Evolutionary determinants of polycystic ovary syndrome: part 2.

Polycystic ovary syndrome (PCOS) is a prehistoric complex genetic trait, perhaps dating back at least 50,000 years. The disorder also represents an evolutionary paradox, demonstrating clear reproductive disadvantages (i.e., lack of evolutionary fitness), albeit persisting tens of thousands of years. Here we examine possible explanations for this paradox. We evaluate a variety of possible benefits accruing to women in ancestral populations who possessed this trait, including considerations of whether dramatic changes in environment and lifestyle from the ancestral past to the contemporary present have altered the selection dynamics operating on the trait. Putative benefits include metabolic functioning, immune system dynamics, patterns of child-rearing and mothering, reproductive longevity, in utero or childhood survival, and musculoskeletal advantages. However, there is limited evidence that the persistence and relative homogeneity in the prevalence of PCOS can be accounted for by direct positive selection. Rather, PCOS evolution has likely been driven by nonadaptive evolutionary mechanisms, including genetic drift due to a serial founder effect and population balance due to sexually antagonistic selection. Ultimately, insights into the evolutionary origins of PCOS will emerge through the study not only of unique characteristics of affected individuals and their environments butalso through a broad consideration of the potential adaptive and beneficial aspects of vulnerability to the disorder, importantly including examination of populations whose fertility, disease load, and diet resemble those of ancestral humans.