Chapter 11 Chapter 6 The Origin of Darwinism-1
In the history of science, no one has received as much attention and criticism as Darwin (for relevant literature, see Loewenberg, 1965; Ruse, 1974; Greene, 1975; Kohn, ed., 1985).In recent decades, Darwin's published works have been reprinted, and historians have edited many of his diaries, notes, and unfinished manuscripts (see References).With the large collection of Darwin's manuscripts in the Cambridge University Library, a large number of historical interpretations have been stimulated.Projects to reprint the complete Darwin correspondence have been initiated (Darwin, 1984, 1986; Burkhardt et al., 1985).It has now been published with annotations (Darwin, 1959b) and with correspondence (Darwin, 1981).Given the amount of material produced by the "Darwin industry" (to borrow Ruth's term), it is difficult to come up with a concise explanation of the origins of Darwinism.The reason for the difficulty is also that relevant historians are unable to reach a fundamental agreement, including disputes over the influence of external factors on the formation of Darwin's thought.
One of the hardest things in explaining Darwin's work is connecting the revolutions it produced in science with Western culture.These two aspects are studied by different historians.Some historians are primarily concerned with the development of science, usually because their original interest was in science.Other historians of ideas may have engaged in a different level of detailed scientific practice, but their real concern was to assess the role of Darwinism in the development of modern thought as a whole.Against these backgrounds, two different views of history and conflicting interpretations of the meaning of Darwin's revolution arise, because these backgrounds represent different values and prejudices.
Historians who study the history of ideas see the revolution in biology as emblematic of a deeper change in Western social values, as the Christian view of man and nature was replaced by materialist ideas.Biologists like to see a revolutionary theory as an expression of this broader movement.Darwinism is often seen as a product of the free-competitive individualism of capitalism typical of the Victorian period, and his theory of choice is seen as an application of this value system to biology.Such insights are important, but pose problems because the issue still affects our sensibilities today. For those who agree with the general decline of dogmatic religion, Darwinism will be enthusiastically supported; but those who do not agree with materialism People who compete endlessly with society may hold a negative attitude towards the development of science.Two prominent modern insights have cast a negative light on Darwinism as a movement and on Darwin himself (Barzun, 1958; Himmelfarb, 1959).Historians who are more concerned with scientific issues have suggested that this view misrepresents Darwin's achievement because it fails to focus on what Darwin was concerned with in the first place.
Scientists, historians don't always see Darwin as a hero.There were complaints about his reluctance to acknowledge the sources of his ideas, and in some cases his actions were accused of plagiarism (Darlington, 1961; Eiseley, 1959).In general, however, historians with a scientific background have taken an overly sympathetic attitude.In their view, Darwin was the ideal researcher, the originator of a solid scientific method whose important concepts still have value in modern biology (De Beer, 1963; Ghiselin, 1969).This attitude is doubly dangerous.It is all too easy to unwittingly read the past using concepts we are now familiar with, and too easily to produce a modern-day Darwinian notion that ignores the confusion of nineteenth-century thought.Moreover, such historians, keen to demonstrate Darwin's method, may find it difficult to acknowledge outside influence in the creation of Darwin's theory.
If "internal historians" failed to see the extensive influence of Darwinism, then "external historians" may have paid too much attention to the influence of culture and neglected scientific issues.Fortunately, there are always those who try to avoid both extremes (eg, Eiseley, 1958; Greene, 1959a).The time may be approaching for general synthesis, and a great deal of work that has hitherto not been done is about to begin.Darwin was a naturalist, and one cannot really understand him without taking this into account.But when a scientist is formulating hypotheses that need to be tested by facts, he may be influenced by various influences. His thinking may be consciously or unconsciously influenced by philosophical or social concepts.Whether the impact produced can have a large impact depends on the response of the scientific community and society at large.
A more serious problem is historical causality.Studies by foreign historians clearly tend to imply that scientific details are not critical in determining events.Such research readily assumes that as the materialistic component of culture increases, scientists naturally employ this new value in their interpretation of nature.In the mind of the scientist, the ideology of the social group to which he belongs is reflected and a worldview is created to justify this ideology (eg, Young, 1969, 1971a, 1973, 1985).The scientist is thus a puppet in the hands of the forces of history, who can only create details in his work.The idea of evolution by natural selection must have been "at hand" in the mid-nineteenth century, waiting for someone to flesh out the details so that the scientific community could recognize it.From this point of view there is no doubt found a second naturalist, Alfred Russell Wallace, who arrived at the theory independently of Darwin.This coincidence reveals that, to a large extent, cultural pressure steers scientists in a certain direction.
