for National Geographic News
Humans started to jog around two million years ago, according to fossil evidence of some distinctive features of the modern human body.
A new study suggests humans may have left their tree-swinging ancestors behind because they developed into endurance runners. This ability, the researchers say, may explain why humans look the way they do today.
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"We are very confident that strong selection for runningwhich came at the expense of the historical ability to live in treeswas instrumental in the origin of the modern human body form," said Dennis Bramble, a biology professor at the University of Utah.
Bramble is co-author of the new study, published tomorrow in the science journal Nature.
The researchers identified a range of physical traits that suggest human ancestors evolved as distance runners. The adaptations helped them chase down prey and compete more effectively with the speedier carnivores on the open plains of Africa, the study says.
The researchers say adaptations for running stretch back more than two million years, allowing humans to evolve from our apelike ancestors Australopithecus.
"We think running is one of the most transforming events in human history," Bramble added. "We are arguing the emergence of humans is tied to the evolution of running."
The conventional theory is that our distinctive body form derives from an improved walking ability in early hominids, and that running was simply a byproduct of this earlier adaptation. Also, humans are considered unaccomplished runners when compared to mammals such as pronghorn antelopes, which can sprint at 40 miles an hour (60 kilometers an hour) for several minutes.
But Bramble says human running ability is often underestimated. "What's important is combining reasonable speed with exceptional endurance," he said.
The study notes that athletic humans can outrun horses and antelopes over extremely long distances. In parts of Africa this technique is still used today by hunters to exhaust their prey.
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