Darwin shapes his theory
Darwin had returned to a scientific world buzzing with ideas of 
"Transmutation of species" to account for the discoveries of extinct 
species, and Whig political reforms founded in the ideas of Thomas 
Malthus. In secret notebooks he worked on ideas he had been developing 
during the voyage.

In January 1837 the ornithologist John Gould informed Darwin that several 
very different species of birds collected in the Galápagos were all 
finches. From the collections of others, including FitzRoy's, he was 
able to relate the finches to separate islands. This, coupled with a 
re-reading of Thomas Malthus' 1798 essay on populations, triggered a 
chain of thought that would culminate in the theory of evolution by 
natural and sexual selection. He developed the hypothesis that, for 
example, where every island in the Galápagos Archipelago had its 
own kind of tortoises, these had originated from a single tortoise 
species and had adapted to life on the different islands in different ways.

Based on these thoughts, he formulated his ideas about the changes 
and developments of species in his Notebook on the Transmutation of 
Species, which was in accordance with Lyell's Principles of Geology 
involving gradual change over a long time, and Thomas Malthus' Essay 
on the Principle of Population which stated that the size of a 
population is limited by the food resources available. Realizing the 
potential of this understanding, Darwin undertook extensive 
experiments with pigeons and plants, and extensive consultation 
with pig breeders and other animal husbanders, in an attempt to 
discover holes in the hypothesis. He took his time with careful 
research until he had enough evidence, knowing that a great deal 
of opposition would likely erupt when he presented his theory.


First writings

In 1842, Darwin formulated a short "Pencil Sketch" of his theory 
and by 1844 had written a 240 page "Essay" which provides an 
expanded version of his early ideas on natural selection. Between 
1844 and 1858, when he would present his theory to the Linnean 
Society of London, Darwin wrote his masterpiece, modifying his 
theory in a number of ways as he wrote.


Announcement of theory

Darwin, as evidenced by his later work, The Descent of Man, was 
well aware of the implication the theory had for the origin of 
humanity; consequently, he withheld publication of his 
accumulated evidence in favour of natural selection for well over
a decade, and to slighly lessen the controversy, he stopped short 
of including mankind as a subject of the work. He was forced into 
publication because of the independent development of a similar 
theory by Alfred Russel Wallace in 1858. It is felt by some that 
Wallace deserves as much credit as Darwin for the theory of natural 
selection, and that he has been rather unfairly marginalised from 
the history of its development.

Darwin's work brought him a correspondence relationship with Alfred 
Russel Wallace, working in the islands of the South Pacific and 
Indonesia. Wallace had been one of Darwin's numerous providers of 
natural history specimens, and was considerably lower in social 
status than Darwin himself. On 18 June 1858, Wallace sought Darwin's 
ideas on a theory Wallace had developed which almost exactly mirrored 
Darwin's own work. Darwin was himself horrified at the prospects of 
being scooped, but also felt bound to respect Wallace's claim to 
priority. Seeking advice from his scientific friends, he was 
encouraged to announce his theory along with Wallace's contribution, 
and to establish that he had in fact started developing the theory 
ten years before Wallace did. On 1 July 1858, Darwin's announcement 
of his theory was read to the Linnean Society, in London, jointly 
with Wallace's paper. Neither men were present at the reading, 
Darwin was at home with his dying son, and Wallace was in the Far 
East somewhere. The paper was entitled On the Tendency of Species 
to form Varieties; and on the Perpetuation of Varieties and 
Species by Natural Means of Selection. Fortunately for Darwin, 
Wallace was satisfied with the arrangement: though he would always 
be second-string to Darwin (his role reduced to that of catalyst), 
to be linked to a well-respected naturalist of high social standing 
like Darwin was still a fantastic career opportunity, perhaps more 
than he could have accomplished himself in the tight-knit circle 
of Victorian-era science.

The initial announcement of the theory garnered little immediate 
attention. It was mentioned briefly in a few small reviews but 
did not yet command much further thought, and was not yet fully 
distinguishable to most people from other varieties of evolutionary 
thought. For the next thirteen months, Darwin would labour to 
produce what was originally to be an abstract of his "big book 
on species". Receiving constant promotion and encouragement from 
his scientific friends, Darwin finally finished On the Origin of 
Species by Means of Natural Selection and arranged to have it 
published. Through his network of social connections and correspondents, 
Darwin's book was given a great deal of initial attention, marketed 
by his scientifically respectable friends as being a worthy 
contribution to scientific thought, and with reviews placed in 
prominent periodicals. Though the book itself only briefly alluded to 
the fact that man, too, would evolve as with the other organisms 
described in his book—"light will be thrown on the origin of man 
and his history," Darwin wrote in deliberate understatement—Darwin's 
view of nature became quickly associated with one in which the 
distinction between man and beast was nonexistent. As attention 
and controversy gathered, the book was translated into numerous 
languages and went through a number of reprints, becoming a staple 
scientific text accessible to a newly curious middle class. It would 
prove to be the most controversial and discussed scientific book 
ever written.

Reaction

It provoked an outraged response from the Church of England. At a 
meeting of the British Association for the Advancement of Science 
in Oxford, 'Soapy Sam' Wilberforce, the Bishop of Oxford, and 
Robert FitzRoy (the Captain of HMS Beagle) argued against Darwin, 
and Thomas Huxley established himself as "Darwin's bulldog" – 
the fiercest defender of evolutionary theory on the Victorian 
stage. On being asked by Wilberforce, whether he was descended 
from monkeys on his grandfather's side or his grandmother's 
side, Huxley, recognizing his opportunity, apparently muttered 
to himself: "The Lord has delivered him into my hands", and then 
replied that he "would rather be descended from an ape than 
from a cultivated man who used his gifts of culture and eloquence 
in the service of prejudice and falsehood" (several alternative 
versions of this supposed quote exist, see Wilberforce and Huxley: 
A Legendary Encounter (http://users.ox.ac.uk/~jrlucas/legend.html)). 
The story spread around the country: Huxley had said he would 
rather be an ape than a Bishop.

Darwin himself did not personally defend his theories in public, 
though he watched the ongoing debates eagerly. He was constantly 
in ill health, and preferred to garnish support by means of his 
letters and correspondence. A core circle of scientific 
friends–Huxley, Charles Lyell, Joseph Dalton Hooker, and Asa 
Gray–actively pushed his work onto the fore of the scientific 
and public stage, and defended him against his many mounting 
critics. Unexpectedly to Darwin, his theory became not only a 
key scientific controversy of the era, but was also resonated 
with many anti-Victorian sentiments at the time, becoming a 
key fixture of popular culture of the period (and beyond).