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EspañolHISTORY OF EVOLUTIONARY THOUGHT
:''This article is about the history of evolutionary thought in biology. For the history of evolutionary thought in the social sciences, see social evolutionism. For the history of evolutionary thought generally, see evolutionism.''
'Evolutionary thought' has roots in antiquity as philosophical ideas known to the Greeks, Romans, Indians, Chinese and Muslims. Until the 18th century, however, Western biological thought was dominated by essentialism, the idea that living forms are static and unchanging in time. During the Enlightenment, evolutionary cosmology and the mechanical philosophy spread from the physical sciences to natural history, and naturalists such as Maupertuis and Georges-Louis Leclerc, Comte de Buffon focused on the variability of species. The emergence of paleontology (and with it the notion of extinction), as well as the dramatic expansion of known species, helped undermine the traditional static view of nature. The first full theory of evolution was proposed by Jean-Baptiste Lamarck in the early 19th century; Lamarck's theory was based on the idea that species had an innate drive that pushed them up the great chain of being and that the mechanism of inheritance of acquired characteristics helped them adapt to local conditions.
The modern theory referred to as Darwinism was first publicly put forth by Charles Darwin and Alfred Russel Wallace and discussed in great detail in ''On the Origin of Species'', published by Darwin in 1859. Darwinism, which unlike Lamarck's theory proposed common descent and a branching tree of life, was based on natural selection, and synthesized a wide range of evidence from animal husbandry, biogeography, geology, morphology, and embryology. The debate over ''Origin'' would play a key role in the displacement of natural theology by methodological naturalism in the life sciences, and would raise profound questions about human nature and the place of humanity in the natural world.
Darwin's work led to the rapid acceptance of evolution, but his proposed mechanism of natural selection was not widely accepted until the early 20th century. Most biologists preferred inheritance of acquired characteristics (neo-Lamarckism), an innate drive for change (orthogenesis) , or sudden large mutations (saltationism), as driving forces behind evolution. Darwin's theory offered a powerful explanation for a wealth of observed facts in biology. However, inheritance was not well understood at the time of his work. Although the person commonly considered the originator of modern genetic theory, Gregor Mendel, was a contemporary of Darwin, the theory of Mendelian genetics was not developed until the early 20th century. The Darwinian concept of natural selection was combined with Mendelian genetics during the founding of the discipline of population genetics in the 1920s and 1930s. In the 1930s and 1940s population genetics would be integrated with various branches of biology to produce the unified theory of evolution known as the modern evolutionary synthesis, which marked the reemergence of Darwinism as the central evolutionary theory.
Following the synthesis and the rise of evolutionary biology as a formal scientific discipline, evolutionary thought developed in several directons. Studies of mutation and of genetic diversity in natural populations, combined with biogeography and systematics, led to increasingly sophisticated mathematical and causal models of evolutionary change. Paleontology and comparative anatomy allowed increasingly detailed and far-reaching reconstructions of the history of life. Following the rise of molecular genetics and molecular biology, the field of molecular evolution arose, based on "informational macromolecules" such as DNA, RNA, and protein sequences. Gene-centered view of evolution rose to prominence in the 1960s, followed by the neutral theory of molecular evolution; these ideas sparked sustained debates over adaptationism, units of selection, and genetic drift.
In the late 20th century, widespread biological sequencing led to the reorganization of the tree of life into the modern three-domain system, while the recognition of significant symbiogenesis and horizontal gene transfer introduced more complexity into evolutionary history.
As early as 500 BC some Greek philosophers tried to explain the world in a rational way, avoiding superstition, myths and theistic intervention. In particular, the Greek atomists taught that the sun, earth, life, humans, civilization, and society emerged over aeons without divine intervention. It must be remembered that only a sample of the writings of these thinkers has survived, but some generalisations can still be made. Among the pre-Socratic philosophers there were no clear forerunners of evolutionary thinking, though for the most part they attempted to provide rational, material explanations—as opposed to supernatural ones—for the living world. This trend would continue despite Plato[1], whose idealistic tendency led him to eschew empirical investigations.
The pre-Socratic philosophers of the 6th and 5th century BC were the first philosophers of the Western tradition. Their wide range, and the fragmentary survival of their writing, makes any comprehensive assessment unrealistic. Heraclitus (c500 BC) says “those who are lovers of wisdom must be inquirers into many things”. Democritus (c460-370 BC) is a prominent figure in the history of science, because he and his teacher Leucippus (c480-420 BC) believed that the manifold appearance of everyday objects was caused by the arrangement of their invisible particles—atoms—and the void which surrounded them. It was their response to a problem posed by Parmenides (c510-c450 BC) as to how change could occur. With atoms, which are constant, their arrangements can vary and produce the variety seen in the world. For over two thosand years this idea could not be directly tested, but now its modern version is part of science.
Plato (427/8-347/8 BC) was, in the words of biologist-historian Ernst Mayr, "the great antihero of evolutionism."[2] He established the philosophy of essentialism which states, objects observed in the real world are reflections of a limited number of essences or ''eide''. Variation is merely the manifestation of imperfect reflections of constant essences. Plato called this the theory of forms. In his ''Timaeus'', Plato set out the idea that God had created the cosmos and everything in it as, being good and hence "free from jealousy, he desired that all things should be as like himself as they could be." God created all conceivable forms of life as "without them the universe will be incomplete, for it will not contain every kind of animal which it ought to contain, if it is to be perfect". This idea, that all potential life forms are essential in a perfect creation, is called the plenitude principle and greatly influenced Christian thought. Section Three: The Origins of Evolutionary Theory
Aristotle, (384—322 BC) a pupil of Plato, and tutor to Alexander the Great for about four years, was one of the most influential Greek philosophers, and the earliest natural historian whose work has survived in some detail. After Alexander's succession to the throne of Macedon, Aristotle left for Greek Asia Minor (now modern Turkey) and did his research on natural history on the isle of Lesbos. His writings on biology have survived in the form of four books, usually known by their Latin names: [3]
★ de anima (on the essence of life)
★ historia animalium (inquiries about animals)
★ de generatione animalium (reproduction)
★ de partibus animalium (anatomy)
These works contain some remarkable observations and interpretations by Aristotle, along with sundry myths and mistakes reflecting the uneven state of knowledge of his time. The most striking passages are about the sea-life visible from observation on Lesbos and available from the catches of fishermen. His observations on catfish, electric fish (Torpedo) and angler-fish are exceptional, as is his writing on cephalopod molluscs Octopus, Sepia (cuttlefish) and the paper nautilus (Argonauta argo). His description of the hectocotyl arm (see cephalopod) was about two thousand years ahead of its time, and widely disbelieved until the nineteenth century. He separated the aquatic mammals from fish, and knew that sharks and rays were part of the group he called Selachē (selachians). [4]
However, for Charles Singer, "Nothing is more remarkable than [Aristotle's] efforts to [exhibit] the relationships of living things as a ''scala naturae''" [4] Aristotle's ''History of Animals'' classified organisms in relation to a hierarchical "Ladder of Life" (''scala naturae''), placing them according to complexity of structure and function so that higher organisms showed greater vitality and ability to move. Aristotle, of course, is not responsible for the use made of this idea by clerics after the rediscovery of ancient learning (see rennaisance).
There are suggestions of an evolutionary approach in ancient Indian texts, especially the Vedas, where the incarnations of Vishnu reflects the theory of evolution,[6] as well as the writings of Patañjali.
Ideas on evolution were expressed by ancient Chinese thinkers. For example, according to Joseph Needham, Taoism explicitly denied the fixity of biological species.
In the first century BC, the Roman Epicurist and atomist Titus Lucretius Carus (d. 50 BC) wrote the poem ''De rarum natura'' (On the Nature of Things) describing the development of the living earth in stages from atoms colliding in the void as swirls of dust, then early plants and animals springing from the early earth's substance, to a succession of animals including a series of progressively less brutish humans. The essence of Lucretius' ideas was naturalism and the avoidance of supernatural interventions or explanations. Understandably, his memory was besmirched by early Christianity. The influence of Epicurus is clear from the way Lucretius refers to him: "I follow you, glory of the Greek race... You are... the discoverer of reality".
After a long period when classical learning was lost to the West, Christian authors combined Aristotle's classification system with Plato's ideas of the goodness of God and of all potential life forms being present in a perfect creation to organize inanimate, animate, and spiritual beings in a huge interconnected great chain of being. Thus all could be placed in order from the "lowest" to the "highest," with Hell at the bottom and God at the top above an angelic hierarchy marked by the orbits of the planets, with mankind in an intermediate position and worms the lowest of the animals. As the universe was ultimately perfect, the Great Chain was also perfect. That meant that there were no empty links in the chain, and no link was represented by more than one species. This implied that if every link is occupied, and none are occupied twice, no species can ever move from one position to another, since to do so would leave one level empty and put two species on another. Thus, in Plato's perfect universe, species couldn't ever change and must remain ''fixed'' in accordance with Genesis. For humans to forget their position and behave like lower animals or aspire to a higher station was sinful. Creatures on adjacent steps were expected to closely resemble each other, an idea expressed in the saying ''natura non facit saltum'' (nature does not make leaps) which Charles Darwin often quoted.[7] This basic concept greatly influenced the thinking of centuries of Western civilization, and still has an influence today. The great chain of being provided a classification system which was still the major organizing principle for biology in the 17th and 18th centuries, and was part of the argument from design presented by natural theology.
:''Main article: Early Islamic philosophy - Evolution''
Whereas evolutionary ideas more or less died out in Europe after the fall of the Roman Empire, they continued to be propounded by scientists and philosophers in the Islamic civilization during the Middle Ages, where early theories on evolution and natural selection were widely taught in medieval Islamic schools at the time. According to al-Khazini in the 12th century, ideas on evolution were widespread among "common people" in the Islamic world at the time.[8] The 19th century scientist, philosopher and historian John William Draper referred to the early Muslim theories on evolution as the "Mohammedan theory of evolution". The term "Mohammedan" was used to refer to Muslims at the time. He compared the early Muslim theories to the modern Darwinian theory of evolution of his time, arguing that the former was developed "much farther than we are disposed to do, extending them even to inorganic or mineral things." The first Muslim biologist and philosopher to develop a theory of evolution was al-Jahiz in the 9th century. He considered the effects of the environment on the likelihood of an animal to survive, and first described the struggle for existence and an early theory on natural selection.[9][10]
Ibn Miskawayh's ''al-Fawz al-Asghar'' and the Brethren of Purity's ''Encyclopedia of the Brethren of Purity'' (''The Epistles of Ikhwan al-Safa'') expressed evolutionary ideas on how species evolved from matter, into vapor, and then water, then minerals, then plants, then animals, then apes, and then humans.[11]Eloise Hart, ''Pages of Medieval Mideastern History''. (cf. Isma'ili, Yezidi, Sufi, The Brethren Of Purity, Ismaili Heritage Society) English translations of the ''Encyclopedia of the Brethren of Purity'' were available from 1812.[12] Arabic manuscripts of the ''al-Fawz al-Asghar'' and ''The Epistles of Ikhwan al-Safa'' were also available at the University of Cambridge. It has been suggested that these manuscripts may have influenced those interested in the transmutation of species at that time, possibly including Charles Darwin.[13]
The polymath Ibn al-Haytham wrote a book in which he argued for evolutionism (although not natural selection), and numerous other Islamic scholars and scientists, such as Ibn Miskawayh, the Brethren of Purity, and the polymaths Abū Rayhān al-Bīrūnī, Nasir al-Din Tusi, and Ibn Khaldun, discussed and developed these ideas. Translated into Latin, these works began to appear in the West after the Renaissance and appear to have had an impact on Western science.
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. In 1677 Sir Matthew Hale used the term ''evolution'' in attacking the atheistic atomism of Democritus and Epicurus. Hale set out the atomist idea that vibrations and collisions of atoms in the void without divine intervention had formed "Primordial Seeds" (semina) which were the "immediate, primitive, productive Principles of Men, Animals, Birds and Fishes." and called this mechanism an "absurdity" because "it must have potentially at least the whole Systeme of Humane Nature, or at least that Ideal Principle or Configuration thereof, in the evolution whereof the complement and formation of the Humane Nature must consist. . . and all this drawn from a fortuitous coalition of senseless and dead Atoms." Thus, among some ''evolutionist'' theories explored from 1700 to 1850, the earth, life, and universe developed without divine intervention. But most contemporary theories of evolution, including those developed by the German idealist philosophers Schelling and Hegel, held that evolution was a fundamentally spiritual process, with the entire course of natural and human evolution being "a self-disclosing revelation of the Absolute" (Schelling, ''System of Transcendental Idealism'', 1800).
