Dear Skeptics with a “K,”

In a recent episode, you had an evolutionary psychologist on to debunk a number of misconceptions about her field. Kat finished her segment by asking if anyone could supply her with some decent counter-arguments against EvoPsych.

As luck would have it, I’m quite familiar with EvoPsych, having blogged about it multiple times and touched on it in a long read. Here’s the highlights of all that:

  1. EvoPsych holds to a caricature of evolution. It contends that any fitness advantage will prevail in the long run; in contrast, the best evolutionary theory we have now states that evolution is primarily due to neutral genetic drift instead of selection, mild fitness advantages can be rendered extinct due to the froth of neutral drift, and mild fitness losses can survive selective pressures against them. Examples of this are not hard to find: infertility and colour blindness persist despite strong selective pressures against them, and the ability to break down lactose is not universal despite a clear advantage and tens of thousands of years to spread.
  2. It also caricatures how genes express themselves. Biology is messy; something as simple as height is influenced by as many as 400 genes, and the seemingly binary nature of sex isn’t so, with one source I’ve read arguing it was due to complicated interactions between thirty genes. Conversely, trying to change one trait will typically lead to multiple traits changing in unpredictable ways. Yet EvoPsych’s “mind modules” are sharp and well-defined, free of the messy side effects we expect in biology.
  3. EvoPsych relies heavily on assumptions about prehistoric human behaviour which aren’t in evidence. We spent most of our evolutionary history without a sexual division of labour, perhaps only acquiring it when social factors encouraged it. Women participated in battle, explored and settled harsh terrain, both of which also run contrary to the nurturing behaviours that EvoPsych frequently assumes.
  4. If it’s true that behaviour is heavily influenced by evolution, then EvoPsysh researchers have an easy way to silence their critics: do extensive genetic testing and show a strong link between gene expression and behaviour. Yet you rarely hear them talk about genetic testing. If they did, they’d have to make the embarrassing admission that after spending billions of government dollars on the subject, we can’t find a strong link.
  5. As a whole, the field engages in shoddy research practice. One of the strongest results from EvoPsych came from studies of speed dating; over tens of thousands of subjects, they repeatedly found that men are far less picky about partners than women. This seems like a solid result, but one replication asked women to circulate while men sat still, contrary to nearly all previous research. Suddenly, men were the picky ones. EvoPsych researchers made no attempt to look for confounding social factors, and as a result were blind-sided.
  6. As Kat kept bringing up David Buss, I’ll bring up an example involving him too. Back in ’93, he ran a study which found that men preferred to have more sexual partners than women. A replication in 2002 found this too, as well as something unexpected: the data was heavily skewed and obeyed a power law distribution. The mean is very misleading in these situations, yet Buss and his co-authors reported only the mean. When you substitute a measure of central tendency that copes better with outliers, the difference disappears. Either they never did a basic outlier check, they were ignorant of basic statistics, or they didn’t care.
  7. EvoPsych does in fact make strong claims about genetic determinism. Here’s an example from one of David Buss’ textbooks, nicely rebutted by one Richard Dawkins:

    It is part of the male lion’s nature to walk on four legs, grow a large furry mane, and hunt other animals for food. It is part of the butterfly’s nature to enter a flightless pupa state, wrap itself in a cocoon, and emerge to soar, fluttering gracefully in search of food and mates. It is part of a the porcupine’s nature to defend itself with quills, the skunk’s to defend itself with a spray, the stag’s to defend itself with antlers, and the turtle’s to defend itself with a shell. All species have a nature; that nature is different for each species. Each species has faced unique selection pressures during its evolutionary history, and therefore has confronted a unique set of adaptive problems.[1]

    For the mind encased in Platonic blinkers, a rabbit is a rabbit is a rabbit. To suggest that rabbitkind constitutes a kind of shifting cloud of statistical averages, or that today’s typical rabbit might be different from the typical rabbit of a million years ago or the typical rabbit of a million years hence, seems to violate an internal taboo. …

    The word “essentialism” itself wasn’t invented till 1945 and so was not available to Darwin. But he was all too familiar with the biological version of it in the form of the “immutability of species,” and much of his effort was directed towards combatting it under that name. [2]

Now that we’re caught up, we can discuss my main beef with Kat’s segment. Psychology researchers frequently engage in over-generalization. They overwhelmingly study college students, a very WEIRD subject pool, and generalize from them to the entire human population. EvoPsych is no different, and their response to that criticism has been… to ignore it. Or, as Kat does, pretend these cultural differences don’t exist.

