Henrich et al. review a large body of evidence showing that in numerous tasks Westerners (often Americans) behave differently from people in other cultures. The target article raises numerous important questions, including: Which psychological characteristics should we expect to vary from culture to culture (studying these would necessarily be cross-cultural) and which should we expect to be universal (studying these could be done on the basis of samples of convenience)? Why are most examples in Henrich et al.'s article drawn from social psychology? Is social cognition particularly likely to vary from culture to culture? Would we find the same cross-cultural variation if we focused on the phenomena discussed in perceptual and cognitive psychology textbooks (provided the cross-cultural data are available)? Do the findings reviewed by Henrich et al. suggest replacing the traditional search for human psychological universals (our human nature) with the search for laws that connect psychological variation to social and ecological conditions?

Although these questions are fascinating, for the sake of space I will focus only on the following issue: It is unfortunate that Henrich and colleagues chose to say little about the causes of the cross-cultural variation they present evidence about, since the significance of this variation depends on the exact nature of these causes. To illustrate this point, I examine three possible explanations of the cross-cultural variation described by Henrich et al., and I consider how these explanations bear on the significance of the findings presented in the target article.

It is well known that when participants conceptualize a given experimental task differently (perhaps because they have different beliefs about the experimenter's goals), they behave differently. (In fact, this is a well-known experimental problem.) To give a single example, Westerners behave differently in economic games depending on how these are framed (e.g., Hoffman et al. Reference Hoffman, McCabe, Shachat and Smith1994). Some of the findings discussed by Henrich et al. (perhaps many) may simply be due to the fact that experimental participants in different cultures conceptualize the experimental tasks differently. In fact, Henrich's own findings (in previous work with other colleagues: Henrich et al. Reference Henrich, Boyd, Bowles, Gintis, Fehr and Camerer2004; Reference Henrich, Boyd, Bowles, Camerer, Fehr, Gintis, McElreath, Alvard, Barr, Ensminger, Henrich, Hill, Gil-White, Gurven, Marlowe, Patton and Tracer2005) about the cross-cultural variation in the Ultimatum, Dictator, and Public Goods games can be at least partly explained in this way, as some researchers on Henrich's team reported that participants assimilated the economic games to real-life situations (e.g., the Orma identified the Public Goods Game with the harambee, a local financial contribution to collective projects; see also Cronk Reference Cronk2007).

Naturally, when participants in an experimental task (within a given culture or across cultures) behave differently because they conceptualize this task differently, this variation does not show that the individuals who behave differently differ psychologically (i.e., that they have different psychological mechanisms, capacities, characteristics, etc.): If one controlled for the differences in task conceptualization across cultures, the cross-cultural variation would disappear. Thus, much of Henrich et al.'s thunder would be stolen if the findings they describe were due to people in different cultures conceptualizing the tasks differently. True, it would still be incorrect to expect people in different cultures to behave similarly in a given experimental task, but this would not entail that the American mind differs from, for example, the Peruvian mind or the Machiguenga mind.

Consider now a second type of explanation. Human beings have evolved numerous domain-specific mechanisms that are designed to interact with the cultural, social, and ecological environment to produce typically (but not necessarily) locally adaptive psychological phenotypes. Although there is little space here to discuss the various ways of specifying this hypothesis (for detail, see Fessler & Machery, forthcoming), let us consider some possibilities. Some evolved mechanisms might have parameters which are set to different values in different environments during development. If the hypothesis of a universal grammar developed by Chomsky is correct, this is how natural languages work. Some evolved mechanisms might provide a template that is completed with culturally local information (see, e.g., Barrett's [Reference Barrett and Buss2005] hypothesis of a universal, evolved mechanism for learning concepts of dangerous animals). It might also be that humans typically possess various strategies for fulfilling a given psychological function (e.g., categorizing or making decisions under uncertainty) and that they learn to rely preferentially on the strategies that are most efficient in their environment, while being able to revert to the other strategies if needed or primed. Many cross-cultural findings might result from people learning to rely preferentially on a particular strategy among the toolbox of strategies that are available to them, since, as discussed by Henrich et al., it is sometimes easy to prime people to adopt the cognitive styles of cultures they do not belong to. If the cross-cultural variation in experimental tasks described in the target article were due to the interaction of universal processes and local environments, this variation would reflect a genuine psychological variation – a significant conclusion: It would show that across cultures, people do harbor different psychological processes (characteristics, styles, etc.), or, at least, that they preferentially rely on different processes (styles, etc.). However, this type of explanation would undermine the idea, suggested throughout Henrich et al.' article, that the Western mind is really peculiar, since the psychological differences across cultures would emerge from the same basic psychological endowment. In a sense, the cross-cultural variation in psychological phenotype would be shallow (particularly if it is merely a matter of people relying preferentially on different strategies in different cultures). Furthermore, albeit being an incomplete research strategy, in need of complementary cross-cultural work, studying Western participants could cast some light on this basic endowment, exactly as one can learn about the universal grammar by studying English syntax.

Consider, finally, a third explanation. Participants in different cultures behave differently in experimental tasks because people acquire different psychological processes, traits, or capacities across cultures as a result of cultural transmission, domain-general learning mechanisms, and the like. To give a single example, this third explanation plausibly applies to the cross-cultural variation in semantic intuitions (for review, see Machery, forthcoming). Philosophers of language have ignored the possibility that the semantic intuitions on which theories of reference are based might vary across cultures. However, evidence shows that while Americans tend to view the reference of proper names as determined by the causal and historical connections between these names and particular individuals, Chinese are more likely to view the reference of proper names as determined by the information speakers associate with these names (Deutsch et al. Reference Deutsch, Carroll, Sytsma and Machery2010; Machery et al. Reference Machery, Mallon, Nichols and Stich2004). Follow-up studies even suggest that Americans are much more likely to hold the former kind of intuitions than are other Westerners such as French participants (Machery & Stich, forthcoming; Machery et al. Reference Machery, Olivola and de Blanc2009). If this third explanation explained not only the variation in semantic, epistemological, and other intuitions described by experimental philosophers (see Stich's commentary), but also the findings summarized by Henrich et al., these findings would then reveal not only that the human psychological phenotype varies across cultures, but also that this variation does not merely result from the interaction of a basic psychological endowment and local environments. Furthermore, studying American participants, as most American psychologists have done for about a century, would often reveal nothing about universal properties of the mind; rather, American psychology would often just be the psychology of Americans.