Evolutionary thought, the recognition that species change over time and the perceived understanding of how such processes work, has roots in antiquity. With the beginnings of modern biological taxonomy in the late 17th century, two opposed ideas influenced Western biological thinking: essentialism, the belief that every species has essential characteristics that are unalterable, a concept which had developed from medieval Aristotelian metaphysics, and that fit well with natural theology; and the development of the new anti-Aristotelian approach to science. Naturalists began to focus on the variability of species; the emergence of palaeontology with the concept of extinction further undermined static views of nature. In the early 19th century prior to Darwinism, Jean-Baptiste Lamarck proposed his theory of the transmutation of species, the first fully formed theory of evolution. In 1858 Charles Darwin and Alfred Russel Wallace published a new evolutionary theory, explained in detail in Darwin's On the Origin of Species (1859). Darwin's theory, originally called descent with modification, is known contemporarily as Darwinism or Darwinian theory. Unlike Lamarck, Darwin proposed common descent and a branching tree of life, meaning that two very different species could share a common ancestor. Darwin based his theory on the idea of natural selection: it synthesized a broad range of evidence from animal husbandry, biogeography, geology, morphology, and embryology. Debate over Darwin's work led to the rapid acceptance of the general concept of evolution, but the specific mechanism he proposed, natural selection, was not widely accepted until it was revived by developments in biology that occurred during the 1920s through the 1940s. Before that time most biologists regarded other factors as responsible for evolution. Alternatives to natural selection suggested during "the eclipse of Darwinism" (c. 1880 to 1920) included inheritance of acquired characteristics (neo-Lamarckism), an innate drive for change (orthogenesis), and sudden large mutations (saltationism). Mendelian genetics, a series of 19th-century experiments with pea plant variations rediscovered in 1900, was integrated with natural selection by Ronald Fisher, J. B. S. Haldane, and Sewall Wright during the 1910s to 1930s, and resulted in the founding of the new discipline of population genetics. During the 1930s and 1940s population genetics became integrated with other biological fields, resulting in a widely applicable theory of evolution that encompassed much of biology—the modern synthesis. Following the establishment of evolutionary biology, studies of mutation and genetic diversity in natural populations, combined with biogeography and systematics, led to sophisticated mathematical and causal models of evolution. Palaeontology and comparative anatomy allowed more detailed reconstructions of the evolutionary history of life. After the rise of molecular genetics in the 1950s, the field of molecular evolution developed, based on protein sequences and immunological tests, and later incorporating RNA and DNA studies. The gene-centred view of evolution rose to prominence in the 1960s, followed by the neutral theory of molecular evolution, sparking debates over adaptationism, the unit of selection, and the relative importance of genetic drift versus natural selection as causes of evolution. In the late 20th-century, DNA sequencing led to molecular phylogenetics and the reorganization of the tree of life into the three-domain system by Carl Woese. In addition, the newly recognized factors of symbiogenesis and horizontal gene transfer introduced yet more complexity into evolutionary theory. Discoveries in evolutionary biology have made a significant impact not just within the traditional branches of biology, but also in other academic disciplines (for example: anthropology and psychology) and on society at large.
Antiquity
Indigenous cultures Several cultures across the world seem to have a rudimentary understanding of the theory of evolution, seeing humans as descending from certain mammals. These include the Malagasy people, who see humans as descending from indri; the Aboriginal Tasmanians, which see humans as descending from kangaroos; and some Native American cultures, such as the Navajo, whose creation myth details humans changing from animalistic creatures.
Greeks
Proposals that one type of animal, even humans, could descend from other types of animals, are known to go back to the pre-Socratic Greek philosophers. Anaximander of Miletus proposed that the first animals lived in water, during a wet phase of the Earth's past, and that the first land-dwelling ancestors of mankind must have been born in water, and only spent part of their life on land. He also argued that the first human of the form known today must have been the child of a different type of animal (probably a fish), because man needs prolonged nursing to live. In the late nineteenth century, Anaximander was hailed as the "first Darwinist", but this characterization is no longer commonly agreed. Anaximander's hypothesis could be considered "evolution" in a sense, although not a Darwinian one. Empedocles argued that what we call birth and death in animals are just the mingling and separations of elements which cause the countless "tribes of mortal things". Specifically, the first animals and plants were like disjointed parts of the ones we see today, some of which survived by joining in different combinations, and then intermixing during the development of the embryo, and where "everything turned out as it would have if it were on purpose, there the creatures survived, being accidentally compounded in a suitable way." Other philosophers who became more influential at that time, including Plato, Aristotle, and members of the Stoic school of philosophy, believed that the types of all things, not only living things, were fixed by divine design.
