Chapter 12 Chapter 6 The Origin of Darwinism-2

Why was he able to develop such a radical materialism when his contemporaries still believed in design and the unique spiritual place of man?His family's radical traditions may have helped, since the Darwins had been skeptical of orthodox religion since Erasmus.Recent research has identified exactly what ideas in his extensive reading prompted him to break with the design perspective.Manier (1978) noted similarities between Darwin's view of nature and Wordsworth's pessimism expressed in his poetry in a slightly romantic mood.At critical moments, his solution can be strengthened by exposure to the views of the positivist philosopher Auguste Comte (Manier, 1978; Schweber, 1977).Comte proposed that science could reach its highest state only by abandoning theology, and only by understanding the universe in terms of observable causes.Although Darwin learned of Comte's philosophy through David Brewster's critical comments, it was very helpful for him to break with the idea of ​​design.

Gillespie (1979) and Greene (1981) provided alternative explanations for Darwin's view of religion.According to them, Darwin did not abandon the idea of ​​design, but believed that the Creator worked in less direct and obvious ways.His reference to a higher purpose by natural law through evolution is a true expression of his belief that, despite its apparent crudeness, natural selection acts for the good of all living things.Over time, there will be adaptation, even progress, and the will of the Creator will be fulfilled.Ospovat (1979, 1981) even suggested that, in Darwin's early assumptions, the selection mechanism was clearly intended to lead to a "perfect" state of adaptation, according to which unless new environmental changes occurred, otherwise No further struggle needed.Some scholars have noted that Darwin used the analogy of an "existence" that controls the action of natural selection (Young, 1971a; Manier, 1978).This being takes the place of human tamers in artificial selection, and by using the word Darwin prompts us to think that God has indeed been replaced by natural selection.It is all too easy to see nature as a consciously chosen agent, and therefore as the end of God's will.In his most disturbing moments, Darwin certainly recognized that this was merely an anthropomorphic way of describing the effects of struggle, yet his decision to use this analogy may reflect his inability to escape the influence of the design argument.

Whatever our view on the matter, it is important to note that by the late 1830s Darwin had abandoned the natural theological interpretation that was still accepted by most of his contemporaries.Even if he had believed that selection could be reconciled with the idea of ​​design, his mechanistic explanation meant that it was no longer necessary to use Creator intervention as an explanatory tool.Whether you believe that God is watching all things or not, natural selection works because natural selection only depends on what happens every day, it's a law of natural determinism.In fact, it was the driving force behind Darwin's research to discover a theory that accounted for this property.Early in his research he decided that he wanted to treat the question of the origin of species as a purely scientific question so that it could be answered without directly invoking God's control.The reason why this research led him to the discovery of natural selection was that he tried to find a theory acceptable to the scientific community to solve this problem.Although this view today looks like a natural extension of Ryle's uniformist approach to the biological world, Ryle himself was very reluctant to do so.Indeed, most naturalists at the time believed that some form of superior force had interfered with the normal workings of nature and caused new species to arise, a phenomenon they placed outside the realm of scientific investigation.

Looking closely at Darwin's discoveries, one realizes that he was actually aware that what appeared to be a perfectly scientific method of research had to be followed.Primarily because he expanded science into areas that his contemporaries considered unscientific, he decided to base it on a solid methodology in order to minimize the risk of possible criticism.The reason why he later emphasized that his work was based on fact-gathering was to show that he was not just a guesser, not the kind of person who rushes to random theories without relying on a solid factual basis.The role of theory in science was clearly recognized by debates over scientific method at the time, and Ruse (1975b) has pointed out that Sir J. F. W. Herschel and William Sewell were particularly influential on Darwin. important.Herschel (1830) emphasized a balance between theoretical and experimental work.Sewell pointed out that the status of influential scientific theory is established by its ability to connect research in different fields, such as Newton's universal gravitation.This led Darwin to realize that he needed to expand the explanatory power of his theory, especially when he realized that he did not have a solid understanding of the causes of individual variation.

Gruber has already emphasized Darwin's creativity in exploring the mechanism of transformation (Gruber, 1974).Some of the most original ideas in his thinking arose from his efforts to grasp biogeographical issues (Richardson, 1981; Hodge, 1982).It was Darwin who began to believe that evolution was a branching process, that one species could produce many [different] descendants under the influence of geographical isolation.Grinnell (1974) suggested that Darwin's earliest hypotheses only envisaged speciation by isolation itself alone.But this hypothesis fails to take into account the need for a mechanism for adapting changes to the new circumstances faced by isolated groups.By July 1837, Darwin decided to investigate whether ordinary individual variation, accumulated over many generations, could be the key to evolution.He believed that these variations must be genetic, and to confirm this, he decided to investigate the cause of the variations.

