collective behaviour

Meaning: Collective behaviour is action by a fairly large group that arises spontaneously and is not guided by established rules or institutions. Examples are crowds, mobs, riots, panics, fads, and rumours. Three accounts explain it. Contagion theory (Le Bon) says anonymity in a crowd lets emotions spread, so people act unlike they would alone. Convergence theory says people with similar traits or aims gather, so the crowd reflects what individuals already bring. Emergent-norm theory (Turner and Killian) says new norms develop during the event itself, and members then conform to them.

On the MCAT: A passage describes a riot, panic, or viral trend and asks which theory fits. Match the cause: emotion spreading among strangers (contagion), like-minded people gathering (convergence), or rules forming as the event unfolds (emergent norm). Deindividuation and conformity often appear in the same questions.

Common confusion: Collective behaviour is not a social movement. A social movement is more organised and lasts longer, with a goal of promoting or resisting change. Also, contagion and convergence differ in the direction of cause: contagion says the crowd changes individuals, while convergence says individuals make the crowd.