Journal of Experimental Social Psychology 45 (2009) 271–274

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Journal of Experimental Social Psychology

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The primal warrior: Outgroup threat priming enhances intergroupdiscrimination in men but not women

Masaki Yuki *, Kunihiro YokotaHokkaido University, Department of Behavioral Science, N10 W7, Kita-ku, Sapporo, Hokkaido 060-0810, Japan

a r t i c l e i n f o a b s t r a c t

Article history:Received 17 June 2008Revised 11 August 2008Available online 26 August 2008

Keywords:Intergroup discriminationGender differencePrimingOutgroup threatMinimal group paradigmAdaptation

0022-1031/$ - see front matter � 2008 Elsevier Inc. Adoi:10.1016/j.jesp.2008.08.018

* Corresponding author.E-mail address: myuki@let.hokudai.ac.jp (M. Yuki)

Previous evidence suggests that, compared with females, male psychology and behavior is more stronglyoriented toward intergroup conflict and competition. This study tested whether male coalitional psychol-ogy is so deeply ingrained that it could be activated even by subtle cues in the environment suggestingintergroup conflict. We used a priming method to test if being unwittingly exposed to an offensive mes-sage from an outgroup member in one type of intergroup context (i.e., inter-cultural) would enhancemale’s and female’s intergroup discrimination in reward allocation in a completely irrelevant intergroupcontext (i.e., artificial laboratory group). The results showed that, as predicted, the outgroup threat prim-ing enhanced discrimination in men but not women.

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The pervasiveness of intergroup conflict and competition, and itsunderlying psychological mechanisms, has long been one of themost vigorously investigated topics in the scientific study of humanbehavior (e.g., Allport, 1958; Darwin, 1871; Sumner, 1906). Humansspontaneously make ‘‘us versus them” categorizations and quicklydevelop deep emotional attachments to in groups even when mem-bership is based on trivial criteria, such as the flip of a coin (Brewer,1979; Ostrom & Sedikides, 1992; Tajfel & Turner, 1979). Humansreadily discriminate against members of outgroups (Fiske, 2002)and engage in costly altruistic actions to defend their group (De Cre-mer & Van Vugt, 1999; Sherif, Harvey, White, Hood, & Sherif, 1961).

However, evidence also suggests that there may be a sex differ-ence in the tendency to actively engage in intergroup conflict andcompetition, both of which are more prevalent in males than fe-males. For instance, research on traditional societies shows thattribal warfare is almost exclusively in the domain of men (Cha-gnon, 1988). Even in modern societies, intergroup hostility andcompetition predominantly occurs between male groups (Pratto,Sidanius, & Levin, 2006). In social psychological experiments,men were found to engage more actively in competitive be-tween-group interactions than women (Pemberton, Insko, & Scho-pler, 1996), and to show more increased cooperation in publicgoods game when told that the level of cooperation within theirgroup would be compared with that of out groups (Van Vugt, DeCremer, & Janssen, 2007). Furthermore, in line with Pratto et al.’s(2006) suggestion, Yamagishi and Mifune (2008) found that when

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groups were comprised entirely of men, male participants showedingroup bias in cooperation in a Prisoner’s Dilemma game evenwhen no reciprocity from ingroup was expected; however, thispattern was not observed among female participants. Similarly,developmental studies have reported that boys engage more ac-tively in intergroup competition than girls (Benenson, 1993; Lever,1978). Moreover, the male hormonal system has been found to bemore sensitive to intergroup competition than that of females(Wagner, Flinn, & England, 2002). Finally, the tendency for malesto collectively compete with and attack outgroups has also beenobserved among animals other than humans such as chimpanzeeswho also have complex sociality (Wrangham, 1999).