Typically of these theorists, Gottfried Leibniz in 1714 postulated "monads" inside objects causing motion by internal forces, and maintained that "the 'germs' of all things have always existed . . . [and] contain within themselves an internal principle of development which drives them on through a vast series of metamorphoses" to become the geological formations, lifeforms, psychologies, and civilizations of the present. Leibniz clearly held that evolution proceeded on divine principles. In his ''De rerum originatione radicali'', 1697, he wrote that "A cumulative increase of the beauty and universal perfection of the works of God, a perpetual and unrestricted progress of the universe as a whole must be recognized, such that it advances to a higher state of cultivation."
Yet in his "Venus Physique" of 1745, Pierre Louis Maupertuis veered toward more materialistic ground, writing of "Chance" producing "an innumerable multitude of individuals" a small number of which had "fitness" to satisfy their needs, while "another infinitely greater number... perished... The species we see today are but the smallest part of what blind destiny has produced...", anticipating in general terms the idea of natural selection.
Vague and general ideas of evolution continued to proliferate among the mid-eighteenth century philosophers of the Enlightenment. G. L. L. Buffon suggested that what most people referred to as species were just well marked varieties. He thought that members of the same Linnean genus (in terms of modern scientific classification the family) had all been derived through changes driven by the environment from a common ancestor, which had arisen through spontaneous generation. Buffon's concept of evolution was strictly limited. He believed there were "internal moulds" that shaped the spontaneous generation of each family and that the families themselves were eternally distinct. Thus lions, tigers, leopards, pumas, and house cats could all share a common ancestor, but dogs and house cats could not. [14][15] Darwin himself, in his foreword to the 6th edition of the ''Origin of Species'', credited Aristotle with foreshadowing the concept of natural selection, and stated that "the first author who in modern times has treated it in a scientific spirit was Buffon".
Immanuel Kant, in his ''Universal Natural History and Theory of Heaven'' (1755), foreshadowed a theory of the development of unformed matter into the highest types of animals and plants, and suggested that the gradations of structure revealed by comparative anatomy pointed to the existence of blood relationship of all organisms, due to derivation from a common ancestor. He appeared to believe, however, that the successive variations and modifications had arisen in response to mechanical laws of the organisms themselves rather than to the influence of their surroundings. J. G. von Herder suggested that increase by multiplication with the consequent struggle for existence had played a large part in the organic world, but his theme remained vague and undeveloped.
Charles Bonnet applied "Evolutionism" to biology in 1762, asserting that each feature of the embryo was preformed in the parts; some of which came from the egg and some from the sperm. The preformed parts expanded and rearranged themselves to grow into the adult, and so Bonnet was called a "preformationist."
Between 1767 and 1792 James Burnett, Lord Monboddo included in his writings the concepts that man was derived from primates, and that creatures had found methods of transforming their characteristics over long time intervals in response to their environment. He also produced research on the evolution of linguistics. Jan-Andrew Henderson states (Henderson, 2000) that Monboddo was the first to articulate the theory of natural selection.
Between 1794 and 1796 Erasmus Darwin wrote ''Zoönomia'' suggesting "that all warm-blooded animals have arisen from one living filament ... with the power of acquiring new parts" in response to stimuli, with each round of "improvements" being inherited by successive generations. In his "Temple of Nature" of 1802 he described recurring new earths appearing in a cycle of catastrophes, then life springing forth spontaneously to populate the new earth, with animals competing with each other, driven by sex, hunger, "the strongest and most active ... [surviving to] propagate the species, which should thence become improved." Erasmus Darwin cited the work of James Burnett, Lord Monboddo in his ''Temple of Nature'' in 1802.
In 1796 Georges Cuvier published his findings on the differences between living and fossil elephants. His analysis demonstrated that mammoths and mastodons were extinct species different from any living animal, effectively ending what had been a long running debate about whether a species could become extinct.[16] William Smith began the process of ordering rock strata by examining fossils in the layers while he worked on his geologic map of England. Independently, Georges Cuvier and Alexandre Brongniart published an influential study of the geologic history of the region around Paris in 1811 based on the stratigraphic succession of its layers, which helped establish the antiquity of the earth.[17] Cuvier advocated catastrophism to explain the patterns of extinction and faunal succession revealed by the fossil record. Knowledge of the fossil record continued to advance rapidly in the first few decades of the 19th century. By the 1840s the outlines of the geologic timescale were becoming clear, and in 1841 John Phillips named three major eras based on the predominant fauna, the Paleozoic dominated by marine invertebrates and fish, Mesozoic the age of reptiles, and Cenozoic the age of mammals. Even conservative English geologists like Adam Sedgwick and William Buckland accepted this progressive picture of the history of life, which, like Cuvier, they attributed to repeated catastrophic episodes of extinction followed by new episodes of creation.[18] Unlike Cuvier, Buckland and some other English geologists who advocated natural theology made efforts to explicitly link the last catastrophic episode to the biblical flood.[19]
From 1830-1833 Charles Lyell published his multi-volume ''Principles of Geology'' which advocated a uniformitarian theory of geology as an alternative to catastrophism. Lyell claimed that rather than being the products of cataclysmic (and possibly supernatural) events the geologic features of the earth could better be explained as the result of the same geologic forces that could be observed in the present day acting gradually over immensely long periods of time. Although Lyell opposed evolutionary ideas (even questioning the consensus that the fossil record showed true progression), his concept of forces working gradually over an extended period to shape the earth and the immense age of the earth assumed by his theories would influence future evolutionary thinkers, especially Charles Darwin.[20]
Jean-Baptiste Lamarck proposed in his ''Philosophie Zoologique'' of 1809 a theory of the transmutation of species. Lamarck did not believe that all living things shared a common ancestor. Rather he believed that simple forms of life were created by spontaneous generation all of the time. He also believed that an innate life force, which he sometimes characterized as a nervous fluid, drove species to become more complex over time and advance up a linear ladder of complexity that was related to the great chain of being. Lamarck also recognized that species were adapted to their environment. He explained such adaptation by saying that the same nervous fluid that drove increasing complexity from one generation to the next, also caused the organs of an animal (or a plant) to change based on the use or disuse of that organ, just as muscles are affected by exercise, and that such changes would be inherited by the next generation. It was this secondary mechanism of adaptation through the inheritance of acquired characteristics that became closely associated with his name and would influence discussions of evolution into the 20th century.[21][22]
A radical British school of comparative anatomy which included the surgeon Robert Knox and the anatomist Robert Grant was closely in touch with Lamarck's school of French ''Transformationism'', which included Étienne Geoffroy Saint-Hilaire. Grant developed Lamack's and Erasmus Darwin's ideas of transmutation and evolutionism, investigating homology to prove common descent. As a young student Charles Darwin joined Grant in investigations of the life cycle of marine animals. He also studied geology under professor Robert Jameson who wrote an anonymous paper in 1826 praising "Mr. Lamarck" for explaining how the higher animals had "evolved" from the "simplest worms" – this was the first use of the word "evolved" in a modern sense. Jameson's course closed with lectures on the ''"Origin of the Species of Animals"''.
The computing pioneer Charles Babbage published his unofficial ''Ninth Bridgewater Treatise'' in 1837, putting forward the thesis that God had the omnipotence and foresight to create as a divine legislator, making laws (or programs) which then produced species at the appropriate times, rather than continually interfering with ''ad hoc'' miracles each time a new species was required. In 1844 the Scotish publisher Robert Chambers anonymously published an influential, and extremely controversial book of popular science entitled ''Vestiges of the Natural History of Creation''. This book proposed an evolutionary scenario for the origins of the soloar system and life on earth. It claimed that the fossil record showed a progressive ascent of animals with current animals being branches off a main line that lead progressively to humanity. It implied that the transmutations lead to the unfolding of a preordained plan that had been woven into the laws that goverened the universe. In this sense it was less completely materialistic than the ideas of radicals like Robert Grant, but its implication that humans were just the last step in the ascent of animal life inscensed many conservative thinkers. Both conservatives like Adam Sedgwick, and radical materialists like Thomas Henry Huxley, who disliked its implications of preordained progress, were able to find scientific inaccuracies in the book that they could disparage, but the high profile public debate over ''Vestiges'' with its depiction of evolution as a progressive process would greatly influence the perception of Darwin's theory a decade later. [23][24]
Ideas about the transmutation of species were strongly associated with the radical materialism of the enlightenment and were greeted with hostility by more conservative thinkers. Cuvier attacked the ideas of Lamarck and Geoffroy Saint-Hilaire. He agreed with Aristotle that species were immutable. Cuvier believed that the individual parts of an animal were too closely correlated with one another to allow for one part of the anatomy to ever be changed in isolation from all the others, and he believed that the fossil record showed patterns of catastrophic extinctions followed by re-population rather than gradual change over time. He also argued that drawings of animals and animal mummies from Egypt that were thousands of years old, showed no signs of change when compared with modern animals. The strength of Cuvier's arguments and reputation helped keep transmutational ideas out of the scientific mainstream for decades.[25]
In Britain, where the philosophy of natural theology remained influential, William Paley wrote the book ''Natural Theology'' with its famous watchmaker analogy at least in part as a response to the transmutational ideas of Erasmus Darwin.[26] Geologists influenced by natural theology such as Buckland and Sedgwick made a regular practice of attacking the evolutionary ideas of Lamarck and Grant, and Sedgwick wrote a famously harsh review of ''The Vestiges of the Natural History of Creation''. [27][28] Alghough the geologist Charles Lyell opposed scriptural geology he also believed in the immutability of species, and in his ''Principles of Geology'' (1830-1833), criticized and dismissed Lamarck's theories of development. Instead, he advocated a form of progressive creation, in which each species had its "centre of creation" and was designed for the habitat, but would go extinct when the habitat changed.
Another source of opposition to transmutation was a school of naturalists influenced by German philosophers and naturalists such as Goethe, Hegel and Lorenz Oken associated with idealism. Idealists such as Louis Agassiz and Richard Owen believed that each species was fixed and unchangeable because it represented an idea in the mind of the creator. They believed that there were relationships between species that could be discerned from developmental patterns in embryology and in the fossil record, but that these represented an underlying pattern of divine thought in which progressive creation lead to increasing complexity culminating in humanity. Owen developed the idea of "archetypes" in the Divine mind producing a sequence of species related by anatomical homologies such as vertebrate limbs. Owen was concerned by the political implications of the radical ideas of transmutationists like Robert Grant, and he led a public campaign by conservatives that successfully marginalized Grant in the scientific community. In his famous 1841 paper that coined the term dinosaur for the giant reptiles discovered by Buckland and Gideon Mantell, Owen argued that these reptiles contradicted the transmutational ideas of Lamarck because they were more sophisticated than the reptiles of the modern world. Darwin would make good use of the homologies analyzed by Owen in his own theory, but the harsh treatment of Grant, along with the controversy surrounding ''Vestiges'' would be major factors in his decision to delay publishing his ideas for so long.[29][30]
In 1813, William Charles Wells produced essays assuming that there had been evolution of humans, and recognised the principle of natural selection. Charles Darwin and Alfred Russel Wallace were unaware of this work when they jointly published the theory in 1858, but Darwin later acknowledged that Wells had recognised the principle before them.
Augustin de Candolle's ''natural system'' of classification laid emphasis on the "war" between competing species.
Patrick Matthew wrote in ''Naval Timber & Arboriculture'' published in 1831 of "continual balancing of life to circumstance. ... [The] progeny of the same parents, under great differences of circumstance, might, in several generations, even become distinct species, incapable of co-reproduction." Charles Darwin found out about it after publication of the ''Origin'', and wrote that it "briefly but completely anticipates the theory of Nat. Selection ... a complete but not developed anticipation!"
Although the pre-Darwinian writers amongst them invoked nearly every principle that Darwin or his successors have suggested, they failed to carry conviction with regard to evolution, and they neither propounded a coherent philosophy of variation nor suggested a mechanism by which variations that appeared might give rise to new species. The anticipations of Darwin were little more than formal and verbal. As T. H. Huxley pointed out in his essay on the reception of the ''Origin of Species'' in the second volume of ''Darwins Life and Letters'':
Main articles: Inception of Darwin's theory, Development of Darwin's theory, Publication of Darwin's theory
The biogeographical patterns Charles Darwin observed in the Galapagos islands and elsehwere during the voyage of the Beagle caused him to doubt the fixity of species, and in 1837 he started the first of a series of secret notebooks on transmutation. Darwin's biogeographical observations lead him to view transmutation as a process of divergence and branching rather than the ladder like progression envisioned by Lamarck and others. In 1838 he read the new 6th edition of Malthus' ''Essay on the Principle of Population'' and compared this with breeders selecting traits. This led to the inception of Darwin's theory of natural selection. Concerned by the intensity of the controversy raging over other transmutational ideas, Darwin would develop this idea for the next 20 years, sharing it only with a handful of friendly naturalists in private correspondence.[31][32]
Unlike Darwin, Alfred Russel Wallace, heavily influenced by the ''Vestiges of the Natural History of Creation'', was already a believer in the transmutation of species before he began his career as a traveling naturalist. By 1855 his biogeographical observations had made him confident enough in a branching pattern of evolution to claim in an important paper that every species originated in close proximity to an already existing closely allied species. Once again it was consideration of how the ideas of Malthus might apply to animal populations that would lead Wallace to conclusions very similar to the ones reached by Darwin. Wallace, unaware of Darwin's unpublished ideas, wrote up his thoughts into an essay and mailed them to Darwin asking for his opinion. The result was the publication of Darwin's theory of natural selection jointly with Wallace in 1858. Darwin also began work in earnest on the book length treatment of the subject that he would publish in 1859.[33]
.
