The search for origins of communication in a wide variety of species including humans is rapidly becoming a thoroughly interdisciplinary enterprise. In this volume, scientists engaged in the fields of evolutionary biology, linguistics, animal behavior, developmental psychology, philosophy, the cognitive sciences, robotics, and neural network modeling come together to explore a comparative approach to the evolution of communication systems. The comparisons range from parrot talk to squid skin displays, from human language to Aibo the robot dog's language learning, and from monkey babbling to the newborn human infant cry. The authors explore the mysterious circumstances surrounding the emergence of human language, which they propose to be intricately connected with drastic changes in human lifestyle. While it is not yet clear what the physical environmental circumstances were that fostered social changes in the hominid line, the volume offers converging evidence and theory from several lines of research suggesting that language depended upon the restructuring of ancient human social groups. The volume also offers new theoretical treatments of both primitive communication systems and human language, providing new perspectives on how to recognize both their similarities and their differences. Explorations of new technologies in robotics, neural network modeling, and pattern recognition offer many opportunities to simulate and evaluate theoretical proposals. The North American and European scientists who have contributed to this volume represent a vanguard of thinking about how humanity came to have the capacity for language and how nonhumans provide a background of remarkable capabilities that help clarify the foundations of speech.