In Praise of Walking: A New Scientific Exploration

by Shane O'Mara

Is regular activity a form of easily self-administered medicine, because movement is intrinsically good for us? The evolutionary biologist Daniel Lieberman of Harvard University offers an important evolutionary perspective on our odd relationship to physical activity: it’s good for us, yet we tend to avoid it, in order to conserve energy, for the simple reason that’s how we evolved. Until recently physical activity was obligatory, and food sources were scarce. As Lieberman puts it, ‘humans evolved to be adapted for regular moderate amounts of endurance, physical activity, into late age . . . because energy from food was limited, humans were also selected to avoid unnecessary exertion’.29 Consider the following example: many national institutes of health and diet recommend an average daily diet of perhaps up to 2,000 calories for adult females and 2,500 calories for adult males.30 Let’s call that 2,400 for ease: that implies the burn-rate of those calories is 100 calories per hour, on average – that’s through both waking and sleeping hours. Those consumed calories must serve all the needs of the body: breathing, walking, thinking, digesting, secreting and so on. The food itself must be digested, nutrients transported around the body from the roots of the hair on the top of your head all the way to the soles of your feet. Digesting the food you eat costs energy (calories) – high-fibre foods with a low energy density are more costly to digest than are high-calorie foods. Your...