How learning to run put man one step ahead of the apes

Long-distance running shaped the human body into its present form and gave our ancestors an edge over competitors when it came to finding food and avoiding predators.

Long-distance running shaped the human body into its present form and gave our ancestors an edge over competitors when it came to finding food and avoiding predators.

The development of anatomical features which our ape-like relatives do not possess: strong buttocks, flexible necks and long legs, can be explained by the need for early man to become a successful endurance runner.

Dennis Bramble of the University of Utah and Daniel Lieberman of Harvard University argue in the journal Nature that walking alone would not account for many of the physical attributes of the human body.

"We are very confident that strong selection for running, which came at the expense of the historical ability to live in trees, was instrumental in the origin of the modern human body form," Professor Bramble said. "Running has substantially shaped human evolution. Running made us human, at least in an anatomical sense. We think running is one of the most transforming events in human history. We are arguing the emergence of humans is tied to the evolution of running."

Humans are unique among primates in being exceptional endurance runners. The two scientists believe this allowed early humans to hunt or scavenge for meat better than other competing savannah animals.

Bipedalism evolved at least 4.5 million years ago in a group of ape-like ancestors called Australopithecine, yet the upright-walking features did not evolve in their present form for about another 3 million years. This suggests that the ability to walk on two legs does not explain the anatomy of modern humans, said Professor Bramble.

"There was 2.5 million to 3 million years of bipedal walking without ever looking like a human, so is walking going to be what suddenly transforms the hominid body? We're saying walking won't do that, but running will," he said.

Apes such as chimps cannot run for long distances because their anatomy is tied to life in the trees. Their heads and legs are fixed too rigidly to their skeleton and they have no strong bottom muscles - gluteus maximus - to sustain endurance running.

Professor Lieberman said that humans also have a "nuchal ridge" at the base of the skull attached to a broad mass of tissue that keeps the head steady when running.

Large buttocks also help in running upright. "Your gluteus maximus stabilises your trunk as you lean forward in a run. A run is like a controlled fall and the buttocks help to control it," said Professor Lieberman.

The Achilles tendon is also helpful for long-distance running because it acts like a spring storing up energy in each step. The well-developed human Achilles tendon evolved as part of the need to run long distances.