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Darwin, who was born in Shrewsbury, began his university education by studying medicine at Edinburgh (1825), but finding he had no taste for the subject he entered Cambridge University to prepare for the Church. At Cambridge his interest in natural history, first stimulated by the geologist Adam Sedgwick, was encouraged by the professor of botany John Henslow. Their friendship led to Henslow's recommending Darwin to the admiralty for the position of naturalist on HMS Beagle, which was preparing to survey the coast of South America and the Pacific.

The Beagle sailed in 1831 and Darwin, armed with a copy of Charles Lyell's Principles of Geology, initially concerned himself more with the geological aspects of his work. However, his observations of animal species – particularly the way in which they gradually change from region to region – also led him to speculate on the development of life. He was particularly struck by the variation found in the finches of the Galápagos Islands, where he recorded some 14 different species, each thriving in a particular region of the islands. Darwin reasoned that it was highly unlikely that each species was individually created; more probably they had evolved from a parent species of finch on mainland Ecuador. Further considerations, back in England, as to the mechanism that brought this about resulted in probably the most important book in the history of biology.

On returning to England in 1836, Darwin first concerned himself with recording his travels in A Naturalist's Voyage on the Beagle(1839), which received the acclaim of Alexander von Humboldt. His interest in geology was reflected in Structure and Distribution of Coral Reefs (1842) and Geological Observations on Volcanic Islands (1844). These early works, which established his name in the scientific community and won the respect of Lyell, were fundamental to the development of his theories on evolution.

Early on Darwin had perceived that many questions in animal geography, comparative anatomy, and paleontology could only be answered by disregarding the theory of the immutability of the species (an idea widely held at the time) and accepting that one species evolved from another. The idea was not original but Darwin's contribution was to propose a means by which evolution could have occurred and to present his case clearly, backed up by a wealth of evidence. In 1838 he read Thomas Malthus's An Essay on the Principle of Population and quickly saw that Malthus's argument could be extended from man to all other forms of life. Thus environmental pressures, particularly the availability of food, act to select better adapted individuals, which survive to pass on their traits to subsequent generations. Valuable characteristics that arise through natural variability are therefore preserved while others with no survival value die out. If environmental conditions change, the population itself will gradually change as it adapts to the new conditions, and with time this will lead to the formation of new species. Darwin spent over 20 years amassing evidence in support of this theory of evolution by natural selection, so as to provide a buffer against the inevitable uproar that would greet his work on publication. In this period the nature of his studies was divulged only to close friends, such as Joseph Hooker, T.H. Huxley, and Charles Lyell.

The stimulus to publish came in June 1858 when Darwin received, quite unexpectedly, a communication from Alfred Russel Wallace that was effectively a synopsis of his own ideas. The question of priority was resolved through the action of Lyell and Hooker, who arranged for a joint paper to be read to the Linnean Society in July 1858. This consisted of Wallace's essay and a letter, dated 1857, from Darwin to the American botanist Asa Gray outlining Darwin's theories. Darwin later prepared an ‘abstract’ of his work, published in November 1859 as On The Origin of Species by Means of Natural Selection.

As expected the work made him many enemies among orthodox scientists and churchmen since beliefs in the Creation and divine guidance were threatened by Darwin's revelations. Darwin, a retiring man, chose not to defend his views publicly – a task left to (and seemingly immensely enjoyed by) Huxley, ‘Darwin's bulldog’, notably at the famous Oxford debate in 1860. Darwin continued quietly with his work, publishing books that extended and amplified his theories. One of these was The Descent of Man(1871), in which he applied his theory to the evolution of man from subhuman creatures. Many of his books are seen as pioneering works in various fields of biology, such as ecology and ethology.

Darwin was, however, troubled by one flaw in his theory – if inheritance were blending, i.e., if offspring received an average of the features of their parents (the then-held view of heredity), then how could the variation, so essential for natural selection to act on, come about? This problem was put in a nutshell by Fleeming Jenkin, professor of engineering at University College, London, who wrote a review of the Origin in 1867. In this Jenkin pointed out that any individual with a useful trait, assuming it mated with a normal partner, would pass on only 50% of the character to its children, 25% to its grandchildren, 12½% to its greatgrandchildren, and so on until the useful feature disappeared. The logic of this drove Darwin to resort to Lamarckian ideas of inheritance (of acquired characteristics) as elaborated in his theory of pangenesis in the sixth edition of the Origin. The question was not resolved until the rediscovery, nearly 20 years after Darwin's death, of Gregor Mendel's work, which demonstrated the particulate nature of inheritance.

Darwin was troubled through most of his life by continuous illness, which most probably was due to infection by the trypanosome parasite causing Chagas' disease, contracted during his travels on the Beagle. On his death he was buried, despite his agnosticism, in Westminster Abbey.