A comparison of similarity and interdependence as triggers for in-group formation

In four experiments, subjects were informed of a threat from various sources to members of a social category to which they belonged. They were also given the opportunity to help a target person. The results of the first two experiments showed that in-group, bias occurred only when the threat was from a social source rather than a nonsocial source or when there was no threat. The third experiment showed that the bias favored only those similar on the threatened category rather than those similar on another non-threatened category. The fourth experiment showed that when subjects Knew the source of the threat, the bias was against only members of the threatening group, even when the threat was attributed to similar others. These findings indicate that interdependence resulting from a shared threat, rather than similarity alone, seems to play a hey role in the formation of in-group boundaries.