SCIENTISTS have been debating the question for more than a decade: Are men less fertile than they used to be? Some scientists insist sperm counts are plummeting – by up to 50% since 1940, according to a 1992 Danish study. Skeptics say that much of the data used to support the disappearing-sperm theory is flawed; some even claim that sperm counts are increasing.
But one indisputable fact has emerged from this debate: Scientists on both sides of the argument agree that men in some countries have higher sperm counts than men in other nations. In fact, sperm counts can vary dramatically from one city to the next within the same country. Some scientists say these geographic variations offer evidence that a man's environment can influence his fertility.