It is too easy for internal historians to go to the other extreme and see Darwin as a great hero whose insights finally revealed the true structure of nature.By acknowledging that religious pressures created an atmosphere in which to engage in this kind of research, the internal historian's view emphasized the objectivity of the scientific method as a means to the acquisition of genuine knowledge.It was Darwin who did the research that allowed him to pull all the facts together, so it is sheer nonsense to think he was influenced by ideological factors.If another naturalist arrives at the same thought, it can only show that the way to the truth is open to all.This great thought, once published, does its work, even if the world is convinced that the scientific way of seeing things is much better than any outdated religious view.
Between the two extremes, however, other views are possible.Even the most convincing exponents of the sociology of knowledge will probably admit that scientists, like social theorists, have key insights that transform an ideology into a coherent worldview.Perhaps Darwin was ahead of his contemporaries in trying to create a new kind of materialism, and then, in this case, it's important to know exactly why he did it that way.Conversely, internal history theorists should admit that there are cultural influences in the formation of a scientific hypothesis, although the ultimate success is achieved by science.By acknowledging that Darwin's creativity was influenced by the cultural developments of his time, we can take a balanced view of the revolution he unleashed.From this point of view, we can see that everywhere is not affected by this revolution.We can show that Darwin followed a path that none of his contemporaries followed.One might therefore think that the subsequent history of biology, and thought in the West, would have been very different had Darwin died on the voyage of the Beagle.This means that it should not be considered that the scientific details of his research are not insignificant in the development of the whole event, but in fact these research details are an integral part of the development of events in which all other factors are included.
To paint a balanced picture of Darwin's work, the following questions must be considered (for a more detailed analysis, see Oldroyd, 1984):
1. There are two most important features of Darwin's theory, namely its utilitarianism and the use of "group thinking" to replace the original belief that species are shaped according to the type of ideas.It is utilitarian considerations that see adaptation as the only evolutionary drive, that there is no ultimate purpose but a day-to-day check to ensure that those with a useful shape survive.To what extent does this view reflect the utilitarianism of the economic theory of free competition?Likewise, did Darwin's view of species as groups of divergent individuals reflect the individualism of this economic theory?Does his use of competition as a mechanism of selection suggest that the theory is shaped by the brutal ethic of Victorian capitalism?These issues were characteristic of the old inner-historians and outer-historians debate outlined above, and were discussed on the basis of entirely circumstantial evidence.Now more and more people recognize the direct influence of external sources, and the study of Darwin's unpublished articles shows the degree of philosophy and political economy he read.The essays also show the extent to which his biological forays shaped his thinking, with some evidence that a more comprehensive interpretation began to emerge.Therefore, Schweber (1977) believes that Adam Smith's economics has played a great role in Darwin's proposal that the behavior of individuals will have a purposeful mechanism, but he admits that Darwin's biological thinking has already The theory that convinced him of success took into account individual differences.
2. There is considerable disagreement regarding Darwin's religious views and his swift abandonment of the traditional belief that nature was designed by a benevolent God (Brooke, 1985).Many historians of Darwin's early writings believe that by 1838 he had recognized the materialist implications of his theory (Schweber, 1979).It was in this regard that Darwin was skeptical of reconciling natural selection with a watered down natural theology.Many people who have commented on his work have pointed out that his reference to the "purpose" of natural law can be interpreted as either a deliberate idea or an attempt to hide all aspects of his theory from his wife or colleagues. meaning.To understand his position one must either explain how he cut ties with his own cultural milieu on this issue to arrive at such a radical view, or one must point to hitherto unrecognized environmental factors It is possible to promote a very radical view.A thorough reading of Darwin's writings is therefore important (Manier, 1978).A minority disagreed, convinced that Darwin did not immediately become a materialist (Gillespie, 1979; Ospovat, 1981), and that he continued to do so by making the crude point that the aim was to ensure The long-term benefit of each species and the progress of life as a whole is in the view of reconciling natural selection with [God's] design towards higher types.Ospervent points out that the early types of Darwinian theory, because of this influence, differ from the mature views he publishes in .Even these historians admit that, in fact, Darwin gradually discovered the implications in his theory, and he grew disgusted at the prospect of harmony with natural theology.The strength of their explanation is that Darwin's break with the common views of his day was not considered sudden; thus he is portrayed as an ordinary man who came to realize the full implications of the scientific theories he advanced.
3. What exactly was Darwin's scientific method?At one point he was portrayed as a simple observer of nature.Those who oppose the theory of choice think that he has no profound thoughts, while those who support the theory of choice insist that he is guided by the facts and goes to the interpretation of the truth without hesitation.Darwin encouraged this "patient observer" imagination later in life, because in doing so, he helped bring his discoveries closer to the scientific standards of his day.We now know that he was not a simple fact-gatherer.Not only was he well acquainted with the scientific literature of the time, but he also read extensively in philosophy and social theory as a means of grasping the results of his new theories.Ghiselin (1969) shows that some unrelated research on Darwin led him to discover that Darwin actually tested the case for evolution, following the claim that Darwin was essentially a modern follower of the hypothetical-deductive approach.In the early years of evolutionary discovery, we find that Darwin's path to natural selection involved a complex and highly creative process in which different ideas were synthesized and tested (Gruber, 1974).The discussion of scientific method at that time undoubtedly had a deep influence on him, and he tried his best to meet the requirements of a good theory.
