Reflections on the WEIRD Evolution of Human Psychology

Does psychology’s over-reliance on American undergraduates distort our image of the human species?

Imagine you’re in a room with one hundred psychopaths. The first thing you’ll probably want to do is leave that room. However, once you do, you discover a booth installed with one-way glass where you can watch what’s taking place without anyone seeing you. Comfortably seated you observe a strange experiment taking place. A few of the individuals have on white coats and are carrying around clipboards while most are being run through a battery of psychological tests.

Slowly the frantic activity begins to make sense. Some test subjects are looking at video monitors and have sensors attached that measure their galvanic skin response to the images they see. Others are being given questionnaires to elicit their answers to a variety of social situations. Still others are being placed inside an fMRI scanner to measure the blood flow in different regions of their brains. All of these are standard methods in the psychological and brain sciences, but what’s most striking to you is the fact that this study is being conducted on psychopaths by psychopaths.

Some time later, after the subjects of the study have left and the researchers have analyzed their data, you observe the scientists discussing the results. “Subjects reported a consistent disregard for the feelings of others and a lack of remorse in cases where they’ve hurt someone,” reported one researcher from his report based on answers from the questionnaire. “This is consistent with the fMRI results that show significantly less blood flow to the paralimbic system, especially those regions involving emotion,” adds another looking at her analysis of the brain scan data. “The skin conductance data also agree, showing little or no emotional reaction to violent or disturbing imagery,” reports a third who seems to be the one in charge of this strange experiment. “These results suggest that the human species is inherently deceitful, antisocial, and has little regard for others. Evolution has honed us to be selfish actors interested only in maximizing our individual potential at the expense of everyone else.” The other researchers nod in agreement, for that is certainly what the results show.

From where you sit it’s clear that something is terribly wrong with this study. Because they were only testing psychopaths the researchers’ data may be consistent but it’s only applicable for that one group. However, because the researchers were also part of that group and saw the world the same way, they made the false assumption that humans everywhere behaved that way too. This is known in the sciences as confirmation bias, preferring conclusions that support someone’s own personal preferences or outlook even when the evidence is weak to nonexistent. This usually happens unconsciously. It’s the tendency we all have to prefer interpretations that support our preexisting beliefs. This is why scientific studies try to get a large and diverse sample size to draw their conclusions from. Obviously the above example could never happen in real life, but it represents a simplified thought experiment to address a larger question about how research on human cognitive evolution is carried out. What happens if researchers inadvertently fall prey to confirmation bias at a societal level? Would the same false results that affected the hypothetical psychopath study also affect other assumptions about human nature?

Addressing this question Canadian psychologists Joseph Henrich, Steven J. Heine and Ara Norenzayan at the University of British Columbia (where I am also located) recently published a paper in the journal Behavioral and Brain Sciences. Their research documents how most of the studies that psychologists claim show human universals are really just extrapolations from a single social group, the cultural equivalent of the psychopaths in my example. As The New York Times wrote in their review:

According to the study, 68 percent of research subjects in a sample of hundreds of studies in leading psychology journals came from the United States, and 96 percent from Western industrialized nations. Of the American subjects, 67 percent were undergraduates studying psychology — making a randomly selected American undergraduate 4,000 times likelier to be a subject than a random non-Westerner.

The subpopulation that Henrich and colleagues found to be overrepresented are entirely WEIRD (Western, Educated, Industrialized, Rich, and Democratic) societies. While it’s bad enough that WEIRD American undergraduates are serving as our model for human behavior, what their paper goes on to document should be of concern to all behavioral and cognitive researchers (particularly those whose work focuses on human evolutionary explanations). When these affluent American and non-Western populations are compared there are important differences in domains as seemingly unrelated as visual perception, fairness, cooperation, spatial reasoning, moral reasoning, reasoning styles, and even the heritability of IQ. In all cases American undergraduates didn’t simply differ, they differed substantially. Nevertheless, they form the basis of most researchers’ assumptions about human nature even though, as Henrich and colleagues conclude, “this particular subpopulation is highly unrepresentative of the species.”

To highlight one domain in which American undergraduates differ from most other populations in the world consider a neutral category like visual perception. Looking at the figure below, which horizontal line, “a” or “b”, would you estimate is longer?

If you chose “b” than you are in line with a substantial number of Americans (both undergraduates and children) who chose the same one. In fact, both lines are identical in length. This has become known as the Müller-Lyer Illusion, named after the German psychiatrist Franz Carl Müller-Lyer who first discovered it in 1889. However, if you show the same two lines to people in many non-Western societies (particularly hunter-gatherer societies) they will be more likely to identify the two lines as identical. In a series of cross-cultural experiments in 1966 psychologist Marshall H. Segall manipulated the length of line “a” until it reached the point where respondents reported that the two were identical in length. The results of these experiments can be seen in the graph below.

The strength of the Müller-Lyer Illusion in 16 separate societies.
Reproduced from Henrich et al. (2010).

