The publication of Darwin’s The Origin of Species in 1859 marked a dramatic turning point in scientific thought. The volume had taken Darwin more than twenty years to publish, in part because he envisioned the storm of controversy it was certain to unleash. Indeed, selling out its first edition on its first day, The Origin of Species revolutionized science, philosophy, and theology. Darwin’s reasoned, documented arguments carefully advance his theory of natural selection and his assertion that species were not created all at once by a divine hand but started with a few simple forms that mutated and adapted over time. Whether commenting on his own poor health, discussing his experiments to test instinct in bees, or relating a conversation about a South American burrowing rodent, Darwin’s monumental achievement is surprisingly personal and delightfully readable. Its profound ideas remain controversial even today, making it the most influential book in the natural sciences ever written—an important work not just to its time but to the history of humankind.