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Charles Robert Darwin FRS FRGS FLS FZS[2] (/ˈdɑːrwɪn/;[5] 12 February 1809 – 19 April 1882) was an English naturalist, geologist and biologist,[6] best known for his contributions to the science of evolution.[I] His proposition that all species of life have descended over time from common ancestors is now widely accepted, and considered a foundational concept in science.[7] In a joint publication with Alfred Russel Wallace, he introduced his scientific theory that this branching pattern of evolution resulted from a process that he called natural selection, in which the struggle for existence has a similar effect to the artificial selection involved in selective breeding.[8] Darwin has been described as one of the most influential figures in human history,[9] and he was honoured by burial in Westminster Abbey.[10]

Darwin published his theory of evolution with compelling evidence in his 1859 book On the Origin of Species.[11][12] By the 1870s, the scientific community and a majority of the educated public had accepted evolution as a fa

Charles Robert Darwin FRS FRGS FLS FZS[2] (/ˈdɑːrwɪn/;[5] 12 February 1809 – 19 April 1882) was an English naturalist, geologist and biologist,[6] best known for his contributions to the science of evolution.[I] His proposition that all species of life have descended over time from common ancestors is now widely accepted, and considered a foundational concept in science.[7] In a joint publication with Alfred Russel Wallace, he introduced his scientific theory that this branching pattern of evolution resulted from a process that he called natural selection, in which the struggle for existence has a similar effect to the artificial selection involved in selective breeding.[8] Darwin has been described as one of the most influential figures in human history,[9] and he was honoured by burial in Westminster Abbey.[10]

Darwin published his theory of evolution with compelling evidence in his 1859 book On the Origin of Species.[11][12] By the 1870s, the scientific community and a majority of the educated public had accepted evolution as a fact. However, many favoured competing explanations which gave only a minor role to natural selection, and it was not until the emergence of the modern evolutionary synthesis from the 1930s to the 1950s that a broad consensus developed in which natural selection was the basic mechanism of evolution.[13][14] Darwin's scientific discovery is the unifying theory of the life sciences, explaining the diversity of life.[15][16]

Darwin's early interest in nature led him to neglect his medical education at the University of Edinburgh; instead, he helped to investigate marine invertebrates. Studies at the University of Cambridge (Christ's College) encouraged his passion for natural science.Darwin published his theory of evolution with compelling evidence in his 1859 book On the Origin of Species.[11][12] By the 1870s, the scientific community and a majority of the educated public had accepted evolution as a fact. However, many favoured competing explanations which gave only a minor role to natural selection, and it was not until the emergence of the modern evolutionary synthesis from the 1930s to the 1950s that a broad consensus developed in which natural selection was the basic mechanism of evolution.[13][14] Darwin's scientific discovery is the unifying theory of the life sciences, explaining the diversity of life.[15][16]

Darwin's early interest in nature led him to neglect his medical education at the University of Edinburgh; instead, he helped to investigate marine invertebrates. Studies at the University of Cambridge (Christ's College) encouraged his passion for natural science.[17] His five-year voyage on HMS Beagle established him as an eminent geologist whose observations and theories supported Charles Lyell's conception of gradual geological change, and publication of his journal of the voyage made him famous as a popular author.[18]

Puzzled by the geographical distribution of wildlife and fossils he collected on the voyage, Darwin began detailed investigations, and in 1838 conceived his theory of natural selection.[19] Although he discussed his ideas with several naturalists, he needed time for extensive research and his geological work had priority.[20] He was writing up his theory in 1858 when Alfred Russel Wallace sent him an essay that described the same idea, prompting immediate joint publication of both of their theories.[21] Darwin's work established evolutionary descent with modification as the dominant scientific explanation of diversification in nature.[13] In 1871 he examined human evolution and sexual selection in The Descent of Man, and Selection in Relation to Sex, followed by The Expression of the Emotions in Man and Animals (1872). His research on plants was published in a series of books, and in his final book, The Formation of Vegetable Mould, through the Actions of Worms (1881), he examined earthworms and their effect on soil.[22][23]

Charles Robert Darwin was born in Shrewsbury, Shropshire, on 12 February 1809, at his family's home, The Mount.[24][25] He was the fifth of six children of wealthy society doctor and financier Robert Darwin and Susannah Darwin (née Wedgwood). His grandfathers Erasmus Darwin and Josiah Wedgwood were both prominent abolitionists. Erasmus Darwin had praised general concepts of evolution and common descent in his Zoonomia (1794), a poetic fantasy of gradual creation including undeveloped ideas anticipating concepts his grandson expanded.[26]