By the mid‐1990s researchers were arguing that a set of robust experimental findings from behavioral economics were evidence for a set of evolved universal motivations (Fehr & Gächter, 1998; Hoffman, McCabe, & Smith, 1998). Foremost among these experiments, the Ultimatum Game, provides a pair of anonymous subjects with a sum of real money for a one‐shot interaction. One of the pair—the proposer—can offer a portion of this sum to a second subject, the responder. Responders must decide whether to accept or reject the offer. If a responder accepts, she gets the amount of the offer and the proposer takes the remainder; if she rejects both players get zero. If subjects are motivated purely by self‐interest, responders should always accept any positive offer; knowing this, a self‐interested proposer should offer the smallest non‐zero amount. Among subjects from industrialized populations—mostly undergraduates from the U.S., Europe, and Asia—proposers typically offer an amount between 40% and 50% of the total, with a modal offer of 50% (Camerer, 2003). Offers below about 30% are often rejected.[…]

Recent comparative work has dramatically altered this initial picture. Two unified projects (which we call Phase 1 and Phase 2) have deployed the Ultimatum Game and other related experimental tools across thousands of subjects randomly sampled from 23 small‐scale human societies, including foragers, horticulturalists, pastoralists, and subsistence farmers, drawn from Africa, Amazonia, Oceania, Siberia and New Guinea (Henrich et al., 2005; Henrich et al., 2006). Three different experimental measures show that the people in industrialized societies consistently occupy the extreme end of the human distribution. Notably, some of the smallest scale societies, where real life is principally face‐to‐face, behaved in a manner reminiscent of Nowak et. al.’s analysis before they added the reputational information. That is, these populations made low offers and did not reject.[3]

Kat in particular kept bringing up the hip-waist ratio as an example of a human universal; men are consistently drawn to a ratio of 0.7 across all cultures, according to her. Yet, if we do a quick look on Google Scholar, we find…

Unfortunately, the hypothesis of cultural invariance has not been systematically tested. As noted earlier, research has generally been conducted in Western, industrialized settings using college students as subjects. Recently, Yu and Shepard (1998) investigated WHR preferences among the Matsigenka, who practice swidden agriculture in Peru. They found that low WHR was not preferred in groups who were the most isolated from Western influences.

Yu and Shepard also found that heavier females were preferred over thin females. Female weight is an important element in mate choice (Alley and Scully 1994; Franzoi and Herzog 1987; see also Jackson 1992 for a review). Studies investigating the simultaneous effects of both WHR and weight have revealed that the latter is indeed an important consideration (Singh 1993a, 1994a, 1994c; Singh and Luis 1995), with some studies finding that judgments are influenced more by this factor than by WHR (Furnham et al. 1997; Henss 1995).

In Western cultures, there has been a trend over the past few decades to prefer increasingly thinner women (Polivy et al. 1986). However, being too thin is not preferred either (Furnham and Radley 1989), with women of small to medium build being preferred (Salusso-Deonier et al. 1994; Singh 1993a; see also Lundberg and Sheehan 1994). Cross-cultural inquiry reveals that heavier women are considered more attractive is most societies (Brown and Konner 1987). […]

The findings of Yu and Shepard (1998) do not confirm the hypothesis that preferences for low WHR are culturally invariant. More work is needed to validate this result and to identify the range of preferences across human societies.[4]

Complex adaptations are usually expected to be species-typical (e.g., Tooby & Cosmides, 1992). Cross-cultural tests of Singh’s WHR hypothesis are therefore critical. However, forager women have high fecundity, parasite loads, and caloric dependence on fibrous foods (e.g., Kelly, 1995); all increase WHR. These factors vary cross-culturally, so across ancestral populations: (1) normal female WHR was likely often higher than in Western populations; (2) what constituted locally ‘‘low’’ WHR varied; and (3) average WHR of nubile females and of females at peak fertility varied. Correlates of higher WHR usually indicate lower female mate value, but ability to digest quantities of fibrous food or periodic bonanzas of game, which increase WHR by altering stomach extension, would be advantageous in some ancestral environments. Moreover, the WHR values that are indicative of puberty, fertility, and hormonal irregularities may differ among populations, and environmental fluctuations could change the relationship between reproductive value cues and body morphology within lifetimes.[5]

