Male genital mutilation: an adaptation to sexual conflict

Abstract

Male genital mutilation (MGM) takes several forms and occurs in about 25% of societies. This behavior has puzzled anthropologists, doctors and theologians for centuries, and presents an evolutionary challenge since it involves dangerous and costly surgery. I suggest that MGM is likely to reduce insemination efficiency, reducing a man's capacity for extra-pair fertilizations by impairing sperm competition. MGM may therefore represent a hard-to-fake signal of a man's reduced ability to challenge the paternity of older men who are already married. Men who display this signal of sexual obedience may gain social benefits if married men are selected to offer social trust and investment preferentially to peers who are less threatening to their paternity. Clitoridectomy and vaginal infibulation serve a parallel signaling function in women, increasing a husband's paternity certainty and garnering his increased investment. Especially in societies where paternity uncertainty and reproductive conflict are high, the social benefits of MGM as a signal may outweigh its costs. This ‘sexual conflict’ hypothesis predicts that MGM should be associated with polygyny, particularly when co-wives reside far apart, and that MGM should reduce the frequency of extramarital sex. MGM rituals should facilitate access to social benefits; they should be highly public, watched mainly by men, and performed by a nonrelative. I found support for these six predictions in two cross-cultural samples. I also examined an alternative hypothesis suggesting that MGM signals group commitment for collective action, particularly inter-societal warfare. Although other forms of male scarification fit this model, the distribution of MGM is not predicted by frequency of inter-societal warfare.

Introduction

Male genital mutilation (MGM) is any permanent modification of the external genitalia that involves the ablation of tissue and is normative for all males within a society (Murdock, 1967). MGM is present in a substantial minority of pre-industrial human societies and predates recorded history (Dunsmuir & Gordon, 1999). The form of the prescribed mutilation varies among societies. The least extreme is superincision: a longitudinal bisection of the dorsal foreskin. Superincision occurs in Southeast Asia and the insular Pacific (e.g., Shapiro, 1930). The most widespread is circumcision: the ablation of the entire foreskin. Circumcision occurs in societies throughout Africa, Australia, the Middle East and the Insular Pacific (e.g., Beckett, 1967, Dunsmuir & Gordon, 1999, Kennedy, 1970). A more extensive operation is subincision, which exposes the internal urethra ventrally with a longitudinal slit and is practiced in several Australian societies (Ashley-Montagu, 1937). The most extreme mutilation is testicular ablation: extirpation or crushing of one testis. This mutilation is documented historically in the Sidama, Beja and Khoisan cultures of Africa (A Adawi, 1954, Lagercrantz, 1938, Raven-Hart, 1967), and the Ponapeans of Micronesia (Finsch, 1880). These diverse mutilations seem to represent a behavioral syndrome rather than miscellaneous curiosities: they overlap in geographic distribution and often share other features including the presence of sanctions against the unmutilated and social benefits contingent on mutilation; a highly public rite; and observance primarily at adolescence (Schlegel & Barry, 1979). Some societies explicitly equate different forms of MGM. According to Guma (1965), the Sotho of southern Africa view testicular ablation as the original ‘method’ of MGM, and circumcision is held to be a recent adoption from other societies. The Sotho consider ancestral testicular ablation and the more recent practice of circumcision as variants of the lebollo ritual, whose declared purpose by either ‘method’ is to make the boy “strong, fearless, valorous and respectful” (p. 241). Shapiro (1930) describes an interchangeable mosaic of superincision and circumcision in certain Polynesian societies, and indigeneous Australians who practice subincision also perform circumcision as a prerequisite (Ashley-Montagu, 1937). The interlinked forms of MGM are well documented, but their function remains unresolved despite discourse in several disciplines. Here, I develop an evolutionary hypothesis suggesting a common function for the various mutilations and test it using comparative ethnographic data.

