What made us human? Running, study says
By Glennda Chui
San Jose Mercury News

Baby, were we born to run?

In a report Wednesday, scientists suggest that endurance running—a long, steady jog, rather than a sprint—played a major role in human evolution. They say it helped shape our bodies, giving us long legs, big bottoms, knobby ankles and trim waists.

And it may have given our ancestors the ability to pursue the protein-rich diet needed for the development of big brains.

"Running made us human—at least in an anatomical sense. We think running is one of the most transforming events in human history," said Dennis Bramble, a paleontologist at the University of Utah who studies the mechanics and evolution of the body.

Until now, the report said, studies of early human locomotion have focused on walking, one of the key points that distinguishes humans from apes.

"Running has been completely ignored in human evolution," probably because of the general impression that people are lousy runners compared with other animals, said co-author Daniel Lieberman, a paleoanthropologist at Harvard University.

But it turns out that’s not true, the researchers contend in the report published Wednesday in the journal Nature.

"For their body size, humans are really quite good," Bramble said. "And what they do better than almost anything else is combine reasonable speed with really remarkable endurance."

The report draws on studies of how people and animals run and walk, along with information from fossils of human ancestors. There, the researchers say, they found more than two dozen traits associated with running—from a tall, narrow body shape to longer legs and a more balanced head.

Our gluteus maximus muscles had to become bigger and stronger so we would not pitch forward when going at a trot. "If you look at apes— and I have—they’ve got no buns, they honestly don’t," Bramble said.

Our lower legs also slimmed down, allowing a more efficient gait and revealing our ankle bones.

None of these features are found in the primitive hominids known as australopithecenes, which walked on two legs by at least 4.4 million years ago, the authors assert. They appear only about 2 million years ago, after early human species, such as Homo erectus, entered the scene.

Christopher Dean, an anatomy expert at University College in London, said the report makes a compelling case.

"I would imagine most people would look at this package of evidence and say this really does make sense," he said. "Its strength is that it brings together a huge amount of evidence from all regions of the body," from the structure of the feet to the way people freely sweat to get rid of excess heat.

Not everyone agrees, however.

C. Owen Lovejoy of Kent State University in Ohio, an expert on australopithecenes, said these primitive hominids did, in fact, have many of the traits that are supposedly found only in runners.

"My big criticism is not that humans and australopithecenes were not adapted to running. Of course they were," he said. "My criticism is with the argument that they were adapted for endurance running, which is somewhat fictional."

When human ancestors came down from the trees and began prowling the savanna, he said, they would have needed the ability to make a quick dash to get away from danger.

In contrast, Lovejoy said, it’s hard to see why a steady jog would have given them an edge in the fight for survival.

"Suppose you find an animal. You chase it across the savanna for 10 miles until it collapses from exhaustion," he said.

"You’ve been sweating a lot. Did you carry extra water with you? What do you do with the carcass? You’re 10 miles from your home base. Were you carrying really heavy pebble tools to chop it up with? What if you don’t have pebble tools? How do you get it back?"

Lovejoy said one could make an equally valid argument that people evolved to swim or drive cars or pet cats, simply because we now do all those things so well.

However, Bramble, who takes an engineering approach to studying the way animals are designed, said humans are definitely not built to sprint.

"I venture to say you would be chased down promptly by almost any dog on your block, let alone a lion or leopard or whatever," he said. "Those mammals can gallop, and we can’t."

On the other hand, he said, some modern people, such as the Tarahumara Indians of Mexico’s Copper Canyon, are known to run effortlessly for hours, and athletes have run marathons since ancient times.

Although a human on the run moves in a sort of upright trot, rather than a gallop, we have incredibly long strides for our body size, Bramble said. Further, our Achilles tendons and the ligaments in the arches of our feet are powerful springs that recoil every time we push off the ground, helping us run more efficiently.

While there is good evidence that hunter-gatherers sometimes run down prey, Bramble said he doesn’t think hunting spurred the evolution of endurance running.

Instead, he speculates that it might have allowed early humans to beat other scavengers to the carcasses of animals that had been killed by predators, and thus gain access to fresh meat.

Dean said questions like these may be impossible to answer on the basis of the sketchy fossil record.

"Of course you can argue all day about why running could have been an advantage," he said. "I’m not sure we can know why they ran and under what circumstances."