top.
Posted by pikeboss79 (2 comments )
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Well,
I regularly catch my dog riding the leg of a bipedal... :-) Not that I like it tho...
Posted by Steven N (487 comments )
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10 million years ago...
It amazes me how many people still hold on to the THEORY of evolution as the answer and
meaning behind the origins of life. It makes for decent SciFi movies but not real life.

I guess if you're not looking at the obvious, there's nothing else but to hold onto the
science of the day. For example... Today I was studying the web of a spider and how it
formed a triangular semi-circle between the house window shudders and a wood bench
on our porch. It was an architectural wonder (both structurally and aesthetically) that no
man could create. Amazing "intellect" for something that has a "brain" the size of a grain
of sand.

This is one example out of millions!
Posted by ssmiroldo (53 comments )
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Don't mean to burst your bubble but...
It amazes me how many people still hold on to the THEORY of religion as the answer and meaning behind the origins of life. It makes for decent bedtime stories but not real life.

I guess if you're not looking at the obvious, there's nothing else but to hold onto the religious fiction of the day. For example... today I was studying the movement of a robotic spider and how it walks on water just like good 'ol Jesus (<a class="jive-link-external" href="http://news.bbc.co.uk/2/hi/science/nature/3126299.stm" target="_newWindow">http://news.bbc.co.uk/2/hi/science/nature/3126299.stm</a>). It is a scientific wonder (both structurally and mechanically) that no fictional god could ever create. Even transistors have amazing "intellect" for something that has a "brain" the size of a grain of sand (and is made of sand :-)

This is one example out of millions of why man, a product of evolution, is creating his own evolution all around him... even if some intellects can't evolve enough to admit it. Gravity is a "THEORY" too...
Posted by gunplay (18 comments )
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THEORY
A scientific THEORY is a hypothesis backed by facts and observations.

As opposed to religious DOGMA which is superstition backed by burning the heretics.

But hey, feel free to assume that primitive nomadic tribes thousands of years ago - with no knowledge of genetics or biochemistry - are more likely to be right about the relationship between species than modern-day scientists.

As for your hypothesis that spiders are superior to humans perhaps you should ask it what its thought on this matter are...
Posted by JadedGamer (207 comments )
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Whatever
Yawn........
Posted by kenny-J (53 comments )
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What about the back.....
Recent studies blamed all the back problems humans seem to suffer as being a result of bipedalism.

I can't go back to quadrapedalism, so am stuck with bipedalism regardless of why or its problems.

I'd rather hear ways of helping my back problems than some little amount of energy I may or may not be saving.
Posted by kenny-J (53 comments )
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Well that is true BUT
while it is true that many if not all back problems is related to upright walking you have to remember that when we developed into bipeds the life span of an individual was much much shorter then now. with average life span of under 30 years old our predessesors did not have to wory about back pain that much. on average even today the real problems with our backs dose not come into play some time after we are 30yo.(There are some exceptions ofcourse) and if there are individuals that have them before that is is usualy becouse of other issues(like an injury or bad lifestyle) that come in to play not bipedalism.
Posted by vbp1 (15 comments )
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One Reason For Walking On 2 Legs...
There is a very simple reason why humans walk on two legs --- God said so. God made us in His image (Genesis 1:27), and I don't believe He looks like a monkey.
Posted by katkat56 (1 comment )
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So basically what your saying is that God is a bipedal? Infact I'm sure your right, I remember seeing a guy on the corner of a street claiming that he was god, well done you've just converted me :-)!
Posted by Macca567 (1 comment )
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