Charles Darwin developed the theory of evolution by natural selection with Alfred Russel Wallace.
Darwin presented the mechanism in detail in his 1859 book On the Origin of Species. He argued that populations vary, that some variations are heritable, and that organisms with advantageous traits tend to leave more offspring. Across generations, this process can produce adaptation and the divergence of species.
Darwin’s five-year voyage on HMS Beagle, including observations in the Galápagos Islands, contributed to his thinking. However, natural selection was not based on the Galápagos alone; Darwin also studied fossils, domesticated animals, plants, and geographic patterns.
Wallace independently developed a similar theory and sent Darwin an essay in 1858. Their ideas were presented jointly to the Linnean Society of London. Darwin is therefore not best described as the sole discoverer of natural selection, even though his book became the theory’s most influential early exposition.