Evidence of conflict and discrimination between groups is all around, which is not to say that this is inevitable, as many groups coexist peacefully most of the time. Ingroup bias refers to a form of favoritism toward one’s own group or derogation of another group. Many theories of intergroup relations in social psychology try to explain this phenomenon. Ingroups are groups to which a person belongs, and outgroups are groups to which a person does not belong (and which could therefore become target for ingroup bias). There is an almost infinite number of groups to which a person belongs, depending on how he or she categorizes the social world.
Humans are primarily social animals. Not only is group living of clear contemporary importance, but also stands for a fundamental survival strategy that has likely characterized the human species from the beginning. The ways in which people understand their group membership consequently play a critical role in social conflict, agreement and intergroup integration. Sherif et al.’s (1961) first observations demonstrated in addition that intergroup relations begin to sour soon after people classify others in terms of ingroup and outgroup. People are more generous and forgiving in their explanations for the behaviours of ingroup relative to outgroup members. Positive behaviours and successful outcomes are more likely to be attributed to internal, stable characteristics of the ingroup personality than outgroup members, and while negative outcomes are more likely to be credited to the personalities of outgroup members than of ingroup members. It appears that the self is an important factor in forming impressions about new groups. Very small information about an ingroup and outgroup tends to project our own positive features onto the ingroup attributing contrastive features to outgroups. Self-imaging plays an important role in the initial exploratory stages when people become members of a new group. . Because of the centrality of the self in social perception.
There is little empirical research on the motives that underlie contributions to a given intergroup conflict. Halevy et al. [Halevy N, Bornstein G, 2008] presented an experimental design in which subjects who decided to contribute to the collective good of their group had two options. Either they contributed in a way that would not affect the payoffs of outgroup members or in a way that would also decrease the payoffs of the other group. It turned out that contributors hardly chose the option that harmed outgroup members, providing first support for the claim that subjects did not intend to decrease payoffs of outgroup members. In a more elaborate experimental design Abbink et al. found contributions to the group public good to be substantially above the Nash equilibrium prediction (which was strictly positive in their design). Furthermore, the authors reported that there were no significant effects of outgroup past behavior on individuals’ contributions and conjectured that “subjects seem to focus more on the interaction with the other team members than on that with the rival team, but at this point one can only speculate whether this can be generalized and how this is best explained” [Abbink K, 2010].
In conclusion, although related, the two behaviours are not simply two sides of the same coin. Closeness to the in-group, which can be triggered simply by labelling, seems to be the main driving force for in-group favouritism, whilst out-group discrimination is determined by social distance, conflict, and competition between groups.
"In-group love" and "out-group hate", Halevy N, Bornstein G, Sagiv L, Psychol Sci. 2008 Apr; 19(4):405-11.
Abbink K, Brandts J, Herrmann B, Orzen H (2010) Intergroup Conflict and Intra-Group Punishment in an Experimental Contest Game. Am Econ Rev 100: 420–447.