While transmutation of species was accepted by a sizable number of scientists before 1859, it was the publication of Charles Darwin's ''The Origin of Species'' which fundamentally transformed the debate over biological origins. Darwin argued that his branching version of evolution could explain a wealth of facts in biogeography, anatomy, embryology, and other fields of biology and geology. He also provided the first cogent mechanism by which evolutionary change could persist: his theory of natural selection.[34]
One of the earliest and most important naturalists to be converted by ''Origin'' was the British anatomist Thomas Henry Huxley. Huxley recognized that unlike the earlier transmutational ideas of Lamarck and ''Vestiges'', Darwin's theory provided a mechanism for evolution without supernatural involvement. Huxley would make advocacy of evolution a cornerstone of his program to reform and professionalize science by displacing natural theology with methodological naturalism, and ending the domination of the natural sciences in Britain by the clerical establishment. Thanks in significant part to the efforts of Huxley and his fellow members of the X-club, by the early 1870s evolution had replaced special creation as the mainstream scientific explanation for the origin of species throughout the English speaking world. In his campaign for public and scientific acceptance of Darwin's theory Huxley would make extensive use of evidence from two areas of paleontology where significant finds were made in the 1860s and 1870s. One of the areas was as series of fossil finds that suggested that birds had evolved from reptiles, including the discovery of Archaeopteryx in Europe, and a number of fossils of toothed birds found in North America. The other involved fossils that helped trace the evolution of the horse from much smaller five towed ancestors.[35] Acceptance of evolution among scientists in non-English speaking nations such as France, and the countries of southern Europe and Latin America was slower. An exception to this was Germany where both Ernst Haeckel, who used evolution to challenge the established tradition of metaphysical idealism in German biology much as Huxley used it to challenge natural theology in Britain, and August Weismann would champion the idea.[36]
Darwin's theory, though it succeeded in profoundly shaking scientific opinion regarding the development of life (and indeed resulted in a small social revolution), could not explain several critical components of the evolutionary process. Namely, he was unable to explain the source of variation in traits within a species, and he could not provide a mechanism whereby traits were passed faithfully from one generation to the next. Darwin's theory of pangenesis, while relying in part on the inheritance of acquired characteristics, proved to be useful for statistical models of evolution developed by his cousin Francis Galton and the "biometric" school of evolutionary thought. It was, however, found to be of little use to biologists.
Charles Darwin was very aware of the severe reaction from some parts of the scientific community against the suggestion made in ''Vestiges of the Natural History of Creation'' that humans were just the culmination of the process of transmutation in animal species, and he almost completely ignored the topic of human evolution in ''The Origin of Species''. Despite this precaution, the issue featured prominently in the debate that followed its publication. For most of the first half of the 19th century most of the scientific community believed that while geology had shown that the earth, and life, was very old, human beings had appeared suddenly just a few thousand years ago. However, a series of archaeological finds in the 1840s and 1850s showed stone tools associated with the remains of extinct animals. By the early 1860s, as summarized in Charles Lyell's 1863 book ''Geological Evidences of the Antiquity of Man'', it had become widely accepted that humans had existed during a prehistoric period that lasted many thousands of years before the start of written history. This new view of human history was more compatible than the older one with an evolutionary origin for humanity. At the time, there was no fossil evidence of human evolution, since the only human fossils discovered prior to the very end of the 19th century were of anatomically modern humans, or of very similar Neanderthals.[37]
Therefore the debate that immediately followed the publication of ''The Origin of Species'' centered on the similarities and differences between humans and modern apes. Richard Owen vigorously defended the traditional classification suggested by Carolus Linnaeus and Cuvier that placed humans in a completely separate order from any of the other mammals including apes. On the other hand Huxley sought to demonstrate a close anatomical relationship between humans and apes. In one very famous incident, Huxley showed that Owen was mistaken in claiming that the brains of gorillas lacked a structure present in human brains. Huxley summarized his argument in his highly influential 1863 book ''Evidence as to Man's place in Nature''. Some scientists, including Charles Lyell and Alfred Russel Wallace, who had become involved with spiritualism, agreed that humans were biologically related to apes, but questioned whether any purely materialistic mechanism could account for some of the differences between humans and apes, especially some aspects of the human mind.
In 1871 Darwin published ''The Descent of Man, and Selection in Relation to Sex'', which contained his views on human evolution. Darwin believed that the differences between the human mind and the minds of the higher animals were a matter of degree rather than of kind. For example he viewed morality as a natural outgrowth of instincts that would be beneficial to animals living in social groups. He believed that all the differences between humans and apes could be explained by a combination of natural selective pressures resulting from our ancestors forsaking life in the trees for life on the plains, and sexual selection. The debate over human origins, and over the degree of human uniqueness would continue well into the 20th century.
Evolution was widely accepted in scientific circles within a few years after the publication of ''Origin'', but the acceptance of natural selection as its driving mechanism was much less widespread. There were a variety of reasons for this. Natural selection, with its emphasis on death and competition, didn't appeal to many naturalists because they felt it was immoral and because it seemed to leave little room for teleology (purpose), or even the concept of true progress in the development of life. Some felt that it would be too slow a mechanism given the estimates of the age of the earth and sun (10-100 million years) being made by physicists such as Lord Kelvin at the time, and some felt that it could not work because all the models for inheritance at the time involved blending of inherited characteristics. The four major alternatives to natural selection in the late 19th century, were theistic evolution, neo-Lamarckism, orthogenesis, and saltationism.[38][39]
Theistic evolution was the idea that God somehow intervened in the process of evolution to guide it in such a way that the living world could still be considered to be designed. Some of its advocates included Asa Gray, George Jackson Mivart, and the Duke of Argyle. However, it fell out of favor fairly rapidly among scientists as they became more and more committed to the idea of methodological naturalism and came to believe that direct appeals to divine involvement were scientifically unproductive. By 1900 it had completely disappeared from mainstream scientific discussions, although it continued to be used as a way to reconcile religious belief with scientific discoveries among some non-scientists.
The term Lamarckism was used for the idea that characteristics acquired during the course of an organism's life (such changes caused by the use or disuse of a particular organ) could be inherited by the next generation. Although Wallace completely rejected the concept in favor of natural selection, Darwin had included it in ''The Origin of Species'' as a possible supplemental mechanism of evolution. In the late 19th century the term neo-Lamarckism came to be associated with the position of naturalists who viewed it rather than natural selection as the most important evolutionary mechanism. Its advocates included the British biologist and Darwin critic Samuel Butler, the German biologist Ernst Haeckel, and the American paleontologist Edward Drinker Cope. They considered Lamarckism to be philosophically superior to a process based on selective pressure acting on random variations. Butler and Cope both believed that it allowed organisms to effectively drive their own evolution to a certain degree as organisms that developed new behaviors (possibly in response to changes in their environment) would change the use/disuse patterns for their organs and thus kick start the evolutionary process. Cope and Haeckel both believed that evolution was a progressive process. Cope looked for, and thought he found, patterns of linear progression in the fossil record. The idea of linear progress was also an important part of Haeckel's recapitulation theory of evolution, which held that the embryological development of an organism repeats its evolutionary history.
Critics of neo-Lamarckism pointed out that no one had ever produced solid evidence for the inheritance of acquired characteristics. The experimental work of the German biologist August Weismann, which resulted in the germ plasm theory of inheritance, led him to declare that it was flatly impossible. The Weismann barrier would prevent any changes that occurred to the body after birth from being inherited by the next generation. Despite these criticisms, neo-Lamarckism remained the most popular alternative to natural selection at the end of the 19th century, and would remain the position of some naturalists well into the 20th century.
Orthogenesis or orthogenetic evolution was the hypothesis that life has an innate tendency to change, in a unilinear fashion, towards ever greater perfection. It had a significant following in the 19th century, and its proponents included the Russian biologist Leo Berg, and the American paleontologist Henry Fairfield Osborn. Orthogenesis was particularly popular among some paleontologists who believed that fossils indicated a gradual and constant unidirectional change. Those who accepted orthogenesis in this way, however, did not necessarily accept that the mechanism that drove orthogenesis was teleological (goal-directed). The orthogenesis hypothesis began to collapse when it became clear that it could not explain the patterns found by paleontologists in the fossil record, which was non-linear with many complications. A few hung on to the orthogenesis hypothesis as late as the 1950s by claiming that the processes of macroevolution, the long term trends in evolution, were distinct from the processes of microevolution.
Saltationism is the idea that new species arise as a result of large mutations. It was seen as a much faster alternative to the Darwinian concept of a gradual process of small random variations being acted on by natural selection. It was very popular with early geneticists such as Hugo DeVries, William Bateson, and early in his career, T. H. Morgan. They based the mutation theory of evolution on it.
After the rediscovery of Gregor Mendel's laws of inheritance in 1900 there was a fierce debate between two camps. In one camp were the Mendelians, who were focused on discrete variations and the laws of inheritance. They were led by William Bateson (who coined the word genetics) and Hugo de Vries (who coined the word mutation). Their opponents were the biometricians, who were interested in the continuous variation of characteristics within populations. Their leaders Karl Pearson and Walter Frank Raphael Weldon, followed in the tradition of Francis Galton who had focused on measurement and statistical analysis of variation within a population. The biometricians rejected Mendelian genetics because they felt that discrete units of heredity such as genes could not explain the continuous range of variation in various characteristics that they measured in wild populations. Weldon's work with crabs and snails provided evidence that selection pressure from environmental factors could shift the range of variation in real world populations, but the Mendelians maintained that the variations measured by the biometricians were too insignificant to account for the evolution of new species.[40][41]
When T. H. Morgan began experimenting with breeding the fruit fly Drosophila melanogaster he was a saltationist who hoped to demonstrate that a new species could be created in the lab by a large mutation. Instead the work at his lab between 1910 and 1915 reconfirmed Mendelian genetics and provided solid experimental evidence linking it to chromosomal inheritance. It also demonstrated that most mutations had relatively small affects (such as a change in eye color), and that rather than creating a new species in a single step, they served to increase the genetic variation within the existing population.
Main articles: Modern evolutionary synthesis
Eventually, the two models were reconciled and merged, primarily through the work of the British biologist and statistician R.A. Fisher. In a series of papers starting in 1918 and culminating in his 1930 book ''Genetical Theory of Natural Selection'' Fisher showed that the continuous variation measured by the biometricians could be produced by the combined action of many discrete genes, and that it was theoretically possible for natural selection to cause change in gene frequencies in a population and thus drive evolution. In a series of papers starting in 1924 another British geneticist, J.B.S. Haldane, applied statistical analysis to real world examples of natural selection such as the evolution of industrial melanism in peppered moths, and showed that natural selection could work in the real world at a faster rate than even Fisher had assumed was possible. The American biologist Sewall Wright, who had a background in animal breeding experiments, focused on combinations of genes that interacted as complexes, and the effects of inbreeding on small relatively isolated populations, which could exhibit genetic drift. In 1932 Wright produced the concept of an adaptive landscape that held that genetic drift and inbreeding could drive small isolated sub populations away from adaptive peaks, which would then allow natural selection to drive them towards different adaptive peaks. The work of Fisher, Haldane, and Wright founded the discipline of population genetics, which integrated natural selection with Mendelian genetics.[42][43]
In the first couple of decades of the 20th century most field naturalists continued to believe that Lamarckian and orthogenic mechanisms of evolution provided the best explanation for the complexities they observed in the living world. However, as the field of genetics continued to develop, that viewpoint became less and less tenable. Theodosius Dobzhansky, who had been a postdoctoral worker in T. H. Morgan's lab, would help to bridge the divide between the population geneticists and the field biologists with his 1937 book ''Genetics and the origin of species''. Dobzhansky examined the genetic diversity of wild populations, and showed that contrary to the assumptions of the population geneticists, wild populations had large amounts of genetic diversity with marked differences between sub populations. The book also took the highly mathematical work of the population geneticists and put it into a form that was more accessible to field biologists. Ernst Mayr would follow up on Dobzhansky's work with the 1942 book ''Systematics and the Origin of Species'', which emphasized the importance of allopatric speciation in which geographical isolation of a sub population was followed by the development of mechanisms for reproductive isolation in the formation of new species. In the 1944 book ''Mode and Tempo in Evolution'' George Gaylord Simpson would show that the fossil record was consistent with the irregular non directional pattern predicted by the developing evolutionary synthesis, and that the linear trends that earlier paleontologists had claimed supported orthogenesis and neo-Lamarckism did not hold up upon closer examination. In 1950 G. Ledyard Stebbins would publish ''Variation and Evolution in Plants'', which helped integrate botany into the synthesis. The emerging cross-discipline consensus on how evolution worked received is name from the book ''Evolution: the modern synthesis'' by Julian Huxley.
