Physical attractiveness and reproductive success in humans: evidence from the late 20th century United States

Abstract

Physical attractiveness has been associated with mating behavior, but its role in reproductive success of contemporary humans has received surprisingly little attention. In the Wisconsin Longitudinal Study (1244 women, 997 men born between 1937 and 1940), we examined whether attractiveness assessed from photographs taken at age ∼18 years predicted the number of biological children at age 53–56 years. In women, attractiveness predicted higher reproductive success in a nonlinear fashion, so that attractive (second highest quartile) women had 16% and very attractive (highest quartile) women 6% more children than their less attractive counterparts. In men, there was a threshold effect so that men in the lowest attractiveness quartile had 13% fewer children than others who did not differ from each other in the average number of children. These associations were partly but not completely accounted for by attractive participants' increased marriage probability. A linear regression analysis indicated relatively weak directional selection gradient for attractiveness (β=0.06 in women, β=0.07 in men). These findings indicate that physical attractiveness may be associated with reproductive success in humans living in industrialized settings.

Introduction

According to an evolutionary perspective, physical attractiveness functions as a cue of mate quality and reproductive value (Gangestad & Scheyd, 2005, Hume & Montgomerie, 2001, Rhodes, 2006, Rhodes et al., 2005, Thornhill & Gangestad, 1999). People have therefore evolved to pay attention to physically attractive individuals and seek them as partners. Aided by this advantage in the mating market, attractive people are expected to enjoy higher reproductive success. Despite this rather straightforward prediction, surprisingly few studies have directly examined whether physical attractiveness is related to fertility, i.e., the number of children, in humans. Pawlowski, Boothroyd, Perrett, and Kluska (2008) found no association between facial attractiveness and fertility in a sample of contemporary Polish women, but due to the small number of participants (N=47) this null finding may reflect insufficient statistical power rather than absence of association. Physical attractiveness has been shown to correlate with higher age-controlled fertility in Ache women (Hill & Hurtando, 1996; see also Apicella, Feinberg, & Marlowe, 2007), indicating that attractiveness may be related to reproductive success at least in hunter-gatherer populations.

Indirect evidence does suggest that physical attractiveness might contribute to fertility differences even in humans living in industrialized settings. Attractiveness predicts more active sexual behavior and higher mating success (e.g., Rhodes et al., 2005, Weeden & Sabini, 2007), and measures of physical attractiveness have also been associated with healthier reproductive physiology, e.g., women's fecundity, i.e., the capability of having children (e.g., Jasienska, Lipson, Ellison, Thune, & Ziomkiewicz, 2006), and men's semen quality (Soler et al., 2003; but see Peters, Rhodes, & Simmons, 2008). Kanazawa (2007), in turn, has argued that parents' attractiveness should bias the sex distribution of their offspring, as daughters are expected to benefit more than sons from their genetically inherited attractiveness.

Studies of attractiveness and mating success have often considered only linear effects (the more attractive the better), but it is possible that very high attractiveness does not increase fertility even if it increases mating success. People searching for a partner to have children with may not be interested in extremely attractive partners, because such partners may be more likely to leave them for another partner or to have extra-pair relationships (see Boothroyd et al., 2008, Chu et al., 2007, Durante & Li, 2009, Smith, 1995, Waynforth, 2001). Hence, moderately attractive parent candidates might be favored over very attractive ones. Further complicating the issue is the fact that the reproductive advantage of attractiveness may be suppressed by the influences of modernized lifestyle. In particular, attractiveness is related to higher socioeconomic achievement (Dickey-Bryant et al., 1986, Harper, 2000) and possibly to parental socioeconomic status (Harper, 2000), which may confound the attractiveness–fertility association.

The ongoing Wisconsin Longitudinal Study (WLS; Wollmering, 2007) has followed a large sample of high school graduates from 1957 onwards, and data on photograph-based attractiveness ratings are available for a subsample of them. These data allowed us to assess whether physical attractiveness in young adulthood predicted adult reproductive success in humans living in the late 20th century United States. We also examined whether adjusting for parental socioeconomic status, educational achievement and life-course marital status modified the association between attractiveness and reproductive success, and whether attractiveness predicted average interbirth interval, i.e., the time between births of two subsequent children, and offspring sex ratio in addition to the number of children.