“ These findings indicate that the past 20 yr have seen substantial age-independent decreases in male serum T concentrations, decreases that do not appear to be the consequence of the contemporaneous trends in health and lifestyle considered here. It remains unclear to what these apparent population-level decreases in T are attributable.”

My first thought was BPA, but it appears the effects of plasticizers on the male endocrine system are mixed[1].

Still can’t help but think this is something environmental and chemical at work.

[1] https://rbej.biomedcentral.com/articles/10.1186/s12958-018-0...