4. Finally, some debate centers on what scientific factors determined Darwin's thinking.Traditionally, it is believed that the key influences were (a) following the course of the Beagle and discovering the Galapagos warblers, (b) his acceptance of Ryle's uniformist geology, and (c) An analogy to the selection process for artificial breeders.Recent research suggests that these effects need to be re-examined, and questions have been raised about Darwin's own interpretation of the findings in his autobiography.Among Darwin's many influences, Darwin's early literature records even Ryle's influence as insignificant, while Sulloway (1982a) studies the myth of the Galapagos warbler.Some historians have even disputed the role of artificial selection, arguing that Darwin may not have arrived at his theory by analogy (Limo ges, 1970; Herbert, 1971).There is little doubt that Darwin's unique combination of biogeography and the study of animal reproduction helped him to develop his radical view of evolution as an adaptive, open process.Recent research, however, suggests that he was confined to contemporary interest in sexual reproduction as a source of variation in addressing these seemingly 'modern' issues (Hodge, 1985).Thus, his thinking was deeply rooted in an older (by modern standards) non-Darwinian view of nature.The idea of natural selection does not imply a complete break with the past, some radical elements of which may have been present earlier.It can now be argued that Darwin's failure to anticipate Mendelian genetics was the result of his deep involvement with pre-Mendelian views of sexual reproduction.
Darwin: Education and sailing on the Beagle
Charles Robert Darwin was born in 1809.His father was a successful doctor, his mother came from the Wedgwood family of famous pottery merchants; and his grandfather was Erasmus Darwin, author of "The Law of Biology".In his autobiography (the original version was truncated by F. Darwin, 1887; for the full version, see Darwin, 1958), although he admits that he was interested in natural history at an early age, he does not say that he is a good scholar .Darwin was sent to the University of Edinburgh to continue the family tradition of studying medicine, but he felt sick before the operating table and soon gave up his plans to study medicine.The family decided that he should seek a formal position in the church, and he entered Christ's College, Cambridge in late 1827 to this end.
His real intellectual origins are usually traced from his Cambridge years: he read Paley's Natural Theology, he came into contact with the botanist John Henslow and the geologist Adam Sedgwick .Yet earlier influences can be seen in his notes (Hodge, 1985).It would be absurd to think that Darwin derived his theories from his grandfather, or was influenced by the Lamarckism described by Robert Grant in Edinburgh.These early encounters with the last remnants of the Enlightenment's speculative approach to studying nature may have brought to his attention what happened (sexual reproduction).This may have had an impact on his early ideas about species, and directly forged his own theory of heredity, pangenesis.The atmosphere at home and in Edinburgh exposed him to the Radical tradition of thought, and from this it can be explained that, for him, the orthodox influence at Cambridge was shallower by comparison.
Darwin's decision to be educated by the official priests was neither fanaticism nor hypocrisy, when he still accepted the literal interpretation of the Bible and was determined to follow Paley's reasoning.He was delighted to see Paley used as an accommodating example of God's wisdom and goodness.His focus on the meaning of adaptation in nature led him naturally toward the utilitarian school of thought (Cannon, 1961a).A few years later, Darwin would reverse the logic of Paley's proof.In Paley's view, adaptation is a fixed state, according to supernatural design, which can explain the connection between structure and function in adaptation.For Darwin, adaptation was the process by which a species adjusts to changes in its environment by means of purely natural means.According to this variable pattern, adaptation became a central feature of the theory of selection, although Darwin's awareness of the complexity of evolution led him to fail to insist that every structure in every species must have developed for utilitarian purposes .
Darwin received a comprehensive scientific training at Cambridge, but this training came outside the curriculum.He developed a close relationship with Henslow, and Sedgwick took him on a geological trip to Wales in 1831 (Barrett, 1974).Darwin clearly absorbed Sedgwick's theory of cataclysm, although later Darwin's views underwent major changes.He had read Alexander von Humboldt's account of his travels to various parts of the world (Humboldt, 1814-1829), and had longed to study natural history in the tropics.Towards the end of 1831, an opportunity arose.The British Navy sent a small ship, the Beagle, to survey the oceans of South America.The ship's captain, Robert Fitzroy, needed a gentleman to take the tedium out of the voyage, and in compensation he invited a naturalist so he could also describe the places he had visited (Gruber , 1968; Burstyn, 1975).After being recommended by others, Darwin obtained this position. After dispelling the concerns of his family and Fitzroy, he went to sea for five years of voyage discovery (Darwin, 1839, 1845, 1933; Barlow, 1946; Moorehead, 1969; Keynes, 1979).
