Kay Hymowitz writes in The Daily Caller
Still, the biggest reason we probably won't see a lot more college-educated women walking down the aisle with their plumber is one we don't like to say out loud: they want to have smart kids. Educated men and women are drawn to spouses they think will help them produce the children likely to thrive in the contemporary knowledge-based economy. That means high IQ, ambitious, and organized kids who will do their homework and take a lot of AP courses. The preference for alpha kids is the reason there is a luxury market for Ivy League egg and sperm donors. It also explains why, though we don't have solid research distinguishing between elite and State U mating choices, Ms. Harvard will probably not accept a proposal from Mr. Florida State. The economist Greg Mankiw has quipped that "Harvard is probably the world's most elite dating agency." A glance at the New York Times nuptial pages suggests he's right.
In this respect, homogamy, at least educational homogamy, has a profound social downside; it increases economic inequality. Educated couples pass on the smarts and habits to their children that lead to good jobs and nice homes with lots of enriching activities for the grandkids, while the children and grandkids of less-educated men and women remain behind.
Americans don't like to think of themselves as class conscious. But marriage brings out the snob in the most democratic man or woman - for better or worse.
Marriage (and, thus, reproduction) is important enough to bring out the snob in everybody.