outgroup

An outgroup is any social group that a person does not identify with as a member. The term is used in contrast to the ingroup, the group with which one identifies. In biology and anthropology, outgroup refers to a lineage or taxon outside the group under study, used for comparative purposes.

In social psychology, outgroup attitudes are central to studies of prejudice, stereotypes, and discrimination directed at people perceived as not belonging to one’s own group. Researchers have documented biases such as the outgroup homogeneity effect (believing outgroup members are more alike) and in-group favoritism. The minimal group paradigm showed that mere categorization into groups can trigger ingroup bias and hostility toward the outgroup.

In phylogenetics, an outgroup is a taxon outside the ingroup used to root a phylogenetic tree and infer ancestral character states. Outgroup comparison helps establish the polarity of traits and is a standard method in evolutionary analyses.

Membership as an outgroup is not fixed; it varies with context and over time. Intergroup contact, shared goals, and fair treatment can reduce bias toward outgroups, whereas perceived threats can intensify antagonism. The concept is used across disciplines to understand how people categorize others and how these categorizations influence perception, behavior, and evolutionary analysis.

Related concepts include ingroup, in-group bias, outgroup homogeneity, minimal group paradigm, and phylogenetic rooting.