Petr Alekseyevich Kropotkin (1842-1921) and Vero Copner Wynne-Edwards (1906-1997) developed evolutionary theories that emphasized social groups and cooperation rather than the organism-level natural selection of standard Darwinian theory. The most important reason for their alternative interpretations was their experience as field naturalists. Kropotkin and Wynne-Edwards worked in arctic environments and were impressed by aspects of the natural world that differed significantly from those experienced by Darwin or Wallace. These field experiences led to their emphasis on mutual aid and group selection, respectively. Understanding the development of their theories helps to illuminate the continuing debates over evolutionary theory and the current resurgence of interest in group selection.