Why Genes Aren't Enough to Create a Personality

Psychiatrists see a lot of people who are, to use the technical term, screwed up. Psychiatrists' talk, then, often turns around curing, or ameliorating, or at least preventing "bad" behaviors and feelings—drug addiction, violence, learning disabilities, crippling anxieties and the like. And a number of psychiatrists sounded that note at the University of Massachusetts conference on behavioral epigenetics last weekend. But throughout the proceedings, there was an undertow pulling in the opposite direction: A number of researchers objected to the notion that we can or should define some behaviors as better than others.

That seems to be an essential difference between genetics, the study of a fixed inheritance in DNA, and epigenetics, which is the study of how the environment affects those genes, causing different ones to be active at different rates, times and places in the body.

Evolutionary approaches to human behavior have often been framed in terms of "good" and "bad": Why did homosexuality evolve if it's "bad" for the genes, because it reduces the chance that they'll be passed on to a new generation? Why wouldn't an impulsive temperament be "selected against," seeing as its possessors would be more likely to fall off cliffs? Some thinkers have twisted themselves into pretzels trying to explain why a "maladaptive" behavior hasn't disappeared (like the guy who wanted to understand how people could treat their pets better than other human beings, given that people share more genes with other people).

If you want to understand environmental influences on genes, though, these kinds of questions are no help. Epigenetics is the study of how the environment activates or "silences" genes—how, for example, a stressful argument might raise your levels of "fight-or-flight" hormones, whose presence in certain regions of your brain then reduces the number of times a particular gene is used to make copies of a protein that's involved in the formation of memories. Which must some day be part of the biochemical explanation for the fact that high stress interferes with memory.

When we focus on particular genes in your particular cortex turning "on" and "off," the selective forces of evolution aren't our concern. They've done their work; they're history. But your genes, all "winners" in that eons-long Darwinian process of elimination, still permit a range of human behavior. That range runs from a sober, quiet conscientious life at one extreme to, say, playing for the Rolling Stones at the other. From the long-term genetic point of view, everything on that range, no matter how extreme, is as adaptive as any other. Because the same genes make them all possible.

In other words, the epigenetic idea is that your DNA could support many different versions of you; so the particular you that exists is the result of your experiences, which turned your genes "on" and "off" in patterns that would have been different if you'd lived under different conditions. We can say that some of these versions—the one who plans ahead, behaves responsibly, wears a seatbelt, supports its children—are nicer to live with, and better for society, than an alternate version who gets into fights, lies, cheats and spreads herpes. But we can't say the Dr. Jekyll outcome is better in some objective, Darwinian sense. Quite the opposite: It makes more sense to assume that people whom the environment sculpted to be anxious, druggy or impulsive were, at some point, quite well adapted to their circumstances.

For example, in this paper Seth Pollak and his co-authors found that physical abuse and neglect have an effect on children's perception of emotions in others: physically abused 3-, 4- and 5-year-olds more likely to see signs of anger in the expressions of people in photographs. In an emotionally comfortable home, it's easy to see that as a defect to be cured. But, as Edward Tronick said at the conference, being hypersensitive to anger is a pretty good adaptation for an abused kid.

Similarly, despite much use of troubled rats as models for depression or anxiety disorders in people, more than one scientist at the meeting objected to the idea that their stressed-out, obesity-prone rodents are defective.

Michael Meaney's lab at McGill has produced one of the most famous of these models. Meaney and his colleagues showed that rat mothers' behavior has a large effect on how their offspring turn out. Mothers who frequently lick and groom had children who were calmer during stress, learned more quickly, and were less susceptible to obesity and heart trouble, compared to the children of less-attentive mothers—in most circumstances. But, Meaney pointed out at the meeting, when rats are forced to learn something new under stressful conditions, it's the ones with the bad childhoods who do better.

In this paper, for instance (look at the paragraph right after Figure 5), Meaney and his co-authors found that a dose of stress hormone impaired rat neurons' ability to strengthen their synaptic connections, which is crucial to memory and learning. However, this was true only of the "happy childhood" brains. In the brains of rats with relatively neglectful mothers, the jolt of stress hormone increased synaptic connections. "We reject the idea that the offspring of low-licking mothers are at any disadvantage," he said.

An epigenetic map of how environment shapes gene expression is a long way off (another reason some scientists resist talk of "abnormal" human behavior is the fact that we don't know humanity's normal range of epigenetic variation). But already it seems epigenetics demand a different kind of thinking about human behavior—perhaps one that's more accepting of variety, and less eager to define "defects" to cure.

Champagne, D., Bagot, R., van Hasselt, F., Ramakers, G., Meaney, M., de Kloet, E., Joels, M., & Krugers, H. (2008). Maternal Care and Hippocampal Plasticity: Evidence for Experience-Dependent Structural Plasticity, Altered Synaptic Functioning, and Differential Responsiveness to Glucocorticoids and Stress Journal of Neuroscience, 28 (23), 6037-6045 DOI: 10.1523/JNEUROSCI.0526-08.2008  

Pollak, S., Cicchetti, D., Hornung, K., & Reed, A. (2000). Recognizing emotion in faces: Developmental effects of child abuse and neglect. Developmental Psychology, 36 (5), 679-688 DOI: 10.1037//0012-1649.36.5.679

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