Plato was called by biologist Ernst Mayr "the great antihero of evolutionism," because he promoted belief in essentialism, which is also referred to as the theory of Forms. This theory holds that each natural type of object in the observed world is an imperfect manifestation of the ideal, form or "species" which defines that type. In his Timaeus for example, Plato has a character tell a story that the Demiurge created the cosmos and everything in it because, being good, and hence, "free from jealousy, He desired that all things should be as like Himself as they could be." The creator created all conceivable forms of life, since "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 "principle of plenitude"—the idea that all potential forms of life are essential to a perfect creation—greatly influenced Christian thought. However, some historians of science have questioned how much influence Plato's essentialism had on natural philosophy by stating that many philosophers after Plato believed that species might be capable of transformation and that the idea that biologic species were fixed and possessed unchangeable essential characteristics did not become important until the beginning of biological taxonomy in the 17th and 18th centuries. Aristotle, the most influential of the Greek philosophers in Europe, was a student of Plato and is also the earliest natural historian whose work has been preserved in any real detail. His writings on biology resulted from his research into natural history on and around the island of Lesbos, and have survived in the form of four books, usually known by their Latin names, De anima (On the Soul), Historia animalium (History of Animals), De generatione animalium (Generation of Animals), and De partibus animalium (On the Parts of Animals). Aristotle's works contain accurate observations, fitted into his own theories of the body's mechanisms. However, for Charles Singer, "Nothing is more remarkable than [Aristotle's] efforts to [exhibit] the relationships of living things as a scala naturae." This scala naturae, described in Historia animalium, classified organisms in relation to a hierarchical but static "Ladder of Life" or "great chain of being," placing them according to their complexity of structure and function, with organisms that showed greater vitality and ability to move described as "higher organisms." Aristotle believed that features of living organisms showed clearly that they had what he called a final cause, that is to say that their form suited their function. He explicitly rejected the view of Empedocles that living creatures might have originated by chance. Other Greek philosophers, such as Zeno of Citium the founder of the Stoic school of philosophy, agreed with Aristotle and other earlier philosophers that nature showed clear evidence of being designed for a purpose; this view is known as teleology. The Roman Skeptic philosopher Cicero wrote that Zeno was known to have held the view, central to Stoic physics, that nature is primarily "directed and concentrated...to secure for the world...the structure best fitted for survival."
Chinese Ancient Chinese thinkers such as Zhuang Zhou (c. 369 – c. 286 BC), a Taoist philosopher, expressed ideas on changing biological species. According to Joseph Needham, Taoism explicitly denies the fixity of biological species and Taoist philosophers speculated that species had developed differing attributes in response to differing environments. Taoism regards humans, nature and the heavens as existing in a state of "constant transformation" known as the Tao, in contrast with the more static view of nature typical of Western thought.
Roman Empire Lucretius' poem De rerum natura provides the best surviving explanation of the ideas of the Greek Epicurean philosophers. It describes the development of the cosmos, the Earth, living things, and human society through purely naturalistic mechanisms, without any reference to supernatural involvement. De rerum natura would influence the cosmological and evolutionary speculations of philosophers and scientists during and after the Renaissance. This view was in strong contrast with the views of Roman philosophers of the Stoic school such as Seneca the Younger and Pliny the Elder who had a strongly teleological view of the natural world that influenced Christian theology. Cicero reports that the peripatetic and Stoic view of nature as an agency concerned most basically with producing life "best fitted for survival" was taken for granted among the Hellenistic elite.
