  The idea that group selection might explain the evolution of altruism was first broached by Darwin himself. In The Descent of Man (1871), Darwin discussed the origin of altruistic and self-sacrificial behaviour among humans. Such behaviour is obviously disadvantageous at the individual level, as Darwin realized: “he who was ready to sacrifice his life, as many a savage has been, rather than betray his comrades, would often leave no offspring to inherit his noble nature” (p.163). Darwin then argued that self-sacrificial behaviour, though disadvantageous for the individual ‘savage’, might be beneficial at the group level: “a tribe including many members who...were always ready to give aid to each other and sacrifice themselves for the common good, would be victorious over most other tribes; and this would be natural selection” (p.166). Darwin's suggestion is that the altruistic behaviour in question may have evolved by a process of between-group selection.