User:Dave souza/Reception of the Origin

Charles Darwin's On the Origin of Species (published 24 November 1859) is a seminal work in scientific literature and a landmark work in evolutionary biology. The full title was On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, in which "races" refers to biological varieties. For the 6th edition of 1872, the title was changed to The Origin of Species. It introduced the theory that populations evolve over the course of generations through a process of natural selection. Darwin's book presented a body of evidence that the diversity of life arose through a branching pattern of evolution and common descent, evidence he had accumulated on the voyage of the Beagle in the 1830s and subsequently expanded through research, correspondence, and experimentation.

The book was written to be read by non-specialists, and it attracted widespread interest on its publication. Evolution was highly controversial during the first half of the 19th century, as the idea of transmutation of species was at odds with the accepted notion that species were unchanging parts of a designed hierarchy. It was the subject of political and theological debates, with competing ideas of biology trying to explain new findings. Support for evolutionary ideas was already growing among a new generation of anatomists and the general public, but to a scientific establishment closely tied to the Church of England, science was part of natural theology. Some naturalists long committed to natural theology found it difficult to accept that humans were descended from other animals. The evidence Darwin presented in his book generated scientific, philosophical, and religious discussion, which led to widespread acceptance that evolution had occurred, and the replacement of natural theology by methodological naturalism. This shift also contributed significantly to the professionalisation of British science. The theory of evolution has continued to advance since Darwin's time, but the scientific consensus remains that natural selection is the primary explanation for the development of new species, although political and religious controversies continue.

Summary of Darwin's theory
Darwin's theory is based on key facts and inferences drawn from them, which biologist Ernst Mayr summarized as follows:


 * Every species is fertile enough that if all offspring survived to reproduce the population would grow (fact).
 * Despite periodic fluctuations, populations remain roughly the same size (fact).
 * Resources such as food are limited and are relatively stable over time (fact).
 * A struggle for survival ensues (inference).
 * Individuals in a population vary significantly from one another (fact).
 * Much of this variation is inheritable (fact).
 * Individuals less suited to the environment are less likely to survive and less likely to reproduce; individuals more suited to the environment are more likely to survive and more likely to reproduce and leave their inheritable traits to future generations, which produces the process of natural selection (inference).
 * This slowly effected process results in populations changing to adapt to their environments, and ultimately, these variations accumulate over time to form new species (inference).

Developments before Darwin's theory
In Ancient Greece, Empedocles argued that new organisms arose from chance natural processes, but Aristotle disputed this. Early Christian Church Fathers held divergent opinions on the meanings of creation according to Genesis. In Medieval Europe its symbolic importance was emphasised, and scholars saw the Classical great chain of being as a social hierarchy, with organisms described by their mythological and heraldic significance as much as by their physical form. Nature was widely believed to be unstable and capricious, with monstrous births from union between species, and spontaneous generation of life.

The Protestant Reformation inspired Biblical literalism and concepts of creation which conflicted with the findings of emerging science seeking Cartesian mechanical explanations using the empiricism of the Baconian method. The Ussher chronology calculated recent creation. In the Royal Society, formed to seek stability after the religious turmoil of the English civil war, John Ray developed an influential natural theology introducing species as static and fixed, their adaptation and complexity designed by God, with varieties showing minor differences caused by local conditions. In 1735, Carolus Linnaeus used a similar taxonomy to classify enormous numbers of species, fixed according to the divine plan. By the mid 18th century Georges Buffon and Benoit de Maillet had published works claiming the world was older than Ussher's chronology, and Buffon questioned the fixity of species. Among various competing ideas of geology, Werner thought strata were deposits from shrinking seas, but James Hutton proposed a self-maintaining infinite cycle.

In the 1790s Charles Darwin's grandfather Erasmus Darwin outlined a hypothesis of transmutation of species, and in 1809 Jean-Baptiste Lamarck published a more fully developed theory. Both envisaged spontaneous generation producing simple forms of life, which progressively developed greater complexity, adapting to the environment by means of heritable characteristics acquired through use or disuse of organs. This process was later known as Lamarckism. To Lamarck, this supplemented an inherent progressive tendency driving organisms continuously towards greater complexity, in parallel separate lineages with no extinction. Geoffroy took a more idealist view involving saltation and parallels with embryonic development. Transmutation was strongly opposed by Georges Cuvier, whose paleontological work in the 1790s had established the reality of extinction. Cuvier explained extinction by local catastrophes after which other fixed species repopulated the affected areas.

In Britain medical students such as Robert Grant were influenced by Lamarck and Geoffroy, but authorities opposed ideas of transmutation as a threat to divinely appointed social order. William Paley's Natural Theology regarded adaptation as evidence of beneficial "design" by the Creator acting through laws, and in the English universities, controlled by the Church of England, science became a search for these laws. British naturalists adapted catastrophism to show repeated worldwide annihilation and creation of new fixed species adapted to a changed environment, initially identifying the most recent catastrophe as the biblical flood.

Inception of Darwin's theory
Darwin went to Edinburgh University in 1825. In his second year he neglected his medical studies for natural history, and he spent four months assisting Robert Grant's research into marine invertebrates. He was exposed to Grant's transmutational ideas but was unimpressed. At Cambridge University from 1827, Darwin learnt science as natural theology from botanist John Stevens Henslow, and read Paley, John Herschel and Humboldt. Filled with zeal for science, he studied catastrophist geology with Adam Sedgwick.

In December 1831 he joined the Beagle expedition as a geologist and naturalist. He read Charles Lyell's Principles of Geology and from their first stop ashore, at St. Jago, found that uniformitarianism explained the geological history of landscapes. Darwin found fossils resembling huge armadillos, and noted the geographical distribution of modern species in hope of finding their "centre of creation". Three Fuegians they returned to Tierra del Fuego as missionaries were friendly and civilised, yet to Darwin their relatives seemed “miserable, degraded savages”, and he no longer saw an unbridgeable gap between humans and animals. As they neared England in 1836 he noted thoughts that species might not be fixed.

