In this controversial and stimulating book, Michael Ruse explores the ways in which biological theory, expounded in Charles Darwin's great work, `On the Origin of Species', can most fruitfully inform philosophical understanding. Continuing the debate on evolution in general, and Darwinism in particular, the author demonstrates the ways in which accepting our `animal' nature influences our perception of the external world and our moral dealings with other people. `This, I venture to say, is the best book written to date on the philosophy of evolutionary biology. In a distinctively clear, incisive style, Ruse brings natural selection to the front of general philosophy and makes it henceforth unavoidable as part of analysis. Similarly, he shows why philosophy is an essential subject for the future of biology.' `Edward O. Wilson' `Both evolutionary biologists and philosophers will find much in it to ponder with profit.' `Nature' This book is now published in paperback for the first time. Student and professional philosophers, biologists.