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Much research on human behaviour andpsychology assumes that everyoneshares most fundamental cognitive

and affective processes, and that findingsfrom one population apply across the board.A growing body of evidence suggests that thisis not the case.

Experimental findings from several disci-plines indicate considerable variation amonghuman populations in diverse domains, such

as visual perception, analytic reasoning,fairness, cooperation, memory and the herit-ability of IQ1,2. This is in line withwhat anthropologists have longsuggested: that people from West-ern, educated, industrialized, richand democratic (WEIRD) socie-ties and particularly Americanundergraduates are some of themost psychologically unusual peo-ple on Earth1.

So the fact that the vast majorityof studies use WEIRD participantspresents a challenge to the under-

standing of human psychologyand behaviour. A 2008 survey ofthe top psychology journals found that 96% ofsubjects were from Western industrializedcountries which house just 12% of theworlds population3. Strange, then, that researcharticles routinely assume that their results arebroadly representative, rarely adding even acautionary footnote on how far their findingscan be generalized.

The evidence that basic cognitive andmotivational processes vary across populationshas become increasingly difficult to ignore. Forexample, many studies have shown that Ameri-

cans, Canadians and western Europeans rely onanalytical reasoning strategies which separateobjects from their contexts and rely on rules toexplain and predict behaviour substantiallymore than non-Westerners. Research also indi-cates that Americans use analytical thinkingmore than, say, Europeans. By contrast, Asianstend to reason holistically, for example by con-sidering peoples behaviour in terms of theirsituation1. Yet many long-standing theories ofhow humans perceive, categorize and rememberemphasize the centrality of analytical thought.

It is a similar story with social behaviourrelated to fairness and equality. Here, research-

ers often use one-shot economic experimentssuch as the ultimatum game, in which a player

decides how much of a fixed amount to offera second player, who can then accept or rejectthis proposal. If the second player rejects it,neither player gets anything. Participantsfrom industrialized societies tend to dividethe money equally, and reject low offers. Peo-ple from non-industrialized societies behavedifferently, especially in the smallest-scale non-market societies such as foragers in Africa andhorticulturalists in South America, where peo-

ple are neither inclined to make equal offersnor to punish those who make low offers4.

Recent developments in evolutionarybiology, neuroscience and related fields sug-gest that these differences stem from the wayin which populations have adapted to diverseculturally constructed environments. Ama-zonian groups, such as the Piraha, whoselanguages do not include numerals abovethree, are worse at distinguishing large quan-tities digitally than groups using extensivecounting systems, but are similar in their abil-ity to approximate quantities. This suggests thekind of counting system people grow up with

influences how they think about integers1

.

Costly generalizationsUsing study participants from one unusualpopulation could have important practicalconsequences. For example, economists havebeen developing theories of decision-makingincorporating insights from psychology andsocial science such as how to set wages and examining how these might translateinto policy5. Researchers and policy-makersshould recognize that populations vary con-siderably in the extent to which they displaycertain biases, patterns and preferences in

economic decisions, such as those related tooptimism1. Such differences can, for example,

affect the way that experienced investorsmake decisions about the stock market6.

We offer four suggestions to help puttheories of human behaviour and psychologyon a firmer empirical footing. First, editors andreviewers should push researchers to supportany generalizations with evidence. Second,granting agencies, reviewers and editors shouldgive researchers credit for comparing diverseand inconvenient subject pools. Third, granting

agencies should prioritize cross-disciplinary,cross-cultural research. Fourth, researchers

must strive to evaluate how theirfindings apply to other populations.There are several low-cost ways toapproach this in the short term: oneis to select a few judiciously chosenpopulations that provide a toughtest of universality in some domain,such as societies with limited count-ing systems for testing theoriesabout numerical cognition1,2.

A crucial longer-term goal isto establish a set of principles that

researchers can use to distinguishvariable from universal aspects of

psychology. Establishing such principles willremain difficult until behavioural scientistsdevelop interdisciplinary, international researchnetworks for long-term studies on diversepopulations using an array of methods, fromexperimental techniques and ethnography tobrain-imaging and biomarkers.

Recognizing the full extent of human diver-sity does not mean giving up on the quest tounderstand human nature. To the contrary,this recognition illuminates a journey intohuman nature that is more exciting, more

complex, and ultimately more consequentialthan has previously been suspected Joseph Henrich, Steven J. Heine and Ara

Norenzayan are in the Department of Psychology,

University of British Columbia, Vancouver, British

Columbia V6T 1Z4, Canada. Joseph Henrich is

also in the Department of Economics.

e-mail: joseph.henrich@gmail.com

1. Henrich, J., Heine, S. J. & Norenzayan, A. Behav. Brain Sci.doi:10.1017/S0140525X0999152X (2010).

2. Henrich, J., Heine, S. J. & Norenzayan, A.Behav. Brain Sci.doi:10.1017/S0140525X10000725 (2010).

3. Arnett, J.Am. Psychol.63,602614 (2008).4. Henrich, J. et al.Science327, 14801484 (2010).5. Foote, C. L., Goette, L. & Meier, S. Policymaking Insights from

Behavioral Economics (Federal Reserve Bank of Boston, 2009).

6. Ji, L. J., Zhang, Z. Y. & Guo, T. Y.J. Behav. Decis. Making 21,399413 (2008).

Most people are not WEIRDTo understand human psychology, behavioural scientists must stop doing most of their experiments on

Westerners, argue Joseph Henrich, Steven J. Heine and Ara Norenzayan.

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Vol 466|1 July 2010

OPINION

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