Main articles: History of molecular evolution
In the 1940s, following up on Griffith's experiment, Avery, MacLeod and McCarty definitively identified deoxyribonucleic acid (DNA) as the "transforming principle" responsible for transmitting genetic information. In 1953, Francis Crick and James D. Watson published their famous paper on the structure of DNA, based on the research of Rosalind Franklin and Maurice Wilkins. These developments ignited the era of molecular biology and transformed the understanding of evolution into a molecular process: the mutation of segments of DNA.
During this era of molecular biology, it also became clear that a major mechanism for variation within a population is mutations of DNA.
In the mid-1970s, Motoo Kimura formulated the neutral theory of molecular evolution, firmly establishing the importance of genetic drift as a major mechanism of evolution. The theory sparked the "neutralist-selectionist" debate, partially solved by the development of Tomoko Ohta's nearly neutral theory of evolution.
In the mid-1960s, George C. Williams strongly critiqued verbal explanations of adaptations couched in terms of "survival of the species" (essentially group selection arguments). Such explanations were largely replaced by a gene-centered view of evolution, epitomised by the kin selection arguments of W. D. Hamilton, George Price and John Maynard Smith. Models of the period showed that group selection was severely limited in its strength, although these models have since been shown to be too limited and newer models do admit the possibility of significant multi-level selection.
One of the most prominent debates arising during this time period was over the theory of punctuated equilibrium, a theory propounded by Niles Eldredge and Stephen Jay Gould to describe and account for the pattern of fossil species persisting phenotypically unchanged for long periods (what they termed ''stasis''), with relatively brief periods of phenotypic change during speciation.
W. D. Hamilton's work also contributed to the emergence of the discipline of sociobiology. Altruism has been a difficult problem for evolutionary theorists going all the way back to Darwin. Significant progress was made in 1964 when Hamilton formulated the inequality known as Hamilton's rule which showed how eusociality (sterile worker classes) in insects and many other examples of altruistic behavior could have evolved through kin selection. Other theories, some derived from game theory, such as reciprocal altruism followed. In 1975 E.O. Wilson published the influential and highly controversial book '' which claimed evolutionary theory could help explain many aspects of animal, including human, behavior. Critics of sociobiology, including Stephen Jay Gould, and Richard Lewontin, claimed that sociobiology greatly overstated the degree to which complex human behaviors could be determined by genetic factors. They also claimed that the theories of sociobiologists often reflected their own ideological biases. Despite these criticisms significant work in sociobiology and the related discipline of evolutionary psychology, including work on other aspects of the altruism problem, has continued.[44][45]
Microbiology has recently developed into an evolutionary discipline. It was originally ignored due to the paucity of morphological traits and the lack of a species concept in microbiology. Now, evolutionary researchers are taking advantage our extensive understanding of microbial physiology, the ease of microbial genomics, and the quick generation time of some microbes to answer evolutionary questions. Similar features have led to progress in viral evolution, particularly for bacteriophage.
Improvements in sequencing methods have resulted in a large increase of sequenced genomes, allowing for the testing and refining of the theory of evolution with respect to whole genome data. Advances in computational hardware and software have allowed for the testing and extrapolation of increasingly advanced evolutionary models. Discoveries in biotechnology have produced methods for the ''de novo'' synthesis of proteins and, potentially, entire genomes, driving evolutionary studies at the molecular level. Evolutionary biology is increasingly centered on biological information: Daniel Dennett (1995) argues in ''Darwin's Dangerous Idea'' that natural selection is an algorithmic process applicable to many circumstances besides biological evolution. This conception of evolutionary has been dubbed "universal Darwinism".
Main articles: Symbiogenesis
Another extension to the standard modern synthesis, advocated by Lynn Margulis, is symbiogenesis. Symbiogenesis argues that acquisition and accumulation of random mutations or genetic drift are not sufficient to explain how new inherited variations occur in evolution. This theory states that species arise from the merger of independent organisms through symbiosis. Symbiogenesis emphasizes the impact of co-operation rather than Darwinian competition. This commonly occurs in multigenomic organisms throughout nature.
Main articles: Evolutionary developmental biology
Molecular data regarding the mechanisms underlying development started to accrue quickly during the 1980's and '90's. As scientists began to compare the developmental mechanisms in different organisms, they realized that these mechanisms are conserved through deep evolutionary time. By combining the disciplines of phylogenetics, paleontology and comparative developmental biology, scientists try to infer the way in which early organisms developed, thus spawning the new discipline of "evo-devo."
Small RNA or micro RNA (miRNA) appears highly significant in regulation of gene expression during development. [46][47][48] Micro RNA's contribution to evolution is considered an epigenetic mechanism in evolutionary developmental biology. Micro RNA appears to constitute 1% of the human genome. Scientists are designing silencing interference micro RNA in the hopes of shutting down genes involved in cancer, diseases, and the contribution of genes in developmental biology.
In the 1980s and 1990s there was a renewal of structuralist themes in evolutionary biology by biologists such as Brian Goodwin, that incorporates ideas from cybernetics and systems theory, and that emphasizes the role of self-organized processes as being at least as important as the role of natural selection.
It is hypothesized, for example, that the rapid emergence of basic metazoan body plans in the Cambrian Explosion was due in part to changes in the environment acting on inherent properties of cell aggregates, such as differential cell adhesion. Such material-based plasticity led to the spontaneous emergence of metazoan body forms. The resulting forms were later “locked in” by means of stabilizing natural selection. Developmental biologists Stuart Newman and Gerd B. Müller have presented recent work relating to this view in the edited volume, Origination of Organismal Form.
Some variants of this view consider neo-Darwinian forms of natural selection to characterize evolution only in its advanced stages (i.e., after stabilization of the genotype-phenotype relationship has occurred), though most neo-structuralist biologists would not go this far.
Main articles: Horizontal gene transfer
The transfer of genetic material between bacteria was first observed in the 1950s and it has played a major role in the propagation of anti-biotic resistance among different strains of bacteria. More recently, as knowledge of genomes has continued to expand, it has been suggested that lateral transfer of genetic material has played an important role in the evolution of bacteria and archae. Some have proposed that it has also played a role in the evolutionm of eukaryotes including fungi, plants, and animals as well, and that it may have significantly affected both the pattern and pace of evolution.[49].[50][51]
Pierre Teilhard de Chardin formulated theories describing the gradual development of the Universe from subatomic particles to human society, considered by Teilhard as the last stage. (see Gaia theory). These are not generally recognized as scientifically rigorous.
Nine levels of development are described in their scheme. Stages one through five are grouped into the Lithosphere, also called Geosphere or Physiosphere, where the evolution of the structure of organisms is ruled by mechanical laws and coincidence. Levels six, seven, and eight are the classical biological stages. Stages six through eight are collectively called the Biosphere, where the progress of the structure of the organisms is ruled by genetic mechanisms. The last stage, stage 9, is called the Noosphere, where the structure of human society is ruled by psychological, informational and communicative processes.
1. Mayr, ''The Growth of Biological Thought'', pp. 301-304
2. Mayr, ''The Growth of Biological Thought'', p. 304
3. Singer, Charles ''A short history of biology.'' Oxford 1931.
4. Singer, Charles. ''A short history of biology''. Oxford 1931.
5. Singer, Charles. ''A short history of biology''. Oxford 1931.
6. Hinduism and evolution
7. Aristotle and the Great Chain
8. John William Draper (1878). ''History of the Conflict Between Religion and Science'', p. 154-155, 237. ISBN 1603030964.
9. Conway Zirkle (1941). Natural Selection before the "Origin of Species", ''Proceedings of the American Philosophical Society'' '84' (1), p. 71-123.
10. Mehmet Bayrakdar (Third Quarter, 1983). "Al-Jahiz And the Rise of Biological Evolutionism", ''The Islamic Quarterly''. London. [1]
11. Muhammad Hamidullah and Afzal Iqbal (1993), ''The Emergence of Islam: Lectures on the Development of Islamic World-view, Intellectual Tradition and Polity'', p. 143-144. Islamic Research Institute, Islamabad.
12. "Ikhwan as-Safa and their Rasa'il: A Critical Review of a Century and a Half of Research", by A. L. Tibawi, as published in volume 2 of ''The Islamic Quarterly'' in 1955; pgs. 28-46
13. Muhammad Hamidullah and Afzal Iqbal (1993), ''The Emergence of Islam: Lectures on the Development of Islamic World-view, Intellectual Tradition and Polity'', p. 144.
This claim is not supported by Darwin's biographers.
14. Bowler ''Evolution: The History of an Idea'' pp. 75-80
15. Larson Evolution: The Remarkable History of a Scientific Theory pp. 14-15
16. Larson ''Evolution: The Remarkable History of a Scientific Theory'' p. 7
17. Bowler p. 113
18. Larson pp. 29-38
19. Bowler pp. 115-116
20. Bowler pp. 129-134
21. Bowler pp. 86-94
22. Larson pp. 38-41
23. Bowler pp. 134-138
24. Bowler and Morus ''Making Modern Science'' pp. 142-3
25. Larson pp. 5-24
26. Bowler pp. 103-104
27. Larson pp. 37-38
28. Bowler p. 138
29. Bowler pp. 120-129
30. Larson pp. 42-46
31. Bowler and Morus pp. 129-149
32. Larson pp. 55-71
33. Bowler pp. 173-176
34. Larson pp. 79-111
35. Larson pp. 139-40
36. Larson pp. 109-110
37. Bowler pp. 207-216
38. Larson pp. 105-129
39. Bowler pp. 196-253
40. Bowler pp. 256-273
41. Larson pp. 153-174
42. Bowler pp. 325-339
43. Larson pp. 221-243
44. Larson pp. 270-278
45. Bowler pp. 359-361
46. The phylogenetic distribution of metazoan microRNA: insights into evolutionary complexity and constraint.., Sempere LF, Cole CN, McPeek MA, Peterson KJ., , , J Exp Zoolog B Mol Dev Evol, 2006
47. The evolving role of microRNAs in animal gene expression.journal = Bioessays., Massirer KB, Pasquinelli AE., , , , 2006
48. Conservation and divergence of plant microRNA genes., Zhang B, Pan X, Cannon CH, Cobb GP, Anderson TA., , , Plant J., 2006
49. Lateral gene transfer and the nature of bacterial innovation
50. Horizontal Gene Transfer
51. Study: Horizontal gene transfer adds to complexity, speed of evolution
★ Evolution:The History of an Idea, , Peter J., Bowler, University of California Press, ,
★ Making Modern Science, , Peter J., Bowler, The University of Chicago Press, ,
★ Erasmus Darwin, ''The Temple of Nature, or The Origin of Society(1803)'', Martin Priestman, ed. Romantic Circles, August, 2006. (Referenced 11/17/06) http://www.rc.umd.edu/editions/darwin_temple/toc.html
★ Erasmus Darwin, ''Zoonomia, Vol I''. Project Gutenberg. (Referenced 11/17/06) http://www.gutenberg.org/etext/15707
★ The Structure of Evolutionary Theory, , Stephen Jay, Gould, Belknap Press of Harvard University Press, ,
★ Jan-Andrew Henderson (2000), ''The Emperor's Kilt: The Two Secret Histories of Scotland'', Mainstream Publishing
★ Evolution:The Remarkable History of Scientific Theory, , Edward J., Larson, Modern Library, ,
★ The Voyage of the Beagle
★ Galápagos Islands
★ Faith and rationality
★ List of paradigm shifts in science
★ Darwin's precursors and infulences by John Wilkins. Part of the Talk.Origins Archive.
'Evolutionary thought' has roots in antiquity as philosophical ideas known to the Greeks, Romans, Indians, Chinese and Muslims. Until the 18th century, however, Western biological thought was dominated by essentialism, the idea that living forms are static and unchanging in time. During the Enlightenment, evolutionary cosmology and the mechanical philosophy spread from the physical sciences to natural history, and naturalists such as Maupertuis and Georges-Louis Leclerc, Comte de Buffon focused on the variability of species. The emergence of paleontology (and with it the notion of extinction), as well as the dramatic expansion of known species, helped undermine the traditional static view of nature. The first full theory of evolution was proposed by Jean-Baptiste Lamarck in the early 19th century; Lamarck's theory was based on the idea that species had an innate drive that pushed them up the great chain of being and that the mechanism of inheritance of acquired characteristics helped them adapt to local conditions.
The modern theory referred to as Darwinism was first publicly put forth by Charles Darwin and Alfred Russel Wallace and discussed in great detail in ''On the Origin of Species'', published by Darwin in 1859. Darwinism, which unlike Lamarck's theory proposed common descent and a branching tree of life, was based on natural selection, and synthesized a wide range of evidence from animal husbandry, biogeography, geology, morphology, and embryology. The debate over ''Origin'' would play a key role in the displacement of natural theology by methodological naturalism in the life sciences, and would raise profound questions about human nature and the place of humanity in the natural world.
