“Do you believe in evolution?”

That’s the question GOP presidential candidates dread. Governor Scott Walker of Wisconsin is the latest to hem and haw his way through an awkward press conference on the subject.

Of course, some GOP contenders have no need to fear. Ben Carson, for example, is a loud and proud young-earth creationist. But other potential nominees have had to dodge, duck, dive, and dip when the question comes up. Bobby Jindal, a former biology major at an Ivy League college, has confessed that he wants his own children to learn evolution. That doesn’t mean schools must teach it, though. Jindal wants “local schools” to decide what’s right for them. And Marco Rubio famously told GQ magazine that he was “not a scientist, man.”

Walker is the latest GOP notable pressured to answer “The Question.” At a London press conference, Walker did his best to avoid it. In the end, though, Walker felt obliged to clarify that he strongly believed that humanity was created by God, and that faith and science are compatible.

It has become such a staple of GOP press conferences that conservative pundits cry foul. Writing in the pages of the National Review, for example, Jonah Goldberg says these evolution questions are a cheap stunt, a way to make conservative candidates squirm. As Goldberg put it,

To borrow a phrase from the campus left, Darwinism is used to “otherize” certain people of traditional faith — and the politicians who want their vote.

As fellow conservative writer Kevin D. Williamson correctly pointed out, leading mainstream scientists will also insist that they don’t “believe in” evolution. Rather, they simply know it; they take it to be the best current explanation and model for understanding the way species have changed and developed.

Yet no matter how you slice it, “the question” has become a defining feature of Republican presidential candidates. Even candidates who seem personally to embrace mainstream evolutionary science are loath to alienate conservative religious voters. For many of those religious voters, evolution has become a moral litmus test, not just a statement of personal belief.