To be fair I think it is kinda racist to categorize sperm as either "Western" sperm vs "other" sperm. They couldn't do the bare fucking minimum and at least separate by continent or wealth? Health?

It is really weird the original study decided to categorize it this way. Especially because there are potentially drastic environmental differences between say the US and Australia. Same goes for the "Other" category. How are China and Brazil similar?

Maybe it's not the bare minimum? Maybe they had limited funding, largely access only to "Western sperm" (which actually is a reasonable category I would argue because we share a lifestyle to a greater or lesser degree), maybe they had sparse data that covered simply "not the West".

If you have sparse data, then maybe you shouldn't be making grand comparisons or trying to make claims about the entire world?

If they had access largely only to "western" sperm then they could separate it out by country, or income, or something more sane. It's not like the rest of the world shares a lifestyle!

Not a biologist, but that kinda makes sense: you only need one single healthy sperm to reach the egg in order to fertilize it, so even men with pretty bad sperm counts are probably still able to have children. So the average sperm quality may drop for some while without a corresponding drop in fertility. But then the drop in fertility will be all the worse...