The 13 th International Conference on Social Dilemmas

The 13 th International Conference on Social Dilemmas Kyoto, 20 -24 th August 2009 Sex Differences in In-group Bias using a PD Game with Minimal Groups Nobuhiro Mifune Toshio Yamagishi (Hokkaido University)

Ingroup bias Ingroup: the group which one belongs to Outgroup: the group which one does not belong to Ingroup bias: Cooperation or altruism toward ingroup members and/or aggression or discrimination against outgroup members

Ingroup bias is ubiquitous in social life (e. g. , wars and conflict between nations, religions, or races; corporations; schools, etc. ) Social psychologists have conducted many studies, and have shown that ingroup bias occurs even in Minimal Groups (Tajfel et al. , 1971).

Minimal groups Groups formed on a trivial criterion, past interaction, no interdependence between participants A B No Does. Klee ingroup bias occur. Kandinsky when group A participants play. B one-shot. APD games with A A members from the same minimal group B B (ingroup)A or members from the other B B minimal group (outgroup)?

Did ingroup bias occur? Cooperation levels in one-shot PD game (Jin & Yamagishi, 1997) Ps cooperated more with ingroup members than outgroup members: ingroup bias occurred even in minimal groups.

Why does ingroup bias occur? Social Identity Theory: Ø When people are categorized into a group, they like members of their own group, and cooperate with ingroup members accordingly. Ø Simply having a partner from the same group is sufficient for ingroup bias to occur. Is this “true”?

Did ingroup bias occur? Cooperation levels of one-shot PD game (Jin & Yamagishi, 1997) just having a partner from the same group is NOT sufficient for ingroup bias to occur Common Knowledge Private Knowledge

Common Knowledge? Private Knowledge? Common Knowledge My partner is from the same (or different) group. Ps Participants could expect cooperation from their ingroup partner. → ingroup bias occurred

Common Knowledge? Private Knowledge The partner is from the same (or different) group, but… Which group the partner is from? Ps Ps Participants could not expect cooperation from their ingroup partner. So, ingroup bias did not occur

Did Ingroup bias disappear in the private knowledge condition? It has been repeatedly shown that ingroup bias completely disappeared in the private knowledge condition using several different kinds of games. ü PD game (Jin & Yamagishi, 1997; Kiyonari, 2002; Yamagishi, Mifune, Liu & Pauling, 2008) ü Allocator choice game (Suzuki, Konno & Yamagishi, 2007) ü Dictator game (Hashimoto, Mifune & Yamagishi, the 2 nd day presentation; Yamagishi & Mifune, 2008)

Did ingroup bias disappear in the private knowledge condition? (cont’d) Some evolutionary psychologists have predicted that there should be sex differences in ingroup bias. Males’ adaptive tasks in evolutionary history included dealing with intergroup conflict. So, males should have the tendency to cooperate with ingroup member and attack or compete with outgroup member. üMale Warrior Hypothesis (van Vugt, de Cremer & Janssen, 2007) üPrimal Warrior Hypothesis (Yuki & Yokota, 2008)

Did Ingroup bias disappear in the private knowledge condition? (cont’d) However, no sex difference in ingroup bias was found in the past experiments (e. g. , Jin & Yamagishi, 1997; Yamagishi, Mifune, Liu & Pauling, 2008). Is this because of the mixed-sex situation? (i. e. , in the Jin & Yamagishi (1997) or other experiments, both males and females participated at the same time) How about in groups of only male or female Ps?

Experiment: Replication of Jin & Yamagishi Klee Kandinsky Klee Only males Kandinsky Klee Kandinsky

Experiment: Replication of Jin & Yamagishi Kandinsky Klee Kandinsky When we replicate Jin & Yamagishi Only females (1997) using same-sex groups, can we find any sex difference in ingroup bias? Kandinsky Klee

Cooperation levels Result of Jin & Yamagishi (1997) <. 01

Cooperation levels relative to the control condition <. 01 Result of Jin & Yamagishi (1997) <. 01 ns. ns. Aggression or discrimination against Ingroup bias in minimal groups is based on outgroup members did not occur ingroup cooperation, not aggression toward outgroup members (e. g. , Mummendey & Otten) Control: Ps did not know their partner’s group membership

Correlation of Cooperation between Ingroup and Outgroup Partial correlation coefficients between cooperation with ingroup members and outgroup members in the common knowledge condition and private knowledge condition, controlling for the default cooperative tendency (i. e. , cooperation level in the control condition) Female 　 Private Out-group Male In-group 0. 38 　 Private Out-group p = 0. 002 　 Common Out-group In-group 0. 34 p = 0. 007 In-group 0. 21 p = 0. 078 　 Common Out-group In-group 0. 10 p = 0. 430

Correlation of Cooperation between Ingroup and Outgroup Partial correlation coefficients between cooperation with ingroup Outgroup cooperation was not negatively member and that of outgroup member in the common knowledge correlated with ingroup cooperation. condition and that in the private knowledge condition with controlling the default cooperative tendency (i. e. , cooperation Ingroup cooperation level of the control condition) does not entail aggression toward outgroup members (cf. Brewer, 1999) Female 　 Private Out-group Male In-group 0. 38 　 Private Out-group p = 0. 002 　 Common Out-group In-group 0. 34 p = 0. 007 In-group 0. 21 p = 0. 078 　 Common Out-group In-group 0. 10 p = 0. 430

Summary Previous studies (e. g. , Jin & Yamagishi, 1997) ü People cooperated with ingroup members even in the minimal groups. ü Ingroup cooperation occurred only in the common knowledge condition, but not in the private knowledge condition. Current study ü In a same-sex situation (groups of all males or all females), males showed ingroup cooperation regardless of the knowledge condition. ü The results for all-female groups was completely same as in the past experiment (Jin & Yamagishi, 1997). How can we explain these results?

Discussion Why did participants show ingroup cooperation only in the common knowledge condition in the past studies and among females in this study? Group heuristic: People have a “default decision rule” to cooperate with ingroup members. The “Group” is a container of generalized exchange (Yamagishi & Kiyonari, 2000). People assume “If I cooperate with an ingroup member, the other ingroup member may also cooperate with me. ” In other words, when they can expect the cooperation from ingroup members, they will cooperate with ingroup members.

Discussion Why did males show ingroup cooperation even in the private knowledge condition (i. e. , when they could not expect cooperation from their ingroup partner), and yet, they did not show any aggression toward the outgroup? => Male-specific intergroup aggression (Male Warrior Hypothesis or Primal Warrior Hypothesis) cannot explain the two findings simultaneously.

Discussion Why did they cooperate with ingroup members unconditionally? Display of Solidarity Hypothesis (Gould, 1999, 2000) One reason to form groups is to prevent aggression from others. Individuals who successfully show solidarity toward a group can avert aggression. On the other hand, individuals who are in less cohesive groups can become targets of aggression. The unconditional nature of cooperation makes the ingroup solidarity credible. Considering the costs of being attacked (e. g. , death), the incentive for free-riding may not be so high.

Discussion Why are displays of solidarity specific to men? Men are the primary targets of inter-group aggression (Sidanius & Veniegas, 2000). Because of this, it is adaptive for men to be sensitive to detecting intergroup conflict situation in order to avert aggression. If the benefits of displaying solidarity (i. e. , reducing costs of conflict/warfare) are greater among men than among women, such benefits should exceed the costs of displaying group solidarity (unconditional cooperation to the ingroup, etc. ).

Thank you Yamagishi, T. , & Mifune, N. (2009). Social exchange and solidarity: in-group love or out-group hate? Evolution and Human Behavior, 30, 229 -237.