Evolutionary Theories and Men's Preferences for Women's Waist-to-Hip Ratio: Which Hypotheses Remain? A Systematic Review

Evolutionary Theories and Men's Preferences for Women's Waist-to-Hip Ratio: Which Hypotheses Remain? A Systematic Review. Jeanne Bovet. Front. Psychol., June 4 2019https://doi.org/10.3389/fpsyg.2019.01221

Abstract: Over the last 25 years, a large amount of research has been dedicated to identifying men's preferences for women's physical features, and the evolutionary benefits associated with such preferences. Today, this area of research generates substantial controversy and criticism. I argue that part of the crisis is due to inaccuracies in the evolutionary hypotheses used in the field. For this review, I focus on the extensive literature regarding men's adaptive preferences for women's waist-to-hip ratio (WHR), which has become a classic example of the just-so storytelling contributing to the general mistrust toward evolutionary explanations of human behavior. The issues in this literature originate in the vagueness and incompleteness of the theorizing of the evolutionary mechanisms leading to mate preferences. Authors seem to have rushed into testing and debating the effects of WHR on women's attractiveness under various conditions and using different stimuli, without first establishing (a) clear definitions of the central evolution concepts (e.g., female mate value is often reduced to an imprecise concept of “health-and-fertility”), and (b) a complete overview of the distinct evolutionary paths potentially at work (e.g., focusing on fecundability while omitting descendants' quality). Unsound theoretical foundations will lead to imprecise predictions which cannot properly be tested, thus ultimately resulting in the premature rejection of an evolutionary explanation to human mate preferences. This paper provides the first comprehensive review of the existing hypotheses on why men's preferences for a certain WHR in women might be adaptive, as well as an analysis of the theoretical credibility of these hypotheses. By dissecting the evolutionary reasoning behind each hypothesis, I show which hypotheses are plausible and which are unfit to account for men's preferences for female WHR. Moreover, the most cited hypotheses (e.g., WHR as a cue of health or fecundity) are found to not necessarily be the ones with the strongest theoretical support, and some promising hypotheses (e.g., WHR as a cue of parity or current pregnancy) have seemingly been mostly overlooked. Finally, I suggest some directions for future studies on human mate choice, to move this evolutionary psychology literature toward a stronger theoretical foundation.

Introduction

The ratio between the waist and the hips circumferences (Waist-to-Hip Ratio, or WHR) is a physical characteristic often used as an example to show that evolution shaped human mate preferences. It is also an example of just-so storytelling in evolutionary psychology. In 1993, Devendra Singh suggested that WHR represents a strong predictor of women's physical attractiveness (Singh, 1993a). He also argued that men's preference for a mate with a low WHR is adaptive, because a low WHR reflects a woman's high mate value. But what exactly is this “mate value”? During the past 25 years, the evolutionary literature on WHR and women's attractiveness has flourished, but the definition of this “mate value” is rarely expressed. In evolutionary biology, mate value is attached to the concept of reproductive success: a woman with a high mate value will increase the reproductive success of her mate(s). An increase in reproductive success is characterized by an increased number of descendants in next generations and can be achieved in various ways. First, survival until reproduction is indispensable. Second, the number of children born during an individual's lifespan is also crucial. But the survival and the quality of these children will directly impact their own reproductive success, and hence the number of grandchildren in the next generation, thus ultimately influencing the reproductive success of the grandparents. In short, a woman has higher value as a potential mate if she increases the number and quality of descendants a man will have (including the ones he has with other women). The question then is which of these components of reproductive success are actually linked to a mate's WHR? To answer this, I assemble the numerous hypotheses exposed since the idea of the WHR as an indicator of women's mate value was first suggested in 1993. These hypotheses are examined to determine which of the characteristics linked to WHR are most likely, in theory, to be translated into an increase in the reproductive success of the woman's mate.

The objective of this review is 2-fold. The first goal is to gather and pool all the existing evolutionary hypotheses regarding men's preferences for a certain (low, high or average) WHR. There are many reviews about men's preferences for women's WHR, but this is the first exhaustive review of the hypotheses mentioned in these studies. The second purpose of this paper is an in-depth theoretical examination of these hypotheses, which are often only briefly justified and, in some cases, have never been properly developed.

Most of the debate around WHR and attractiveness has centered on two other questions: “Is the preference for a low WHR universal?” and “Is WHR the best predictor of the attractiveness of women's bodies?” I will not address these two questions extensively here (it is beyond the scope of this paper), but a brief commentary seems necessary at this point. A preference for a relatively low WHR (i.e., low relatively to men's WHR, or low relatively to the average female WHR) has been observed in a large number of studies, including a wide range of populations and methods. With that in mind, results show that there is some variation in what is the exact value of the ideal WHR [reviewed in Brooks et al. (2015) and Cashdan (2008)]. The second debate concerns WHR as the “best” predictor for attractiveness. Authors have debated whether WHR or BMI is the best predictor of attractiveness and mate value (Tassinary and Hansen, 1998; Tovée et al., 1999; Furnham et al., 2005; Cornelissen et al., 2009a,b). As could be expected, the results vary according to the population and stimuli used. Other measurements have also been proposed to replace WHR (for example, hip or waist size alone, abdominal depth or waist/stature ratio: Brooks et al., 2010, 2015; Lassek and Gaulin, 2016). The objective of this paper is not to decide if WHR is the best measure of physical attractiveness or if the ideal WHR is universal or not. For our purposes, it is sufficient to note that the effect of WHR on attractiveness is widespread (even if the value of the preferred WHR varies), and large enough to warrant questions about its possible adaptive basis.