March 2010

If you are health conscious or have been in a sporting goods store lately, you might have heard about a new fitness trend: barefoot running. Enthusiasts hit the pavement (or the grass, or the track) sans shoes entirely or with minimal foot protection — and the trend is catching on. Clubs dedicated to barefoot running have sprung up, devotees crash marathons to run barefoot, and shoe companies are jumping on the bandwagon with shoes that mimic the effect of running barefoot — including some that look like rubber gloves for your feet. Barefoot running may sound like just another fitness fad, soon to go the way of hula-hoops or jazzercise, but this trend has a surprising connection to evolution.

Where's the evolution?

Though counterintuitive, new research suggests that we put less potentially injurious stress on our feet and legs when we run barefoot instead of shod. A team of researchers led by evolutionary biologist Daniel Lieberman found that people who run in shoes tend to strike the ground with their heels, while barefoot runners tend to strike with the balls of their feet first to avoid the pain of a heel collision. Notably, the runners who ran heel-first (even those wearing running shoes), experienced a spike of force that the front-first runners did not. Such intense forces could make shod runners more prone to injuries like stress fractures.

Lieberman and his team argue that this makes sense from an evolutionary perspective. After all, when the modern human body evolved from that of our Australopithecine ancestors, fancy running shoes were not yet available. Natural selection would have favored the evolution of foot anatomy and running behaviors that minimized the risk of injury without shoes — and at that time, humans probably ran hitting the ground with the balls of the feet first. Are we shunning the benefits of millions of years of natural selection by wearing shoes to run and hitting the ground heel first? Many barefoot runners would say yes, though plenty of other runners and podiatrists would disagree. Both sides will have to wait for a final answer until researchers compare injury rates among barefoot and shod runners.

If further studies support Lieberman’s results and show that running injuries are exacerbated by wearing shoes, it will serve as one more example of a mismatch between humanity’s evolutionary history and modern life. Natural selection has no foresight. It is a mechanistic process that shapes life based on which individuals reproduce most successfully in the current environment. It has no way of knowing how that environment might change in the next few years or the next few millennia — whether that will mean a colder or warmer climate, a shift in the makeup of Earth’s atmosphere, a change in resource availability, or the invention of sneakers.

The ubiquity of sugars and fats in modern diets represents a similar evolutionary issue to the widespread use of running shoes, but with more profound health implications. In the environments of our Pleistocene ancestors, these resources were scarce but supplied of valuable calories. Individuals who were genetically predisposed to prefer such foods likely ate more of them, had more energy stores, and were better able to survive and reproduce. In the Pleistocene, eating all the high-fat and high-sugar foods you could was a good thing; hence, we evolved to prefer such foods. But now that they are easy to get in abundance, our preference for these foods has become the root of an obesity and diabetes epidemic. The traits that were survival advantages in the Pleistocene may now be killing us — or, in the case of shod running, merely giving us shin splints.

All of this highlights just how much evolutionary theory can inform modern medicine. Viewing humans as a result of historic evolutionary processes and recognizing that we are still evolving, even in the modern world, can help us identify evolutionary constraints or predispositions that affect our health. This give us new insight into the origins of our ailments and may affect the treatment choices we make — whether that means forgoing potato chips at lunch or forgoing sneakers the next time you hit the track.