Psychological and Physiological Adaptations to Sperm Competition in Humans

Abstract

Postcopulatory competition between males, in the form of sperm competition, is a widespread phenomenon in many animal species. The extent to which sperm competition has been an important selective pressure during human evolution remains controversial, however. The authors review critically the evidence that human males and females have psychological, behavioral, and physiological adaptations that evolved in response to selection pressures associated with sperm competition. The authors consider, using evidence from contemporary societies, whether sperm competition is likely to have been a significant adaptive problem for ancestral humans and examine the evidence suggesting that human males have physiological and psychological mechanisms that allow for "prudent" sperm allocation in response to variations in the risk of sperm competition.

Absence makes the adaptations grow fonder: Proportion of time apart from partner, male sexual psychology, and sperm competition in humans (Homo sapiens).

“…Humans are socially monogamous, with both sexes engaging in extra-pair copulation under predictable conditions (Baker & Bellis, 1989, 1995Buss, 2003;Gangestad, Thornhill, & Garver-Apgar, 2005a). Smith (1984) provided empirical and theoretical arguments that female extra-pair copulation is the primary context for sperm competition in humans (also see Baker & Bellis, 1989, 1993, 1995Shackelford & Goetz, in press;Shackelford et al, 2005;Starratt et al, in press). …”

“…When the sperm of two or more males concurrently occupy the reproductive tract of a female and compete to fertilize her egg(s), sperm competition occurs (Parker, 1970a). Sperm competition has been documented or inferred to exist in many species, ranging from molluscs (Baur, 1998), crustaceans (Van Son & Thiel, 2006), and insects (Simmons, 2001) to birds (Birkhead & Møller, 1992), reptiles (Rivas & Burghardt, 2005), and humans (Baker & Bellis, 1989, 1993Gallup et al, 2003;Shackelford & Goetz, in press;Shackelford, Pound, & Goetz, 2005;Smith, 1984;Starratt, Shackelford, Goetz, & McKibbin, in press). Avian sperm competition research is particularly interesting for students of human mating because humans and many avian species share similar mating systems, adaptive problems, and adaptive solutions .…”

Do Female Sex Fantasies Reflect Adaptations for Sperm Competition?

“…Our findings contribute to the growing body of evidence suggesting that sexual fantasies may provide an interesting perspective on the biologically understandable desires of human behaviour (Ellis & Symons 1990, Shackelford et al 2005, Easton et al 2010. Previous studies focusing on female fantasies have seldom separated more than one or two types of multi-partner fantasies.…”

“…Sexual fantasies that include multiple concurrent partners are common among males and relatively common among females (e.g. Arndt et al 1985, Rokach 2001, Shackelford et al 2005.…”

“…Increasing evidence in recent decades suggests that female sexual selection is a composite of many parallel and sequential functions of which those that promote sperm competition are important throughout the animal kingdom (e.g. Birkhead & Møller 1998, Shackelford et al 2005.…”