Abstract:
Attractiveness conveys reliable information about a woman's age, health, and fertility. Body fat distribution, as measured by waist-to-hip ratio (WHR), is a reliable cue to a woman's age, health, and fertility, and affects judgment of women's attractiveness. WHR is positively correlated with overall body weight or body mass index (BMI). Some researchers have argued that BMI, rather than WHR, affects judgments of female attractiveness. To evaluate the role of WHR, independent of BMI, we secured photographs of pre- and post-operative women who have undergone micro-fat grafting surgery. In this surgery, surgeons harvest fat tissue from the waist region and implant it on the buttocks. Post-operatively, all women have a lower WHR but some gain weight whereas others lose body weight. Results indicate that participants judge post-operative photographs as more attractive than pre-operative photographs, independent of post-operative changes in body weight or BMI. These results indicate that WHR is a key feature of women's attractiveness.

Excepts

Introduction: A large body of evidence indicates that physical attractiveness is consensual (people agree about who is and is not attractive both within and across cultures) and is an important determinant of interpersonal and romantic relationships. Evolutionary psychologists offer a clear and testable explanation for the functional significance of attractiveness: physical attractiveness provides reliable cues to a person's health and reproductive potential. It is argued that a recurrent adaptive problem ancestral people faced was to assess prospective mates according to "mate value" (attractiveness as a mate relative to available others in local mating market). The variables that determine mate value, such as genetic quality, health, and fertility, cannot be directly observed but there are specific observable characteristics of the body that reliably convey this information. Sexual selection thus produces mechanisms of mate selection that extract and process information based on specific observable characteristics of the body, linked to good health and reproductive ability.