Early Church Fathers
Origen of Alexandria In line with earlier Greek thought, the third-century Christian philosopher and Church Father Origen of Alexandria argued that the creation story in the Book of Genesis should be interpreted as an allegory for the falling of human souls away from the glory of the divine, and not as a literal, historical account:
For who that has understanding will suppose that the first, and second, and third day, and the evening and the morning, existed without a sun, and moon, and stars? And that the first day was, as it were, also without a sky? And who is so foolish as to suppose that God, after the manner of a husbandman, planted a paradise in Eden, towards the east, and placed in it a tree of life, visible and palpable, so that one tasting of the fruit by the bodily teeth obtained life? And again, that one was a partaker of good and evil by masticating what was taken from the tree? And if God is said to walk in the paradise in the evening, and Adam to hide himself under a tree, I do not suppose that anyone doubts that these things figuratively indicate certain mysteries, the history having taken place in appearance, and not literally.
Gregory of Nyssa Gregory of Nyssa wrote:Scripture informs us that the Deity proceeded by a sort of graduated and ordered advance to the creation of man. After the foundations of the universe were laid, as the history records, man did not appear on the earth at once, but the creation of the brutes preceded him, and the plants preceded them. Thereby Scripture shows that the vital forces blended with the world of matter according to a gradation; first it infused itself into insensate nature; and in continuation of this advanced into the sentient world; and then ascended to intelligent and rational beings (emphasis added).Henry Fairfield Osborn wrote in his work on the history of evolutionary thought, From the Greeks to Darwin (1894):
Among the Christian Fathers the movement towards a partly naturalistic interpretation of the order of Creation was made by Gregory of Nyssa in the fourth century, and was completed by Augustine in the fourth and fifth centuries. ...[Gregory of Nyssa] taught that Creation was potential. God imparted to matter its fundamental properties and laws. The objects and completed forms of the Universe developed gradually out of chaotic material.
Augustine of Hippo
In the fourth century AD, the bishop and theologian Augustine of Hippo followed Origen in arguing that Christians should read the Genesis creation story allegorically. In his book De Genesi ad litteram (On the Literal Meaning of Genesis), he prefaces his account with the following:
In all sacred books, we should consider the eternal truths that are taught, the facts that are narrated, the future events that are predicted, and the precepts or counsels that are given. In the case of a narrative of events, the question arises whether everything must be taken according to the figurative sense only, or whether it must be expounded and defended also as a faithful record of what happened. No Christian would dare say that the narrative must not be taken in a figurative sense. For St. Paul says: Now all these things that happened to them were symbolic [1 Cor 10:11]. And he explains the statement in Genesis, And they shall be two in one flesh [Eph 5:32], as a great mystery in reference to Christ and to the Church. Later he differentiates between the days of the Genesis 1 creation narrative and 24 hour days that humans experience (arguing that "we know [the days of creation] are different from the ordinary day of which we are familiar") before describing what could be called an early form of theistic evolution:
The things [God] had potentially created... [came] forth in the course of time on different days according to their different kinds... [and] the rest of the earth [was] filled with its various kinds of creatures, [which] produced their appropriate forms in due time. Augustine deployed the concept of rationes seminales to blend the idea of divine creation with subsequent development. This idea "that forms of life had been transformed 'slowly over time'" prompted Father Giuseppe Tanzella-Nitti, Professor of Theology at the Pontifical Santa Croce University in Rome, to claim that Augustine had suggested a form of evolution. Henry Fairfield Osborn wrote in From the Greeks to Darwin (1894):
If the orthodoxy of Augustine had remained the teaching of the Church, the final establishment of Evolution would have come far earlier than it did, certainly during the eighteenth instead of the nineteenth century, and the bitter controversy over this truth of Nature would never have arisen. ... Plainly as the direct or instantaneous Creation of animals and plants appeared to be taught in Genesis, Augustine read this in the light of primary causation and the gradual development from the imperfect to the perfect of Aristotle. This most influential teacher thus handed down to his followers opinions which closely conform to the progressive views of those theologians of the present day who have accepted the Evolution theory. In A History of the Warfare of Science with Theology in Christendom (1896), Andrew Dickson White wrote about Augustine's attempts to preserve the ancient evolutionary approach to the creation as follows:
