جذابیت و رفتار جنسی: آیا جذابیت باعث افزایش موفقیت جفت یابی می شود؟

If attractiveness is an important cue for mate choice, as proposed by evolutionary psychologists, then attractive individuals should have greater mating success than their peers. We tested this hypothesis in a large sample of adults. Facial attractiveness correlated with the number of short-term, but not long-term, sexual partners, for males, and with the number of long-term, but not short-term, sexual partners and age of first sex, for females. Body attractiveness also correlated significantly with the number of short-term, but not long-term, sexual partners, for males, and attractive males became sexually active earlier than their peers. Body attractiveness did not correlate with any sexual behavior variable for females. To determine which aspects of attractiveness were important, we examined associations between sexual behaviors and three components of attractiveness: sexual dimorphism, averageness, and symmetry. Sexual dimorphism showed the clearest associations with sexual behaviors. Masculine males (bodies, similar trend for faces) had more short-term sexual partners, and feminine females (faces) had more long-term sexual partners than their peers. Feminine females (faces) also became sexually active earlier than their peers. Average males (faces and bodies) had more short-term sexual partners and more extra-pair copulations (EPC) than their peers. Symmetric women (faces) became sexually active earlier than their peers. Given that male reproductive success depends more on short-term mating opportunities than does female reproductive success, these findings suggest that individuals of high phenotypic quality have higher mating success than their lower quality counterparts.

Impressed by cultural diversity in beautification practices, Darwin (1874) concluded that humans lacked universal, biologically based standards of beauty. However, evidence that perceptions of attractiveness are similar across cultures (Langlois et al., 2000) and emerge early in development (Rubenstein et al., 1999 and Slater et al., 1998) challenge this view. Evolutionary psychologists propose that perceptions of attractiveness are species-wide, sexually selected adaptations for finding good mates (Fink & Penton-Voak, 2002, Rhodes & Zebrowitz, 2002 and Thornhill & Gangestad, 1999). If attractive traits and preferences for them are under sexual selection, then those traits should be associated with individual variation in mating success. The present study was designed to test this hypothesis. In most animals, differential parental investment by males and females leads to different mating strategies. A greater investment by females (gestation, lactation, etc.) means that their reproductive potential is lower than that of males (Clutton-Brock & Parker, 1992, Trivers, 1972 and Williams, 1975). Males, with a minimum investment in sperm, can increase their reproductive success by obtaining fertilizations with several females, although they may also benefit from providing parental care in the context of long-term relationships. Females have less to gain from mating with several males (Arnold & Duvall, 1994 and Bateman, 1948), and it is more important to secure male parental investment for reproductive success (Buss & Schmitt, 1993, Clutton-Brock, 1991, Daly & Wilson, 1983, Symons, 1979 and Trivers, 1972). Such investment can be provided either by one (monogamy) or a series (serial monogamy) of long-term mates. Therefore, if attractive individuals have a reproductive advantage over their peers, then we would expect attractive males to have more short-term mating success, and attractive females to have more long-term mating success than their peers. The lifetime reproductive success of both sexes can also be enhanced by becoming sexually active as soon as the individual is fertile. Therefore, we would expect attractive traits to be negatively correlated with age of first sex in both males and females. For species that form pair bonds, both males and females can gain additional reproductive success through extra-pair copulations (EPCs). Males can always enhance their reproductive success through seeking additional mates, and in some human societies, men will seek EPCs given the opportunity (e.g., Marlowe, 1999). Females can also benefit from EPCs. In nonhuman animals, such as birds, females who are paired with low-quality males have been shown to enhance their reproductive success by seeking EPCs with males of higher quality than their long-term partner (Hasselquist et al., 1996 and Kempenaers et al., 1992). Male EPC activity is likely to be constrained primarily by females' willingness to participate. Therefore, for males, we would expect attractive traits to be positively