Historians analyzing Darwin's early writings on "genesis" (or reproduction) have found a crucial new insight in his thinking (Kohn, 1980; Hodge, 1985; Sloan, 1985).Of course, it is not denied that some of the most original ideas of his thinking came from his study of biogeography, but it may now be discovered that throughout his academic career he considered evolution as a process by which the environment Linked to the reproductive system of the organisms that make up the group.It was out of these early conjectures that Darwin arrived at his own theory of "heredity" - pangenesis, though this theory was not published until much later.Modern biologists draw a clear distinction between growth and inheritance: evolution is the activity of how new hereditary traits enter populations, and how those traits arise in growing organisms is a secondary concern.Instead, Darwin saw variation as a disturbance in the growth process of living things.He, like many at the time, saw both variation and heredity as functions of the integration of reproduction and growth.Evolution thus evolved as an interaction between the environment and the genesis of new organisms.

As Hodge has pointed out (Hodge, 1985), this view allows us to see a different picture of Darwin's science, one that emphasizes the pre-Mendelian features of his thought.The older generation of historians believed that Darwin failed to discover the law of heredity, but we must now admit that his work was limited by the times, and the division of the entire concept system at that time was completely different from what we have today.It is unlikely to think that Darwin's theory is completely cut off from the old traditions, such as Buffon's study of biological clues to understand the origin of life. Early nineteenth-century conjectures about generation may have also paved the way for Darwin's materialism (Sloan, 1986).For his long-term adherence to "fusion" inheritance, and his inability to completely break with Lamarckism, it must be regarded as a by-product of this pre-Mendelian research on reproduction.In view of the later acceptance of this theory, it may be suggested that Darwin's failure to discard the view that evolution is a purposive process determining the growth of individuals was due to his own faithful belief that growth was the ultimate source of variation .

Strong among the ideas that Darwin developed before arriving at his theory of natural selection was the possibility that new species "come into being" during fixed cycles of life, after which they become extinct .He soon turned to the assumption that due to the influence of external conditions on the reproductive system of individuals, their offspring can adapt to changes in the environment.He also imagined that new habits might affect species (Grinnel, 1985).It is impossible not to think that these ideas may have been influenced by his knowledge of Lamarck.A crucial step in the development of his own theory was taken when he abandoned this view in favor of a less intimate connection between the environment and living things.He never gave up the belief that variation was caused by external conditions disturbing the growth process of individuals, but he soon suggested that most of these changes were random rather than purposeful.

Darwin thus abandoned the idea that individual growth could direct evolution in a purposeful direction, and set out to explore a mechanism for selecting occasional variations that might be useful to organisms.Forced to admit that his investigation of the causes of variation was hampered, he simply acknowledged the existence of random individual differences as observable facts upon which a theory could be built.By calling variation "random," his point implies that not only is the direction of variation uncertain (useful and useless), but also that the cause of variation is impossible to analyze directly.Darwin thus opened up a new avenue of scientific explanation that became characteristic of the late nineteenth century (Merz, 1896-1903).The method of using populations requires acceptance of explanations based on factors that can only be described statistically, without reducing everything to absolute fixed laws.Like the kinetic theory of gases, Darwin's theory also requires that scientists use laws that must appear to be merely the average effect of a large number of individual events, each of which has a cause but is indescribable to a certain level.

Darwin's turn to a hypothesis based on random variation was closely related to his work on animal trainers (Secord, 1981).Through this research, he confirmed his own belief that individual differences are heritable.And he must have recognized that the success of the trainers was due to their ability to pick out those mutations that suited their purposes.Darwin declared in his autobiography that this was central to his exploration of the role of nature in parallel to artificial selection.It has recently been suggested that this type may not be critical, since there are only a few references to the selection process in Darwin's notes (Limoges, 1970; Herbert, 1971).In this view, Darwin only later found artificial selection a useful analogy in describing natural selection, so he eventually believed that artificial selection was helpful to his original discoveries.However, Darwin does mention "selection" several times in his notes, and it is hard to believe that Darwin's mind was not ready for a mechanism according to the same model (Ruse, 1975a; Mayr, 1977; Cornell, 1985; Hodge and Kohn, 1985).

