Sexy Silhouettes: Slim Waists, Broad Hips, and Fertility

Did natural selection drive men to prefer women with wasp-like waists?

Posted Dec 14, 2018

Original cartoon by Alex Martin
Source: Original cartoon by Alex Martin

Men undoubtedly show strong preferences for female body shape. Countless tests with various images have yielded persuasive results regarding women’s attractiveness. Perhaps the most widely cited example of shape cues, launched by Devendra Singh in 1993, is the waist:hip ratio (WHR)—waist width divided by hip width. WHR is recognized as a key indicator of female attractiveness reflecting fat distribution.

So far so good. But many authors push things further, proposing that natural selection forged men’s preferences to optimize mate choice. Combined with the conviction that female body shape signals health and fertility, this amounts to claiming that beauty resides in the genes of the beholder. Karl Grammer and colleagues baldly stated this notion in 2003: "...particular proportions of waists and hips are only considered to be beautiful because our ancestors with such preferences left more healthy offspring than the individuals in the population without the preferences."

Wikimedia Commons; unknown illustrator; work in the public domain in the USA.
Good Sense corsets for the family, from an 1890 catalogue. Carried away by enthusiasm for “wasp waists”, manufacturers ended up producing corsets for all female family members, regardless of age.
Source: Wikimedia Commons; unknown illustrator; work in the public domain in the USA.

In an earlier blog piece (Waists, Hips and the Sexy Hourglass Shape, posted July 20, 2015), I urged caution in interpreting male preferences for simple body shape indicators. This applies particularly to those infamous Victorian era “wasp-waist” corsets, seen by some as extreme exaggeration of an evolved cue to female fertility and health. Now, twin papers by William Lassek and Steven Gaulin have shaken the very foundations of evolutionary interpretations by demonstrating that preferred female proportions are not optimal indicators of health and fertility.

Problems with WHR

Various doubts had surfaced even before Lassek and Gaulin radically questioned whether male preferences have an evolutionary basis. For starters, it is unrealistic to take a single indicator such as WHR as a satisfactory indicator of female attractiveness in the complex arena of human mate choice. WHR does not even clearly gauge body fat. The long-established medical approach is to calculate Body Mass Index (BMI), dividing body weight by height squared. Various authors have argued that BMI is the primary factor influencing men’s preferences for women’s body shape. A 2001 paper by Martin Tovée and Piers Cornelissen clearly showed that attractiveness ratings relate more consistently to BMI than to WHR. Subsequently, Ian Holliday and colleagues tested preferences of both sexes with computer-generated 3D female images differing in either BMI or WHR. Results reported in 2011 indicate that attractiveness ratings reflect differences in BMI rather than WHR. Brain scans during tests revealed that changes in BMI, but not WHR, influenced activity in the reward system. Other evidence indicates that satisfactory interpretations require examination of both BMI and WHR—and many other features as well.

Redrawn combination of figures from Tovée & Cornelissen (2001)
A plot of attractiveness ratings for Body Mass Index (BMI) and Waist:Hip Ratio for 50 test profiles shown to 40 male and 40 female students. Males (blue points) and females (red points) showed similar patterns. The relationship of attractiveness scores with BMI is clearly tighter than that with AHR.
Source: Redrawn combination of figures from Tovée & Cornelissen (2001)

A second, particularly important issue is variation across human populations. To be plausibly interpreted as a product of evolution, any feature should be consistently present across different cultures. Studies of WHR were initially confined to the industrialized world, mainly Europe and the USA. Singh’s pioneering studies indicated that men generally tended to rate female images with a WHR around 0.7—a waist span 70% percent of hip width—as more attractive than any with higher values. Subsequent studies in Europe and New Zealand replicated Singh’s findings, abundantly confirming that men in well-nourished societies commonly prefer a female WHR in the range of 0.6 to 0.8. However, it is now known that men in populations close to nature, living at subsistence level, prefer higher WHR values extending up to 0.9.

Note that average WHR in European and American women exceeds 0.75. A WHR between 0.65 and 0.75 is below average, while anything less than 0.55 is very low, approaching the extreme Victorian “wasp waist” value around 0.30. WHR values between 0.75 and 0.85 are above average, while really high values above 0.85 correspond to an almost tubular thick-waisted condition. In fact, a 2008 report from the World Health Organization cited a WHR value of 0.85 as the threshold for obesity.

