Friday, November 21, 2008

Anna and Vronsky, Kitty and Levin

I've been happily married for more than half-a-century. Is it because I happened to wed an irresistibly lovable partner? Or has my wandering eye been restrained by residual Catholic guilt? Or does the credit go to a variant of my AVPR1a gene?

Just one of the intriguing questions raised in a special section of last week's issue of Science: The Genetics of Behavior (November 7, 2008).

And indeed there does appear to be evidence (not yet reliably reproduced) that a tendency toward stable marital relationships is in the DNA.

Few questions in science have raised more hackles than nature vs. nurture. That is to say: How many of our behaviors are we born with, and how many are inculcated socially. Is there a math gene (or genes)? An aggression gene (or genes)? An anxiety gene (or genes)? A liberal or conservative gene (or genes)? A God gene (or genes)? There was a time not so long ago -- back in the 1970s --when scientists were scratching each other's eyes out over these issues, mainly in response to E. O. Wilson's book Sociobiology, which emphasized the genetic basis of behaviors. These days there is rather more of a consensus that behaviors are a little bit of this and a little bit of that.

As the authors of one review article in Science say:
Genes do not specify behavior directly but rather encode for molecular products that build and govern the functioning of the brain through which behavior is expressed. Brain development, brain activity, and behavior all depend on both inherited and environmental influences, and there is increasing appreciation that social information can alter brain gene expression and behavior. Furthermore, variation in behavior shapes the evolution of genomic elements that influence social behavior through the feedback of natural selection.
In other words, as a species we are what we are at least partly because of what we have been, and what we will become is a least partly determined by what we are.

We are surely less free of our genome and its expression than we might like to believe. Perhaps my fidelity genes and my hanky-panky genes battle it out with dueling hormones and neurotransmitters, with perhaps a bit of true love and Catholic guilt thrown in. But no scientist that I know of thinks we are prisoners of our genome. The authors of the previously mentioned article state:
There are many levels of neural and neuroendocrine regulation that lie between the genome and a social behavior, including transcription, translation, posttranslational modifications, epigenetic changes, brain metabolism, neural (electrochemical) activity, and neuromodulation. Moreover, this regulation occurs in complex and dispersed temporal and spatial patterns within the brain, over physiological time, developmental time, and throughout an individual's life. The study of social behavior adds an additional tier of complexity because it depends on interactions and communication among individuals. In most cases, social behavior must be studied in a natural context in which the full repertoire of environmental influences and behaviors are expressed.
Which is to say, we are wonderfully complex molecular machines in interaction with an almost infinitely variable environment. In the next few decades we'll be learning a lot more about the genetic and environmental roots of behavior. None of this will change the perennial dynamics of trying to live an ethical life. A complete transcription of Anna Karenina's genome would not change a whit the worth of her story.

(More on Anna tomorrow.)