An evolutionary approach to MGM may complement efforts in other fields. Medical doctors have given considerable attention to circumcision, debating the ethics and effects of performing this mutilation neonatally, but they have tended to overlook the other forms of MGM (e.g., Hutson, 2004, Short, 2004). Several doctors have suggested that circumcision arose to improve hygiene by removing skin in which dirt or sand could accumulate (e.g., Hutson, 2004; Winberg et al., 1989). Darby (2005) offered the most recent challenge to this ‘hygiene hypothesis,’ but his conclusion that “health had nothing to do with it” had been noted at least 70 years earlier by anthropologists such as Bryk (1934), who observed that imagined health complications of sand or dirt under the foreskin could hardly match the often fatal risks of hemorrhage and sepsis that arise when boys are universally mutilated under nonsterile conditions by individuals with little or no training, using crude tools or even fingernails. Forty-five men arrived at an African hospital with sepsis following ritual circumcision in December 1988 alone, resulting in a 9% mortality rate (Crowley & Kesner, 1990). Between 1995 and 2004, 243 deaths and 216 genital amputations occurred at traditional ‘circumcision schools’ in a single province of South Africa (Sidley, 2006). Several societies have specific customs governing death during initiation rites, suggesting this has not been historically uncommon (e.g., Guma, 1965). The hygiene hypothesis also fails to explain why circumcision is limited to a minority of societies despite the universality of dirt and sand, and it is unclear why a supposedly protective mutilation is almost always delayed until adolescence. Most importantly, evolutionary theory does not predict fitness benefits from extirpating normal tissue. Genital anatomy is extremely variable, and if the mammalian prepuce were detrimental to overall fitness, selection would presumably have reduced it over evolutionary time. If sand or dirt represented a selective pressure to expose the glans, we would surely observe this outcome frequently in desert-dwelling mammals, yet we do not. As one example, the Arabian camel (Camelus dromedarius) retains a ‘voluminous’ prepuce (Mobarak, ElWishy, & Samira, 1972).

Recent medical studies have confirmed a protective effect of circumcision against HIV infection for adult males in high seroprevalence regions of Africa (Auvert et al., 2005, Gray et al., 2007). However, a ‘prophylactic’ hypothesis is unlikely to represent the adaptive function of MGM behavior, as it shares many weaknesses of ‘hygienic’ explanations. Circumcision obviously predates HIV itself, and the degree to which the prophylaxis generalizes to other STDs is unclear. The currently suggested mechanism of protection is relatively specific, involving a reduction in the preputial mucosa which contains vulnerable CD4 and CCR5 cell-surface receptors (Szabo & Short, 2000). If the result did generalize to other sexual infections, it would remain unclear under a prophylactic hypothesis why natural selection should have retained the foreskin despite millennia of selection in populations suffering from STDs. If exposing and keratinizing the glans by reducing sexual mucosa brought overall fitness benefits through prophylaxis, we would expect selection to have produced this outcome not only in humans, but especially in promiscuous primates with the highest STD loads (Nunn, Gittleman, & Antonovics, 2000). Contrary to this prediction, promiscuous taxa actually have the most elaborate penises, including a well-developed prepuce and other structures with high surface areas of mucosa (Dixson, 1987, 1998). This suggests that primate STDs may not have been a sufficiently important selective pressure to drive evolutionary or cultural ablation of otherwise adaptive sexual tissue, although prophylaxis may be an incidental effect of reductions undertaken for other reasons. If circumcision functions to reduce STDs, it is also curious that it should be followed by subincision in Australian societies: subincision permanently exposes the internal urethral mucosa and is associated with recurrent penile bleeding (Ashley-Montagu, 1937), which would certainly tend to counteract any prophylactic benefits of circumcision. Testicular ablation is similarly inexplicable as STD prophylaxis.

Anthropologists have also given considerable attention to MGM, with a similar focus on circumcision. Silverman (2004) stated that circumcision “dramatizes unease over separation-individuation through a symbolism that affirms yet blurs the normative boundaries between masculinity and motherhood” (p. 423); Paige and Paige (1981) suggested it represents “a ceremonial solution to the dilemma of fission in strong fraternal interest group societies” (p. 166); Whiting, Kluckhohn, and Anthony (1958) concluded that it resolves a gender-identity conflict caused by a boy's underexposure to males and “excessively strong dependence upon the mother” that would otherwise manifest as “open rivalry with his father [and] incestuous approaches to his mother” (p. 370). The validity of their cross-cultural evidence for this oedipal interpretation is disputed by Korotayev and de Munck (2003). These psychodynamic hypotheses have value as proximate explanations of the psychology that may drive MGM. However, it is vital to address the selective pressures that ultimately underpin such psychology itself. At the functional level of analysis, we must seek complementary hypotheses that share the predictions of existing proximate explanations, but whose premises are supported by evolutionary theory in addition to psychodynamic thought.