Richard Owen showed that the fossils Darwin found in South America of extinct species were allied to current species in the same continent, and in March 1837 John Gould revealed that Rheas with overlapping territory were separate species, that mockingbirds collected on the Galápagos Islands represented three separate species each unique to a particular island, and that several distinct birds from those islands were all species of finches. 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.

Unusually for the time, Darwin questioned fancy pigeon and animal breeders as well as established scientists. At the zoo he had his first sight of an ape, and was profoundly impressed by how human the orang-utan seemed.

In late September 1838 he started reading Thomas Malthus's An Essay on the Principle of Population, and was reminded of its statistical proof that human populations breed beyond their means and struggle to survive. Darwin related this to the struggle for existence among wildlife and de Candolle’s “warring of the species” of plants. He saw at once that favourable variations would tend to be preserved and unfavourable ones destroyed in a kind of wedging, forcing the well adapted into gaps in the economy of nature as weaker structures were thrust out, resulting in the formation of new species. By December 1838 he saw a similarity between breeders selecting traits and a Malthusian Nature selecting from variants thrown up by "chance" so that "every part of newly acquired structure is fully practical and perfected".

Darwin now had the framework of his theory of natural selection “by which to work”. He continued to research and extensively revise his theory, in the background to his main occupation, publication of the scientific results of the Beagle voyage.

Further development


Darwin tentatively wrote about his ideas to Lyell in January 1842, then in June he roughed out a 35-page "Pencil Sketch" of his theory. In January 1844 he began correspondence about his theorising with the botanist Joseph Dalton Hooker. By July, Darwin had expanded his “sketch” into a 230-page “Essay”, to be expanded with his research results if he died prematurely.

In November 1844 the anonymously published popular science book Vestiges of the Natural History of Creation by Scottish publisher Robert Chambers brought wide interest in transmutation of species. It used evidence from the fossil record and embryology to claim that living things had progressed from the simple to the more complex over time. It proposed linear progression, not the branching common descent of the theory Darwin was working on, and it ignored adaptation. Darwin read it soon after publication and scorned its amateurish geology and zoology. When leading scientists including Adam Sedgwick attacked its morality and scientific errors, Darwin carefully reviewed his own arguments. Vestiges had significant influence on public opinion, and the intense debate helped to pave the way for the acceptance of the more scientifically sophisticated Origin by moving evolutionary speculation into the mainstream. While few naturalists were willing to consider transmutation, Herbert Spencer became an active proponent of Lamarckism and progressive development in the 1850s.

In January 1847 Hooker was persuaded to take away a copy of the "Essay". He eventually sent a page of notes, giving Darwin much needed feedback. Reminded of his lack of expertise in taxonomy, Darwin made an eight year study of barnacles, becoming the leading expert on their classification. Using his theory, he found homologies showing that slightly changed body parts served different functions to meet new conditions, and an intermediate stage in the evolution of distinct sexes.

From the barnacle specimens, Darwin came to believe that variation arose all the time and not just in response to changed circumstances. Around 1854 his views changed from expecting speciation where populations are isolated, as on islands, to giving more emphasis to speciation without isolation, where increasing specialisation within large stable populations continuously exploited new ecological niches. He began empirical research to gather more data for his theory, experimenting with the help of his son Francis on ways that plant seeds and animals might disperse across oceans to colonize distant islands. He studied the developmental and anatomical differences between different breeds of many domestic animals and became actively involved in fancy pigeon breeding. By 1856 his theory was much more sophisticated, and had a mass of supporting evidence.

Events leading to publication
An 1855 paper on the "introduction" of species written by Alfred Russel Wallace claimed that patterns in the geographical distribution of species and fossils could be explained if every new species always came into existence near an already existing species closely related to it. Charles Lyell, unlike Darwin, recognized the implications of Wallace’s paper and its possible connection to Darwin’s work, and in the spring of 1856 Lyell urged Darwin to publish to establish priority. Darwin was torn between the desire to set out a full and convincing account and the pressure to quickly produce a short paper. He decided he did not want to expose his ideas to review by an editor as would have been required to publish in an academic journal. On 14 May 1856 he began a "sketch" account and, by July, had decided to produce a full technical treatise on species.

Darwin was hard at work on his big book on Natural Selection, when on 18 June 1858 he received a parcel from Wallace, who was working in Borneo. It enclosed about twenty pages describing an evolutionary mechanism, a response to Darwin's recent encouragement, with a request to send it on to Lyell if Darwin thought it worthwhile. The mechanism was similar to Darwin's own theory. Darwin wrote to Lyell that "your words have come true with a vengeance,... forestalled" and he would, "of course, at once write and offer to send [it] to any journal" that Wallace chose, adding that "all my originality, whatever it may amount to, will be smashed". Lyell and Hooker agreed that a joint paper should be presented at the Linnean Society, and on 1 July 1858 the Wallace and Darwin papers titled respectively On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection were read out to little reaction. While Darwin considered Wallace's idea to be identical to his concept of natural selection, historians have pointed out differences. Darwin described natural selection as being analogous to the artificial selection practiced by animal breeders, and emphasised competition between individuals; Wallace drew no comparison to selective breeding, and focused on ecological pressures keeping different varieties adapted to local conditions.

On 20 July 1858 Darwin started work on an "abstract" trimmed from his Natural Selection, writing much of it from memory. Lyell made arrangements with publisher John Murray, who agreed to publish the manuscript sight unseen and to pay Darwin two-thirds of the net proceeds. Darwin had initially decided to call his book An abstract of an Essay/on the/Origin/of/Species and Varieties/Through natural selection/, but with Murray's persuasion it was eventually changed to the snappier title: On the Origin of Species with the title page adding by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. Here the term "races" is used as an alternative for "varieties" and does not carry the modern connotation of human races&mdash;the first use in the book refers to "the several races, for instance, of the cabbage", and Darwin proceeds to discuss "the hereditary varieties or races of our domestic animals and plants".

