On the Origin of Species

This article is about Charles Darwin's book. For the Outer Limits episode of the same name, see Origin of Species (The Outer Limits).

On the Origin of Species
by Means of Natural Selection

The title page of the 1859 edition of On the Origin of Species
Author	Charles Darwin
Country	United Kingdom
Language	English
Subject	Evolutionary biology
Publisher	John Murray
Publication date	24 November 1859
Media type	Print (Hardback & Paperback)
ISBN	ISBN 0-486-45006-6

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 book's full title is On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. In 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 contains a wealth of evidence that the diversity of life arose through a branching pattern of evolution and common descent – evidence which he had accumulated on the voyage of the Beagle in the 1830s and expanded through research, correspondence, and experiments after his return.

The book is readable even for the non-specialist and attracted widespread interest on publication. The topic of evolution had been highly controversial during the first half of the 19th century, since transmutation of species contradicted the long accepted idea that species were unchanging parts of a designed hierarchy. It had been 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 professional anatomists and the general public, but to a scientific establishment closely tied to the Church of England, science was part of natural theology. An older generation of naturalists found it very hard to accept that humans descended from animals.

The mass of evidence presented by a scientist of Darwin's eminence generated respectful discussion on scientific, philosophical, and religious grounds. The debate over the book would lead to widespread acceptance among educated people that evolution had occurred, and contributed significantly to the movement to professionalize British science by replacing natural theology with methodological naturalism and ending the Church's domination of the scientific community. The scientific theory of evolution has continued to advance since Darwin's contributions, but natural selection remains the most widely accepted scientific explanation for the development of new species. Despite the overwhelming scientific consensus, political and religious challenges to the theory of evolution continue in some countries.

Summary

Darwin's theory is based on key observations and inferences drawn from them:

1. Every species is fertile enough that if all offspring survived to reproduce the population would grow.
2. Yet populations remain roughly the same size, with small changes.
3. Resources such as food are limited and are relatively stable over time.
4. A struggle for survival ensues.
5. In sexually reproducing species, generally no two individuals are identical.
6. Some of these variations directly affect the ability of an individual to survive in a given environment.
7. Much of this variation is inheritable.
8. Individuals less suited to the environment are less likely to survive and less likely to reproduce, while individuals more suited to the environment are more likely to survive and more likely to reproduce.
9. The individuals that survive are most likely to leave their inheritable traits to future generations.
10. This slowly effected process results in populations that adapt to the environment over time, and ultimately, after interminable generations, these variations accumulate to form new varieties, and ultimately, new species.

Background

Main articles: History of evolutionary thought and History of biology

Developments before Darwin's theory

The idea of biological evolution was around long before Darwin published On The Origin. Some have traced the concept back as far as Aristotle. However, Christian thought in Medieval Europe involved complete faith in the ancient Biblical teachings of creation according to Genesis. Its concepts including "Created kinds" were interpreted by the priesthood as theology not scientific fact, but the Protestant Reformation widened access to the Bible and brought more literal interpretations. Natural philosophers exploring the wonders of what they saw as God's works in nature made many discoveries, and naturalists such as Carolus Linnaeus categorised an enormous number of species. By the time of Darwin's birth in 1809, it was widely believed in England that both the natural world and the hierarchical social order were held stable, fixed by God's will, with nothing happening purely naturally and spontaneously.

The paleontological work of Georges Cuvier established the reality of extinction in the 1790s. Several competing theories of geology were put forward; James Hutton's uniformitarian theory of 1785, which was expanded and explained by Charles Lyell in his Principles of Geology in the 1830s, envisioned gradual change over aeons of time. Evolutionary concepts were put forward as well. In the 18th century Georges-Louis Leclerc, Comte de Buffon suggested that species might change, within limits, over time and that some similar species (such as lions, tigers, house cats) might be related by common descent. At the end of the 18th century Charles Darwin's grandfather Erasmus Darwin described more general ideas of common descent with all warm blooded creatures sharing a common ancestor and with organisms "acquiring new parts" in response to stimuli then passing these changes to their offspring. In 1809 Jean-Baptiste Lamarck published the first fully developed scientific theory of evolution, which he called transmutation of species. Lamarck proposed two mechanisms of evolution. One was an inherent progressive tendency that drove species towards greater complexity. The second, which became known as Lamarckian inheritance or inheritance of acquired characteristics, was the ability of organisms to inherit changes brought about through increased use or disuse of organs in response to the organism's environment, producing adaptation. Lamarck did not propose common descent. Instead his concept was of separate lineages each progressing towards greater complexity.

