Nature/Nurture of What?

The Olivia Judson blog at the NY Times is a great source of interesting biological science. She's been having guest bloggers, this week Sandra Aamodt and Sam Wang take on genes and environment and the strange interactions between them in an article entitled "Mugged by Our Genes?". Read the whole thing, but for me the key bit was...

Major depression arises from a vicious cycle between genes and environment. Let’s start with genetics: a particular gene influences the sensitivity of individuals to bad experiences. One famous paper demonstrated a complex interaction between the serotonin transporter gene and negative events. (The gene encodes a protein that removes the neurotransmitter serotonin from the synapse after a neuron releases it. The action of this protein is inhibited by antidepressants like Prozac.) People with two copies of the high-risk variant of the gene are likely to develop depression in response to multiple stressful experiences like divorce or assault, but they are fine if their environment remains benign.

In contrast, people with two copies of the low-risk form of the gene are resilient against depression, even when they experience environmental stressors. People with one copy of each variant fall somewhere in between, as you might expect.

Genes that predispose people to depression, though, also influence their risk of experiencing negative environmental events. In one study, women whose identical twin suffered from depression were significantly more likely to have been assaulted, lost a job, divorced, or had a serious illness or major financial problems than people whose fraternal twin was depressed. (It’s not known which genes are responsible for this effect.) These bad events did not occur because the women were depressed, as the correlations persisted even when women who were currently depressed were excluded from the study. Thus, genes can act on the same disorder by making people more sensitive to stressful environmental events and by making these events more likely to occur.

The interaction between genetic tendencies and life experiences may explain another puzzling finding: the heritability of many psychological traits — from intelligence to anxiety — increases as people mature. This result seems odd at first glance, since genes are most important in brain development in babies and children. But children also have less control over their environment than adults. As people get older, they become more able to determine their own circumstances, and they may be able to choose environments that reinforce their natural personality tendencies. Apparently those of us who suspect we are turning into our parents as we get older may have a valid point.

After all this, you may wonder if your genes are ultimately to blame for your fortunes, good or ill. That’s hardly the case: only one-fourth of the variation in life events is heritable, which means that three-fourths is not. So you have plenty of opportunity to influence your circumstances. Whether that’s better than turning into your parents, we’ll leave to your judgment.

I remember as a kid the excitement of the early decoding of DNA. The central dogma was that one gene codes for one protein and all information flowed one way. Now there is epigenetics which puts this on its head and creates a much more complex palette for development.