For ages a widely accepted doctrine had been that water, filth, and carrion had received power from the Creator to generate worms, insects, and a multitude of the smaller animals; and this doctrine had been especially welcomed by St. Augustine and many of the fathers, since it relieved the Almighty of making, Adam of naming, and Noah of living in the ark with these innumerable despised species. In Augustine's De Genesi contra Manichæos, on Genesis he says: "To suppose that God formed man from the dust with bodily hands is very childish. ... God neither formed man with bodily hands nor did he breathe upon him with throat and lips." Augustine suggests in other work his theory of the later development of insects out of carrion, and the adoption of the old emanation or evolution theory, showing that "certain very small animals may not have been created on the fifth and sixth days, but may have originated later from putrefying matter." Concerning Augustine's De Trinitate (On the Trinity), White wrote that Augustine "develops at length the view that in the creation of living beings there was something like a growth—that God is the ultimate author, but works through secondary causes; and finally argues that certain substances are endowed by God with the power of producing certain classes of plants and animals." Augustine implies that whatever science shows, the Bible must teach:
Usually, even a non-Christian knows something about the earth, the heavens, and the other elements of this world, about the motion and orbit of the stars ... Now, it is a disgraceful and dangerous thing for an infidel to hear a Christian, presumably giving the meaning of Holy Scripture, talking non-sense on these topics; and we should take all means to prevent such an embarrassing situation, in which people show up vast ignorance in a Christian and laugh it to scorn. The shame is not so much that an ignorant individual is derided, but that people outside the household of the faith think our sacred writers held such opinions, and, to the great loss of those for whose salvation we toil, the writers of our Scripture are criticized and rejected as unlearned men.
Middle Ages
Islamic philosophy and the struggle for existence
Although Greek and Roman evolutionary ideas died out in Western Europe after the fall of the Roman Empire, they were not lost to Islamic philosophers and scientists (nor to the culturally Greek Byzantine Empire). In the Islamic Golden Age of the 8th to the 13th centuries, philosophers explored ideas about natural history. These ideas included transmutation from non-living to living: "from mineral to plant, from plant to animal, and from animal to man." In the medieval Islamic world, the scholar al-Jāḥiẓ wrote his Book of Animals in the 9th century. Conway Zirkle, writing about the history of natural selection in 1941, said that an excerpt from this work was the only relevant passage he had found from an Arabian scholar. He provided a quotation describing the struggle for existence, citing a Spanish translation of this work: "Every weak animal devours those weaker than itself. Strong animals cannot escape being devoured by other animals stronger than they. And in this respect, men do not differ from animals, some with respect to others, although they do not arrive at the same extremes. In short, God has disposed some human beings as a cause of life for others, and likewise, he has disposed the latter as a cause of the death of the former." Al-Jāḥiẓ also wrote descriptions of food chains. Some of Ibn Khaldūn's thoughts, according to some commentators, anticipate the biological theory of evolution. In 1377, Ibn Khaldūn wrote the Muqaddimah in which he asserted that humans developed from "the world of the monkeys," in a process by which "species become more numerous". In chapter 1 he writes: "This world with all the created things in it has a certain order and solid construction. It shows nexuses between causes and things caused, combinations of some parts of creation with others, and transformations of some existent things into others, in a pattern that is both remarkable and endless." The Muqaddimah also states in chapter 6:
We explained there that the whole of existence in (all) its simple and composite worlds is arranged in a natural order of ascent and descent, so that everything constitutes an uninterrupted continuum. The essences at the end of each particular stage of the worlds are by nature prepared to be transformed into the essence adjacent to them, either above or below them. This is the case with the simple material elements; it is the case with palms and vines, (which constitute) the last stage of plants, in their relation to snails and shellfish, (which constitute) the (lowest) stage of animals. It is also the case with monkeys, creatures combining in themselves cleverness and perception, in their relation to man, the being who has the ability to think and to reflect. The preparedness (for transformation) that exists on either side, at each stage of the worlds, is meant when (we speak about) their connection.
