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Study identifies energy efficiency as reason for evolution of upright walking
July 17, 2007A new study provides support for the hypothesis that walking on two legs, or bipedalism, evolved because it used less energy than quadrupedal knucklewalking.
David Raichlen, an assistant professor of anthropology at The University of Arizona, conducted the study with Michael Sockol from the University of California, Davis, who was the lead author of the paper, and Herman Pontzer from Washington University in St. Louis.
Raichlen and his colleagues will publish the article, "Chimpanzee locomotor energetics and the origin of human bipedalism" in the online early edition of the Proceedings of the National Academy of Sciences (PNAS) during the week of July 16. The print issue will be published on July 24.
Bipedalism marks a critical divergence between humans and other apes and is considered a defining characteristic of human ancestors. It has been hypothesized that the reduced energy cost of walking upright would have provided evolutionary advantages by decreasing the cost of foraging.
"For decades now researchers have debated the role of energetics and the evolution of bipedalism," said Raichlen. "The big problem in the study of bipedalism was that there was little data out there."
The researches collected metabolic, kinematic and kenetic data from five chimpanzees and four adult humans walking on a treadmill. The chimpanzees were trained to walk quadrupedally and bipedally on the treadmill.
Humans walking on two legs only used one-quarter of the energy that chimpanzees who knuckle-walked on four legs did. On average, the chimpanzees used the same amount of energy using two legs as they did when they used four legs. However, there was variability among chimpanzees in how much energy they used, and this difference corresponded to their different gaits and anatomy.
"We were able to tie the energetic cost in chimps to their anatomy," said Raichlen. "We were able to show exactly why certain individuals were able to walk bipedally more cheaply than others, and we did that with biomechanical modeling."
The biomechanical modeling revealed that more energy is used with shorter steps or more active muscle mass. Indeed, the chimpanzee with the longest stride was the most efficient walking upright.
"What those results allowed us to do was to look at the fossil record and see whether fossil hominins show adaptations that would have reduced bipedal energy expenditures," said Raichlen. "We and many others have found these adaptations [such as slight increases in hindlimb extension or length] in early hominins, which tells us that energetics played a pretty large role in the evolution of bipedalism."
University of Arizona
Bipedalism marks a critical divergence between humans and other apes and is considered a defining characteristic of human ancestors. It has been hypothesized that the reduced energy cost of walking upright would have provided evolutionary advantages by decreasing the cost of foraging.
"For decades now researchers have debated the role of energetics and the evolution of bipedalism," said Raichlen. "The big problem in the study of bipedalism was that there was little data out there."
The researches collected metabolic, kinematic and kenetic data from five chimpanzees and four adult humans walking on a treadmill. The chimpanzees were trained to walk quadrupedally and bipedally on the treadmill.
Humans walking on two legs only used one-quarter of the energy that chimpanzees who knuckle-walked on four legs did. On average, the chimpanzees used the same amount of energy using two legs as they did when they used four legs. However, there was variability among chimpanzees in how much energy they used, and this difference corresponded to their different gaits and anatomy.
"We were able to tie the energetic cost in chimps to their anatomy," said Raichlen. "We were able to show exactly why certain individuals were able to walk bipedally more cheaply than others, and we did that with biomechanical modeling."
The biomechanical modeling revealed that more energy is used with shorter steps or more active muscle mass. Indeed, the chimpanzee with the longest stride was the most efficient walking upright.
"What those results allowed us to do was to look at the fossil record and see whether fossil hominins show adaptations that would have reduced bipedal energy expenditures," said Raichlen. "We and many others have found these adaptations [such as slight increases in hindlimb extension or length] in early hominins, which tells us that energetics played a pretty large role in the evolution of bipedalism."
University of Arizona
Bipedalism Current Events and Bipedalism News RSSEarly hominid first walked on two legs in the woods
Among the many surprises associated with the discovery of the oldest known, nearly complete skeleton of a hominid is the finding that this species took its first steps toward bipedalism not on the open, grassy savanna, as generations of scientists - going back to Charles Darwin - hypothesized, but in a wooded landscape.
Anthropologist's studies of childbirth bring new focus on women in evolution
Contrary to the TV sitcom where the wife experiencing strong labor pains screams at her husband to stay away from her, women rarely give birth alone. There are typically doctors, nurses and husbands in hospital delivery rooms, and sometimes even other relatives and friends. Midwives often are called on to help with births at home.
Did walking on 2 feet begin with a shuffle?
Somewhere in the murky past, between four and seven million years ago, a hungry common ancestor of today's primates, including humans, did something novel.
Evolution tied to Earth movement
Scientists long have focused on how climate and vegetation allowed human ancestors to evolve in Africa. Now, University of Utah geologists are calling renewed attention to the idea that ground movements formed mountains and valleys, creating environments that favored the emergence of humanity.
New findings solve human origins mystery
An extraordinary advance in human origins research reveals evidence of the emergence of the upright human body plan over 15 million years earlier than most experts have believed.
Study Sheds Light on Why Humans Walk on Two Legs
A team of anthropologists that studied chimpanzees trained to use treadmills has gathered new evidence suggesting that our earliest apelike ancestors started walking on two legs because it required less energy than getting around on all fours.
The origin of human bipedalism
While no one has an authoritative answer, anthropologists have long theorized that early humans began walking on two legs as a way to reduce locomotor energy costs.
Early human ancestors walked on the wild side
Arizona State University anthropologist and Institute of Human Origins researcher Gary Schwartz, along with fellow anthropologist Dan Gebo from Northern Illinois University, DeKalb, have studied fossil anklebones of some early ancestors of modern humans and discovered that they walked on the wild side.
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