The Twofold Brain: Exploring Fundamental Questions about Brain Lateralization challenges the traditional view that brain asymmetry is exclusive to human brains, showing that it is instead widespread in animals. This unique book deals with new and original ideas about asymmetry of the brain and its functions. It first demonstrates how asymmetry emerged early as a biological strategy long before language or culture evolved and was conserved because it worked. It also discusses how, from an evolutionary perspective, bilateral bodies create a fundamental problem of duplication – two sides mean redundant sensors, muscles, and neural circuits – but by biasing certain functions towards one side, organisms reduce conflict, speed up processing, and stabilize behaviour. This book then explores the role of interaction among asymmetric organisms in generating individual- or population-level asymmetries as evolutionarily stable strategies, showing that asymmetry thus appears to be a foundational aspect of all nervous systems. The authors' comprehensive approach to brain lateralization allows readers to understand it as an integral aspect of both large and small brains. Each chapter is crafted to answer specific questions, making this book accessible and engaging for both experts and general readers alike. This book will appeal not only to specialists in neurosciences but also to a broader audience with a keen interest in understanding the intricacies of mental processes. Whether you're delving into the nuances of cognitive neuroscience or simply intrigued by the mysteries of the mind, this book offers a captivating journey into the fascinating world of lateralization in human and non-human species.