Darwin's work led to the rapid acceptance of evolution, but his proposed mechanism of natural selection was not widely accepted until the early 20th century. Most biologists preferred inheritance of acquired characteristics (neo-Lamarckism), an innate drive for change (orthogenesis) , or sudden large mutations (saltationism), as driving forces behind evolution. Darwin's theory offered a powerful explanation for a wealth of observed facts in biology. However, inheritance was not well understood at the time of his work. Although the person commonly considered the originator of modern genetic theory, Gregor Mendel, was a contemporary of Darwin, the theory of Mendelian genetics was not developed until the early 20th century. The Darwinian concept of natural selection was combined with Mendelian genetics during the founding of the discipline of population genetics in the 1920s and 1930s. In the 1930s and 1940s population genetics would be integrated with various branches of biology to produce the unified theory of evolution known as the modern evolutionary synthesis, which marked the reemergence of Darwinism as the central evolutionary theory.
Following the synthesis and the rise of evolutionary biology as a formal scientific discipline, evolutionary thought developed in several directons. Studies of mutation and of genetic diversity in natural populations, combined with biogeography and systematics, led to increasingly sophisticated mathematical and causal models of evolutionary change. Paleontology and comparative anatomy allowed increasingly detailed and far-reaching reconstructions of the history of life. Following the rise of molecular genetics and molecular biology, the field of molecular evolution arose, based on "informational macromolecules" such as DNA, RNA, and protein sequences. Gene-centered view of evolution rose to prominence in the 1960s, followed by the neutral theory of molecular evolution; these ideas sparked sustained debates over adaptationism, units of selection, and genetic drift.
In the late 20th century, widespread biological sequencing led to the reorganization of the tree of life into the modern three-domain system, while the recognition of significant symbiogenesis and horizontal gene transfer introduced more complexity into evolutionary history.
Antiquity
Greek thought
As early as 500 BC some Greek philosophers tried to explain the world in a rational way, avoiding superstition, myths and theistic intervention. In particular, the Greek atomists taught that the sun, earth, life, humans, civilization, and society emerged over aeons without divine intervention. It must be remembered that only a sample of the writings of these thinkers has survived, but some generalisations can still be made. Among the pre-Socratic philosophers there were no clear forerunners of evolutionary thinking, though for the most part they attempted to provide rational, material explanations—as opposed to supernatural ones—for the living world. This trend would continue despite Plato[1], whose idealistic tendency led him to eschew empirical investigations.
Pre-Socratic thought
The pre-Socratic philosophers of the 6th and 5th century BC were the first philosophers of the Western tradition. Their wide range, and the fragmentary survival of their writing, makes any comprehensive assessment unrealistic. Heraclitus (c500 BC) says “those who are lovers of wisdom must be inquirers into many things”. Democritus (c460-370 BC) is a prominent figure in the history of science, because he and his teacher Leucippus (c480-420 BC) believed that the manifold appearance of everyday objects was caused by the arrangement of their invisible particles—atoms—and the void which surrounded them. It was their response to a problem posed by Parmenides (c510-c450 BC) as to how change could occur. With atoms, which are constant, their arrangements can vary and produce the variety seen in the world. For over two thosand years this idea could not be directly tested, but now its modern version is part of science.
Plato and the theory of forms
Plato (427/8-347/8 BC) was, in the words of biologist-historian Ernst Mayr, "the great antihero of evolutionism."[2] He established the philosophy of essentialism which states, objects observed in the real world are reflections of a limited number of essences or ''eide''. Variation is merely the manifestation of imperfect reflections of constant essences. Plato called this the theory of forms. In his ''Timaeus'', Plato set out the idea that God had created the cosmos and everything in it as, being good and hence "free from jealousy, he desired that all things should be as like himself as they could be." God created all conceivable forms of life as "without them the universe will be incomplete, for it will not contain every kind of animal which it ought to contain, if it is to be perfect". This idea, that all potential life forms are essential in a perfect creation, is called the plenitude principle and greatly influenced Christian thought. Section Three: The Origins of Evolutionary Theory
Aristotle and the ladder of life
Aristotle, (384—322 BC) a pupil of Plato, and tutor to Alexander the Great for about four years, was one of the most influential Greek philosophers, and the earliest natural historian whose work has survived in some detail. After Alexander's succession to the throne of Macedon, Aristotle left for Greek Asia Minor (now modern Turkey) and did his research on natural history on the isle of Lesbos. His writings on biology have survived in the form of four books, usually known by their Latin names: [3]
★ de anima (on the essence of life)
★ historia animalium (inquiries about animals)
★ de generatione animalium (reproduction)
★ de partibus animalium (anatomy)
These works contain some remarkable observations and interpretations by Aristotle, along with sundry myths and mistakes reflecting the uneven state of knowledge of his time. The most striking passages are about the sea-life visible from observation on Lesbos and available from the catches of fishermen. His observations on catfish, electric fish (Torpedo) and angler-fish are exceptional, as is his writing on cephalopod molluscs Octopus, Sepia (cuttlefish) and the paper nautilus (Argonauta argo). His description of the hectocotyl arm (see cephalopod) was about two thousand years ahead of its time, and widely disbelieved until the nineteenth century. He separated the aquatic mammals from fish, and knew that sharks and rays were part of the group he called Selachē (selachians). [4]
However, for Charles Singer, "Nothing is more remarkable than [Aristotle's] efforts to [exhibit] the relationships of living things as a ''scala naturae''" [4] Aristotle's ''History of Animals'' classified organisms in relation to a hierarchical "Ladder of Life" (''scala naturae''), placing them according to complexity of structure and function so that higher organisms showed greater vitality and ability to move. Aristotle, of course, is not responsible for the use made of this idea by clerics after the rediscovery of ancient learning (see rennaisance).
Indian thought
There are suggestions of an evolutionary approach in ancient Indian texts, especially the Vedas, where the incarnations of Vishnu reflects the theory of evolution,[6] as well as the writings of Patañjali.
Chinese thought
Ideas on evolution were expressed by ancient Chinese thinkers. For example, according to Joseph Needham, Taoism explicitly denied the fixity of biological species.
Roman thought
In the first century BC, the Roman Epicurist and atomist Titus Lucretius Carus (d. 50 BC) wrote the poem ''De rarum natura'' (On the Nature of Things) describing the development of the living earth in stages from atoms colliding in the void as swirls of dust, then early plants and animals springing from the early earth's substance, to a succession of animals including a series of progressively less brutish humans. The essence of Lucretius' ideas was naturalism and the avoidance of supernatural interventions or explanations. Understandably, his memory was besmirched by early Christianity. The influence of Epicurus is clear from the way Lucretius refers to him: "I follow you, glory of the Greek race... You are... the discoverer of reality".
Middle Ages
Christian thought - the great chain of being
After a long period when classical learning was lost to the West, Christian authors combined Aristotle's classification system with Plato's ideas of the goodness of God and of all potential life forms being present in a perfect creation to organize inanimate, animate, and spiritual beings in a huge interconnected great chain of being. Thus all could be placed in order from the "lowest" to the "highest," with Hell at the bottom and God at the top above an angelic hierarchy marked by the orbits of the planets, with mankind in an intermediate position and worms the lowest of the animals. As the universe was ultimately perfect, the Great Chain was also perfect. That meant that there were no empty links in the chain, and no link was represented by more than one species. This implied that if every link is occupied, and none are occupied twice, no species can ever move from one position to another, since to do so would leave one level empty and put two species on another. Thus, in Plato's perfect universe, species couldn't ever change and must remain ''fixed'' in accordance with Genesis. For humans to forget their position and behave like lower animals or aspire to a higher station was sinful. Creatures on adjacent steps were expected to closely resemble each other, an idea expressed in the saying ''natura non facit saltum'' (nature does not make leaps) which Charles Darwin often quoted.[7] This basic concept greatly influenced the thinking of centuries of Western civilization, and still has an influence today. The great chain of being provided a classification system which was still the major organizing principle for biology in the 17th and 18th centuries, and was part of the argument from design presented by natural theology.
Islamic thought
:''Main article: Early Islamic philosophy - Evolution''
Whereas evolutionary ideas more or less died out in Europe after the fall of the Roman Empire, they continued to be propounded by scientists and philosophers in the Islamic civilization during the Middle Ages, where early theories on evolution and natural selection were widely taught in medieval Islamic schools at the time. According to al-Khazini in the 12th century, ideas on evolution were widespread among "common people" in the Islamic world at the time.[8] The 19th century scientist, philosopher and historian John William Draper referred to the early Muslim theories on evolution as the "Mohammedan theory of evolution". The term "Mohammedan" was used to refer to Muslims at the time. He compared the early Muslim theories to the modern Darwinian theory of evolution of his time, arguing that the former was developed "much farther than we are disposed to do, extending them even to inorganic or mineral things." The first Muslim biologist and philosopher to develop a theory of evolution was al-Jahiz in the 9th century. He considered the effects of the environment on the likelihood of an animal to survive, and first described the struggle for existence and an early theory on natural selection.[9][10]
Ibn Miskawayh and Brethren of Purity
Ibn Miskawayh's ''al-Fawz al-Asghar'' and the Brethren of Purity's ''Encyclopedia of the Brethren of Purity'' (''The Epistles of Ikhwan al-Safa'') expressed evolutionary ideas on how species evolved from matter, into vapor, and then water, then minerals, then plants, then animals, then apes, and then humans.[11]Eloise Hart, ''Pages of Medieval Mideastern History''. (cf. Isma'ili, Yezidi, Sufi, The Brethren Of Purity, Ismaili Heritage Society) English translations of the ''Encyclopedia of the Brethren of Purity'' were available from 1812.[12] Arabic manuscripts of the ''al-Fawz al-Asghar'' and ''The Epistles of Ikhwan al-Safa'' were also available at the University of Cambridge. It has been suggested that these manuscripts may have influenced those interested in the transmutation of species at that time, possibly including Charles Darwin.[13]
Other Muslim supporters
The polymath Ibn al-Haytham wrote a book in which he argued for evolutionism (although not natural selection), and numerous other Islamic scholars and scientists, such as Ibn Miskawayh, the Brethren of Purity, and the polymaths Abū Rayhān al-Bīrūnī, Nasir al-Din Tusi, and Ibn Khaldun, discussed and developed these ideas. Translated into Latin, these works began to appear in the West after the Renaissance and appear to have had an impact on Western science.
Modern period
Early modern thought
Pierre Belon compared the skeletons of birds and humans in his ''Book of Birds'' (1555)
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. In 1677 Sir Matthew Hale used the term ''evolution'' in attacking the atheistic atomism of Democritus and Epicurus. Hale set out the atomist idea that vibrations and collisions of atoms in the void without divine intervention had formed "Primordial Seeds" (semina) which were the "immediate, primitive, productive Principles of Men, Animals, Birds and Fishes." and called this mechanism an "absurdity" because "it must have potentially at least the whole Systeme of Humane Nature, or at least that Ideal Principle or Configuration thereof, in the evolution whereof the complement and formation of the Humane Nature must consist. . . and all this drawn from a fortuitous coalition of senseless and dead Atoms." Thus, among some ''evolutionist'' theories explored from 1700 to 1850, the earth, life, and universe developed without divine intervention. But most contemporary theories of evolution, including those developed by the German idealist philosophers Schelling and Hegel, held that evolution was a fundamentally spiritual process, with the entire course of natural and human evolution being "a self-disclosing revelation of the Absolute" (Schelling, ''System of Transcendental Idealism'', 1800).
Typically of these theorists, Gottfried Leibniz in 1714 postulated "monads" inside objects causing motion by internal forces, and maintained that "the 'germs' of all things have always existed . . . [and] contain within themselves an internal principle of development which drives them on through a vast series of metamorphoses" to become the geological formations, lifeforms, psychologies, and civilizations of the present. Leibniz clearly held that evolution proceeded on divine principles. In his ''De rerum originatione radicali'', 1697, he wrote that "A cumulative increase of the beauty and universal perfection of the works of God, a perpetual and unrestricted progress of the universe as a whole must be recognized, such that it advances to a higher state of cultivation."
Yet in his "Venus Physique" of 1745, Pierre Louis Maupertuis veered toward more materialistic ground, writing of "Chance" producing "an innumerable multitude of individuals" a small number of which had "fitness" to satisfy their needs, while "another infinitely greater number... perished... The species we see today are but the smallest part of what blind destiny has produced...", anticipating in general terms the idea of natural selection.