While his fellow shipmates explored the South American coast, Darwin traveled the vast interior of South America.He thus acquired a wealth of information which changed his outlook on the whole of geology and natural history.At the beginning of this voyage he had acquired the first volume of Ryle's Principles of Geology, and the second volume while in South America.Darwin's observations of geological phenomena in South America that matched Ryle's ideas soon led him to believe in uniformity.The only thing Darwin could not accept was Ryle's utterly static worldview.Although he is not a simple progressist, he does not doubt that the biological history of the entire earth has a direction.The class of vertebrates appeared successively over time, and based on this phenomenon, a certain theory of evolution can be established.Darwin, however, found that there was much support for Ryle's view that the surface features were formed by natural causes to the extent they are today.He thus becomes a uniformist in the modern sense, not a Lyleian.
The most profound evidence for Darwin is that earthquakes can cause permanent effects on the land surface.He witnessed first-hand the effects of the 1835 Concepignon, Chile, earthquake, and noted that the adjacent coastline had risen 10 feet at the same time.Even more amazing, shells can be found in some of the rising beaches above sea level in coastal areas.Darwin found that Tertiary shell fossils were very similar to extant species, but the fossils were covered with very thick rocks, indicating that these fossils had been brought to great depths.Clearly Ryle was right: Earthquakes not only shake the land, but they can lift it up and down a lot.Over long periods of such movement, large-scale effects can be produced, such as the formation of mountains.Darwin continued to use Ryle's idea of a gradual uplift and sinking of the Earth's surface in creative ways.He developed a successful theory of coral reefs based on the gradual sinking of the Pacific Ocean floor (Darwin, 1842).He was less fortunate in explaining the curious formation of the famous Glen Roy Parallel Road in Scotland (Rudwick, 1974b).
Darwin also discovered a large number of vertebrate fossils during his expeditions, including giant relatives of modern armadillos, sloths and llamas.The resemblance between extinct and modern types suggests that there was continuity in the development of South American organisms.In order to explain this fact, Darwin later proposed the "law of type alternation", arguing that in the course of geological history, the animals living in a specific area are similar.This law differs from other theories of transformation in which life is forced to climb the predetermined ladder of creation, such as Chambers' Traces of Natural Creation History.When Darwin formulated his theory, he had to think of each group as "branching" separately along its own specific path, and even within each group there could be further branching, because the smaller modern Organisms cannot have evolved directly from their giant ancestors.This larger type should be considered a modern extinct offshoot of the taxon's evolution, while other branches continued to evolve into smaller modern types.Darwin's theory should therefore be viewed as a theory of branching rather than linear development.What other naturalists recognized in the 1850s, Darwin had accepted in the 1830s.
Figure 18. Darwin's theory of coral reefs. Corals are formed by tiny sea creatures that can only live in relatively shallow water.Darwin's theory proposes that coral reefs form in areas of land subsidence, because only in this environment can corals form large colonies in the same area as the original land.The subsidence of the land must be relatively slow, so that the coral will not sink to the deep sea and die.In the top image, an island emerges from the sea level, and corals are beginning to form along the coast of the island (the darker part).As the islands sank, the sea level appeared to rise gradually, but the coral continued to grow, approaching sea level, and eventually forming a lagoon around the site where the original island sank.Eventually the whole island sank, but the coral continued to grow, outcropping the sea level and forming a coral reef surrounding an empty lagoon—the atoll (taken from Darwin, 1842).
Fossils are important clues, but the evidence that actually convinced Darwin of the transformation came from his studies of the geographical distribution of species (Sulloway, 1982b).Darwin noticed this problem while reading Humboldt and Ryle, but his observations during the voyage with Beagle were the key factor.Darwin first noticed that the distribution of living things could be explained by combining the theory of evolution with the study of how species migrated around the world.The resulting new research in biogeography and ecology formed a unique framework within which he formulated his theory.
Natural theology once gave a simple explanation of the geographical distribution of living things.Due to the design of the Creator, each species lives in a certain area.But this line of thinking doesn't touch on the complexity that Darwin recognized.For example, he discovered a new flightless bird from South America, the rhea.He had become familiar with the common rhea when he explored the open Patagonia, but he didn't realize it was a new species until he cooked and ate it at parties.Once this new form was established, the question arose: Why, in some indeterminate places on this plain, did the common rhea become a new species?There is no sharp boundary between the domains of the two ostrich species, and the species apparently lives in a middle ground in symbiosis with the others.Even if one imagined that species with this type of life were created to adapt to slightly different environmental conditions, they would obviously compete with other species in the middle ground.Darwin had to abandon the old concept of ecological balance and recognize a less optimistic view: species often compete with competitors to occupy territory.