In Britain, in the aftermath of the American and French Revolutions such ideas were considered a threat to the social order. In England, natural history was dominated by the universities which trained clergy for the Church of England in William Paley's Natural Theology which sought evidence of beneficial "design" by a Creator in nature. British naturalists adopted Cuvier's explanation of the fossil record by catastrophism, the concept that animals and plants were periodically annihilated and their places filled by the creation of new species, modifying it to support the biblical account of Noah's flood, but Lamarck's ideas were taken up by Radicals who wanted to overturn the establishment.

Inception of Darwin's theory

Main article: Inception of Darwin's theory

Charles Darwin's education at the University of Edinburgh exposed him to Robert Grant's efforts to develop the evolutionary ideas of Erasmus Darwin and Jean-Baptiste Lamarck using marine invertebrate anatomy. Then at Cambridge University his theology studies convinced him of William Paley's argument of "design" by a Creator while his interest in natural history was increased by botanist John Stevens Henslow and geologist Adam Sedgwick, both of whom believed in the importance of natural theology. During the voyage of the Beagle Charles Darwin was impressed by Charles Lyell's uniformitarianism and puzzled over discrepancies between Lyell's uniformitarian idea that each species had its "centre of creation" and the evidence he saw. On his return Richard Owen showed that fossils Darwin had found were of extinct species related to current species in the same locality. Also John Gould startlingly revealed that a group of birds with completely different beak structures from the Galápagos Islands were all finches, and that the mockingbirds collected from those same islands represented three separate species each endemic to a particular island.

By early 1837 Darwin was speculating on transmutation in a series of secret notebooks. He investigated the breeding of domestic animals, consulting William Yarrell and reading a pamphlet by Yarrell's friend Sir John Sebright which commented that "A severe winter, or a scarcity of food, by destroying the weak and the unhealthy, has all the good effects of the most skilful selection." At the zoo in 1838 he had his first sight of an ape, and the orang-utan's antics impressed him as being "just like a naughty child" which from his experience of the natives of Tierra del Fuego made him think that there was little gulf between man and animals.

In late September 1838 he began reading the 6th edition of Thomas Malthus's An Essay on the Principle of Population which reminded him of Malthus's statistical proof that human populations breed beyond their means and compete to survive, at a time when he was primed to apply these ideas to animal species. Darwin applied to his search for the Creator's laws the ideas of utilitarian economists like Malthus and Adam Smith who emphasised the importance of competition and individual struggle; ideas that profoundly influenced English society in the 1830s. By December 1838 he was seeing 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", thinking this "is a beautiful part of my theory".

Further development

Main article: Development of Darwin's theory

This diagram of the skulls of different pigeon breeds is from Darwin's Variation of Plants and Animals Under Domestication revised by his son Francis in 1905.

Darwin now had the framework of his theory of natural selection “by which to work” as his “prime hobby”. His research included animal husbandry and extensive experiments with plants, finding evidence that species were not fixed and investigating many detailed ideas to refine and substantiate his theory. For more than a decade this work was in the background to his main occupation, publication of the scientific results of the Beagle voyage.

In January 1842 Darwin sent a tentative description of his ideas in a letter to Lyell, who was touring America. Lyell noted that his ally "denies seeing a beginning to each crop of species”. Despite problems with illness, Darwin formulated a 35 page "Pencil Sketch" of his theory in June 1842, then worked it up into a larger "essay". Botanist Joseph Dalton Hooker became Darwin's mainstay, and late in 1845 Darwin offered his "rough Sketch" for comments without immediate success, but in January 1847 when Darwin was particularly ill Hooker took away a copy of the "Sketch". After some delays he sent a page of notes, giving Darwin the calm critical feedback that he needed. Over eight years Darwin made a huge study of barnacles, using his theory to find homologies showing that slightly changed body parts served different functions to meet new conditions, and finding an intermediate stage in evolution of distinct sexes.

