I have previously reported Philip Longman's argument that the religious people will produce a growing part of future generations because they have many more kids than the secular do.
Longman also argues that families, and societies, with a patriarchal structure, will produce a growing part of future generations for the same reason: they have many more kids than the gender egalitarians do. In an article in Foreign Policy (March 2006) he argues that in all the industrialized nations, the families that emphasize paternal headship, investment, and service to the family produce larger families in this generation, which multiplies enormously in the next. Whereas family structure liberals average a little over one child per family, family structure conservatives are the overwhelming majority of the four-and-more-kid families. In France, for example, the early Gen-Xers who had three-plus kids have produced 50% of the younger generation.
With this kind of advantage in natural growth, Longman says we can anticipate continuing waves of conservative social movements and voting patterns, as the children of conservatives gain ground demographically in each generation.