I think it is natural selection. genetic variation also could be a factor for physical variation over the years.
The Testes are responsible for the production of sperm. The Epididymis is the next stage of sperm production and utilization; and is used for storage of sperm. The seminal vesicle, at the end of the Vas Deferens as the sperm is about to be ejected produces a substance that increases the motility of the sperm. The last organ to contribute to the sperm would be the Prostate, which provides nourishment to the sperm
Since smokers are not allowed to smoke within restaurants, office buildings, airports, schools, and many other places, far fewer people are being exposed to secondhand smoke. People with asthma and allergies to cigarette smoke are now able to breathe more easily as well. Children are no longer being exposed to secondhand smoke in spaces outside of their homes.