Vestiges of the Natural History of Creation was a popular science book written and published anonymously by Scottish publisher Robert Chambers in 1844. Vestiges 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. Vestiges was widely read and provoked intense debate. It had more influence on public opinion than on the opinion of leading scientists, some of whom pointed out various scientific errors in negative reviews. The debate over Vestiges helped pave the way for the acceptance of the more scientifically sophisticated Origin by moving evolutionary speculation into the mainstream. Darwin scorned its amateurish geology and zoology but carefully reviewed his own arguments.

After Darwin finally finished his research on barnacles in 1854, he started a programme of empirical research to gather more data for his theory. He investigated experimentally, sometimes with the help of his son Francis, 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 pigeon breeding.

Publication

Main article: Publication of Darwin's theory

Events leading to publication

An 1855 paper on the "introduction" of species written by Alfred Russel Wallace, a naturalist working in Borneo, analyzed patterns in biogeography and the fossil record, claiming they could best be explained if every new species always came into existence nearby to 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 ruled out exposing himself to an editor or counsel which 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 pressed on, overworking, and was throwing himself into his work with his book on Natural Selection well under way, when on 18 June 1858 he received a parcel from Alfred Russel Wallace enclosing about twenty pages describing an evolutionary mechanism, an unexpected response to Darwin's recent encouragement, with a request to send it on to Lyell. 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 surprisingly little reaction.

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—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".

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, and added "by the Creator" into the closing sentence, so that from then on it 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 published On the Genesis of Species, the cleverest and most devastating critique of natural selection in Darwin's lifetime. Darwin took it personally, and from April to the end of the year he made extensive revisions to the Origin, using the word "evolution" for the first time and adding a new chapter 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.

Content

After the words "On the Origin of Species" on page i, page ii shows quotations. The first, by William Whewell from his Bridgewater Treatise, sets out the idea that in natural theology events in the material world are brought about "by the establishment of general laws" rather than by individual miracles. The second by Francis Bacon from his Advancement of Learning argues that we should study both the word of God in the Bible and the works of God in nature together, so that the works of God teach us how to interpret the word of God. From the second to sixth editions, a third quotation is included, from the Analogy of Revealed Religion by the eighteenth century bishop Joseph Butler. This describes natural as meaning "stated, fixed or settled" by "an intelligent agent" who can equally carry out single supernatural miracles.

These quotations relate theology to nature, and in the book Darwin includes various comments aiming to harmonise science and religion, in line with Isaac Newton's belief in the glory of a rational God who established a law-abiding cosmos rather than a capricious deity. The quotations are followed by the title page then the index. The book then begins with the Introduction, though from the 3rd edition onwards this is preceded by An Historical Sketch giving credit to his predecessors in ideas of evolution and natural selection.

Introduction

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.

Darwin starts with a reference to the distribution of rheas, Galapagos tortoises and mockingbirds inspiring doubts in species being fixed, and the close relationship of fossils he found in South America to animals currently living on the same continent. He then cites the question which John Herschel had raised in correspondence with Charles Lyell shortly before Darwin met Herschel in South Africa, “that mystery of mysteries, the replacement of extinct species by others” as “a natural in contradistinction to a miraculous process”. Darwin mentions 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 then outlines his ideas, and sets out its 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 discusses the considerable amount of variation of plants and animals in conditions of domestication. Darwin partly attributes this to different conditions of life, and (incorrectly) to domestication itself as well as to changed habits producing an inherited effect. He discusses how domestication has been going on since the neolithic period, then turns in detail to his studies of domestic pigeons. "The diversity of the breeds is something astonishing", yet all show evidence of being descendants of the same species of rock pigeons. He describes breeding methods and introduces the term artificial selection (though environmental changes, such as more food and protection from predators, were also factors).

In chapter II Darwin considers variation under nature. He wrote that the nineteenth-century definition of species was chiefly a matter of opinion, since the discovery of new linking forms often degraded species to varieties, and in many cases experts were unable to agree whether different forms represented different varieties of the same species or different species of the same genus. He then points out that in large genera with many species the species also tend to have numerous varieties. Darwin goes on to state "I believe a well-marked variety may be justly called an incipient species" and "that species are only strongly marked and permanent varieties". Historians have pointed out that these two chapters present one of the most important of the new ideas in Origin. Naturalists had long known that the individuals of a species differed from one another in many ways, but for the most part had considered such variations to be limited and unimportant with the basic character of each species representing an unchanging ideal in the mind of God. The ideas of Darwin and Wallace elevated variations among individuals within a species from being trivial details to being central to understanding the way the natural world worked.

