Darwin After Dark: Evolution of Attraction

Introduction

Human beings are inherently limited. The burdens of life cannot be addressed at once, shrugged off our shoulders or borne alone. Every action is taken at the consequence of another action and every goal is asserted at the cost of another goal. One could choose the pursuit of food over sex, or the pursuit of money over relaxation, but all too often the simultaneous pursuits of these goals are impossible - or at least cause tension. Human evolution is no different. Life and living things can be conceptualized as bodies acquiring and expending energy. Everything has a cost, so one must choose wisely what they do. Throughout time, certain choices, so to speak, have resulted in the perpetuation of traits that were functional, meaning more likely to help an individual or group survive and reproduce. Some of those traits are directly tied to human relationships. Unlike the desire for water, which can exist well outside the bounds of the social world, the desire for sex, and relationships, is inherently social. So certain traits, that pertain to sex and relationships, are perpetuated by human selection. That is to say, that the human being, consciousness, plays a role in evolution via mate selection. Our constraints demanded functional strategies that produced the dynamics of modern relationships. Here, I will lay out evidence of evolution’s fingerprint on our most personal pass-time: sexual pursuit. 

Attraction

Attraction, from the Latin attractionem, means so to “draw together or pull '', and anyone who’s found themselves attracted to another individual has felt the gravitational grip around their heart draw them into orbit. And while this phenomenon is the subject of countless pieces of art and pop culture, from Romeo and Juliet to How I Met Your Mother, it may best be explained through evolution; admittedly an objective description versus a description of the subjective phenomenon. What are the criteria for attraction - what about an individual is attractive? Generally speaking research has shown that, when searching for a mate, men put a greater emphasis on good looks, while women put a greater emphasis on financial prospects, suggesting the potential for resource acquisition, and personality, though depending on the context (Buss, Schackelford, Kirkpatrick, & Larsen, 2001; Braun & Bryan, 2006). 

Men to Women

To increase the resolution on that generality, I’ll begin with the signals that attract men, beginning with sexual dimorphism, the differences in appearances between the sexes. Women with more slender cheekbones and fuller lips, generally feminine features, have been found to be more attractive - cross culturally and including traditional South American groups with little exposure to western beauty standards (Gangestad & Scheyd, 2005). While fascinating, this begs the question: why? One answer is reproductive value (RV), the generally age-based likelihood of reproductive success. To elaborate, feminine features were more likely to be present in women of a certain age. Women at that age were more likely to reproduce successfully. Then the men who were attracted to the feminine features, were more likely to mate with women who were at the age where they could successfully reproduce - perpetuating both the feminine features that acted as a signal for the likelihood of reproductive success, and the attraction to such features. It may also be a marker of condition or health. One study found that masculine features in women were positively correlated with respiratory disease. And the number of days infected was associated with facial symmetry (Thornhill & Gangestad, 2006). This is evidence in favor of this position. It could be that the traits that leave one exposed to diseases also affect facial symmetry and dimorphism. So those who selected for these traits were more likely to have a healthy partner, and reproduce - thus perpetuating attraction to, and the trait itself.

One peculiar, if not interesting, study found that women’s reproductive cycle also plays a role. Exotic dancers were found to be tipped more when in estrus than in any other period measured (Miller, Tybur, & Jordan, 2007). This suggests that sexual readiness influences the attractiveness of females… and the pocket books of men. The evolutionary theory being that men who found women in estrus more attractive were far more likely, should they mate, to reproduce successfully. 

There’s also been evidence for the waist-to-hip ratio (WHR) as being attractive to men. In a cross cultural study conducted by Furnham, Moutafi, and Baguma, they found that a smaller WHR was considered more attractive by all the cultures tested, and by both men and women (2002). An evolutionary explanation of this is that women with wider hips and a slimmer waist are more likely to reproduce successfully while also indicating general health. This is reinforced by another study that found that women with large breasts and a small WHR had greater fecundity, measured as 17-beta-oestradiol (E2) and progesterone (Jasienska, Ziomkiewicz, Ellison, Lipson, & Thune, 2004). This harkens back to the RV hypothesis. Given that WHR is a trait associated with greater likelihood of reproduction, those that were attracted to those traits were more likely to successfully reproduce - perpetuating the trait itself and the attraction to it.

Women to Men

While masculine facial features play less of a role in women’s attraction to men, other male-typical, testosterone induced, body features do (Gangestad & Scheyd, 2005). One physical feature that is associated with female attraction to men is the waist to shoulder ratio (WSR). In a remarkably rich study done by Margaret Braun and Angela Bryan (2006), waist to shoulder ratio positively predicted the desire for a one-time sexual encounter. However, personality played a role as well. 

Our findings suggest that body shape and personality do influence the desirability of a potential mate, though in different ways for men and women. Men, to a greater extent than women, self-reported that physical features including face, body, and weight were important to their judgments of the desirability of a target. Conversely, women considered personality, intelligence, and career choice to be significantly more important in determining target desirability than did men. (p. 814) 

Specifically, they found that the personality trait Agreeableness predicted the desire for dating and long term relationships - in both men and women - though the effect was greater with women. Also, in a 2010 study of 20,000 couples, the personality traits agreeableness and conscientiousness were found to be predictors of marital satisfaction (Dyrenforth, Kashy, Donnellan, & Lucas). This shows that women’s preferences tend towards personality, generally, and men’s towards physicality, by contrast. 

Why might this be? The reasoning may harken back to human limitation on energy but the constant need for resources. According to Kenrick, Sadalla, Groth, and Trost (1990), and the parental investment model, women are more stringent in their long term mate selection because they have traditionally held a greater investment in the child. Meaning, women carry a greater risk in a relationship because, when pregnant, they are stuck with the child - and  are vulnerable as a result. Women may need a partner that can provide during that trying time so they stringently select a partner more likely to do so. 

Conclusion

There is no system we know of that is more complex than the human being and our interactions. As a result, this foray into the world of human relationships has, tragically, been inevitably inadequate in explaining human relationships. However general, some conclusions may be asserted: human beings have developed strategies for selecting mates. In short term relationships or sexual encounters, the criteria is, predictably, skin deep. In long term relationships, both men and women look for personality characteristics. Across the sexes, men tend towards physical traits, aimed at the health and reproductive value of their mate and the species, by extension, and women aim more for personality, reliability, and ability to acquire resources, or the character of the mate and the species by extension. Men and women have major overlaps in the traits they find desirable, but when they differ, they compensate for each other to ensure the quality of health and character of their children and the species.

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