An evolutionary model of premenstrual syndrome.

PMS has existed at least since the beginning of medical writing, and is estimated to affect large proportions of women worldwide. But the etiology remains unknown, diagnostic definition and methods vary tremendously, and treatment is wholly symptom-oriented. This poor state of understanding has been attributed to a lack of theoretical perspective. The current work provides such a theoretical perspective from an evolutionary paradigm. PMS is not evolutionarily adaptive in and of itself. Rather, it is part of a cyclic pattern that results from the cessation of heightened, positive physical and sociobehavioral states that are evolutionarily favored during the fertile phase of the menstrual cycle for some women. When the advantage of these positive states diminishes, they cease, causing relatively lower states that are subjectively experienced as symptoms. In its clinical extreme, this is PMS. However, eons of evolution would result in modern women who are choosy about the conditions under which they reproduce. Thus, women whose conditions suggest a high probability of successful immediate reproduction are expected to experience the heightened, positive states during the fertile phase of the menstrual cycle to attract mates and fertilizations; these women will experience symptoms premenstrually. But women whose conditions suggest a low probability of successful immediate reproduction are expected to experience the heightened, positive states during the premenstruum to retain mates, accrue or maintain resources, and/or otherwise improve their conditions; these women will experience symptoms during the fertile phase of the menstrual cycle ("pseudo-PMS"). In addition, the heightened states are expected to shift in response to changes in conditions throughout women's lives, being expressed at whatever point is most evolutionarily beneficial given current conditions. This suggests that our conceptualization of PMS should be reframed within a facultative (condition-sensitive), evolutionary model. It also generates predictions both within- and between women that should elucidate the syndrome.