Lately Rick Santorum has been singing every tune from the Culture Wars: Greatest Hits album. So of course he soon came around to attacking higher education, charging that going to college makes people less religious, that universities are "indoctrination mills" and even that liberal Penn State profs docked his grades to punish his conservatism when he was a student there.

It didn't take long for liberals to produce liberal academic social science to disprove Santorum's claims about the secularizing influence of academia. How perfect: but don't expect Santorum to change his mind upon being refuted. We have liberal academic social science on that, too -- and it suggests he's more likely to double down on his original assertion.

In truth, Santorum isn't quite as off base here as he is on, say, his denial of global warming. He's absolutely right that higher education is a liberal and secular force in our society at present. But he's also highly simplistic in his view that it creates liberals, or atheists -- or that it intentionally discriminates against conservatives or the devout.

If anything, when it comes to the liberalism of academia, much of the causation may well run in the opposite direction from the one that Santorum assumes. Rather than colleges making people liberal, liberals may instead make colleges the way they are by choosing to attend and, even more importantly, choosing to stay and pursue advanced degrees.

Lying behind Santorum's remarks is the seemingly obvious -- but actually quite suspicious -- idea that colleges engage in some form of liberal brainwashing or indoctrination. The idea seems to be that you go off to school, your gods and beliefs are assaulted and you come out a non-virgin tree-hugger who has tried lots of substances, and maybe even picked up an odor.

It's certainly true that college professors are overwhelmingly liberal -- as are scientists. As I reported last year in The American Prospect, the best research suggests that just 14 percent of professors are Republicans. Similarly, just 6 percent of American Association for the Advancement of Science members back the honorable elephant of the GOP.

But why? Sociologist Neil Gross of the University of British Columbia, along with his colleagues Ethan Fosse and Jeremy Freese, make a compelling case that the liberalism of academia is partly driven by "self-selection": for liberals, pursuing an academic career is naturally appealing. So they tend to stay at universities and pursue graduate degrees and doctorates, and ultimately, come to make up most of the professoriate.

By contrast, conservatives have a different set of values, interests, and priorities. They are, for instance, more likely to want to go into the business world and make gobs of money. Such things push young conservatives away from academia, or at least from staying there very long. Thus, they leave these institutions open to being dominated by liberals.

It certainly doesn't help that the right has been attacking colleges for decades. So liberals have learned to like them, and conservatives have learned to distrust them.

Who, then, needs questionable theories of brainwashing and indoctrination to explain the liberalism of academia? Ironically, it looks like what's actually going on here is market forces at work. And some of these forces may even be acting before students go to college in the first place, and get exposed to the admittedly liberal environment that prevails there (which then exerts its own influence, and assuredly does make conservatives feel like outsiders).

I personally find the explanation offered by Gross, Fosse and Freese to be quite plausible -- but also not fully satisfying. It's purely sociological in nature, and to me that limits its power. It is surely part of the truth, but perhaps not all of it.

As these scholars themselves admit, there are also psychological reasons to think that young liberals naturally want to stay at universities and pursue advanced degrees. Indeed, there are psychological reasons to think they may gravitate towards universities even before they fully know that they are liberals.

It's clear that humans beings have different personalities -- some more open to new and abstract ideas and more exploratory, some more closed and defensive -- and these personalities have strong political implications. I discussed some of this research in my last piece here, and much more extensively in my forthcoming book The Republican Brain.

If all of this is right -- and the body of evidence is extensive and compelling -- then liberals just are the kind of people who like to hang out in places like universities and try out new ideas (and substances, and music, and... use your imagination). By this analysis, universities are a lot like coffee shops and Cambridge, Massachusetts: the kind of places where liberals just feel like they belong. And Santorum is as powerless in the face of this as we all are in the face of human nature.

Conservatives, supposedly, support tradition and stability and doing things the way they've always been done. And they support building the institutions of society in such a way as to realistically reflect who we are, and who we always will be.

Well, perhaps the liberalism of colleges and of scientific inquiry is a core part of that picture. And if so, not only is there no point complaining about it, but there's every reason to be happy about it -- at least if you're really "conservative."

Perhaps we'll always have liberals, hanging out in colleges, pushing conservatives' buttons. And perhaps we'll always have conservatives feeling uneasy about it, or worse -- denouncing universities as liberal bastions and claiming they're indoctrination mills.

Just call it tradition.