Humboldt had already raised the need to study the factors that limit the number of species populations in a given area (Vorzimmer, 1965; Egerton, 1970a).Ryle made a greater contribution to the establishment of the modern ecological point of view (Egerton, 1968).The old, static, harmoniously designed idea of natural balance is being replaced by the ecological notion of a "niche," according to which each species has its own environment.Ryle found that because of geographic factors and assumed environmental conditions that must have changed over time due to geologic activity, the environment over large areas could not remain uniform.Thus species will not be perfectly adapted to a single environmental condition, nor will a group of species living in a given area form a perfectly harmonious system.As Darwin himself recognized, a given species must have been adapted to an environment in one place, and a competing species not far away, with a slightly different type of life, might have its advantage.At the intersection of the two, the two types will fight for occupying the areas open to them.Ryle cites the botanist Alphonse Condor to illustrate the effect of warfare between all species in a given area.Long-term climate change may have a long-term impact on the balance of power in this region, even causing the extinction of unfavorable species (Kinch, 1980).
It was not easy to find situations where one species was replaced by another in one place, as Darwin had discovered with the rhea.Some gradual changes in environmental conditions are supposed to be beneficial to one species and unfavorable to others.But it is believed that the competition to occupy as many areas as possible determined Darwin's later attitude.He came to this view perhaps inspired by what he saw how land-hungry Europeans wiped out South American Indians.The influence of this social situation of the time clearly shows perhaps the most important aspect of this new conception of struggle.The fiercest competition in nature is not between species and food supplies, or between species and predators.The fiercest competition occurs between a species and its closest ecologically related competitors, that is, with neighboring (or immigrated) forms of similar life-types which, if changed in environmental conditions, gain some advantage If not, it will kill competing species.
It is often assumed that nineteenth-century Europeans were fascinated by the idea of competition (Gale, 1972).If we are to understand the role of the various concepts of struggle in Darwin's theory, we must distinguish these concepts.When Lord Alfred Tennyson wrote "Nature, stained tooth and claw" in "Remembrance," he was certainly challenging traditional views of natural theology.The implication of his words is to acknowledge that struggle is an integral part of nature, rather than to understand something rationally in order to maintain the belief that there is a benevolent God.This view represents an important change in the climate of thought which may help naturalists to speculate along new lines of thought, but which is only an indirect clue to the origins of Darwinism, since this Thoughts only focus on the relationship between predator and prey.A lion killing a zebra is "staining its teeth and claws red", but a zebra eating grass is also predation, although no one worries about cruelty to grass.What's more, Tennyson's words did not reflect the ecological competition that Darwin had absorbed from Ryle and his experiences in South America.Rivalry between contenders is truly ruthless, with the penalty of extinction for the loser, yet it can also take place without bloodshed.The recognition that nature and society may be based on struggle rather than harmony became an important basis for natural history change.But naturalists like Ryle and Darwin had to change the atmosphere, and they took a constructive approach to addressing issues such as the geographic distribution of living things.It is impossible for them to simply borrow metaphors from poetry and apply them directly to their interpretations of nature.
An ecology based on struggle presumably became an important part of Darwin's attitude, but this ecology does not provide direct evidence of transformation, it does not provide the exact concept of struggle that Darwin would later use as the driving force of natural selection .Although Ryle recognized the disruption of the balance of nature, he still believed that species are fixed and therefore doomed to extinction under the influence of environmental change.What Ryle doesn't realize is that what Condor calls "war in nature" can be used within each species, where individuals are chosen through struggle and only the most capable adapt to change.
Ultimately, Darwin became convinced that evolution occurred by studying how physical barriers such as oceans affected the geographic distribution of species.He was troubled by the fact that rheas and African ostriches, for example, were markedly different even though they were both adapted to a similar life in the open savannah.Why do continents like South America and Africa have distinct populations?If adaptation were only the work of God, one would expect him to create the same species in all regions with the same environmental conditions.Ryle proposed that the seas were a barrier, limiting the migration of species, so that each continent was inhabited by its own "creative centers" of characteristic types; but Darwin needed to find a natural explanation for why populations differed in the original regions.Eventually, he realized that evolution would actually explain the phenomenon.Once a continent is isolated from the rest of the world, there is little force that can cause life on that continent to evolve along the same lines as life in other parts of the world.They must have adapted to changing environments in their own unique way, and thus eventually acquired unique characteristics that differed from organisms in other regions.
It is the study of the isolated islands, is God endowing these islands with unique flora and fauna through different miracles?Or did the flora and fauna on the islands migrate across the sea from neighboring continents?The fact that the island's flora and fauna populations were similar to those on the nearest continent suggests the latter possibility.In order to confirm this, Darwin later spent a long time studying the dispersal mechanism of animals and plants, showing that species can sometimes span wide oceans.Birds may fly with stormy winds, other animals may float at sea on raft-like plants, and by such accidents eventually there will be populations of flora and fauna on distant islands.But the real problem emerges when it is realized that species isolated on islands are not the same as those on the nearest mainland, but only related.An isolated species, once separated from its original form, undergoes a transformational change of some sort.
