Abstract

In this essay review of Samir Okasha's Agents and Goals in Evolution, I reflect on the rationale for agential thinking in biology, and consider whether the rationale is the same for genes as for organisms. I also discuss Okasha's ingenious examples of the evolution of irrational behaviour, and in particular the evolution of violations of the "independence axiom" of rational choice theory. These examples rely on a crucial distinction between aggregate and idiosyncratic risk.