Struggle for existence, natural selection, and divergence

At the start of chapter III on struggle for existence, Darwin reiterates how this 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 and 6th editions he added "But the expression often used by Mr. Herbert Spencer, of the Survival of the Fittest, is more accurate, and is sometimes equally convenient." He discusses the universal struggle for existence as shown by A. P. de Candolle and Charles Lyell, emphasising that he uses the term "in a large and metaphorical sense, including dependence of one being on another". The rate of increase in population which would follow if all offspring survived leads to a Malthusian struggle: "It is the doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms". In reviewing checks to such increase he discusses the complex interdependencies which we now term ecology. He notes that competition is most severe between closely related forms, "which fill nearly the same place in the economy of nature".

Chapter IV details 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 takes as an example a country where a change in conditions leads to extinction of some species, possibly immigration of others more suited and, where suitable variations occur, descendants of species becoming increasingly adapted to the changed conditions. Darwin points out that the artificial selection practiced by animal breeders frequently produces a sharp divergence in character between different breeds, and he suggests natural selection might do the same. He says:

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 pointed out that in this passage Darwin has anticipated the modern concept of an ecological niche and the role such niches play in supporting biological diversity. He does not suggest that every individual with a favourable variation must be selected, or that the selected or favoured animals are better or higher, but merely that they are more adapted to their surroundings. Having no knowledge of Mendelian genetics, he tries to deal with anticipated blending of inherited characteristics.

The tree diagram used to show the divergence of species. It is the only illustration in the Origin of Species.

Darwin then introduces what he calls sexual selection to explain seemingly non-functional differences between sexes, as in beautiful plumage of birds. He draws attention to cross-breeding between varieties giving "vigour and fertility to the offspring", with close interbreeding or self fertilization having the opposite effect, explaining features found in flowers which avoid self-fertilisation and attract insects to cross-pollinate. He thinks that natural selection leading to new species is most favoured by isolation of a population, or by open areas with large populations leading to increased numbers of variations. The effect of natural selection in forming species is expected to be very slow, and often intermittent, but given the effectiveness of artificial selection, he "can 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 indicates the "divergence of character" from original species into multiple new species and genera, branches stopping or falling off as extinction occurs, while fresh buds form new branches in "the great Tree of life... with its ever branching and beautiful ramifications."

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 believe that Darwin chose to start his argument with the case for natural selection rather than with evidence that evolution had occurred because he was aware that most of his readers would already have been familiar with earlier arguments for the transmutation of species. He was also aware that these earlier arguments had failed to find wide acceptance among leading scientists in large part because they lacked any plausible mechanism for evolutionary change. Therefore Darwin wanted to begin his argument by convincing his readers that his theory had a viable scientific explanation for how evolutionary change occurred before he discussed the evidence that it had..

Variation and heredity

One of the chief difficulties for Darwin and other naturalists in his time was that there was no agreed-upon model of heredity; early in chapter one Darwin states "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 5 (of the first edition) discusses what he calls 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. Besides changes he attributes to the use and disuse of organs (such as the loss of eyes in cave dwelling species) Darwin discusses acclimatization to environmental conditions and correlations in the growth of different parts of an organism, where variations in certain characteristics of some organisms seemed to be correlated with variations in other characteristics, as factors that could produce inheritable variation. Darwin did state 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 instead. In later additions of Origin Darwin expands the role attributed to the inheritance of acquired characteristics.

It was not until the early 20th century, with the advent of the modern evolutionary synthesis, that a model of heredity became completely integrated with a model of variation. It is a common theme in the history 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 about his idea of natural selection, but later historians of science have adequately documented the fact that this was not the source of most objections to Darwin, and that later scientists, such as Karl Pearson and the biometric school, could develop compelling models of evolution by natural selection with even a relatively simple "blending" model of heredity such as that used by Darwin.

