 Section 3  indicated that John Maynard Smith and Eörs Szathmáry drew explicitly on the concept of living organisms in characterizing the chief theme of their influential work on the major transitions in the history of life. However, reflection on organisms as living agents generally has been backgrounded in work concentrating on evolutionary individuals. This is perhaps for the obvious reason that many evolutionary individuals—including genes, lineages, and clades—are not themselves living things. Yet physiological individuals are paradigms of living agents and a more complete sense of the conceptual space that biological individuals occupy calls for some discussion of life, including the roles that an appeal to life cycles and agency play in characterizing physiological individuals. 