Female genital cutting in five West African nations is frequency-dependent and is associated with higher reproductive success among ethnicities in which cutting predominates, a fitness advantage that may outweigh its costs to physical and psychological health.
Female genital mutilation/cutting (FGM/C), or female ‘circumcision’, describes a suite of procedures to alter the external female genitalia for non-medical purposes. The international community, including UNICEF and WHO, considers FGC a violation of girls' health and human rights. Despite decades of efforts to eliminate FGC, the practice persists in many communities, predominantly in sub-Saharan Africa. Scholars have offered many explanations for FGC's apparent intractability, including some that draw on evolutionary perspectives on human behaviour. In this issue of Nature Ecology & Evolution, Howard and Gibson1 provide evidence that FGC in West Africa is indeed consistent with cultural evolution: girls' families seem to be adopting the practice that predominates in the mother's ethnic group. Moreover, FGC seems to increase women's reproductive success, but only when cut women are in the majority. These findings have tremendous implications for scholars of FGC and human evolution, as well as interventions aimed at ending the practice.
FGC incorporates a diverse set of practices, in which the severity of cutting ranges widely. In West Africa, FGC typically consists of cutting of the external clitoris (clitoridectomy) and/or labia minora (excision), while the more extensive practice of infibulation (cutting of the external clitoris, labia minora and labia majora, and narrowing of the vaginal opening by binding the labia majora during healing) is rare. The cultural context of FGC is equally variable: the religious meaning, ‘motivations’ for the practice, girl's age, physical setting, individuals involved, and ensuing seclusion and celebration all differ across contexts. The prevalence of FGC varies across nations, ethnic groups and, within some groups in West Africa, lineage, with only some lineages having an FGC tradition. Despite this diversity, some generalizations are possible: FGC is often necessary for a woman's full acceptance and participation in society, fundamental to cut women's identity, and considered a valued tradition. ‘Tradition’ is frequently cited as a primary motivation for FGC.
FGC is a practice in flux, with international and national pressures instigating dialogue within families and communities, and changes in how, and even whether, girls are cut. While families' decision-making processes are complex, there are also some consistent patterns in outcomes of this process: the primary factor influencing whether a girl is cut is, unsurprisingly, whether FGC is a tradition in her family; in surveys, this is usually captured as whether her mother is cut. In addition, daughters of better-educated mothers are less likely to be cut2.
Although FGC is valued by its practitioners, to outsiders its persistence is puzzling. It poses real risks, with no apparent benefit. To explain this, some have proposed that FGC may be a product of cultural evolution. Cultural evolution refers to change over time in norms, beliefs, and practices (rather than allele frequencies), shaped by forces comparable to those shaping biological evolution (selection and drift). Cultural evolution may occur through a variety of mechanisms3,4, the essence of which is reliance on social learning, subject to certain biases, such as a bias toward more common norms, beliefs or practices. Such mechanisms would, generally, lead to the adoption of practices that became more common in a population by enhancing reproductive success. However, this kind of social learning could occasionally lead to widespread adoption and persistence of disadvantageous practices that initially became common through random or anomalous events. If FGC is maintained by mechanisms of cultural evolution, we can make two predictions: FGC decisions should be frequency-dependent; and, FGC might affect women's reproductive success. Howard and Gibson find support for both predictions.
Howard and Gibson show that FGC is frequency-dependent in five West African nations: a girl's odds of being cut increased with the prevalence of FGC in her mother's ethnic group (typically, but not always, the girl's ethnic group). This finding is subtler than merely observing that FGC is common where FGC is common. Consider daughters of cut women: one might expect the tradition to be deterministic, and essentially all daughters of cut women to be cut. But this tradition is dynamic, and some are not cut. Among daughters of cut mothers, girls were more likely to be cut the more common FGC was in their mother's ethnic group. In one setting, Mali, this also held true for daughters of uncut mothers.
This finding is consistent with the hypothesis that FGC is a product of cultural evolution. For interventions on the ground in West Africa, this suggests that even small successes in reducing rates of FGC can benefit long-term goals of community-wide abandonment. (Currently, many programmes work from the premise that the only route to community-wide abandonment is community-wide consensus, and so focus their effort on coordinating large-scale pledges of abandonment5.)
Howard and Gibson further demonstrate that FGC affects women's reproductive success. As a proxy measure for reproductive success, the authors use a woman's total number of surviving children at age 40. This is imperfect (women may have children after age 40, and those who died before age 40, possibly due to FGC, are not considered); however, estimating fitness in humans is difficult, and this proxy comes closer than many. Cut women had more surviving children than uncut women, but only in the ethnic groups with a high prevalence of FGC. Among groups with a low prevalence of FGC, cut women had fewer children.
This finding is remarkable, and truly novel. It suggests that not only is FGC a product of human capacity for social learning, but that FGC itself is a target of selection, maintained because it enhances evolutionary fitness. While the fitness costs of FGC are likely to be physical and psychological, the fitness benefits are likely to be social. FGC may enhance a woman's marriageability6, or it may enhance her ability to form social connections with other cut women (her social capital)7. The frequency-dependent nature of these benefits may favour the latter explanation, as a benefit that increases with the prevalence of FGC (and becomes negative as FGC becomes rare) can be seen as the cumulative effect of cut women's individual decisions to include or exclude cut women from their social networks.
It is probably disheartening to those working to protect girls from FGC to think of cutting as ‘beneficial’; nonetheless, understanding FGC in these terms points to a new target for intervention: the cost–benefit balance of FGC. For example, if the mechanism by which women benefit from being cut is through accrual of social capital, interventions may attempt to foster social connections between cut and uncut women in a community to alleviate the social cost to remaining uncut, shifting the balance between costs and benefits away from cutting.
Future directions for human cultural evolution research should include comparison of FGC to other human characteristics, such as participation in warfare8, thought to arise from social learning. There probably exist informative similarities and differences across these practices. Future directions for FGC research should seek to understand its hypothesized social benefits (that is, marriageability or social capital) in West Africa. Meanwhile, interventions in West Africa may consider piloting programs to foster social connections between cut and uncut women. Social network intervention models based on alteration — which assume social networks are not static, and work to build new connections9,10 — have been successful in other realms of behaviour, and may provide appropriate models.