Earlier quoted context omitted.
Human fertility itself isn't in decline. Fertility and human births are conflated in the US government definition, implying that we are somehow losing the physical ability to reproduce. What's actually happening is that our society is getting so complex that our agency of reproduction is impaired. It's entirely social; it's all in our heads.
Jury is still out, but there's accumulating evidence that male fertility isn't doing well across the developing world: http://ehp.niehs.nih.gov/121-a46/ http://www.wsj.com/articles/SB100014241278873233945045786076... http://www.dailymail.co.uk/health/article-158463/Why-male-fe... http://jezebel.com/finally-an-answer-to-declining-male-ferti...
Recent years have seen many similar reports of falling human sperm counts, but there has been much debate over whether the problem is real. “The principal trouble has been selection bias,” says Joëlle Le Moal, an environmental health epidemiologist at the Institut de Veille Sanitaire in Saint Maurice, France, and joint first author of the new article with colleague Matthieu Rolland. She explains that few studies have involved sperm samples collected from randomly selected members of the general population; for the few that did, only a small percentage of men agreed to be included, and the studies were run in restricted areas. So most studies have had to rely on sperm donors or couples coming to fertility clinics, which do not represent the general population.
That article focuses on France, which is rarely counted among developing worlds. The second article is paywalled. The third two could easily be considered Submarine Articles[0] for male supplements and stimulants.