Time taken to publish
By December 1838 Darwin had his basic theory of natural selection “by which to work”, yet when Wallace's letter arrived on 18 June 1858 Darwin was still not ready to publish his theory. It is commonly thought that Darwin avoided or delayed making his ideas public, and historians have suggested various reasons, including fear of religious persecution or social disgrace if his views were revealed, and concern about upsetting his wife Emma's devout faith. Desmond and Moore highlight how in Britain in the repressive aftermath of the Napoleonic Wars transmutation of species was associated with materialism, Radicalism and revolutionary threats to the established social order, as reasons for Darwin to keep his theory secret. They also point out the huge workload Darwin took on when establishing himself as a geologist and getting his Beagle collections described and published. They note the repeated delays to all this work caused by Charles Darwin's illness.

The historian of science John van Wyhe, director of The Complete Works of Charles Darwin Online, has found that the idea of delay only dates back to the 1940s, and was absent from earlier biographies. Darwin's correspondence shows that he discussed transmutation with a large number of people, and his close friends were not outraged by such opinions. The idea of delay ignores Darwin's practice of finishing one book before starting another that he had already been researching. His species research was an immense and innovative research programme, and in letters he estimated it needing five years work once he had finished his geological work. His earlier estimates aimed at publication in 1853, but additional work on barnacles, overruns and time lost from illness meant that he started full time work on transmutation of species in September 1854. His concerns then were about dealing with the large and complex scope of the work, and far from being deterred by anticipated criticism, he stated his intention to publish regardless. In conclusion, van Wyne describes Darwin and his contemporaries writing of the twenty years it had taken overall as reasonable time well spent, and notes Darwin remarking that he never intended to publish a brief sketch until Lyell suggested it.

Publication and subsequent editions
On the Origin of Species was first published on 24 November 1859, at a price of fifteen shillings. The book had been offered to booksellers at Murray's autumn sale on 22 November, and all available copies had been taken up immediately. In total 1,250 copies were printed, but after deducting presentation and review copies, and five for Stationers' Hall copyright, around 1,170 copies were available for sale. The second edition of 3,000 copies was quickly brought out on 7 January 1860, with the phrase "by the Creator" added to the closing sentence, which from then on read: "There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone circling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved." While some commentators, such as Richard Dawkins, have taken this as an indication that Darwin was bowing to pressure to make concessions to religion, biographer James Moore describes Darwin's vision as being of God creating life through the laws of nature. Even in the first edition the term Creator appears several times, and at the start of the previous paragraph Darwin contrasts his idea "with the view that each species has been independently created. To my mind it accords better with what we know of the laws impressed on matter by the Creator, that the production and extinction of the past and present inhabitants of the world should have been due to secondary causes, like those determining the birth and death of the individual."

During Darwin's lifetime the book went through six editions, with cumulative changes and revisions to deal with counter-arguments raised. The third edition came out in 1861 with a number of sentences rewritten or added and an introductory appendix, An Historical Sketch of the Recent Progress of Opinion on the Origin of Species, while the fourth in 1866 had further revisions. The fifth edition published on 10 February 1869 incorporated more changes and for the first time included the phrase "survival of the fittest", which had been coined by the philosopher Herbert Spencer in his Principles of Biology (1864).

In January 1871 George Jackson Mivart's On the Genesis of Species listed detailed arguments against natural selection and claimed it included false metaphysics. Darwin took this personally, and made extensive revisions to the Origin, using the word "evolution" for the first time and adding a new chapter VII to refute Mivart. He told Murray of working men in Lancashire clubbing together to buy the 5th edition at fifteen shillings, and he wanted a new cheap edition to make it more widely available.

The sixth edition was published by Murray on 19 February 1872 with "On" dropped from the title, at a price halved to 7s 6d by using minute print. Sales increased from 60 to 250 per month.

Publication outside Great Britain
In the United States, Asa Gray negotiated with a Boston publisher for publication of an authorised American version, but learnt that two New York publishing firms were already planning to exploit the absence of international copyright to print Origin. Darwin was delighted by the popularity of the book, and asked Gray to keep any profits. Gray managed to negotiate a 5 per cent royalty with Appleton's of New York, who got their edition out in mid January, and the other two withdrew. In a May letter Darwin mentioned a print run of 2,500 copies, but it is not clear if this was the first printing alone as there were four that year.

Darwin had distributed presentation copies in France and Germany, hoping that suitable applicants would come forward as at that time translators were expected to take the initiative and make their own arrangements with a local publisher. He welcomed the distinguished elderly naturalist and geologist Heinrich Georg Bronn, but the German translation published in 1860 imposed Bronn's own ideas, adding to the misgivings of conservative thinkers, but matching the ideas already supported by philosophical radicals. In 1862 Bronn had produced a second edition based on the third English edition and Darwin's suggested additions, but then died of a heart attack. Darwin corresponded closely with Julius Victor Carus, who published an improved translation in 1867.

Darwin's attempts to find a translator in France fell through, and the translation by Clémence Royer published in 1862 added an introduction praising Darwin's ideas as an alternative to religious revelation and promoting ideas anticipating social Darwinism and eugenics, as well as numerous explanatory notes giving her own answers to the doubts that Darwin expressed. Darwin corresponded with Royer about a second edition published in 1866 and a third in 1870, but he had difficulty in getting her to remove her notes and was offended by her third edition. He remained unsatisfied until a translation by Edmond Barbier was published in 1876.