Difficulties for the theory

In chapters VI – VIII (of the first edition) Darwin addresses possible difficulties for the theory. Darwin starts with the question of why often there are no intermediate forms between closely related species found in nature. He attributes this to the fact that competition between different forms, combined with the relatively small number of individuals of intermediate forms, result in such forms frequently becoming extinct, leaving only well differentiated and 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 make use of them, in cases where it would be difficult to imagine how transitional intermediate forms could be functional. Darwin says:

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 fully functional and adaptive for their life styles. He discusses flying squirrels, which are a relatively straight forward modification of ordinary squirrels, and flying lemurs as examples of how bats might possibly have evolved from non-flying ancestors. He discusses 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 from much simpler structures. 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 addresses the issue of the evolution of complex instincts in chapter VII. He examines a number of examples. Among them are two that he had investigated with experiments: slave making ants and the construction of hexagonal cells by honey bees. In the case of slave making ants Darwin points out that there is a range of behaviour between different species, with some slave making species far more dependant on slave workers than others, and he observes that many ant species will collect the pupae of other species to store as food; he sees no problem with species with an extreme dependency on slave workers, having evolved in incremental steps from non slave making ancestors. He discusses in detail how bees making hexagonal cells could have evolved in incremental steps from bees that made round cells to minimize wax use. Darwin concludes the chapter by saying: "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."

In chapter VIII (of the first edition) Darwin launches into a very detailed discussion about the hybridization of plant and animal species. He addresses the idea that species had some how been imbued with some special characteristic that prevented viable and fertile hybrids from occurring in order to permanently preserve species as separate specially created entities. Darwin argues that far from being universally constant, the difficulty in producing hybrids of closely related species, and the viability and fertility of the hybrids produced, varied greatly from species to species, especially among plants. In a few cases what were nearly universally considered to be separate species produced viable fertile hybrid offspring freely, and in a few other cases what were generally considered to be mere varieties of the same species could only be crossed with great difficulty. Darwin concludes: "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

In chapters IX and X of the first edition Darwin discusses evidence from the geological record. In chapter IX, On The Imperfection of the Geological Record, he addresses the issue of whether or not there had been enough time for the slow process of evolution by natural selection. He cites 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 addresses the concern that the fossil record didn't contain innumerable intermediate forms. Darwin points out that geological formations are intermittent with gaps of unknown (at the time of his writing) length 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 states that fossils are only rarely preserved, and that 19th century fossil collections were extremely fragmentary. Darwin says: "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".

In chapter X, On the Geological Succession of Organic Beings, Darwin argues that despite the imperfections discussed in the previous chapter the fossil record shows certain broad patterns that are better explained by his theory of branching divergence caused by natural selection than by the idea that species are individually created and remain largely unchanged. Darwin points out 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 much 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 some later point. He also states 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, for example mammals, extinct species that have lived more recently tend to be much more similar to species still existing today than species that lived much longer ago, and frequently extinct species can be found that have characteristics intermediate between two more recent groups. He says: "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 discusses the fact, that at least in the most recent geological periods, extinct organism tend to resemble those organisms still living in the area. He says: "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

In chapters XI and XII of the first edition Darwin discusses evidence from the geographical distribution of animals and plants, what would later come to be called biogeography. He starts by pointing out that the differences in flora and fauna between different regions can not 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 is 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 for these facts is a combination of migration and descent with modification. He goes 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 then goes on to compare the then current idea that each species had its own separate center of creation with his idea of dispersal followed by descent with modification. He discusses how a volcanic island formed a few hundred miles from a continent might be colonized over time 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 discusses possible mechanisms of dispersal across oceans in great detail; he had investigated many such possible mechanisms himself experimentally. He also speculates at some length about how the recent ice age might have effected the geographic distribution of some species.

In chapter XII Darwin discusses the distribution of fresh water species. He returns to the topic of oceanic islands and describes their many peculiarities, such as the fact that on many such islands the roles played by mammals on continents are played by other kinds of organisms such as flightless birds or reptiles. In the chapter summary he 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 starts chapter XIII by discussing the classification of living things. He points out that classification is based on the fact that species resemble one another to varying degrees and that they can be grouped together in a multilevel system with groups such as families that contain subordinate groups such as genera. He discusses classification issues in some detail and concludes:

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,...

