Polarization via Evolution?

Our deepening political divide explained as the result of education and evolution. - from The Atlantic


A familiar explanation for our deepening partisan divide is Bill Bishop’s Big Sorthypothesis. He contends that over the past 40 years, Americans have been sorting themselves into communities where people increasingly live, think, and vote like their neighbors. In 1976, for example, just more than a quarter of Americans resided in counties where presidential candidates won the election by a margin of 20 percent or more; but by the year 2004, nearly half of Americans lived in these more politically homogeneous counties.

Bishop’s idea is a convincing description of what is happening. But why is it happening? Thanks to research in demographics and anthropology, it’s now possible to get a clearer picture of the underlying reasons: education and evolution.

The dynamics that fuel the Big Sort accelerated in the second half of the 20th century, coinciding with a massive increase in education. Between 1960 and 2008, for instance, the proportion of women with bachelor’s degrees nearlyquintupled. The dramatic rise in educational attainment has a couple of unexpected side effects. For one, research shows that higher education has a polarizing effect on people: Highly educated liberals become more liberal, while highly educated conservatives grow more conservative. Second, people with college degrees enjoy greater freedoms, including social and geographic mobility. During the 1980s and 1990s, 45 percent of college-educated Americans moved to a new state within five years of graduation, compared with only 19 percent of their counterparts who had only a high-school diploma.

Meanwhile, evolutionary forces are pulling these more mobile, like-minded individuals together, because our political orientations play a key role in our choice of a mate. In society as a whole, spouses tend to resemble one another—at least a bit more than they would if coupling occurred at random—on most biometric and social traits. These traits include everything from skin color to earlobe size to income to major personality dimensions like Extraversion. Most of these statistical relationships are quite weak. But one of the strongest of all correlations between spouses by far is between their political orientations (0.65, to be precise). Spouses tend to have similar attitudes on moral issues like school prayer and abortion not because they converge over time, but rather because “birds of a feather flock together.” Biologists call this assortative mating.