Vague and general ideas of evolution continued to proliferate among the mid-eighteenth century philosophers of the Enlightenment. G. L. L. Buffon suggested that what most people referred to as species were just well marked varieties. He thought that members of the same Linnean genus (in terms of modern scientific classification the family) had all been derived through changes driven by the environment from a common ancestor, which had arisen through spontaneous generation. Buffon's concept of evolution was strictly limited. He believed there were "internal moulds" that shaped the spontaneous generation of each family and that the families themselves were eternally distinct. Thus lions, tigers, leopards, pumas, and house cats could all share a common ancestor, but dogs and house cats could not. [14][15] Darwin himself, in his foreword to the 6th edition of the ''Origin of Species'', credited Aristotle with foreshadowing the concept of natural selection, and stated that "the first author who in modern times has treated it in a scientific spirit was Buffon".
Immanuel Kant, in his ''Universal Natural History and Theory of Heaven'' (1755), foreshadowed a theory of the development of unformed matter into the highest types of animals and plants, and suggested that the gradations of structure revealed by comparative anatomy pointed to the existence of blood relationship of all organisms, due to derivation from a common ancestor. He appeared to believe, however, that the successive variations and modifications had arisen in response to mechanical laws of the organisms themselves rather than to the influence of their surroundings. J. G. von Herder suggested that increase by multiplication with the consequent struggle for existence had played a large part in the organic world, but his theme remained vague and undeveloped.
Charles Bonnet applied "Evolutionism" to biology in 1762, asserting that each feature of the embryo was preformed in the parts; some of which came from the egg and some from the sperm. The preformed parts expanded and rearranged themselves to grow into the adult, and so Bonnet was called a "preformationist."
Between 1767 and 1792 James Burnett, Lord Monboddo included in his writings the concepts that man was derived from primates, and that creatures had found methods of transforming their characteristics over long time intervals in response to their environment. He also produced research on the evolution of linguistics. Jan-Andrew Henderson states (Henderson, 2000) that Monboddo was the first to articulate the theory of natural selection.
Between 1794 and 1796 Erasmus Darwin wrote ''Zoönomia'' suggesting "that all warm-blooded animals have arisen from one living filament ... with the power of acquiring new parts" in response to stimuli, with each round of "improvements" being inherited by successive generations. In his "Temple of Nature" of 1802 he described recurring new earths appearing in a cycle of catastrophes, then life springing forth spontaneously to populate the new earth, with animals competing with each other, driven by sex, hunger, "the strongest and most active ... [surviving to] propagate the species, which should thence become improved." Erasmus Darwin cited the work of James Burnett, Lord Monboddo in his ''Temple of Nature'' in 1802.
Early 19th century
Diagram of geologic timescale from an 1861 book by Richard Owen shows the appearance of major animal types
Emergence of paleontology and other developments in geology
In 1796 Georges Cuvier published his findings on the differences between living and fossil elephants. His analysis demonstrated that mammoths and mastodons were extinct species different from any living animal, effectively ending what had been a long running debate about whether a species could become extinct.[16] William Smith began the process of ordering rock strata by examining fossils in the layers while he worked on his geologic map of England. Independently, Georges Cuvier and Alexandre Brongniart published an influential study of the geologic history of the region around Paris in 1811 based on the stratigraphic succession of its layers, which helped establish the antiquity of the earth.[17] Cuvier advocated catastrophism to explain the patterns of extinction and faunal succession revealed by the fossil record. Knowledge of the fossil record continued to advance rapidly in the first few decades of the 19th century. By the 1840s the outlines of the geologic timescale were becoming clear, and in 1841 John Phillips named three major eras based on the predominant fauna, the Paleozoic dominated by marine invertebrates and fish, Mesozoic the age of reptiles, and Cenozoic the age of mammals. Even conservative English geologists like Adam Sedgwick and William Buckland accepted this progressive picture of the history of life, which, like Cuvier, they attributed to repeated catastrophic episodes of extinction followed by new episodes of creation.[18] Unlike Cuvier, Buckland and some other English geologists who advocated natural theology made efforts to explicitly link the last catastrophic episode to the biblical flood.[19]
From 1830-1833 Charles Lyell published his multi-volume ''Principles of Geology'' which advocated a uniformitarian theory of geology as an alternative to catastrophism. Lyell claimed that rather than being the products of cataclysmic (and possibly supernatural) events the geologic features of the earth could better be explained as the result of the same geologic forces that could be observed in the present day acting gradually over immensely long periods of time. Although Lyell opposed evolutionary ideas (even questioning the consensus that the fossil record showed true progression), his concept of forces working gradually over an extended period to shape the earth and the immense age of the earth assumed by his theories would influence future evolutionary thinkers, especially Charles Darwin.[20]
Lamarckism and the transmutation of species
Jean-Baptiste Lamarck proposed in his ''Philosophie Zoologique'' of 1809 a theory of the transmutation of species. Lamarck did not believe that all living things shared a common ancestor. Rather he believed that simple forms of life were created by spontaneous generation all of the time. He also believed that an innate life force, which he sometimes characterized as a nervous fluid, drove species to become more complex over time and advance up a linear ladder of complexity that was related to the great chain of being. Lamarck also recognized that species were adapted to their environment. He explained such adaptation by saying that the same nervous fluid that drove increasing complexity from one generation to the next, also caused the organs of an animal (or a plant) to change based on the use or disuse of that organ, just as muscles are affected by exercise, and that such changes would be inherited by the next generation. It was this secondary mechanism of adaptation through the inheritance of acquired characteristics that became closely associated with his name and would influence discussions of evolution into the 20th century.[21][22]
A radical British school of comparative anatomy which included the surgeon Robert Knox and the anatomist Robert Grant was closely in touch with Lamarck's school of French ''Transformationism'', which included Étienne Geoffroy Saint-Hilaire. Grant developed Lamack's and Erasmus Darwin's ideas of transmutation and evolutionism, investigating homology to prove common descent. As a young student Charles Darwin joined Grant in investigations of the life cycle of marine animals. He also studied geology under professor Robert Jameson who wrote an anonymous paper in 1826 praising "Mr. Lamarck" for explaining how the higher animals had "evolved" from the "simplest worms" – this was the first use of the word "evolved" in a modern sense. Jameson's course closed with lectures on the ''"Origin of the Species of Animals"''.
The computing pioneer Charles Babbage published his unofficial ''Ninth Bridgewater Treatise'' in 1837, putting forward the thesis that God had the omnipotence and foresight to create as a divine legislator, making laws (or programs) which then produced species at the appropriate times, rather than continually interfering with ''ad hoc'' miracles each time a new species was required. In 1844 the Scotish publisher Robert Chambers anonymously published an influential, and extremely controversial book of popular science entitled ''Vestiges of the Natural History of Creation''. This book proposed an evolutionary scenario for the origins of the soloar system and life on earth. It claimed that the fossil record showed a progressive ascent of animals with current animals being branches off a main line that lead progressively to humanity. It implied that the transmutations lead to the unfolding of a preordained plan that had been woven into the laws that goverened the universe. In this sense it was less completely materialistic than the ideas of radicals like Robert Grant, but its implication that humans were just the last step in the ascent of animal life inscensed many conservative thinkers. Both conservatives like Adam Sedgwick, and radical materialists like Thomas Henry Huxley, who disliked its implications of preordained progress, were able to find scientific inaccuracies in the book that they could disparage, but the high profile public debate over ''Vestiges'' with its depiction of evolution as a progressive process would greatly influence the perception of Darwin's theory a decade later. [23][24]
Opposition to the transmutation of species
Ideas about the transmutation of species were strongly associated with the radical materialism of the enlightenment and were greeted with hostility by more conservative thinkers. Cuvier attacked the ideas of Lamarck and Geoffroy Saint-Hilaire. He agreed with Aristotle that species were immutable. Cuvier believed that the individual parts of an animal were too closely correlated with one another to allow for one part of the anatomy to ever be changed in isolation from all the others, and he believed that the fossil record showed patterns of catastrophic extinctions followed by re-population rather than gradual change over time. He also argued that drawings of animals and animal mummies from Egypt that were thousands of years old, showed no signs of change when compared with modern animals. The strength of Cuvier's arguments and reputation helped keep transmutational ideas out of the scientific mainstream for decades.[25]
In Britain, where the philosophy of natural theology remained influential, William Paley wrote the book ''Natural Theology'' with its famous watchmaker analogy at least in part as a response to the transmutational ideas of Erasmus Darwin.[26] Geologists influenced by natural theology such as Buckland and Sedgwick made a regular practice of attacking the evolutionary ideas of Lamarck and Grant, and Sedgwick wrote a famously harsh review of ''The Vestiges of the Natural History of Creation''. [27][28] Alghough the geologist Charles Lyell opposed scriptural geology he also believed in the immutability of species, and in his ''Principles of Geology'' (1830-1833), criticized and dismissed Lamarck's theories of development. Instead, he advocated a form of progressive creation, in which each species had its "centre of creation" and was designed for the habitat, but would go extinct when the habitat changed.
Another source of opposition to transmutation was a school of naturalists influenced by German philosophers and naturalists such as Goethe, Hegel and Lorenz Oken associated with idealism. Idealists such as Louis Agassiz and Richard Owen believed that each species was fixed and unchangeable because it represented an idea in the mind of the creator. They believed that there were relationships between species that could be discerned from developmental patterns in embryology and in the fossil record, but that these represented an underlying pattern of divine thought in which progressive creation lead to increasing complexity culminating in humanity. Owen developed the idea of "archetypes" in the Divine mind producing a sequence of species related by anatomical homologies such as vertebrate limbs. Owen was concerned by the political implications of the radical ideas of transmutationists like Robert Grant, and he led a public campaign by conservatives that successfully marginalized Grant in the scientific community. In his famous 1841 paper that coined the term dinosaur for the giant reptiles discovered by Buckland and Gideon Mantell, Owen argued that these reptiles contradicted the transmutational ideas of Lamarck because they were more sophisticated than the reptiles of the modern world. Darwin would make good use of the homologies analyzed by Owen in his own theory, but the harsh treatment of Grant, along with the controversy surrounding ''Vestiges'' would be major factors in his decision to delay publishing his ideas for so long.[29][30]
Anticipations of Darwinian thought
In 1813, William Charles Wells produced essays assuming that there had been evolution of humans, and recognised the principle of natural selection. Charles Darwin and Alfred Russel Wallace were unaware of this work when they jointly published the theory in 1858, but Darwin later acknowledged that Wells had recognised the principle before them.
Augustin de Candolle's ''natural system'' of classification laid emphasis on the "war" between competing species.
Patrick Matthew wrote in ''Naval Timber & Arboriculture'' published in 1831 of "continual balancing of life to circumstance. ... [The] progeny of the same parents, under great differences of circumstance, might, in several generations, even become distinct species, incapable of co-reproduction." Charles Darwin found out about it after publication of the ''Origin'', and wrote that it "briefly but completely anticipates the theory of Nat. Selection ... a complete but not developed anticipation!"
Although the pre-Darwinian writers amongst them invoked nearly every principle that Darwin or his successors have suggested, they failed to carry conviction with regard to evolution, and they neither propounded a coherent philosophy of variation nor suggested a mechanism by which variations that appeared might give rise to new species. The anticipations of Darwin were little more than formal and verbal. As T. H. Huxley pointed out in his essay on the reception of the ''Origin of Species'' in the second volume of ''Darwins Life and Letters'':
''The suggestion that new species may result from the selective action of external conditions upon the variations from their specific type which individuals present and which we call spontaneous because we are ignorant of their causation is as wholly unknown to the historian of scientific ideas as it was to biological specialists before 1858. But that suggestion is the central idea of the ''Origin of Species'', and contains the quintessence of Darwinism.''
Darwin's first sketch of an evolutionary tree from his ''First Notebook on Transmutation of Species'' (1837)
Natural selection
Main articles: Inception of Darwin's theory, Development of Darwin's theory, Publication of Darwin's theory
The biogeographical patterns Charles Darwin observed in the Galapagos islands and elsehwere during the voyage of the Beagle caused him to doubt the fixity of species, and in 1837 he started the first of a series of secret notebooks on transmutation. Darwin's biogeographical observations lead him to view transmutation as a process of divergence and branching rather than the ladder like progression envisioned by Lamarck and others. In 1838 he read the new 6th edition of Malthus' ''Essay on the Principle of Population'' and compared this with breeders selecting traits. This led to the inception of Darwin's theory of natural selection. Concerned by the intensity of the controversy raging over other transmutational ideas, Darwin would develop this idea for the next 20 years, sharing it only with a handful of friendly naturalists in private correspondence.[31][32]
Unlike Darwin, Alfred Russel Wallace, heavily influenced by the ''Vestiges of the Natural History of Creation'', was already a believer in the transmutation of species before he began his career as a traveling naturalist. By 1855 his biogeographical observations had made him confident enough in a branching pattern of evolution to claim in an important paper that every species originated in close proximity to an already existing closely allied species. Once again it was consideration of how the ideas of Malthus might apply to animal populations that would lead Wallace to conclusions very similar to the ones reached by Darwin. Wallace, unaware of Darwin's unpublished ideas, wrote up his thoughts into an essay and mailed them to Darwin asking for his opinion. The result was the publication of Darwin's theory of natural selection jointly with Wallace in 1858. Darwin also began work in earnest on the book length treatment of the subject that he would publish in 1859.[33]
.
