Jogging is a popular form of exercise that is not only an enjoyable pastime, but some scientists think endurance running contributed to the evolution of modern humans.
Most anthropologists studying early humans have tended to focus their attention on the time when prehistoric man began to walk upright. They think this ability, between four and six million years ago, separated prehistoric humans from other species.
Biological anthropologist Daniel Lieberman of Harvard University in Massachusetts also subscribed to the notion that prehistoric humans were probably not good short-distance runners because modern humans are not.
"After all we are very slow and we are very awkward and we fall down easily, and it costs us a lot of energy to run," he said.
Professor Lieberman and a colleague then wondered about endurance running. After studying the fossil record, they concluded that ancient humans were probably excellent endurance runners.
Unlike walking, Professor Lieberman says running requires physical characteristics, such as spring-like tendons. There is no evidence that such characteristics evolved from prehistoric primates and their two-legged descendants.
"If you look at the legs of a chimpanzee, there are no springs in the leg. They are all muscles," he said. "The tendons are just a centimeter or so long. But humans have these huge Achilles tendons and various other tendons in our legs. They have no role whatsoever in walking. But they are crucial when you run."
Since it is easier for humans to outrun most animals for long stretches, Professor Lieberman thinks ancient humans may have developed the capability of long-distance running to elude predators or to exhaust prey to get close enough to kill them with rocks.
Daniel Lieberman says there may be another reason why long distance running was an evolutionary trait.
"It also feels good," he said. "People who run really like to run. And the reason why it feels good is that we have bodies that are well-designed to do so."
The article on endurance running as an evolutionary trait is published in the journal Nature.