Differences over space and time

Hugo Felix/Shutterstock.
Two extremes of idealized body shape from the 18-nation survey Perceptions of Perfection — the slimmest from China and one close to the opposite end of the spectrum from Romania.
Source: Fair use permission to repost images granted by Superdrug Online Doctor. Original image credit: Hugo Felix/Shutterstock.

Less formal information concerning cultural influences stems from two recent surveys of female body shape commissioned by Superdrug Online Doctor. The first, entitled Perceptions of Perfection, aimed to assess variation in beauty standards around the globe. Female graphic designers in 18 countries received the same starting photograph of a bikini-clad woman and were asked to render it more attractive for compatriots using Photoshop. Surprisingly big differences between countries emerged. At one extreme, the idealized image from China indicated a body weight of 7.3 stones (46 kg), with WHR of 0.66 and BMI of 16, dangerously thin and in the anorexic range. Near the opposite extreme, the idealized image from Romania corresponded to a weight of 10.4 stones (66 kg), with WHR of 0.69 and BMI of 24, close to the overweight threshold.

The second survey, dubbed The Evolution of Miss Universe, reviewed the history of this international beauty pageant from its origin in 1952 through to 2015. The data show that the BMI of Miss Universe gradually declined by 16 percent over that 63-year period. By contrast, during that same interval, the BMI of the average American woman steadily increased, crossing the overweight threshold of 25 in 1990 and ending up 40 percent higher by 2015. Around 1990, the average BMI for a Miss Universe winner declined below the underweight boundary of 18.5! Body shape of Miss Universe also changed, as illustrated by a comparison of the 1957 winner from Peru with the 2014 winner from Colombia (both from South America). Yet WHR differs by only 8 percent between those two women: 0.71 versus  0.65). Remarkably, the average weight of Miss Universe winners remained virtually unchanged throughout. These findings fit well with those reported by Jeanne Bovet and Michel Raymond in a 2015 analysis of winners of beauty pageants and Playboy centerfold models, which also reviewed classical artworks 1500 to 2500 years ago. Over that 1000-year period, average WHR remained steady and close to the modern European average.

Hugo Felix/Shutterstock.
Contrasting images of Miss Universe 1957 (from Peru, WHR = 0.71) with Miss Universe 2014 (from Colombia, WHR = 0.65), both from South America. Whereas Body Mass Index of women in the general US population increased from about 20 to around 28 between 1952 and 2014, it declined from close to 20 to about 17.5 for Miss Universe winners over that same period. Horizontal dotted lines indicate the threshold for overweight status (BMI greater than 24.9) and the boundary between normal and underweight (BMI less than 18.5).
Source: Fair use permission to repost images granted by Superdrug Online Doctor. Original image credit: Hugo Felix/Shutterstock.

Are WHR and BMI preferences products of evolution?

Doubts about the proposal that evolved features of human mate choice underlie men’s preferences for WHR and BMI are greatly strengthened by two new papers by William Lassek and Steven Gaulin. In a nutshell, claims that low values of WHR and/or BMI reliably indicate fertility and health, hence being targets for natural selection, are incorrect. The reason is very simple. It has long been assumed that fertility and health continuously increase as WHR and BMI decrease. The twin papers by Lassek and Gaulin—one addressing fertility and the other health—review extensive evidence indicating that decreased fertility and poorer health are associated not only with higher values of WHR and BMI but also with the lowest values. Poorer outcomes at the lower end of the spectrum generally remained undetected because effects of the lowest values were rarely tested.

Two successive papers from the same research team neatly illustrate the fundamental problem identified by Lassek and Gaulin. In 2004, Grazyna Jasieńska and colleagues reported that women with low WHR (narrow waists) have higher oestrogen levels. This study has been widely cited as evidence that low WHRs signal enhanced fertility. However, these authors conducted only a two-way comparison of levels between women with WHR values below 0.7 and those with values above 0.8, leaving out those in the middle. Fortunately, four years later the same authors (led by Anna Ziomkiewicz) published a follow-up paper comparing four WHR categories: very low, low, average, high. They found that oestrogen levels are highest in the middle two categories and lowest at the two extremes.

