The Way We Eat Now explains how human lifestyles — in terms of diet and exercise — have changed:
The old order Amish of Ontario, Canada, have escaped much of that advertising, and the TV viewing as well. They have an obesity rate of 4 percent, less than one-seventh the U.S. norm. Yet the Amish eat heartily, and not all health food: pancakes, ham, cake, and milk — but also ample amounts of fresh fruits and vegetables. It seems that the secret to the “Amish paradox” is their low-technology lifestyle, which entails vastly more physical activity than its modern correlate. David R. Bassett, a professor of exercise science at the University of Tennessee, gave pedometers to 98 of these Amish adults and found that the men averaged 18,000 steps per day, the women 14,000 — about nine miles and seven miles, respectively. The Amish men averaged 10 hours a week of vigorous activities like shoveling or tossing bales of hay (women, 3.5 hours) and 43 hours of moderate exertion like gardening or doing laundry (women, 39 hours).“The Amish are not freaks,” says professor of anthropology Daniel Lieberman, a skeletal biologist. “They are just anachronisms. Human beings are adapted for endurance exercise. We evolved to be long-distance runners?running a marathon is not a freak activity. We can outrun just about any other creature.”
Though only a few pockets of hunter-gatherers remain on Earth, for the first couple of million years of our species’ evolution — 99.5 percent of the human experience — all people sustained themselves by hunting animals and gathering food from wild plants. Agriculture arose only 10,000 to 12,000 years ago, permitting more stable settlements and food supplies. Hunter-gatherers spend much of every day traveling: “Who ever heard of a sedentary hunter-gatherer?” asks Lieberman, laughing. (There were a few sedentary hunter-gatherers, he notes?in the Pacific Northwest where salmon ran plentifully.) But although humans are designed to be highly active, the chronic ailments of sedentary life and obesity, like diabetes and heart disease, typically turn fatal only when people are past reproductive age. Thus, natural selection doesn’t weed out couch potatoes.
Since the Industrial Revolution, and particularly in the last half-century, technology has enabled us to conduct an increasingly immobile daily life.
Humans, by the way, evolved to eat energy-dense foods like meat, nuts, and roots — which are difficult to eat without cooking (or other preparation):
Chimps’ jaws and teeth are bigger than ours, and they like to eat meat — they will work hard to get it — “but they can’t chew meat at all fast,” Wrangham says. “The rate at which they chew and swallow meat is equivalent to the way they eat fruits: 300 to 400 calories per hour.” In contrast, humans eating cooked, softened food of high caloric density can take in 2,000 calories during their daily hour of chewing and swallowing.
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“The size of the human face has gotten about 12 percent smaller since the Paleolithic,” Lieberman says, “particularly around the oral cavity, due to the effects of mechanical loading on the size of the face. Fourteen thousand years ago, a much larger proportion of the face was between the bottom of the jaw and the nostrils.” The size of teeth has not decreased as fast (genetic factors control more of their variation); hence, modern teeth are actually too big for our mouths — wisdom teeth become impacted and require extraction.