Original Article
Condition-dependent calibration of men’s uncommitted mating orientation: evidence from multiple samples

https://doi.org/10.1016/j.evolhumbehav.2014.03.002Get rights and content

Abstract

Physical strength and physical attractiveness are both hypothesized as indicators of overall phenotypic condition in humans. Strategic Pluralism Theory (Gangestad & Simpson, 2000) predicts that men’s orientation toward uncommitted mating is facultatively calibrated (i.e. contingently adjusted over ontogeny) in response to condition-dependent physical features, such as strength and attractiveness. Herein, we suggest that previous research bearing on this hypothesis has been limited because (a) researchers have often neglected to distinguish between mating orientations and past sexual behavior and (b) sample sizes have not always been large enough to reliably detect correlations of moderate magnitude. To address these issues and extend previous findings, we present aggregated data from three independent samples of young adults that permit us to examine multiple measures of physical strength and attractiveness in relation to uncommitted mating orientation, committed mating orientation, and past sexual behavior. As predicted, meta-analyses across samples demonstrated that strength and attractiveness were positively correlated with men’s (but not women’s) uncommitted mating orientation (but not committed mating orientation). In addition, strength (in men only) and attractiveness (in both sexes) positively predicted participants’ number of past sex partners. Moreover, path analyses demonstrated that the association of men’s physical features with their number of sex partners was mediated via uncommitted mating orientation. These results (a) provide the most extensive support to date for the hypothesis that men’s uncommitted mating orientation is calibrated to condition-dependent features and (b) clarify the sex-specific functional links among physical features, mating orientations and sexual behavior.

Introduction

Human mating systems include multiple types of relationships, from monogamous pair bonds to brief sexual affairs and extra-pair copulations (Gurven et al., 2009, Kelly, 1995, Pillsworth and Haselton, 2006, Winking et al., 2007). This manifest variation, in turn, reflects a diverse range of mating orientations (Buss and Schmitt, 1993, Gangestad and Simpson, 2000). For example, because the maximum potential reproductive rate is higher among men than women, men are also higher than women on average in the motivation to pursue sex in the absence of long-term commitment (Buss and Schmitt, 1993, Jackson and Kirkpatrick, 2007). However, there is also massive variation in mating orientations within each sex, such that an individual, whether male or female, may primarily seek uncommitted affairs, exclusively seek monogamous pair bonds, or pursue some combination of these types of relationships (Buss and Schmitt, 1993, Gangestad and Simpson, 2000, Jackson and Kirkpatrick, 2007, Larson et al., 2012, Pillsworth and Haselton, 2006). Thus, a foundational question in the study of human mating concerns the origins of individual differences in mating orientations: What explains within-sex variation in the pursuit of committed pair bonds and uncommitted sex?

Strategic Pluralism Theory (Gangestad & Simpson, 2000) posits that individual differences in mating orientations are facultatively calibrated (i.e. contingently adjusted over ontogeny) in response to cues that have predicted the fitness costs and benefits of alternative behavioral phenotypes over human evolutionary history. One of this theory’s key postulates, for example, is that (a) ancestral men in better phenotypic condition (i.e. who could more efficiently convert energy into fitness) were more likely to succeed in acquiring sexual partners outside of committed relationships, and therefore (b) men’s uncommitted mating orientation will be calibrated to variations in their condition-dependent phenotypic features (e.g., physical attractiveness). As we review below, extant research has often supported this condition-dependent calibration hypothesis by demonstrating positive associations of condition-dependent physical features with men’s orientation toward uncommitted mating. However, certain methodological limitations have also led to some contradictory findings, and important theoretical distinctions implied by this hypothesis remain untested.

In this paper, we provide the most extensive and multi-faceted test to date of the hypothesis that men’s (but not women’s) orientation toward uncommitted (but not committed) mating is calibrated to variations in condition-dependent features—in this case, physical strength and physical attractiveness. To this end, we examine multiple measures of strength and attractiveness in relation to context-specific mating orientations and past sexual behavior in three independent samples of young adults.

