Genes, environment, and who we become

I've blogged before about how environment can affect our genes. Besides epigenetics, chemical modifications to DNA that don't change the genes but instead change how the genes are expressed, the separation between genes and environment, nature and nurture keeps growing blurrier.

Cutting edge research (some of which I write about for my job, much of which I follow because it's interesting and I'm a geek) is showing that not only is separating genes and environment futile, it's also impossible. Our environment affects our genes--look at someone with cancer, and you'll know that's true. But our genes also affect our environment, and although the effects are much more subtle, they're just as real.

In the "Origins" column in last week's New York Times, titled "Mugged by our genes?," neurobiologists Sandra Aamodt and Sam Wang looked at this very subject. "Do genes dictate our fate?" they asked. "Of course not — but they do have a say in who we become."

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?

Similar things are seen in people with body dysmorphic disorder. A 2004 study found that 20% of people with BDD had occupations in art or design, only 7% of those with major depression did, 3% of those with OCD, and 0% of those with PTSD. Other studies have found that anxious parents were more likely to identify threats in both their own and their children's environment, which could inadvertently influence the development of an anxiety disorder in those children.

It's pretty obvious, then, that classifying eating disorders (classifying anything, really) as "biological" or "psychological" or "social" is meaningless in the grand scheme of things. I do believe that EDs are biologically based mental illnesses, and you would have to have a helluva sheaf of research backing your claims to make me budge from that stance. But this isn't the same as biological determinism. Environment is still important; environment matters.

This strange thing called life is turning out to be far more complicated than anyone ever imagined.


Anonymous said...

Very nice post Carrie.

Kim said...

This is extremely interesting. I never thought about it that way before -- how our genes direct us to a certain environment. I definitely sought out areas where I could get external praise (school, for example). I looked for areas where my perfectionism would be welcomed with open arms. This was a really good read. Thank you!

Hope said...

What a fascinating way of looking at the gene/environment interaction. It makes real sense, too. You said it very well!!

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I'm a science writer, a jewelry design artist, a bookworm, a complete geek, and mom to a wonderful kitty. I am also recovering from a decade-plus battle with anorexia nervosa. I believe that complete recovery is possible, and that the first step along that path is full nutrition.

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nour·ish: (v); to sustain with food or nutriment; supply with what is necessary for life, health, and growth; to cherish, foster, keep alive; to strengthen, build up, or promote


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