There was growing support for such ideas among dissident anatomists and the general public, but during the first half of the 19th century the English scientific establishment was closely tied to the Church of England, while science was part of natural theology.

Within two decades, there was widespread scientific agreement that evolution, with a branching pattern of common descent, had occurred, but scientists were slow to give natural selection the significance that Darwin thought appropriate.

[8] Early Christian Church Fathers and Medieval European scholars interpreted the Genesis creation narrative allegorically rather than as a literal historical account;[9] organisms were described by their mythological and heraldic significance as well as by their physical form.

[10] The Protestant Reformation inspired a literal interpretation of the Bible, with concepts of creation that conflicted with the findings of an emerging science seeking explanations congruent with the mechanical philosophy of René Descartes and the empiricism of the Baconian method.

John Ray developed an influential natural theology of rational order; in his taxonomy, species were static and fixed, their adaptation and complexity designed by God, and varieties showed minor differences caused by local conditions.

[12] Geoffroy contended that embryonic development recapitulated transformations of organisms in past eras when the environment acted on embryos, and that animal structures were determined by a constant plan as demonstrated by homologies.

[21] The three Fuegian missionaries the expedition returned to Tierra del Fuego were friendly and civilised, yet to Darwin their relatives on the island seemed "miserable, degraded savages",[22] and he no longer saw an unbridgeable gap between humans and animals.

[26] Darwin began speculating, in a series of notebooks, on the possibility that "one species does change into another" to explain these findings, and around July sketched a genealogical branching of a single evolutionary tree, discarding Lamarck's independent lineages progressing to higher forms.

[34] Darwin now had the basic framework of his theory of natural selection, but he was fully occupied with his career as a geologist and held back from compiling it until his book on The Structure and Distribution of Coral Reefs was completed.

[39] Darwin began correspondence about his theorising with the botanist Joseph Dalton Hooker in January 1844, and by July had rounded out his "sketch" into a 230-page "Essay", to be expanded with his research results and published if he died prematurely.

[40] In November 1844, the anonymously published popular science book Vestiges of the Natural History of Creation, written by Scottish journalist Robert Chambers, widened public interest in the concept of transmutation of species.

Darwin read it soon after publication, and scorned its amateurish geology and zoology,[41] but he carefully reviewed his own arguments after leading scientists, including Adam Sedgwick, attacked its morality and scientific errors.

Using his theory, he discovered homologies showing that slightly changed body parts served different functions to meet new conditions, and he found an intermediate stage in the evolution of distinct sexes.

[82] The second edition of 3,000 copies was quickly brought out on 7 January 1860,[83] and incorporated numerous corrections as well as a response to religious objections by the addition of a new epigraph on page ii, a quotation from Charles Kingsley, and the phrase "by the Creator" added to the closing sentence.

[105][106] Page ii contains quotations by William Whewell and Francis Bacon on the theology of natural laws,[107] harmonising science and religion in accordance with Isaac Newton's belief in a rational God who established a law-abiding cosmos.

[113] In that sketch he acknowledged that Patrick Matthew had, unknown to Wallace or himself, anticipated the concept of natural selection in an appendix to a book published in 1831;[114] in the fourth edition he mentioned that William Charles Wells had done so as early as 1813.

He recounted how Lord Morton's mare apparently demonstrated telegony, offspring inheriting characteristics of a previous mate of the female parent, and accepted this process as increasing the variation available for natural selection.

Much of the chapter responds to George Jackson Mivart's criticisms, including his claim that features such as baleen filters in whales, flatfish with both eyes on one side and the camouflage of stick insects could not have evolved through natural selection because intermediate stages would not have been adaptive.

[157][158] To show that there had been enough time for natural selection to work slowly, he cited the example of The Weald as discussed in Principles of Geology together with other observations from Hugh Miller, James Smith of Jordanhill and Andrew Ramsay.

This made no sense under doctrines of independent creation of species, as even Richard Owen had admitted, but the "explanation is manifest on the theory of the natural selection of successive slight modifications" showing common descent.

"[31][172] Darwin ends with a passage that became well known and much quoted: It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us ...

Darwin presents supporting facts drawn from many disciplines, showing that his theory could explain a myriad of observations from many fields of natural history that were inexplicable under the alternative concept that species had been individually created.

[188] In 1856, his "big book on species" titled Natural Selection was to include a "note on Man", but when Wallace enquired in December 1857, Darwin replied; "You ask whether I shall discuss 'man';—I think I shall avoid whole subject, as so surrounded with prejudices, though I fully admit that it is the highest & most interesting problem for the naturalist.

Darwin's scientific method was also disputed, with his proponents favouring the empiricism of John Stuart Mill's A System of Logic, while opponents held to the idealist school of William Whewell's Philosophy of the Inductive Sciences, in which investigation could begin with the intuitive idea that species were fixed objects created by design.

[230] Others, including Charles Lyell and Alfred Russel Wallace, thought that humans shared a common ancestor with apes, but higher mental faculties could not have evolved through a purely material process.

[101] The intelligentsia in Russia had accepted the general phenomenon of evolution for several years before Darwin had published his theory, and scientists were quick to take it into account, although the Malthusian aspects were felt to be relatively unimportant.

The political economy of struggle was criticised as a British stereotype by Karl Marx and by Leo Tolstoy, who had the character Levin in his novel Anna Karenina voice sharp criticism of the morality of Darwin's views.

Developments in geology meant that there was little opposition based on a literal reading of Genesis,[242] but defence of the argument from design and natural theology was central to debates over the book in the English-speaking world.

This conflict could be reconciled by supposing there was some supernatural intervention on the path leading to humans, or viewing evolution as a purposeful and progressive ascent to mankind's position at the head of nature.

It makes sense of the geological record, biogeography, parallels in embryonic development, biological homologies, vestigiality, cladistics, phylogenetics and other fields, with unrivalled explanatory power; it has also become essential to applied sciences such as medicine and agriculture.