Last week, British researchers released the results of a study suggesting intriguing differences in brain structure between liberals and conservatives. The study found that the anterior cingulate, the part of the brain dealing with complexity and uncertainty was larger in liberals than it was in conservatives. Conversely, the amygdala, the part of the brain associated with fear and raw emotion was larger in conservatives. One can't draw definitive conclusions from one study, of course. A slow trickle of evidence over the past few years appears to show brain-related differences between liberals and conservatives, but this kind of research is clearly in its infancy.
Nevertheless, these findings do track quite well with the book that Marc Hetherington and I wrote in 2009. In Authoritarianism and Polarization in American Politics, we adduced substantial evidence that the American political system has been increasingly sorting itself out along a basic personality dimension - the authoritarian personality. We argued that less authoritarian-minded individuals have been gravitating toward the Democratic Party and more authoritarian-minded ones toward the Republican Party and that this sorting process was having profound consequences for the nature of political conflict in the United States.
This doesn't mean, of course, that all Democrats are non-authoritarian, or that all Republicans are authoritarian (like independents, both major parties comprise individuals from across the authoritarianism scale). It certainly doesn't mean that only one side has a monopoly on either partisanship or a tendency to defend actions of its own leaders that, were the other party's leader to engage in, those same people would find abhorrent. Nor does it true that all public policy battles are fought neatly along these lines. And certainly, public preferences do not determine all policy outcomes in a political system heavily influenced by elite interests.
But since we wrote the book, evidence has mounted that this personality-based is only deepening. And data from a large recent survey, the 2010 Cooperative Congressional Election Study (CCES), provides further confirmation that Americans are becoming more polarized according to basic personality differences.
One party, the GOP, has attracted, at its base, a large subset of individuals with a greater tendency to see the world in black and white terms, rather than in shades of gray, colored by greater suspicion of people who look and sound different and grounded in the conviction that hand-wringing and hesitating in the face of clear, categorical threats to well-being is a recipe for disaster. The other party, the Democratic Party, though much less coherent at its base (partly because non-authoritarians are a much smaller segment of the population than are authoritarians), sees the world in very different terms. In that worldview, threats to our well-being are complex, multi-faceted and need to be addressed by inclusive rather than exclusive approaches to problem-solving. Furthermore, through this lens, the gravest threats come from reducing the world to simplistic good-versus-evil terms.
The 2010 CCES data show that the relationship between party identification and an individual's level of authoritarianism is as strong as it's ever been. To give a sense of what this looks like, those scoring at the low end of the authoritarianism are more than three times more likely to be Democrats than they are to be Republicans. Conversely, those scoring highest in authoritarianism are nearly three times more likely to be Republicans than they are to be Democrats. In terms of Tea Party support, less than fifteen percent who score at the authoritarianism minimum profess support for the movement. More than forty percent of those scoring at the maximum do.
This doesn't mean that Tea Party support is uni-dimensional. But it appears that personality explains a substantial portion of support or lack thereof for this new and significant current in Republican politics.
In the book, we argued that a changing issue agenda over the past forty years - the emergence of issues like race, women's rights, sexuality and the war on terror - played an important role in driving what we described as a worldview divide. Authoritarians and non-authoritarians, we argued, responded very differently to the parties' increasingly distinctive images on so-called cultural and security issues.
But especially noteworthy about the deepening of this personality-based chasm is that it is now rooting itself firmly at the heart of a broad range of issue debates, from climate change, to the size of government, health care reform and so on.
So, it's no surprise that, according to the 2010 sample, 85% of low authoritarians supported repeal of Don't Ask, Don't Tell, whereas only 34% of high authoritarians did. Or that only 29% of non-authoritarians supported warrantless wire-tapping, while 90% of high authoritarians did. But also of interest is that nearly 80% of low authoritarians supported health care reform, whereas only 30% of high authoritarians did. And also striking is that 74% of low authoritarians supported the stimulus package, whereas only 43% of high authoritarians did. These are all enormous, striking differences.
The British study categorized people as liberal or conservative. Historically, these ideological labels have had a less clear-cut relationship to an identifiable personality dimension, like authoritarianism, than they do now. That the American party system is increasingly sorting itself out along such starkly opposed lines suggests that Americans on one side of the fault line are going to have growing difficulty fathoming how those on the other side understand the world as they do.
I am clearly on one side of that fence. So, I scratch my head in amazement (if not surprise) that Donald Trump's birtherism appears to have vaulted him (for the moment anyway) to the top of the GOP presidential field (and the other leader in the field, Mike Huckabee, has himself dabbled in birtherism).
But the bigger picture point is that many factors are conspiring to reinforce and intensify a fundamental rift in Americans' political self-identification based on deep-seated personality characteristics. In turn, our politics are likely to feel evermore acrimonious and irreconcilable, at least for the foreseeable future.