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But according to a new, heavily promoted book, there is powerful evidence to support another hypothesis. Our Stolen Future (Dutton; $24.95) says a wide range of reproduction-related ills may be caused by chemical pollutants in the environment, including DDT, some forms of dioxins and PCBs, and a number of other synthetic substances. The idea is that exposure to even traces of these chemicals in the womb can interfere with proper development of the reproductive system, leading to serious consequences years or decades later. Male infertility is just one part of the problem, say the authors; these pollutants may also be responsible for a rise in breast and other cancers in humans, along with aberrant mating behavior and genital malformations in animals (minuscule penises among pesticide-contaminated Florida alligators, for example).
Chemical manufacturers dismiss these speculations, arguing that nobody has come close to showing a cause-and-effect relationship. In fact, the evidence for a chemical-infertility link does remain largely circumstantial. "There is no smoking gun," admits J.P. Myers, who is director of the environmentalist W. Alton Jones Foundation and one of the book's co-authors. (The others are science reporter Dianne Dumanoski and World Wildlife Fund zoologist Theo Colborn.)
What scientists do know is that water, air and soil all over the world are tainted with small amounts of many of these chemicals. They know that once the pollutants get inside the body, they can bind with receptors that normally recognize estrogen and other natural hormones. They know that these hormones are crucial to the development of a normal reproductive system. And they know that--in lab tests on animals, at least--vanishingly small amounts of industrial chemicals, delivered at just the crucial stage of fetal development, can "feminize" a male embryo, producing smaller testicles, low sperm output and a miniaturized or missing penis.
But until 1992 scientists didn't know of any convincing evidence that men were experiencing reproductive problems on a large scale. Then came the groundbreaking report by a Danish endocrinologist, Dr. Niels Skakkebaek of the National University Hospital in Copenhagen. Skakkebaek and his colleagues did what is called a meta-analysis: they combined the results of 61 separate studies of sperm count and quality over the past 50 years in men around the world, and found that the average sperm count had fallen from about 113 million per ml in 1938 to 66 million in 1990.
After Skakkebaek's paper appeared, says Myers, "it immediately became apparent that nature is sending a very strong signal that something is amiss." Just as theoretical chemistry in the 1970s presaged the discovery of the ozone hole a decade later, he argues, "laboratory work on environmental toxins presaged the discovery of the decline in sperm count."
Initially, many medical researchers were highly skeptical. Among them was Pierre Jouannet, a reproductive biologist at the Center for the Study and Conservation of Eggs and Sperm at the Cochin Hospital, in Paris, who began his own study a year later. Says Jouannet: "When we started our work in 1993, we thought that the previous analyses were biased." His data, however, undermined those doubts: Parisian sperm was clearly on a downslide.