This book was first published in 2004. Unraveling the origin of biodiversity is fundamental for understanding our biosphere. This book clarifies how adaptive processes, rather than geographic isolation, can cause speciation. Adaptive speciation occurs when biological interactions induce disruptive selection and the evolution of assortative mating, thus triggering the splitting of lineages. Internationally recognized leaders in the field explain exciting developments in modeling speciation, together with celebrated examples of rapid speciation by natural selection. Written for students and researchers in biology, physics, and mathematics, this book is a groundbreaking treatment of modern speciation science.