Much ado about ‘n’othing

This article argues that a core area of the philosophy of biology—the philosophy of fitness—has for decades rested on fundamental conceptual and mathematical errors. These errors have been leveraged to support the position in the philosophy of biology known as statisticalism, which holds that biological fitness does not cause evolution, but is merely a kind of statistical summary of evolutionary outcomes. This is opposed to causalism, which holds that fitness is based on (causally efficacious) probabilistic propensities, a position known as the propensity interpretation of fitness. The error I focus on is the idea that fitness depends on population size, n, and because population size is not a causal quantity, fitness cannot be causal. In this paper, I show that fitness is not dependent on n and therefore a central critique of the propensity interpretation of fitness is ill founded.