In September 1838 he conceived his theory of natural selection as the cause of evolution, then as well as developing his career as a geologist and writer worked privately on finding evidence and answering possible objections.
Alfred Russel Wallace, a naturalist working in Borneo, had a paper on the "introduction" of species published in Annals and Magazine of Natural History.
However, he spelt out the details of Natural Selection to Lyell, who found the idea hard to accept but urged Darwin to publish to establish priority.
Wallace wrote his paper On The Tendency of Varieties to Depart Indefinitely from the Original Type at Ternate in February 1858 and sent it to Darwin with a request to send it on to Lyell.
Darwin received it on 18 June 1858,[3] and wrote to Lyell that "your words have come true with a vengeance,... forestalled" and "If Wallace had my MS. sketch written out in 1842, he could not have made a better short abstract!"
[5] Lyell and Hooker had decided on a joint publication at the Linnean Society of London of Wallace's paper together with an extract from Darwin's essay and his letter to Asa Gray.
The last meeting of the society before the summer recess had been postponed following the death of former president the botanist Robert Brown on 10 June 1858, and was to be held on 1 July.
Hooker later said there was "no semblance of a discussion", though "it was talked over with bated breath" at tea afterwards, and in his reminiscences many years later thought "the subject [was] too ominous for the old school to enter the lists before armouring.
They next rented a villa in Sandown and Darwin pressed on, with the facts he felt necessary to support his "abstract" expanding far beyond the thirty pages Hooker had originally suggested.
the Laws which affect the Production of Varieties, Races, and Species, contain the results of the investigations of two indefatigable naturalists, Mr. Charles Darwin and Mr. Alfred Wallace.
The gentlemen having, independently and unknown to one another, conceived the same very ingenious theory to account for the appearance and perpetuation of varieties and of specific forms on our planet, and both fairly claim the merit of being original thinkers in this important line of inquiry; but neither of them having published his views, though Mr. Darwin has for many years past been repeatedly urged by us to do so, and both authors having now unreservedly placed their papers in our hands, we think it would best promote the interests of science that a selection from them should be laid before the Linnean Society.
So highly did Mr. Darwin appreciate the value of the views therein set forth, that he proposed, in a letter to Sir Charles Lyell, to obtain Mr. Wallace's consent to allow the Essay to be published as soon as possible.
Of this step we highly approved, provided Mr. Darwin did not withhold from the public, as he was strongly inclined to do (in favour of Mr. Wallace), the memoir which he had himself written on the same subject, and which, as before stated, one of us had perused in 1844, and the contents of which we had both of us been privy to for many years.
[14] The Linnean Society President Thomas Bell in his presidential report of May 1859 wrote that "The year which has passed has not, indeed, been marked by any of those striking discoveries which at once revolutionize, so to speak, the department of science on which they bear".
"[17] Despite illness, Darwin pressed on with writing the "abstract" of his "big book" on Natural Selection; this condensed version was published in November 1859 as On the Origin of Species.