In the tradition of strategic pluralism theory (Gangestad & Simpson, 2000), a number of theorists have discussed the hypothesis that men’s uncommitted mating orientation is facultatively calibrated in response to phenotypic features dependent on overall phenotypic condition (Buss, 2009, Frederick and Haselton, 2007, Gangestad et al., 2001, Rhodes et al., 2005). Broadly speaking, “phenotypic condition” refers to an individual’s ability to efficiently convert energy into fitness-enhancing traits and outcomes (Tomkins, Radwan, Kotiaho, & Tregenza, 2004). This ability is determined by a variety of factors, including genome-wide mutation load, possession of genotypes that are well adapted to local pathogens, and exposure to developmental insults (Gangestad et al., 2010, Gangestad et al., 2001, Penke et al., 2007, Tomkins et al., 2004). Importantly, phenotypic condition alters the trade-offs inherent in investing energy into traits that promote intrasexual competition and mate attraction. For instance, all else equal, an individual in better phenotypic condition will need to allocate less energy toward somatic maintenance and pathogen defense, and will therefore be able to invest more heavily in developing energetically expensive musculature for competing with rivals (Frederick and Haselton, 2007, Gallup et al., 2007, Gangestad et al., 2007, Lassek and Gaulin, 2009, Lukaszewski and Roney, 2011). Thus, although low physical strength alone does not necessarily indicate poor overall condition (because energy is finite and can be allocated in multiple ways), high physical strength is a positive indicator of being in good enough condition to invest heavily in muscle growth and maintenance (Frederick and Haselton, 2007, Lassek and Gaulin, 2009). Similarly, physical attributes that are judged as sexually attractive (e.g., symmetry; cues to sex hormone levels) theoretically indicate the relative absence of harmful mutations that disrupt optimal development and/or immune function (Gangestad et al., 2001, Little et al., 2011, Roney, 2009). It is for reasons such as these that physical strength and physical attractiveness are hypothesized to be condition-dependent features in humans.

There are at least two routes through which higher physical strength and attractiveness theoretically enabled ancestral men to engage in uncommitted mating. First, because much of the heritable variance in condition-dependent features is maintained over evolutionary time through stochastic processes such as mutation-selection balance (Penke et al., 2007, Tomkins et al., 2004), both strength and attractiveness functioned as indicators of men’s genetic quality ancestrally (Frederick and Haselton, 2007, Gangestad and Simpson, 2000). Therefore, ancestral women likely found these features sexually attractive and preferred them in partners for uncommitted affairs. Consistent with this, modern women prefer these features in mates—and more so in uncommitted relative to committed mating contexts (Frederick and Haselton, 2007, Gangestad et al., 2007, Li and Kenrick, 2006). Second, because sex without commitment is a valuable reproductive resource for men, pursuing uncommitted matings would have often elicited direct intrasexual aggression from rivals (Daly and Wilson, 2005, Puts, 2010, Simpson et al., 1999). Ancestrally, physically stronger men would have been more likely to prevail in intrasexual contests and/or sustain lower levels of conflict-related injury than physically weaker men (see Hill et al., 2013, Puts, 2010, Sell et al., 2012, Simpson et al., 1999).

Taken together, these arguments suggest that ancestral men who were physically stronger or more attractive would have been relatively likely to secure net reproductive benefits by pursuing sex without commitment. If so, it follows than men’s uncommitted mating orientation may be facultatively calibrated over ontogeny via evolved conditional rules of the form: “To the extent that I am [(physically stronger) (more attractive)] than other men, invest in the pursuit of uncommitted mating opportunities.

Importantly, this condition-dependent calibration hypothesis applies only to men. Given differences between the sexes in their levels of obligatory parental investment, ancestral men could theoretically accrue dramatic increases in fitness through short-term sexual affairs, whereas women faced a much lower ceiling on the number of offspring they could produce via sex with multiple partners (Buss & Schmitt, 1993). Moreover, to the extent that uncommitted sex partners were likely to provide less paternal investment in offspring than committed partners, ancestral women engaging in purely sexual affairs would have been left with a disproportionate share of the childrearing responsibility (Gangestad & Simpson, 2000). It would not have been adaptive on average, therefore, for more attractive women to be differentially motivated to engage in uncommitted mating—especially because women in better phenotypic condition were in the best position to elicit monogamous investment from high-quality men (Buss and Schmitt, 1993, Buss and Shackelford, 2008, Larson et al., 2012).

Additionally, the logic of strategic pluralism predicts that the orientation toward committed mating will not be calibrated to condition-dependent features in either sex. Theories of human reproduction generally posit that long-term bonds took hold as a common pillar of human mating systems, because of the massive fitness benefits they generate for both sexes via cooperative investment in offspring and the sexual division of labor (Buss and Schmitt, 1993, Gangestad and Simpson, 2000, Gurven et al., 2009). For this reason, what distinguishes men in better phenotypic condition from those in poorer condition should not likely be that they are inclined to forego the benefits of committed relationships, but that they can more often afford to pursue uncommitted mating opportunities as a supplemental tactic (Buss and Schmitt, 1993, Gangestad and Simpson, 2000).

