A sad new study proves that moms are the top earners in four of ten American households. It may seem like a positive thing that these working women are top earners, but it either means the woman is a single mother or that the "dad" is unemployed.

Even though women are generally smarter than men, they earn less because of the entrenched patriarchy. (Women are not necessarily smart, they're just smarter than men, the way birds are smarter than snails or whatever.) When a single woman is the "main breadwinner," the household has less money than when the woman is the top earner in a two-income family.

These “breadwinner moms” are made up of two very different groups: 5.1 million (37%) are married mothers who have a higher income than their husbands, and 8.6 million (63%) are single mothers.1

The income gap between the two groups is quite large. The median total family income of married mothers who earn more than their husbands was nearly $80,000 in 2011, well above the national median of $57,100 for all families with children, and nearly four times the $23,000 median for families led by a single mother.

Did you know women were not even allowed to vote or go to bars or even get tattoos not so long ago? History is full of such examples.

Anyway:

"This change is just another milestone in the dramatic transformation we have seen in family structure and family dynamics over the past 50 years or so," said Kim Parker, associate director with the Pew Social & Demographic Trends Project. "Women's roles have changed, marriage rates have declined — the family looks a lot different than it used to. The rise of breadwinner moms highlights the fact that, not only are more mothers balancing work and family these days, but the economic contributions mothers are making to their households have grown immensely."

In 1960, only 11% of moms were the big breadwinners. The rest lounged around in costumes from that Mad Men show. Things have changed. It is now impossible to raise children, three out of four parents say, because mom and dad (if he's even around) both have to work all the time to pay the mortgage and the credit cards and probably the student loans. It's just a crushing grind, ending in death. Plus, kids! Who watches the kids? It's just impossible, this whole situation. And Marissa Mayer is all, "Now you have to come to the office every day so you can read on Google News how Yahoo! just bought American Apparel and the Coachella festival."

One way to be the default Top Earner in your house is to be a single mom. A recent study showed 77% of women under 30 shack up with a dude instead of marrying. And that's fine, except economically it's a road to a place with no money.

The loss of manufacturing and "skilled labor" positions is one reason why so few American men have jobs today. Women are now more likely to have a college degree than men, who are dumber, so those jobs requiring an education are increasingly filled by women. But women are still paid less than a man in the same job, if that man had a degree and could get a job.

At the same time, marriage rates have fallen to record lows. Forty percent of births now occur out of wedlock, leading to a rise in single-mother households. Many of these mothers are low-income with low education, and more likely to be black or Hispanic.

In all, 13.7 million U.S. households with children under age 18 now include mothers who are the main breadwinners. Of those, 5.1 million, or 37 percent, are married, while 8.6 million, or 63 percent, are single. The income gap between the families is large—$80,000 in median family income for married couples vs. $23,000 for single mothers.

It's pretty hard to find even a single sustainable part of the American economy and social structure.

[Photo via Shutterstock.]