Darwin's Origin of Species was published on November 24, 1859.
In his work, whose full title is On the Origin of Species by Means of Natural Selection, Darwin theorized that organisms gradually – gradually as in thousands or even millions of years - evolve through "natural selection" – those with genetic variations that suit their environment tend to propagate more descendants than organisms of the same species that lack the variation, thus influencing the overall genetic makeup of the species.
Darwin acquired most of the evidence for his theory during a five-year expedition aboard the HMS Beagle in the 1830s. Visiting such diverse places as the Galapagos Islands and New Zealand, Darwin studied – and brought back with him – much of the flora and fauna of those lands. Over the next 20 years he carefully developed his theory.
Actually he had formulated his theory by 1844, but he was wary to reveal his thesis to the public because it so obviously contradicted the Biblical account of creation. In 1858, with Darwin still remaining silent about his findings, the British naturalist Alfred Russel Wallace independently published a paper that essentially echoed Darwin's theory. Darwin and Wallace gave a joint lecture on evolution before the Linnean Society of London in July 1858.
After Origin of Species was published, Darwin was besieged. Orthodox Christians condemned it as heresy. The controversy only deepened with his publication of The Descent of Man (1871), in which he presented evidence of man's evolution from apes.
Darwin himself had suffered a crisis of faith. He was tormented, not so much by what the public thought, but by his theory's implications for religious faith. "I cannot persuade myself that a beneficent and omnipotent God would have designedly created parasitic wasps with the express intention of their feeding within the living bodies of Caterpillars," he wrote.
The death of his daughter, Annie, was, for Darwin, one of the final nails in the coffin of his Christian belief. He said that the best word to describe his religious views was "agnostic."
Most sources say that Darwin's last words were "I am not in the least afraid to die." His daughter, Henrietta, who was present, however, said that they were directed at her mother: "Remember what a good wife you have been." She also refuted the story that her father had undergone a deathbed conversion back to Christianity.
Darwin was buried in Westminster Abbey.
"Believing as I do that man in the distant future will be a far more perfect creature than he now is," Darwin wrote, "it is an intolerable thought that he and all other sentient beings are doomed to complete annihilation after such long-continued slow progress."
He also said: "A man who dares to waste one hour of life has not discovered the value of life."