Why humans need type 5 phosphodiesterase inhibitors.
Erectile dysfunction (ED) is a widespread medical condition affecting millions of males at any age and requiring medical treatment. ED may simply reflect a limit of human physiology, yet ED equates to genetic death and the high prevalence of ED is a clear evolutionary paradox. Why is a condition which totally blocks reproduction so widespread? Epidemiology shows that impotence is a common symptom of almost all major diseases and male reproductive physiology is sensitive to general health and to environmental, psychological, and physical stressors. Moreover, erectile dysfunction is a predictor of myocardial infarction and stroke. Briefly, efficient erection is a marker of good health and good health prognosis. In the animal kingdom, mate choice is often based on extravagant and cumbersome physical traits (such as the peacock's tail). These traits, that are necessary for gene propagation, are at the same time efficient handicaps which reduce the survival of the carrier. What animal studies show, is that these handicaps can function as honest indicators of the individual's fitness. In other words, their expression is condition-dependent and only individuals with high phenotypic quality present the trait. By mating with males which express the trait, females indirectly select for individuals of superior fitness which will be inherited by the offspring. Erection is very clearly a condition-dependent trait in the human species. We suggest that the fragility of male sexual physiology is a sexually selected handicap which hampers the reproduction of individuals with lower phenotypic quality.