An article in the Times...

...last week about the impact of exercise on one's health, "One Twin Exercises, the Other Doesn’t," got me to thinking on a different subject, that whole "Nature vs. Nurture" debate.*

From the piece (my emphasis): 

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.

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. 

All of this makes identical twins so valuable. By definition, these pairs have the same DNA. If they were raised in the same household, they also had similar upbringing. So they can provide a way to study the effects of changes in lifestyle among people with the same genes and pasts. 

Same nature, same nurture -- but different outcomes. So that settles it then; we all have free will, right? Not so fast:

The researchers were looking for young adult identical twins in their early- to mid-20s whose exercise habits had substantially diverged after they had left their childhood homes. These twins were not easy to find. Most of the pairs had maintained remarkably similar exercise routines, despite living apart.

And the sample size was small: 

But eventually the researchers homed in on 10 pairs of male identical twins, one of whom regularly exercised, while the other did not, usually because of work or family pressures, the researchers determined.

Of course, the study was small and not a formal randomized trial, although it involved identical twins.

But, still: 

More subtly, the findings also point out that genetics and environment “do not have to be” destiny when it comes to exercise habits, Dr. Kujala said. For these particular twins, whether their genes and childhoods nudged them toward exercising regularly or slumping on the couch, one of the pair overcame that legacy and did the opposite (for better and worse). 

The debate goes on...

* Right now I'm about 90 percent nature, 10 percent nurture.