Marathons come naturally

By Daniel Lieberman | April 15, 2007

TO THE VAST majority of humans today, the idea of running a marathon is as preposterous as volunteering to have one's teeth extracted. Thanks to our sedentary lives, media hype, and the occasional boastful runner, running 26.2 miles has become the ultimate symbol of human endurance. The story of Pheidippides does little to dispel this myth. According to legend, Pheidippides ran the distance from Marathon to Athens in 490 BC to announce the victory of the Greeks over the Persians -- and he died upon arriving.

Fortunately, the more than 20,000 runners who will slog through the rain tomorrow from Hopkinton to Copley Square will probably do just fine. The elite runners are truly astonishing athletes, capable of running each mile in less than 5 minutes. But what about the rest of the runners, many of whom will take more than four hours to cover the same distance? How remarkable are they?

Despite the many myths surrounding the marathon, it turns out that running long distances such as 26.2 miles is something that almost any human can do with a reasonable amount of training. Distance running is a hallmark of being human. In fact, humans are better at running long distances than almost any other animal, particularly when it is hot and dry. On a warm day, most human runners can outrun any dog over a few miles, and good human runners can even beat a full-sized horse over marathon-length distances.

Why are humans, even average runners, so good at running mile after mile with relative ease? One answer lies in the many special features we have evolved. Perhaps the most important ones keep us from overheating when we run. Humans uniquely cool down by sweating; we lack fur and have millions more sweat glands than any other animal. In addition, unlike our cousins, the African apes, we have long legs, bouncy arches in our feet, and long tendons that act as springs.

Most of us also have a high percentage of slow-twitch muscle fibers which use energy efficiently, but which prevent us from sprinting very fast. Additionally, we have narrow waists that allow the torso to twist independently of the hips. We have low, wide shoulders so we can pump our arms in opposition to our legs, keeping us from weaving from side to side. Another unique human feature is the remarkably large gluteus maximus. This muscle, the largest in the human body, helps keep the trunk from pitching forward every time we land. Some of these and other features are useful in both walking and running, but many are useful only for running.

In short, millions of years of evolution shaped the human body into a remarkable running machine. Most of today's marathoners run because it makes them feel good both physically and mentally. But, for our ancestors, running was a means of bringing home the bacon. About 2 million years ago, our ancestor, Homo erectus, hunted big animals armed with nothing more than a sharp un tipped spear (stone spearheads were invented only about 200,000 to 300,000 years ago). Killing a big animal like a kudu or a wildebeest with a sharp stick isn't easy, because one must get very close to the animal to spear it. One kick from the prey's legs or a blow from its horns can kill a hunter.

Running changed all that. Human hunters can run for miles at speeds that require most mammals to gallop. Since quadrupeds lack our ability to sweat profusely, and they cannot gallop and pant at the same time, human hunters can pursue their prey in the midday sun until the animals collapse from heat exhaustion. This kind of persistence hunting is rare today, but was probably an important way to hunt before the comparatively recent invention of the bow and arrow within the last 100,000 years.

Tomorrow's finishers have every right to feel proud, especially given the dismal weather forecast. But it is time to dispel the myth that running a marathon is a bizarre, unnatural feat of athletic prowess. Let's celebrate instead the quintessential human ability to run long distances. Thanks to our evolutionary history, almost anyone can run 26.2 miles.

Perhaps next year I will finally get around to celebrating this part my heritage by running the marathon instead of jogging my usual five miles. My problem is that I can't see the point of running so far without a kudu or wildebeest to chase in the heat.

Daniel Lieberman is a professor of biological anthropology at Harvard University.
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