Diagram by O.C. Marsh of the evolution of horse feet and teeth over time as reproduced in T.H Huxley's 1876 book ''Professor Huxley in America''
1859-1930s: Darwin and after Darwin
While transmutation of species was accepted by a sizable number of scientists before 1859, it was the publication of Charles Darwin's ''The Origin of Species'' which fundamentally transformed the debate over biological origins. Darwin argued that his branching version of evolution could explain a wealth of facts in biogeography, anatomy, embryology, and other fields of biology and geology. He also provided the first cogent mechanism by which evolutionary change could persist: his theory of natural selection.[34]
One of the earliest and most important naturalists to be converted by ''Origin'' was the British anatomist Thomas Henry Huxley. Huxley recognized that unlike the earlier transmutational ideas of Lamarck and ''Vestiges'', Darwin's theory provided a mechanism for evolution without supernatural involvement. Huxley would make advocacy of evolution a cornerstone of his program to reform and professionalize science by displacing natural theology with methodological naturalism, and ending the domination of the natural sciences in Britain by the clerical establishment. Thanks in significant part to the efforts of Huxley and his fellow members of the X-club, by the early 1870s evolution had replaced special creation as the mainstream scientific explanation for the origin of species throughout the English speaking world. In his campaign for public and scientific acceptance of Darwin's theory Huxley would make extensive use of evidence from two areas of paleontology where significant finds were made in the 1860s and 1870s. One of the areas was as series of fossil finds that suggested that birds had evolved from reptiles, including the discovery of Archaeopteryx in Europe, and a number of fossils of toothed birds found in North America. The other involved fossils that helped trace the evolution of the horse from much smaller five towed ancestors.[35] Acceptance of evolution among scientists in non-English speaking nations such as France, and the countries of southern Europe and Latin America was slower. An exception to this was Germany where both Ernst Haeckel, who used evolution to challenge the established tradition of metaphysical idealism in German biology much as Huxley used it to challenge natural theology in Britain, and August Weismann would champion the idea.[36]
Darwin's theory, though it succeeded in profoundly shaking scientific opinion regarding the development of life (and indeed resulted in a small social revolution), could not explain several critical components of the evolutionary process. Namely, he was unable to explain the source of variation in traits within a species, and he could not provide a mechanism whereby traits were passed faithfully from one generation to the next. Darwin's theory of pangenesis, while relying in part on the inheritance of acquired characteristics, proved to be useful for statistical models of evolution developed by his cousin Francis Galton and the "biometric" school of evolutionary thought. It was, however, found to be of little use to biologists.
Application of the theory to humans
Thomas Henry Huxley's frontispiece to ''Evidence as to Man's Place in Nature'' (1863).
Charles Darwin was very aware of the severe reaction from some parts of the scientific community against the suggestion made in ''Vestiges of the Natural History of Creation'' that humans were just the culmination of the process of transmutation in animal species, and he almost completely ignored the topic of human evolution in ''The Origin of Species''. Despite this precaution, the issue featured prominently in the debate that followed its publication. For most of the first half of the 19th century most of the scientific community believed that while geology had shown that the earth, and life, was very old, human beings had appeared suddenly just a few thousand years ago. However, a series of archaeological finds in the 1840s and 1850s showed stone tools associated with the remains of extinct animals. By the early 1860s, as summarized in Charles Lyell's 1863 book ''Geological Evidences of the Antiquity of Man'', it had become widely accepted that humans had existed during a prehistoric period that lasted many thousands of years before the start of written history. This new view of human history was more compatible than the older one with an evolutionary origin for humanity. At the time, there was no fossil evidence of human evolution, since the only human fossils discovered prior to the very end of the 19th century were of anatomically modern humans, or of very similar Neanderthals.[37]
Therefore the debate that immediately followed the publication of ''The Origin of Species'' centered on the similarities and differences between humans and modern apes. Richard Owen vigorously defended the traditional classification suggested by Carolus Linnaeus and Cuvier that placed humans in a completely separate order from any of the other mammals including apes. On the other hand Huxley sought to demonstrate a close anatomical relationship between humans and apes. In one very famous incident, Huxley showed that Owen was mistaken in claiming that the brains of gorillas lacked a structure present in human brains. Huxley summarized his argument in his highly influential 1863 book ''Evidence as to Man's place in Nature''. Some scientists, including Charles Lyell and Alfred Russel Wallace, who had become involved with spiritualism, agreed that humans were biologically related to apes, but questioned whether any purely materialistic mechanism could account for some of the differences between humans and apes, especially some aspects of the human mind.
In 1871 Darwin published ''The Descent of Man, and Selection in Relation to Sex'', which contained his views on human evolution. Darwin believed that the differences between the human mind and the minds of the higher animals were a matter of degree rather than of kind. For example he viewed morality as a natural outgrowth of instincts that would be beneficial to animals living in social groups. He believed that all the differences between humans and apes could be explained by a combination of natural selective pressures resulting from our ancestors forsaking life in the trees for life on the plains, and sexual selection. The debate over human origins, and over the degree of human uniqueness would continue well into the 20th century.
Alternatives to natural selection - theistic evolution, orthogenesis, saltationism, and neo-Lamarckism
This photo is from Henry Fairfield Osborn's 1918 book ''Origin and Evolution of Life'', and it shows models depicting the evolution of Titanothere horns over time, which Osborn claimed was an example of an orthogenic trend in evolution.
Evolution was widely accepted in scientific circles within a few years after the publication of ''Origin'', but the acceptance of natural selection as its driving mechanism was much less widespread. There were a variety of reasons for this. Natural selection, with its emphasis on death and competition, didn't appeal to many naturalists because they felt it was immoral and because it seemed to leave little room for teleology (purpose), or even the concept of true progress in the development of life. Some felt that it would be too slow a mechanism given the estimates of the age of the earth and sun (10-100 million years) being made by physicists such as Lord Kelvin at the time, and some felt that it could not work because all the models for inheritance at the time involved blending of inherited characteristics. The four major alternatives to natural selection in the late 19th century, were theistic evolution, neo-Lamarckism, orthogenesis, and saltationism.[38][39]
Theistic evolution was the idea that God somehow intervened in the process of evolution to guide it in such a way that the living world could still be considered to be designed. Some of its advocates included Asa Gray, George Jackson Mivart, and the Duke of Argyle. However, it fell out of favor fairly rapidly among scientists as they became more and more committed to the idea of methodological naturalism and came to believe that direct appeals to divine involvement were scientifically unproductive. By 1900 it had completely disappeared from mainstream scientific discussions, although it continued to be used as a way to reconcile religious belief with scientific discoveries among some non-scientists.
The term Lamarckism was used for the idea that characteristics acquired during the course of an organism's life (such changes caused by the use or disuse of a particular organ) could be inherited by the next generation. Although Wallace completely rejected the concept in favor of natural selection, Darwin had included it in ''The Origin of Species'' as a possible supplemental mechanism of evolution. In the late 19th century the term neo-Lamarckism came to be associated with the position of naturalists who viewed it rather than natural selection as the most important evolutionary mechanism. Its advocates included the British biologist and Darwin critic Samuel Butler, the German biologist Ernst Haeckel, and the American paleontologist Edward Drinker Cope. They considered Lamarckism to be philosophically superior to a process based on selective pressure acting on random variations. Butler and Cope both believed that it allowed organisms to effectively drive their own evolution to a certain degree as organisms that developed new behaviors (possibly in response to changes in their environment) would change the use/disuse patterns for their organs and thus kick start the evolutionary process. Cope and Haeckel both believed that evolution was a progressive process. Cope looked for, and thought he found, patterns of linear progression in the fossil record. The idea of linear progress was also an important part of Haeckel's recapitulation theory of evolution, which held that the embryological development of an organism repeats its evolutionary history.
Critics of neo-Lamarckism pointed out that no one had ever produced solid evidence for the inheritance of acquired characteristics. The experimental work of the German biologist August Weismann, which resulted in the germ plasm theory of inheritance, led him to declare that it was flatly impossible. The Weismann barrier would prevent any changes that occurred to the body after birth from being inherited by the next generation. Despite these criticisms, neo-Lamarckism remained the most popular alternative to natural selection at the end of the 19th century, and would remain the position of some naturalists well into the 20th century.
Orthogenesis or orthogenetic evolution was the hypothesis that life has an innate tendency to change, in a unilinear fashion, towards ever greater perfection. It had a significant following in the 19th century, and its proponents included the Russian biologist Leo Berg, and the American paleontologist Henry Fairfield Osborn. Orthogenesis was particularly popular among some paleontologists who believed that fossils indicated a gradual and constant unidirectional change. Those who accepted orthogenesis in this way, however, did not necessarily accept that the mechanism that drove orthogenesis was teleological (goal-directed). The orthogenesis hypothesis began to collapse when it became clear that it could not explain the patterns found by paleontologists in the fossil record, which was non-linear with many complications. A few hung on to the orthogenesis hypothesis as late as the 1950s by claiming that the processes of macroevolution, the long term trends in evolution, were distinct from the processes of microevolution.
Saltationism is the idea that new species arise as a result of large mutations. It was seen as a much faster alternative to the Darwinian concept of a gradual process of small random variations being acted on by natural selection. It was very popular with early geneticists such as Hugo DeVries, William Bateson, and early in his career, T. H. Morgan. They based the mutation theory of evolution on it.
Diagram from T.H. Morgan's 1919 book ''The Physical Basis of Heredity'' shows the sex linked inheritance of the white eyed mutation in Drosophilia melanogaster.
The Mendelian-biometrician debates and the nature of variation
After the rediscovery of Gregor Mendel's laws of inheritance in 1900 there was a fierce debate between two camps. In one camp were the Mendelians, who were focused on discrete variations and the laws of inheritance. They were led by William Bateson (who coined the word genetics) and Hugo de Vries (who coined the word mutation). Their opponents were the biometricians, who were interested in the continuous variation of characteristics within populations. Their leaders Karl Pearson and Walter Frank Raphael Weldon, followed in the tradition of Francis Galton who had focused on measurement and statistical analysis of variation within a population. The biometricians rejected Mendelian genetics because they felt that discrete units of heredity such as genes could not explain the continuous range of variation in various characteristics that they measured in wild populations. Weldon's work with crabs and snails provided evidence that selection pressure from environmental factors could shift the range of variation in real world populations, but the Mendelians maintained that the variations measured by the biometricians were too insignificant to account for the evolution of new species.[40][41]
When T. H. Morgan began experimenting with breeding the fruit fly Drosophila melanogaster he was a saltationist who hoped to demonstrate that a new species could be created in the lab by a large mutation. Instead the work at his lab between 1910 and 1915 reconfirmed Mendelian genetics and provided solid experimental evidence linking it to chromosomal inheritance. It also demonstrated that most mutations had relatively small affects (such as a change in eye color), and that rather than creating a new species in a single step, they served to increase the genetic variation within the existing population.
1920s-1940s: population genetics and the modern evolutionary synthesis
Main articles: Modern evolutionary synthesis
''Biston betularia f. typica'', the white-bodied peppered moth.
''Biston betularia f. carbonaria'', the black-bodied peppered moth.
Eventually, the two models were reconciled and merged, primarily through the work of the British biologist and statistician R.A. Fisher. In a series of papers starting in 1918 and culminating in his 1930 book ''Genetical Theory of Natural Selection'' Fisher showed that the continuous variation measured by the biometricians could be produced by the combined action of many discrete genes, and that it was theoretically possible for natural selection to cause change in gene frequencies in a population and thus drive evolution. In a series of papers starting in 1924 another British geneticist, J.B.S. Haldane, applied statistical analysis to real world examples of natural selection such as the evolution of industrial melanism in peppered moths, and showed that natural selection could work in the real world at a faster rate than even Fisher had assumed was possible. The American biologist Sewall Wright, who had a background in animal breeding experiments, focused on combinations of genes that interacted as complexes, and the effects of inbreeding on small relatively isolated populations, which could exhibit genetic drift. In 1932 Wright produced the concept of an adaptive landscape that held that genetic drift and inbreeding could drive small isolated sub populations away from adaptive peaks, which would then allow natural selection to drive them towards different adaptive peaks. The work of Fisher, Haldane, and Wright founded the discipline of population genetics, which integrated natural selection with Mendelian genetics.[42][43]
In the first couple of decades of the 20th century most field naturalists continued to believe that Lamarckian and orthogenic mechanisms of evolution provided the best explanation for the complexities they observed in the living world. However, as the field of genetics continued to develop, that viewpoint became less and less tenable. Theodosius Dobzhansky, who had been a postdoctoral worker in T. H. Morgan's lab, would help to bridge the divide between the population geneticists and the field biologists with his 1937 book ''Genetics and the origin of species''. Dobzhansky examined the genetic diversity of wild populations, and showed that contrary to the assumptions of the population geneticists, wild populations had large amounts of genetic diversity with marked differences between sub populations. The book also took the highly mathematical work of the population geneticists and put it into a form that was more accessible to field biologists. Ernst Mayr would follow up on Dobzhansky's work with the 1942 book ''Systematics and the Origin of Species'', which emphasized the importance of allopatric speciation in which geographical isolation of a sub population was followed by the development of mechanisms for reproductive isolation in the formation of new species. In the 1944 book ''Mode and Tempo in Evolution'' George Gaylord Simpson would show that the fossil record was consistent with the irregular non directional pattern predicted by the developing evolutionary synthesis, and that the linear trends that earlier paleontologists had claimed supported orthogenesis and neo-Lamarckism did not hold up upon closer examination. In 1950 G. Ledyard Stebbins would publish ''Variation and Evolution in Plants'', which helped integrate botany into the synthesis. The emerging cross-discipline consensus on how evolution worked received is name from the book ''Evolution: the modern synthesis'' by Julian Huxley.
