Boston ? Just think of all the time we wasted worrying about the culture gap, the religious gap, the class gap and even the gender gap. Now we are told that the political future will rest in the fertility gap.

This is the latest bulletin from the demography-is-destiny crowd. The fate of red and blue America will come down to who is filling those pink and blue nurseries.

These tidings were brought to us recently by Phillip Longman, who worried in The Washington Post that liberals aren’t having enough little liberals: “Conservative, religiously minded Americans are putting far more of their genes into the future than their liberal, secular counterparts.”

I never knew there was a conservative gene. If so, can it be tweaked? Is that another reason to support stem cell research?

Longman went on to say, “When secular-minded Americans decide to have few, if any, children, they unwittingly give a strong evolutionary advantage to the other side of the culture divide.” Imagine giving an evolutionary advantage to folks who don’t believe in evolution.

Longman is the author of “The Empty Cradle,” a book warning that the empty cradle won’t be able to support a full rocking chair. But he isn’t the only one saying that the right is out-breeding the left.

Earlier this month, James Pinkerton agreed archly in a Newsday column that “the left has birth-controlled, aborted and maybe also gay-libbed itself into a smaller role in American society.” And last winter, The Wall Street Journal’s James Taranto explained the “Roe effect”: “It’s almost a truism that women who have abortions are more pro-choice … so that if liberal women are having abortions, the next generation will be more conservative than it otherwise would be.” Apparently good liberal women should give up their right to choose in order to protect it.

We now have a number of, um, fertile male minds from left, right, and center — talk about your strange wombmates — agreeing that the political future belongs to the fecund female.

This idea hinges on some numbers from 2000. High fertility states such as Utah went red. Low fertility states such as Massachusetts went blue. As Longman figured it, women in Gore states were having 12 percent fewer babies than women in Bush states. Presumably that doesn’t include Florida, where the hanging chads were post-menopausal.

I confess to a certain weakness for statistics. I love to correlate things like, say, sushi eating and support for the Global Warming Treaty. (I made that up.) One of my all-time favorites was Pete du Pont’s post-2000 correlation between porn-watchers and Gore voters. And what to make of the fact that Bush won in most states with the highest percentage of teenage mothers?

But I’m wary of numbers that may be, in the statisticians’ terms “true, true, but unrelated.” We live in a world that’s been through tremendous technological and social change. The average woman in the world had 4.48 children in 1970 and has 2.69 now. Anyone who thinks that a low birth rate produces a conservative takeover hasn’t been to Italy lately.

I am even far more dubious of the claim that political labels are handed down through the DNA or even around the dinner table. In our own swiftly changing country, parents who dutifully plant one ideological seed get some pretty different sprouts. Yet only Pinkerton suggested that persuasion could be a match for procreation.

There’s a long history of Americans worrying about right and wrong wombs.

A century ago, there was a panic over the fact that the first generation of college-educated women weren’t reproducing while immigrants were. Theodore Roosevelt was so worried that he put a line in his State of the Union address accusing them of “willful sterility — the one sin for which the penalty is national death, race suicide.” And that man was a progressive.

But as immigrants went up the economic ladder, their fertility rates dropped. Meanwhile, those college-educated women found other ways of spreading the word and leaving a legacy. Anyone who thinks the first generation of feminists lost the evolutionary struggle hasn’t been watching the Title IX soccer players.

Are we supposed to worry about right and left wombs? I hear a rather odd echo in all this. Remember when liberals were told to be “Clean for Gene”? (If so, you are beyond your reproducing years anyway.) Are women now supposed to be Fertile for John?

In the last presidential election nearly 9 million women in those fertile years between 18 and 25 didn’t vote. Let’s not worry about getting them to the maternity wards. Let’s just get them to the polling booths.

— Ellen Goodman is a columnist for Washington Post Writers Group.