The astounding breadth of diversity of life on earth intrigues and amazes many people, while the future of world biodiversity is a cause for widespread concern. Within the current context of global interest in biological diversity, this is a timely review of the most recent research into the evolutionary origins of biological diversity and the processes of speciation, from a stellar cast of contributors. Recent studies have discovered considerable genetic and morphological variation both between and within populations of the same species. Yet the relation between this intraspecific variation and the processes of speciation remains poorly understood. When, how, and why do new species arise? The chapters in this book explore the question of how variation arises within species; some emphasize the ecological and behavioural basis of differentiation; others argue for the role of natural selection in generating speciation. Several chapters focus on the important emerging links between sexual selection, sexual conflict, and population differentiation. The final chapters of the book take a broader perspective on the question, and explore the fossil record for data on the origination of species diversity - and extinctions - in the past. This book is a must-have for all researchers and graduate students in the biological sciences who want to be abreast of the latest thinking on the evolution of biological diversity.