Higher education leans left. But why? And so what?

Unsuccessful GOP gubernatorial candidate Tom Emmer thought he had an offer last year to teach at Hamline University. Until he didn't.

"We don't have any further comment on that," Hamline's communications director told me recently.

Actually, administrators never offered much explanation, leaving many to infer that a liberal faculty howled about Emmer's conservative views and a battle-shy administration caved.

Regardless, the incident raises the question: Why are university faculties so demonstrably lacking in conservatives? And, does it matter?

That faculties are liberal is beyond dispute. In a rigorous survey, University of British Columbia sociology Prof. Neil Gross concluded, "professors currently compose the most liberal major occupational group in American society."

Gross got interested in this issue in 2005, when he was at Harvard, where president Lawrence Summers suggested that the underrepresentation of women at the highest levels of math and science might be due to "different availability of aptitude at the high end."

Says Gross: "I was quite intrigued by the way Summers was ... pilloried by the left -- and martyred by conservatives."

So Gross and Solon Simmons of George Mason University surveyed more than 1,400 full-time professors at more than 900 American institutions. Only 19.7 percent of professors identified themselves as "any shade of conservative" (compared with 31.9 percent of the general population), while 62.2 percent identified themselves as some flavor of liberal (compared with 23.3 percent of Americans overall).

Gross found variation between disciplines. Social sciences and humanities contained the highest concentration of liberals. Conservatives were as numerous as liberals in business, health sciences, computer science and engineering.

Why so liberal? The most obvious explanation -- one favored by conservative activists -- is discrimination. Even some liberals buy it.

"This is a statistically impossible lack of diversity," proclaimed the not-especially-conservative social psychologist Jonathan Haidt at last year's Society for Personality and Social Psychology annual meeting.

A show of hands had revealed three self-proclaimed conservatives in a gathering of 1,000 psychologists. Presented with such underrepresentation by gender or race, Haidt said, "our minds jump to discrimination as the explanation."

Discrimination is exactly where Teresa Wagner's mind jumped. A conservative, anti-abortion activist, Wagner was passed over for a job at the University of Iowa.

She sued the law school for violating her First Amendment rights to free speech. Wagner lost in district court, but the U.S. Eighth Circuit Court of Appeal found enough merit in her argument to reinstate the case early this year.

Despite cases such as Wagner's and Emmer's, Gross says the discrimination argument -- at least in explaining a shortage of conservatives in colleges across the country -- founders on the rocks of evidence.

Or lack of it. "If you look at surveys that have asked professors whether they've been discriminated against on political grounds ... only something like 7 percent of those surveyed said they have been," says Gross.

Another factor that argues against overt discrimination in the hiring process is that graduate school, the pipeline to the professoriate, is also dominated by liberals. So the candidate pool's "numbers are almost exactly the same as we find in the professoriate," says Gross.

Might there be discrimination in admission to grad school? Are conservatives being rejected or subtly steered into other endeavors?

Gross and colleagues devised a sneaky survey. They identified hundreds of top-ranked graduate programs in sociology, economics, English, political science and history. Posing as prospective grad students, they sent two e-mail inquires to the director of each program.

The first was a control, expressing general interest in grad school. The second e-mail was similar, but contained a political marker. Some directors received letters from a fictitious student who casually mentioned he had worked on the Obama campaign. Others received letters from a faux McCain volunteer.

Responses from graduate directors, Gross said, might have revealed a political bias among directors themselves, or they might have served as warnings to prospective students that a department was "off-limits to conservative applicants."

But he said that the researchers found "only the slightest hint -- no significant evidence -- of bias or discrimination." In only one response out of 450 did a director seem to suggest that a conservative applicant keep his political views to himself.

Alternate explanations

As Haidt noted, when conservatives are underrepresented, rather than African-Americans or women, "suddenly everyone finds it quite easy to generate alternate explanations." Indeed, researchers have done just that.

