NY Times article on brain differences between Democrats and Republicans:
A team of U.C.L.A. researchers analyzed the neural activity of Republicans and Democrats as they viewed a series of images from campaign ads. And the early data suggested that the most salient predictor of a ''Democrat brain'' was amygdala activity responding to certain images of violence: either the Bush ads that featured shots of a smoldering ground zero or the famous ''Daisy'' ad from Lyndon B. Johnson's 1964 campaign that ends with a mushroom cloud. Such brain activity indicates a kind of gut response, operating below the level of conscious control.
What would that kind of insight tell us that we didn't know already? One thing is certain: evidence of a neurological difference between liberal and conservative brains would not be another instance of genetic determinism, since patterns of brain activity are shaped by experience as much as by genes. (Those who suffer from post-traumatic stress syndrome also show unusual patterns of amygdala activity, but those patterns are almost inevitably the imprint of a specific event, and not the long arm of DNA.)
But a recent study by Paul Goren at Arizona State found that voters typically formed their party affiliations before developing specific political values. They become Democrats first and then decide that they, say, oppose capital punishment and support trade unions. But how do they make that initial decision to be a Democrat?
Say you're inclined to form strong emotional responses to images of violence or human suffering, and over the course of your formative years, most of the people you meet who respond to these images with comparable affect turn out to be Democrats. That's a commonality of experience that exists beneath conscious political affiliation -- it's closer to a gut instinct than a rational choice -- but if you meet enough Democrats who share that experience, sooner or later you start carrying the card yourself. Political identity starts with a shared temperament and only afterward deposits a layer of positions on the issues.