Paul Griffiths is University Professorial Research Fellow at the University of Sydney. He is the author of What Emotions Really Are: The Problem of Psychological Categories (1997) and Sex and Death: An Introduction to the Philosophy of Biology (with K. Sterelny, 1999). He is the editor of Trees of Life: Essays in Philosophy of Biology (1992), Biology and Philosophy (2000) and Cycles of Contingency: Developmental Systems and Evolution (with S. Oyama and R. D. Gray, 2001).