This book challenges the received view that Darwinism generated essentially aggressive and warlike social values and pugnacious images of humankind. Paul Crook reconstructs the influential discourse of "peace biology," whose liberal vision was of a basically free humanity, not fettered by iron laws of biological necessity or governed by violent genes. By exploring a gamut of Darwinian readings of history and war, mainly in the English-speaking world prior to 1919, this study throws important new light on militarism, peace movements, the origins of World War I and British social thought.