Three quarter length portrait of seated boy smiling and looking at the viewer. He has straight mid-brown hair, and wears dark clothes with a large frilly white collar. In his lap he holds a pot of flowering plants
Painting of the seven-year-old Charles Darwin in 1816, by Ellen Sharples

Both families were largely Unitarian, though the Wedgwoods were adopting Anglicanism. Robert Darwin, himself quietly a freethinker, had baby Charles baptised in November 1809 in the Anglican St Chad's Church, Shrewsbury, but Charles and his siblings attended the Unitarian chapel with their mother. The eight-year-old Charles already had a taste for natural history and collecting when he joined the day school run by its preacher in 1817. That July, his mother died. From September 1818, he joined his older brother Erasmus attending the nearby Anglican Shrewsbury School as a boarder.[27]

Darwin spent the summer of 1825 as an apprentice doctor, helping his father treat the poor of Shropshire, before going to the University of Edinburgh Medical School (at the time the best medical school in the UK) with his brother Erasmus in October 1825. Darwin found lectures dull and surgery distressing, so he neglected his studies. He learned taxidermy in around 40 daily hour-long sessions from John Edmonstone, a freed black slave who had accompanied Charles Waterton in the South American rainforest.[28]

In Darwin's second year at the university he joined the Plinian Society, a student natural-history group featuring lively debates in which radical democratic students with materialistic views challenged orthodox religious concepts of science.[29] He assisted Robert Edmond Grant's investigations of the anatomy and life cycle of marine invertebrates in the Firth of Forth, and on 27 March 1827 presented at the Plinian his own discovery that black spores found in oyster shells were the eggs of a skate leech. One day, Grant praised Lamarck's evolutionary ideas. Darwin was astonished by Grant's audacity, but had recently read similar ideas in his grandfather Erasmus' journals.[

Both families were largely Unitarian, though the Wedgwoods were adopting Anglicanism. Robert Darwin, himself quietly a freethinker, had baby Charles baptised in November 1809 in the Anglican St Chad's Church, Shrewsbury, but Charles and his siblings attended the Unitarian chapel with their mother. The eight-year-old Charles already had a taste for natural history and collecting when he joined the day school run by its preacher in 1817. That July, his mother died. From September 1818, he joined his older brother Erasmus attending the nearby Anglican Shrewsbury School as a boarder.[27]

Darwin spent the summer of 1825 as an apprentice doctor, helping his father treat the poor of Shropshire, before going to the University of Edinburgh Medical School (at the time the best medical school in the UK) with his brother Erasmus in October 1825. Darwin found lectures dull and surgery distressing, so he neglected his studies. He learned taxidermy in around 40 daily hour-long sessions from John Edmonstone, a freed black slave who had accompanied Charles Waterton in the South American rainforest.[28]

In Darwin's second year at the university he joined the Plinian Society, a student University of Edinburgh Medical School (at the time the best medical school in the UK) with his brother Erasmus in October 1825. Darwin found lectures dull and surgery distressing, so he neglected his studies. He learned taxidermy in around 40 daily hour-long sessions from John Edmonstone, a freed black slave who had accompanied Charles Waterton in the South American rainforest.[28]

In Darwin's second year at the university he joined the Plinian Society, a student natural-history group featuring lively debates in which radical democratic students with materialistic views challenged orthodox religious concepts of science.[29] He assisted Robert Edmond Grant's investigations of the anatomy and life cycle of marine invertebrates in the Firth of Forth, and on 27 March 1827 presented at the Plinian his own discovery that black spores found in oyster shells were the eggs of a skate leech. One day, Grant praised Lamarck's evolutionary ideas. Darwin was astonished by Grant's audacity, but had recently read similar ideas in his grandfather Erasmus' journals.[30] Darwin was rather bored by Robert Jameson's natural-history course, which covered geology—including the debate between Neptunism and Plutonism. He learned the classification of plants, and assisted with work on the collections of the University Museum, one of the largest museums in Europe at the time.[31]