One argument centers on values: Conservatives place greater value on making money and head into business. But "the values hypothesis doesn't have great explanatory power either," says Gross.

"On the question of moneymaking, for example, there are relatively few differences between people on the left and people on the right."

What about personality? Conservatives value order and hierarchy -- prized traits in the military, not so much in university endeavors.

Indeed, "personality differences will always guarantee that academe is mostly liberal," says Haidt.

Research "consistently shows that liberals are higher on openness to experience. They're more interested in novel ideas, and in trying to use science to improve society. So of course our field is and always will be mostly liberal."

Gross favors a different explanation -- that a process of "political typing" encourages self-selection among both liberals and conservatives.

By this line of thinking, the American research university came of age during the Progressive Era, with lines of inquiry challenging the status quo and power of the rich. Such endeavors naturally attracted liberals.

"This reputation built on itself over the years. And it was reinforced by others, like social movements in the 1960s and '70s."

Universities became known as hotbeds of liberalism. "And that helps pull liberals in year after year and keeps conservatives out," Gross says.

But does it matter?

Any litmus test of the professoriate that doesn't focus exclusively on teaching and research is an intrusion on academic freedom, according to Stanley Fish, a professor of humanities and law at Florida International University and columnist for the New York Times.

In Fish's view, hiring for "diversity" -- in race, gender or politics -- is irrelevant to the principal academic enterprise.

Gross isn't so sure. "In my field of sociology, people will say your politics incidentally will shape what you study, but it doesn't necessarily shape what you find."

The presumed academic benefit of "diversity" is the hope of recruiting original minds willing to challenge intellectual conventions. Yet it's not at all clear that hiring a mix of liberals and conservatives -- or Jews, Evangelicals, African-American Baptists or Chinese nationals -- is an effective way to find those minds.

For example, I've recently written about Macalester biology Prof. Mark Davis, who has challenged the orthodoxy that exotic animal and plant species are intrinsically threatening. But is his position liberal or conservative? Is it foreordained by his status as a white, middle-aged man?

If original viewpoints are the goal, perhaps the most direct way to get them is to hire candidates who have produced, well, original work.

Haidt argues that political views don't matter much in natural sciences, where it is usually possible to devise controlled experiments that minimize the influence of human beliefs and bias. That's much more difficult in social sciences, such as Haidt's field of social psychology.

"Our shared values make it difficult for us to entertain alternative hypotheses," he says. "[W]e humans are experts at using reasoning to find evidence for whatever conclusions we want to reach. We are terrible at searching for contradictory evidence."

Haidt adds: "When a scientific community shares sacred values ... a tribal moral community arises, one that actively suppresses ideas that are sacrilegious, and that discourages nonbelievers from entering. I argued that my field has become a tribal moral community, and the absence of conservatives, not just their underrepresentation, has serious consequences for the quality of our science."

All the same, the liberal academy seems destined to remain so, if only because of Republican political strategy. Demagoguing against "elites" (consider Karl Rove's quip that a Democrat is "somebody with a doctorate") reinforces the perception that only liberals belong in academia.

Now that Jon Huntsman has quit his presidential campaign, no Republican remains who is willing to unequivocally defend evolution and climate change. What self-respecting scientist wouldn't reject such politics?

Conservative accusations of liberal bias seem designed more to discredit academics than to redress the balance. And maybe that suits activists best.

"Looked at over the long haul, it's not clear that it's really that great for a political movement to have big academic representation -- that [it] really helps movements to succeed," says Gross. "Perhaps all this is to the good as far as the conservative movement is concerned."

Unfortunately, the estrangement will serve only to reinforce the lopsidedness of university politics, undermine the confidence of a large share of the public in expert opinion, and jeopardize the role of the university in public life whenever conservatives are in power.

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Greg Breining, of St. Paul, writes about science, nature and travel. He is the author of "Paddle North: Canoeing the Boundary Waters-Quetico Wilderness" and "Wild Shore: Exploring Lake Superior by Kayak."