By the summer of 1838, Darwin's research in biology had led him on the long road to natural selection.He knew that in segregated populations, shifts would occur through changes in the proportion of individuals, presumably through environmental selection of useful traits.It was at this point, as he reports in his autobiography, that he read Malthus, and it dawned on him that group pressure must lead to a struggle for existence in which only the fittest survive and reproduce.This statement leads us to some of the most heated debates about the development of Darwin's thought.Was Malthus's role merely to bring to light the mechanisms of selection that Darwin had already concluded through pure research (De Beer, 1963)?Or did the principle of population represent the ideological character of the doctrine of selection, and Darwin simply converted the competitive ethos of Victorian capitalism into a principle of nature (Young, 1969; Gale, 1972)? The situation is now further complicated by the fact that Darwin's notes already show other non-scientific influences on Darwin's reading at the time (Manier, 1977; Schweber, 1977).Brewster's comments on Comte's work led Darwin to discover that a theory needs to be based on mathematical principles, so the logic of arithmetic in the principle of crowd population should play a role.Darwin also read other political economy literature, and the literature on Adam Smith and free competition may have helped to convince him that a mechanism based on the interaction of individuals with purposeful dispositions could be established .In his search for a way to measure variation, he read the work of the Belgian anthropologist Lambert Keitel (Quetelet, English translation, 1842), a pioneer in the application of statistics to the study of groups.Keitel showed that there is a variable distribution between the two extremes, with most individuals being distributed near the middle, a phenomenon we now know to be a frequency distribution curve.Here is an excellent illustration of the idea of ​​variation and groups, the idea of ​​viewing species (including humans) as groups of divergent individuals rather than as a single homogenous type.Keitel also commented on Malthus, thus provoking Darwin's critical reading on the principle of population. Some historians, who have portrayed Malthus as a midwife who merely pulled together the threads that Darwin already had in mind, have suggested that it was the mathematical power of the principle of population that made Darwin's vague ideas a spontaneous one. The correct theory of natural selection.Darwin had realized that adapted varieties must do better than other types, and his ecological insights had led him to recognize competing elements in nature.Malthus made him see that within species there must be a perpetual struggle to weed out unfit individuals (Herbert, 1971).Not only do unfit individuals not have a reproductive advantage: the struggle for survival exerts strong selective pressure at all times by preventing unfit individuals from mating maturely.The emotional impact of this insight allowed Darwin to confirm what he had long suspected, that death actually played a creative role in the world (Kohn, 1980). Even those modern explanations that give more weight to "external" factors (eg, Schweber, 1977) emphasize the need for a balanced explanation of factors, influencing Darwin.Darwin's notebooks attest to how far he was from discovering natural selection through the study of biology.His reading of the literature on the economics of free competition only reinforced the group thinking he had already acquired from animal handlers.Malthus's view was not an insight that fell from the sky, revealing that the degree of struggle that necessarily exists in society also exists in nature.However, those who think that Malthus played a significant role do not base their analysis on Darwin's notes entirely, because Malthus' views represent the prevailing ideological influence on Darwin's thinking.Even as a midwife, the concept of individual struggle was greatly strengthened in Darwin's mind, and it seems to have been due to reading Malthus's books.Whatever the source of Darwin's idea of ​​a struggle for existence, we may still ask why the metaphor of struggle appealed so strongly to him, and whether it was because he himself lived in a society