In 1864 translations were published in Dutch, Italian and Russian. During Darwin's lifetime it was also published in 1869 in Swedish, 1872 Danish, 1873 Polish, 1873–1874 Hungarian, 1877 Spanish and in 1878 in Serbian. By 1977 it had appeared in a further eighteen languages.

Title pages and introduction
Page ii shows quotations by William Whewell saying that natural theology depended on events in nature being driven by natural law rather than miracles, and Francis Bacon on the importance of studying the natural world to help interpret the word of God. These quotations related theology to nature, and in the book Darwin included comments to harmonise science and religion, in line with Isaac Newton's belief in a rational God who established a law-abiding cosmos rather than a capricious deity. The book begins with the Introduction, though from the 3rd edition on this is preceded by An Historical Sketch giving credit to his predecessors in ideas of evolution and natural selection. The introduction begins:

WHEN on board H.M.S. 'Beagle,' as naturalist, I was much struck with certain facts in the distribution of the inhabitants of South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seemed to me to throw some light on the origin of species—that mystery of mysteries, as it has been called by one of our greatest philosophers.

Following that reference to the leading philosopher of science John Herschel, Darwin set out his major themes. He referred to the distribution of rheas, Galapagos tortoises and mockingbirds having inspired doubts in species being fixed, and the close relationship of fossils he found in South America to animals still living on that continent. He mentioned his years of work on his theory, and Wallace arriving at the same conclusion leading him to "publish this Abstract" of his incomplete work. He outlined his ideas, and set out the essence of his theory: 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 of surviving, and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.

Variation under domestication and under nature
Chapter I on variation in plants and animals under domestication covers animal and plant breeding going back to ancient Egypt. Darwin began with contemporary opinions on the origins of the many distinct breeds under cultivation, then described his study of fancy pigeon breeding and the cumulative effect of selection. "The diversity of the breeds is something astonishing", yet all appeared to have descended from the same species of rock pigeon.

In Chapter II Darwin discussed variation in nature and described the definition of species as having no clear distinction between species and varieties. Experts were often unable to agree on such classification, or had to change their decisions when new forms were found. In large genera with many species the species also often had numerous varieties. Darwin believed that "a well-marked variety may be justly called an incipient species" and that "species are only strongly marked and permanent varieties". Historians note that these two chapters present an important new idea. Naturalists had long known that the individuals of a species differed from one another, but had mostly considered such variations to be limited and unimportant deviations from the archetype of each species which was a fixed ideal in the mind of God. Darwin and Wallace made variation among individuals of the same species central to understanding the natural world.

Struggle for existence, natural selection, and divergence
At the start of Chapter III, Darwin reiterated how the struggle for existence results in varieties, "which I have called incipient species", becoming distinct species, grouped into genera. Owing to this struggle for life, any variation, however slight and from whatever cause proceeding, if it be in any degree profitable to an individual of any species, in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring.... I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection, in order to mark its relation to man's power of selection.

In the 5th edition Darwin added "But the expression often used by Mr. Herbert Spencer, of the Survival of the Fittest, is more accurate, and is sometimes equally convenient." After mentioning earlier descriptions of universal struggle for existence as shown by A. P. de Candolle and Charles Lyell, Darwin emphasised that he used the term "in a large and metaphorical sense, including dependence of one being on another". All organisms produce enough offspring to lead to a huge population increase if they all survived, so there is a continuing Malthusian struggle: "It is the doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms". Darwin reviewed checks to such increase, including the complex interdependencies which we now term ecology, and noted that competition is most severe between closely related forms, "which fill nearly the same place in the economy of nature".

Chapter IV describes natural selection under the "infinitely complex and close-fitting ... mutual relations of all organic beings to each other and to their physical conditions of life". Darwin took as an example a country where a change in conditions led to extinction of some species, possibly immigration of others, and where suitable variations occurred, descendents of some species becoming increasingly adapted to new conditions. Darwin remarked that the artificial selection practiced by animal breeders frequently produced a sharp divergence in character between different breeds, and suggested that natural selection might do the same: But how, it may be asked, can any analogous principle apply in nature? I believe it can and does apply most efficiently, from the simple circumstance that the more diversified the descendants from any one species become in structure, constitution, and habits, by so much will they be better enabled to seize on many and widely diversified places in the polity of nature, and so be enabled to increase in numbers. Historians have remarked that in this passage Darwin had anticipated the modern concept of an ecological niche and the role of such niches in supporting biological diversity. He did not suggest that every individual with a favourable variation must be selected, or that the selected or favoured animals were better or higher, but merely that they are more adapted to their surroundings.



Darwin introduced what he called sexual selection to explain seemingly non-functional differences between sexes, as in beautiful plumage of birds. The effect of natural selection in forming species was expected to be very slow, and intermittent, but given the effectiveness of artificial selection, he could "see no limit to the amount of change, to the beauty and infinite complexity of the coadaptations between all organic beings, one with another and with their physical conditions of life, which may be effected in the long course of time by nature's power of selection." With the aid of a tree diagram and calculations he indicated the "divergence of character" from original species into multiple new species and genera, branches stopping or falling off as extinction occurs, while fresh buds formed new branches in "the great Tree of life ... with its ever branching and beautiful ramifications."

Variation and heredity
A difficulty for Darwin was that in his time there was no agreed-upon model of heredity; early in Chapter I Darwin stated "The laws governing inheritance are quite unknown". He accepted a version of the inheritance of acquired characteristics (which after Darwin's death came to be called Lamarckism), and Chapter V discusses what he called the effects of use and disuse, writing that he thought "there can be little doubt that use in our domestic animals strengthens and enlarges certain parts, and disuse diminishes them; and that such modifications are inherited" and that this also applied in nature. Darwin stated that some changes that were commonly attributed to use and disuse, such as the loss of functional wings in some island dwelling insects, might well be a product of natural selection. In later additions of Origin Darwin expanded the role attributed to the inheritance of acquired characteristics. Darwin also admitted ignorance of the source of inheritable variations, but speculated they might be produced by environmental factors.

