Why is everyone suddenly talking about tanning their testicles?

Stuart Ritchie in his Substack newsletter, Science Fictions:

Let’s start with something everyone agrees on: the world’s fertility rate has declined. Whether you’re in a low-, middle-, or high-income country, with few exceptions the “total fertility rate”—the number of children per woman—dropped pretty precipitously across the latter part of the 20th Century.

The vast majority of this decline has absolutely nothing to do with testosterone. The main reason for it is economic development: people tend to have fewer children as they and their countries become richer – and that’s incredibly good news. Other things that lower the fertility rate are also related to progress and prosperity: education (particularly of women), urbanisation, the availability of contraception, and so on.

But there also might be negative trends in fecundity – meaning a person’s biological ability to have kids, as opposed to simply whether they have kids or not (the latter being what people call “fertility”). It would be more worrying if fecundity was dropping, because that would take the choice of whether to have kids out of many people’s hands.

More here.