It has been confirmed that Darwin's experience in the Galapagos Islands was crucial.This group of volcanic islands lies hundreds of miles off the Pacific coast of South America and straddles the equator.The Beagle made several visits so Darwin could collect specimens from different islands, but Darwin didn't realize the real problem until he left: he learned that the locals could identify the island a turtle belonged to by its shell.As he sailed home he had been pondering this curious fact, wondering if it had any general significance.Ever since David Lack (1947) studied "Darwin's warblers", it has been suggested that these birds in particular were the key inspiration for his belief in divergent evolution under conditions of geographical isolation.On this view, Darwin realized that when the South American warblers were isolated on the various islands of the Galapagos, populations of warblers from the original species must have become distinct species.Each group has adapted to its new environment and has a different life type, resulting in the evolution of a distinctive beak shape.Eventually, the differences between groups become so great that each group becomes a distinct species.
Now Sulloway (1982a) has shown that the Galapagos warbler did not play such a pivotal role in the formation of Darwin's thought.While the Galapagos warbler is indeed an excellent example of speciation, the real situation was so complicated that Darwin didn't immediately recognize what was going on.In fact, the structure of the warblers' beaks is so distinct that Darwin did not realize that they were closely related when he collected them.It was Zoological Society ornithologist John Gould who correctly identified the warblers as a closely related group after the Beagle returned.Needless to say, recognizing the significance of geographical isolation, Darwin even failed to label his specimens from which island they were collected.Once he was convinced of the truth of evolution, he had to reconstruct the history of these warblers from other collections.即使这时，他还是打算简化事情，因为事实上已经不能确定这些莺鸟所属的岛屿。由于不能在现代的南美找到假设的莺鸟祖先，要搞清楚这个案例的意义就更困难了。
进化的线索来自加拉帕格斯群岛的嘲鸫，因为达尔文本人可以识别出有些嘲鸫物种与美洲的类型有明显的相似。一旦他确信加拉帕格斯群岛上相似的类型不仅是单一物种的变种，而且是一群特征明显（但是密切相关）的物种，达尔文便陷入困惑之中。设想每一个岛上特有的类型都是造物主的产物显然是不合理的，因为造物主没有充分的理由在每一个岛上形成一种独特的物种。而相信原产南美的类型迁到群岛，并在各个岛上沿着不同的方向进化，要合理得多。由于缺乏原先常见的竞争者，又具有各种生态位，每一个群体采用特化的不同生命方式而适应环境。然而接受这一点，对于达尔文来说是必要的，因为他得承认适应新环境条件不仅意味着产生出变种，而且要产生出全新的物种，这些新种之间，以及新种与原先物种类型之间，不能相互配育。
