 Lewontin’s requirements for evolution by natural selection contain an ambiguity. “Fitness” could refer either to offspring number or to fitness variables of the sort found in the genotypic selection equation above (the \(w\)’s). Godfrey-Smith, in noting that some formalisms do not feature fitness variables at all, is using the term in the latter sense (2007: 496), while Okasha’s treatment of Lewontin’s requirements uses fitness in the former sense. Suppose fitness means offspring number and suppose further that the requirements play the role of determining under what circumstances evolutionary theory may be deployed. If these things hold, then the circularity problem arises: we must know that the variants in the system have different numbers of offspring in order to apply Lewontin’s requirements to deploy the theory that would explain the very same offspring production despite such production serving to license the theory’s deployment in the first place.