Humanity was born to run.
More than by brain size or tool-making ability, the human species was set apart from its ancestors by the ability to jog mile after lung-stabbing mile with greater endurance than any other primate, according to research published today in the journal Nature.
Indeed, human beings evolved as the cross-country stars of a primordial runner's world 2 million years before the advent of jogging shoes, tracksuits and arthroscopic knee surgery.
Mounting a challenge to the conventional wisdom about human origins, researchers at Harvard University and the University of Utah concluded that the ability to run long distances was the driving force shaping the modern human anatomy.
Such running ability could have given early humans a survival edge in scavenging on the open savannas of Africa.
The earliest humans, the researchers said, were marathon men and women from the tips of their distinctively short toes and long Achilles tendons to the tops of their biomechanically balanced heads.
"We have gone all this time somehow missing this truly important aspect of humans -- this [long-distance running] behavior and its impact on the design of the human body," said University of Utah biologist Dennis Bramble, who co-wrote the study.
"Primates don't do distance running," Bramble said. "We should have recognized that humans are very odd."
In a detailed biomechanical analysis, Bramble and colleague Daniel Lieberman at Harvard University suggested that distance running was not a minor byproduct of the ability to walk upright on two legs.
It ultimately led to the development of the large brain that sets modern humans apart from all other creatures.
If natural selection had not favored running, Bramble said, "We would still look a lot like apes."
The researchers compared human anatomy to early apes and hominids and found telling differences.
Take the distinctive bulge of the buttocks at the back of the human silhouette. Humans have large, well-muscled buttocks that help stabilize the body during running.
The muscles connect the femur -- the large bone in each upper leg -- to the trunk and keep the body from over-balancing with each step.
Great apes, by contrast, have narrow hips and no rump to speak of.
Chimpanzees and gorillas walk on their knuckles. Humans have a lengthy arm-swinging stride, as long in proportion for a human runner as that of a galloping horse.
