Sex. Life. Death. What is it that drives us toward sex, fuels life, and makes death inevitable? ...as it turns out, it's the same thing: Testosterone. Not only does testosterone fuel the passion for reproduction and play a critical role in the length of our lives, it is an integral component to the mechanism of human civilization-its triumphs and its tragedies. In order to understand the forces that drive the life cycles of human cultures and that form the engine of history, The Testosterone Hypothesis goes to the most fundamental building blocks of human neuroscience. Our hormones are the impetus for our history. This groundbreaking research proposes that the profound transformations in social mood that bring the rise and fall of civilizations are caused by biological cycles and directed by hormones. Hormones regulate and control the way the human mind perceives the world, understands the nature of the good, and forms social organizations and political orders accordingly. At a time when the course of civilization seems to be more uncertain than ever, driven toward pessimism and even despair, it is enlightening to take a new multi-disciplinary approach to studying the history of Western civilization. Overthrowing the conventional, reductionist approach to science by integrating different disciplines-from evolution, biology, neuroscience, and psychology to the history and philosophy of Western civilization-we can reach a new understanding of the human mind and of our civilization as a complex, adaptive, living system. To subdue the animalistic impulses that motivate our actions means to be guided by rational thought rather than primordial instincts and behavior: this will propel man to the next leap forward in human evolution. Our civilization is aging into a pathological state of depression. The insights of The Testosterone Hypothesis can guide us to solutions with which we can restore the vibrant mindset that built the modern world.