Samir Okasha is Professor of Philosophy of Science at the University of Bristol. He is the author of Evolution and the Levels of Selection (2006), awarded the Lakatos Prize for an outstanding contribution to the philosophy of science, Agents and Goals in Evolution (2018), and Philosophy of Biology: A Very Short Introduction (2019). Bengt Autzen is Lecturer in Philosophy at University College Cork. He is the author of a number of articles in journals including Biology and Philosophy, Philosophy of Science, European Journal for Philosophy of Science and British Journal for the Philosophy of Science.

'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

• Introduction; 1. The 'philosophy of fitness'; 2. Understanding theoretical concepts; 3. The theoretical role of fitness; 4. The complexification of fitness; 5. Fitness controversies; 6. Further conceptual issues about fitness; Appendix 1; Appendix 2; Bibliography; Index.

Samir Okasha is Professor of Philosophy of Science at the University of Bristol. He is the author of Evolution and the Levels of Selection (2006), awarded the Lakatos Prize for an outstanding contribution to the philosophy of science, Agents and Goals in Evolution (2018), and Philosophy of Biology: A Very Short Introduction (2019). Bengt Autzen is Lecturer in Philosophy at University College Cork. He is the author of a number of articles in journals including Biology and Philosophy, Philosophy of Science, European Journal for Philosophy of Science and British Journal for the Philosophy of Science.

'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

• Introduction; 1. The 'philosophy of fitness'; 2. Understanding theoretical concepts; 3. The theoretical role of fitness; 4. The complexification of fitness; 5. Fitness controversies; 6. Further conceptual issues about fitness; Appendix 1; Appendix 2; Bibliography; Index.

Samir Okasha is Professor of Philosophy of Science at the University of Bristol. He is the author of Evolution and the Levels of Selection (2006), awarded the Lakatos Prize for an outstanding contribution to the philosophy of science, Agents and Goals in Evolution (2018), and Philosophy of Biology: A Very Short Introduction (2019). Bengt Autzen is Lecturer in Philosophy at University College Cork. He is the author of a number of articles in journals including Biology and Philosophy, Philosophy of Science, European Journal for Philosophy of Science and British Journal for the Philosophy of Science.

'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

• Introduction; 1. The 'philosophy of fitness'; 2. Understanding theoretical concepts; 3. The theoretical role of fitness; 4. The complexification of fitness; 5. Fitness controversies; 6. Further conceptual issues about fitness; Appendix 1; Appendix 2; Bibliography; Index.