The inception of Darwin's theory occurred during an intensively busy period which began when Charles Darwin returned from the survey voyage of the Beagle, with his reputation as a fossil collector and geologist already established. He was given an allowance from his father to become a gentleman naturalist rather than a clergyman, and his first tasks were to find suitable experts to describe his collections, write out his Journal and Remarks, and present papers on his findings to the Geological Society of London.
At Darwin's geological début, the anatomist Richard Owen's reports on the fossils showed that extinct species were related to current species in the same locality, and the ornithologist John Gould showed that bird specimens from the Galápagos Islands were of distinct species related to places, not just varieties. These points convinced Darwin that transmutation of species must be occurring, and in his Red Notebook he jotted down his first evolutionary ideas. He began specific transmutation notebooks with speculations on variation in offspring "to adapt & alter the race to changing world", and sketched an "irregularly branched" genealogical branching of a single evolutionary tree.
Animal observations of an orangutan at the zoo showed how human its expressions looked, confirming his thoughts from the Beagle voyage that there was little gulf between man and animals. He investigated animal breeding and found parallels to nature removing runts and keeping the fit, with farmers deliberately selecting breeding animals so that through "a thousand intermediate forms" their descendants were significantly changed. His speculations on instincts and mental traits suggested habits, beliefs and facial expressions having evolved, and considered the social implications. While this was his "prime hobby", he was struggling with an immense workload and began suffering from his illness. Having taken a break from work, his thoughts of marriage turned to his cousin Emma Wedgwood.
Reading about Malthus and natural law led him to apply to his search the Malthusian logic of social thinking of struggle for survival with no handouts, and he "had at last got a theory by which to work". He proposed to Emma and was accepted. In his theory, he compared breeders selecting traits to natural selection from variants thrown up by "chance", and continued to look to the countryside for supporting information. On 24 January 1839 he was elected as Fellow of the Royal Society, and on the 29th married Emma. The development of Darwin's theory followed.
Background Darwin was not the first to propose that species of organisms could become modified over time. In the third edition of On the Origin of Species Darwin provided a historical sketch of his predecessors in writing of descent with modification or natural selection, including those whom he had only learned of after the 1859 publication of The Origin. His account essentially deals with 19th-century authors; "Passing over authors from the classical period to that of Buffon, with whose writings I am not familiar, Lamarck was the first man whose conclusions on this subject excited much attention." However, in a footnote he remarks on how his grandfather, Dr. Erasmus Darwin, Goethe and Geoffroy Saint Hilaire came to the same conclusion on the origin of species in the years 1794–95, anticipating Lamarck.
After his early life in a Unitarian family, Charles Darwin developed his interest in natural history. At Edinburgh University his work as a student of Robert Edmund Grant involved him in pioneering investigations of the ideas of Lamarck and Erasmus Darwin on homology showing common descent, but he also saw how controversial and troubling such theories were. Robert Jameson's course taught Darwin stratigraphic geology, and closed with lectures on the "Origin of the Species of Animals". At Christ's College, Cambridge to qualify as an Anglican clergyman, Darwin became passionate about beetle collecting, then shone in John Stevens Henslow's botany course. He was convinced by Paley's Natural Theology which set out the Teleological argument that complexity of "design" in nature proved God's role as Creator, and by the views of Paley and John Herschel that creation was by laws which science could discover, not by intermittent miracles. The geology course of Adam Sedgwick and summer work mapping strata in Wales emphasised that life on earth went back over eons of time.
Then on his voyage on the Beagle Darwin became convinced by Charles Lyell's uniformitarian theory of gradual geological process (see Lyell's Principles of Geology, which Darwin took along on the Beagle), and puzzled over how various theories of creation fitted the evidence he saw. However, Darwin did not conceive the theory of evolution during the Beagles voyage, later recounting that: it was equally evident that neither the action of the surrounding conditions, nor the will of the organisms (especially in the case of plants), could account for the innumerable cases in which organisms of every kind are beautifully adapted to their habitats of life—for instance, a woodpecker or a tree-frog to climb trees, or a seed for dispersal by hooks or plumes. I had always been much struck by such adaptations, and until these could be explained it seemed to me almost useless to endeavour to prove by indirect evidence that species have been modified.
