The human body is built for distance

Pam LeBlanc / Cox Newspapers /

Published Dec 27, 2012 at 04:00AM

AUSTIN, Texas — Good luck convincing your aching muscles and joints of it, but some scientists believe your body evolved to run long distances.

Your feet, your neck, your ears — they’re all part of a physique perfectly adapted to covering 10 or 20 leg-powered miles a day.

The problem is, modern humans no longer run that far to hunt down prey. We hop in a car and drive to the grocery store, where many of us load up on Fritos and Oreos, then head home and instinctively hunker down on the sofa.

Dan Lieberman, an evolutionary biologist from Harvard University, dropped by Southwestern University recently, where he shared thoughts on humans and exercise — and why we need to do it despite our general dislike of breaking a sweat.

It all goes back to early humans, he says. They lived on the razor’s edge, hunting and gathering to get enough fuel that they could continue to hunt and gather. They ate what they caught and rested when they could, conserving energy whenever possible.

“What do foragers do when they’re not foraging? They rest. It’s adaptive for them not to burn energy,” Lieberman said.

Their normal state was lean and hungry, and they moved up to 20 or so miles a day in pursuit of prey. Fitness, for them, was all about the ability to survive and pass along genes to the next generation.

Today, though, most Americans have easy access to food. Given the choice between an escalator and a flight of stairs, most opt for the escalator. We may cover twice the distance in a day, but it’s in a car while we sit on our bottoms.

“That’s not because people are lazy slobs,” said Lieberman, who was featured in the best-seller “Born to Run” by Chris McDougall. “It’s instinct to take it easy when we can.”

In the prehistoric world of persistence hunting, before the advent of projectiles, early humans couldn’t afford to relax. They hunted prey that could move more quickly than they could — over short distances. They had to get close to the animal to club it or stab it with a sharpened stick. The only way to do that was by exhausting it, and that meant covering long distances.

Humans, it turns out, have an advantage. We sweat to stay cool, and have the ability to sweat while we run. Quadrupeds, on the other hand, cool themselves by panting — but can’t pant on the fly. A horse can’t gallop 20 miles straight; it has to stop to cool off.

Thus, a human could chase its four-legged dinner. When the animal stopped to rest, the human kept going. Eventually, the animal’s body temperature rose until it collapsed from heat stroke and the human could walk up and kill it. That typically happened in 22 or fewer miles.

Humans improved their odds by hunting in the middle of the day, when it’s warmest, and by targeting larger animals, which would overheat more quickly. And our bodies, Lieberman says, were designed by natural selection to do what they had to do.

“We’re literally adapted to running from our toes to our head,” Lieberman said. “We evolved to be endurance athletes.”

Consider our short toes, the arches in our feet, our short heel bones, long Achilles tendon and sizable glutes, which help steady our trunks when we run. We sweat, we’re fur-free, the ligaments in our neck hold our head in place and the semicircular canals in our ears stabilize our gaze when we run.

“All these features that make us superlative runners are different than what we would need if we just walked,” Lieberman said.

But most modern humans rarely run, unless they’re trying to catch a bus or because a doctor ordered them to for health reasons. That’s problematic. Our hearts and skeletons require stimulus to properly grow. If they’re not stressed, and most people’s aren’t, they don’t develop properly.

Over the past 10 generations, we’ve changed in other ways, too. Our lives are filled with elevators, washers and other labor-saving machines. Instead of pursuing prey through the wilds, we sit at a desk much of the day. We drive to restaurants and convenience stores. We eat more calories and we expend less energy, creating a surplus of fat.

“We think it’s normal to eat breakfast cereal from a box and fly in a plane. We sit in plush comfy chairs and sleep on mattresses,” Lieberman said. “But we didn’t evolve for any of that.”

All of which means we’re headed down a road mined with heart attacks and diabetes. “It’s abnormal not to be physically active,” Lieberman said. “And if we don’t solve this problem now, we’re in trouble.”

Those buff hunter-gatherers didn’t suffer heart disease, diabetes or osteoporosis, Lieberman points out. Today, about 70 percent of health-care costs go toward treating diseases that wouldn’t exist if we were more active and ate a nutritious diet.

So what do we do? We exercise — at least the 30 minutes a day, five times a week, that experts recommend (and fewer than 20 percent of Americans do that.)

“There is no medicine known to be as effective as exercise,” said Lieberman, who runs 30 to 40 miles a week and signs up for periodic races to ensure year-round motivation.

Unfortunately, we didn’t evolve to enjoy exercise. But do it often enough and it becomes easier. Some folks get hooked.

And it’s a heck of a lot easier than chasing down dinner.

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