Unification, T-theoreticity, and Testing: The Case of Fitness in Natural Selection

Abstract Theoreticity and unification are two main issues discussed in philosophy of science. The first attempts to clarify the different roles of concepts used in a scientific theory. The second concerns the role of unification in scientific explanation and scientific progress. Both discussions have followed separate, independent paths. In this paper, we examine the interrelatedness of these two notions by focusing on classical particle mechanics and the theory of natural selection. We claim that they are interconnected in two distinct ways. On the one hand, a theory’s unifying power relies on the presence of some theoretical concepts that apply to heterogeneous phenomena through the assumption of a (sometimes unstated) general principle. On the other hand, a sensible application of the theoreticity criterion to these integrating concepts requires the unification not being spurious. We conclude that a correct determination of the theoreticty status requires analyzing how specific applications of different parts of a theory interact with each other.