For a time, it all seemed to work. From 1950 to 1965, divorce rates dropped, fertility rates rose, and the American nuclear family seemed to be in wonderful shape. And most people seemed prosperous and happy. In these years, a kind of cult formed around this type of family—what McCall’s, the leading women’s magazine of the day, called “togetherness.” Healthy people lived in two-parent families. In a 1957 survey, more than half of the respondents said that unmarried people were “sick,” “immoral,” or “neurotic.”

During this period, a certain family ideal became engraved in our minds: a married couple with 2.5 kids. When we think of the American family, many of us still revert to this ideal. When we have debates about how to strengthen the family, we are thinking of the two-parent nuclear family, with one or two kids, probably living in some detached family home on some suburban street. We take it as the norm, even though this wasn’t the way most humans lived during the tens of thousands of years before 1950, and it isn’t the way most humans have lived during the 55 years since 1965.

Today, only a minority of American households are traditional two-parent nuclear families and only one-third of American individuals live in this kind of family. That 1950–65 window was not normal. It was a freakish historical moment when all of society conspired, wittingly and not, to obscure the essential fragility of the nuclear family.