The middle class isn't just shrinking, it's changing in one key way

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According to "The Changing Economics and Demographics of Young Adulthood: 1975–2016," a report released this month by the United States Census Bureau, being a grown up means something very different these days than it did forty years ago. "Marrying and having children," the report states, are not seen as "very important." Instead, young people prioritize "educational and economic accomplishments."

It's not just ideas that are changing, though. The middle class is shifting altogether. It's not just getting smaller; it's also becoming more female.

The Census Bureau reports that men are increasingly taking on salaries both at the top and at the bottom of the income distribution. Ever larger numbers of men — now 41 percent of them, up from 25 percent in 1975 — make under $30,000 a year.

Male workers still predominate at the top of the income scale, too:

Growth at the bottom, and to a smaller extent the top, came at the expense of the middle. Between 1975 and 2016, the share of young men with incomes in the middle ($30,000 to $59,999) fell from 49 percent to 35 percent, while the share at the very top ($100,000 or more) grew from three percent to eight percent.

As young men drift to the extremes, women are taking over the middle.

The report states that "young women have made considerable economic gains ... The share of young women who earned $60,000 or more grew from about two percent to 13 percent — a minority, but still a sizable change." Though in part because the men at the top still make so much more, young women's median incomes remain "$11,000 lower than the income of young men."

Women of all ages still hold many fewer of the most highly paid jobs. According to BLS data, there are a handful of jobs in which women make at least $1,300 a week, but as CNBC reported this year in honor of Equal Pay Day, "In the most lucrative professions, women make up less than 30 percent in each role."