Darwin's Theory of Evolution by Natural Selection

Charles Darwin's On the Origin of Species (1859) presented natural selection as the mechanism driving evolution, explaining the diversity of all 8.7 million known species without invoking supernatural design. Darwin unified biology the way Newton's gravity unified physics—providing a single explanatory framework for anatomy, behavior, ecology, and medicine. The modern evolutionary synthesis later confirmed and extended his insight, making natural selection the organizing principle of life sciences 165 years later. Darwin's 20-year evidence gathering yielded a theory that remains more fundamental to modern medicine and agriculture than any other biological framework.