BRYAN CAPLAN: The Obvious-Once-You-Think-About-It Reason Why Education Cuts Fertility.

Education changes students’ values. Never mind rare heavy-handed propaganda about overpopulation. Education dethrones fertility via emphasis. Telling kids that academic and career success should be their top priority implicitly says, “And having kids should be a lower priority.” Not teaching religion and traditional values implicitly says, “Religion and traditional values aren’t very important.” And so on.

Though I’ve long preferred the latter story to the former, only recently did I realize that I’ve been overlooking a far simpler and practically bulletproof mechanism that explains why education reduces fertility. Namely: Almost everyone wants to finish their education before having kids — and there is a strong stigma against those who do otherwise.

If school ends in 12th grade, this norm lets you start having kids at 19 or 20.

If school ends after you get your B.A., this norm lets you start having kids at 23 or 24. (And since most students don’t finish on time, that should usually get bumped up to 26 or 27).

If school ends after your get your second Ph.D., this norm lets you start having kids around the age of 38.

Key point: Staying in school longer does nothing to alter the effect of biological age on fertility. The later you start having kids, therefore, the fewer kids you are ever likely to have. Late fertility almost automatically means low fertility.

One of many reasons why we should not mindlessly extend the years of schooling.