2) More women in the workforce. In 1959, 37.2 percent of women had a job or were actively looking for one. In 2012, it was 57.7 percent. That said, it's still hard for women to lean in when they have to plan their careers around when they have kids, when daycare is so damn expensive, and when husbands don't always do their share of the housework. That's why men still dominate the highest-paying jobs that require an inhuman number of hours as a show of your semi-feudal obligation to work. And even if women do break through, they still don't get paid as much as men do for the same work—though, as Hanna Rosin points out, the gap is more like 9 cents for every dollar men make, and not 23 cents.

3) More financial insecurity. You used to be able to afford a solidly middle-class lifestyle with just a high school diploma. That seems inconceivable today, when two college degrees aren't always enough, depending on how pricy your zip code is. But it's true. In 1960, a married couple of high school graduates made 103.1 percent of the average income. In 2005, that same couple would have made 82.7 percent of the average—and that's despite women working more. College-educated couples haven't fallen back, but outsized inflation in things like housing, healthcare, and college tuition have made staying ahead harder than getting ahead.

4) More marital expectations. Men don't just want a homemaker, and women don't just want a good provider. Men and women both want a good partner. That means someone to help with the mortgage, the homework, the housework, and watch House of Cards with. Someone ... like themselves.

5) More assortative mating. Take a look below at the same chart breaking down marriage by each partner's education, but updated for 2005. The first thing you'll notice is how much more likely high school dropouts are to marry each other than by chance. But look again. Every group is disproportionately more likely to marry someone like themselves than any other.

Now, it sure doesn't look like highly-educated people are more likely to marry each other today than before. But that's just because there's more of them. In 1960, there were so few people with college, let alone advanced, degrees that any marriages between them would be disproportionate. Today, higher ed is more democratized, but marriages aren't. The opposite, actually. You can see that in the shaded parts above—college-educated men are much less likely to marry women who aren't than they were before. By 2005, someone who had at least graduated from college was more likely to marry someone else who had than not: 24.2 of married couples both had college degrees, while 22.2 percent had a single partner with one.

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It's a classic story. Boy meets girl in college. Girl dislikes boy, but then asks to be friends five years later. Boy says no, but changes his mind mind after they both go through bad breakups. Girl and boy start falling for each other. Boy freaks out after they finally act on their sexual tension. Girl doesn't want to see boy anymore. But then boy confesses his love, and they live happily ever after—with two nice incomes.