Despite the widespread use of high-heeled footwear in both developing and modernized societies, we lack an understanding of this behavioral phenomenon at both proximate and distal levels of explanation. The current manuscript advances and tests a novel, evolutionarily anchored hypothesis for why women wear high heels, and provides convergent support for this hypothesis across multiple methods. Using a recently discovered evolved mate preference, we hypothesized that high heels influence women’s attractiveness via effects on their lumbar curvature. Independent studies that employed distinct methods, eliminated multiple confounds, and ruled out alternative explanations showed that when women wear high heels, their lumbar curvature increased and they were perceived as more attractive. Closer analysis revealed an even more precise pattern aligning with human evolved psychology: high-heeled footwear increased women’s attractiveness only when wearing heels altered their lumbar curvature to be closer to an evolutionarily optimal angle. These findings illustrate how human evolved psychology can contribute to and intersect with aspects of cultural evolution, highlighting that the two are not independent or autonomous processes but rather are deeply intertwined.
Introduction
“A woman’s beauty lies, not in any exaggeration of the specialized zones, nor in any general harmony that could be worked out by means of the sectio aurea or a similar aesthetic superstition; but in the arabesque of the spine.”
– John Updike, Pigeon Feathers and Other Stories
Women’s use of high-heeled shoes is a prevalent phenomenon in both developing and modernized societies (Miller, 1990; Freeman, 1999). In the United States alone, over $8,000,000,000 is spent annually on high-fashion footwear (Rossi, 1993). Several scholars (e.g., Roth, 1929; Smith, 1999; Morris et al., 2013; Guéguen, 2015) have advanced hypotheses about the function of high-heeled shoes for women. These ideas have ranged from the proposal of media-created associations between high heels and sexuality (e.g., Smith, 1999) to influences on specific biomechanical properties on women’s gait (e.g., Morris et al., 2013). However, these scholars have either not empirically tested their ideas or have found results suggesting that the reasons women wear high heels do not include the one they hypothesized (e.g., see Morris et al., 2013; Guéguen, 2015). In short, despite the widespread prevalence of high heels, the reasons why women wear high heels are not well understood.
Recent research by Lewis et al. (2015) may provide insight into this unexplained phenomenon. Lewis et al. (2015) took into consideration an adaptive problem uniquely faced by bipedal hominin females: (1) a forward shifting center of mass during pregnancy, and (2) a morphological adaptation that evolved to solve this adaptive problem: wedging in women’s third-to-last lumbar vertebra (Whitcome et al., 2007). These researchers reasoned that ancestral women who possessed an intermediate degree of vertebral wedging would have experienced important fitness benefits, such as being able to sustain multiple pregnancies without suffering spinal injury and being able to forage longer into pregnancy. The fitness benefits experienced by these women, in turn, would have created selective conditions for the evolution of a male mate preference for such women. Ancestrally, a woman’s lumbar curvature would have been a reliable, observable cue to her vertebral wedging (George et al., 2003). Based on this, Lewis et al. (2015) hypothesized that men have an evolved mate preference for a lumbar angle of approximately 45.5° – a value that cues the ability to shift the gravid center of mass back over the hips and simultaneously avoids the adaptive problems of excessive lumbar curvature (hyperlordosis) and insufficient lumbar curvature (hypolordosis). In support of their hypothesis, Lewis et al. (2015) found that men’s attraction toward women peaks at this angle – the optimal angle for helping ancestral women mitigate the biomechanical costs of a bipedal fetal load and minimizing the likelihood of both hyperlordosis and hypolordosis.
If lumbar curvature is an important attractiveness cue, and women possess psychological mechanisms to enhance their physical appearance (see Singh and Bronstad, 1997), then we might expect women to attempt to manipulate their lumbar curvature in ways that increase perceptions of their attractiveness. Independently, researchers interested in biomechanics and ergonomics have proposed that high-heeled shoes increase lumbar curvature (e.g., Lee et al., 2001). Together, these ideas yield a novel hypothesis about why women wear high heels: women may increase their attractiveness by manipulating their lumbar curvature with high-heeled shoes.
