THE BODY IN MOTION
“Let food be your medicine.” That quote is frequently attributed to the “father of modern medicine,” Hippocrates (c.460–c.370 BC), although it is not found in his writings. But another quote from the Greek physician is believed to be authentic: “Walking is man’s best medicine.” Researchers today agree but are less specific: They say any activity that raises your heart rate and burns calories—including walking—is good for your health and counts as exercise.
Man has evolved to become the best runner on the planet. While a cheetah may be the world’s fastest land animal, a human runner leaves the cheetah in the dust if the race is long enough. Human endurance gives us the capability to outrun cheetahs, wolves, and sometimes even horses. While horses sweat just like we do, they do so less efficiently, overheat more quickly, and have to slow down before a human runner would. Some of the runners in the animal world— wolves and dogs, for example—may total 12 miles in a day, but a marathon is more than twice that distance, and a human runner does it nonstop.
HOW HUNGRY IS THE BRAIN?
Human beings became the dominant animal on the planet in part because of our speed and endurance. There are indications the early humans may have had a success rate of up to 50% when they were hunting—an activity that provided them with high-calorie food. Hunting also rewarded strategic thinking and promoted cooperation within a group. As weapons improved the better-organized hunters became increasingly successful, and the new inventions in addition to discussions of strategy made even more complex thinking necessary. And that required a bigger brain.
The 3-pound human brain of today accounts for only around 2% of the average adult’s weight but consumes around 20% of the body’s energy. To provide that energy, we’ve developed a much higher metabolic rate. “Over the course of our evolution, humans became ever more hypermetabolic,” says Carel van Schaik, a University of Zurich biological anthropologist. “We turned up the thermostat.” In fact, we burn calories more than 25% faster than chimpanzees.
But there is a downside, of course. Once humans were equipped with a faster metabolism and bigger brain, natural selection would have favored individuals who were naturally fatter.
“If you are going to burn fuel faster, then you have to have a backup tank,” says Herman Pontzer, an evolutionary anthropologist at Duke University. Human beings today are fatter than other primates, and there is evidence that modern humans are significantly heavier than our early ancestors had been. We also sleep much less than other primates. Back when we were still hunter-gatherers, that gave us more time to find food. The endurance that hunting and gathering required would’ve also favored development of the slow-twitch muscles that are needed for sustained activity. In fact, while the human ratio of slow- to fasttwitch fibers is 70:30, it is practically reversed in chimpanzees (33:66). And that affords us far better endurance than the other primates.
THE EXERCISE EDGE
This was a huge advantage until the industrial revolution came along. Then machines started doing most of the hard work, and our physiques began to suffer. “People used to work much harder before the industrial revolution,” says Australian anthropologist Peter Mcallister. “Meanwhile, we’ve lost a lot of the bone mass in our arms and legs as a consequence.” Thanks to modern civilization, we appear to be returning in some ways to the leisurely pace of chimpanzees. That could be life-threatening if we don’t continue to get at least moderate exercise, however. “We are born to run,” says Pontzer, adding, “Exercise does not make our bodies work more so much as it makes our bodies work better.” So heed this counsel and run with it!
When the deliberate production of food emerged about 12,000 years ago, people were not prepared for its consequences.”
CAREL VAN SCHAIK, anthropologist, University of Zurich