关键岁月：1836年—1839年
1836年10月贝格尔号抵达伦敦。在第二年的3月，达尔文寄宿在伦敦，开始经历了他后来所描述的他一生中最忙碌的两年。他在地质学会阅读论文，并参加了首都的科学活动（Rudwick，1982），同时他在思考他在航海期间的发现，特别是在加拉帕格斯群岛上的发现。不时有人提出，达尔文在航海的最后阶段已经接受了物种转变的观点。然而多数现代的史学家相信他回到英国后思想才发生转变，尤其是在1837年3月到7月之间。迈尔（Mayr，1977）称这是达尔文的第一次革命：在这期间，达尔文已经接受物种的形成是自然过程的思想，但是并没有发现变化的实际机制。又经过了一年，他在几本笔记中记下了他关于物种转变的可能性及其含义的思想（现在已经发表：Darwin，1960-61，1967，1974，1979；全本，1987）。1838年9月他在阅读马尔萨斯关于人口的论述时，最终导致他将自然选择的观点汇总到一起，由此出发，他根据自己全新的理论对自然史重新作出了综合的解释。
达尔文后来在自传中对导致他的发现的事件作了描述，不过近来一些学者已经表明，应该根据他的笔记重新认识他发现的历程。达尔文在自传中暗示，他的发现是以传统的培根式归纳方法收集事实开始的，他随机地收集事实，以期最后一个图景可以显现出来。我们现在知道他的思想中早已有了一些假说，而且经过了各种尝试，才找到成功的假说。达尔文在自传中还宣称，他是通过对动物驯养的研究得出选择思想的。然后他探索这种选择活动的自然平衡，并且在群体压力导致的生存斗争中找到了。一些现代的研究提出，达尔文在自传中极大地夸大了人工选择所起到过的作用，甚至那些承认人工选择起到过重要作用的人也同意，这个发现的过程绝不是简单的。马尔萨斯的人口原理到底起了什么作用也存在着争议，有人认为它是关键的见解，有人却认为那只是近乎完成的演绎的最后一步。
正如迈尔（Mayr，1977）所指出的，在尝试重建达尔文思想过程中有两种方式。一是通过对自然选择论据的逻辑分析，以确定达尔文在将这样一种新的、激进的概念汇总中，到底哪一步是至关重要的。另一种方式是研究达尔文的笔记本身，以确定当时对达尔文留下最深印象的是什么，以及他是如何利用所获取的信息。第一种方式的用途在于我们可以看出最终产生的这个理论的结构，及其关于自然的基本假定。关于这一发现的正统故事，可以确立这个发现的概念基础，不过这种抽象的解释未能认识到达尔文在其笔记中记载的实际思想的极大复杂性，而且使我们不能认识到对他思想形成的多元影响。因此，我们学习的第二个时期必须了解最近的学术成果，这些成果基于对达尔文产生自然选择思想过程的实际细节的认识。
现在有一件事情已经清楚了：达尔文的自然选择思想并不是从早期学者那里借用而来的。有些学者被誉为率先发现了自然选择，主要是威廉·查尔斯·威尔斯，帕特里克·马修和爱德华·布莱奇（Eiseley，1959；McKinney，ed.，1971；Wells，1973a，1973b；Bedda ll，1972，1973；Schwartz，1974）。达尔文的笔记证实，事实上这些来源对他并没有关键性的影响，因而这些所谓的选择论的先驱是否预先设计到达尔文理论的真正精神，是值得怀疑的。
我们先来看一下自然选择所依据的基本论据的轮廓。尽管达尔文后来的著作中具有散漫的特征，但是这个理论确实建立在关于自然设想的一个坚实的逻辑结构上（Ruse，1971b ）。或许其中最重要的基础是，对生物学的物种到底是什么有了一个新的解释。达尔文率先提出了迈尔所称的“群体思想”，以取代旧的类型学的物种观。这种群体思想是要将物种看成是由独特个体组成的群体，事实上这些个体之间具有潜在的相互配育的能力。物种是群体，组成这个群体的个体之间，存在着一定的物理结构上的变异。物种并不是由理念类型限定的，并非其中的个体是按照理念类型的模式塑造的。变异并非理念类型的轻微干扰，而是群体、乃至物种的本质特征发生变化。假如外界条件有利于群体的某些个体，而不利于该群体的其他个体，那么这个群体的平均性质就会发生改变，当然，整个物种也要发生改变。
第二个主要的因素是合适的遗传概念。个体一定要能够将它独特的性状传递给后代。达尔文早期对拉马克主义的兴趣表明，他愿意承认现在说白了的“软”遗传：即相信亲本因外界原因造成的变化可以传递给后代。但是假如环境可以控制遗传，那么就不会有什么个体变异，因为一个群体中的所有成员都要经受同样的影响。为了使选择学说更能站得住脚，达尔文不得不放弃“软”遗传，赞成“硬”遗传：即相信后代从亲本继承的物质并不受外界的影响，而只取决于它从亲本中继承了什么。这样个体变异便有了更深的意义，从而使得达尔文可以认识到是如何通过淘汰遗传所保留的一定种类的变异而改变了群体。
达尔文在尽力了解动植物的可变性时，开始从动物驯养者和园艺师那里收集了大量的信息。他感兴趣的是自然状况下的变异。作为赖尔的追随者，为了要研究过去生命的发展，他必然要转而研究可以在今天观察到的生物变化。动植物驯养提供了研究变异效应的实验途径。但是首先由动植物驯养者发现可变性和硬遗传的意义并非出于偶然，他们知道要获得成功的品种，就必须通过选择控制可变性和硬遗传的因素。达尔文经常通过与人工选择进行类比来说明自然选择。驯养者从他所饲养的种群中，挑选出那些具有他所需要的性状的个体，并且单独通过这种个体来繁殖下一代。因此他将所需的性状隔离开，并且按照同样的方向选择进一步的变异，这样就会使后代发生改善。
