This book brings together important essays by one of the leading philosophers of science at work today. Elisabeth A. Lloyd examines several of the central topics in philosophy of biology, including the structure of evolutionary theory, units of selection, and evolutionary psychology, as well as the Science Wars, feminism and science, and sexuality and objectivity. Lloyd challenges the current evolutionary accounts of the female orgasm and analyses them for bias. She also offers an innovative analysis of the concept of objectivity. Lloyd analyses the structure of evolutionary theory and unlocks the puzzle of the units of selection debates into four distinct aspects, illuminating several mysteries in the biology literature. Central to all essays in this book is the author's abiding concern for evidence and empirical data.