A straightforward test of this evolutionary explanation would be to identify a feature of the body known to be linked with health and reproductive capability and to demonstrate that the systematic variation in that feature produces systematic changes in judgments of attractiveness. Body fat distribution, as measured by waist-to-hip ratio (WHR), may be an ideal feature. First, WHR, unlike overall body weight, is an unambiguous indicator of age in men and women. Prior to puberty, the sexes have similar WHR because body fat distribution is essentially similar. However, during puberty, increases in sex hormones induce an increase in pelvic width and regulate the anatomical location of body fat deposits. Estrogen selectively inhibits fat deposition in abdominal and waist regions and facilitates fat deposition in the gluteofemoral (buttocks and thighs) region in the females, whereas testosterone inhibits fat depositions in the gluteofemoral region and facilitates fat deposition on the waist and upper body in the males . After puberty, healthy women have a WHR between 0.67 and 0.79, whereas healthy men havea WHR between 0.8 and 0.95. As women age and their production of estrogen decreases, their WHR moves into the male range. WHR, thus, reliably signals a woman's reproductive (pre-, post-pubertal, pre-, post-menopausal) status unlike any other observable body feature.
• • •
Given that WHR is a signal of youth, health, biological sex, non-pregnancy status, and reproductive capability, do changes in the size of WHR cause changes in judgment of female attractiveness? To investigate this issue, Singh (1993a, 1993b) developed 12 line drawings of female figures representing three body weight categories (underweight, normal, overweight) and two levels of feminine (0.7, 0.8), and two levels of masculine (0.9 and 1.0) WHR within each body weight category. The findings indicate that variations in WHR, in female figures, produce systematic changes in the judgments of attractiveness.
• • •
In the original studies, the relationship between attractiveness and WHR depended on body weight category; the normal weight figure with 0.7 WHR was judged most attractive, followed by the underweight figure, whereas the overweight figure was judged not to be attractive (Singh, 1993). Singh concluded that, "...neither body weight, nor WHR alone can explain attractiveness. To be attractive, women must have a low WHR and deviate little from normal weight" . In spite of this reported intricate relationship between WHR and body weight, some researchers have opted to treat body weight or degree of obesity (body mass index - BMI) and WHR as independent variables and have reported that body weight accounts for more variance than WHR in female attractiveness judgments. Tovee and Cornelissen (1999) have even suggested that an attractiveness judgment based on WHR is an artifact of BMI. They argue that reduction of the size of WHR, for example, from 0.8 to 0.7, reduces BMI regardless of body weight category and that this reduction in BMI is responsible for attractiveness ratings for figures with low WHR. These arguments are, however, based on misunderstandings about the nature of WHR. WHR describes the nature of body fat distribution, and therefore bodyweight is critical in evaluating the effect of WHR on attractiveness judgments.
• • •
Nevertheless, because WHR and BMI are correlated, it can be difficult to conclude that changes in attractiveness judgments are due to WHR alone. One needs to assess the relative contribution of WHR and BMI to attractiveness ratings.
• • •
The optimal solution is to use stimulus for which BMI and WHR are independent. A recent surgical technique provides a means to examine the role of different sizes of WHR on attractiveness, independent of BMI. The surgical procedure includes liposuction of the circumference of the waist and then using purified fat cells to graft to the buttocks. This procedure both narrows the waist and enhances the buttocks (without affecting pelvic morphology), having a synergetic effect on WHR without altering BMI. In his practice, aesthetic plastic surgeon Roberts measures pre-and post-operative waist and buttocks circumferences and records pre-and post-operative BMI. Post-operative measurements and photographs are taken about two to three months after surgery to allow for healing and scar disappearance. Although all patients have a lower post-operative WHR, some patients gain weight and other patients lose weight post-operatively. These patients provide a unique opportunity to examine the independent effects of WHR and body weight, or BMI on attractiveness. Furthermore, because pre-and post-operative photographs of the same woman are evaluated, the contributions of other factors (e.g., skin complexion, dimples, and moles) are controlled. The current research tests the hypothesis that if WHR, more than BMI, affects attractiveness, participants will judge post-operative photographs as more attractive regardless of any change in BMI.
• • •
Method
A total of 66 Caucasian males (range = 20-68 years) and 47 females (range = 18-53 years) were tested. A packet containing photographs and an attractiveness rating scale was given to various professional and semi-skilled workers . Each participant individually rated the photographic material and placed the rating scale in an envelope that was collected by the researchers. • • • Pre-and post-operative photographs of the plastic surgery patients were used. This surgical procedure does not reduce the body weight or BMI but redistributes the body fat. Plastic surgeons photographed the patient and obtained information about height, body weight, age, and measured the patients' hip and waist circumferences prior to surgery and after surgery. We obtained 15 pre-and post-operative photographs (9 Caucasian, 4 Asian-American, and 2 African-American) showing a back or oblique view of their lower torso, including upper thighs. Post-operative photographs were taken two to three months after surgery.
• • •
Discussion
Post-operative attractiveness ratings, corrected for the pre-operative ratings, are highly predicted by WHR. BMI, in the range investigated in this study, does not significantly predict attractiveness. Thus, the argument that previously reported affects of WHR on attractiveness are due to minor changes in BMI, is not supported. Furthermore, maximum attractiveness was found to be close to 0.7 (0.73), similar to findings of previous reports using line drawings (Singh, 1993).
• • •
If WHR is an important cue for mate choice, then it is important to show that variation in WHR leads to variation in mating success due to competition among rivals through contest, mate choice, or any other mechanisms of sexual selection. Women with low WHR flirt more often and have more sex partners. Hughes and Gallup were the first to demonstrate the effect of WHR on female sexual behavior, independent of BMI. These investigators found that a woman with lower WHR reported earlier age of first sexual intercourse, had more sex partners, and engaged more often in sexual intercourse with men involved in other relationships. No such relationship was evident for BMI, except in predicting delay in age of first sexual intercourse. In another study, Hughes, Dispenza, and Gallup found that lower WHR was correlated with higher opposite sex rating of voice attractiveness, but there was no correlation between BMI and the voice attractiveness. Jamaican men with high genotypical and phenotypical quality (as measured by the degree of bilateral body part symmetry) prefer women with low WHR as a romantic mate.
• • •
Historical and modern manipulation by women to increase or decrease attractiveness are testaments to the importance of WHR. The popularity of corsets during the Victorian era (despite internal injuries caused to women) and fashionable clothing that highlights tiny waists and exaggerated hips cannot be explained by arguing that women were trying to decrease their body weight. Clothing and fashion can be made to make a political or personal statement (or may be designed for comfort), rather than for attracting the mating attention of prospective mates. When women attempt to convey that they are not sexually available they often deemphasize the body form (e.g., nun's habit, business suit, and the chador to hide the female body in Iran and some Arab countries). When the objective is to make oneself sexually alluring, a persistent method has been to emphasize the narrow waist, as it is historically evident in early Greek paintings and presently evident in Western female fashion using corsets, bustle, and other devices . In a recent study, Rozmus-Wrzesinska and Pawlowski found that female attractiveness judgments are influenced more by a change in female waist size, compared with changes in hip size. Women are aware of and seem to manipulate this evolved preference. For instance, when asked what they do to make themselves attractive to potential mates, young women most often report "sucking stomach in" as tactic after make-up application. Taken together, it seems that the current trend of defining and assessing women's attractiveness solely according to bodyweight or BMI provides an incomplete and perhaps inaccurate picture of female attractiveness.
• • •