By the start of 1856, Darwin was investigating whether eggs and seeds could survive travel across seawater to spread species across oceans.
Hooker increasingly doubted the traditional view that species were fixed, but their young friend Thomas Henry Huxley was still firmly against the transmutation of species.
Lyell was intrigued by Darwin's speculations without realising their extent.
When he read a paper by Alfred Russel Wallace, "On the Law which has Regulated the Introduction of New Species", he saw similarities with Darwin's thoughts and urged him to publish to establish precedence.
Though Darwin saw no threat, on 14 May 1856 he began writing a short paper.
Finding answers to difficult questions held him up repeatedly, and he expanded his plans to a "big book on species" titled Natural Selection, which was to include his "note on Man".
He continued his researches, obtaining information and specimens from naturalists worldwide including Wallace who was working in Borneo.
In mid-1857 he added a section heading; "Theory applied to Races of Man", but did not add text on this topic.
On 5 September 1857, Darwin sent the American botanist Asa Gray a detailed outline of his ideas, including an abstract of Natural Selection, which omitted human origins and sexual selection.
In December, Darwin received a letter from Wallace asking if the book would examine human origins.
He responded that he would avoid that subject, "so surrounded with prejudices", while encouraging Wallace's theorising and adding that "I go much further than you."

Darwin's book was only partly written when, on 18 June 1858, he received a paper from Wallace describing natural selection.
Shocked that he had been "forestalled", Darwin sent it on that day to Lyell, as requested by Wallace, and although Wallace had not asked for publication, Darwin suggested he would send it to any journal that Wallace chose.
His family was in crisis with children in the village dying of scarlet fever, and he put matters in the hands of his friends.
After some discussion, with no reliable way of involving Wallace, Lyell and Hooker decided on a joint presentation at the Linnean Society on 1 July of On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection.
On the evening of 28 June, Darwin's baby son died of scarlet fever after almost a week of severe illness, and he was too distraught to attend.

There was little immediate attention to this announcement of the theory; the president of the Linnean Society remarked in May 1859 that the year had not been marked by any revolutionary discoveries.
Only one review rankled enough for Darwin to recall it later; Professor Samuel Haughton of Dublin claimed that "all that was new in them was false, and what was true was old".
Darwin struggled for thirteen months to produce an abstract of his "big book", suffering from ill health but getting constant encouragement from his scientific friends.
Lyell arranged to have it published by John Murray.

On the Origin of Species proved unexpectedly popular, with the entire stock of 1,250 copies oversubscribed when it went on sale to booksellers on 22 November 1859.
In the book, Darwin set out "one long argument" of detailed observations, inferences and consideration of anticipated objections.
In making the case for common descent, he included evidence of homologies between humans and other mammals.
Having outlined sexual selection, he hinted that it could explain differences between human races.
He avoided explicit discussion of human origins, but implied the significance of his work with the sentence; "Light will be thrown on the origin of man and his history."
His theory is simply stated in the introduction:
As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance
By the start of 1856, Darwin was investigating whether eggs and seeds could survive travel across seawater to spread species across oceans. Hooker increasingly doubted the traditional view that species were fixed, but their young friend Thomas Henry Huxley was still firmly against the transmutation of species. Lyell was intrigued by Darwin's speculations without realising their extent. When he read a paper by Alfred Russel Wallace, "On the Law which has Regulated the Introduction of New Species", he saw similarities with Darwin's thoughts and urged him to publish to establish precedence. Though Darwin saw no threat, on 14 May 1856 he began writing a short paper. Finding answers to difficult questions held him up repeatedly, and he expanded his plans to a "big book on species" titled Natural Selection, which was to include his "note on Man". He continued his researches, obtaining information and specimens from naturalists worldwide including Wallace who was working in Borneo. In mid-1857 he added a section heading; "Theory applied to Races of Man", but did not add text on this topic. On 5 September 1857, Darwin sent the American botanist Asa Gray a detailed outline of his ideas, including an abstract of Natural Selection, which omitted human origins and sexual selection. In December, Darwin received a letter from Wallace asking if the book would examine human origins. He responded that he would avoid that subject, "so surrounded with prejudices", while encouraging Wallace's theorising and adding that "I go much further than you."
Darwin's book was only partly written when, on 18 June 1858, he received a paper from Wallace describing natural selection. Shocked that he had been "forestalled", Darwin sent it on that day to Lyell, as requested by Wallace, and although Wallace had not asked for publication, Darwin suggested he would send it to any journal that Wallace chose. His family was in crisis with children in the village dying of scarlet fever, and he put matters in the hands of his friends. After some discussion, with no reliable way of involving Wallace, Lyell and Hooker decided on a joint presentation at the Linnean Society on 1 July of On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection. On the evening of 28 June, Darwin's baby son died of scarlet fever after almost a week of severe illness, and he was too distraught to attend.
There was little immediate attention to this announcement of the theory; the president of the Linnean Society remarked in May 1859 that the year had not been marked by any revolutionary discoveries. Only one review rankled enough for Darwin to recall it later; Professor Samuel Haughton of Dublin claimed that "all that was new in them was false, and what was true was old". Darwin struggled for thirteen months to produce an abstract of his "big book", suffering from ill health but getting constant encouragement from his scientific friends. Lyell arranged to have it published by John Murray.
On the Origin of Species proved unexpectedly popular, with the entire stock of 1,250 copies oversubscribed when it went on sale to booksellers on 22 November 1859. In the book, Darwin set out "one long argument" of detailed observations, inferences and consideration of anticipated objections. In making the case for common descent, he included evidence of homologies between humans and other mammals. Having outlined sexual selection, he hinted that it could explain differences between human races. He avoided explicit discussion of human origins, but implied the significance of his work with the sentence; "Light will be thrown on the origin of man and his history." His theory is simply stated in the introduction:
As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance 
Charles Darwin