Abstract

Elliott Sober can be understood as advancing two distinct arguments that similarly conclude that evolutionary theory does not say that Scriven’s infamous twins have the same fitness, despite the twins’ identical genotypes and phenotypes. The first argument relies on denying that evolutionary theory can say that the twins are in the same environment, and the second relies on asserting an epistemic access asymmetry between token fitness and trait fitness. Motivated by good reasons, I respond to both of these arguments by showing that the theory of evolution by natural selection has adequate means for determining whether the twins are in the same environment via causal-probabilistic decomposition, and that equivalence in fitness can be asserted even from a partial theory of fitness, regardless of epistemology. Finally, I point out an absurd result regarding genetic drift as indiscriminate sampling that follows if Sober’s conclusion is true.