Some evolutionary minded social scientists have argued that thispropensity toward intergroup conflict and competition in males hasbeen selected for through humankind’s ancestral history of frequentand violent intergroup conflict. The ‘male-warrior hypothesis’ (VanVugt et al., 2007) maintains that, compared with women, men aremore likely to engage in intergroup rivalry for (reproductive) benefits,for example, access to mates and prestige, frequently outweigh thecosts associated with participation in intergroup conflict, such as in-jury and death (Buss, 1999; Chagnon, 1988; Tooby & Cosmides,1988). Consequently, men have acquired a complex coalitional psy-chology: a set of domain-specific cognitive systems that are designedto cope with intergroup competition (Kurzban & Leary, 2001) .

The current study

One question, however, remains unanswered: exactly how dee-ply ingrained is coalitional psychology in males? If intergroup con-

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272 M. Yuki, K. Yokota / Journal of Experimental Social Psychology 45 (2009) 271–274

flict was a primary adaptive task for males, and if selection pres-sure has shaped a male, but not female, domain-specific mecha-nism to cope with it, males may be particularly sensitive to cuesin the environment that suggest intergroup conflict. Furthermore,when attending to these cues, men may more readily execute‘adaptive’ behaviors (i.e., ingroup cooperation and outgroup dero-gation) to defend the ingroup/defeat the outgroup, even if the cuesare not directly relevant to the focal intergroup context. In order totest this hypothesis, we examined if exposure to cues of outgroupthreat in one intergroup context (e.g., an inter-cultural context)would enhance men’s and women’s intergroup discrimination ina completely irrelevant context (i.e., an artificial group setting ina laboratory). We used the priming technique (Higgins, Rholes, &Jones, 1977) to manipulate outgroup threat cues, because previousresearch has suggested that priming of an adaptive task can elicitpsychology and behaviors to cope with the task (Navarrete, Kurz-ban, Fessler, & Kirkpatrick, 2004). We predicted that unwittinglybeing exposed to cues of outgroup threat would enhance inter-group discrimination in men, but not women.

Experiment

Design and procedure

Participants were 115 undergraduate students (63 males and 52females) at Hokkaido University, Japan. They were randomly as-signed to either the control or outgroup threat condition.1 Six per-sons participated in each experimental session. If less than sixparticipants were available in the session, confederates were usedto fill in.

The experimental session consisted of two ostensibly unrelatedexperiments in sequential order. First, the experimenter in the‘‘first experiment” asked participants to engage in a so-called ‘‘lan-guage task.” The task was to search for and circle all the nouns inthree essays within 5 min. The actual purpose of the task was toprime outgroup threat, which was done by manipulating the con-tent of the second essay. In the outgroup threat condition, the es-say was supposedly written by a person from another culture, whocriticized the participants’ own culture in a very offensive way.2 Onthe other hand, the essay in the control condition was about art, andhad nothing to do with intergroup relations. After this task, partici-pants engaged in a simple calculation task for 30 min which servedas a distraction.

After the first experiment, a new experimenter entered theroom and started the ‘‘second experiment.” Although the experi-menter in the first experiment had been casually dressed, thenew experimenter wore a white lab coat; this was to make it obvi-ous that the two ‘‘experiments” were unrelated. Although partici-pants were told that they were to work on two decision makingtasks, the actual purpose was to assess intergroup discriminationin artificial laboratory groups using the minimal group paradigm(Tajfel, Billig, Bundy, & Flament, 1971). First, participants wereasked about their preference for 7 pairs of abstract paintings. Then,they were told that they were to be divided into two 3-persongroups based on their artistic preferences that had just been as-sessed (Klee group vs. Kandinsky group). They were notified oftheir own group memberships (for convenience, everyone was as-signed to the Klee group), group memberships of others in thegroup remained unknown.

Next, participants performed a reward allocation task. In orderto control for an alternative motivation to produce intergroup dis-crimination in the minimal group paradigm, or maintenance of re-

1 Gender ratio varied across experimental sessions.2 An English translation of the scenario can be found in the Appendix.

ciprocal exchange with ingroup members, we employed themethod used by Karp, Jin, Yamagishi, and Shinotsuka (1993). Morespecifically, participants were asked to draw a lottery, and werethen informed that as the result of the lottery, only themselvesand one outgroup member had been selected to perform the allo-cation task. Participants were aware that their own reward was al-ready fixed, and would be distributed by the experimenter afterthe whole session was finished. Other participants were suppos-edly to work on different tasks, which did not involve distributionof rewards. In actuality, however, all participants were assigned tothe reward allocation task (see Yamagishi, Jin, & Kiyonari, 1999, forthe detailed logic behind this procedure).