Darwin's neglect of medical studies annoyed his father, who shrewdly sent him to Christ's College, Cambridge, to study for a Bachelor of Arts degree as the first step towards becoming an Anglican country parson. As Darwin was unqualified for the Tripos, he joined the ordinary degree course in January 1828.[32] He preferred riding and shooting to studying. During the first few months of Darwin's enrollment, his second cousin William Darwin Fox was also studying at Christ's Church. Fox impressed him with his butterfly collection, introducing Darwin to entomology and influencing him to pursue beetle collecting.[33][34] He did this zealously, and had some of his finds published in James Francis Stephens' Illustrations of British entomology (1829–32).[34][35] Also through Fox, Darwin became a close friend and follower of botany professor John Stevens Henslow.[33] He met other leading parson-naturalists who saw scientific work as religious natural theology, becoming known to these dons as "the man who walks with Henslow". When his own exams drew near, Darwin applied himself to his studies and was delighted by the language and logic of William Paley's Evidences of Christianity[36] (1794). In his final examination in January 1831 Darwin did well, coming tenth out of 178 candidates for the ordinary degree.[37]

Darwin had to stay at Cambridge until June 1831. He studied Paley's Natural Theology or Evidences of the Existence and Attributes of the Deity (first published in 1802), which made an argument for divine design in nature, explaining adaptation as God acting through laws of nature.[38] He read John Herschel's new book, Preliminary Discourse on the Study of Natural Philosophy (1831), which described the highest aim of natural philosophy as understanding such laws through inductive reasoning based on observation, and Alexander von Humboldt's Personal Narrative of scientific travels in 1799–1804. Inspired with "a burning zeal" to contribute, Darwin planned to visit Tenerife with some classmates after graduation to study natural history in the tropics. In preparation, he joined Adam Sedgwick's geology course, then on 4 August travelled with him to spend a fortnight mapping strata in Wales.[39][40]

After leaving Sedgwick in Wales, Darwin spent a week with student friends at Barmouth, then returned home on 29 August to find a letter from Henslow proposing him as a suitable (if unfinished) naturalist for a self-funded supernumerary place on HMS Beagle with captain Robert FitzRoy, emphasising that this was a position for a gentleman rather than "a mere collector". The ship was to leave in four weeks on an expedition to chart the coastline of South America.[41] Robert Darwin objected to his son's planned two-year voyage, regarding it as a waste of time, but was persuaded by his brother-in-law, Josiah Wedgwood II, to agree to (and fund) his son's participation.[42] Darwin took care to remain in a private capacity to retain control over his collection, intending it for a major scientific institution.[43]

After delays, the voyage began on 27 December 1831; it lasted almost five years. As FitzRoy had intended, Darwin spent most of that time on land investigating geology and making natural history collections, while HMS Beagle surveyed and charted coasts.[13][44] He kept careful notes of his observations and theoretical speculations, and at intervals during the voyage his specimens were sent to Cambridge together with letters including a copy of his journal for his family.[45] He had some expertise in geology, beetle collecting and dissecting marine invertebrates, but in all other areas was a novice and ably collected specimens for expert appraisal.[46] Despite suffering badly from seasickness, Darwin wrote copious notes while on board the ship. Most of his zoology notes are about marine invertebrates, starting with plankton collected in a calm spell.[44][47]<

After delays, the voyage began on 27 December 1831; it lasted almost five years. As FitzRoy had intended, Darwin spent most of that time on land investigating geology and making natural history collections, while HMS Beagle surveyed and charted coasts.[13][44] He kept careful notes of his observations and theoretical speculations, and at intervals during the voyage his specimens were sent to Cambridge together with letters including a copy of his journal for his family.[45] He had some expertise in geology, beetle collecting and dissecting marine invertebrates, but in all other areas was a novice and ably collected specimens for expert appraisal.[46] Despite suffering badly from seasickness, Darwin wrote copious notes while on board the ship. Most of his zoology notes are about marine invertebrates, starting with plankton collected in a calm spell.[44][47]

On their first stop ashore at St Jago in Cape Verde, Darwin found that a white band high in the volcanic rock cliffs included seashells. FitzRoy had given him the first volume of Charles Lyell's Principles of Geology, which set out uniformitarian concepts of land slowly rising or falling over immense periods,[II] and Darwin saw things Lyell's way, theorising and thinking of writing a book on geology.[48] When they reached Brazil, Darwin was delighted by the tropical forest,[49] but detested the sight of slavery, and disputed this issue with Fitzroy.[50]

The survey continued to the south in Patagonia. They stopped at Bahía Blanca, and in cliffs near Punta Alta Darwin made a major find of fossil bones of huge extinct mammals beside modern seashells, indicating recent extinction with no signs of change in climate or catastrophe. He identified the little-known Megatherium by a tooth and its association with bony armour, which had at first seemed to him to be like a giant version of the armour on local armadillos. The finds brought great interest when they reached England.[51][52]