The vertical column represents the Point of Subjective Equality (PSE), or how long line “a” had to be before respondents said they were the same length. In other words, PSE is a measure of how effective the illusion is for different populations. As the graph indicates, Americans (labeled as “Evanston” for where Segall tested undergraduates at Northwestern University in Illinois) were the population most fooled by this illusion and required line “a” to be an average of one-fifth longer than line “b” for both to be perceived as equal. They were followed by white South Africans from Johannesburg. In contrast, the San foragers of the Kalahari were not affected by the illusion while most other societies in the study were only marginally affected.

Why would Americans be so susceptible to this illusion? Our environment. Because most Americans are raised in a society where horizontal lines and sharp corners make up much of modern architecture. The brains of American children (and, presumably, most children in highly industrialized countries) have adapted to make optical calibrations as a result of their unique environment. The San and many other small-scale forager or horticultural societies don’t grow up in a manufactured environment so their brains are unaffected by such illusions.

A similar difference can be found in what psychologists call “folkbiological reasoning.” Cognitive scientists testing children drawn from U.S. urban centers (where most universities are located) have developed an influential developmental theory suggesting that there is a cognitive shift that takes place between ages 7 and 10. As Henrich and colleagues state in their paper:

Before age 7, urban children reason about biological phenomena by analogy to, and by extension from, humans. Between ages 7 and 10, urban children undergo a conceptual shift to the adult pattern of viewing humans as one animal among many.

This shift has been considered a process that all human children go through. The problem with this reasoning, Henrich points out, is that it only applies to one subset of children: those who live in urban environments. Similar cognitive tests of children in Native American communities in Wisconsin and among the Yukatek Maya communities in Mexico showed none of the empirical patterns that the American urban children displayed. The answer, of course, is that urban children grow up in an impoverished environment where they will rarely, if ever, interact with animals other than humans (with the occasional dog or cat kept as a pet). This is a very different environment from many non-Western societies, and certainly from the one our remote ancestors lived in.

As a result, the “unnatural” environment of these WEIRD children resulted in anthropocentric assumptions about the natural world until they were taught differently by teachers or from television (though I often wonder how an increased exposure to nature when they’re young might influence adult attitudes about the importance of environmental issues). Given this, as Henrich points out, it makes as much sense to use urban children in studies of human cognition as it would to study “normal” physical growth in malnourished children. Because the psychologists who carried out these studies likely grew up in an urban environment themselves (rural students are significantly less likely to attend graduate school, particularly at top-ranking institutions) the confirmation bias of such studies are perpetuated. It’s almost as if psychopaths were conducting research on themselves and claiming their results were universal.

Of course, there is one important difference between psychopaths and American society. Psychopathy, and Anti-Social Personality Disorder more generally, is a diagnosed mental disorder that has a partial basis in genetics, not just the environment. Nevertheless, the confirmation bias that exists in many psychological studies represents a distortion of reality that has just as much potential to be passed on to subsequent generations. The fact that empirical differences exist on identical psychological studies when replicated cross-culturally should make evolutionary researchers take caution (especially Evolutionary Psychologists who are most guilty of essentializing these studies). What Henrich and colleagues have called for is a renewed effort to conduct similar cross-cultural research before making grand claims about the species as a whole. At the very least it means that researchers and science journalists alike should be careful not to perpetuate ideas that appeal to their own beliefs but which may have no basis in other societies. To do otherwise would be to confuse our own reflection in a hall of mirrors with a crowd of people making identical movements. That would clearly be psychotic.


Henrich, J., Heine, S., & Norenzayan, A. (2010). The weirdest people in the world? Behavioral and Brain Sciences, 33 (2-3), 61-83 DOI: 10.1017/S0140525X0999152X

Guest Blogger Profile: ERIC MICHAEL JOHNSON has a master’s degree in evolutionary anthropology focusing on great ape behavioral ecology. He is currently a doctoral student in the history of science looking at the interplay between evolutionary biology and the sociopolitical lives of scientists. His work has appeared in the Journal of Human Evolution, the American Journal of Physical Anthropology, Discover, Seed, Wildlife Conservation, ScienceBlogs, and The Huffington Post. This guest post by Eric Michael Johnson is part of his Primate Diaries in Exile blog tour. You can follow other stops on this tour through his RSS feed, The Primate Diaries on Facebook, or by following him on Twitter.

photo provided courtesy of Ben Jones

Related Posts Plugin for WordPress, Blogger...
This entry was posted in Guest Post and tagged , , . Bookmark the permalink.

30 Responses to Reflections on the WEIRD Evolution of Human Psychology

  1. As a postscript I think it’s important to point out that “psychopath” is not the current terminology. I used the outdated form as a literary device because of its cultural connotations. As of 2000, according to the DSM-IV-TR, psychopathy and sociopathy are both classified under Antisocial Personality Disorder — but, see Hervé & Yuille (2007) for a reassessment.

