On the Origin of Species — Darwin (1859)

Charles Darwin's On the Origin of Species is the most consequential scientific book ever published, providing for the first time a coherent, evidence-based account of life's diversity without supernatural explanation. It transformed not just biology but anthropology, psychology, economics, philosophy, and theology. Richard Dawkins called it "the most important book ever written." Its arguments have only been strengthened by 165 years of subsequent evidence.