1940s-1960s: developments following molecular biology
Main articles: History of molecular evolution
In the 1940s, following up on Griffith's experiment, Avery, MacLeod and McCarty definitively identified deoxyribonucleic acid (DNA) as the "transforming principle" responsible for transmitting genetic information. In 1953, Francis Crick and James D. Watson published their famous paper on the structure of DNA, based on the research of Rosalind Franklin and Maurice Wilkins. These developments ignited the era of molecular biology and transformed the understanding of evolution into a molecular process: the mutation of segments of DNA.
During this era of molecular biology, it also became clear that a major mechanism for variation within a population is mutations of DNA.
In the mid-1970s, Motoo Kimura formulated the neutral theory of molecular evolution, firmly establishing the importance of genetic drift as a major mechanism of evolution. The theory sparked the "neutralist-selectionist" debate, partially solved by the development of Tomoko Ohta's nearly neutral theory of evolution.
1960s-1980s: Gene centered view of evolution, punctuated equilibrium, sociobiology
In the mid-1960s, George C. Williams strongly critiqued verbal explanations of adaptations couched in terms of "survival of the species" (essentially group selection arguments). Such explanations were largely replaced by a gene-centered view of evolution, epitomised by the kin selection arguments of W. D. Hamilton, George Price and John Maynard Smith. Models of the period showed that group selection was severely limited in its strength, although these models have since been shown to be too limited and newer models do admit the possibility of significant multi-level selection.
One of the most prominent debates arising during this time period was over the theory of punctuated equilibrium, a theory propounded by Niles Eldredge and Stephen Jay Gould to describe and account for the pattern of fossil species persisting phenotypically unchanged for long periods (what they termed ''stasis''), with relatively brief periods of phenotypic change during speciation.
W. D. Hamilton's work also contributed to the emergence of the discipline of sociobiology. Altruism has been a difficult problem for evolutionary theorists going all the way back to Darwin. Significant progress was made in 1964 when Hamilton formulated the inequality known as Hamilton's rule which showed how eusociality (sterile worker classes) in insects and many other examples of altruistic behavior could have evolved through kin selection. Other theories, some derived from game theory, such as reciprocal altruism followed. In 1975 E.O. Wilson published the influential and highly controversial book '' which claimed evolutionary theory could help explain many aspects of animal, including human, behavior. Critics of sociobiology, including Stephen Jay Gould, and Richard Lewontin, claimed that sociobiology greatly overstated the degree to which complex human behaviors could be determined by genetic factors. They also claimed that the theories of sociobiologists often reflected their own ideological biases. Despite these criticisms significant work in sociobiology and the related discipline of evolutionary psychology, including work on other aspects of the altruism problem, has continued.[44][45]
1970s-2000s: evolutionary biology as a discipline
Microbiology has recently developed into an evolutionary discipline. It was originally ignored due to the paucity of morphological traits and the lack of a species concept in microbiology. Now, evolutionary researchers are taking advantage our extensive understanding of microbial physiology, the ease of microbial genomics, and the quick generation time of some microbes to answer evolutionary questions. Similar features have led to progress in viral evolution, particularly for bacteriophage.
Recent developments in evolutionary theory
Improvements in sequencing methods have resulted in a large increase of sequenced genomes, allowing for the testing and refining of the theory of evolution with respect to whole genome data. Advances in computational hardware and software have allowed for the testing and extrapolation of increasingly advanced evolutionary models. Discoveries in biotechnology have produced methods for the ''de novo'' synthesis of proteins and, potentially, entire genomes, driving evolutionary studies at the molecular level. Evolutionary biology is increasingly centered on biological information: Daniel Dennett (1995) argues in ''Darwin's Dangerous Idea'' that natural selection is an algorithmic process applicable to many circumstances besides biological evolution. This conception of evolutionary has been dubbed "universal Darwinism".
Symbiogenesis
Main articles: Symbiogenesis
Another extension to the standard modern synthesis, advocated by Lynn Margulis, is symbiogenesis. Symbiogenesis argues that acquisition and accumulation of random mutations or genetic drift are not sufficient to explain how new inherited variations occur in evolution. This theory states that species arise from the merger of independent organisms through symbiosis. Symbiogenesis emphasizes the impact of co-operation rather than Darwinian competition. This commonly occurs in multigenomic organisms throughout nature.
Evo-devo
Main articles: Evolutionary developmental biology
Molecular data regarding the mechanisms underlying development started to accrue quickly during the 1980's and '90's. As scientists began to compare the developmental mechanisms in different organisms, they realized that these mechanisms are conserved through deep evolutionary time. By combining the disciplines of phylogenetics, paleontology and comparative developmental biology, scientists try to infer the way in which early organisms developed, thus spawning the new discipline of "evo-devo."
Small RNA or micro RNA (miRNA) appears highly significant in regulation of gene expression during development. [46][47][48] Micro RNA's contribution to evolution is considered an epigenetic mechanism in evolutionary developmental biology. Micro RNA appears to constitute 1% of the human genome. Scientists are designing silencing interference micro RNA in the hopes of shutting down genes involved in cancer, diseases, and the contribution of genes in developmental biology.
Neo-structuralist themes in evolutionary theory
In the 1980s and 1990s there was a renewal of structuralist themes in evolutionary biology by biologists such as Brian Goodwin, that incorporates ideas from cybernetics and systems theory, and that emphasizes the role of self-organized processes as being at least as important as the role of natural selection.
It is hypothesized, for example, that the rapid emergence of basic metazoan body plans in the Cambrian Explosion was due in part to changes in the environment acting on inherent properties of cell aggregates, such as differential cell adhesion. Such material-based plasticity led to the spontaneous emergence of metazoan body forms. The resulting forms were later “locked in” by means of stabilizing natural selection. Developmental biologists Stuart Newman and Gerd B. Müller have presented recent work relating to this view in the edited volume, Origination of Organismal Form.
Some variants of this view consider neo-Darwinian forms of natural selection to characterize evolution only in its advanced stages (i.e., after stabilization of the genotype-phenotype relationship has occurred), though most neo-structuralist biologists would not go this far.
Horizontal gene transfer
Main articles: Horizontal gene transfer
The transfer of genetic material between bacteria was first observed in the 1950s and it has played a major role in the propagation of anti-biotic resistance among different strains of bacteria. More recently, as knowledge of genomes has continued to expand, it has been suggested that lateral transfer of genetic material has played an important role in the evolution of bacteria and archae. Some have proposed that it has also played a role in the evolutionm of eukaryotes including fungi, plants, and animals as well, and that it may have significantly affected both the pattern and pace of evolution.[49].[50][51]
Unconventional extensions to evolutionary ideas
Teilhard de Chardin's ideas
Pierre Teilhard de Chardin formulated theories describing the gradual development of the Universe from subatomic particles to human society, considered by Teilhard as the last stage. (see Gaia theory). These are not generally recognized as scientifically rigorous.
Nine levels of development are described in their scheme. Stages one through five are grouped into the Lithosphere, also called Geosphere or Physiosphere, where the evolution of the structure of organisms is ruled by mechanical laws and coincidence. Levels six, seven, and eight are the classical biological stages. Stages six through eight are collectively called the Biosphere, where the progress of the structure of the organisms is ruled by genetic mechanisms. The last stage, stage 9, is called the Noosphere, where the structure of human society is ruled by psychological, informational and communicative processes.
Notes
1. Mayr, ''The Growth of Biological Thought'', pp. 301-304
2. Mayr, ''The Growth of Biological Thought'', p. 304
3. Singer, Charles ''A short history of biology.'' Oxford 1931.
4. Singer, Charles. ''A short history of biology''. Oxford 1931.
5. Singer, Charles. ''A short history of biology''. Oxford 1931.
6. Hinduism and evolution
7. Aristotle and the Great Chain
8. John William Draper (1878). ''History of the Conflict Between Religion and Science'', p. 154-155, 237. ISBN 1603030964.
9. Conway Zirkle (1941). Natural Selection before the "Origin of Species", ''Proceedings of the American Philosophical Society'' '84' (1), p. 71-123.
10. Mehmet Bayrakdar (Third Quarter, 1983). "Al-Jahiz And the Rise of Biological Evolutionism", ''The Islamic Quarterly''. London. [1]
11. Muhammad Hamidullah and Afzal Iqbal (1993), ''The Emergence of Islam: Lectures on the Development of Islamic World-view, Intellectual Tradition and Polity'', p. 143-144. Islamic Research Institute, Islamabad.
12. "Ikhwan as-Safa and their Rasa'il: A Critical Review of a Century and a Half of Research", by A. L. Tibawi, as published in volume 2 of ''The Islamic Quarterly'' in 1955; pgs. 28-46
13. Muhammad Hamidullah and Afzal Iqbal (1993), ''The Emergence of Islam: Lectures on the Development of Islamic World-view, Intellectual Tradition and Polity'', p. 144.
This claim is not supported by Darwin's biographers.
14. Bowler ''Evolution: The History of an Idea'' pp. 75-80
15. Larson Evolution: The Remarkable History of a Scientific Theory pp. 14-15
16. Larson ''Evolution: The Remarkable History of a Scientific Theory'' p. 7
17. Bowler p. 113
18. Larson pp. 29-38
19. Bowler pp. 115-116
20. Bowler pp. 129-134
21. Bowler pp. 86-94
22. Larson pp. 38-41
23. Bowler pp. 134-138
24. Bowler and Morus ''Making Modern Science'' pp. 142-3
25. Larson pp. 5-24
26. Bowler pp. 103-104
27. Larson pp. 37-38
28. Bowler p. 138
29. Bowler pp. 120-129
30. Larson pp. 42-46
31. Bowler and Morus pp. 129-149
32. Larson pp. 55-71
33. Bowler pp. 173-176
34. Larson pp. 79-111
35. Larson pp. 139-40
36. Larson pp. 109-110
37. Bowler pp. 207-216
38. Larson pp. 105-129
39. Bowler pp. 196-253
40. Bowler pp. 256-273
41. Larson pp. 153-174
42. Bowler pp. 325-339
43. Larson pp. 221-243
44. Larson pp. 270-278
45. Bowler pp. 359-361
46. The phylogenetic distribution of metazoan microRNA: insights into evolutionary complexity and constraint.., Sempere LF, Cole CN, McPeek MA, Peterson KJ., , , J Exp Zoolog B Mol Dev Evol, 2006
47. The evolving role of microRNAs in animal gene expression.journal = Bioessays., Massirer KB, Pasquinelli AE., , , , 2006
48. Conservation and divergence of plant microRNA genes., Zhang B, Pan X, Cannon CH, Cobb GP, Anderson TA., , , Plant J., 2006
49. Lateral gene transfer and the nature of bacterial innovation
50. Horizontal Gene Transfer
51. Study: Horizontal gene transfer adds to complexity, speed of evolution
References
★ Evolution:The History of an Idea, , Peter J., Bowler, University of California Press, ,
★ Making Modern Science, , Peter J., Bowler, The University of Chicago Press, ,
★ Erasmus Darwin, ''The Temple of Nature, or The Origin of Society(1803)'', Martin Priestman, ed. Romantic Circles, August, 2006. (Referenced 11/17/06) http://www.rc.umd.edu/editions/darwin_temple/toc.html
★ Erasmus Darwin, ''Zoonomia, Vol I''. Project Gutenberg. (Referenced 11/17/06) http://www.gutenberg.org/etext/15707
★ The Structure of Evolutionary Theory, , Stephen Jay, Gould, Belknap Press of Harvard University Press, ,
★ Jan-Andrew Henderson (2000), ''The Emperor's Kilt: The Two Secret Histories of Scotland'', Mainstream Publishing
★ Evolution:The Remarkable History of Scientific Theory, , Edward J., Larson, Modern Library, ,
See also
★ The Voyage of the Beagle
★ Galápagos Islands
★ Faith and rationality
★ List of paradigm shifts in science
External links
★ Darwin's precursors and infulences by John Wilkins. Part of the Talk.Origins Archive.
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