Americans seem increasingly to be sorting themselves into communities of the like-minded. This new political segregation is evident in nearly all institutions of American life — from the neighborhoods we call home to the mass media we consume. It is also reshaping classrooms in America’s universities — one of the few institutions capable of encouraging civil and reasonable disagreement in our polarized nation.

Whatever your ideological leaning, this is intensely troubling. America needs ideological diversity in its classrooms, particularly in those that touch on political and social issues.

A decade ago Stephen R. Porter and Paul D. Umbach, experts in education policy, assessed factors that predict undergraduate major choice by surveying undergraduates at an unnamed elite liberal arts college. They found, after controlling for many variables, that politics were a powerful predictor of major, rivaled only by personality. Conservative students, say Porter and Umbach, are far less likely to major in the humanities and social sciences than their liberal peers.

So what explains this difference? Some suggest that conservatives are more likely than liberals to choose engineering than, say, history because they are more concerned with making money.

It’s a plausible theory with only one major problem: It isn’t true. When undergraduates are queried by the nationwide College Senior Survey, conservatives tend to place only slightly more emphasis on making money. Apparently, the desire for wealth is bipartisan.