On rides with gauchos into the interior to explore geology and collect more fossils, Darwin gained social, political and anthropological insights into both native and colonial people at a time of revolution, and learnt that two types of rhea had separate but overlapping territories.[53][54] Further south, he saw stepped plains of shingle and seashells as raised beaches showing a series of elevations. He read Lyell's second volume and accepted its view of "centres of creation" of species, but his discoveries and theorising challenged Lyell's ideas of smooth continuity and of extinction of species.[55][56]

Three Fuegians on board had been seized during the first Beagle voyage, then during a year in England were educated as missionaries. Darwin found them friendly and civilised, yet at Tierra del Fuego he met "miserable, degraded savages", as different as wild from domesticated animals.[57] He remained convinced that, despite this diversity, all humans were interrelated with a shared origin and potential for improvement towards civilisation. Unlike his scientist friends, he now thought there was no unbridgeable gap between humans and animals.[58] A year on, the mission had been abandoned. The Fuegian they had named Jemmy Button lived like the other natives, had a wife, and had no wish to return to England.[59]

Darwin experienced an earthquake in Chile in 1835 and saw signs that the land had just been raised, including mussel-beds stranded above high tide. High in the Andes he saw seashells, and several fossil trees that had grown on a sand beach. He theorised that as the land rose, oceanic islands sank, and coral reefs round them grew to form atolls.[60][61]

On the geologically new Galápagos Islands, Darwin looked for evidence attaching wildlife to an older "centre of creation", and found mockingbirds allied to those in Chile but differing from island to island. He

Darwin experienced an earthquake in Chile in 1835 and saw signs that the land had just been raised, including mussel-beds stranded above high tide. High in the Andes he saw seashells, and several fossil trees that had grown on a sand beach. He theorised that as the land rose, oceanic islands sank, and coral reefs round them grew to form atolls.[60][61]

On the geologically new Galápagos Islands, Darwin looked for evidence attaching wildlife to an older "centre of creation", and found mockingbirds allied to those in Chile but differing from island to island. He heard that slight variations in the shape of tortoise shells showed which island they came from, but failed to collect them, even after eating tortoises taken on board as food.[62][63] In Australia, the marsupial rat-kangaroo and the platypus seemed so unusual that Darwin thought it was almost as though two distinct Creators had been at work.[64] He found the Aborigines "good-humoured & pleasant", and noted their depletion by European settlement.[65]

FitzRoy investigated how the atolls of the Cocos (Keeling) Islands had formed, and the survey supported Darwin's theorising.[61] FitzRoy began writing the official Narrative of the Beagle voyages, and after reading Darwin's diary he proposed incorporating it into the account.[66] Darwin's Journal was eventually rewritten as a separate third volume, on natural history.[67]

In Cape Town, South Africa, Darwin and FitzRoy met John Herschel, who had recently written to Lyell praising his uniformitarianism as opening bold speculation on "that mystery of mysteries, the replacement of extinct species by others" as "a natural in contradistinction to a miraculous process".[68] When organising his notes as the ship sailed home, Darwin wrote that, if his growing suspicions about the mockingbirds, the tortoises and the Falkland Islands fox were correct, "such facts undermine the stability of Species", then cautiously added "would" before "undermine".[69] He later wrote that such facts "seemed to me to throw some light on the origin of species".[70]

By the time Darwin returned to England, he was already a celebrity in scientific circles as in December 1835 Henslow had fostered his former pupil's reputation by publishing a pamphlet of Darwin's geological letters for select naturalists.[71] On 2 October 1836 the ship anchored at Falmouth, Cornwall. Darwin promptly made the long coach journey to Shrewsbury to visit his home and see relatives. He then hurried to Cambridge to see Henslow, who advised him on finding naturalists available to catalogue Darwin's animal collections and who agreed to take on the botanical specimens. Darwin's father organised investments, enabling his son to be a self-funded gentleman scientist, and an excited Darwin went round the London institutions being fêted and seeking experts to describe the collections. British zoologists at the time had a huge backlog of work due to natural history collecting being promoted and encouraged through the British Empire, and there was a danger of specimens just being left in storage.[72]