dominated by competition among individuals. The view that Malthus did not produce in Darwin's mind a thought naturally based on struggle is reinforced by a detailed study of Malthus himself regarding the interpretation of his principles.Many historians have suggested that Malthus himself deduced that population pressure necessarily led to a struggle for existence (Vorzimmer, 1969a; Young, 1969).Thus, Malthus's ideas are not necessarily related to Darwin's, since the idea that overpopulation may be eliminated is also available through other sources.Malthus only used the term "struggle for existence" when discussing savage tribes, arguing that in his society population pressure could be eliminated by educating the poor to have fewer children (Population, Chapter 4; Bowler, 1976b).Therefore, Darwin only grasped a relatively small part of the Malthusian system, while ignoring the main content of "Population", which is consistent with the traditional assumption that free competition can balance society. If Malthus had not intended to emphasize the competitive nature of capitalist society, we must ask why Darwin suggested that struggle must be the inevitable result of group pressure.Those who want to see Malthus as the leading exponent of the view of struggle have answered this question by asserting a subtle ideological connection.In the society in which Darwin lived, competition among individuals was increasingly recognized as the driving force of economic progress.Malthus and competitive economists may have attempted to rationalize this situation by arguing that competition would ultimately be good for all, but the common people probably had a clear idea of ​​what was really going on.With the success of the Industrial Revolution, the business class, with a new sense of their own achievements, was ready to admit that the wealth they acquired was a reward for their individual efforts, of course at the expense of the incompetent .This view was common, if not the orthodoxy in political economy, in the literature of the time (Gale, 1972).Perhaps unconsciously Darwin assimilated this brutal attitude, and so he consciously prepared himself to see the struggle for existence as the natural way by which the stability of the crowd would be maintained.A comparative study of Darwin now reveals that the influence of his ideas was widespread, but does not resolve the debate about the ideological origins of natural selection.Some of the external influences considered by historians to be the most important may belong to a less direct way, the existence of which we have not yet been able to prove.The connection between Darwin's theories and capitalism is too pervasive to be confirmed by his consciously recorded notes of thought.Rather, it is based on the general consistency between Darwin's idea of ​​struggle and the social reality of the nineteenth century.The historian must choose whether to accept the logic of the arguments for this insight, or to focus on the wealth of scientific insights revealed in Darwin's notes. The Development of Darwin's Theory: 1840-1859 After Darwin compiled the general naturalistic theory of species transformation, he spent the next 20 years exploring the details of this theory and expanding its explanatory power. In 1842 he wrote a brief synopsis, and two years later a more substantial essay for publication in the event of his death (reprinted in Darwin and Wallace, 1958).He did not intend to publish it at the time, especially because of reflections on Chambers' Traces of Natural Creation History, which revealed strong public and scientific opposition to transformation theory (Egerton, 1970b).Darwin only gradually made known to a few friends, including Ryle, the botanists Joseph Hooker and Asa Gray (Colp, 1986).He set out to create an informal scientific community that preached a new view of evolution (Mannier, 1980).It was only in the 1850s that he began to write a tome to be published (Darwin, ed. Stauffer, 1975). In 1858, due to Wallace's article on natural selection, he stopped writing and started writing a shorter work, ie. The situation at the time of the publication of this book was very different from that of earlier years. In 1839 Darwin married and moved to Down in the Kent countryside.Soon he contracted the disease, and his health has been poor ever since.It was never clear what