It was not until the advent of the modern evolutionary synthesis in the 20th century, that a model of heredity became completely integrated with a model of variation. It is a theme in some histories of evolution and genetics written by scientists, rather than historians, to claim that Darwin's lack of an adequate model of heredity was the source of suspicion of natural selection, but later historians of science have documented that this was not the source of most objections to Darwin, and that later scientists, such as Karl Pearson and the biometric school, developed models of evolution by natural selection with a "blending" model of heredity like that used by Darwin.

Difficulties for the theory
Chapters VI – VIII (of the first edition) address difficulties for the theory, beginning with why there are often no intermediate forms between closely related species found in nature. Darwin attributed this to competition between different forms, combined with the relatively small number of individuals of intermediate forms, resulting in the extinction of such forms, leaving only distinct forms to be found. The rest of Chapter VI is concerned with whether natural selection could produce complex specialized structures, and the habits to use them, in cases where it would be difficult to imagine how intermediate forms could be functional. Darwin said: Secondly, is it possible that an animal having, for instance, the structure and habits of a bat, could have been formed by the modification of some animal with wholly different habits? Can we believe that natural selection could produce, on the one hand, organs of trifling importance, such as the tail of a giraffe, which serves as a fly-flapper, and, on the other hand, organs of such wonderful structure, as the eye, of which we hardly as yet fully understand the inimitable perfection? His answer was that in many cases animals exist with intermediate habits and structures that are functional and adaptive. He discussed flying squirrels, a relatively straightforward modification of ordinary squirrels, and flying lemurs as examples of how bats might have evolved from non-flying ancestors. He discussed various simple eyes found in invertebrates, starting with nothing more than an optic nerve coated with pigment, as examples of how the vertebrate eye could have evolved in steps. Darwin concludes: "If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find out no such case."

Darwin addressed the issue of the evolution of complex instincts in Chapter VII. Among the examples he examined were two that he had investigated experimentally: slave making ants and the construction of hexagonal cells by honey bees. Darwin stated that there was a range of behaviour between different species of slave making ants, with some species more dependent on slaves than others, and he observed that many ant species will collect and store the pupae of other species as food; he saw no problem with species with an extreme dependency on slave workers, having evolved in incremental steps. He discussed how bees making hexagonal cells could have evolved in steps from bees that made round cells with natural selection acting to economize wax. Darwin concluded: Finally, it may not be a logical deduction, but to my imagination it is far more satisfactory to look at such instincts as the young cuckoo ejecting its foster-brothers,—ants making slaves,—the larvæ of ichneumonidæ feeding within the live bodies of caterpillars,—not as specially endowed or created instincts, but as small consequences of one general law, leading to the advancement of all organic beings, namely, multiply, vary, let the strongest live and the weakest die. Chapter VIII (of the first edition) discusses hybridization. Darwin addressed the idea that species had been imbued with some special characteristic that prevented viable and fertile hybrids in order to permanently preserve separately created species. He said that far from being universally constant, the difficulty in producing hybrids of closely related species, and the viability and fertility of the hybrids, varied greatly, especially among plants. In a few cases what were widely considered to be separate species produced viable fertile hybrid offspring freely, and in a few other cases what were considered to be mere varieties of the same species could only be crossed with difficulty. Darwin concluded: "Finally, then, the facts briefly given in this chapter do not seem to me opposed to, but even rather to support the view, that there is no fundamental distinction between species and varieties."

Geologic record
Chapters IX and X of the first edition discuss evidence from the geological record. In Chapter IX, "On The Imperfection of the Geological Record", Darwin addressed the issue of whether there had been enough time for the slow process of evolution by natural selection. He cited Charles Lyell's work Principles of Geology as well as his own geological observations to argue "how incomprehensibly vast have been the past periods of time". Darwin also addressed the concern that the fossil record did not contain innumerable intermediate forms. He said that geological formations are intermittent with gaps of unknown duration between periods when sedimentary layers are deposited at any one location, and that every geologic formation is missing layers corresponding to periods known from other formations. He also stated that fossils are only rarely preserved, and that 19th-century fossil collections were extremely fragmentary. Darwin said: "That our palæontological collections are very imperfect, is admitted by every one ... Only a small portion of the surface of the earth has been geologically explored, and no part with sufficient care, as the important discoveries made every year in Europe prove". Darwin noted that the apparently sudden appearance of entire groups of well developed organisms without predecessors in the oldest fossil bearing layers posed a potentially serious problem for his theory, but expressed the hope that future discoveries might resolve the issue. A scientist noted that it was not until the 1950s that fossil evidence of pre-Cambrian life would be accepted, but that by the end of the 20th century the history of life had been extended back billions of years, resolving Darwin's dilemma.

Chapter X, "On the Geological Succession of Organic Beings", argues that despite the imperfections discussed in the previous chapter the fossil record shows broad patterns that are better explained by the theory of branching divergence caused by natural selection than by the idea that species are individually created and remain unchanged. Darwin stated that once a group of related species appears and then disappears from the fossil record, members of that group do not suddenly reappear in a later epoch. Also, usually, only a few members of such a group appear at first, with the number of member species increasing over time until the group reaches its maximum diversity at a later point. He also said that the fossil record, especially of marine organisms, shows an overall pattern of successive change that is consistent across widely separated formations. Furthermore within a group like mammals extinct species that have lived more recently tend to be more similar to species still existing today than do species that lived longer ago, and frequently extinct species can be found that have characteristics intermediate between two more recent groups. He said: "With respect to the Vertebrata, whole pages could be filled with striking illustrations from our great palæontologist, Owen, showing how extinct animals fall in between existing groups." Darwin then mentioned that at least in the most recent geological periods, fossils tend to resemble those organisms still living in the same area. He said: "Mr. Clift many years ago showed that the fossil mammals from the Australian caves were closely allied to the living marsupials of that continent. In South America, a similar relationship is manifest, even to an uneducated eye ..."

