Who they were
After a five-year voyage on HMS Beagle, during which he observed the wildlife of South America and the Galápagos, Darwin spent decades gathering evidence before publishing On the Origin of Species in 1859. It argued that all species descend with modification from common ancestors, shaped by natural selection; The Descent of Man (1871) applied the idea to humans.
What they did
He gave biology a unifying mechanism, replacing separate creation with common descent and explaining the diversity of life.
Legacy
Evolution by natural selection is now the foundation of the life sciences, confirmed by genetics and molecular biology. Darwin’s theory reshaped science and, controversially in his time, humanity’s view of its own origins.