Elsevier

Evolution and Human Behavior

Volume 31, Issue 5, September 2010, Pages 365-372
Evolution and Human Behavior

Original Article
Intrasexual competition and eating restriction in heterosexual and homosexual individuals

https://doi.org/10.1016/j.evolhumbehav.2010.05.004Get rights and content

Abstract

Restrictive eating attitudes and behaviors have been hypothesized to be related to processes of intrasexual competition. According to this perspective, within-sex competition for status serves the adaptive purpose of attracting mates. As such, status competition salience may lead to concerns of mating desirability. For heterosexual women and gay men, such concerns revolve around appearing youthful and, thus, thinner. Following this logic, we examined how exposure to high-status and competitive (but not thin or highly attractive) same-sex individuals would influence body image and eating attitudes in heterosexual and in gay/lesbian individuals. Results indicated that for heterosexuals, intrasexual competition cues led to greater body image dissatisfaction and more restrictive eating attitudes for women, but not for men. In contrast, for homosexual individuals, intrasexual competition cues led to worse body image and eating attitudes for gay men, but not for lesbian women. These findings support the idea that the ultimate explanation for eating disorders is related to intrasexual competition.

Introduction

Approximately 11 million Americans suffer from an eating disorder such as anorexia nervosa or bulimia nervosa (National Eating Disorders Association, 2006). Anorexia nervosa is the deadliest psychological illness, resulting in a 10% death rate (e.g., Birmingham, Su, Hlynsky, Goldner & Goa, 2005). Many more people simply want to be thin and feel averse toward eating. Indeed, 80% of women report being dissatisfied with their body shape (Smolak, 1996). Such dissatisfaction tends to be firmly established in adolescence (e.g., Vohs, Heatherton & Herrin, 2001), whereby half of teenage girls skip meals, vomit or engage in other extreme weight control practices (Neumark-Sztainer, 2005). From an evolutionary perspective, self-destructive eating behaviors seem paradoxical. Voluntarily starving or purging food would generally not have been favored by natural selection. Yet, the prevalence of eating disorders suggests that an adaptive mechanism might underlie this phenomenon.

We examined the idea that eating restriction in pursuit of thinness may be linked to intrasexual competition for status and, ultimately, for mates (Abed, 1998, Faer et al., 2005). Specifically, eating restriction may result from perpetual competition with same-sex individuals. Although the nature of such competition is adaptive, the underlying mechanisms may be excessively triggered by abundant competitive stimuli in the modern world.

In their review of attitudes toward female body fat, Anderson, Crawford, Nadeau and Lindberg (1992) noted the cross-cultural variability in such attitudes. Thinness in females, as well as both major forms of eating pathologies (anorexia nervosa and bulimia nervosa), is more prevalent in Western vs. non-Western (e.g., Makino, Tsuboi & Dennerstein, 2002) and in industrialized vs. nonindustrialized nations (e.g., Choudry & Mumford, 1992). Accordingly, many researchers have attributed eating restriction and related issues to cultural norms for female thinness (e.g., Polivy, Garner & Garfinkel, 1986), made salient through media (e.g., Thompson, Heinberg, Altabe & Tantleff-Dunn, 1999). Indeed, viewing thin vs. nonthin magazine models results in more negative mood, body dissatisfaction and eating disorder symptoms among Western women (Hawkins, Richards, Granley & Stein, 2004). Similarly, viewing TV commercials (Heinberg & Thompson, 1995) or music videos (Tiggemann & Slater, 2004) highlighting actresses' appearances negatively impacts women's body image satisfaction. Such studies, however, have rarely considered where the cultural preferences originated and why media images are so readily processed (Anderson et al., 1992).

Searching for more ultimate explanations, some researchers have proposed evolutionary hypotheses for restrictive eating and the desire for thinness (see Anderson et al., 1992). One promising hypothesis concerns adaptive reproductive suppression. That is, when female mammals face ecological conditions unfavorable for rearing offspring, they may temporarily halt fertility through the restriction of eating, which causes body fat to drop below the minimal level needed for ovulation (Surbey, 1987, Voland and Voland, 1989, Wasser and Barash, 1983). For adolescent girls and women, whether or not ovulation occurs may be sensitive to small changes in weight if their body fat composition is near the critical level (Frisch, 1990). As such, in environments where social support is variable, it may be adaptive to generally be slender and to be especially averse to weight gain and eating when social support for childrearing is lacking (Anderson et al., 1992).

Support for this hypothesis has been found through studies linking social conditions and relevant attitudes. For example, perceived lack of social support (Juda, Campbell & Crawford, 2004) and local norms valuing women in the workforce (Anderson et al., 1992) are associated with dieting and negative attitudes toward female body fat. Furthermore, Salmon, Crawford, Dane & Zuberbier (2008) found that merely imagining oneself in various stressful situations can induce greater body dissatisfaction and restrictive eating attitudes in women. Although it is a plausible ultimate explanation, reproductive suppression tends to be limited to explaining symptoms of anorexia nervosa and does not address the development of similarly negative eating attitudes and behaviors in men. Indeed, although eating disorders are typically associated with women, up to 15% of individuals with eating disorders are men (Carlat and Camargo, 1991).

