Book excerpt: The field of forensic psychology explores the intersection of psychology and the law. The purpose of this book is to examine topics in the field using the powerful, multidisciplinary, conceptually integrated approach that the natural sciences have embraced for decades with great success. Darwin's theory of evolution by natural selection is the meta-theoretical framework that unifies the field of biology. It unites research and understanding of the development, control, and organization of behavior. The study of humans, which includes all of the social sciences, is part of the field of biology. Darwin's theory provides a powerful meta-theoretical framework that can unify and energize forensic psychology, just as it has the biological sciences. Evolutionary processes undoubtedly shaped physiological characteristics to help solve problems of survival and reproduction. The lungs, for example, with their vast surface area and moist membranes are marvelous adaptions for extracting oxygen and releasing carbon dioxide. Natural selection is the only known process capable of shaping complex functional mechanisms. Just as it shaped physiological adaptations with specific problem-solving functions, it also shaped our thoughts and emotions to guide behaviors toward solving recurrent problems of survival and reproduction. With this logic, we can use knowledge of ancestral problems to guide our understanding of how the mind works. Evolutionary Forensic Psychology is a necessary step toward a unified and complete understanding of psychology and the law. It recognizes that crimes such as murder, non-lethal violence, rape, and theft are manifestations of evolutionarily recurrent selection when they gave individuals an advantage in competition for resources. Each of the chapters that comprise this volume has been selected to provide the first unified examination of important research contributions and future directions of Evolutionary Forensic Psychology.