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The Origin of Species

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The 1859 edition of On the Origin of Species

First published in 1859, 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 is one of the pivotal works in scientific history, and arguably the pre-eminent work in biology. In it, Darwin makes "one long argument" for his theory that organisms gradually evolve through natural selection—a mechanism effectively introduced to the public at large in the work—by presenting scientific evidence he had accumulated on his voyage on the HMS Beagle in the 1830s. His theory was opposed to the then widely accepted theory of catastrophism.

The book was (and still is) quite readable, even by the non-specialist. Although the ideas presented in it are now supported by overwhelming scientific evidence and are widely accepted by scientists today, they are still highly controversial among certain non-scientists who perceive it to contradict literal interpretations of various religious texts and who often support alternative creationist explanations.

Contents

Before "The Origin"

See also History of creationism

In the 16th century discoveries showing the extinction of species were explained by catastrophism. This propounded 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). The extinct organisms could then be observed in the fossil record and their replacements were considered to be immutable. This explanation agreed with the story of the Flood in the Bible, and with the observation that in the fossil record, species remained constant until replaced by others, and was supported by the English scientific establishment which was dominated by the Church of England.

By the early 19th century, several alternative and radical ideas started to emerge. Charles's grandfather Erasmus Darwin hypothesized that all warm-blooded animals sprang from a single living "filament" long, long ago. Another theory was developed by Jean-Baptiste Lamarck (17441829), who observed that every new generation inherits some characteristics of its ancestors. His suggested mechanism for this process was that an individual's traits or organs became enhanced with repeated use, and weakened or removed by disuse. These changes would then be passed directly on to its offspring. As well as being developed in France, these theories were supported by Radicals in Britain like Robert Edmund Grant and developed into the idea of Transmutation. Another important influence on radical thought was the work of Thomas Malthus on populations, which influenced the Whig Poor Law of the 1830s.

From 1830 to 1833, the eminent British geologist and clergyman Sir Charles Lyell released a three volume publication called Principles of Geology which effectively rejected the Catastrophism Theory. This gave additional support to the concept of uniformitarianism, which stated that the Earth's surface gradually altered over eons of time by the constant action of natural geological processes. In the second volume Lyell set out a gradualist variation of Creationism in which each species had its "centre of creation" and was designed for the habitat, but would go extinct when the habitat changed. To Lyell's delight these ideas were developed by John Herschel and by Charles Babbage with the concept that God set up laws that operated to produce species, as a divine programmer. Another theory was explained to Darwin by Richard Owen who followed Johannes Peter Mller 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.

While the scientific establishment was buzzing with these theories, plant and animal breeders were developing practical knowledge and ideas. When Darwin investigated their knowledge he found a pamphlet by Sir John Sebright with a passage reading: "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. In cold or barren countries no animals can live to the age of maturity, but those who have strong constitutions; the weak and the unhealthy do not live to propagate their infirmities."

Development of Darwin's theory

For a detailed account including context see Development of Darwin's theory.

During the Voyage of the Beagle Charles Darwin became convinced by Lyell's uniformitarianism, and puzzled over how various theories of creation fitted the evidence he saw. On his return Richard Owen showed that the fossils were of extinct species related to current species in the same locality, and John Gould startlingly revealed that completely different birds from the Galpagos Islands were species of finches distinct to each island.

By early 1837 Darwin was speculating on transmutation in his "Red Notebook" which he had begun on the Beagle. In July 1837 as his speculation deepened he started the first of a series of notebooks on transmutation which he kept secret because in the political and religious context of the time such ideas could destroy respectability and ruin his career.

By February 1838 Darwin was on to a new pocketbook, the maroon C notebook, and was investigating the breeding of domestic animals, consulting William Yarrell and reading the pamphlet by Yarrell's friend Sebright. At the zoo on 28 March 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 new 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

In January 1842 Darwin 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".

Illness was a continuing problem, and he and his wife Emma left London for rest and quiet, visiting her parents at Maer then moving on to Shrewsbury on 15 June 1842. Here Darwin formulated a 35 page "Pencil Sketch" of his theory. Darwin worked up his "Sketch" into a 189 page "essay" and in July entrusted the manuscript to the local schoolmaster to copy. The copied "Essay", now 231 pages, was returned to him for corrections in September.

Hooker became Darwin's mainstay in the search to find and explain anomalous facts. 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. Their debates continued, sometimes argumentatively, until in November Hooker set off to India.


Between then and 1858, when he would present his theory to the Linnean Society of London, Darwin wrote his masterpiece, modifying his theory in a number of ways as he wrote.

Publication

The Origin was first published on 24 November 1859, and was oversubscribed, so that all 1250 copies were claimed by booksellers that day. The second edition came out in January 1860, and during Darwin's lifetime the book went through six editions, with cumulative changes and revisions to deal with counter-arguments raised. It was highly controversial when first published, as it contradicted the then-prevailing theory of scientists, of immediate, divine design in nature, and conflicted with a literal reading of the biblical creation stories in the Book of Genesis.

Darwin, as evidenced by his later work, The Descent of Man, was well aware of the implication the theory had for the origin of humanity; consequently, he withheld publication of his accumulated evidence in favour of natural selection for well over a decade, and to slighly lessen the controversy, he stopped short of including mankind as a subject of the work. He was forced into publication because of the independent development of a similar theory by Alfred Russel Wallace in 1858. It is felt by some that Wallace deserves as much credit as Darwin for the theory of natural selection, and that he has been rather unfairly marginalised from the history of its development.

Darwin's theory, as presented

Darwin's theory of evolution 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 heritable.

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 further infers that natural selection, if carried far enough, makes changes in a population, eventually leading to new species. He puts forward a myriad of 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.

Mistakenly, Darwin also supposes that Lamarckian inheritance is valid. For example, in the first edition, he states, "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". Lamarckism is now thoroughly scientifically discredited.

For further information on the development of the theory and the initial reaction, see Charles Darwin

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 by means of natural selection was widely discussed and debated, especially among naturalists and some learned religious. Though Darwin was supported by some scientists (e.g., T.H. Huxley), others hesitated to accept the theory due to the unexplained ability of individuals to pass their special abilities to their offspring (though Darwin put forth his own theory of heredity—pangenesis—it was unconvincing, and the lack of a coherent mechanism was a difficult aspect of his theory until the re-discovery of the work of Gregor Mendel in the early 20th century). On the whole, however, his greatest accomplishment was to move the idea of evolution into the realm of serious scientific debate.

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 sceptical 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-Lamarkism, 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 Mendelian genetics.

Today, whilst the overwhelming majority of biologists consider Darwin's basic theory correct, a significant fraction of the general population, particularly in the United States, disagree mainly on religious grounds (see creationism).

Misconceptions, and comparison to Wallace's theory

Contrary to popular understanding, Darwin did not "discover" evolution as it was conjectured by a few since the beginning of the 1800s, and even in his own day it was a well-known concept, although not one defended by the scientific community. Instead, he and Wallace put forth the first convincing and coherent mechanism of evolution: natural selection. Darwin's work, however, 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 6th edition of The Origin of Species, giving due credit to the philosopher Herbert Spencer 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."

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.

References

External links

Basic topics in evolutionary biology
Processes of evolution: macroevolution - microevolution - speciation
Mechanisms: selection - genetic drift - gene flow - mutation
Modes: anagenesis - catagenesis - cladogenesis
History: Charles Darwin - The Origin of Species - modern evolutionary synthesis
Subfields: population genetics - ecological genetics - human evolution - molecular evolution - phylogenetics - systematics - evo-devo
List of evolutionary biology topics | Timeline of evolution
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