Fitness is a central concept in modern biology, integral to the theory of evolution by natural selection. However, statements to the effect that fitness is 'complex', 'ambiguous' and 'impossible to define' abound in the literature. Why has fitness sparked so much confusion, given that natural selection itself is a well understood process? This book offers a novel answer using tools from the philosophy of science. The central argument is that fitness is a theoretical concept and thus defined by its role in evolutionary theory. However there turn out to be four subtly different roles that the concept has been called on to play. This analysis helps to shed light on numerous “fitness controversies” among evolutionists and to unify the philosophical and biological literatures on fitness. This title is also available as open access on Cambridge Core.

‘Okasha and Autzen make a convincing case for thinking that the appropriate interpretation of fitness in evolutionary biology depends on the kind of situation one wants to model. There is no such thing as a single ‘master equation' that says what fitness really is. This book will be of great interest to philosophers of biology and to evolutionary theorists.'

Elliott Sober - Stanford University and University of Wisconsin-Madison