After more detailed discussion of classification Darwin goes on to talk about morphology including the importance of homologous structures. He says "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?". Then he turns to embryology discussing the fact that animals of the same class often have extremely similar embryos. He cites the example of a leading naturalist who having failed to label an early stage vertebrate embryo was unable to determine later whether it was a mammal, bird, or reptile. Finally Darwin discusses evidence from rudimentary organs such as the wings of flightless birds, and the rudiments of pelvis and leg bones found in some snakes. He points out that some such rudimentary organs, such as teeth in baleen whales, are found only in embryos not in adults.

Concluding remarks

In the final chapter Darwin recapitulates major points from all the earlier chapters and concludes by hoping that his theory may produce revolutionary changes in many fields of natural history. He ends the book with the following paragraph:

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. These laws, taken in the largest sense, being Growth with Reproduction; Inheritance which is almost implied by reproduction; Variability from the indirect and direct action of the external conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the Extinction of less-improved forms. 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.

Historians say that Darwin was at his best, piling on supporting fact after fact from different disciplines, in the last few chapters of the book. They point out 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.

Public reaction

Main article: Reaction to Darwin's theory

As "Darwinism" became widely accepted in the 1870s, good-humoured caricatures of him with an ape or monkey body, such as this example from the Hornet magazine, symbolised evolution.

Public reaction can be partitioned into three overlapping realms: scientific, religious, and philosophical.

The book aroused international interest, with less controversy than had greeted the popular Vestiges of Creation in 1844. Both Vestiges and George Combe's The Constitution of Man of 1828 were amongst books that had already converted a large public audience to the belief that both nature and human society were governed by natural laws. At the time of publication, the educated public generally held the belief that science was a "friend of humanity" and that the natural world was orderly. This belief was based in part on advances made by Frenchman Louis Pasteur, who, in 1859, finally laid to rest the theory of spontaneous generation, and Newton's laws of motion and gravitation, which were perceived as timeless and absolute.

Darwin had only said "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. Huxley's popular "working-men's lectures" drew on public interest in this idea. With the publication of the 6th edition, the book's price was halved, increasing sales and disseminating Darwin's revolutionary ideas even more widely. A version of evolution loosely related to Darwin's ideas was popularised by people such as Herbert Spencer, later labeled Social Darwinists, who promoted the virtues of competition outside of biology.

Religious

The Church of England's response was mixed. Some saw it as direct threat to natural theology, which played an important role in the Church's doctrine. Darwin’s old Cambridge tutors Adam Sedgwick and John Stevens Henslow dismissed his ideas, but 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". In 1860, the publication of Essays and Reviews by seven liberal Anglican theologians diverted clerical attention from Darwin, with its ideas including higher criticism attacked by church authorities as heresy. In it, Baden Powell argued that miracles broke God’s laws, so belief in them was atheistic, and praised “Mr Darwin’s masterly volume [supporting] the grand principle of the self-evolving powers of nature”. American botanist and Darwin promoter Asa Gray tried to reconcile design doctrine with evolution by arguing 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.

The book contradicted widely held creation myths that held that the Creator ordained not only the laws of nature but also directly created kinds. By the mid 19th century developments in geology had already led many to abandon a literal reading of Genesis. However, the argument from design was still an important part of Christian belief. The idea of supernatural design in nature served two purposes; one scientific, and the other religious. Design made nature orderly, and hence made science possible. Supernatural design also gave sanction to "the moral and religious endeavours of man."

Religious controversy was fuelled in part by one of Darwin's most vigorous defenders, Thomas Henry Huxley, who opposed church control over science and coined the term Darwinism in the April 1860 issue of the Westminster Review. and hailed the book as, "a veritable Whitworth gun in the armoury of liberalism", promoting scientific naturalism over theology and praising the usefulness of Darwin's ideas while expressing professional reservations about Darwin's gradualism and doubting if it could be proved that natural selection could form new species, Huxley compared Darwin's achievement to that of Nicolaus Copernicus in explaining planetary motion:

What if the orbit of Darwinism should be a little too circular? What if species should offer residual phenomena, here and there, not explicable by natural selection? Twenty years hence naturalists may be in a position to say whether this is, or is not, the case; but in either event they will owe the author of "The Origin of Species" an immense debt of gratitude...... And viewed as a whole, we do not believe that, since the publication of Von Baer's "Researches on Development," thirty years ago, any work has appeared calculated to exert so large an influence, not only on the future of Biology, but in extending the domination of Science over regions of thought into which she has, as yet, hardly penetrated.

