On Evolutionary Explanations of Restrictive Eating Disorders, and the Value of Radical Ideas

Evolutionary theory posits that every psychological, behavioural and physical trait expressed by an organism was selected for by aiding the organism in its survival and/or reproduction, and therefore had a functional purpose for existing at some point in evolutionary time. A trait could never exist if the environment was not conducive for its expression (i.e. hinders the organism in survival or reproduction).

By this logic, it might therefore be reasonably assumed (however inconceivably) that there could have been some adaptive function for the existence of anorexia and bulimia at some point in our evolutionary history. They are annoyances in our modern world because there could be a mismatch between its usefulness in the ancestral past and the environment today.

There are at least five major evolutionary explanations for restrictive eating disorders, each with its own flaws, as outlined by Dr Igor Kardum and colleagues from the University of Rijeka in a 2008 paper reviewing evolutionary accounts of anorexia and bulimia, namely (1) the reproduction suppression hypothesis (Wasser & Barash, 1983), (2) the model of parental manipulation (Voland & Voland, 1989), (3) the sexual competition hypothesis (Abed, 1998), (4) the adapted to flee from famine hypothesis (Guisinger, 2003), and (5) the combined concepts of 'social attention holding power' and the 'need to belong' (Gatward, 2007).

The most palatable (and, thus, conventional and popular) idea tends to revolve around competition among females catalysed by the media (sexual competition hypothesis). It is the notion that in wealthier societies, to be able to resist food is seen as a mark of having high status, while in poorer societies, to be able to get food is conversely the indicator of high status; thus anorexia is more prevalent in modernised societies while relatively larger-sized females are exemplified as beautiful. This is propagated via media imagery.

I will not go into detail with all the ideas as it can get rather technical, but in particular I wanted to point out two radical ideas put forth that, while still works-in-progress, were really interesting and reflective of creative, convention-defying attempts to think of new ways to consider this issue.

In particular, I thought Voland and Voland's (1989) model of parental manipulation interestingly attempts to account for why eating disorders tended to happen more with wealthier, higher class individuals. This model draws on kin selection theory and asserts that anorexia may be adaptive (useful) insofar as it increases an anorexic's helping behaviour to her own kin's survival and reproduction while suppressing her own reproductive success (because anorexia leads to a decline in fertility). Non-evolutionary research in the 70s showed that members of anorexic families possessed mutually overprotective attitudes, and anorexic individuals tended to worry constantly about the well-being of their families. In the ancestral past when families were larger, anorexic female helpers could suppress their own reproduction and therefore divert their own resources towards helping collateral kin, leading to greater inclusive fitness (genes belonging to family members). This sets the precedent for some interesting speculations. The model of parental manipulation suggests that anorexia is actually somehow exacerbated by parental influence. Many studies report significant correlations between dominant and overprotective mothers and the probability of anorexic reactions of their daughters. Anorexia reduces a female's fertility and hinders her from bearing additional offspring. Additionally, when a daughter is overprotected and dominated by her mother, her ability to find a mate is also reduced. In wealthy families, males are the more valuable sex as they have the resources to attain more mates. By inducing anorexia (thereby restricting the reproduction of daughters and also reducing their food intake), especially for families in higher societal strata and class, parents can then concentrate investment potential towards sons, who in wealthier families have higher reproductive value.

The next radical idea is Gatward's (2007) combined concepts of 'social attention holding power' and 'the need to belong'. 'Social attention holding power' is defined as an individual's ability to hold attention and gain investment from other members of the group, and this concept is closely related to the degree to which a person feels in control. Naturally, higher status individuals hold more social attention in their group and feel more in control. The need for belonging to a group is a fundamental human need, as ancestors who did not belong to any group were unlikely to survive for long in the harsher environments of the past. Because survival depended on belonging to a group, people had to compete for resources and this competition could lead to exclusion, if one wasn't careful. Anorexia might therefore have been adaptive in the past to prevent competition for food and resources, as well as compete in a more nuanced manner for status (a reference to the more conventional sexual competition hypothesis outlined above), thereby promoting group harmony and reducing the likelihood that one might get expelled. I would personally go on to speculate that in our modern society (essentially functioning and subconsciously perceived as a really large group), nobody feels like the highest status female who doesn't need to conform to restrictive eating disorder, because there is an implicit assumption that the highest status female is the one they see artificially created by the media. So everyone else who feels subordinate will increase her tendency to engage in restrictive eating disorder, an adaptation brought on by the need to maintain the large group's social harmony.

