The ability to run long distances was instrumental in the evolution of the modern human body, a new theory says.

The theory appearing in Nature magazine's new issue says, "No primates other than humans are capable of endurance running."

It is the ability to run long distances that made possible modern humans' evolutionary branching off from its primitive ape-like ancestors.

The new evolution theory could be termed in Cartesian lingo as "we run long, therefore we are!". The 17th century French philosopher-mathematician Rene Descartes in his postulations on modern humans had said, "I think, therefore I am".

The features that made possible long distance running helped humans succeed in long and tiresome hunting and scavenging, the theory says.

Scientists noted that compared to chimps, humans have shorter arms, longer legs, springy calf and foot tendons, shoulders that rotate and bulky buttocks for better balance.

"Apes, such as chimpanzees, can sprint rapidly, but they do so rarely and only for short distances," the researchers said.

While human would not outrun horses, dogs or antelopes over short distance, they could keep running for many miles and even outrun most animals.

"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," the magazine quotes Dennis Bramble, who teaches biology in the University of Utah in Salt Lake City, US.

"Running made us human, at least in an anatomical sense."

He and a team of scientists from Harvard University in Cambridge, Massachusetts, had listed 26 physiological traits that made enduring the strain of long distance running possible in humans.

"Your gluteus maximus (main buttock muscles) stabilises your trunk as you lean forward in a run," said Daniel Lieberman, who headed the Harvard team.

"A run is like a controlled fall, and the buttocks help to control it."

A tissue at the back of the skull and neck that humans developed early acts as a shock absorber and helps the arms and shoulders counterbalance the head as it bobs up and down during a run, the scientists say.

"These esoteric features make humans surprisingly good runners," Lieberman said.

--Indo-Asian News Service