Geographic distribution
Chapters XI and XII of the first edition discuss evidence from the geographical distribution of species, what would later come to be called biogeography. He started by saying that the differences in flora and fauna between different regions cannot be explained by environmental differences such as climates. For example South America, Africa, and Australia all have regions with similar climates at similar latitudes, but those regions have dramatically different plants and animals. The species found in one area of any of the continents are much more closely allied with species found in other regions of the same continent, even if those other regions have dramatically different climates. Darwin's next point was that barriers to migration play an important role in the differences between the species of different regions. For example the sea life off the Atlantic and Pacific coasts of Central America had almost no species in common even though the Isthmus of Panama was only a few miles wide. His explanation was a combination of migration and descent with modification. He went on to say: "On this principle of inheritance with modification, we can understand how it is that sections of genera, whole genera, and even families are confined to the same areas, as is so commonly and notoriously the case." Darwin discussed how a volcanic island formed a few hundred miles from a continent might be colonized by a few species from the continent, which would then be modified over time but which would still be related to species found on the continent, a common pattern. Darwin discussed possible mechanisms of dispersal across oceans; many of which he had investigated experimentally.

In Chapter XII Darwin returned to the topic of oceanic islands and describes their many peculiarities; for instance on many such islands the roles played by mammals on continents are played by other kinds of organisms such as flightless birds or reptiles. The chapter summary says:

... I think all the grand leading facts of geographical distribution are explicable on the theory of migration (generally of the more dominant forms of life), together with subsequent modification and the multiplication of new forms. We can thus understand the high importance of barriers, whether of land or water, which separate our several zoological and botanical provinces. We can thus understand the localisation of sub-genera, genera, and families; and how it is that under different latitudes, for instance in South America, the inhabitants of the plains and mountains, of the forests, marshes, and deserts, are in so mysterious a manner linked together by affinity, and are likewise linked to the extinct beings which formerly inhabited the same continent ... On these same principles, we can understand, as I have endeavoured to show, why oceanic islands should have few inhabitants, but of these a great number should be endemic or peculiar; ...

Classification, morphology, embryology, rudimentary organs
Darwin started Chapter XIII by discussing the classification of living things. He stated that classification is based on species resembling one another to varying degrees and that they can be grouped together in a multilevel system of groups and sub groups. After discussing classification issues he concluded:

All the foregoing rules and aids and difficulties in classification are explained, if I do not greatly deceive myself, on the view that the natural system is founded on descent with modification; that the characters which naturalists consider as showing true affinity between any two or more species, are those which have been inherited from a common parent, and, in so far, all true classification is genealogical; that community of descent is the hidden bond which naturalists have been unconsciously seeking, ...

Darwin then discussed morphology including the importance of  homologous structures. He said "What can be more curious than that the hand of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern, and should include the same bones, in the same relative positions?". He turned to embryology mentioning that animals of the same class often have extremely similar embryos. Darwin discussed evidence from rudimentary organs such as the wings of flightless birds, and the rudiments of pelvis and leg bones found in some snakes, and remarked that some rudimentary organs, such as teeth in baleen whales, are found only in embryonic stages.

Concluding remarks
In the final chapter Darwin recapitulated major points from all the earlier chapters and concluded by hoping that his theory may produce revolutionary changes in many fields of natural history. He ended with:

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... Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.

Nature of Darwin's argument
After the introduction, which provides an overview of what led Darwin to his conclusions, the first four chapters lay out the case for natural selection as an agent of evolution analogous to the artificial selection practiced by animal breeders. Historians have said that Darwin started with the case for natural selection rather than with evidence that evolution had occurred, because he was aware most of his readers had already seen earlier arguments for the transmutation of species, and that those arguments had been rejected by many leading scientists in part for lack of plausible evolutionary mechanisms. Therefore Darwin wanted to begin his argument by convincing his readers that he had a viable scientific explanation for how evolutionary change occurred before he discussed the evidence that it had.

Only deep into the book does he turn to that evidence. Historians have stated that these last chapters are the strongest part of Darwin's argument, because of the supporting facts presented from many disciplines. They have indicated that he never claimed to be able to directly prove that new species arose through a process of branching evolution driven by natural selection. Instead Darwin's argument was based on showing that his theory could explain a myriad of observations from many different fields of natural history that were inexplicable under alternate theories, such as species being individually created.

Literary style
The Examiner review of 3 December 1859 stressed that "Much of Mr. Darwin's volume is what ordinary readers would call 'tough reading;' that is, writing which to comprehend requires concentrated attention and some preparation for the task. All, however, is by no means of this description, and many parts of the book abound in information, easy to comprehend and both instructive and entertaining."

James Secord has said that while the book was readable enough to sell, its dryness ensured that it was seen as aimed at specialist scientists and could not be dismissed as mere journalism or imaginative fiction. Unlike the still popular Vestiges, it avoided the narrative of the historical novel and cosmological speculation, though the closing sentence clearly hinted at cosmic progression. Darwin had long been immersed in the literary forms and practices of specialist science, and made effective use of his skills in structuring arguments.

David Quammen has said that the book was written in everyday language because it was intended for a wide audience. However, Darwin's literary style was uneven; in some places he used convoluted sentences that are difficult to read; in other places his writing was beautiful. Quammen also said Darwin weakened the book in later editions by making concessions and adding details to address his critics, and recommended the first edition.

