In spite of its checkered intellectual history, and in spite of the myriadproposals of alternative models that claim both to account for the range of humanbehavior and to dispense with the need for selection above the organism level, a mul-tilevel selection framework allowing for biological as well as cultural group selectionremains the only coherent means of accounting for the persistence and spread ofbehavioral inclinations which, at least upon first appearance at low frequency, wouldhave been biologically altruistic. This argument is advanced on three tracks: througha r eview of experimental and observational evidence inconsistent with a narrow ver-sion of rational choice theory, through a critique of models or explanations purportingto account for prosocial behavior through other means, and via elaboration of t hemechanisms, plausibility, and intellectual history of biological group selection.