Control of Paternity
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The behavior of male mammals may be optimized to maximize reproductive success in various ways related to control of paternity— by competing with other males, by sexually coercing females, by concentrating mating activity with reproductively viable females, by biasing paternal care toward putative biological offspring, and by engaging in culturally-based practices designed to control female sexuality. Humans expand the arsenal of tactics designed to enhance male reproductive success and optimize paternal investment in part because the stakes are higher: humans exhibit a remarkable degree of paternal care, including in contrast to Great Apes or most mammals generally. In most Great Apes (chimpanzees, bonobos and orangutans), there is no unequivocal control of paternity. In fact, the social structure of some great apes prevents males from knowing the paternity of children, possibly working as a mechanism to prevent infanticide.
Ever since Darwin (1871), the core features of sexual selection and their general patterning have been appreciated: male-male competition and female choice. More recently, scholars have argued for inclusion of sexual coercion as another form of sexual selection, particularly in mammals in which sex differences in reproductive investment are quite marked. In mammals, including the Great Apes, male-male competition has been well documented, female choice recognized, and sexual coercion increasingly suggested. These considerations suggest that mammalian male behavior often occurs as if it were designed to enhance paternity—to achieve maximal reproductive success, even in the absence of knowing how biological paternity is conferred.
Male behavior in the Great Apes entails competition over social rank and access to females. Many of the sexually dimorphic traits, or traits differing between the sexes, in the Great Apes may have their origins in these contexts; as examples, greater male body sizes in all Great Apes may facilitate male-male competition, and orangutan fleshy cheek pads may facilitate male long-distance vocalizations to deter potential male competitors and attract cycling females (Dixson 2009; Wrangham and Peterson 1996). Among chimpanzees, various contexts in which male sexual coercion is expressed (more often targeting parous females over nulliparous females; associated with enhanced mating access) suggest that it benefits male reproductive success; in other words, male sexual coercion yields increased paternity (Muller and Wrangham 2009).
Among gorillas, control of paternity appears related to the potential for male infanticide. Gorillas live in polygynous groups based on one or sometimes two adult males, multiple adult females and their offspring (Robbins 2007). If a mated gorilla male is challenged successfully by an unmated male, then the unmated male is at risk of killing young offspring sired by the previous male. By killing the unrelated offspring, this facilitates nursing, non-cycling females beginning to cycle again, in turn raising the potential for the new male challenger to father offspring with them. This risk of infanticide suggests an important male strategy to control paternity in the one Great Ape characterized by long-term reproductive bonds (of a female to a given male, and of a given male to several females).
Whether or how male gorillas—or other mammals for that matter—recognize paternity is a question subject to increased scrutiny (Lehmann 2008). Among baboons residing in multi-male, multi-female groups, males intervened on behalf of their biological offspring to deter harassment more often than chance (Buchan et al. 2003). In several other species of primates, preferential associations of males with their biological offspring or between paternal siblings have been recognized. Most speculation suggests that males employ either “phenotype matching” (does the offspring look or smell like me) or experience with the mother of offspring (having preferred relationship partners or recalling sexual experience with certain mothers) as cues when biasing behavior toward biological offspring.
In humans, elements of male-male competition, female choice, and male sexual coercion are present, suggestive of homologous characteristics with the Great Apes and a wider phylogenetic scope. Other features of human male behavior related to control of paternity appear derived. As an example of the latter, most of human male sexual coercion takes place within the early stages of or in ongoing partner relationships; consistent with male control of paternity, coercion such as beating or verbal abuse may increase the costs to a female of leaving a relationship or engaging in extrapair sexual behavior.
A host of tactics have arisen whereby human males enhance control over paternity and paternity certainty. As chronicled by various scholars (e.g., Wilson and Daly 1992; Potts and Short 1999), these include chastity belts in Europe and North America; female genital modifications ranging from removal of the labia minora to the clitoris to an extreme of infibulations involving sewing up the labial opening to prevent intercourse; cloistering women away from men; encouraging women to cover themselves extensively with veils or other forms of clothing; and encouraging foot binding as a means of reducing a woman’s mobility. Women often actively participate in these practices; whether a woman performing a genital modification on another woman or foot binding emerging as a fashion fueled among women, there is a recognition that these paternity-controlling traits help entice potential mates.
Because of the derived nature of human paternal care, with gorillas the closest to a Great Ape analogue (in that gorilla males seem concerned with paternity established in long-term reproductive bonds), humans appear to exhibit a greater concern over paternity certainty. The question for humans isn’t just how to mate with a reproductive viable female but additionally how to ensure that one’s paternal care is channeled to his biological offspring rather than those sired by another man. Accordingly, humans exhibit a concern with paternity certainty manifest in various ways. Like for other mammals, putative human fathers can employ phenotype matching and experience mating with a mother as cues to paternity. Some studies suggest that putative human fathers rely on visual cues of resemblance and mating experience with a mother to inform their paternity certainty (or uncertainty). Additionally, humans can employ gossip or even DNA-based paternity testing kits to hone in on paternity (Gray and Anderson 2010).
A review of 67 human paternity studies revealed that when males think they are the biological father, they typically are (1.7% false paternity estimate in 22 studies); when they think they might not be the father, they often aren’t (29.8% false paternity in 31 studies); and in more ambiguous studies, an intermediate rate of false paternity applies (16.7% in 14 studies) (Anderson 2006). While various surveys quantify rates and patterns of human extrapair sex, these paternity estimates suggest how often those incidents translate to false paternity. Additionally, various features of human reproductive anatomy and physiology indicate relatively low sperm competition pressures (or pressures for the sperm of different males to compete within a female’s reproductive tract), another line of evidence suggesting that female multi-male mating has been relatively rare across recent hominin evolutionary history (Dixson 2009).
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