Rates of ADHD were higher as well—15.5 compared to 7.1 percent. The same is true for learning disabilities: 14.1 vs. 8 percent.

The study’s author, sociologist Paul Sullins, assessed a variety of different hypotheses about the differences, including comparative residential stability, experience of stigma or bullying, parental emotional problems (6.1 percent among same-sex parents vs. 3.4 percent among opposite-sex ones), and biological attachment.

Each of these factors predictably aggravated children’s emotional health, but only the last of these—biological parentage—accounted for nearly all of the variation in emotional problems.