Return to England When Beagle returned, it anchored at Falmouth, Cornwall, on 2 October 1836. That same stormy night, Darwin set off on the mail coach for two days' travel to his family home – The Mount House in Shrewsbury, Shropshire. He arrived late at night on 4 October. and having taken the coach for his last visit, had thought he might sleep at the Lion coaching inn rather disturb them "in the dead of the night". He greeted his family at breakfast in the morning, and began catching up with news of his family and of the country: "all England appears changed". The Reform Bill had brought what the Tory Duke of Wellington described as a shift in power from decent Tory Anglicans to Whig manufacturers, shopkeepers and atheists. Educated people were discussing the writings of Thomas Malthus on population outstripping resources as the New Poor Law, described by opponents as "a Malthusian bill designed to force the poor to emigrate, to work for lower wages, to live on a coarser sort of food", brought the construction of workhouses in the southern counties despite riots and arson. The government had not yet dared introduce these measures to London and the industrial north, and recession was bringing threats of mass unemployment.
Darwin wrote to Henslow that he was still "giddy with joy & confusion... I want your advice on so many points, indeed I am in the clouds" and on 15 October went on to Cambridge to get advice from Henslow and Sedgwick on the task of organising the description and cataloguing of his collections accumulated from the Beagle expedition. Henslow took on the plants, and Darwin was given introductions to the best London naturalists with a warning that they would already be busy with other work.
Charles went on to stay with his brother Erasmus in London, near the scientific institutions which were in the throes of renovation, while the city itself was being torn up to install new sewers and gas lighting. He went round the British Museum, the Royal College of Surgeons, the Linnean, the Zoological Society and Geological Society, trying to get the experts to take on his collections. Henslow had already established his former pupil's reputation during the Beagle expedition by giving selected naturalists access to fossil specimens sent back, as well as reading out Extracts from Letters to Henslow to the Cambridge Philosophical Society, which had them privately printed for distribution, while Darwin's geological notes from the letters were summarised by Sedgwick at the Geological Society, and extracts appeared in magazines. Darwin went "in most exciting dissipation amongst the Dons in science", and as Charles Bunbury reported, "[he] seems to be a universal collector" finding new species "to the surprise of all the big wigs". While geologists were quick to take on the rock samples, zoologists already had more specimens arriving than they could deal with. Their institutions were in turmoil as democrats argued for reforms replacing the aristocratic amateurs with professional salaried scientists as in the French research institutes. At the Zoological Society the reformers were led by Darwin's tutor from Edinburgh days, Robert Edmund Grant. Darwin now had an allowance plus stocks from his father, bringing him around £400 per year, and his sympathies were with the amateur clerical "Dons in science" of Cambridge.
Owen and fossils The geologist Charles Lyell invited Darwin to dinner on 29 October 1836. Over dinner Lyell listened eagerly to Darwin's stories (which supported Lyell's uniformitarianism) and introduced him to Richard Owen and William Broderip, Tories who had just been involved in voting Grant out of a position at the Zoological Society. Owen was rapidly ousting Grant as the country's leading anatomist. Darwin went to visit him at his Royal College of Surgeons, and Owen agreed to work on some animal specimens in spirits and the fossil bones. Owen shared Darwin's enthusiasm. He was a proponent of German ideas of "organising energy" and vehemently opposed to Grant's evolution. At around this time Grant was one of the few to volunteer his help with cataloguing the collection. Darwin turned down the offer, not wanting to be associated with a disreputable radical who denounced his Cambridge friends.
On 12 November Darwin visited his Wedgwood relatives at Maer Hall, and they encouraged him to publish a book of his travels based on his diary, an idea his sisters picked up when he visited his home.
On 2 December he returned to London and began finding takers for his specimens, with Thomas Bell and the Revd. William Buckland interested in the reptiles. Darwin's reputation was being made by the giant mammal fossils. Owen's first surprising revelation was that a hippopotamus-sized fossil skull 2 feet 4 inches (710 mm) long which Darwin had bought for about two shillings near Mercedes while on a "galloping" trip 120 miles (190 km) from Montevideo was of an extinct rodent-like creature resembling a giant capybara, which Owen named Toxodon. Darwin wrote to his sister Caroline that "[the fossils] are turning out great treasures" and of the Toxodon, "There is another head, as large as a Rhinoceros which as far as they can guess, must have been a gnawing animal. Conceive a Rat or a Hare of such a size – What famous Cats they ought to have had in those days!" The College of Surgeons distributed casts of the fossils to the major scientific institutions.