Initially, empirical studies supported the existence of a cross-cultural preference for low WHR, as this preference was found among a range of populations, including Caucasians, Hispanics, Indonesians, and Kenyans (e.g., Furnham, McClelland, & Omer, 2003; Furnham, Tan, & McManus, 1997; Henss, 1995; Singh, 1993; Singh & Luis, 1995). However, there is growing evidence that WHR preferences also differ between cultures, especially when comparing Western and non-Western, more isolated populations (Marlowe & Wetsman, 2001; Wetsman & Marlowe, 1999; Yu & Shepard, 1998). Some researchers have explained these cultural differences in terms of context-sensitive adaptation, that is, males might adjust their preferred attributes in females, including WHR, contingent on the specific tradeoffs posed by their local ecology (e.g., Anderson, Crawford, Nadeau, & Lindberg, 1992; Marlowe, Apicella, & Reed, 2005; Marlowe & Wetsman, 2001; Pillsworth, 2008; Sugiyama, 2004). In societies where food shortages are common, for instance, a higher female WHR may be associated with health and reproductive success, and this could lead to a local male preference for high WHRs (Sugiyama, 2004). Such context-sensitive mate preferences can become incorporated into the local cultural norms of a society (Gangestad, Haselton, & Buss, 2006), while cultural transmission processes may in turn reinforce and fine-tune these preferences, including preferences for certain bodyshapes (e.g., Swami, Einon, & Furnham, 2007; Yu, Proulx, & Shepard, 2008).[6]

The main findings of the present study are twofold: firstly, there are cross-cultural differences in what men perceive as an attractive and healthy female body shape and secondly, (and perhaps more importantly), different groups of men find attractive divergent body configurations in different groups of women (in this instance, varying by ethnicity). Specifically, our results showed that South African men found attractive the high-WHR black figure with large breasts and the high-WHR white figure with small breasts. By contrast, British Caucasians and British Africans showed a preference for the high-WHR black figure with small breasts and the high-WHR white figure with large breasts. Overall, then, the present findings dispel many universality myths by showing that perceptions of attractiveness vary not only with the observer’s culture, but also with the perceived ethno-cultural affiliation of the person being observed.[7]

Mixed in with studies like those are a number claiming the waist-hip ratio is universal across all cultures, but when reading over them you quickly realize that a) they’re written by Evolutionary Psychologists, and b) a substantial number are authored or co-authored by one person.

Singh, Devendra. “Body shape and women’s attractiveness.” Human Nature 4.3 (1993): 297-321.

Singh, Devendra. “Adaptive significance of female physical attractiveness: role of waist-to-hip ratio.” Journal of personality and social psychology 65.2 (1993): 293.

Singh, Devendra. “Is thin really beautiful and good? Relationship between waist-to-hip ratio (WHR) and female attractiveness.” Personality and Individual Differences 16.1 (1994): 123-132.

Singh, Devendrá. “Waist-to-hip ratio and judgment of attractiveness and healthiness of female figures by male and female physicians.” International journal of obesity and related metabolic disorders: journal of the International Association for the Study of Obesity 18.11 (1994): 731-737.

Singh, Devendra, and Suwardi Luis. “Ethnic and gender consensus for the effect of waist-to-hip ratio on judgment of women’s attractiveness.” Human Nature 6.1 (1995): 51-65.

Singh, Devendra, and Robert K. Young. “Body weight, waist-to-hip ratio, breasts, and hips: Role in judgments of female attractiveness and desirability for relationships.” Ethology and Sociobiology 16.6 (1995): 483-507.

Singh, Devendra. “Female judgment of male attractiveness and desirability for relationships: role of waist-to-hip ratio and financial status.” Journal of personality and social psychology 69.6 (1995): 1089.

Singh, Devendra. “Female health, attractiveness, and desirability for relationships: Role of breast asymmetry and waist-to-hip ratio.” Ethology and Sociobiology 16.6 (1995): 465-481.

Singh, Devendra, and Robert J. Zambarano. “Offspring sex ratio in women with android body fat distribution.” Human Biology (1997): 545-556.

