Another reason to doubt the infertility-->declining birth rate story is that some populations that live in similar environments have maintained very high fertility rates.
Ultra Orthodox Jews live close to other city dweller in the US, have high-ish levels of obesity (implying similar food environment to average westerner, which is a reason to think Amish living as farmers might be exempt), and have high fertility rates.
Also, there are some factors, like much better treatment of STDs, that should, all other things being equal, reduce infertility rates. Historically, STDs could be a major cause of infertility.
Also, the relationship between sperm count and conception rates is not linear. IIRC, after about 20 million/ML, higher sperm counts don’t mean higher conception rates. So a 25% reduction in sperm count might not have much effect on conception rates for most men above that threshold, if that decline is even real.
(Apologies for the lack of citations, on mobile, will link later)
Another reason to doubt the infertility-->declining birth rate story is that some populations that live in similar environments have maintained very high fertility rates.
Ultra Orthodox Jews live close to other city dweller in the US, have high-ish levels of obesity (implying similar food environment to average westerner, which is a reason to think Amish living as farmers might be exempt), and have high fertility rates.
Also, there are some factors, like much better treatment of STDs, that should, all other things being equal, reduce infertility rates. Historically, STDs could be a major cause of infertility.
Also, the relationship between sperm count and conception rates is not linear. IIRC, after about 20 million/ML, higher sperm counts don’t mean higher conception rates. So a 25% reduction in sperm count might not have much effect on conception rates for most men above that threshold, if that decline is even real.
(Apologies for the lack of citations, on mobile, will link later)