Running turned humans into what they are today, U. of U. biologist says Marathoners: A new study says our physiology proves people gave up trees for running, but it can't explain why By Greg Lavine The Salt Lake Tribune Runners check watches before the start of the first Salt Lake City Marathon in April. University of Utah and Harvard scientists say the ability to run long distances made humans into what we look like today. (Al Hartmann/Tribune file photo) The thousands of runners who step up to the starting lines of marathons each year may be following in the footsteps of our earliest human ancestors. Scientists in Utah and Massachusetts suggest in a new study that the act of long-distance running made us into what we look like today. In a sense, humans were born - or at least evolved - to run. It remains unclear what motivated early humans to start running across the savannahs of Africa 2 million years ago, said University of Utah biologist Dennis Bramble, who along with Harvard University anthropologist Dan Lieberman authored the study that appears in today's edition of the journal Nature. Some possible explanations include running animal prey to exhaustion on the scorching plains or racing other creatures to reach freshly killed carcasses. The link between human evolution and endurance running intrigued Draper marathoner Dennis Simonaitis, who said the "universal challenge" of the sport helps drive him to run. And an arduous training regiment gets him to the finish line. "I've always thought we were not meant to do this," Simonaitis said, noting the body's incredible fuel requirements needed for long-distance running. Bramble agreed that people were not designed to dash 26 miles. But a review of fossil evidence and previous studies point to the idea that early humans were well-suited to run a few miles at a time. About 2 million years ago, early humans developed adaptations that set them further apart from their primate cousins. Changes in the lower leg and foot allowed efficient running, Bramble said. "If we had only walked, we would not look like the people we do today," Bramble said. "No amount of walking would do that." Lieberman said that developments like the Achilles tendon - which essentially acts as a spring - are only used in the act of running. Evolving features, such as longer legs and arched feet, also aided in running. One possible reason researchers have overlooked running is the fact that people are not exactly speed demons on the track, he said. "Your typical Chihuahua could probably outrun a human over short distances," said Lieberman, who runs a few miles a day. "We're pathetic sprinters." But take a longer view of running, and humans start looking better. Bramble first heard of this idea from a former graduate student, and current colleague, David Carrier, in the 1980s. Carrier looked at how humans regulate temperature while in motion, and thought that maybe people were made to run. Perhaps early humans ran animals to exhaustion. "I didn't buy it," Bramble said of Carrier's initial running claims. But the research started Bramble thinking. Why early humans ran stands as a lingering question. Lieberman said while it is possible people could have run down prey, it is a costly way to live. Lieberman and Bramble instead lean toward the idea that ancient humans living on the plains would look for signs of food, such as vultures circling above a carcass. Breaking into a trot would allow people to get to the food source faster to feast on meat, bone marrow and brain, he said. An early human, Australopithecus, had an ape-like appearance but could walk upright. These ancient ancestors, dating back to 4.5 million years ago, could also climb the trees of their forest homes. "This paper shows that Australopithecus was adapted for short distance walking and tree climbing, but early Homo [sapien] had a suite of changes in the body that were adapted to endurance running," said Henry McHenry, an anthropologist at the University of California, Davis, who was not part of the study. Bramble said humans gradually traded in their tree-climbing traits, like short legs and long arms, for the ability to run. "Our hope is that this will help us have a better understanding of human evolution," Bramble said.