In order to prevent confounds resulting from a specific measureof intergroup discrimination, participants were asked to completetwo different sets of measures of intergroup discrimination: a fixedmoney allocation task, and a Tajfel matrix. The fixed money alloca-tion task (Karp et al., 1993) consisted of one simple question, ask-ing participants to decide how much to allocate between oneingroup member and one outgroup member from the total of500 Japanese yen (approximately 5 US dollars). The Tajfel Matrices(Billig & Tajfel, 1973; Tajfel et al., 1971) asked participants tochoose one of thirteen pairs that combined amount of rewards to-ward an ingroup member and toward an outgroup member. Partic-ipants made decisions on six types of randomly ordered matrices.They were led to believe that the allocated money would be con-verted into real money to be given to the ingroup- and outgroup-receivers at the completion of the experiment.

After the allocation task, participants were probed for suspicionregarding the cover story of the experiments, and then debriefed,paid, and thanked for their cooperation.

Results

We first ran a 2 (gender: male vs. female) � 2 (priming: controlvs. outgroup threat) analysis of variance on the fixed money alloca-tion. There was no significant main effect of gender, F(1,111) = .16,p = .69, g2

p ¼ :001, while the main effect of priming was significant,F(1,111) = 4.37, p = .039, g2

p ¼ :038. It was, however, qualified bythe predicted Gender � Priming interaction, F(1,111) = 3.93,p = .050, g2

p ¼ :034. As shown in Fig. 1a, simple main effects analy-ses showed that, for males, the amount allocated to the ingroupmember was greater in the outgroup threat condition(M = 281.86, SD = 79.84), than in the control condition(M = 237.18, SD = 71.78), F(1,111) = 9.30, p = .003, g2

p ¼ :077,whereas no significant effect of priming was obtained for females(female control: M = 254.52, SD = 13.38; female outgroup threat:M = 255.71, SD = 21.81), F(1,111) = .005, p = .94, g2

p ¼ :000.3

Next, we performed the same 2 (gender: male vs. female) � 2(priming: control vs. outgroup threat) ANOVA on the Favoritismscore, a composite index of intergroup discrimination calculatedfrom Tajfel’s Matrices (r = .35, p < .01: see Grieve & Hogg, 1999,for the method for calculation). There was no main effect of gender,F(1,117) = 3.07, p = .083, g2

p ¼ :027, but a significant main effect ofpriming, F(1,117) = 11.67, p = .001, g2

p ¼ :095. This effect was, how-ever, qualified by a significant Gender � Priming interaction,F(1,117) = 5.23, p = .024, g2

p ¼ :045. Simple main effects analysesshowed that, exactly replicating the pattern obtained for the fixedmoney allocation (see Fig. 1b), male’s intergroup discriminationwas greater in the outgroup threat condition (M = 2.24,SD = 3.63), than in the control condition (M = .55, SD = 1.31),

The simple main effect between males and females in the control condition wasnot significant: F(1,111) = 1.32, p = .25, g2

p ¼ :012. Significance tests from equality(250 yen): male control: t(27) = �.945, p = .353, d = .179; male outgroup threat:t(34) = 2.36, p = .024, d = .399; female control: t(30) = 1.88, p = .070, d = .338; femaleoutgroup threat: t(20) = 1.20, p = .244, d = .262.

220

250

280

310

Female

Ingr

oup

Allo

catio

n (i

n JP

yen

)ControlOutgroup threat

-1

0

1

2

3

Female

ControlOutgroup threat

Male

Favo

ritis

m S

core

Male

A

B

Fig. 1. Mean intergroup discrimination, assessed by (a) (upper panel) the amount ofreward allocated to the ingroup member (as opposed to the outgroup member) outof the total of 500 Japanese yen (0–500 yen), and (b) (lower panel) the Favoritismscore (�13–+13), as a function of gender and priming condition. Error barsrepresent standard errors above and below the mean.

