Like many other nonhuman primates, men and women engage in sexual intercourse for a myriad of reasons: to satisfy their own sexual desires, to satisfy the desires of their partners, to gain access to resources, and every once in a while, to procreate. A woman’s ability pass her genes on to healthy offspring contributes to her genetic fitness, and this ability is closely tied to the timing and frequency of sexual intercourse. From an evolutionary perspective, there should then be selection pressure for alleles that are associated with high sexual arousal and desire in women.
Epidemiological data, however, indicate that is not the case—recent estimates have suggested that up to 50% of women experience sexual dysfunction, characterized by dampened sexual arousal or desire, or inability to reliably experience orgasm during intercourse. But if natural selection favors alleles related to high sexual desire and arousal (and subsequently, the creation of offspring), why does the prevalence of sexual dysfunction in women remain so high?
A recent article in Adaptive Human Behavior and Physiology by anthropologist Menelaos Apostolou suggests that these clinical concepts we’ve labeled as ‘dysfunctions’ did not represent genuine dysfunctions in the pre-industrial environments where the majority of human evolution has taken place. In such pre-industrial environments, women’s sexuality was strictly regulated by parental and societal forces. Women were required by their parents to refrain from intercourse outside of the context of marriage, and were often married off to partners chosen by the parents. Once in that marriage, it was not illegal for husbands to force intercourse upon their wives. In this sort of environment, what we today would consider ‘sexual dysfunctions’ were not dysfunctions at all, as they did not contribute to a woman’s reproductive fitness—having high sexual arousal or desire would not significantly modulate a woman’s frequency and timing of sexual activity. In fact, low sexual desire and arousal may have even been a good thing, as such women would not be motivated to seek intercourse before marriage or with partners other than one’s husband.
Fast forward to the post-industrial society we live in currently, and the regulation of women’s sexuality in many parts of the world has changed considerably. Rather than being potentially maladaptive as they were during much of human evolution, high sexual desire and arousal are traits that now actually increase a woman’s reproductive fitness. In a society where women freely choose their mates and regulate their own sexual behavior, those with greater arousal and desire may engage in intercourse more often, and thus be more likely to pass on their genes.
This concept, of traits being disadvantageous currently when they were advantageous in ancestral societies, is called ancestral neutrality. The argument that Apostolou makes is that we have not lived in post-industrial societies with unregulated female sexuality long enough for evolution to catch up and ‘weed out’ alleles for low sexual desire and arousal, which explains the high prevalence of sexual ‘dysfunctions’ reported. However, depending on the extent to which low sexual arousal and desire decrease a woman’s reproductive fitness in this post-industrial context, it is likely that the alleles for these traits will become increasingly rare over time.
Apostolou’s paper highlights the important point that our conceptualizations of ideas such as health and illness are strongly time and culture-dependent. Low sexual arousal and desire have transformed from being advantageous traits in pre-industrial societies to being natural variants in female sexuality in the late 20th century, to then being dysfunctions warranting DSM-V categorizations and development of drugs to ‘cure’ them. (Sidenote: women’s sexual function has not been the only arena in which societal views modulate what we view as normal or abnormal. Rather than being labeled as having a mental illness, individuals with what the DSM-V would categorize as schizophrenia in ancestral societies were often regarded as shamans with significant spiritual and healing powers.) It will be interesting to keep tracking how societies define health and illness as they relate to female sexuality as our conceptualizations of sexuality continually develop.