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The Origin of Species

2007 Schools Wikipedia Selection. Related subjects: Evolution and
reproduction

   The title page of the 1859 edition of On the Origin of Species.
   Enlarge
   The title page of the 1859 edition of On the Origin of Species.

   The Origin of Species (full title: On the Origin of Species by Means of
   Natural Selection, or the Preservation of Favoured Races in the
   Struggle for Life) by British naturalist Charles Darwin, first
   published on 24 November 1859, is one of the pivotal works in
   scientific history and arguably the pre-eminent work in biology.

   In it, Darwin makes "one long argument", with copious empirical
   examples as support, for his theory that organisms gradually evolve not
   individually but in "groups" (now called populations) through the
   process of natural selection, a mechanism the book effectively
   introduced to the public. The work presents detailed scientific
   evidence that Darwin had accumulated on the Voyage of the Beagle in the
   1830s and since his return, painstakingly laying out his theory and
   refuting the doctrine of " Created kinds", which underlay the then
   widely accepted theories of Creation biology.

   The book is quite readable even for the non-specialist and attracted
   widespread interest on publication. Although its ideas are supported by
   an overwhelming body of scientific evidence and are widely accepted by
   scientists today, they are still highly controversial in some parts of
   the world, particularly among American non-scientists who perceive them
   to contradict various religious texts (see Creation-evolution
   controversy).

Background

Before The Origin

   The idea of biological evolution was supported in Classical times by
   the Greek and Roman atomists, notably Lucretius. With the rise of
   Christianity came belief in the Biblical idea of creation according to
   Genesis, with the doctrine that God had directly " Created kinds" of
   organisms which were immutable. Other ideas resurfaced, and in 17th
   century English the word evolution (from the Latin word "evolutio",
   meaning "unroll like a scroll") began to be used to refer to an orderly
   sequence of events, particularly one in which the outcome was somehow
   contained within it from the start.

   Natural history, aiming to investigate and catalogue the wonders of
   God's works, developed greatly in the 18th century. Discoveries showing
   the extinction of species were explained by catastrophism, the belief
   that animals and plants were periodically annihilated as a result of
   natural catastrophes and that their places were taken by new species
   created ex nihilo (out of nothing). Countering this, James Hutton's
   uniformitarian theory of 1785 envisioned gradual development over aeons
   of time. Georges-Louis Leclerc, Comte de Buffon, Charles Bonnet, Lord
   Monboddo and Jean-Baptiste Lamarck played roles in the foreshadowing of
   evolutionary thought in the mid 18th and early 19th centuries.

   By 1796 Charles Darwin's grandfather Erasmus Darwin had put forward
   ideas of common descent with organisms "acquiring new parts" in
   response to stimuli then passing these changes to their offspring, and
   in 1802 he hinted at natural selection. In 1809 Jean-Baptiste Lamarck
   developed a similar theory, with "needed" traits being acquired then
   passed on. These theories of Transmutation were developed by Radicals
   in Britain like Robert Edmund Grant. At this time the work of Thomas
   Malthus showing that human populations increased to exceed resources
   influenced liberal thinking, resulting in the Whig Poor Law of the
   1830s.

   Various ideas were developed to reconcile Creation biology with
   scientific findings, including Charles Lyell's uniformitarian idea that
   each species had its "centre of creation" and was designed for the
   habitat, but would go extinct when the habitat changed. Charles Babbage
   believed God set up laws that operated to produce species, as a divine
   programmer, and Richard Owen followed Johannes Peter Müller in thinking
   that living matter had an "organising energy", a life-force that
   directed the growth of tissues and also determined the lifespan of the
   individual and of the species.

   The publication of the anonymous Vestiges of the Natural History of
   Creation ( 1844) then paved the way for the acceptance of Origin.

Inception of Darwin's theory

   Charles Darwin's education at the University of Edinburgh gave him
   direct involvement in Robert Edmund Grant's evolutionist developments
   of the ideas of Erasmus Darwin and Jean-Baptiste Lamarck. 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 the botanist John Stevens Henslow and the
   geologist Adam Sedgwick, both of whom believed strongly in divine
   creation and in a uniformitarian ancient earth. During the Voyage of
   the Beagle Charles Darwin became convinced by Charles Lyell's
   uniformitarianism, and puzzled over how various theories of creation
   fitted 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, and John Gould startlingly revealed that
   completely different birds from the Galápagos Islands were species of
   finches distinct to each 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 despite the theological doctrine that only
   mankind possessed a soul.

   In late September 1838 he began reading the 6th edition of Malthus's
   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 Whig social thinking of struggle for survival with no hand-outs. 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
   practised and perfected", thinking this "the most beautiful part of my
   theory".

