According to an editorial in the Wall Street Journal, conservatives are not only beating liberals at the polls, they're outbreeding them too:

According to the 2004 General Social Survey, if you picked 100 unrelated politically liberal adults at random, you would find that they had, between them, 147 children. If you picked 100 conservatives, you would find 208 kids. That’s a “fertility gap” of 41%.

It seems a little strange that the birthrates of today's Democrats and Republicans can influence elections decades from now, but given that "about 80% of people with an identifiable party preference grow up to vote the same way as their parents", the outcomes of future elections seem almost predictable. In other words, what most of us consider as an exercise in free thought and personal choice is often determined before we're even born.

But I'm not entirely convinced Democrats' fates are sealed. Although the WSJ editorial makes a valid point, demographics, particularly in developed nations, are influenced by more than interal birthrates. Immigration, whether legal or not, plays an important role, and studies suggest minorities will make up the majority of the U.S. population in a few decades.

Most minority groups have traditionally voted Democrat, which may make up for their lack of baby-making. However, Hispanic voters have been lured by conservative Republicans in recent elections. Success, for Democrats and Republicans, may depend more on how effectively they court the Hispanic demographic than how many kids they're having.