Male reproductive physiology as a sexually selected handicap? Erectile dysfunction is correlated with general health and health prognosis and may have evolved as a marker of poor phenotypic quality.

Many extravagant physical traits are selected because they are used as cues for mate choice (sexual selection). Why is mate choice driven by costly ornaments? A theory of sexual selection posits that extravagant traits are preferred because are reliable indicators of superior (heritable) phenotypic quality. In particular, the preferred traits can be expressed only in individuals with superior conditions because are handicaps which impose a high cost to the carrier. The human penis achieves its reproductive function by the complex neuro-vascular mechanisms that controls erection. Surprisingly, erectile dysfunction and infertility, two condition which nearly annihilate fitness, are widespread medical conditions which affect millions of people of any age worldwide. The very high incidence of erectile dysfunction appears as an evolutionary paradox. Impotence is associated with all major systemic diseases as well depression and stress. Stress is also one of the causes of infertility. Therefore, male reproduction appears to be extremely sensitive to internal and external stressors. Moreover, erectile dysfunction is a predictor of myocardial infarction and stroke, whereas men with regular sexual activity have lower risk of death due to coronary disease. This large body of medical literature makes erection the best case for a fitness indicator in the human male. We suggest that the fragility of male sexual physiology observed in modern society is the specific consequence of an evolutionary process driven by the handicap principle.