ailment he had.It was once thought that Darwin suffered from a neurological disease transmitted by South American insects.Until recently, it was suggested that he was poisoned by a new drug (Winslow, 1971) or that his illness was caused by psychological stress (Colp, 1977).Due to illness, Darwin could only work a few hours a day, and it prevented him from participating in public life, except for attending local events. Modern historians pay more attention to two problems in the development of Darwin's theory during this period.One question concerns the relationship between the large natural history projects that Darwin undertook, particularly the barnacles, which he mainly studied (Darwin, 1851-53).We can now see that these projects were not Darwin's sidelines, that Darwin did not undertake such work to establish his reputation as a brilliant biologist.Instead, these works were used to directly test evolution and to explore general biological implications from the study of barnacles (Ghiselin, 1959; Gale, 1982).A more important issue is the development of the theory of evolution itself. The explanations in the 1844 "Papers" were incomplete, and more recently there has been growing concern that he had to start focusing on additions.Darwin was beginning to see at this time that natural selection should be linked to the broader history of life, especially to the specialization of the many tendencies recorded in stable branched fossils.Only after he had explained the problem by means of his "principle of disproportionation" did he feel confident enough to write his great book on the species problem.During this period, his thoughts on the role of geographical isolation and other factors have undergone great changes. Darwin's interest in barnacles came from unusual specimens he found during his voyage with the Beagle.At this time he found that a complete description of this little-studied subclass was the ideal way to test his evolutionary views with actual morphology and taxonomy (Ghiselin, 1969; Ghiselin and Jaffe, 1973).His intentions are not obvious from his published monographs, but Darwin effectively explored the effects of evolution through the study of {biological} interrelationships in nature by biologists.When his theory was finally published, he had been able to show that organisms within a taxonomic group were alike not due to some fantastic archetype, but due to a common origin.The theory of evolution allows Linnaeus' system of classification to be explained by the fact that the different groups arose by branching, and that the characteristics of the common ancestor were retained in the apparently altered descendants.Darwin also recognized that there are different degrees of possible variation among branches from a particular root.Some clades vary so much that we don't want to group them into the same genealogical group when we classify them.What is disputed is what level of divergence must be reached to definitely identify a new lineage group, and taxonomists often debate this issue. The study of barnacles also taught Darwin the amount of variation possible within a species.In the mid-nineteenth century, a gossip circulated in natural history that naturalists were divided on related groups, unable to determine whether they were varieties of a single species or belonged to different species.From a technical point of view, the solution to this question depends on whether the groups were interbreeding at all; but in practice it is impossible to determine this, and the naturalist has to decide by the degree of the morphological difference.Some varieties combine to form closely related varieties of a single species, while some are treated as distinct species because of distinct characteristics.Darwin wished to show that species generally divided into varieties, because he believed that this was the first step in speciation (the creation of new species).The resulting variety becomes the original species.Since the reproductive isolation of a species was finally established gradually, Darwin was able to explain the long-running dispute among naturalists over the status of varieties.In many cases, the divergence of species has intermediate stages, making it difficult to determine the true status of different groups. The sterile trait was once the cornerstone of creationists, who believed in the