To test this hypothesis, we conducted two independent studies, one using archival photos from the Internet, and the second employing a controlled, laboratory-based design.
Study 1
Introduction
High Heels and Lumbar Curvature
To date, findings bearing on the relationship between lumbar curvature and high-heeled footwear have been equivocal (Russell, 2010). They have been based on small samples (e.g., 11 participants), employed measures with low validity (Fedorak et al., 2003), and produced mixed results (e.g., Snow and Williams, 1994). As such, although the belief that high-heeled shoes are associated with greater lumbar curvature is widespread, reliable evidence supporting this relationship is lacking (see Russell, 2010 for a review). The first purpose of this study was therefore to investigate the relationship between wearing high heels and lumbar curvature.
High Heels, Lumbar Curvature, and Attractiveness
Lewis et al.’s (2015) research establishes the importance of lumbar curvature as an attractiveness cue, but to date no studies have concurrently measured women’s lumbar curvature and attractiveness as a function of high-heeled footwear usage. The second central purpose of Study 1 was therefore to establish whether women are perceived as more attractive when they wear high heels.
Materials and Methods
This study was carried out in accordance with the recommendations of The University of Texas at Austin Institutional Review Board. In accordance with the Declaration of Helsinki, all participants provided informed consent. Because data were collected online, participants indicated their consent electronically in lieu of providing a written signature. All participants indicated their consent in this manner, and the protocol was approved by The University of Texas Institutional Review Board.
Photographic Stimuli
Photographs of women wearing high-heeled and flat-soled shoes were downloaded from publically accessible websites on the Internet (links available upon request). Because individual differences in physical attractiveness are large enough to render undetectable any between-individual effects of high-heeled shoes on attractiveness (e.g., comparing the attractiveness of one woman in flats to another woman in heels), we employed a within-woman design. This required us to find images on the Internet of the same woman photographed twice, once in heels and once in flats. We also needed to be able to assess the women’s lumbar curvature, which can only be measured from the side, as in profile photographs. These constraints resulted in celebrity females representing an ideal source of data; a sufficiently wide selection of photographs of celebrity females was available on the Internet to identify two photographs of each woman, once in heels and once in flats, and both in profile. For each celebrity, we selected the first profile images that a Google search produced of the woman in heels and flats, respectively. We completed this procedure for 15 different female celebrities (list available upon request), resulting in a total stimulus set of 30 images.
Lumbar Curvature Measurements
We measured the women’s lumbar curvature by superimposing a virtual protractor tool (Screen Protractor, Iconico, Inc.) on a line parallel to the top of the lower back and a line parallel to the top of the buttocks, an operationalization of lumbar curvature used in clinical orthopedic settings (e.g., see George et al., 2003).
Raters and Attractiveness Assessments
One hundred twenty-six men (Mage = 19.77, SDage = 4.00, range = 17–52) rated the attractiveness of the photographic stimuli. Raters were randomly assigned to either view the 15 targets wearing flat-soled shoes or to view the 15 targets wearing high-heel shoes. The images were displayed in random order to the raters, who rated the attractiveness of each target on a 10-point scale (1 = extremely unattractive, 10 = extremely attractive).
Results
First, we set out to test whether the women’s lumbar curvature was greater while wearing high-heeled shoes than while wearing flat-soled shoes. A paired-samples t-test revealed that women’s lumbar curvature in high-heeled shoes (M = 43.37, SD = 9.06) was greater than their lumbar curvature in flat-soled shoes (M = 30.64, SD = 7.71), t(14) = 4.48, p = 0.001, d = 1.16. Second, we tested whether the women were perceived as more attractive in high heels than in flats. The women were perceived as more attractive when they were wearing high heels (M = 7.37, SD = 0.69) than when they were in flats (M = 6.47, SD = 1.11), t(14) = 3.10, p = 0.008, d = 0.94.