Charles Lyell eagerly met Darwin for the first time on 29 October and soon introduced him to the up-and-coming anatomist Richard Owen, who had the facilities of the Royal College of Surgeons to work on the fossil bones collected by Darwin. Owen's surprising results included other gigantic extinct ground sloths as well as the Megatherium, a near complete skeleton of the unknown Scelidotherium and a hippopotamus-sized rodent-like skull named Toxodon resembling a giant capybara. The armour fragments were actually from Glyptodon, a huge armadillo-like creature as Darwin had initially thought.[73][52] These extinct creatures were related to living species in South America.[74]

In mid-December, Darwin took lodgings in Cambridge to organise work on his collections and rewri

Charles Lyell eagerly met Darwin for the first time on 29 October and soon introduced him to the up-and-coming anatomist Richard Owen, who had the facilities of the Royal College of Surgeons to work on the fossil bones collected by Darwin. Owen's surprising results included other gigantic extinct ground sloths as well as the Megatherium, a near complete skeleton of the unknown Scelidotherium and a hippopotamus-sized rodent-like skull named Toxodon resembling a giant capybara. The armour fragments were actually from Glyptodon, a huge armadillo-like creature as Darwin had initially thought.[73][52] These extinct creatures were related to living species in South America.[74]

In mid-December, Darwin took lodgings in Cambridge to organise work on his collections and rewrite his Journal.[75] He wrote his first paper, showing that the South American landmass was slowly rising, and with Lyell's enthusiastic backing read it to the Geological Society of London on 4 January 1837. On the same day, he presented his mammal and bird specimens to the Zoological Society. The ornithologist John Gould soon announced that the Galapagos birds that Darwin had thought a mixture of blackbirds, "gros-beaks" and finches, were, in fact, twelve separate species of finches. On 17 February, Darwin was elected to the Council of the Geological Society, and Lyell's presidential address presented Owen's findings on Darwin's fossils, stressing geographical continuity of species as supporting his uniformitarian ideas.[76]

Early in March, Darwin moved to London to be near this work, joining Lyell's social circle of scientists and experts such as Charles Babbage,[77] who described God as a programmer of laws. Darwin stayed with his freethinking brother Erasmus, part of this Whig circle and a close friend of the writer Harriet Martineau, who promoted Malthusianism underlying the controversial Whig Poor Law reforms to stop welfare from causing overpopulation and more poverty. As a Unitarian, she welcomed the radical implications of transmutation of species, promoted by Grant and younger surgeons influenced by Geoffroy. Transmutation was anathema to Anglicans defending social order,[78] but reputable scientists openly discussed the subject and there was wide interest in John Herschel's letter praising Lyell's approach as a way to find a natural cause of the origin of new species.[68]

Gould met Darwin and told him that the Galápagos mockingbirds from different islands were separate species, not just varieties, and what Darwin had thought was a "wren" was also in the finch group. Darwin had not labelled the finches by island, but from the notes of others on the ship, including FitzRoy, he allocated species to islands.[79] The two rheas were also distinct species, and on 14 March Darwin announced how their distribution changed going southwards.[80]

By mid-March 1837, barely six months after his return to England, Darwin was speculating in his Red Notebook on the possibility that "one species does change into another" to explain the geographical distribution of living species such as the rheas, and extinct ones such as the strange extinct mammal Macrauchenia, which resembled a giant guanaco, a llama relative. His thoughts on lifespan, asexual reproduction and sexual reproduction developed in his "B" notebook around mid-July on to variation in offspring "to adapt & alter the race to changing world" explaining the Galápagos tortoises, mockingbirds and rheas. He sketched branching descent, then a genealogical branching of a single evolutionary tree, in which "It is absurd to talk of one animal being higher than another", discarding Lamarck's independent lineages progressing to higher forms.[81]

Overwork, illness, and marriage

While developing this intensive study of transmutation, Darwin became mired in more work. Still rewriting his Journal, he took on editing and publishing the expert reports on his collections, and with Henslow's help obtained a Treasury grant of £1,000 to sponsor this multi-volume Zoology of the Voyage of H.M.S. Beagle, a sum equivalent to about £92,000 in 2018.[82] He stretch

While developing this intensive study of transmutation, Darwin became mired in more work. Still rewriting his Journal, he took on editing and publishing the expert reports on his collections, and with Henslow's help obtained a Treasury grant of £1,000 to sponsor this multi-volume Zoology of the Voyage of H.M.S. Beagle, a sum equivalent to about £92,000 in 2018.[82] He stretched the funding to include his planned books on geology, and agreed to unrealistic dates with the publisher.[83] As the Victorian era began, Darwin pressed on with writing his Journal, and in August 1837 began correcting printer's proofs.[84]