First writings on the theory

   Darwin was well aware of the implication the theory had for the origin
   of humanity and the real danger to his career and reputation as an
   eminent geologist of being convicted of blasphemy. He worked in secret
   to consider all objections and prepare overwhelming evidence supporting
   his theory. He increasingly wanted to discuss his ideas with his
   colleagues, and in January 1842 sent a tentative description of his
   ideas in a letter to Lyell, who was then touring America. Lyell,
   dismayed that his erstwhile ally had become a Transmutationist, noted
   that Darwin "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". The 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.
   Darwin made a huge study of barnacles which established his credentials
   as a biologist and provided more evidence supporting his theory.

Publication

   In the spring of 1856 Lyell drew Darwin's attention to a paper on the
   "introduction" of species written by Alfred Russel Wallace, a
   naturalist working in Borneo, and urged Darwin to publish to establish
   priority. Darwin was now 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 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 entitled
   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.

   Darwin now worked hard on an "abstract" trimmed from his Natural
   Selection, writing much of it from memory. Lyell made arrangements with
   the publisher John Murray, who agreed to publish the manuscript sight
   unseen, and to pay Darwin two-thirds of the net proceeds. Darwin had
   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 reduced to the snappier On the Origin of
   Species through Natural Selection.

Publication of The Origin

   The Origin was first published on 24 November 1859, price fifteen
   shillings, and was oversubscribed, so that all 1250 copies were claimed
   by booksellers that day. The second edition came 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."

   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, and the fourth in 1866, each with
   an increasing number of sentences rewritten or added. The fifth edition
   published on 10 February 1869 incorporated more changes again, and for
   the first time included Herbert Spencer's phrase " survival of the
   fittest".

   In January 1871 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 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 a month.

Darwin's theory, as presented

   Darwin opened his argument by pointing to the results of domestication,
   mostly through artificial selection (though environmental changes, such
   as more food and protection from predators, were also factors).
   Comparing domesticated and wild varieties, Darwin showed 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.

Basic theory

   Darwin's theory is based on five key observations and inferences drawn
   from them, as summarized by the biologist Ernst Mayr:
    1. Species have great fertility. They make more offspring than can
       grow to adulthood.
    2. Populations remain roughly the same size, with modest fluctuations.
    3. Food resources are limited, but are relatively constant most of the
       time. From these three observations it may be inferred that in such
       an environment there will be a struggle for survival among
       individuals.
    4. In sexually reproducing species, generally no two individuals are
       identical. Variation is rampant.
    5. Much of this variation is inheritable.

   From this Darwin infers: In a world of stable populations where each
   individual must struggle to survive, those with the "best"
   characteristics will be more likely to survive, and those desirable
   traits will be passed to their offspring; and that these advantageous
   characteristics are inherited by following generations, becoming
   dominant among the population through time. This is natural selection.

   Darwin did not suggest that every variation and every character must
   have a selection value. However, he pointed out that, because of our
   ignorance of animal physiology and its relationship with the
   environment, it was extremely rash to set down any characters as
   valueless to their owners. It is even more important to notice that he
   did not suggest that every individual with a favorable variation must
   be selected, or that the selected or favored animals were better or
   higher, but merely that they were more adapted to their surroundings.

   Darwin further infers that natural selection, if carried far enough,
   makes changes in a population, eventually leading to new species. He
   puts forward myriad observations as demonstrations of this, and also
   claims that the fossil record can be interpreted as supporting these
   observations. Darwin imagined it might be possible that all life is
   descended from an original species from ancient times. Modern DNA
   evidence is consistent with this idea.

   In later editions of his book, starting in the fifth edition, in some
   instances where Darwin used the wording, Natural Selection, this was
   modified to "Natural Selection, or the Survival of the Fittest" in
   varying ways, borrowing the term survival of the fittest from Herbert
   Spencer.

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 — in fact, the
   idea of heredity had not been completely separated conceptually from
   the idea of the development of the organism. Darwin himself saw
   variation and heredity as two essentially antagonistic forces, with
   most heredity working to preserve the fixity of a type rather than
   acting as the agent of species variability. Darwin's own model of
   heredity worked out in later works, which he dubbed " Pangenesis", was
   a mixture of a number of different ideas about heredity at the time. It
   contained what are now considered to be essentially Lamarckian aspects,
   whereby the effects of use and dis-use of different parts of the body
   in the parent could be transmitted to the child. Beyond this, it was
   essentially a model of "blended" heredity, by which the contributions
   of two parents (in the form of particles he called "gemmules") were
   roughly equal. Darwin was confident that even in this model, over long
   periods of time species would still be able to evolve.

