Women with endometriosis tend to demonstrate traits consistent with increased levels of estrogen relative to testosterone, such as lower waist-to-hip ratio and female-typical patterns of body fat. One controversial (and retracted) study even suggested that women with severe endometriosis are more facially attractive than women without the disease. We review literature to investigate the hypothesis that endometriosis risk involves female-biased expression of sexually dimorphic traits, including traits that signal fertility. Our results suggest that male selection for female fertility and attractiveness may help explain the presence of endometriosis risk in the human species.

Diametric disorders is a useful framework in evolutionary medicine that describes the presence of paired diseases with opposite symptoms and causes. Such diseases can manifest when a given trait or biological system is expressed at a very low or very high degree. For example, autoimmunity involves very high activation of the immune system, in contrast to infection which involves low activation of the immune system. We investigate the hypothesis that endometriosis and PCOS, two common female reproductive disorders, involve opposite levels of prenatal testosterone exposure. Our results, drawn from several fields of research, indicate that endometriosis risk involves low prenatal testosterone, in contrast to the high prenatal testosterone which is a known cause of PCOS.

Oxytocin is a neurohormone with diverse effects on the mind and body. We examined the hypothesis that elevated activity of the oxytocin system jointly contributes to risk of endometriosis and bipolar disorder. Previous clinicians and researchers suggest that these two conditions tend to co-occur within women. Our review supports this view, and points toward oxytocin as a key cause of the link. Increased oxytocin levels contribute to upregulated uterine contractility as well as behavioural activation, which are risk factors for endometriosis and bipolar disorder, respectively.

(Art by Minette Vári)