1. Introduction

Strategic pluralism suggests that women should generally engage in long-term mating strategies. However, if the benefits (e.g., genetic benefits for offspring) outweigh the costs of short-term mating (e.g., less parental investment, partner loss, unwanted pregnancy, etc.), then women should take advantage of short-term mating opportunities (Gangestad & Simpson, 2000). Evidence for strategic pluralism comes from women's preferences across the menstrual cycle. Because masculinity in faces (Penton-Voak & Chen, 2004), voices, body shape, and social displays (see Zitzmann & Nieschlag, 2001, for a review of the previous three factors) is associated with high testosterone levels and testosterone is an immunosuppressant, highly masculine healthy males are likely to be particularly immunocompetent (Folstad & Karter, 1992). Immunocompetency is a heritable genetic benefit available to a woman's offspring; thus, women engaging in short-term relationships should prefer highly masculine mates. Research has demonstrated that fertile women, as compared to nonfertile women, prefer higher levels of masculinity in faces (Johnston et al., 2001, Penton-Voak & Perrett, 2000, Penton-Voak et al., 1999) and voices (Feinberg et al., 2006), as well as dominant male social displays (Gangestad, Simpson, Cousins, Garver-Apgar, & Niels Christensen, 2004).

Further evidence of strategic pluralism in human mating is demonstrated through research investigating the interindividual difference of sociosexual orientation. Sociosexual orientation represents a person's openness to short-term mating. People with relatively unrestricted sociosexual orientation, indicated by high scores on the Sociosexual Orientation Inventory (SOI; Simpson & Gangestad, 1991), are more likely to engage in short-term relationships than people with a restricted sociosexual orientation. Generally employing a short-term mating strategy, as compared to a long-term mating strategy, yields fewer nongenetic resources (i.e., parental effort) and increases the importance of receiving genetic benefits from sexual partners (Gangestad & Simpson, 2000). Thus, similar to women at times of peak fertility, women with unrestricted sociosexuality should prefer high levels of masculinity. Work by Provost, Kormos, Kosokowski, and Quinsey (2006) has demonstrated that unrestricted sociosexuality is related to greater attraction to the masculine mesomorph body type, as compared to average, endomorph, or ectomorph body types, and attraction to a male confederate for short-term relationships in a mock speed dating paradigm. Similarly, Waynforth, Delwadia, and Camm (2005) demonstrated that unrestricted sociosexuality in women was associated with attraction to male and female faces with masculine features.

Although there is evidence that both menstrual cycle status and sociosexuality are related to preference for masculinity, this research has only used static images and comparative judgments among stimuli that may have been confounded by variations in such characteristics as age, skin color, and health. These variables themselves influence interpersonal attraction (see, e.g.,Kenrick & Keefe, 1992, for age; Fink, Grammer, & Thornhill, 2001, for skin color; Buss et al., 1990, for health; and Jones, Little, Burt, & Perrett, 2004, for healthy skin in particular). In this study, we investigated the effect of menstrual cycle stage and sociosexuality on female attraction to masculinity using point-light displays of human walkers. Point-light displays limit the influence of confounding variables and, thus, are beneficial in testing specifically for a preference for masculinity. These stimuli contain information on walker structure and walking dynamics, both of which are key components in sex discrimination. For example, in addition to the hormonally influenced structural differences between men and women (e.g., broader shoulders and narrower hips in men compared to women), male walkers, as compared to female walkers, have a larger upper-body lateral sway (Mather & Murdoch, 1994), whereas women have a hip rotation that is in the opposite phase to vertical leg motion (Troje, 2003), resulting in more pronounced hip movement. Using point-light displays of biological motion, we investigated the unique effect of masculinity on attractiveness with fewer confounding variables. The first study investigated women's attraction to masculinity as a function of their female fertility, and the second study investigated women's attraction to masculinity as a function of their sociosexuality.

2. Study 1

2.2. Results

One NHBC woman gave a value for the most attractive walker greater than 2.5 standard deviations away from the mean value; thus, she was removed from further analyses. Using a one-sample t test, we compared the average z score indicated by women (both HBC women and NHBC women in either the late follicular or luteal stages during their first visit; mean=4.9, S.D.=1.9) as their most attractive walker to zero (the value of the average walker). There was an overall preference for male masculinity [t(56)=18.6, p<.001, F=2.6]. To ensure that ethnicity did not affect results, we performed a t test between White (mean=4.83, S.D.=2.11) and non-White (mean=4.95, S.D.=1.53) participants. There was no difference between the ethnic groups [t(55)=0.21, ns]. A one-way ANOVA between women in the late follicular stage during their first visit (mean=5.12, S.D.=1.96, n=20), women in the luteal stage during their first visit (mean=4.49, S.D.=1.95, n=18), and HBC women (mean=4.96, S.D.=1.99, n=19) indicated no difference between the groups [F(2, 26)<1, ns]. A paired t test showed that women in the late follicular phase (mean=5.02,S.D.=1.87), as compared to when they were in the luteal phase (mean=4.42, S.D.=2.14), preferred a higher level of masculinity [t(19)=2.1, p=.05, d=.3]. To ensure that order did not affect the results of the repeated measures test, we calculated a difference score by subtracting the discriminative value given as most attractive by women in the luteal phase from the score given in the late follicular phase and investigated the difference by group. Using confidence interval analysis, women who first did the task in the late follicular phase had a similar difference score from women who first did the task in the luteal phase (see Table 1 for means and bounds of 95% confidence intervals).

