About 40 percent of men with male infertility have a condition that does not fall neatly into any of the known causes. Many of these may be genetic, but medical science has not yet worked out the genetic causes fully.
In fact, it is just scratching the surface. Some of these causes may be environmental, yet science is still only beginning to understand the complexities of environmental toxins and their relationship to fertility, not only in men but in other species as well. Effects on a fetus prior to birth that are not genetic may result in male infertility later in ways that scientists do not fully understand yet. Even if the causes remain a mystery, techniques currently available can still help these men father children in the majority of cases.