 He devoted much of the extensive efforts of his Structure of Evolutionary Theory to defending an interpretation of Darwinian evolutionary theory as resting on a revisable “tripod of necessary support” (Gould 2002: 586)—one whose three critical supports were challenged by proposed expansions to evolutionary theory, but which nonetheless could be buttressed via integration with these challenges, rather than replacement by them. In short, the later Gould argues that Darwinian evolution traditionally emphasizes organismic selection, adaptationism, and extrapolationism; that punctuated equilibria, stabilizing selection, and species selection challenge the first of these supports, developmental and other constraints challenge the second, and major evolutionary transitions challenge the third; but that all three of these challenges can be accommodated by a revised but still Darwinian conception of evolutionary theory.