These are certainly radical theories that need to withstand more empirical testing, but it is exciting to read them because they represent interesting attempts to get away from more conventional and acceptable ideas that do not necessarily get us very far, as evidenced by the fact that many extant theories on the causes of eating disorders still have ambiguities and gaps. Of course, there has to be a deal of initial plausibility, lacking which we would just think the idea is quack. But science is ultimately pushed by great thinkers with ground-breaking insights.

On a concluding note, the authors of the review paper highlight one consistent element found among all proposed evolutionary theories of restrictive eating disorders - response to threat. All the major evolutionary explanations can be reasoned as a form of response to threat (to survival and/or reproduction) that leads people (especially females) to develop symptoms of eating disorders. This independently corroborates research linking eating disorders with feelings of insecurity and need for control.



Abed, R. (1998). The sexual competition hypothesis for eating disorders British Journal of Medical Psychology, 71 (4), 525-547 DOI: 10.1111/j.2044-8341.1998.tb01007.x

Gatward N (2007). Anorexia nervosa: an evolutionary puzzle. European eating disorders review : the journal of the Eating Disorders Association, 15 (1), 1-12 PMID: 17676667

Guisinger S (2003). Adapted to flee famine: adding an evolutionary perspective on anorexia nervosa. Psychological review, 110 (4), 745-61 PMID: 14599241

Kardum, I., Gračanin, A., & Hudek-Knežević, J. (2008). Evolutionary explanations of eating disorders Psychological Topics, 17 (2), 247-263.

Voland, E., & Voland, R. (1989). Evolutionary biology and psychiatry: The case of anorexia nervosa Ethology and Sociobiology, 10, 223-240

Wasser, S., & Barash, D. (1983). Reproductive Suppression Among Female Mammals: Implications for Biomedicine and Sexual Selection Theory The Quarterly Review of Biology, 58 (4) DOI: 10.1086/413545

Jealousy, Turning Saints into the Sea?

"Not so long ago jealousy was considered a pointless, archaic institution in need of reform. But like other denials of human nature from the 1960s, this bromide has not aged well. ... The rock musician who wrote 'If you love somebody set them free' also wrote 'Every breath you take, I'll be watching you.'"

- Steven Pinker, on David Buss's The Dangerous Passion


Have you ever felt threatened in the presence of others you perceive to be superior to you? I recall one time when I was a teaching assistant in an introductory psychology course and, in the middle of a discussion about how jealousy is experienced when your partner interacts with someone else who appears to have higher mate value than you, an eager student asked, “Professor, but how do you know if that person has a higher mate value than you?” To which the professor smiled and cheekily said, “Oh, you just know.”

To humour the bemused student, the professor gave some scenarios. If you’re a guy, just imagine this. Some other socially dominant male is talking to your girlfriend or wife, and he’s trying to make her laugh. Worse, she actually laughs along and looks like she’s having a very comfortable and enjoyable time. If you’re a lady, imagine the reverse – your boyfriend or husband has met a younger and physically attractive woman, and now he’s the one trying to make her laugh, and she’s playing along and being very reciprocative. That creeping feeling of alarm bells and jealousy becomes just a tad more resonant.

In the dating and mating game, what exactly are those social cues that get us to be on our guard, to experience inferiority and to feel threatened? Gutierres, Kenrick and Partch (1999), researchers looking at the issue through an evolutionary perspective, explored the oft-cited mating preferences of men for physical attractiveness and women for status and social dominance, and elucidated interesting sex differences in contrast effects.

The researchers gathered data from 91 undergraduate females and 99 undergraduate males and primed the men with either physically attractive men or socially dominant men while, on the other hand, priming the women with either physically attractive women or socially dominant women. Exposure to physically attractive men or women was done by showing participants photographs of people, while exposure to socially dominant men or women was done by getting participants to read a descriptive profile of a person with high dominance.

Interestingly, their study found that men’s self-assessments of desirability were adversely affected by exposure to highly socially dominant men and were relatively unaffected by exposure to physically attractive men. Conversely, women’s self-reports of their mate value were more affected by the physical attractiveness than by the social dominance of the women to whom they were exposed. This demonstrated that humans are sensitive to the selective mate preferences of the opposite gender. If we consistently fail to match up to the quality of our rivals, this can have an effect on how we perceive our own desirability!

More recently, another set of experiments conducted by Maner, Gailliot, Rouby and Miller (2007) also looked at how our state of mind affects the level of attention we give to stimulus objects in our environment.

