Why do humans walk on two legs? To save energy

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.


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.

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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.

The new world's tallest building

On July 21, construction reached 1,680 feet on the 141st floor of the Burj Dubai tower in Dubai, United Arab Emirates, making it the largest building in the world. The skyscraper is now 13 feet above the former record holder, Tapei 101 in Taiwan, which is 1,667 feet above the ground.
Burj Dubai is the tallest building now, and according to the official site, it's nowhere near finished. The final height and number of stories are a secret.
Credit: PRNewsFoto/Skidmore, Owings & Merrill LLP

A dry-weather crisis for Hoover Dam

HOOVER DAM, Ariz.--To get a sense of what seven years of drought in the Colorado River basin looks like, all you have to do is gaze out at Lake Mead from the top of the dam here and view the 108 feet of brightly colored earth below the familiar red walls rising from the water.
Lake Mead is 108 feet below its traditional level, the result of the many years of low rainfall, and these dry years could soon have some serious effects on the region.
I visited Hoover Dam on my Road Trip around the Southwest and was given a behind-the-scenes tour by Robert Walsh, the external affairs officer for the lower Colorado region of the U.S. Bureau of Reclamation, which manages the dam.
And Walsh was not in an optimistic mood.
He explained to me that while there have been several severe droughts in the dam's history--including one that lasted 12 years in the 1950s, as well as some in the 1970s and 1980s--this one is more serious because the population in the region has exploded, due in large part to the tremendous growth of the Las Vegas area.
Now, Secretary of the Interior Dirk Kempthorne, who has legal control over the dam, has mandated that the Bureau of Reclamation come up with a plan for how to deal with potential shortages in available water for California, Nevada and Arizona, should continued low rainfall eventually mean that the Colorado River--and thus Hoover Dam--not be able to meet those states' water demands.
The problem, Walsh said, begins with the 7.5 million acre-feet of water allotted to the lower Colorado River basin region under the Boulder Canyon Act enacted by Congress in 1928. Every year, the river has been able to provide Arizona, California and Nevada with that much water--or more--but it is beginning to look like there may be a shortfall in the future if the drought doesn't end.
Ironically, in the 1990s, the basin had a surplus of water, and Reclamation began to work on guidelines for how to share the extra water. The guidelines were completed and implemented in 2000, according to Walsh, just as the drought began.
The situation is actually quite complex, it turns out, and has to do with the interior secretary's annual responsibility to make a determination of whether there is a surplus, a shortage or a normal supply of water.
And now that it looks like we're in for the first shortage year, the secretary has demanded that Reclamation have a plan ready by this winter.
What seemed to me to have Walsh--and presumably many others--pessimistic is the sense that the likely scenario would be to come up with a plan that mandates stretching the existing supply out as long as possible, which means drawing supplies from the water table, something that can never be replaced.
Of course, one option could be to demand severe conservation on the part of southern Nevada, southern California and Arizona--the constituencies of the Lower Colorado River basin region--but who can imagine that happening?
Walsh said that all those constituencies recognize that the circumstances surrounding the river--and its water production--have changed since the dam was opened in the 1930s, and that the states understand that they have to work together to solve the serious problem that could come from continued drought and presumably water shortage.
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Yet, no one knows how to solve the problem.
Reclamation has come up with a complex matrix of possible scenarios (click here for PDF), and we may see the bureau demand some of those be implemented when it makes its determination of what to do in the case of a shortage in December.
It does appear that conservation is part of the bureau's preferred plan, and that would be good.
But judging from Walsh's assessment, it's not necessarily a bright future for the region. Droughts do come and go, but water demand is only going up, and over time, it seems certain that the region is going to need more water than is available.
And unless it comes up with some way to drastically alter its water use, the future is a more than a little scary.

YouTube video debate actually worked

It may have seemed wacky at first, but the idea of allowing Americans to pose questions to presidential candidates through brief YouTube videos turned out to be a success.
The video questions posed in Monday's Democratic debate were more personal and more direct than the circumlocutions that political journalists tend to prefer, which I admit may not be a compliment to our profession.
But the problem was that the politicians ducked, weaved and often replied without giving a straight answer. (Ironically, the first user-submitted video, which asked the candidates to "actually answer the questions that are posed to you tonight," anticipated this problem but was insufficiently persuasive.)
An example: Gary Berry, a department chairman at the American Military University and 26-year Army veteran, asked a perfectly straightforward two-part question. He wanted to know on what date after the 2009 presidential inauguration all U.S. troops will be gone from Iraq and, second, "How many family members do you have serving in uniform?"
Hillary Clinton, Christopher Dodd, Bill Richardson, Joe Biden, and Dennis Kucinich responded to the question. Only Dodd actually answered it fully, saying he served in the Army Reserves and had immediate family with military careers, though not mentioning that his stint ended back in 1975.
The ducking was embarrassingly obvious. It called to mind what Rep. Charles Rangel, D-N.Y., said last year: "This president and this administration would never have invaded Iraq, especially on the flimsy evidence that was presented to the Congress, if indeed we had a draft and members of Congress and the administration thought that their kids from their communities would be placed in harm's way."
Unfortunately, CNN moderator Anderson Cooper only infrequently pressed the candidates for a direct answer.
Questions posed by YouTube videos ranged from topics such as Iraq and Social Security to unusual queries about Al Gore and Barack Obama being "black enough."
According to the format worked out in advance by CNN and YouTube, which is owned by Google, Monday evening's Democratic Party-sanctioned debate in Charleston, S.C., was based on video questions submitted the public by Sunday evening. CNN received nearly 3,000 videos and its editors selected 39 for use during the two-hour debate.
Many of the questions were more pointed than what traditional moderators might ask. One video submitted by Rob Porter of Irvine, Calif., asked Clinton: "How do would you define the word 'liberal?' Would you use this word to describe yourself?"
Clinton replied that liberal "originally meant" someone who supported freedom, but "in the last 30 to 40 years it has been turned up on its head." Clinton said she is a "modern progressive" and agreed with the moderator that she would not consider herself to be a liberal.
Another pointed question came from Jordan Williams, a black student in Kansas, who asked Sen. Barack Obama, D-Ill., how he would handle concerns about the senator not being "authentically black enough?" (Cooper, the moderator, repeated the question and then apologized for asking it.)
Obama's response: "When I'm catching a cab in Manhattan in the past I've given my credentials. Race permeates our society. It is still a critical problem. But I do believe in the core decency of the American people."