  2. Ollitapio Pursiainen says:

    It´s amazing to know this. I guess test is not guite right. In university people might be some way antisosial or something like that. They like to work alone. But it´s not necessarily because they are psykopathy or sociopthy. For examble asperger syndrom might give some advance in studying if life is in order.

    • Thanks for your comment, Ollitapio. My intent in using the hypothetical psychopath study was not to say that American undergrads have a mental disorder (insert joke here) but that looking only at one group can bias scientific results, even if multiple studies are done to confirm their empirical accuracy. When 96% of psychology studies are done on WEIRD populations, you can only make conclusive claims about WEIRD groups. When these findings are extended to the entire human species it is assuming that everyone (regardless of environment) is the same. Henrich has shown that there is reason to doubt this assumption.

  3. Pingback: Quick Links | A Blog Around The Clock

  4. Pingback: Scientia Pro Publica: Answers to 28 popular and not-so-popular questions

  5. Pingback: Open Laboratory 2010 – submissions so far | A Blog Around The Clock

  6. Pingback: News » Blog Archive » Editor’s selections: WEIRD evolution, pelican’s beak, and rainforest reactors

  7. Dusty says:

    Drawing universal conclusions on the human physiological condition from some people I went to college with is a bit of a scary thought. It’s nice to focus placed on how we know something, rather than what we think we know, especially in terms of extrapolating results to a far larger population. Glad to see you’re still getting your writing out there, despite the SB debacle.

  8. Thanks Dusty, it’s great to hear from you.

  9. Yoron says:

    Very nice, it’s so appearant that we work this way but so many refuse to acknowledge it. We are truly social creatures, adapting handsomely to our environment, expecting our adaption to reflect ‘universal truths’.

    As for the difference between a sociopath and a psychopath?
    If you’re in the same room as one, there isn’t :)

  10. Phil Moon says:

    The good thing about this revealing study is that now, corrections and adjustments can be made and new studies done to check the results. The sad part is that anti-science types will see this as a reason to further discount science. Still, it’s an interesting and enlightening study. That for the great read.

  11. Pingback: Open Laboratory 2010 – submissions so far | A Blog Around The Clock

  12. Pingback: Open Laboratory 2010 – submissions so far | A Blog Around The Clock

  13. Pingback: Open Laboratory 2010 – submissions so far | A Blog Around The Clock

  14. Pingback: Open Laboratory 2010 – three weeks to go! | A Blog Around The Clock

  15. Pingback: WEIRD : Ne sommes-nous tous que des étudiants américains ? | Evopsy

  16. Pingback: Open Laboratory 2010 – two weeks to go! | A Blog Around The Clock

  17. Pingback: Open Laboratory 2010 – only eight days till the deadline! | A Blog Around The Clock

  18. Pingback: Only three days to go – Open Laboratory final stretch for submissions! | A Blog Around The Clock

  19. Pingback: It’s getting hot – submissions for Open Laboratory 2011 are flying in by the dozens per hour… how about you? | A Blog Around The Clock

  20. Pingback: Open Laboratory 2010 – the final stretch! | A Blog Around The Clock

  21. Pingback: Open Laboratory 2010 – submissions now closed – see all the entries | A Blog Around The Clock

  22. Annie says:

    If we subscribe to the theory that we all evolved from apes, would that not mean that we all would have the same genetics?

    Would just like a professional opinion on this.

    Your article is quite well written, thank you for taking the time to post it.

  23. EMJ says:

    Thanks for the question Annie. There is still genetic variability even within the same species whether we’re looking at humans or other animals. But this genetic variability is small compared to the difference between one species and another. Every generation there are small modifications to the DNA that has been passed on from an individual’s parents. Most of these are neutral and a few are harmful. But every once in a while these changes will allow an individual to do better in their specific environment and allow them to have more offspring. This allows their gene variant to become spread more widely. These changes represent the raw material that evolution has to work with.

  24. Gerald Fnord says:

    Well, I’d say that this sort of science were suffering from a reaction to pre- and counter-Enlightenment thought, which tended to err (wildly) on the side of people of different lands, races, cultures, and relgions’ being fundamentally different. (J. de Maistre, a leading counter-Enlightenment thinker, stated baldly that there is no such thing as an ‘human being’—there are Frenchmen, Englishmen,….)

    This is not to excuse the error, but to explain it, because understanding something is preferable to not doing…though that might jsut be my strong Enlightenement bias showing, as is caring about my biases.

  25. Pingback: More than models | Gene Expression | Discover Magazine

  26. Pingback: More than models | Biology News by Biologged

  27. Pingback: Links November 2011 | Revolusionline

  28. Pingback: Carnival of Evolution No. 28 | Jeremy Yoder

  29. Pingback: ResearchBlogging editor’s selections: WEIRD evolution, pelican’s beak, and rainforest reactors | Skulls in the Stars