A total of three studies were done on undergraduate students to explore how this interacts in the scene of human mating. It was found that when participants were primed with feelings of romantic and sexual arousal, a ‘mate-search’ psychological mechanism was activated which resulted in greater attentional adhesion* towards attractive members of the opposite sex. On the contrary, when participants were evoked with feelings of jealousy (imagining a scenario that perhaps closely resembles the one that the professor had painted), a ‘mate-guard’ state of mind was primed which led to greater attentional adhesion to attractive same-sex targets.

So is jealousy simply a manifestation of insecurity? Perhaps the answer is both yes and no. Yes, because it does seem apparent that the mind is designed to experience jealousy when the environment provides feedback on where you stand. If there are many people of the same sex as you in the room who are far more attractive, that’s good reason to feel insecure especially when being evaluated by members of the opposite sex. But jealousy isn’t only just a manifestation of insecurity because it serves an important adaptive function – to alert us to the potential dangers of losing your mate, telling us to be aware of snakes and wolves in the environment, and getting us to turn on our A-game where necessary. As David Buss writes in The Dangerous Passion, jealousy is as necessary as love and sex.

* Attentional adhesion refers to how readily a person tends to a particular stimulus. In most documented cases, this is determined by measuring participants' reaction time taken to respond to stimulus.


Maner JK, Gailliot MT, Rouby DA, & Miller SL (2007). Can't take my eyes off you: Attentional adhesion to mates and rivals. Journal of personality and social psychology, 93 (3), 389-401 PMID: 17723055

Gutierres, S., Kenrick, D., & Partch, J. (1999). Beauty, Dominance, and the Mating Game: Contrast Effects in Self-Assessment Reflect Gender Differences in Mate Selection Personality and Social Psychology Bulletin, 25 (9), 1126-1134 DOI: 10.1177/01461672992512006

Buss, D. M. (2000). The Dangerous Passion: Why Jealousy Is As Necessary As Love and Sex. New York: Free Press.

Racial Differences in the Concept of Beauty

Are average composite faces the most attractive faces or are highly attractive faces markedly different from average faces? Rhee & Lee (2010) agrees with Perrett & Yoshikawa (1994) that the most attractive face is actually the average of attractive faces and that an average face; while attractive, is not the most attractive.

They also argue that previous concepts of beauty such as the divine proportion (golden ratio) are not a good measure of beauty across different races and should not be used as an overarching universal indicator of beauty. Between different races, there appears to be different characteristics that are deemed beautiful. They merged some of the most attractive female faces of African, Caucasian, Chinese and Japanese people respectively, to create the images below.

They also mentioned some of the defining characteristics of beauty for the different races.

• African: Narrow nose, smaller and more acute eyes, smaller upper lip, slender chin compared to the average African face.
• Caucasian: Somewhat masculine, narrow palpebral (eyelids) height, angulated and squared mandible (lower jaw), protruding cheek and fuller lips compared to the average Caucasian face.
• Chinese: Narrow cheek, slim and thin face, lantern jaw.
• Japanese: relatively longer face, slightly slanted eyes, sharp chin and chubby cheeks.
  

Unfortunately, they did not conduct any experimental study to compare attractiveness ratings of such faces versus other faces that are considered beautiful based on traditional morphometrics. It would also have been interesting to look at how the male composite faces would look like. 

Rhee SC, & Lee SH (2010). Attractive Composite Faces of Different Races. Aesthetic plastic surgery PMID: 20953953

Perrett DI, May KA, & Yoshikawa S (1994). Facial shape and judgements of female attractiveness. Nature, 368 (6468), 239-42 PMID: 8145822

What the Presence of Attractive Young Women can do to Men

Much has been said about the female preference for resources and the male preference for physical attractiveness, but at the time of James R. Roney's (2003) writing little had been done to tease out cognitive mechanisms that underlie this adaptive preference.

Roney thus set out to ascertain the ability of ecological cues to prime and activate psychological constructs related to mate attraction and establish linkages between human mating and social cognition.

In his first study, participants - young students from the 10th and 12th grades of a Midwestern high school - were made to answer three large booklets of surveys. However, the manipulation of the environment within which the surveys were answered was as follows: in the first condition, all participants were male; in the second condition, all participants were female; in the last condition, males and females were present during the study. Without knowing what the experimenter was up to, participants answered questions in the surveys, and nested in those surveys were questions related to one's attitudes towards wealth and resources.

The results fascinatingly appear to support evolutionary theories about human mating. Male students in the mixed-sex environment reported higher valuations of material wealth than did male students in the same-sex environment.