A number of extant studies have tested associations of physical strength and physical attractiveness with the orientation toward uncommitted mating. Most of these have operationalized the latter in one of two ways. First, many studies have employed the Sociosexual Orientation Inventory (SOI; Simpson & Gangestad, 1991) or Revised SOI (SOI-R; Penke & Asendorpf, 2008)—both of which index one’s willingness to engage in sex without commitment. Second, some studies have used peoples’ number of past sex partners as a proxy for their uncommitted mating orientation.

Research using these methods has produced mixed support for the condition-dependent calibration hypothesis as defined above—which, to reiterate, predicts that men’s (but not women’s) uncommitted mating orientation is calibrated to condition-dependent features. For example, among both men and women, SOI (or SOI-R) scores have been found to correlate positively with self-rated physical attractiveness (Clark, 2004, Penke and Asendorpf, 2008, Perilloux et al., 2013) as well as third-party ratings of attractiveness (Honekopp et al., 2007, Rhodes et al., 2005, Thornhill and Gangestad, 1994). Likewise, among both sexes, number of past sex partners has been found to correlate positively with measures of self-rated physical attractiveness (Penke and Asendorpf, 2008, Perilloux et al., 2013) and third-party ratings of attractiveness (Gangestad et al., 2001, Honekopp et al., 2007, Rhodes et al., 2005, Thornhill and Gangestad, 1994). Additionally, measures of physical strength and muscularity have been found to positively predict men’s SOI scores (Gangestad et al., 2007) and their number of past sex partners (Frederick and Haselton, 2007, Gallup et al., 2007, Hill et al., 2013). Taken together, then, these findings support the prediction that men’s phenotypic condition is positively correlated with their uncommitted mating orientation. However, counter to the prediction that this association should be limited to men, these results also appear to indicate that physical attractiveness positively predicts women’s orientation toward uncommitted mating.

Further complicating the overall picture is the fact that some studies have failed to replicate the positive correlations reported above. For example, published studies have reported non-significant associations of women’s rated attractiveness with their SOI scores (Perilloux et al., 2013, Stillman and Maner, 2009) and also their number of sex partners (Perilloux et al., 2013). Moreover, one study reported a null association between men’s actual physical strength and their SOI scores (Simmons & Roney, 2011), and another even reported a negative association between men’s rated facial attractiveness and SOI (Boothroyd, Jones, Burt, DeBruine, & Perrett, 2008).

In summary, previous studies reporting associations of physical attractiveness and strength with measures of mating orientation have yielded mixed results—certain of which are inconsistent with the hypothesis that men’s (but not women’s) uncommitted mating orientation is calibrated to condition-dependent physical features. If this hypothesis is correct, for instance, then why are men’s attractiveness and strength somewhat inconsistently correlated with their mating orientations across studies? And why do some studies find that attractive women engage in uncommitted mating more frequently than less attractive women?

In what follows, we argue that prior studies may not have provided clear evidence for the condition-dependent calibration hypothesis described above because (a) they have employed operational definitions that do not distinguish between strategic mating orientations and past sexual behavior and (b) sample sizes in individual studies have not always been large enough to detect small-to-moderate correlations.

A notable feature of the original SOI (Simpson & Gangestad, 1991) is its very broad bandwidth, resulting from the fact that it aggregates items that assess uncommitted mating orientation (the willingness to engage in sex without commitment) and past sexual behavior (number of sex partners). Importantly, recent research has supported the claim that these should often be treated as separate components (Jackson and Kirkpatrick, 2007, Penke and Asendorpf, 2008, Webster and Bryan, 2007). This is because a person’s past sexual behavior is constrained and influenced by a number of factors other than strategic mating orientations. To take one example, a man may be highly motivated to engage in uncommitted mating, but unable to fully actualize his desire during a given time period due to a local paucity of women who are willing to engage in casual sex (although men should be expected to adjust their strategies to long-term trends in mating opportunities; see Kenrick, Li, & Butner, 2003). As such, men’s phenotypic condition may tend to show a larger or more consistent association with their motivation to engage in uncommitted mating than with their previous success in acquiring sexual partners. If so, the SOI’s aggregation of items assessing mating orientation and past sexual behavior, respectively, could lead to the underestimation of correlations between men’s condition-dependent features and their uncommitted mating orientation.

The aggregation of mating orientations and past sexual behavior in previous research may also help explain why women’s attractiveness appears to positively predict their uncommitted mating orientation in some studies. Specifically, even if attractive women are not differentially open to casual sex, they will presumably be subject to more advances from attractive men—many of which may, whether accurately or deceptively, signal long-term romantic interest (Haselton, Buss, Oubaid, & Angleitner, 2005). As such, more attractive women may end up having more partners than less attractive women simply by virtue of the larger number of courtship attempts they receive (Jackson and Kirkpatrick, 2007, Perilloux et al., 2013). If so, attractive women will tend to exhibit higher overall SOI scores even if they are not more motivated or willing to engage in uncommitted mating (Jackson & Kirkpatrick, 2007).

