The other day an interesting, if depressing, piece by Jessica Grose popped up into my Twitter feed. It's from last year, but still worth the time: an extensive study of Harvard Business School graduates found that—even among this elite cohort with almost limitless earning potential—men's careers took precedence over women's careers.

About 40 percent of Gen X and boomer women said their spouses’ careers took priority over theirs, while only about 20 percent of them had planned on their careers taking a back seat. Compare that with the men: More than 70 percent of Gen X and boomer men say their careers are more important than their wives’.

And that wasn't the only traditionally gendered divide.

When you look at child care responsibilities, the numbers are starker. A full 86 percent of Gen X and boomer men said their wives take primary responsibility for child care, and the women agree: 65 percent of Gen X women and 72 percent of boomer women—all HBS grads, most of whom work—say they’re the ones who do most of the child care in their relationships.

The next day, a new study led by University of Chicago economist Marianne Bertrand popped up in my feed, which explains why that might be the case. If women do start earning more than their husbands—which, in the case of the long hours that elite business-school grads tend to work, suggests their work taking precedence—those couples are more likely to split up. "Such a possibility echoes Al Roth's Iron Law of Marriage," the authors write. "You cannot be happier than your spouse":

[W]e find that if the wife earns more than the husband, spouses are 7 percentage points (15%) less likely to report that their marriage is very happy, 8 percentage points (32%) more likely to report marital troubles in the past year, and 6 percentage points (46%) more likely to have discussed separating in the past year.

Unsurprisingly, divorce tends to follow: "we find that when the wife earns more than the husband, the likelihood of divorce increases by about 6 percentage points. Since 12 percent of couples in the sample get divorced, this estimate implies that having the wife earn more increases the likelihood of divorce by 50 percent."

Interestingly, relative income didn't matter—just whether the wife made more money or not: "the norm that the husband should earn more than the wife has been violated."

Grose's piece also, as noted, mentioned huge differences in how much child care husbands and wives do. Even for the high-earning, presumably quite busy women in the Harvard cohort, many more reported doing the majority of the child care (though that percentage fell in the Gen X generation).

Bertrand and her coauthors have an interesting explanation for this, too. If violating gendered expectations of labor leads to unhappiness, then one way of redressing that imbalance between traditional roles is for the woman to take on more traditional responsibilities. Which is exactly what they found: "once a wife earns more than her husband she starts to compensate for it by spending more time on chores and childcare." And they aren't alone in this finding.

The increased earning potential of women is hardly the only influence on marriage and divorce rates; from a more positive perspective, women's liberation and the increased economic independence of women surely play a role. But these seemingly outdated gender roles are powerful: The authors conclude that about a third of the decline in marriage rates can be explained by the income taboo.