Study 2
Introduction
The findings from Study 1 provide the first simultaneous evidence of the relationships between (1) high heels and lumbar curvature and (2) high heels and physical attractiveness. However, these results were based on photographs that differed not only in the women’s footwear, but also in many other variables that influence women’s physical appearance (e.g., cosmetics, revealing nature of clothing). Consequently, the relationship observed in Study 1 between donning high heels and being perceived as more attractive carries with it the attendant concerns about directionality and the third variable problem. Based on these Study 1 limitations, we conducted a second, controlled, laboratory-based study to better isolate and establish (1) the effect of high heels on lumbar curvature, (2) the relationship between high heels and attractiveness, and (3) the role that lumbar curvature plays in the high heels-attractiveness relationship.
Why High Heels Increase Attractiveness
Other researchers have proposed that high-heeled shoes increase women’s attractiveness, but have either neglected to explain why they increase attractiveness (e.g., Roth, 1929; Smith, 1999), or have advanced hypotheses that are not consistent with extant data. For example, Morris et al. (2013) hypothesize that high heels increase women’s attractiveness through their effects on specific biomechanical properties of women’s gait. Consistent with the notion that high heels increase women’s attractiveness, Morris et al. (2013, p. 180) found that women were perceived as more attractive in heels. However, they found “no consistent pattern of correlations between the biomechanical measures and the judgements of attractiveness of the individual walkers.” Guéguen (2015) subsequently purported to test Morris and colleagues’ hypothesis. Guéguen conducted multiple studies documenting a link between (1) women wearing high heels and (2) men engaging in behaviors thought to be indicators of increased attraction. For example, in two studies, he demonstrated that men were more likely to be willing to participate in a survey when the solicitation to participate came from a woman wearing high heels rather than flat-soled shoes. Importantly, he obtained these results using women who were “stationed” in front of a retail store and asked passers-by to participate – he obtained these results without gait cues. Morris et al.’s (2013) and Guéguen’s (2015) findings that high heels increase attractiveness in the absence of gait cues provide strong evidence that the gait hypothesis, even if partially correct, cannot account for high heels’ effect on women’s attractiveness when gait cues are absent. There must be other reasons that high heels increase women’s attractiveness, which, as yet, have not been identified.
The lumbar curvature hypothesis represents one potential explanation. Moreover, the lumbar curvature hypothesis yields unique, specific a priori predictions about the effect of high heels on women’s attractiveness. Whereas other hypotheses generate the general prediction that women will be perceived as more attractive when they wear high heels, the lumbar curvature hypothesis offers a more nuanced set of predictions. Men do not simply prefer greater lumbar curvature. Rather, Lewis et al. (2015) document that men’s attraction to women increases as women’s lumbar curvature approaches a proposed theoretically optimum value—45.5°. If men are attracted to women in high heels partly because heels influence women’s lumbar curvature, then we should expect high heels to increase women’s attractiveness only when wearing heels shifts their lumbar curvature closer to the theoretical optimum, but not when the heels shift curvature away from this optimum.
To test these predictions, control for other potential high-heel-related influences on attractiveness, and rule out alternative hypotheses, we conducted a second, controlled, laboratory-based study.
Materials and Methods
This study was carried out in accordance with the recommendations of The University of Texas at Arlington institutional review board. In accordance with the Declaration of Helsinki, all participants provided informed consent. Because data were collected online from rater participants, they indicated their consent electronically in lieu of providing a written signature. All model participants provided written informed consent. The protocol was approved by The University of Texas at Arlington institutional review board.
Participants
Fifty-six women (Mage = 19.36, SDage = 1.77, age range = 18–26) were recruited from a large public university in the Southwestern United States and received partial course credit for their participation.
Procedure
Participants were instructed to come to their scheduled lab session in form-fitting clothing (e.g., tight jeans, yoga pants, non-baggy tee-shirts) with a pair of their own flat-soled shoes (e.g., tennis shoes). Upon arrival at the laboratory, participants were greeted by a research assistant and told that they would be participating in a study examining female appearances. Participants were taken individually to a private room to be photographed. Two photographs were taken of each participant, once in flat-soled shoes and once in heeled footwear1. For each photograph, the assistant instructed the participant to stand against the wall with the right side of her body facing the wall. The assistant then took a full-body profile photograph. The same instructions were used for both photographs.
Photographic Stimuli
We generated a stimulus set of two images for each female participant. One image was generated from the photo of the woman in heels and the other was generated from her photo in flat-soled shoes (Figure 1).
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