My theory goes like this;

> In the recently released research, no significant decline in sperm quality was seen in men from non-Western countries, but this segment made up only about a quarter of the results.

There is something in developed countries that the male do not experience during his lifetime. It can be lack of fear, adrenalin, less activity, or something else. I think statistics hold up with the historic wars as well. As WW2 ends and people starts living without any fear of life, male sperm quality drops.

I think it is about what male experiences and which hormons are triggered in his lifetime.