   It was not until the early twentieth century that a model of heredity
   would become completely integrated with a model of variation, with the
   advent of the modern evolutionary synthesis known as neo-Darwinism. It
   is a common trope 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
   theory, 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. (Bowler 1989)

   This article incorporates text from the Encyclopædia Britannica
   Eleventh Edition, a publication now in the public domain.

Compatibility with Lamarckian inheritance

   Contrarily to a common opinion, Darwin did not rule out at first the
   possibility of inherited acquired traits, and even mentions it
   explicitly in chapter 7 :

   "When the first tendency was once displayed, methodical selection and
   the inherited effects of compulsory training in each successive
   generation would soon complete the work; and unconscious selection is
   still at work, as each man tries to procure, without intending to
   improve the breed, dogs which will stand and hunt best. On the other
   hand, habit alone in some cases has sufficed; no animal is more
   difficult to tame than the young of the wild rabbit; scarcely any
   animal is tamer than the young of the tame rabbit; but I do not suppose
   that domestic rabbits have ever been selected for tameness; and I
   presume that we must attribute the whole of the inherited change from
   extreme wildness to extreme tameness, simply to habit and
   long-continued close confinement".

   Nevertheless, there is a quantum leap between Lamarck's theory and
   Darwin's one: while Darwin's theory stays valid whether acquired traits
   are transmitted or not, Lamarck's theory becomes inoperative if
   acquired traits cannot be transmitted.

Public reaction

   Caricature of Darwin as an ape in the Hornet magazine.
   Enlarge
   Caricature of Darwin as an ape in the Hornet magazine.

   After the publication of Darwin's book, evolution was widely discussed
   and debated. As well as attracting attention from naturalists and
   learned religious people, Huxley's "working-men's lectures" proved very
   popular and the 6th edition was halved in price, successfully
   increasing sales to meet this demand.

   The book was highly controversial when first published, as it
   contradicted the then-prevailing theory of establishment scientists, of
   immediate, divine design in nature, and conflicted with a literal
   reading of the biblical creation stories in the Book of Genesis. Most
   of the debates did not centre around Darwin's specifically proposed
   mechanism for evolution — natural selection — but rather on the concept
   of evolution in general, which Darwin was credited for having given
   compelling scientific support. Though Darwin himself was too sickly to
   defend his work in public, four of his close scientific friends took up
   the cause of promoting Darwin's work and defending it against critics.
   Chief among these were Thomas Henry Huxley, who argued for the evidence
   of evolution in anatomical morphology, and Joseph Dalton Hooker, the
   Royal botanist at Kew Gardens. In the United States, Asa Gray worked in
   close correspondence with Darwin to assure the theory's spread despite
   the opposition of one of the most prominent scientists in the country
   at the time, Louis Agassiz, and helped to facilitate American
   publication of the book. Darwin himself worked over the years with
   translators who published his work in both French and German as well.
   Darwin's friend Thomas Henry Huxley became a vigorous supporter of the
   theory of evolution, and specifically used his knowledge about the
   anatomy of apes to argue for human evolution. In his 1863 Evidence as
   to Man's Place in Nature, Huxley made the anatomical argument explicit
   in the above frontispiece.
   Enlarge
   Darwin's friend Thomas Henry Huxley became a vigorous supporter of the
   theory of evolution, and specifically used his knowledge about the
   anatomy of apes to argue for human evolution. In his 1863 Evidence as
   to Man's Place in Nature, Huxley made the anatomical argument explicit
   in the above frontispiece.

   Scientific reaction to Darwin's theory was mixed. Many well-respected
   members of the scientific community, such as the aforementioned Agassiz
   and the anatomist Richard Owen, came out strongly against Darwin's
   work. On the whole, though, Darwin was successful in convincing many
   scientists, especially of the younger generations, that evolution had
   happened in one form or another. Over the course of the next two
   decades, most scientists and educated lay-people would come to believe
   that evolution had occurred. Natural selection, though, did not find
   wide support, and was actively attacked and relatively unpopular until
   its revival during the creation of the modern evolutionary synthesis in
   the 1920 and 1930s. Similarly, Darwin's notion 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.

   In 1874, the theologian Charles Hodge accused Darwin of denying the
   existence of God by defining humans to be a result of a natural process
   rather than a creation designed by God. This is an argument that had
   been made by many almost immediately after Darwin's first publication.
   Evolution is in complete contradiction with literal readings of many of
   the legendary or religious stories of how the world's life originated;
   therefore, those who accepted the theory grew more skeptical of the
   Bible or other religious sources. 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.

   Darwin's theory changed the way humans saw themselves and their world.
   If one accepted that humans were descended from animals, it became
   clear that humans also are animals. The natural world took on a darker
   tinge in the minds of many, as animals in the wild are understood to be
   in a constant state of deadly competition with one another. The world
   was also seen in a less permanent fashion; since the world was
   apparently much different millions of years ago, it dawned on many that
   the impact of human beings would lessen and perhaps disappear
   altogether over time.