Huxley opined that Christianity is "a compound of some of the best and some of the worst elements of Paganism and Judaism, moulded in practice by the innate character of certain people of the Western World." In a legendary confrontation at the public 1860 Oxford evolution debate during a meeting of the British Association for the Advancement of Science, the Bishop of Oxford Samuel Wilberforce, though not opposed to transmutation of species, argued against Darwin's explanation. In the ensuing debate Joseph Hooker argued strongly for Darwin, and Thomas Huxley established himself as “Darwin’s bulldog”. Both sides came away feeling victorious, with Huxley claiming that on being asked by Wilberforce whether he was descended from monkeys on his grandfather’s side or his grandmother’s side, Huxley muttered: “The Lord has delivered him into my hands” and replied that he “would rather be descended from an ape than from a cultivated man who used his gifts of culture and eloquence in the service of prejudice and falsehood”.

Theologian Charles Hodge, a critic of Darwin's theories, also praised Darwin for his intellectual honesty.

Ernst Heinrick Haeckel, a German professor of biology, affirmed that nothing spiritual exists, and instead asserted that all life descended from protoplasm that spontaneously combined from essential protoplasmic elements in antiquity. In his 1874 critique "What is Darwinism?" the theologian Charles Hodge argued that Darwin's theories were tantamount to atheism. This is an argument that had been made by many almost immediately after Darwin's first publication. As Hodge pointed out, evolution does not seem to originate from a divine source, and some viewed God as a less powerful force in the universe. Asa Gray responded that Hodge's accusation of atheism misrepresented the text by not acknowledging Darwin's explicit references to the laws impressed on matter by the Creator, and less "ultra-orthodox" theologians accepted creation by evolution, with Kingsley proposing that "We know of old that God was so wise that he could make all things; but, behold, he is so much wiser than even that, that he can make all things make themselves".

While religious controversies continue, some modern theologians have accomodated the theory with their religion. Pope Pius XII stated in an encyclical in 1950, “the Teaching authority does not forbid that in conformity with the present state of human sciences and sacred theology, research and discussions, on the part of men experienced in both fields, take place with regard to the doctrine of evolution, in as far as it inquired into the origin of the human body as coming from pre-existence and living matter- … faith obliges us to hold that souls were immediately created by God” .

Reception outside of 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 wrote "I never dreamed of my Book being so successful with general readers: I believe I sh^d. have laughed at the idea of sending the sheets to America." 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. Gray promoted and defended the work against some naturalists with an idealist approach, including Jeffries Wyman, and one of the most prominent scientists in the country at the time, geologist and anatomist Louis Agassiz whose idealism viewed every species as a distinct unit in the mind of the Creator, including as species what others considered merely varieties. Agassiz's many students would come to accept evolution but most would prefer Lamarckian mechanisms over natural selection. At Gray's urging, Wyman wrote to Darwin agreeing that "progressive development is a far more probable theory than progressive creations", and they corresponded about research.

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. 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 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 misgiving of conservative thinkers, but was welcomed by philosophical radicals already used to transformationist ideas of metamorphosis and monadology. Some German scientists, while not accepting natural selection, enlisted it 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. Haeckel and other German scientists went on to take the lead in an ambitious programme to reconstruct the history of life using mophology and embryology. By 1864 Darwin's work was gaining wide support in Germany and Switzerland. 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. French speaking naturalists in several countries showed appreciation of the translation, but Darwin's ideas had little impact. Royer had made it more palatable to Lamarckian scientists, and that remained the preferred approach in France. 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. 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. 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.

Muslims were also being introduced to Darwinism, but a religious crisis as seen in the West did not arise. The immediate response was an overall rejection of the theory, but this was not caused so much by direct religious objections as it was by poor translations of the book. Little debate about the the theory occurred until many years later when better translations began to circulate. Its controversy rooted from the origination of the theory from the west. Science from the west is viewed as materialistic and is subject to rejection. As time passed and better translations of the book were available the scientific side of the theory was promoted and became integrated into the Islamic religion by some scholars.