belief that species were true entities formed by God, while varieties were regional, accidental creations of nature.It has sometimes been suggested that Darwin's theory made species an artificial figment of the taxonomist's imagination by suggesting that one species gradually changed into another through intermediate varieties.The principle of continuity does lead to this idea.For example, Lamarck's theory does not emphasize that the origin of species is a complete destruction of the concept of species.By proposing that every well-characterized form is insensibly transformed into another species, the taxonomist is compelled to draw a limit according to convenience in determining "species."This is not, however, the result of linkage changes in a divergent system, since branches are morphologically discontinuous as branch branches separate.Darwin could thus argue that species are real, ie, that they are distinct entities, although there is no inherent essence that fixes their characteristics (Kottler, 1978).According to modern Darwinism, species are identified as interbreeding groups with distinct characteristics, and some critics argue that Darwin came a long way to this idea.It is generally agreed that he did not completely abandon the traditional method of identifying species based on morphological characteristics (Beaty, 1982). Figure 19. The relationship between species and varieties According to Darwin's theory, varieties are "initial species" - if they can survive and continue to change, they may eventually become a unique species.This diagram shows how from the original one species came the subsequent three species.In the first stage of this process, three distinct populations are formed, which may be variants of one species.Under normal circumstances, the three groups may not be isolated from each other, because members of each group can successfully breed with each other from a physical point of view.At a later stage, the differences between the three populations have become too great to interbreed with each other.These three groups at this time had completely distinct characteristics and could be considered distinct species.But there is no clear line between species and variety.The process of divergence is continuous, during which the possibility of interbreeding gradually decreases.  Darwin's interest in reproductive processes was sparked by the discovery that although most barnacles are hermaphroditic, a few males sometimes parasitize females briefly.He also found a situation where, in hermaphrodites, the males were smaller.He reasoned that entire groups of barnacles were originally hermaphroditic, and that some types had males that evolved separately (Ghiselin, 1969).The fact that hermaphrodites have distinct males suggests that his theory can explain the well-known trace organ problem.In this case, males become redundant and degenerate.Many other types also have this trace structure; a notable example is the teeth of some whales, which must never be used for feeding, and which are very small and do not show the gums.If Darwin's theory is correct, then these structures cannot be considered to be ready for future use by the [HTSS]: natural selection can only increase those structures which are in all respects immediately useful in their development.Although this view raises an important conceptual problem, since Darwin envisioned that complex organs, such as the human eye, go through intermediate stages of development, this view is crucial to clearing away teleology.In the case of the human eye, however, Darwin was relieved to find eyes of varying complexity in many animals, suggesting that each stage of development had some sort of perfect function.In contrast, trace organs once served some purpose, but are now degraded because they serve no purpose and consume biologically produced energy.It should be added that Darwin intended that degeneration might be caused by ineffective inheritance, since he always admitted that Lamarckian mechanisms would play a subsidiary role in evolution. Turning now to the development of the theory of natural selection, we must first note that there was disagreement about the state of Darwin's mind in the 1840s.It is generally assumed that by this time he had seen natural selection as a ruthless force, a struggle for existence that continually promotes the