correlated with EPCs (Gangestad & Thornhill, 1997 and Møller & Thornhill, 1998). In contrast, for females, we might expect attractive traits to be negatively correlated with EPCs if attractive females are able to attract males of high quality as their long-term partners. Physical attractiveness is important in a potential mate (Buss & Schmitt, 1993), but so are other traits, and the precise role of attractiveness in mating behavior remains unclear. Surprisingly, few studies have investigated the relationship between attractiveness and reproductive behavior, and these have generally used poor measures of attractiveness (either self-reported attractiveness or attractiveness rated by only a few observers; for a review, see Wiederman & Hurst, 1998). A few studies have examined the relationship between the attractive trait of body symmetry and sexual behavior (Gangestad & Thornhill, 1997 and Thornhill & Gangestad, 1994). Low levels of body symmetry (high asymmetry) appear to be associated with low self-reported lifetime number of sexual partners (controlling for age) in men and women, late self-reported age of first sex in men (Thornhill & Gangestad, 1994), and low numbers of EPCs in men (Gangestad & Thornhill, 1997). These results have been presented as evidence that sexual selection favors individuals of high genetic quality, as indicated by low levels of fluctuating asymmetry (FA). However, FA was not formally isolated from other forms of asymmetry, which do not reflect mate quality, rendering the conclusions equivocal (Tomkins & Simmons, 2003). No studies have examined the relationship between sexual behavior and facial symmetry or other attractive face or body traits. Here, we examined whether attractive individuals have higher mating success than their peers, as expected if traits that contribute to attractiveness are under sexual selection. Specifically, we investigated whether face and body attractiveness correlate with sexual behaviors that would be associated with reproductive success in the absence of contraception. To determine which attractive traits are responsible for any such correlations, we examined correlations between sexual behaviors and three components of attractiveness: averageness, symmetry, and sexual dimorphism (masculinity in males, femininity in females). For faces, these traits are attractive across cultures (for reviews, see Fink & Penton-Voak, 2002, Rhodes & Zebrowitz, 2002 and Thornhill & Gangestad, 1999) and may reflect developmental stability and health (Møller & Swaddle, 1997, Rhodes et al., 2001 and Thornhill & Møller, 1997). Evidence that facial sexual dimorphism is attractive is clearer for femininity than for masculinity (for a review, see Zebrowitz & Rhodes, 2002), but an association with health has only been found for masculinity (Rhodes, Chan, Zebrowitz, & Simmons, 2003). Body symmetry and sexual dimorphism are both attractive (Gangestad et al., 2001, Gangestad & Thornhill, 1997, Singh, 1993, Singh, 1995, Thornhill & Gangestad, 1994, Tovée et al., 1999 and Tovée et al., 2000). No studies have yet assessed the attractiveness of body averageness, but it seems likely to be attractive given the curvilinear association between body mass index and attractiveness (for female bodies), which can be recast as a linear association with body averageness (Tovée et al., 1999). Finally, to validate our approach, we measured height, which is known to correlate with reproductive success (greater for tall men and short women) in contemporary societies (Mueller & Mazur, 2001, Nettle, 2002a, Nettle, 2002b and Pawlowski et al., 2000). Attractiveness and its components were assessed by ratings because measurements are generally too simplistic, relying on a limited number of landmark points that provide partial information about facial structure but no information about fat deposits, skin texture, or color (e.g., Grammer & Thornhill, 1994, Koehler et al., 2004 and Simmons et al., 2004). Raters are sensitive to subtle differences in facial averageness, symmetry, and sexual dimorphism, and ratings of averageness and symmetry vary systematically with physical manipulations of these traits (Rhodes et al., 2000, Rhodes et al., 1998 and Rhodes & Tremewan, 1996). Facial symmetry ratings are also sensitive to differences in facial FA but not directional asymmetry (Simmons et al., 2004), and ratings of sexual dimorphism are sensitive to variation in sexually dimorphic traits, such as the chin and jaw (Koehler et al., 2004). We assumed that raters would also be sensitive to variation in these traits in bodies. We also measured body FA, to facilitate comparison with previous studies showing that this is associated with sexual behavior (Gangestad & Thornhill, 1997 and Thornhill & Gangestad, 1994).