Christian philosophy
Thomas Aquinas on creation and natural processes While most Christian theologians held that the natural world was part of an unchanging designed hierarchy, some theologians speculated that the world might have developed through natural processes. Thomas Aquinas expounded on Augustine of Hippo's early idea of theistic evolution On the day on which God created the heaven and the earth, He created also every plant of the field, not, indeed, actually, but 'before it sprung up in the earth,' that is, potentially... All things were not distinguished and adorned together, not from a want of power on God's part, as requiring time in which to work, but that due order might be observed in the instituting of the world.He saw that the autonomy of nature was a sign of God's goodness, and detected no conflict between a divinely created universe and the idea that the universe had developed over time through natural mechanisms. However, Aquinas disputed the views of those (like the ancient Greek philosopher Empedocles) who held that such natural processes showed that the universe could have developed without an underlying purpose. Aquinas rather held that: "Hence, it is clear that nature is nothing but a certain kind of art, i.e., the divine art, impressed upon things, by which these things are moved to a determinate end. It is as if the shipbuilder were able to give to timbers that by which they would move themselves to take the form of a ship."
Scientific Revolution and Enlightenment
In the first half of the 17th century, René Descartes' mechanical philosophy encouraged the use of the metaphor of the universe as a machine, a concept that would come to characterise the Scientific Revolution. Between 1650 and 1800, some naturalists, such as Benoît de Maillet, produced theories that maintained that the universe, the Earth, and life, had developed mechanically, without divine guidance. In contrast, most contemporary theories of evolution, such of those of Gottfried Leibniz and Johann Gottfried Herder, regarded evolution as a fundamentally spiritual process. In 1751, Pierre Louis Maupertuis veered toward more materialist ground. He wrote of natural modifications occurring during reproduction and accumulating over the course of many generations, producing races and even new species, a description that anticipated in general terms the concept of natural selection. Maupertuis' ideas were in opposition to the influence of early taxonomists like John Ray. In the late 17th century, Ray had given the first formal definition of a biological species, which he described as being characterized by essential unchanging features, and stated the seed of one species could never give rise to another. The ideas of Ray and other 17th-century taxonomists were influenced by natural theology and the argument from design. The word evolution (from the Latin evolutio, meaning "to unroll like a scroll") was initially used to refer to embryological development; its first use in relation to development of species came in 1762, when Charles Bonnet used it for his concept of "pre-formation," in which females carried a miniature form of all future generations. The term gradually gained a more general meaning of growth or progressive development. Later in the 18th century, the French philosopher Georges-Louis Leclerc, Comte de Buffon, one of the leading naturalists of the time, suggested that what most people referred to as species were really just well-marked varieties, modified from an original form by environmental factors. For example, he believed that lions, tigers, leopards, and house cats might all have a common ancestor. He further speculated that the 200 or so species of mammals then known might have descended from as few as 38 original animal forms. Buffon's evolutionary ideas were limited; he believed each of the original forms had arisen through spontaneous generation and that each was shaped by "internal moulds" that limited the amount of change. Buffon's works, Histoire naturelle (1749–1789) and Époques de la nature (1778), containing well-developed theories about a completely materialistic origin for the Earth and his ideas questioning the fixity of species, were extremely influential. Another French philosopher, Denis Diderot, also wrote that living things might have first arisen through spontaneous generation, and that species were always changing through a constant process of experiment where new forms arose and survived or not based on trial and error; an idea that can be considered a partial anticipation of natural selection. Between 1767 and 1792, James Burnett, Lord Monboddo, included in his writings not only the concept that man had descended from primates, but also that, in response to the environment, creatures had found methods of transforming their characteristics over long time intervals. Charles Darwin's grandfather, Erasmus Darwin, published Zoonomia (1794–1796) which suggested that "all warm-blooded animals have arisen from one living filament." In his poem Temple of Nature (1803), he described the rise of life from minute organisms living in mud to all of its modern diversity.
