Intergroup behavior cannot be explained by individual psychology alone.

Evidence

Researchers studying social identity and intergroup relations have traditionally approached group behavior as an interaction between the individual, the group, and the social context in which the individual and group are embedded. This approach has been quite fruitful, as evidenced by the proliferation of theories and studies over the last several decades that have identified the psychological and sociocontextual features that are likely to give rise to particular group behaviors (e.g., in-group bias, discrimination, intergroup hostility). However, these theories are based largely on how individuals are predicted to respond and behave under particular circumstances, often without explicit consideration of the interdependence among individuals or the group-level outcomes that may emerge as a result of the interactions among individual actors. This approach is similar to a traffic engineer attempting to understand traffic patterns by examining the motivations and behaviors of individual drivers. Individual-level theories may tell the engineer that drivers attempt to maximize the speed of their car and avoid erratic fellow drivers. But understanding why traffic jams occur requires consideration of how the behavior of one driver affects the behavior of multiple other drivers and how these behaviors unfold over time. — Roderick M. Kramer, Geoffrey J. Leonardelli, Robert W. Livingston, Social Cognition, Social Identity, and…, 809

Categorization

• QUESTION: Implication: group-level prejudice phenomena like segregation or stereotype contagion may resist individual-attitude explanations entirely - worth reconciling with the Allport individual-cognition frame.
• XREF: Speaks to the reader’s ongoing prejudice-psychology reassessment - the methodological limit described here parallels debates over whether prejudice is an individual attitude or an emergent collective property.
• corroborated: 2 independent passages support this claim — Roderick M. Kramer, Geoffrey J. Leonardelli, Robert W. Livingston, Social Cognition, Social Identity, and…, 809