One of the other interesting implications of this gap, which is mostly attributable to education, is that it leads to far more income inequality, which in turn leads to a host of nasty problems. For instance, as the divide between the haves and the have-nots becomes wider, it becomes harder to change one's station in life, leading to cycles of poverty.

In previous generations, people were more likely to marry outside of their education level and their family's economic class. So you might get a solidly middle-class, white-collar guy marrying a woman from a working-class family who never went to college, and they lived off one income.

But nowadays, it is much more likely that both spouses work, and also that people marry within their own class and education level. So, in general, you get either two low-income earners, two middle-income earners, or two high-income earners.

That greatly widens the household income gap, because now you're dealing with a combination of two incomes of roughly the same degree.

And so it becomes much harder for people to make changes to their economic status, because dual-income households are the norm, and if both spouses have to work, they have less time and opportunity, particularly at the lower end, to do things (like earn a degree) that might help them improve their economic status.