But Middle East experts can provide a long list of reasons why a survival-of-the-fittest theory might not necessarily be the best way to conduct American foreign policy in Iraq. First, they say, it’s always dangerous to take sides in a civil war. Second, siding with the Shiites in a Shiite-Sunni war is particularly dangerous since most of the Arab world is Sunni and America’s major Arab allies are Sunni. Besides Iraq, Shiites form a large majority only in Iran, and, well, enough said there.

If America has problems now with Muslim extremists around the world, those would likely worsen if the United States was believed to have aided the uprooting or extermination of Iraq’s Sunni population.

On Monday, a group of prominent Saudi clerics called on Sunni Muslims everywhere to mobilize against Shiites in Iraq, complaining that Sunnis were being murdered and marginalized by Shiites.

So, where is the Darwin Principle coming from?

Well, there’s no proof Mr. Cheney really even backs it. Unnamed government officials with knowledge in the matter say the proposal comes from his office, but they stop short of saying it comes from Mr. Cheney himself.

Other top officials say it is highly unlikely that the administration would pursue such a radical course. (Of course, the radical nature of the Darwin Principle is all the more reason to assume it comes from Mr. Cheney himself.) But it is difficult to imagine the administration actually publicly announcing such a course even if it decided on it.

Can you just hear President Bush’s speech to the nation? “My Fellow Americans, the United States has decided that there are more Shiites than Sunnis in Iraq, so we are therefore going to side with the people most likely to win a fight to the death. We’ll figure out how to deal with the rest of the Arab world, where there are more Sunnis than Shiites, later.”

Still, somewhere deep inside the Beltway, someone has laid out the intellectual basis for the Shiite option. So some people with knowledge of the thinking behind the proposal were asked to explain it. None agreed to be identified, citing an administration edict against talking about President Bush’s change-of-strategy in Iraq before the president articulates exactly what that change will be. But here’s what they said:

America abandoned the Shiites in 1991 and look where that got us. Mr. Cheney has argued that America can’t repeat what it did after the Persian Gulf war, when it called on the Shiites to rise up against Saddam Hussein, then left them to be slaughtered when they did. The result was 12 more years of the Iraqi dictator’s iron-fisted rule, which ended up leading to war anyway.