Impact on the scientific community

Many of the debates did not centre around Darwin's specific proposal of natural selection as the mechanism for evolution, but rather on the concept of evolution in general. Though Darwin was too sickly to defend his work in public, his close scientific friends took up the cause of promoting Darwin's work and defending it against critics. Chief among these were Huxley, who argued for the evidence of evolution in anatomical morphology, Joseph Dalton Hooker, the Royal botanist at Kew Gardens, the geologist Charles Lyell and Asa Gray, the leading botanist in America.

In his 1863 Evidence as to Man's Place in Nature, Darwin's friend Thomas Huxley exaggerated the size of the Gibbon while presenting the anatomical argument explicit in the above frontispiece.

Immediate scientific reaction to Darwin's theory was mixed. Many well-respected members of the scientific community, such as Agassiz and the anatomist Richard Owen, came out strongly against Darwin's work. On the whole, though, Darwin was successful in convincing most scientists, especially the younger ones, that evolution had happened and that the diversity of modern species resulted from a branching pattern of descent from common ancestors. Over the course of the next two decades, most scientifically literate people would come to believe that evolution had occurred. Natural selection, though, did not find such wide support and was actively attacked by many scientists. Similarly, Darwin's view that evolution occurred gradually was also often attacked, and many of the evolutionary theories which flourished during what Peter J. Bowler has called "the eclipse of Darwinism" were forms of "saltationism", in which new species arose through "jumps" rather than gradual adaptation. Others were forms of neo-Lamarckism that emphasised the importance of the inheritance of acquired characteristics and relegated natural selection to a minor role, or forms of orthogenesis that claimed that species had an inherent tendency to change in a particular direction.

Natural selection was not generally accepted as the main driving force of evolution by scientists until the 1930s when the work of 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 Mendelian genetics as part of the modern evolutionary synthesis. The ultimate impact of Darwin's ideas on scientific opinion can be seen in the fact that according to a 1987 Newsweek article, a contemporary survey of U.S. earth and life scientists revealed that less than 0.2% "gave credence" to creation science, as an alternative explanation for the diversity of life on earth to the modern evolutionary synthesis.

Comparison with Wallace's ideas

Darwin's explanation of natural selection was slightly different from that given by Alfred Russel Wallace. Darwin used comparison to selective breeding and artificial selection as a means for understanding natural selection. Wallace made no such connection; he expressed it simply as a basic process of nature. Also while Darwin emphasised competition between individuals of the same species, Wallace focused on ecological pressures keeping different varieties adapted to local conditions.

Wallace was not entirely happy with the term natural selection, and he encouraged Darwin to replace it with Spencer's "survival of the fittest" in later editions. He also ruled out the concession to Lamarckian inheritance present in Darwin's work, considering it unnecessary. Darwin and Wallace would disagree on many substantive issues later in their lives, especially on the question of whether human consciousness had itself evolved by natural selection; to Darwin's dismay, Wallace felt that the higher human mental faculties could not have evolved through a purely material process and would eventually embrace Spiritualism. Also Wallace did not believe that sexual selection was nearly as important a factor as Darwin did.

References

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• Browne, E. Janet (1995), Charles Darwin: vol. 1 Voyaging, London: Jonathan Cape, ISBN 1-84413-314-1
• Browne, E. Janet (2002), Charles Darwin: vol. 2 The Power of Place, London: Jonathan Cape, ISBN 0-7126-6837-3
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• Darwin, Charles (1842), "Pencil Sketch of 1842", in Darwin, Francis (ed.), The foundations of The origin of species: Two essays written in 1842 and 1844., Cambridge University Press (published 1909)
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Further reading

• Janet Browne (2007). Darwin's Origin of Species: A Biography. ISBN 978-0871139535

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.

External links

• The complete work of Charles Darwin online: Table of contents, bibliography of On the Origin of Species:
  Both web pages provide links to text and images of all editions of The Origin of Species, including translations in German, Danish, and Russian.
• Full text of 1st edition in pdf format at University of New South Wales
• Full text of 1st edition at TalkOrigins Archive
• Origin of Species, full text with embedded audio.
• Origin of Species, 1st Edition at Project Gutenberg
• Origin of Species, 6th Edition at Project Gutenberg
• DarwinMiscSep99 Changes in the six editions from 1859 – 1872.
• Victorian Science Texts