这种类比唯一的问题是，必须在自然中找到某些可以代替动物驯养者所经常选择使用的因素。达尔文最终对于生存斗争来充当这样的角色很满意，通过生存斗争可以挑选出最适应环境的个体。这样就可以对适应进化作出自然的解释，而不用援引神的监督。达尔文从马尔萨斯的人口原理中，推导出斗争的选择力量，结合了观察到的任何物种的群体必须多少保持数量恒定这个事实。马尔萨斯的原理表明，任何物种的数量都具有按照指数速率增长的潜力。然而，观察和常识告诉我们，野生物种的群体不可能年年都有明显的增长，因为自然界中食物的供给是有限的。每一代中出生的个体都会提前死去，因为可以获得的资源供应并不能满足群体潜在增长的需求。根据这一点，达尔文推导出在自然中一定存在永久的生存斗争，因为个体之间要通过竞争从有限的食物供给中获得食物以维持生存和繁衍。
将这些观点汇总在一起，自然选择的论据便显现出来。如果个体存在一定程度的变异，那么显然有些个体就会在生存斗争表现得更出色，而且会通过繁殖，将它们获得的优势性状传递下去。我们可以通过重新说明拉马克的著名的长颈鹿进化出长颈一取食树叶例子，来发展这个论点。在原来食草长颈鹿群体中，有些长颈鹿偶尔具有了比一般颈要长的颈，有些则更短。当草消失后，那些具有长颈的个体更容易获得树上的叶子；这样它们就可以更有效地开发替代的食源，它们就会更健康，会比较容易地繁衍；它们的后代数就会更多，而且遗传了比较长的颈。反之，那些颈较短的个体获得的食物就少，而且不会轻易地繁殖；严重的情况下还会饿死，尽管整个机制需要的是生殖速率上的差异。这样，在后代中，来源于长颈亲本的个体数量，要多于来源于短颈亲本的个体；由于通过遗传保留了这种性状，在群体中，颈的平均长度会增加。如果在以后的世代中继续有变异，选择的过程也将继续，最终使物种发生了明显的变化，比如出现现代长颈鹿的长颈。
选择的论点大致比较清楚了，但是正如上面所指出的那样，还没有提到达尔文主要关注的一个问题：即一个种是如何分成一些“姊妹”种的。而且达尔文的笔记表明，达尔文只是经过了艰难的思想探索后，才得出这种思想的。一旦他开始确信新的物种一定是通过自然的方式来源于原先的物种，他就开始尝试各种假说，以说明这个过程是如何进行的，检查他自己的经验和通过广泛的阅读科学文献获得的信息。同时，他认识到，任何进化学说最终都要用来说明人类，因而他开始广泛研究心理学和社会理论，以努力确保他的观点可以得到广泛的应用。他把阅读政治经济学，包括阅读马尔萨斯的书籍，作为他精心考虑的研究纲领的一部分。为了描述达尔文得出自然选择学说所经历的道路，一项主要的工作就是要确定科学因素和非科学因素对他思想的相对影响。然而，我们首先必须确定达尔文研究这些问题时的心态，特别是他在探讨进化的自然机制时，对于其中的哲学和宗教含义的态度。
由于达尔文原来相信佩利关于设计的论点，所以他一定曾经相信是造物主的作用导致新物种的产生。他随贝格尔号考察的经历使他不再相信奇迹的发生；加拉帕格斯群岛的发现提供了对于简单特创论的一种归谬法。这时他已经相信，是由于自然法则创造和设计了适应新环境的新物种。但是这并非一定意味着他变成了无神论者，或者他一定反对任何设计的概念。许多博物学家依然相信，自然法则本身是设计出来的，从而使上帝的计划可以在物质宇宙中实现。达尔文开始时大概也信奉这个观念；他在最早的一个进化机制假说中设想，变异的产生是对环境要求的直接反映。生物以适应的、进步的方式自动地发生改变，这种观点当然符合变异的法则是由一个仁慈的造物主设计的观点。但是当达尔文相信不存在这种对环境的直接反映，以及生物与它们生居的环境之间一定存在比较粗糙的关系时，他的信念发生了什么变化？
多数研究达尔文笔记的史学家得出结论，达尔文很快认识到，他现在发展的系统将很难（也许不可能）转变法则与由一个仁慈的上帝设计的信念协调起来（Limoges，1970；Gru ber，1974；Schweber，1977；Manier，1978；Brooke，1985）。当他认识到在贝格尔号航行期间获得的生态学见解的充分含义时，沿着这个方向的第一步便迈出了。如果不存在自然的平衡，只是竞争物种之间为了占据同一区域而展开的残酷竞争，那么对于不成功者来说，灭绝就是不可避免的。当达尔文也开始认识到，实质上努力适应环境的随机变种之间的差异生存必然会产生转变，他又一次不得不怀疑一个仁慈的上帝怎么会依赖于这样一个粗糙不协调的过程。个体之间的竞争并不使整个群体受益，因为只有那些有足够运气的生存者，才喜欢进步的结果。无情的选择给出了一种新的、与设计并不协调的决定论，根据这一点，有可能会认为达尔文即使不是一个赤裸裸的、也是一个不可知论的无神论者。顶多他是不断地触及到符合人愿的思想，他曾经表达过一种含糊的希望，认为通过个体之间的斗争，也许会产生出最终的善。
无论是不是无神论者，达尔文从一开始就清楚地认识到，这种新的唯物论具有令人震惊的关于人类地位的含义（Gruber，1974；Herbert，1974，1977）。他开始收集有关心理学和社会问题的信息，目的是要理解如何认为通过自然进化可以产生人类的独特性。最后，他的立场是，人类的本性并非固定不变的，而是通过动物已经拥有的那种自然力的扩展产生的。因此，他阅读政治经济学的文献，并非像他在自传中所说是出于偶然，而是他希望获得有关人类社会进化见解的有意行为。