Charles Robert Darwin FRS (12 February 1809 – 19 April 1882) was an English naturalist who realised that all species of life have evolved over time from common ancestors, and published compelling supporting evidence of this in his 1859 book On the Origin of Species in which he presented his scientific theory that this branching pattern of evolution resulted from a process that he called natural selection. The fact that evolution occurs became accepted by the scientific community and much of the general public in his lifetime, but it was not until the emergence of the modern evolutionary synthesis from the 1930s to the 1950s that a broad consensus developed that natural selection was the basic mechanism of evolution. In modified form, Darwin's scientific discovery is the unifying theory of the life sciences, explaining the diversity of life.

Darwin's early interest in nature led him to neglect his course in medicine at Edinburgh University and instead help to investigate marine invertebrates, then the University of Cambridge encouraged a passion for natural science. His five-year voyage on HMS Beagle established him as an eminent geologist whose observations and theories supported Charles Lyell's uniformitarian ideas, and publication of his journal of the voyage made him famous as a popular author.

Puzzled by the geographical distribution of wildlife and fossils he collected on the voyage, Darwin investigated the transmutation of species and conceived his theory of natural selection in 1838. Although he discussed his ideas with several naturalists, he needed time for extensive research and his geological work had priority. He was writing up his theory in 1858 when Alfred Russel Wallace sent him an essay which described the same idea, prompting immediate joint publication of both of their theories. Darwin's work established evolutionary descent with modification as the dominant scientific explanation of diversification in nature. In 1871 he examined human evolution and sexual selection in The Descent of Man, and Selection in Relation to Sex, followed by The Expression of the Emotions in Man and Animals. His research on plants was published in a series of books, and in his final book, he examined earthworms and their effect on soil.