The young men in the mixed-sex condition also reported higher ratings of having an active dating life. These findings suggest that the presence of females may have primed implicit mate attraction goals and, subsequently, the activation of cognitive attitudes associated with mating objectives (detailed manipulation checks were conducted via cleverly placed questions on items such as current relationship status and mate preferences, reducing the possibility of confounding variables).

Now that the first experiment appears to be consistent with evolutionary theory predictions, Roney sought to find out if other mating goal-related attributes in men can be primed. In his second study, male participants were exposed to advertisements featuring either younger female models or older female models, after which they filled out a questionnaire.

The results again confirm evolutionary theory hypotheses - men in the younger models condition reported higher valuations of wealth (replicating the findings of the first study), had a greater desire to display/showcase talent and, interestingly, listed self-descriptive traits that increase men's odds of attracting women (this was confirmed through separate ratings of the male participants' self-descriptive traits by women), such as ambitiousness and aggressiveness.

Roney's study thus brings evolutionary psychology one step further by utilizing ecologically realistic stimuli, in the process demonstrating powerful but previously unknown psychological effects. Specific to this study, visual exposure to young women caused significant changes in the attitudes and personality trait descriptions of the young male participants. In particular, young men who were exposed to young women reported far more favourable attitudes towards material wealth than did men exposed to either other men or older women.

This makes sense because if securing a mate was an important task in ensuring the survival of one's lineage (without which those of us alive today wouldn't be here), then there should be psychological mechanisms present to facilitate the achievement of such goals, and men should thus be sensitive to cues that relate to both potential mates and resources. Using an adaptive basis for understanding psychology can also prove useful, because without this evolutionary context of mating, such stable behavioural changes demonstrated in Roney's study can, at best, only appear random and lead to invalid conclusions.


Roney, J. (2003). Effects of Visual Exposure to the Opposite Sex: Cognitive Aspects of Mate Attraction in Human Males Personality and Social Psychology Bulletin, 29 (3), 393-404 DOI: 10.1177/0146167202250221

Spicy food and collectivism: How the brain shapes culture

We are used to thinking of culture as a social factor and not a biological factor. We attribute dispositions such as being individualistic or being collectivist to the country that one was brought up in, but no one has really looked into why certain cultures tend to be that way. An emerging field of research called cultural neuroscience says that cultural values can be shaped by the brain and genes.


For example, in one striking example I read about quite recently, one hypothesis put forth for the reason why Asian people like spicy food was because spices conferred natural bacteria killing properties that was especially important in a humid climate where food went bad. Over time, the hypothesis goes, people who liked spicy food more and ate more spicy food were less prone to stomach diseases that killed the others, thus passing on their genes for the next generation. A similar finding was found when examining lactose intolerance. Lactose intolerance is far more prevalent in certain regions of Asia where the rearing of lifestock for milk is less common. In Europe however, up to 95% are able to digest lactose, and this is reflected in their preference for milk products like cream and cheese.


In this review by Way and Lieberman, they sought to answer the question as to why certain cultures tend towards individualism and collectivism. They reason that because of evolution, genes that change brain function and influence the cultural norms we adopt and we institute are selected for between people born in different regions. For people brought up in one region that was say marked by famine, grouping together and helping one another might have brought about greater survival for the people, hence the genes that promote this thinking get passed on. In a separate part of the world, marked by conflict perhaps, survival would favor people who think for themselves and for their immediate family members. Over time, those different selective pressures would have promoted different social behaviors in different regions.


What mechanisms might have promoted these behaviors? They reviewed work from scientists studying the distribution of several genetic alleles. Previous work has shown that variation in the serotonin transporter gene, a very important neurotransmitter associated with emotion and reward, was associated with individual differences in social sensitivity. People with the short version show greater reaction to social events such as death or birth of children, regardless of whether it was positive or negative. When these scientists studied the distribution of these alleles in different cultures, surprise surprise! They found that the short version of this allele was much more prevalent in collectivist cultures than individualist cultures.



*higher score on individualism collectivism scale indicates higher individualism.


The authors hypothesize that since this allele makes people more sensitive to being socially excluded, it promotes individuals to tend and befriend, leading to a cultural trend of being more collectivist. There's more to read about other such alleles in the review, but seeing as to how this post is quite wordy already, I'll stop here :)




Sherman, P., & Billing, J. (1999). Darwinian Gastronomy: Why We Use Spices BioScience, 49 (6) DOI: 10.2307/1313553

Way, B., & Lieberman, M. (2010). Is there a genetic contribution to cultural differences? ... SCAN, 5 (2-3), 203-211 DOI: 10.1093/scan/nsq059