Last summer, a meta-analysis of 185 studies in which semen was collected over the past 40 years indicated that sperm concentration seemed to have consistently and remarkably declined in the course of a generation.

Different clusters of people — urologists, anthropologists, men’s rights activists and start-up founders — became quietly concerned about the state of sperm. Quiet, probably, because Americans are more used to talking about women and fecundity. And also quiet because there has not been much research aimed at discovering if anything is actually happening.

Still, the study has had social impact. Some men’s rights communities are gathering around the idea that sperm counts are dropping because men are being feminized by society. There is now growing interest in testosterone replacement therapy, which some believe boosts sperm count. At the same time, smartphone-enabled at-home sperm tests are entering a heated market.