In Evolutionary Race, Humans Went the Extra Mile, Study Says
By Robert Lee Hotz
Times Staff Writer
November 18, 2004
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.
Long ligaments and tendons  including the Achilles tendon  serve as springs that store and release mechanical energy during running. The Achilles tendon on an ape is a mere stub.
The researchers also identified other anatomical features:
• A more balanced head with a flatter face, smaller teeth and short snout, compared with prehuman species. That makes it easier to balance the head during the up and down shocks of running.
• A ligament that runs from the back of the skull and neck down to the thoracic vertebrae. It acts as a shock absorber and helps the arms and shoulders counterbalance the head during running.
• Wide shoulders that allow the body to rotate during running. A narrow trunk, waist and pelvis allow the upper body to counteract the movement of the legs.
• The stiff arch of the human foot. That allows a runner to push off the ground more efficiently and utilize ligaments on the bottom of the feet as springs. Humans also have an enlarged heel bone for better shock absorption, as well as shorter toes.
The new theory immediately stirred a scholarly controversy among experts in biomechanics, human origins and comparative anatomy.
"I question whether endurance running was the evolutionary turning point that helped morph us into our modern form," said anthropologist Ken Mowbray at the American Museum of Natural History in New York. "I think a lot of other things had to take place."
But Richard Klein, an expert in human origins at Stanford University, said: "I think they make a strong case that, from the beginning, an important advantage of modern bipedalism was that it facilitated long-distance running."
Until now, the importance of running as an evolutionary force has been lost in the debate over why humanity's early ancestors first evolved their upright stance, said Christopher Ruff, director of the Center for Functional Anatomy and Evolution at Johns Hopkins University.
Randall Susman, an expert in comparative early human anatomy at the State University of New York at Stonybrook, said that humanity's pathetic performance as a sprinter made the ability easy to overlook.
People are so slow in the short run that almost any dog can chase down a fleeing human being, as many postal carriers have learned from experience.
When it comes to long-distance running, however, a healthy human jogger can outrun most animals, sustaining a pace of 15 miles a day or more for extended periods of time.
"That is an astonishing capability," said Lieberman, who specializes in biological anthropology at Harvard. "Most animals can't do that.
"Generations of anthropologists have focused on walking and left running completely out of the picture," he said. "But there are a lot of features of our bodies that only make sense in terms of running."
The muscles, tendons and bone structures necessary for efficient long-distance running are quite different from those needed for steady walking.
"We don't appreciate how dramatic the differences between walking and running are because the transition between them is so smooth," Bramble said. "But the biomechanics are fundamentally different."
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