Spark: The Revolutionary New Science of Exercise and the Brain

by John J. Ratey

From the time Homo sapiens emerged two million years ago, until the agricultural revolution, ten thousand years ago, everyone was a hunter-gatherer, and life was marked by periods of intense physical activity followed by days of rest. It was feast or famine. By calculating how much our forebears “exercised” and comparing it to figures from today, it’s easy to see where the problem lies: Our average energy expenditure per unit of body mass is less than 38 percent of that of our Stone Age ancestors. And I think it’s fair to say that our calorie intake has increased quite a bit. The kicker is that even if we followed the most demanding governmental recommendations for exercise and logged thirty minutes of physical activity a day, we’d still be at less than half the energy expenditure for which our genes are encoded. Paleolithic man had to walk five to ten miles on an average day, just to be able to eat.