This book review summarizes Yuval Noah Harari's book "Sapiens: A Brief History of Humankind". The book traces the evolution of human species from early hominids to modern Homo sapiens. It divides this history into four major parts: the cognitive revolution 70,000 years ago; the agricultural revolution 10,000 years ago; the unification of humankind into political organizations; and the scientific revolution starting in 1500 CE. The book argues that while modern humans live very differently than our ancestors, our underlying psychology and desires have not evolved much. It also suggests people may have been happier in pre-agricultural stone age societies compared to modern lives.