As Darwin worked under pressure, his health suffered. On 20 September he had "an uncomfortable palpitation of the heart", so his doctors urged him to "knock off all work" and live in the country for a few weeks. After visiting Shrewsbury he joined his Wedgwood relatives at Maer Hall, Staffordshire, but found them t

As Darwin worked under pressure, his health suffered. On 20 September he had "an uncomfortable palpitation of the heart", so his doctors urged him to "knock off all work" and live in the country for a few weeks. After visiting Shrewsbury he joined his Wedgwood relatives at Maer Hall, Staffordshire, but found them too eager for tales of his travels to give him much rest. His charming, intelligent, and cultured cousin Emma Wedgwood, nine months older than Darwin, was nursing his invalid aunt. His uncle Josiah pointed out an area of ground where cinders had disappeared under loam and suggested that this might have been the work of earthworms, inspiring "a new & important theory" on their role in soil formation, which Darwin presented at the Geological Society on 1 November 1837.[85]

William Whewell pushed Darwin to take on the duties of Secretary of the Geological Society. After initially declining the work, he accepted the post in March 1838.[86] Despite the grind of writing and editing the Beagle reports, Darwin made remarkable progress on transmutation, taking every opportunity to question expert naturalists and, unconventionally, people with practical experience in selective breeding such as farmers and pigeon fanciers.[13][87] Over time, his research drew on information from his relatives and children, the family butler, neighbours, colonists and former shipmates.[88] He included mankind in his speculations from the outset, and on seeing an orangutan in the zoo on 28 March 1838 noted its childlike behaviour.[89]

The strain took a toll, and by June he was being laid up for days on end with stomach problems, headaches and heart symptoms. For the rest of his life, he was repeatedly incapacitated with episodes of stomach pains, vomiting, severe boils, palpitations, trembling and other symptoms, particularly during times of stress, such as attending meetings or making social visits. The cause of Darwin's illness remained unknown, and attempts at treatment had only ephemeral success.[90]

On 23 June, he took a break and went "geologising" in Scotland. He visited Glen Roy in glorious weather to see the parallel "roads" cut into the hillsides at three heights. He later published his view that these were marine raised beaches, but then had to accept that they were shorelines of a proglacial lake.[91]

Fully recuperated, he returned to Shrewsbury in July. Used to jotting down daily notes on animal breeding, he scrawled rambling thoughts about marriage, career and prospects on two scraps of paper, one with columns headed "Marry" and "Not Marry". Advantages under "Marry" included "constant companion and a friend in old age ... better than a dog anyhow", against points such as "less money for books" and "terrible loss of time."Glen Roy in glorious weather to see the parallel "roads" cut into the hillsides at three heights. He later published his view that these were marine raised beaches, but then had to accept that they were shorelines of a proglacial lake.[91]

Fully recuperated, he returned to Shrewsbury in July. Used to jotting down daily notes on animal breeding, he scrawled rambling thoughts about marriage, career and prospects on two scraps of paper, one with columns headed "Marry" and "Not Marry". Advantages under "Marry" included "constant companion and a friend in old age ... better than a dog anyhow", against points such as "less money for books" and "terrible loss of time."[92] Having decided in favour of marriage, he discussed it with his father, then went to visit his cousin Emma on 29 July. He did not get around to proposing, but against his father's advice he mentioned his ideas on transmutation.[93]

Continuing his research in London, Darwin's wide reading now included the sixth edition of Malthus's An Essay on the Principle of Population, and on 28 September 1838 he noted its assertion that human "population, when unchecked, goes on doubling itself every twenty five years, or increases in a geometrical ratio", a geometric progression so that population soon exceeds food supply in what is known as a Malthusian catastrophe. Darwin was well prepared to compare this to de Candolle's "warring of the species" of plants and the struggle for existence among wildlife, explaining how numbers of a species kept roughly stable. As species always breed beyond available resources, favourable variations would make organisms better at surviving and passing the variations on to their offspring, while unfavourable variations would be lost. He wrote that the "final cause of all this wedging, must be to sort out proper structure, & adapt it to changes", so that "One may say there is a force like a hundred thousand wedges trying force into every kind of adapted structure into the gaps of in the economy of nature, or rather forming gaps by thrusting out weaker ones."[13][94] This would result in the formation of new species.[13][95] As he later wrote in his Autobiography: