Claire Cain Miller and Quoctrung Bui write at The New York Times:
Assortative mating is the idea that people marry people like themselves, with similar education and earnings potential and the values and lifestyle that come with them. It was common in the early 20th century, dipped in the middle of the century and has sharply risen in recent years — a pattern that roughly mirrors income inequality in the United States, according to research by Robert Mare, a sociologist at the University of California, Los Angeles. People are now more likely to marry people with similar educational attainment — even after controlling for differences between men and women, like the fact that women were once less likely to attend college.
Researchers say the rise in assortative mating is closely linked to income inequality. The two have increased in tandem, Dr. [Christine] Schwartz, the sociologist from the University of Wisconsin, said: “People who are married tend to be more advantaged, and on top of that, more advantaged people are marrying people like themselves, so those people tend to be doubly advantaged.”
The effects could become more pronounced in future generations. Studies tell us that parents’ income and education have an enormous effect on children’s opportunities and achievements — and children today are more likely to grow up in homes in which parents are more similar than different.