For quite some time, psychologists have used studies of identical twins to assess the relative importance of nature and nurture in human development.
They studied identical twins that had been separated at birth, and thus had been brought up in radically different familial and cultural environments. The comparison, they believed, could offer insights into how much of development was inborn and how much was culturally determined.
The results surprised everyone. In general terms, nature played a far more important role than anyone had imagined. It may not all be in your genes, but a lot of it is.
I mention these studies to introduce a new study from Finland. Researchers there compared the mental and physical well-being of several pairs of twins. The twins were not separated at birth, but they had, in adulthood adopted significantly different exercise habits. One twin participated in vigorous exercise while the other did not.
The New York Times reports:
Identical twins in Finland who shared the same sports and other physical activities as youngsters but different exercise habits as adults soon developed quite different bodies and brains, according to a fascinating new study that highlights the extent to which exercise shapes our health, even in people who have identical genes and nurturing.
The researchers were addressing the difficulties they have had in demonstrating the value of exercise. Different people are, frankly, different.
To prove that exercise directly causes a change in people’s bodies, scientists must mount randomized controlled trials, during which one group of people works out while a control group does not. But these experiments are complicated and costly and, even in the best circumstances, cannot control for volunteers’ genetics and backgrounds.
And genetics and upbringing matter when it comes to exercise. Genes affect our innate endurance capacity, how well we respond to different types of exercise, and whether we enjoy working out at all. Childhood environment also influences all of this, muddying the results of even well-conducted exercise experiments.
Thus, the importance of studying the exercise habits of identical twins.
The researchers could only find ten pairs of twins. Thus, the sampling seems to be rather small, by scientific standards. On the other hand, one is amazed that they could even find ten.
Note that the twins tended to have similar diets:
It turned out that these genetically identical twins looked surprisingly different beneath the skin and skull. The sedentary twins had lower endurance capacities, higher body fat percentages, and signs of insulin resistance, signaling the onset of metabolic problems. (Interestingly, the twins tended to have very similar diets, whatever their workout routines, so food choices were unlikely to have contributed to health differences.)
The twins’ brains also were unalike. The active twins had significantly more grey matter than the sedentary twins, especially in areas of the brain involved in motor control and coordination.
Presumably, all of these differences in the young men’s bodies and brains had developed during their few, brief years of divergent workouts, underscoring how rapidly and robustly exercising — or not — can affect health, said Dr. Urho Kujala, a professor of sports and exercise medicine at the University of Jyvaskyla who oversaw the study.
Among his other conclusions, Prof. Kujala noted that genetic predisposition does not determine whether you exercise or not.
Even if we cannot yet offer a definitive Q.E.D., this ought to get you up off the couch and on to the treadmill.