A new analysis from Pew Research Center looks at the composition of modern families.

Compared to 1970, far fewer adults are living with a spouse and at least one child.

It reflects how socioeconomic challenges are changing what families look like.

In 1970, nearly 70% of American adults ages 25 to 49 were living with a spouse and at least one child. As of 2021 — the most recent year for which they have data — that's fallen to 37%. At the same time, other family arrangements have become more common: In 1970, essentially no one was reported to be cohabitating unmarried with kids; by 2021, that rose to 5%. And, significantly, 18% of American adults were married with no kids in 1970. As of 2021, that's risen to 21%.

"Family living arrangements are becoming more and more diverse in their composition," Carolina Aragão, one of the authors of the Pew report, told Insider. While married adults with kids are still the most common family arrangement, "they are far less common than they were in the past."