altruism

Meaning: Altruism is a type of prosocial behavior (any action meant to benefit others) in which the helper pays a cost, such as time, effort, or risk. Accounts of why it occurs differ. The empathy-altruism hypothesis says empathic concern for someone in need produces helping aimed at that person's welfare. Social exchange theory says people help when perceived benefits, such as reputation or relief of their own distress, outweigh the costs. Evolutionary accounts explain costly helping through kin selection (aiding relatives spreads shared genes, raising inclusive fitness) and reciprocal altruism (helping now raises the chance of being helped later).

On the MCAT: A passage describes someone helping a stranger, an anonymous donation, or animal behavior such as alarm calls or sterile worker insects, then asks which explanation fits. Expect to predict that helping rises with empathy and with relatedness, and falls as the number of bystanders grows because of diffusion of responsibility.

Common confusion: Students treat all helping as altruism. Helping done for a payoff is prosocial but fits social exchange better than strict altruism. Also, psychology defines altruism by motive, while evolutionary biology defines it by fitness cost to the helper, so the same act can be labeled differently depending on the framework.