   From the 1860s up until the 1930s, Darwinian "selectionist" evolution
   was not universally accepted by scientists, while evolution of some
   form generally was (a variety of evolutionary theories competed for
   scientific approval, including neo-Darwinism, neo-Lamarckism,
   orthogenesis, and mutation theory). In the 1930s, the work of a number
   of biologists and statisticians (especially R. A. Fisher) created the
   modern synthesis of evolution, which merged Darwinian selection theory
   with sophisticated statistical understandings of Mendelian genetics.

   Today, whilst the overwhelming majority of scientists in the fields of
   earth and life sciences (over 99.9%) consider Darwin's theory correct ,
   a significant proportion of non-scientists in the United States and a
   few other countries disagree mainly on religious grounds (see
   creation-evolution controversy).

Misconceptions, and comparison to Wallace's theory

   Like many great scientists, Darwin did not invent his theory from the
   ground up, rather, he seized upon earlier research to create a
   comprehensive and defendable theory. Darwin did not "discover"
   evolution as is clear from the history of evolutionary thought. Even in
   his own day it was a well-known concept, although not one defended by
   the scientific community. As he subsequently acknowledged, others
   before him published brief statements outlining the principle of
   natural selection, but he was not aware of these little known
   statements until after publication of the Origin. Instead, he and
   Wallace put forth the first convincing and coherent mechanism of
   evolution: natural selection. Darwin's work, through its long list of
   facts and its support by prominent naturalists, established for most
   that evolution of some form did occur—that there was no fixity of
   species—even if there was considerable disagreement on the mechanism.
   Also contrary to a common understanding, Darwin did not invent the
   phrase " survival of the fittest", but added this in the 5th edition of
   The Origin of Species, giving due credit to the philosopher Herbert
   Spencer (who had introduced the phrase in his Principles of Biology of
   1864) and usually using the phrase "Natural Selection, or the Survival
   of the Fittest". Other aspects of Darwin's overall theory which
   themselves evolved over time were: common descent, sexual selection,
   gradualism, and pangenesis.

   Darwin's explanation of natural selection was slightly different from
   that given by Wallace. Darwin used comparison to selective breeding and
   artificial selection as a means for understanding natural selection. No
   such connection between selective breeding and natural selection was
   made by Wallace; he expressed it simply as a basic process of nature
   and did not think the phenomena were in any way related. On Wallace's
   own first edition of The Origin of Species, he crossed out every
   instance of the phrase "natural selection" and replaced with it
   Spencer's "survival of the fittest." He also ruled out much of the
   ideas of Lamarckian inheritance present in Darwin's work, calling it
   "quite unnecessary." Darwin and Wallace would disagree on many
   substantive issues later in their lives especially, most bitterly on
   the question of whether human consciousness had itself evolved (to
   Darwin's horror, Wallace eventually turned against this and towards
   spiritualism).

Philosophical implications

   According to Ernst Mayr, Darwin's evolutionary thinking rests on a
   rejection of essentialism, which assumes the existence of some perfect,
   essential form for any particular class of existent, and treats
   differences between individuals as imperfections or deviations away
   from the perfect essential form. Darwin embraced instead what Mayr
   calls " population thinking", which denies the existence of any
   essential form and holds that a class is the conceptualization of the
   numerous unique individuals. Individuals, in short, are real in an
   objective sense, while the class is an abstraction, an artifact of
   epistemology. This emphasis on the importance of individual differences
   is necessary if one believes that the mechanism of evolution, natural
   selection, operates on individual differences.

   Mayr claims essentialism had dominated Western thinking for two
   thousand years, and that Darwin's theories thus represent an important
   and radical break from traditional Western philosophy. Ripples of
   Darwin's thought can now be seen in fields such as economics and
   complexity theory, suggesting that Darwin's influence extends well
   beyond the field of biology.

   The historian of science Peter J. Bowler has suggested that many of the
   "implications" attributed to Darwinism had little to do with Darwin's
   theories themselves. Many of the so-called "Darwinists" of the
   late-nineteenth century, such as Herbert Spencer and Ernst Haeckel,
   were actually very non-Darwinian in many aspects of their thought and
   theory, and even the biggest supporters of Darwin, such as Thomas Henry
   Huxley, were suspicious as to whether natural selection was really what
   caused evolution. Nevertheless, Darwin became quickly identified with
   evolution in general and hailed as the figurehead of many conceptual
   changes in both science and society, whether or not all of these ideas
   were stated explicitly or at all in Darwin's work itself. (Bowler 1989)

   The philosopher Daniel Dennett recapitulated those philosophical
   implications in his book Darwin's Dangerous Idea.
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