Singh, Devendra, and M. Haywood. “Waist-to-hip ratio representation in ardent sculptures from four cultures.” Annual meeting of the Human Behavior and Evolution Society, Salt Lake City. 1999.

Singh, Devendra. “Waist-to-hip ratio: An indicator of female mate value.” Kyoto Symposium on Human Mate Choice. November. 2000.

Singh, Devendra. “Female mate value at a glance: Relationship of waist-to-hip ratio to health, fecundity and attractiveness.” Neuroendocrinology letters 23.Suppl 4 (2002): 81-91.

Singh, Devendra, and Dorian Singh. “Role of body fat and body shape on judgment of female health and attractiveness: An evolutionary perspective.” Psihologijske teme 15.2 (2006): 331-350.

Singh, Devendra, and Patrick K. Randall. “Beauty is in the eye of the plastic surgeon: Waist–hip ratio (WHR) and women’s attractiveness.” Personality and Individual Differences 43.2 (2007): 329-340.

Singh, Devendra, Peter Renn, and Adrian Singh. “Did the perils of abdominal obesity affect depiction of feminine beauty in the sixteenth to eighteenth century British literature? Exploring the health and beauty link.” Proceedings of the Royal Society of London B: Biological Sciences 274.1611 (2007): 891-894.

Platek, Steven M., and Devendra Singh. “Optimal waist-to-hip ratios in women activate neural reward centers in men.” PLoS One 5.2 (2010): e9042.

Singh, Devendra, and Dorian Singh. “Shape and significance of feminine beauty: An evolutionary perspective.” Sex Roles 64.9-10 (2011): 723-731.

This isn’t necessarily a bad thing. It’s possible a senior researcher could gather enough information about a single topic as to be dominant. If that’s the case, however, we’d expect their later work to be bullet-proof.

It isn’t. One of Singh’s last papers came in 2010. Can you spot the methodological flaws?

Plastic surgeons obtained preoperative measurements of the WHR and BMI of 10 women requesting micrograft surgery [changing their WHR[ for cosmetic reasons. The measurements were repeated postoperatively once healing was complete …. Preoperative and postoperative color photographs were obtained of these same patients (directly from the back, and from an oblique angle; see Fig. 1). Two views were taken of each woman in order to control for possible effects of pose upon attractiveness judgments. The postoperative photographs were taken a few months after surgery allowing for the healing of scars. To control for any differences in skin blemishes between the pre- and postoperative photographs, the images were scanned into a computer and modeled using Adobe Photoshop version 7.0 in order to match their skin tones.[8]

While the main goal of that surgery was waist-hip ratio adjustment, a quick glance at the example photos the skin was also tightened and appears shinier. Were the subjects responding to the skin changes, or the WHR? There’s also no mention of blinding by the people administering the questionnaire, nor of the person who Photoshopped the images. Even though the surgery wasn’t intended to reduce BMI, there was still an average reduction in BMI that came fairly close to hitting statistical significance. There’s also a rich history of fudging before and after photos, and even if none of the participants intended this it’s also easy to unconsciously tweak things.

A decade and a half on, you’d expect the claims about WHR to be getting stronger, not weaker.

Besides being a reliable signal of reproductive age and reproductive capability, low WHR also accurately signals health as defined by absence of major diseases. A large number of studies have found that the risk-factor profile for major obesity-related diseases such as diabetes, heart attack, and stroke varies with the distribution of fat rather than total amount of fat (Bjorntorp, 1988,1991b; Leibel, Edens, & Fried, 1989). WHR, which measures body fat distribution, therefore turns out to be a more powerful predictor of various diseases and symptoms than most other anthropometric measures. […]

In summary, WHR reliably signals female reproductive status (pre- or postpubertal and menopausal), reproductive capability, and, to a certain degree, health status, as inferred from risk for major diseases. If the attributes of good health and reproductive capability are critical in mate selection as posited by evolutionarily based theories, then men should possess mechanisms (conscious or unconscious) to detect these features in women and assign them greater importance than other bodily features in assessing female attractiveness.[9]

Thus, WHR rather than BMI crucially determined cross-cultural concordance in judgments of female attractiveness. This is not to imply that BMI is of no importance in male judgments of female attractiveness. Furnham, Moutafi and Baguma (2002) reported that men in Uganda judge heavier women with low WHR as most attractive. Likewise, it should not be expected that men in all populations would rate one value of the female WHR as most attractive.

