We tend to think of the environment as something that just happens to us, but in fact animals actively seek out surroundings that are compatible with their genetic predispositions. Teenagers in the chess club choose to be exposed to different influences from their hockey-player counterparts. Such differences don’t even have to be voluntary: tall kids may be picked more often for the basketball team and end up better at the game because they have more opportunities to develop their skills.

Aamodt and Wang point out that some people are more likely to be mugged than others, and the siblings of alcoholics are more likely to be arrested and be robbed than people in the general population. Moreso, some of this variation is attributable to genetics. Why? A person who has low dopamine levels and seeks out risk is probably more likely to walk down a dark street in a sketchy neighborhood. Someone with addictive and impulsive tendencies may get into more fights ("bar fights," for example, say Aamodt and Wang).

What connects our genetic inheritance to environmental experiences? Most likely it is personality, which is known to depend on genes. In one study, three common measures of personality — extroversion, neuroticism and openness to experience — were enough to explain the entire heritability of some life events. In general, neurotic people are more likely to experience negative life events, while extroverted people are more likely to experience positive and controllable life events.

So some of the effects that we call “genetic” (or “nature”) are the indirect result of people being drawn to particular environments because of their personality. Or to put it another way, some “environmental” (or “nurture”) effects are actually attributable to genetic tendencies.

This seeming paradox underscores the point that the “genes versus environment” debate is asking the wrong question. It is said that parents of one child believe that upbringing determines personality, but parents with two children believe in genetic tendencies. The evidence points to something more complex: genetic predispositions interact with circumstances to produce unique individuals.

Could these gene/environment interactions help explain why EDs are so incredibly common in ballet dancers and models, in cross-country runners and valedictorians? The thin-at-all-costs motto clearly has a large role to play, but could it be that people predisposed to EDs seek out these activities because of an innate predisposition? That the neurotic tendency to remember every hurt and be exquisitely sensitive to others' emotions means that an off-hand comment about your weight will sear and burn long after everyone else has forgotten it?