Optimality Models and the Propensity Interpretation of Fitness

Abstract

The propensity account of fitness intends to solve the classical tautologicity issue by identifying fitness with a disposition, the ability to survive and reproduce. As proponents recognized early on, this account requires operational independence from actual reproductive success to avoid circularity and vacuousness charges. They suggested that operational independence is achieved by measuring fitness values through optimality models. Our goal in this article is to develop this suggestion. We show that one plausible procedure by which these independent operationalizations could be thought to take place, and which is in accordance with what is said in the optimality literature, is unsound. We provide two independent lines of reasoning to show this. We then provide a sketch of a more adequate account of the role of optimality models in evolutionary contexts and draw some consequences.

Darwin’s empirical claim and the janiform character of fitness proxies

“…Popper is right, of course, that this grants empirical content to the fitness principle. The propensity view therefore abounded in the philosophy of biology (Mills and Beatty 1979;Richardson and Burian 1992;Bouchard and Rosenberg 2004;Roffé and Ginnobili 2020). The difference between the expected and actual number of offspring is considered to be relevant for evolutionary explanations (e.g., Pence and Ramsey 2013), so fitness as a propensity is a good candidate for figuring in these explanations.…”

“…These models are very convenient whenever a certain set of parameters can change continuously. Roffé and Ginnobili (2020) explicitly stress this aspect, because it allows them to infer fitness values in a straightforward way from the optimality parameter. However, the models will not be applicable when comparing two organisms with a trait present in one and absent in the other.…”

“…Popper later on considered his view having been influenced byWaddington, Fisher, Haldane, and Simpson (Popper 1978, p. 344).10 To mention a counter-example:Waddington (1960, p. 385), who also diagnosed the tautology, didn't consider it being problematic. 11 For more recent comments and reviews of the tautology problem, cf (Grene and Depew 2004;Rosenberg and Bouchard 2005;Hunt 2014;Roffé and Ginnobili 2020)…”