Table 1. Means of difference scores and 95% confidence intervals demonstrating that the difference scores between z scores given for the most attractive walker when women were in the late follicular phase versus luteal phase were similar for both groups

		Mean difference score	Lower bound	Upper bound
	Late follicular first	0.78	−0.02	1.59
	Luteal first	0.24	−0.85	1.33

3. Study 2

3.2. Results

Participants indicating values more than 2.5 standard deviations (with respect to the distribution of the subjects' ratings) away from the mean on most attractive masculinity and SOI (n=1 and n=2, respectively) were removed from the analysis. Values women gave for their most attractive walker were normally distributed (mean=4.88 z scores, S.D.=1.97). SOI scores (mean=23.60, S.D.=16.39) were slightly skewed; hence, they were submitted to a square root transformation. As predicted, women with higher SOI scores found men with high levels of masculinity to be most attractive (r=.40, p=.001; similar results were found with untransformed data, r=.41, p=.001; see Fig. 1).

Fig. 1. Increasing SOI scores are associated with increased preference for high levels of masculinity, expressed in terms of the distance of a male walker from the gender-neutral walker.

4. General discussion

These studies demonstrated that women are attracted to high levels of masculinity in situations where short-term mating is more probable than long-term mating. In Study 1, women had a stronger preference for masculinity when they were fertile than when they were not. In Study 2, openness to short-term mating, measured through sociosexual orientation, also was related to preference for masculinity. Because women, on average, entered values in the masculine end of the gender continuum, we believe that the influence of female fertility status and sociosexual orientation on specific masculinity level reflects a preference for higher masculinity, not just a preference for a masculine walker compared to a feminine walker. In addition, because the presented stimulus was a point-light walker on the screen, we are confident that these results show preference for masculinity and are less confounded than previous research investigating preference for masculinity by other possible variables such as age, ethnicity, or health. The use of point-light displays of biological motion, therefore, may be an interesting tool for investigating female preference for other traits, for example, social dominance. It is important to investigate the role gait plays in nonverbal communications. In particular, in what circumstances would gait be informative and how much information does it supply compared to other cues? The amount of control that people have over their gait is also unknown. How gaits change and how others view the changes depend on circumstances (e.g., is a man going to walk differently in front of numerous women than if he is walking on his own? How would a woman rate a recording of such a gait?). Point-light gait displays provide the methodology to investigate these questions.

However, point-light displays also have their drawbacks. As with any stimulus generation that creates a continuum along a given dimension from a discrete group of individuals, it is possible to generate examples of stimuli that do not exist in the natural environment. In addition, walks were obtained from 44 men to generate the stimulus, and it is unlikely that these men encompass the entire natural range of walking masculinity in the world. Thus, it is possible that the stimuli are not ecologically representative. However, it is unlikely that the masculinity and femininity of actual walkers are a discrete function. Even if the participants in this study have not encountered every walker along the presented continuum in their actual life, they would still be able to make judgments along the axis. Likewise, the 44 men who were used to generate the stimuli provided enough of a contrast from the women walkers to create a function that could be extrapolated to a wide range of masculine walkers. Thus, although participants may not have indicated preferences for the masculinity levels of walkers they regularly encounter, they still indicated preferences for variations in masculinity.

However, the operational definition of masculinity in this study also requires that the results be interpreted with caution. In these studies, women manipulated the appearance of motion that was created by contrasting male and female walkers, and the results are consistent with the theoretical predictions that include the assumption that masculinity in gait is associated with testosterone. However, we have no evidence that sex-typical walking pattern is related to levels of circulating or developmentally pertinent sex-typical hormones. Thus, we do not know if women prefer more masculine walkers or simply prefer less feminine walkers. Although the structural effects of sex hormones are known, there is limited research on the role of hormones on the dynamic aspect of walking. Further research needs to investigate the influence of hormonal levels on walking patterns specifically, as well as how the hormonally influenced morphology of a person affects the way people walk.

In addition, the results from Study 2 support the notion that individual differences such as sociosexuality are part of women's pluralistic strategies. There is further research necessary to hash out this role. In particular, what is the cost/benefit ratio of engaging in short-term relationships versus long-term relationships for women with an unrestricted sociosexual orientation? In addition, if sociosexual orientation is a facultative mating strategy, what are the ontogenetic processes involved in developing and maintaining this strategy? Further theoretical and empirical work must be done to further investigate the role of sociosexuality in human life history strategies.

Overall, these studies demonstrate that women who are likely to engage in short-term relationships (i.e., women in the late follicular phase of their menstrual cycle or women with relatively unrestricted sociosexuality) are attracted to masculinity as presented through point-light displays of biological motion. Although the displays may not represent actual male walkers, they do demonstrate that women who are expected to be more interested in obtaining genetic benefits from a romantic liaison prefer displays of masculinity. Thus, these studies both supported and expanded research on the strategic pluralism model of female mating strategies while demonstrating the usefulness of biological motion as stimuli to investigate interpersonal attraction.