Early 19th century
Paleontology and geology
In 1796, Georges Cuvier published his findings on the differences between living elephants and those found in the fossil record. His analysis identified mammoths and mastodons as distinct species, different from any living animal, and effectively ended a long-running debate over whether a species could become extinct. In 1788, James Hutton described gradual geological processes operating continuously over deep time. In the 1790s, 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, in 1811, Cuvier and Alexandre Brongniart published an influential study of the geologic history of the region around Paris, based on the stratigraphic succession of rock layers. These works helped establish the antiquity of the Earth. 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 during 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 of each: the Paleozoic, dominated by marine invertebrates and fish, the Mesozoic, the age of reptiles, and the current Cenozoic age of mammals. This progressive picture of the history of life was accepted even by conservative English geologists like Adam Sedgwick and William Buckland; however, like Cuvier, they attributed the progression to repeated catastrophic episodes of extinction followed by new episodes of creation. Unlike Cuvier, Buckland and some other advocates of natural theology among British geologists made efforts to explicitly link the last catastrophic episode proposed by Cuvier to the biblical flood. From 1830 to 1833, geologist Charles Lyell published his multi-volume work Principles of Geology, which, building on Hutton's ideas, advocated a uniformitarian alternative to the catastrophic theory of geology. Lyell claimed that, rather than being the products of cataclysmic (and possibly supernatural) events, the geologic features of the Earth are better explained as the result of the same gradual geologic forces observable in the present day—but acting over immensely long periods of time. Although Lyell opposed evolutionary ideas (even questioning the consensus that the fossil record demonstrates a true progression), his concept that the Earth was shaped by forces working gradually over an extended period, and the immense age of the Earth assumed by his theories, would strongly influence future evolutionary thinkers such as Charles Darwin.
Transmutation of species
Jean-Baptiste Lamarck proposed, in his Philosophie zoologique of 1809, a theory of the transmutation of species (transformisme). Lamarck did not believe that all living things shared a common ancestor but rather that simple forms of life were created continuously by spontaneous generation. He also believed that an innate life force drove species to become more complex over time, advancing up a linear ladder of complexity that was related to the great chain of being. Lamarck recognized that species adapted to their environment. He explained this by saying that the same innate force driving increasing complexity caused the organs of an animal (or a plant) to change based on the use or disuse of those organs, just as exercise affects muscles. He argued that these changes would be inherited by the next generation and produce slow adaptation to the environment. It was this secondary mechanism of adaptation through the inheritance of acquired characteristics that would become known as Lamarckism and would influence discussions of evolution into the 20th century. A radical British school of comparative anatomy that included the anatomist Robert Edmond Grant was closely in touch with Lamarck's French school of Transformationism. One of the French scientists who influenced Grant was the anatomist Étienne Geoffroy Saint-Hilaire, whose ideas on the unity of various animal body plans and the homology of certain anatomical structures would be widely influential and lead to intense debate with his colleague Georges Cuvier. Grant became an authority on the anatomy and reproduction of marine invertebrates. He developed Lamarck's and Erasmus Darwin's ideas of transmutation and evolutionism, and investigated homology, even proposing that plants and animals had a common evolutionary starting point. As a young student, Charles Darwin joined Grant in investigations of the life cycle of marine animals. In 1826, an anonymous paper, probably written by Robert Jameson, praised Lamarck for explaining how higher animals had "evolved" from the simplest worms; this was the first use of the word "evolved" in a modern sense.
In 1844, the Scottish publisher Robert Chambers anonymously published an extremely controversial but widely read book entitled Vestiges of the Natural History of Creation. This book proposed an evolutionary scenario for the origins of the Solar System and of life on Earth. It claimed that the fossil record showed a progressive ascent of animals, with current animals branching off a main line that leads progressively to humanity. It implied that the transmutations lead to the unfolding of a preordained plan that had been woven into the laws that governed the universe. In this sense it was less completely materialistic than the ideas of radicals like Grant, but its implication that humans were only the last step in the ascent of animal life incensed many conservative thinkers. The high profile of the 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. Ideas about the transmutation of species were associated with the radical materialism of the Enlightenment and were attacked by more conservative thinkers. Cuvier attacked the ideas of Lamarck and Geoffroy, agreeing 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 change in isolation from the others, and argued that the fossil record showed patterns of catastrophic extinctions followed by repopulation, rather than gradual change over time. He also noted that drawings of animals and animal mummies from Egypt, which were thousands of years old, showed no signs of change when compared with modern animals. The strength of Cuvier's arguments and his scientific reputation helped keep transmutational ideas out of the mainstream for decades.
