Is 'fitness' a primitive or a propensity? Diagnosing the role of explanatory reductionism on differing standards of scientific definitions

Abstract

This thesis explores the disagreement between the two earliest attempts by philosophers of biology to explain the meaning and explanatory role of evolutionary fitness in the theory of natural selection. I compare two interpretations of fitness: the propensity interpretation and the primitivist interpretation. Both aimed to solve the charge that due to the way fitness had been construed by biologists, the theory of natural selection offers circular explanations. I argue that their disagreement was not in their different understanding of what fitness is, but in their standards for a successful definition of fitness that would solve the charge. The primitivist interpretation required a reductive definition of fitness, while the propensity interpretation did not.