Darwin's Origin of Species
In November 1859, the English naturalist Charles Darwin published On the Origin of Species, a book arguing that living species were not fixed and unchanging but had descended with modification from common ancestors. Its central mechanism, natural selection, offered a testable natural explanation for the diversity and apparent design of life. The book became one of the most influential works in the history of science, and it reshaped biology, and with it debates about religion, society, and humanity's place in nature.
Darwin had been developing his ideas for more than twenty years. As the ship's naturalist on HMS Beagle, which sailed from 1831 to 1836, he observed fossils in South America, the distribution of animals and plants, and the distinctive species of the Galápagos Islands. Back in England, he read Thomas Malthus's essay on population, which stressed that organisms tend to produce more offspring than can survive, and he came to see how this struggle could drive change. He also drew on the geologist Charles Lyell's view that Earth was very old and shaped by slow processes. Darwin wrote out a sketch of his theory in the 1840s but held back, partly from caution about the controversy it would cause.
What finally prompted publication was a letter in 1858 from another naturalist, Alfred Russel Wallace, who had independently arrived at a very similar idea. Short papers by both men were presented together to the Linnean Society, and Darwin then hurried to complete what he called an "abstract" of his larger project. The result was a long, carefully argued book that assembled evidence from animal breeding, comparative anatomy, embryology, biogeography, and the fossil record. The first printing sold out quickly.
Reactions were mixed. Some scientists were quickly persuaded, notably Thomas Henry Huxley, who became a vigorous public defender. Others accepted that species change but doubted natural selection as the main cause. Religious responses varied widely, and the often-told story of a single dramatic clash at the 1860 Oxford meeting of the British Association has been somewhat embellished over time. The book said little directly about human origins, though the implications were obvious, and Darwin addressed them explicitly in The Descent of Man in 1871.
A significant gap remained in Darwin's theory: he did not know how traits are inherited. That puzzle was resolved only in the early twentieth century, when genetics was combined with natural selection in what is called the modern synthesis. Today evolution by natural selection is the foundation of the life sciences, supported by evidence from fields Darwin could not have imagined, including molecular biology and DNA sequencing.