M. Yuki, K. Yokota / Journal of Experimental Social Psychology 45 (2009) 271–274 273

F(1,111) = 9.14, p = .003, g2p ¼ :007, whereas this difference was not

significant for females (female control: M = .08, SD = .89; femaleoutgroup threat: M = �.14, SD = 1.06), F(1,111) = .13, p = .72,g2

p ¼ :000.4

Discussion

A number of previous studies have suggested that, comparedwith women, men tend to engage more actively in intergroup con-flict and competition. In the present study, we found that, for menbut not women, unwittingly being exposed to cues of outgroupthreat in one intergroup context (i.e., inter-cultural) enhancedintergroup discrimination in the subsequent reward allocation taskin the completely irrelevant context (i.e., an artificial group settingin a laboratory). These findings are in line with the view that selec-tion pressure has shaped male, but not female, coalitional psychol-ogy, or a deeply ingrained domain-specific mechanism to copewith intergroup conflict and competition. As a result, males areparticularly attentive even to subtle situational cues indicatingoutgroup threat around them, and readily show ingroup-defend-ing/outgroup-defeating behavior even when unwittingly exposedto such cues.

The present findings have important implications for theories ofintergroup behavior. Some theorists have argued that discrimina-tion in the minimal group paradigm requires the expectation that

4 The simple main effect between males and females in the control condition wasnot significant: F(1,111) = .68, p = .41, g2

p ¼ :006. Significance tests from the scalemidpoint: male control: t(27) = 2.23, p = .034, d = .423; male outgroup threat:t(34) = 3.66, p = .001, d = .619; female control: t(30) = .507, p = .616, d = .091; femaleoutgroup threat: t(20) = �.616, p = .545, d = .134.

one will be favorably treated by other members of one’s own group(Rabbie, Schot, & Visser, 1989; Yamagishi et al., 1999), and havedemonstrated that discrimination disappeared when participantsare led to believe that they were the only one in the ingroupwho performed the reward allocation task (e.g., Karp et al.,1993). In the present study, however, male participants showedapparent intergroup discrimination in exactly the same experi-mental situation as that of Karp et al. (1993), with the only excep-tion being that participants in this study were unwittingly exposedto cues of outgroup threat in a seemingly irrelevant context in ad-vance. While there are certainly multiple sources for intergroupdiscrimination (e.g., Cottrell & Neuberg, 2005; Kurzban & Neuberg,2005; Stroebe, Lodewijkx, & Spears, 2005), coalitional psychologyadapted to cope with intergroup conflict and cooperation is astrong and deeply ingrained force which underlies men’s inter-group discrimination in the minimal group paradigm, and probablydiscriminatory behaviors in the real world as well.

There are some issues worthy of future investigation. First, itwould be good to include manipulation check items to assess par-ticipants’ perception of outgroup threat in general. Second, futurestudies should investigate what specific psychological process(es)mediate the priming effect of outgroup threat on discriminatorybehaviors among males.

Acknowledgements

This research was supported by Grant-in-Aid for Encourage-ment of Scientists (A) from the Ministry of Education, Culture,Sports, Science, and Technology of Japan to Masaki Yuki(13710053). The authors would like to thank Kosuke Takemurafor his help throughout this project, Dr. Toshio Yamagishi and Dr.Toko Kiyonari for kindly showing us their research protocols andmaterials, and Joanna Schug and Vicki Yeung for their helpful com-ments on earlier versions of this article. Finally, we would like tothank colleagues at Hokkaido University who helped us recruitingpotential participants from their classes. Correspondence shouldbe sent to Masaki Yuki, Department of Behavioral Science, Hokka-ido University, N10 W7 Kita-ku, Sapporo, Hokkaido 060-0810 Ja-pan; email: myuki@let.hokudai.ac.jp.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.jesp.2008.08.018.

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