The so-called birthers can't accept that President Obama is really a natural-born American citizen. Part of what's behind this seemingly irrational belief may lie in what's called implicit social cognition-the deep-rooted assumptions we all carry around, and may act on without realizing it.

Harvard's Mahzarin Banaji studies such implicit cognition. Last fall she talked to journalists at the annual conference of the Council for the Advancement of Science Writing about research into bias against Asian-Americans. "So we thought, what if we picked Asians who are very well known to be American. What about Connie Chung? Are they going to be seen as less American than, let's say, Hugh Grant? And so we thought this was a bizarre study to do but we did it anyway."

Amazingly, white Americans did see a white European like Hugh Grant as being somehow more American than the Asian-American Connie Chung. And similar research in 2008 found that whites thought of ex-British Prime Minister Tony Blair as somehow more American than Obama. So the mental framework to believe that Obama is foreign probably was, to use a health care term, a preexisting condition.