This book examines these issues, tracing the historical debate that raged over the biological causes and effects of war between the publication of Darwin's Origin of Species in 1859 and World War l. It reconstructs the theories of war and juman pugnacity of thinkers such as Charles Darwin, Herbert Spencer, Walter Bagehot, Alfred Wallace, T. H. Huxley, Karl Pearson, Peter Kroptkin, Jacques Novicow, William McDougall, Peter Chalmers Mitchell and a host of now-forgotten naturalist, biometricians, geneticist, eugenists, physicians, psychologist, professionals and minor savant of the time.