Redrawn version of a figure from Ziomkiewicz et al. (2004).
Plot of oestrogen levels in saliva across the menstrual cycle in women in four different categories of estimated body fat: very low, low, average and high. Women with low or average fat consistently have higher estrogen levels — indicative of enhanced fertility — than women with very low or high fat.
Source: Redrawn version of a figure from Ziomkiewicz et al. (2004).

Lassek and Gaulin provide extensive evidence that maximal and minimal values of both BMI and WHR, indicating fat deposits, are also associated with poorer health, as indicated by mortality and several other indicators. It makes sense that any signals of fertility and health associated with BMI and WHR should not reflect unusually low values. As with human height, it is the intermediate values that are seemingly favoured by natural selection, representing a compromise solution. The average condition, rather than either extreme, is more likely to represent the optimum.

Implications

Accepted notions of purportedly evolved signals indicating fertility and health evidently need reconsideration. Compelling evidence that very low values for WHR and BMI—far from being desirable—reflect low fertility and poor health has far-reaching implications. In particular, it carries a clear message that we should be wary of unattainable beauty standards, which lead many women quite unnecessarily to suffer from a poor self-image. Beauty pageants and the like have contributed to an escalating divergence between idealized images of beauty and real-world conditions.

References

Bovet, J. & Raymond, M. (2015) Preferred women’s waist-to-hip ratio variation over the last 2,500 years. PLoS One 10(4),e0123284:1-13.

Grammer, K., Fink, B., Møller, A.P. & Thornhill, R. (2003). Darwinian aesthetics: Sexual selection and the biology of beauty. Biological Reviews 78:385-407.

Holliday, I.E., Longe, O.A., Thai, N., Hancock, P.B. & Tovée, M.J. (2011) BMI not WHR modulates BOLD fMRI responses in a sub-cortical reward network when participants judge the attractiveness of human female bodies. PLoS One 6(11):e27255.

Jasieńska, G., Ziomkiewicz, A., Lipson, S.F., Ellison, P.T. & Thune, I. (2004) Large breasts and narrow waist indicate high reproductive potential in women. Proceedings of the Royal Society of London B 271:1213-1217.

Lassek, W.D. & Gaulin, S.J.C. (2016) What makes Jessica Rabbit sexy? Contrasting roles of waist and hip size. Evolutionary Psychology evp643459:1-16.

Lassek, W.D. & Gaulin, S.J.C. (2018) Do the low WHRs and BMIs judged most attractive indicate higher fertility? Evolutionary Psychology 16(4), 1474704918800063,2:1-16.

Lassek, W.D. & Gaulin, S.J.C. (2018) Do the low WHRs and BMIs judged most attractive indicate better health? Evolutionary Psychology 16(4), 1474704918803998,8:1-13.

Reiches, M., Shattuck-Heidorn, H., Boulicault, M., Noll, N., Weir, B. & Richardson, S. (2018, November 14) Did men evolve to go for Jessica Rabbit? https://projects.iq.harvard.edu/gendersci/blog/did-men-evolve-go-jessica-rabbit-two-new-papers-take-measure-waist-hip-ratio

Singh, D. (1993) Body shape and women's attractiveness: the critical role of waist-to-hip ratio. Human Nature 4:297-321.

Superdrug Online Doctor Survey 1: Perceptions of Perfection https://onlinedoctor.superdrug.com/perceptions-of-perfection/

Superdrug Online Doctor Survey 2: The Evolution of Miss Universe https://onlinedoctor.superdrug.com/evolution-miss-universe/

Tovée, M.J. & Cornelissen, P.L. (2001) Female and male perceptions of female physical attractiveness in front-view and profile. British Journal of Psychology 92:391-402.

World Health Organisation (2008) Waist Circumference and Waist–Hip Ratio: Report of a WHO Expert Consultation. (pp. 1-39) Geneva: World Health Organization.

Yu, D.W. & Shepard, G.H. (1998) Is beauty in the eye of the beholder? Nature 396:321-322.

Ziomkiewicz, A., Ellison, P.T., Lipson, S.F., Thune, I. & Jasienska, G. (2008) Body fat, energy balance and estradiol levels: A study based on hormonal profiles from complete menstrual cycles. Human Reproduction 23:2555-2563.