Reception


The book aroused international interest, and a widespread debate with no sharp line between scientific issues and ideological, social and religious implications. Much of the initial reaction was hostile, but Darwin had to be taken seriously as a prominent and respected name in science. There was much less controversy than had greeted the 1844 publication Vestiges of Creation which had been rejected by scientists, but had converted a wide public readership to the belief that nature and human society were governed by natural laws. The Origin of Species as a book of wide general interest became associated with specific ideas of reform. Its proponents made full use of a surge in publishing including new review journals, and it was given more popular attention than almost any other scientific work, though it failed to match the continuing sales of Vestiges. Darwin's book legitimised scientific discussion of evolutionary mechanisms, and the newly coined term Darwinism was used to cover the whole range of evolutionism, not just his own ideas. By the mid 1870s evolutionism was triumphant.

In the final chapter Darwin merely hinted that "Light will be thrown on the origin of man", but the first review claimed it made a creed of the “men from monkeys” idea from Vestiges. Human evolution became central to the debate and was strongly argued by Huxley who featured it in his popular "working-men's lectures". Darwin did not publish his own views on this until 1871. The naturalism of natural selection conflicted with presumptions of purpose in nature and while this could be reconciled by theistic evolution, other mechanisms implying more progress or purpose were more acceptable. Herbert Spencer had already incorporated Lamarckism into his popular philosophy of progressive free market human society. He popularised the terms evolution and survival of the fittest, and many thought Spencer was central to evolutionary thinking.

Impact on the scientific community
Scientific readers were already aware of arguments for a lawful process of change in species, but Lamarckism and the vague "law of development" of Vestiges were discredited. Darwin presented natural selection as a scientifically testable mechanism but remained open to other possibilities, including inheritance of acquired characters. His strategy established that evolution through laws was worthy of scientific study, and by 1875 most scientists accepted that evolution occurred, but few gave significance to natural selection. His scientific method was disputed, with his supporters 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 truth that species were fixed objects created by design.

Early support for Darwin's ideas came from studies by field naturalists studying biogeography and ecology, including Joseph Dalton Hooker in 1860, and Asa Gray in 1862. Henry Walter Bates presented research in 1861 that explained insect mimicry using natural selection. Alfred Russel Wallace discussed evidence from his research in the Malay archipelago including an 1864 paper with an evolutionary explanation for the Wallace line.

Evolution had less obvious use in anatomy and morphology. Thomas Henry Huxley strongly supported Darwin on evolution, but called for experiments to show whether natural selection could form new species, and doubted if Darwin's gradualism was sufficient without sudden leaps to cause speciation. In April 1860 he coined the term Darwinism for his efforts to secularise and professionalise science, and it was soon used to refer to a whole range of evolutionary ideas.

Gray promoted and defended the work against American naturalists with an idealist approach, notably the geologist and anatomist Louis Agassiz who viewed every species as a distinct fixed unit in the mind of the Creator, including as species what others considered merely varieties. The leading naturalist in Britain was the anatomist Richard Owen, an idealist who had moved in the 1850s to the view that the history of life was the gradual unfolding of a divine plan. Owen's review of the Origin in the April 1860 Edinburgh Review bitterly attacked Huxley, Hooker and Darwin, but also signalled acceptance of a kind of evolution as a teleological plan in a continuous "ordained becoming", with new species appearing by natural birth. Others rejecting natural selection but supporting "creation by birth" included the Duke of Argyll who explained beauty in plumage by design. Since 1858 Huxley had emphasised anatomical similarities between apes and humans, contesting Owen's view that humans were a separate sub-class. Their disagreement over human origins came to the fore at the British Association for the Advancement of Science meeting featuring the legendary 1860 Oxford evolution debate. The "great hippocampus debate" became a public battle, in which Huxley discredited Owen over details of brain structure. In another school of thought, supported by Charles Lyell and Alfred Russel Wallace, humans shared a common ancestor with apes, but higher mental faculties could not have evolved through a purely material process. Huxley gained influence, and initiated the X Club which shaped much of late Victorian science.

Some German scientists, while not fully accepting natural selection, enlisted Darwin's work in their fight against conservatism. Ernst Haeckel was particularly ardent, aiming to synthesise Darwin's ideas with those of Lamarck and Goethe while still reflecting the spirit of Naturphilosophie. These scientists took the lead in an ambitious programme to reconstruct the history of life using morphology and embryology. Huxley joined in this effort, which was supported by discoveries in paleontology. Haeckel went far beyond Darwin in using embryology to reconstrunct the history of life with his recapitulation theory that embodied a progressive, almost linear model of evolution. Darwin was cautious about such histories, and had already noted that von Baer's laws of embryology supported his idea of complex branching.

There were serious scientific objections, including Karl von Nägeli's insistence that a trivial characteristic with no adaptive advantage could not be developed by selection. Darwin conceded that these could be linked to adaptive characteristics. He had most difficulty with the geologic time scale when his estimate of the time taken for erosion of The Weald was disputed, with Kelvin arguing that the Earth had cooled in less than 100 million years, and with heredity when Fleeming Jenkin argued that blending inheritance would make selection ineffective. Darwin tried to meet these objections in the 5th edition, and made considerable changes to the 6th edition in response to Mivart's compilation of scientific and religious objections. The problems of geologic time and heredity were only resolved by discoveries in the 20th century.

By the mid 1870s most scientists accepted evolution, but relegated natural selection to a minor role as they believed evolution was purposeful and progressive. The range of evolutionary theories during "the eclipse of Darwinism" included forms of "saltationism" in which new species were thought to arise through "jumps" rather than gradual adaptation, forms of orthogenesis claiming that species had an inherent tendency to change in a particular direction, and forms of neo-Lamarckism in which inheritance of acquired characteristics led to progress. The minority view of August Weismann that natural selection was the only mechanism was called neo-Darwinism. The rediscovery of Mendelian inheritance was thought to further invalidate Darwin, and natural selection only became accepted as the main driving force of evolution when a number of biologists and statisticians (especially R. A. Fisher, Sewall Wright, and J.B.S. Haldane) merged Darwinian selection theory with sophisticated statistical understandings of inheritance in the 1930s and 1940s as part of the modern evolutionary synthesis.

