The role of optimality models in the study of adaptation has been a focus of continued foundational debate in evolutionary biology. Nevertheless, a central question at the core of the debate has been explicitly addressed only recently: the issue of evolutionary stability, which conceptually unifies research in fields like life-history evolution, behavioural evolution, and phenotypic plasticity, to name a few. What is the theoretical force of the notion of stability in the study of adaptation? Is it a theoretical virtue of evolutionary modeling, or a vice? I will argue that it is a virtue. But to properly address these questions one needs to distinguish theoretical understanding from explanation. Indeed, I see theoretical understanding as a necessary — but insufficient — condition for explanation. We have theoretical understanding when phenomena become intelligible to us, that is, in a crucial sense, conceptualizable, and such conceptualization is a requisite for explanation. Thus, modeling adaptation through a notion of stability has made adaptive evolution intelligible as a biological phenomenon. I develop this thesis by interpreting recent results in the biological literature and by giving an old idea of Richard Levins foundational significance as a principle for the intelligibility of adaptation: that populations in nature should differ in the direction of their optima.
Alirio Rosales is currently finishing his PhD work (supervised by Prof. John Beatty) at the University of British Columbia, Vancouver. He previously taught philosophy of biology at the Universidad Central de Venezuela.