In Great Britain, the philosophy of natural theology remained influential. William Paley's 1802 book Natural Theology with its famous watchmaker analogy had been written at least in part as a response to the transmutational ideas of Erasmus Darwin. Geologists influenced by natural theology, such as Buckland and Sedgwick, made a regular practice of attacking the evolutionary ideas of Lamarck, Grant, and Vestiges. Although Charles Lyell opposed scriptural geology, he also believed in the immutability of species, and in his Principles of Geology, he criticized Lamarck's theories of development. 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 relationships between species could be discerned from developmental patterns in embryology, as well as in the fossil record, but that these relationships represented an underlying pattern of divine thought, with progressive creation leading to increasing complexity and culminating in humanity. Owen developed the idea of "archetypes" in the Divine mind that would produce a sequence of species related by anatomical homologies, such as vertebrate limbs. Owen led a public campaign that successfully marginalized Grant in the scientific community. Darwin would make good use of the homologies analyzed by Owen in his own theory, but the harsh treatment of Grant, and the controversy surrounding Vestiges, showed him the need to ensure that his own ideas were scientifically sound.
Anticipations of natural selection It is possible to look through the history of biology from the ancient Greeks onwards and discover anticipations of almost all of Charles Darwin's key ideas. As an example, Loren Eiseley has found isolated passages written by Buffon suggesting he was almost ready to piece together a theory of natural selection, but states that such anticipations should not be taken out of the full context of the writings or of cultural values of the time which made Darwinian ideas of evolution unthinkable. When Darwin was developing his theory, he investigated selective breeding and was impressed by John Sebright's observation that "A severe winter, or a scarcity of food, by destroying the weak and the unhealthy, has all the good effects of the most skilful selection" so that "the weak and the unhealthy do not live to propagate their infirmities." Darwin was influenced by Charles Lyell's ideas of environmental change causing ecological shifts, leading to what Augustin de Candolle had called a war between competing plant species, competition well described by the botanist William Herbert. Darwin was struck by Thomas Robert Malthus' phrase "struggle for existence" used of warring human tribes. Several writers anticipated evolutionary aspects of Darwin's theory, and in the third edition of On the Origin of Species published in 1861 Darwin named those he knew about in an introductory appendix, An Historical Sketch of the Recent Progress of Opinion on the Origin of Species, which he expanded in later editions. In 1813, William Charles Wells read before the Royal Society essays assuming that there had been evolution of humans, and recognising the principle of natural selection. 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, writing that the paper "An Account of a White Female, part of whose Skin resembles that of a Negro" was published in 1818, and "he distinctly recognises the principle of natural selection, and this is the first recognition which has been indicated; but he applies it only to the races of man, and to certain characters alone." Patrick Matthew wrote in his book On Naval Timber and Arboriculture (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." Darwin implies that he discovered this work after the initial publication of the Origin. In the brief historical sketch that Darwin included in the third edition he says "Unfortunately the view was given by Mr. Matthew very briefly in scattered passages in an Appendix to a work on a different subject ... He clearly saw, however, the full force of the principle of natural selection." However, as historian of science Peter J. Bowler says, "Through a combination of bold theorizing and comprehensive evaluation, Darwin came up with a concept of evolution that was unique for the time." Bowler goes on to say that simple priority alone is not enough to secure a place in the history of science; someone has to develop an idea and convince others of its importance to have a real impact. Thomas Henry Huxley said in his essay on the reception of On the Origin of Species:
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.
Natural selection
The biogeographical patterns Charles Darwin observed in places such as the Galápagos Islands during the second voyage of HMS Beagle caused him to doubt the fixity of species, and in 1837 Darwin started the first of a series of secret notebooks on transmutation. Darwin's observations led him to view transmutation as a process of divergence and branching, rather than the ladder-like progression envisioned by Jean-Baptiste Lamarck and others. In 1838 he read the new sixth edition of An Essay on the Principle of Population, written in the late 18th century by Thomas Robert Malthus. Malthus' idea of population growth leading to a struggle for survival combined with Darwin's knowledge on how breeders selected traits, led to the inception of Darwin's theory of natural selection. Darwin did not publish his ideas on evolution for 20 years. However, he did share them with certain other naturalists and friends, starting with Joseph Dalton Hooker, with whom he discussed his unpublished 1844 essay on natural selection. During this period he used the time he could spare from his other scientific work to slowly refine his ideas and, aware of the intense controversy around transmutation, amass evidence to support them. In September 1854 he began full-time work on writing his book on natural selection. Unlike Darwin, Alfred Russel Wallace, influenced by the book Vestiges of the Natural History of Creation, already suspected that transmutation of species occurred when he began his career as a naturalist. By 1855, hi