system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why have male testosterone levels been dropping for the last 60 years?
gpt
Just from quick googling, it seems that this whole idea that testosterone levels are declining comes from a single study printed in the *Journal of Clinical Endocrinology and Metabolism* in 2007. I'd caution against drawing broad conclusions--the study only sampled a small group of men in the Massachusetts area born between 1915 and 1945, and didn't even obtain a baseline sample until the 1980s. Not sure anything meaningful can be derived from this data. If there are other sources I'd be curious to see them.