It is also important to stress that the men in all populations should not be expected to rate one value of the female WHR as most attractive. Adaptive mechanisms designed by selection process have a degree of flexibility allowing for variation in ecological conditions in human groups (Symons, 1995). Therefore, men in different populations may judge attractiveness of women with different sizes of WHR but not beyond the range of the WHR value (e.g., higher than 0.80). Research shows that the preferences expressed by men in different populations range from a female WHR of 0.60 (e.g., in the Hadza hunter–gatherers of Tanzania; Marlowe, Apicella, & Reed, 2005), through to 0.80 (e.g., in the Bakossi people of Cameroon; Dixson, Dixson, Morgan, & Anderson, 2007), with a WHR value of 0.70 being preferred in a number of populations (Singh, 2006).[8]

So which is it? Is waist-hip ratio a powerful signal of fertility, or a weak one easily overwhelmed by cultural factors or environmental factors? Is 0.7 the ideal we all aim for, or does this critical factor have a fuzzy range? If you can’t hear the goalposts squeaking yet, let’s take a look at the waist-hip ratios of actual women.[10]

Hadza (n=53): 0.83 (0.69–0.94)
Shiwiar horticulturist–foragers of Ecuador (n=38): 0.89 (0.81–1.02)
Young American students (n=68): 0.73 (0.65–0.83)
Poland (n=119): 0.73 (0.64–0.86)
American students (n=55): 0.77 (0.69–0.87)

If men are attracted to women with a waist-to-hip ratio between 0.6 and 0.8, yet the average ratio in various populations range between 0.7 and 0.9, it turns the impressively-scientific sounding claim “men desire women with a WHR of 0.7” into “men generally like women with hips a little thinner than average for where they live.” You might as well shelve that one next to “people like things that are a little exotic, but not too much.”

Evolutionary Psychology isn’t a science; its core assumptions run contrary to the facts, and the methodology of its practitioners is consistently lousy. After reading over a textbook and multiple papers on the subject, it comes across to me as a self-contradictory shotgun blast of folk wisdom, wrapped in a lab coat.


[1] Buss, David M. Evolutionary Psychology: The New Science Of The Mind, 3/E. Pearson Education India, 2009. Pg. 49.

[2] Dawkins, Richard. The greatest show on earth: The evidence for evolution. Simon and Schuster, 2009. pg 23-26.

[3] Henrich, Joseph, Steven J. Heine, and Ara Norenzayan. “The weirdest people in the world?.” Behavioral and brain sciences 33.2-3 (2010): 61-83.

[4] Wetsman, Adam, and Frank Marlowe. “How Universal Are Preferences for Female Waist-to-Hip Ratios? Evidence from the Hadza of Tanzania.” Evolution and Human Behavior 20, no. 4 (July 1999): 219–28. doi:10.1016/S1090-5138(99)00007-0.

[5] Sugiyama, Lawrence S. “Is beauty in the context-sensitive adaptations of the beholder?: Shiwiar use of waist-to-hip ratio in assessments of female mate value.Evolution and Human Behavior 25.1 (2004): 51-62.

[6] Karremans, Johan C., Willem E. Frankenhuis, and Sander Arons. “Blind men prefer a low waist-to-hip ratio.Evolution and Human Behavior 31.3 (2010): 182-186.

[7] Swami, Viren, et al. “Men’s preferences for women’s profile waist‐to‐hip ratio, breast size, and ethnic group in Britain and South Africa.British Journal of Psychology 100.2 (2009): 313-325.

[8] Singh, Devendra, et al. “Cross-cultural consensus for waist–hip ratio and women’s attractiveness.” Evolution and Human Behavior 31.3 (2010): 176-181.

[9] Singh, Devendra. “Adaptive significance of female physical attractiveness: role of waist-to-hip ratio.” Journal of personality and social psychology 65.2 (1993): 293.

[10] Marlowe, Frank, Coren Apicella, and Dorian Reed. “Men’s preferences for women’s profile waist-to-hip ratio in two societies.” Evolution and human behavior 26.6 (2005): 458-468.