Altruistic behaviors are quite impressive features in nature and call for selective explanation. Ever since Darwin, many biologists have appealed to group selection to explain altruism. In the 1960s, Williams knocked down these naïve group selectionists and alternatively promoted gene selectionism. However, group selection was highlighted again in the 1980s by Wilson and Sober, who suggested a hierarchical conception of evolution. Opposing to this conception, some philosophers, together with some biologists, proposed to adopt a pluralistic stance toward various models of selection. These three approaches give different explanations of the evolution of altruism. I compare them and show a pluralistic one is the most valid among them.
