There has been much ado about declining testosterone levels and sperm counts. I decided to see if I could identify the primary sources of these assertions. Secondary sources abound but my search for primary sources proved frustrating. I did find what appears to be a well researched and well written survey paper by a Columbia University professor which debunks the idea that sperm counts and quality are precipitously declining.

https://harryfisch.com/wp-content/uploads/PDF-RP-Declining-Worldwide-Sperm-Counts-Disproving-a-Myth.pdf

Seems the results of research vary greatly and that only research that raises alarm bells is being reported. Makes a certain amount of sense as an all is well finding is hardly news.

If anyone can find a similar summary or survey regarding testosterone level research I'd love the link.