Until the 1970′s, more men than women attended college. Now, not only do more women than men attend college, but more women than men earn Bachelor’s (Bachelorette’s?) degrees and Master’s (Mistress’s?) degrees.
Back in those halcyon days, educated men worked with less educated women. Those women might be particularly intelligent, or they might not. Personality and beauty reigned over intellect. A young, beautiful, sweet girl could marry an educated man for whom she worked as a secretary, or whom she met in the grocery store or at church.
Now, college-educated men meet their wives either in college or at work. As such, we are selection sorting by intellect. Educated men marry educated women, and uneducated men marry uneducated women. This stratifies society by broadening the IQ curve — more intelligent couples have more intelligent children, and less intelligent people have less intelligent children.
Such selection sorting by intellect necessarily increases the income inequality, as the intellectual inequality increases.
Exacerbating this trend is the fact that less-educated women (who tend, naturally, to be less intelligent) have more children, earlier in life, than do those with more education. In fact, according to that study, college-educated women average fewer than two children over their lifetimes. They are not even at replacement rate. Meanwhile, women with only a high-school education are having an average of 2.7 children over their lifetimes.
Further exaggerating this stratification is that less-educated have those children at younger ages. Let’s figure that women with only a high school education have an average of 2.7 children, at an average age of 25, and that college-educated women have 1.8 children at an average age of 33. By the age of 100, a less-educated woman will have 53 great-great-grandchildren (from 16 great-great-grand-parents). The educated woman, however, will have about six great-grandchildren (from eight great-grandparents).
The less-educated (generally less intelligent) people increase, while the more-educated (generally more intelligent) people decrease.
So by more widespread education of women, we have greater stratification because of the selection sorting by education level (a proxy for intellect), and we have a demographic shift toward fewer intelligent offspring.