fittest at the expense of the unfit, even when circumstances are stable.But Ospovat (1978, 1981) has pointed out that, in its early forms, the theory of natural selection did not escape the influence of Paley's natural theology.Even in Darwin's 1844 paper, he still suggested that species are usually in a state of perfect adaptation, with little or no individual variation, so that the struggle for survival is not necessary.Individual variation arises only when the environment changes, thus providing the raw material needed for natural selection, under which the species changes until the species is once again perfectly adapted to the new environmental conditions , natural selection stops again.According to this explanation, it took Darwin more than ten years to gradually realize the full meaning of group pressure, that is, under group pressure, no matter how the external conditions change, no matter how much the individual variation is, a struggle for survival will occur.Only then did his theory approach maturity, and he realized that evolution is not a process between periods of stabilization, but an ongoing force capable of not only adapting species to new environments, but improving even during periods of environmental stabilization. level of adaptation.It was only then that he began to realize that it was difficult to reconcile a mechanism based on constant struggle with the idea of ​​a benevolent God. Whether we accept Ospowant's ideas about the origin of Darwin's theory or not, Darwin did increasingly recognize that natural selection can steadily promote the specialization of functions.He has always understood that evolution is a process of disproportionation, which is the inevitable result of discovering that new species are produced after the formation of geographical isolation under new environmental conditions and the divergence of small groups from existing forms.This view was taken for granted at first, but a problem arose when Darwin realized that after the initial disproportionation there was a continuum of further disproportionation, causing types to diverge even more from each other.His own research must have contributed to his realization, but Ospovat (1981) suggested that the main inspiration came from W. B. Carpenter, Richard Owen, and Henry Mainey -Edwards and other naturalists' studies on disproportionation and specialization.These naturalists based their conception of development on the basis of K. E. von Baer's theory of embryonic growth, suggesting that not all species are perfectly adapted to their own way of life.Instead, species exhibit processes of specialization and disproportionation that differ from the archetypal types of their taxa.Carpenter and Owen also showed that, during geological processes, the degree of disproportionation within a group increases, as shown by the fossil record (see also Bowler, 1976a).This led Darwin to see evolution not only as a process of maintaining adaptation, but also as a developmental force acting on unspecified forms from which classes later diverged, giving rise to The first batch of branches is produced, and each branch is continuously specialized to adapt to its own way of life. By explaining evolutionary recurrence as a process of continuous specialization, Darwin was able to relate his theory to the work of more traditional naturalists.In it, he even cites Owen's work on the issue through paleontology as evidence in support of his own theory.Looking at the details, it turns out that Darwin's objection to teleology prevented him from agreeing with most of his contemporaries' explanations of evolutionary trends.On the whole, however, his theories by this time were consistent with recent advances made by those who had taken more traditional approaches to the study of morphology, paleontology, and embryology.His theory may better meet the need to reinterpret existing knowledge at this time, rather than promote the establishment of an entirely new picture of life history. The connection between evolution and embryology is often misunderstood.Darwin apparently did not follow others in illustrating the history of life on Earth using the development of the human embryo towards its ultimate goal as a model.His theory needed something to do with von Baer's work on embryos, as it was with the concept of branching development, although Darwin was apparently not aware of von Baer's writings (Oppenheimer, 1967).Darwin's theory is different from the popular view and the insights of some evolutionists later, it does not require the growth of embryos to repeat the evolutionary history of species (Gould, 1977b).Variation has no target and must be considered as a disturbance to the growth process.