A more general ultimate explanation that may also apply to eating restriction, as well as a wider range of disordered eating behaviors, is that it is rooted in adaptive mechanisms for intrasexual competition. Across species, a primary function of competing with members of one's own sex is to attract viable mates (Darwin, 1871). Indeed, for human males and females, tactics for competing intrasexually for status are essentially mate attraction tactics (Buss, 1988, Walters and Crawford, 1994). Because men value cues of youth and fertility in their mates (Symons, 1979), women compete intrasexually on physical attractiveness for status. The dimensions that are specifically valued may depend on local social input. In Western societies, people tend to gain weight with age as metabolic rates and physical activity decrease (e.g., Cohen, 1989, Keel et al., 2007) and female thinness tends to be equated with youth and status (Sobal & Stunkard, 1989). Thus, abundant media images of thin females may be overactivating an otherwise adaptive mechanism to compete against one's actual peers on appearance.

To date, many studies have demonstrated the negative effects of media-portrayed thinness and, more generally, physical attractiveness on body image and eating attitudes. Most of these studies posit that the desire for thinness is driven by modeling and social norms, whereby exposure to glamorous images of attractive, thin women leads young women to imitate such models. However, an intrasexual competition model suggests that a wider range of stimuli should be capable of triggering a desire for thinness and, thus, restrictive eating. That is, if intrasexual competition for status ultimately serves the adaptive purpose of attracting mates, then a general activation of intrasexual competition motives — even when cues related to appearance, attraction or mating are absent — may be enough to trigger mating desirability concerns. For women, such concerns are oriented around appearing more youthful and fertile (i.e., nubile). In contrast, women tend not to be romantically interested in men who are very young (Kenrick & Keefe, 1992). Thus, the triggering of mating desirability through intrasexual competition would be expected to bring about desires for thinness and eating restriction in women, but not in men.

Although eating restriction should be a female — but not a male — response to intrasexual competition cues, the opposite may apply for homosexual individuals. Gay men, but not lesbian women, especially value physical attractiveness (Bailey et al., 1994) and youth (Kenrick, Keefe, Bryan, Barr & Brown, 1995) in their romantic partners. Compared with heterosexual men, gay men report greater body dissatisfaction (e.g., Beren, Hayden, Wilfley & Grilo, 1996) and disordered eating tendencies (Herzog et al., 1984, Yager et al., 1988). In contrast, lesbian women score lower than or equal to heterosexual women on such measures (e.g., Stiegel-Moore, Tucker & Hsu, 1990). If the intrasexual competition perspective is correct, then gay men — but not lesbian women — should also respond to intrasexual competition cues by competing on thinness to increase their status as desirable mates.

We sought to elucidate the evolutionary underpinnings of eating restriction by examining whether adaptive processes of intrasexual status competition might underlie the prevalence of eating restriction in pursuit of thinness. In Study 1, we experimentally manipulated intrasexual status competition by having participants view same-sex individuals who were described either as competitive and having high status, or as noncompetitive and having relatively low status. Considering the ultimate function of intrasexual competition, we predicted that cues to intrasexual competition among women — but not among men — would be manifest in concerns of thinness and restrictive eating attitudes.

In Study 2, we more extensively tested the intrasexual competition hypothesis, extending it beyond the reach of the reproductive suppression hypothesis. Specifically, we examined the effects of intrasexual competition cues not only on restrictive eating attitudes but also on body image and expanded our participants to include a gay and a lesbian sample.

Section snippets

Study 1: intrasexual competition and eating attitudes

We examined how priming people with intrasexual competition cues influences their attitudes toward eating. Competition cues consisted of photos and profiles of high-status, competitive same-sex individuals. Importantly, photos in the control and the competition conditions did not differ in attractiveness or body weight. Similar status-competition priming procedures have recently been used by others (e.g., Ermer, Cosmides & Tooby, 2008). Based on an intrasexual-status-competition model, we

Study 2: heterosexual and homosexual individuals

Next, we expanded our investigation in two ways. First, we included body image, a construct closely related to eating attitudes (e.g., Hawkins et al., 2004), as a dependent variable. If intrasexual competition cues are inducing more restrictive and aversive eating attitudes through concerns over mating desirability, then the cues should also lead to more negative body image in heterosexual women. Second, we examined how intrasexual competition cues would influence eating attitudes in homosexual

General discussion

We examined the hypothesis that eating restriction in the pursuit of thinness may reflect underlying motives for intrasexual competition. In two studies, we measured how simple exposure to competitive vs. noncompetitive same-sex individuals influenced men's and women's eating attitudes and body image in both a heterosexual and a homosexual population.

As predicted, cues to intrasexual competition led heterosexual women and gay men to report worse body image and more restrictive eating attitudes.

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    This research was supported, in part, by a grant from the National Institute of Mental Health (NIMH) to April R. Smith (F31 MH083382).

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