When Are Similar Individuals a Group? Early Reasoning About Similarity and In-Group Support

Beginning in infancy, children expect individuals in a group to care for and be loyal to in-group members. One prominent cue that children use to infer that individuals belong to the same group is similarity. Does any salient similarity among individuals elicit an expectation of in-group preference, or does contextual information modulate these expectations? In Experiments 1 and 2, 12-month-old infants expected in-group preference between two individuals who wore the same novel outfit, but they dismissed this similarity if one of the outfits was used to fulfill an instrumental purpose. In Experiment 3, 26-month-old toddlers expected in-group preference between two individuals who uttered the same novel labels, but they dismissed this similarity if the labels were used to convey incidental as opposed to categorical information about the individuals. Together, the results of these experiments (N = 96) provide converging evidence that from early in life, children possess a context-sensitive mechanism for determining whether similarities mark groups.