 Another model of non-reductive unification is historical and diachronic: it emphasizes the genealogical and historical identity of disciplines, which has become complex through interaction. The interaction extends to relations between specific sciences, philosophy and philosophy of science (Hull 1988). Hull has endorsed an image of science as a process, modeling historical unity after a Darwinian-style pattern of evolution (developing an earlier suggestion by Popper). Part of the account is the idea of disciplines as evolutionary historical individuals, which can be revised with the help of more recent ideas of biological individuality: hybrid unity as an external model of unity as integration or coordination of individual disciplines and disciplinary projects, e.g., characterized by a form of occurrence, evolution or development whose tracking and identification involves a conjunction with other disciplines, projects and domains of resources, from within science or outside science. This diachronic perspective can accommodate models of discovery, in which genealogical unity integrates a variety of resources that can be both theoretical and applied, or scientific and non-scientific (an example, from physics, the discovery of superconductivity, can be found in Holton, Chang and Jurkowitz 1996). Some models of unity below provide further examples.