Darwin had identified natural selection as the mechanism of evolution by about 1837. In 1844, he articulated the concept in a manuscript, which he did *not* submit but left in his study with a letter to his wife instructing her to publish it “in case of my sudden death.”
In 1857 he sent a summary of his theory to Asa Gray, a botanist at Harvard. Yet he did still not publish it.

Darwin decided to publish his theory only when in 1858 he received a manuscript entitled “On the Tendency of Variations to Depart Indefinitely from the Original Type.”
from Alfred Russel Wallace, which had been sent from the Malay Archipelago. Wallace had independently deduced a large part of Darwin’s theory of natural selection.

In a panic, Wallace Darwin wrote to friends – Joseph Hooker, a biologist, and Charles Lyell, a geologist- of his fear that “all my originality, whatever it may amount to, will be smashed.”

Lyell wrote back asking what Darwin had on paper to establish priority. Darwin recalled the 1844 paper, which Hooker had read, as well as the paragraphs he had recently sent to Asa Gray. Lyell and Hooker’s suggested a joint presentation of Darwin’s paper and Wallace’s at the next Linnean Society meeting, where the papers caused not the slightest bit of controversy.

As a campaigner for the abolition of slavery, Darwin would seem to have been remarkably desultory.