Religious
There was a wide range of attitudes about the implications and significance of Darwin's ideas for religion and for the secularisation of thought in the Victorian era. Although this debate has been depicted as polarised, issues were complex and there was a large middle ground. Other religious disputes such as the much larger row over Essays and Reviews raised more concern at the time, but are now forgotten. By the time of publication developments in geology meant that few educated people held a literal reading of Genesis, but the idea of supernatural design in nature expressed in natural theology was an important part of philosophy in the English speaking world. Design made nature orderly, and hence made science possible, and supernatural design also gave sanction to "the moral and religious endeavours of man."

Natural theology was not a unified doctrine, and while some such as Louis Agassiz were strongly opposed to any idea of evolution, others sought a reconciliation in which evolution was seen as purposeful. In the Church of England, some liberal clergymen interpreted natural selection as an instrument of God's design, with the cleric Charles Kingsley seeing it as "just as noble a conception of Deity". Baden Powell argued that miracles broke God’s laws, so belief in them was atheistic, and praised “Mr Darwin’s masterly volume &#91;supporting&#93; the grand principle of the self-evolving powers of nature”. In America Asa Gray argued that evolution is the secondary effect, or modus operandi, of the first cause, design. He discussed teleology with Darwin, who imported and distributed Gray’s pamphlet on theistic evolution, Natural Selection is not inconsistent with Natural Theology. Theistic evolution became a popular compromise, and Mivart was among those accepting evolution but attacking Darwin's mechanism to leave room for supernatural intervention. It was eventually realised that such intervention could not be a scientific explanation, and naturalistic mechanisms such as neo-Lamarckism were favoured as being more compatible with purpose.

Thomas Henry Huxley wanted science to be secular, without religious interference, and his article in the April 1860 Westminster Review promoted scientific naturalism over theology, praising Darwin for "extending the domination of Science over regions of thought into which she has, as yet, hardly penetrated." Though the 1860 Oxford evolution debate had no clear winner, Huxley used the legend that it was a battle over human origins in which he had been insulted by the Bishop of Oxford Samuel Wilberforce, and had put the Bishop in his place.

Human evolution was at the centre of debate, as mental and moral qualities were seen as spiritual aspects of the immaterial soul, and it was believed that animals did not have spiritual qualities. This could be reconciled by supposing 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. Darwin put forward an evolutionary explanation of such attributes in the Descent of Man in 1871.

While many conservative theologians accepted evolution, Charles Hodge argued in his 1874 critique "What is Darwinism?" that "Darwinism" defined narrowly as including rejection of design was atheism, though he accepted that Asa Gray did not reject design. Asa Gray responded that this charge misrepresented Darwin's text. By the early 20th century even authors of The Fundamentals were mostly explicitly open to the possibility that God created through evolution. The first phase of the American creation–evolution controversy, inspired by fundamentalism, occurred in the 1920s.

Reception outside Great Britain
The book sold well in the United States, with unauthorised versions being published even before Asa Gray negotiated publication of an authorised American version. Darwin wrote "I never dreamed of my Book being so successful with general readers: I believe I shd. have laughed at the idea of sending the sheets to America."

The book was widely translated in Darwin's life time, but problems arose with translating concepts and metaphors, and some translations were biased by the translator's own agenda. Heinrich Georg Bronn's German translation published in 1860 imposed Bronn's own ideas, adding controversial themes that Darwin had deliberately omitted. Bronn translated "favoured races" as "perfected races", and added essays on issues including the origin of life, as well as a final chapter on religious implications partly inspired by Bronn's adherence to Naturphilosophie. The translation deviated from Darwin's intentions and added to the misgivings of conservative thinkers, but was welcomed by philosophical radicals already used to transformationist ideas of metamorphosis and monadology. By 1864 Darwin's work was gaining wide support in Germany and Switzerland.

French speaking naturalists in several countries showed appreciation of the much modified French translation by Clémence Royer published in 1862 which promoted her own ideas, including anticipations of social Darwinism and eugenics, but Darwin's ideas had little impact. Royer had made it more palatable to Lamarckian scientists, and that remained the preferred approach in France.

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, though 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.

Modern influence
With the modern evolutionary synthesis becoming established and being further developed into modern evolutionary theory, Darwin's theory of natural selection has become the unifying theory of the life sciences, explaining diversity of living organisms and their adaptation to the biophysical environment. It makes sense of the geologic record, biogeography, parallels in embryonic development, biological homologies, vestigiality, cladistics and other fields, providing reconciliation between findings in a way not achieved by any alternative hypothesis. Darwin's writings have continued to interest a very wide range of readers.

In 2009 the 150th anniversary of the publication of On the Origin of Species and the bicentenary of Darwin's birth are being commemorated by worldwide events and exhibitions, celebrating the ideas which "over the last 150 years have revolutionised our understanding of nature and our place within it."

Contemporary reviews

 * William Benjamin Carpenter Darwin on the Origin of Species. National Review 10: December 1859 188-214.
 * Thomas Henry Huxley Time and life: Mr Darwin's "Origin of species." Macmillan's Magazine 1: 1859 142-148.
 * Richard Owen Review of Darwin's Origin of Species, Edinburgh Review, 3, April 1860, pp. 487-532.
 * Thomas Henry Huxley Review of The Origin of Species, Westminster Review 17 (n.s.) April 1860, pp. 541-70.
 * Samuel Wilberforce (Review of) ‘On the origin of species’, Quarterly Review, June 1860, pp. 225-264.
 * Andrew Murray On Mr Darwin's theory of the origin of species. Proceedings of the Royal Society of Edinburgh 4: 1860 274-291.
 * Fleeming Jenkin 'Review of Darwin's The origin of species' The North British Review, June 1867, 46, pp. 277-318.