Moreover, it follows from the logic described above that the association of men’s condition-dependent physical features with their number of sex partners should actually be mediated through the orientation toward uncommitted mating—such that stronger and more attractive men are calibrated to pursue uncommitted mating opportunities, and thereby acquire more sex partners. Importantly, however, the aggregation of items assessing mating orientation and past sexual behavior precludes examination of this meditational hypothesis. Indeed, to our knowledge, no prior studies have tested the hypothesis that effects of men’s strength or attractiveness on mating success are mediated via their uncommitted mating orientation.

Finally, many of the individual studies reviewed above may have been somewhat underpowered to reliably detect associations of men’s physical features with mating orientations and past sexual behavior. On average, the extant research suggests that these associations, when present, are small-to-moderate in magnitude. Given the inevitability of sampling error, it is not reasonable to expect that true correlations will replicate in all samples, especially if the relevant samples and/or population-level effect sizes are not exceptionally large. Indeed, recent research using Monte-Carlo simulations (Schonbrodt & Perugini, 2013) indicates that estimates of effect sizes for relatively small correlations (e.g., r = .25) do not stabilize until sample sizes reach 200–250—a threshold that has not typically been approached for sex-specific samples in prior studies. As such, some of the inconsistent findings in the literature could simply reflect sampling error across studies with limited power to detect the predicted correlations.

In sum, because of these issues pertaining to the operational definition of variables and limited statistical power, respectively, previous studies may have partially concealed adaptively patterned sex-specific associations among condition-dependent physical features, context-specific mating orientations, and past sexual behavior.

In the current research, we sought to provide a test of the condition-dependent calibration hypothesis that (a) includes multiple measures of physical strength and attractiveness; (b) distinguishes between uncommitted mating orientation, committed mating orientation, and past sexual behavior; and (c) is adequately powered to detect the predicted associations. To these ends, we collected measures of actual physical strength, self-rated physical strength, other-rated physical attractiveness, and self-rated physical attractiveness from three independent samples of young adults. In addition, participants completed measures of uncommitted mating orientation and committed mating orientation, and reported on their past numbers of sex partners and one-night stands.

Taken together, the logic described above suggests five specific predictions:

  • -

    Prediction 1: Physical strength and physical attractiveness will positively predict men’s uncommitted mating orientation. There will be no such associations for women.

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    Prediction 2: Neither physical strength nor attractiveness will predict committed mating orientation in either sex.

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    Prediction 3: Physical strength and attractiveness will positively predict men’s number of past sex partners and one-night stands.

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    Prediction 4: Physical attractiveness will positively predict women’s number of past sex partners and one-night stands.

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    Prediction 5: The associations of men’s physical strength and attractiveness with their number of past sex partners will be mediated via their uncommitted mating orientation. There will be no such mediation among women.

Section snippets

Participants

Participants were from three independent samples of undergraduates from two university campuses on the west coast of the United States. Sample 1 included 186 men who were part of a study on attraction at UCLA (mean age = 21.3 years, SD = 4.7). Sample 2 included 175 undergraduates (86 men; 89 women) who were part of a study on personality origins at UCSB (mean age = 19.4 years, SD = 1.3). Sample 3 included 209 undergraduates (110 men; 99 women) who were part of a different study at UCSB (mean age = 18.7 

Results

In support of Prediction 1, the meta-analyses indicated that men’s physical strength and physical attractiveness were each positively correlated with their uncommitted mating orientation (Table 1). Also in support of Prediction 1, these associations were small and non-significant among women (Table 1). In support of Prediction 2, neither strength nor attractiveness was significantly associated with committed mating orientation in either sex (Table 1). Together, Predictions 1 and 2 indicate that

Discussion

Findings from multiple independent samples of young adults supported all five of our specific predictions regarding adaptively patterned associations of condition-dependent physical features with context-specific mating orientations and past sexual behavior. Crucially, composite measures of physical strength and attractiveness were positively correlated with measures of men’s (but not women’s) uncommitted mating orientation (but not committed orientation)—which is consistent with the hypothesis

Author note

The authors thank Britt Ahlstrom, Melissa Fales, David Pinsof, Shimon Saphire-Bernstein, Zach Simmons, and three anonymous reviewers for their insightful feedback on previous versions of this manuscript.

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