因此没有必要推断出成体的结构应该还原成一种类型进化后裔胚胎中的一个阶段。但是这并不意味着胚胎学对于帮助理解物种之间的关系没有价值。有时两个区别很大的成体类型胚胎结构却相似，这表明它们是进化上的亲戚。然而达尔文并没有期望胚胎的生长会揭示出一种加速的进化图景。个体发育（个体成长）重演系统发生（进化的历程）的信念是19世纪后期一些倡导新拉马克主义观点的博物学家嫁接到进化论上的。 分支进化的概念必定要动摇人类是生物进步预定目标的传统观念，但是分支进化一定会摧毁整个进步思想吗？在分支进化图景中，不可能存在一个清晰的阶层体系，其中每个类型都有指定的位置。相反，按照分支进化，有可能建立一个生物复杂化的抽象图景，其中排列着完全不同的生物结构种类。达尔文意识到，在实际工作中这样做会很难，但是他承认多数博物学家是本能地感到有些生物比其他生物“高等”。在这个案例中，如果有可能认为进化是进步的，那只是认为进化促使每一种类型在其特有的结构范围内组织化程度更高。达尔文愿意相信不断增加的特化是一种进步形式，因为这意味着后代比其祖先有更好的条件来适应一种特定的生命方式。这样看问题有利于使他保持自己旧有的信念，即，整体上看自然选择具有目标性。然而他不得不承认，有些特化，例如寄生，实际上是退化的结果。导致建立全新纲的进化突破，显然并不是来自于以前纲的一些高度特化的成员。只有那些不太特化的类型，才能经历这样剧烈的结构变化，而特化可能容易成为一个陷井，阻止物种适应它所生活环境的迅速变化，并因此导致灭绝。达尔文仍然相信自然选择可以产生一种进步形式，但是他也不得不承认这种进步顶多是选择机制主要适应功能的缓慢而不定的副产品。 将达尔文主义与分支进化联系起来，会产生出许多特征，我们可以在现代形式的进化论中发现这些特征。当然这样的联系也为达尔文带来了一个很大的问题，他不得不解释为什么自然选择会使特化水平不断提高。按照他原来形式的理论，物种形成将一个类型分裂成若干不同的分支，但是并没有明显的理由认为分支会继续再分。在这里，似乎生物地理学在导致达尔文提出进一步多样性的解释中起到了重要的作用（Browne，1980）。他开始检查有关属的大小（即属中的种数）和一些复合种的多样化程度。小的属显然可以分成两种类型：一种类型是其中的相似类型很少，还有一种类型中含有少数趋异的变体成员。达尔文终于认识到，这些代表了两个阶段，分别是历史进程的开始和结束。当物种形成从原初类型中创造出属，所有复合种仍然彼此很相似。随着时间的流逝，趋异增加了物种的数量和物种之间的差异。然而，在这个过程结束时，当这个属被其他更成功的类型替代后，在多数物种都走向灭绝时，只有少数高度趋异的物种可以保存下来。 到了1854年，对于这一点的认识极大地启发了达尔文对选择如何起作用的看法。有利于一个属内趋异的最好地区显然是一个拥挤的地区，那里可能没有地理隔离。只有在属的发展历史中才发生向更广阔的地域扩展现象。这样达尔文开始重新考虑原先对加拉帕格斯群岛生物的看法，原先他认为地理隔离对于物种形成是至关重要的（Sulloway，1979）。他并没有完全否定隔离的作用，但是这时他已经开始认为，隔离对于原种群的分化并不是必需的。他提出了一种替代的思想，他认为自然选择的作用可以促使原群体分布两头类型的生命方式出现差异。换句话说，选择本身的力量足以在群体中产生分化，通过选择的适应压力使原类群分成两部分。这样，达尔文的思想转变为相信现在所谓的同域物种形成（没有地理隔离情况下的物种形成）。 虽然我们现在可以看出为什么达尔文转变了对隔离重要性的认识，但是他的决定对于他的理论在以后的发展带来了一个重大的问题。现代的多数博物学家相信，同域的物种形成是不可能的；群体的初始分化总是发生在分布区不重叠的情况下，即要求至少在分化的初始阶段存在地理隔离，以防止相互配育。一旦群体已经建立了防止相互配育的“隔离机制”——这些机制可能是行为上的，而不是遗传上的，即一种类型不愿意与其他类型交配——即使地理障碍不存在，分化仍将继续进行。当我们考虑到传统的达尔文主义认为所有的变化都是缓慢而逐渐的时候，与同域物种形成有关的一个的问题便产生了。这样很难设想自然选择怎么能够阻止一个群体的两部分之间的相互交配，如果存在一个过渡区，选择压力在这里就不能起作用，生活在过渡区两边的生物仍然可以相互交配。通过过渡发生的相互配育就可能使趋异的性状融合，就不可能实现物种形成所要求的配育群体之间的必要分离。 应该注意，上面提到的“融合”并不是一些史学家（例如Eiseley，1958）为了说明达尔文关于遗传的观点中存在着缺陷时所讨论的融合。我们这里谈的是由于整个群体之间的相互配育导致的性状融合，并不是亲本的性状在子代中融合。在缺乏孟德尔遗传学的情况下，达尔文及其大多数同代人的确都相信“融合遗传”，即相信子代融合或均分亲代的性状（Vorzimmer，1963）。后一种融合遗传引发了另一个不同的问题，也就是一种对达尔文的批评所指出的，交配没有变化的话，不久就会冲淡任何个体天然具有的优良品质的优势（Bowl er，1974b，见第七章）。达尔文有时写道，有利的变异极为稀少，在这种情况下，融合不久就会清除有利个体的影响，就像一滴黑油漆混入到一捅白油漆中一样。达尔文最初逃避这个问题的方式是仰仗隔离，他认为，在隔离的情况下，小的群体会防止变异完全被清除。然而，当他转而相信同域物种形成时，又不能依靠这种解决方式了，这样就直接提出了融合遗传的问题。达尔文在回答后一个问题时，更加坚定地站在渐变论的立场上，强调有利的变异并不是个体本身，而是影响整个群体变异性的综合部分。 . 无论他的解决方式有何功过，达尔文这时已经将生物地理学和趋异程度增加的化石记录联系了起来。而且他已经确信选择要比他当初所想象的更具威力，而且也更残酷。这种最新的决定再次使得他难以将进化论与上帝设计的观点协调起来。但是他仍然必须要解释为什么选择能够不断地以这种方式起作用产生生物的歧化。选择已经变得不再是使物种适应变化环境的被动力量了。他再一次在与经济学的类比中发现了答案，那就是劳动的分工（Limoge s，1970；Schweber，1980；Ospovat，1981）。在经济活动中，大量工人从事制造过程中的某一方面的专门劳动，要比一个人做整个工作能够创造出更多的价值。法国心理学家亨利·迈尔尼爱德华兹已经将这种现象与个体生物的作用作了类比，他认为每一个器官只有一种功能会更有效。达尔文这时认识到，可以将同样的类比用于生态学和进化中。如果两个物种非常相似，那么它们之间就存在彼此竞争的趋势，而这对她们二者的前途是有害的。如果它们能够歧化的话，便获得了优势，每一个物种经过特化之后适应了不同的生活方式，这样就减少了竞争的机会。而且如果大量不同的生物分化成不同的类型，每一种类型能够以不同的方式汲取领域中的资源的话，那么同样的一个区域，就可以供养大量这类不同的生物。因为自然选择可以使每一种类型获益，这样就可以增加多样化的水平，即使在环境稳定的情况下，也可以使每一种类型特化，适应自己的生活方式。这种多样化原理至少会使自然选择成为达尔文所要求的具有主动性的力量。 当达尔文在1856年将这些难题都汇总到一起的时候，他认为他的理论完整了。由于认为歧化是自然选择的必然结果，于是他便可以解释大量生物现象，而不像原先的理论那样可以解释的现象范围很窄。只有到这时他才有充分的信心撰写他计划中的关于物种问题的“大书”（Darwin，ed.Stauffer，1975；Hodge，1977），然而，不久这个计划却因为他决定撰写而搁置。 华莱士与进化论的发表 促使达尔文发表他的理论的原因是1858年他接到了一篇论文，在这篇论文中勾勒了一个类似的自然选择学说。这篇论文的作者是阿尔弗莱德·拉塞尔·华莱士，他因此确立了作为自然选择独立发现者的地位（Marchant，1916；George，1964；Beddall，1968；William s-Ellis，1969；McKinney，1972；Fichman，1981）。对华莱士工作的一些解释暗示，历史对他不太公平。如果说华莱士同样对进化的发现有贡献，为什么这个理论叫做“达尔文主义”？有人暗示，达尔文本人曾试图消弱华莱士的作用，以保证他自己的优先权。对这个问题的一项最近的研究显示，达尔文从华莱士那里剽窃了歧化原理（Brackman，1980；Brooks，1983；反驳观点见Kohn，1981）。 有大量的原因可以认为这种静悄悄的平反在夸大事实。说明华莱士没有起到与达尔文同样大的作用的最明显的事实是，华莱士的发现要比达尔文的晚二十多年。这时，华莱士花了很长时间研究出分支进化的含义，但是直到1858年，他才想到选择是实际起作用的机制。即使我们承认他的简要文中章包含了整个进化论的实质，但是这篇文章本身的影响很小。当这篇文章与达尔文著作的梗概发表时，在科学共同体中没有造成什么影响。要完善这个理论本身，华莱士还要再花上几年。达尔文的基础工作已经完成，万事俱备，所有他能够将他自己的思想浓缩在一卷本的书中，这就是我们熟悉的。 华莱士出身贫寒，后来成为了一个职业采集者，他靠出售在世界遥远地方采集到的标本来维持生活。他第一次探险是1848年至1852年，与他的朋友亨利·沃尔特·贝茨在南美（Beddall，1969）。这次探险使他关注了那些当初引发达尔文思考进化、生态和地理分布的问题。带有华莱士标本的船在返回英国的路上被大火吞食了，幸运的是他却安然无恙；不久，他又启程了，这次去的是远东的马来群岛，即现在的印度尼西亚。在马来，一次发烧期间，他得出了自然选择的思想。他当时在不太出名的济罗罗岛上，而不是如他所称以盛产香料著称的德那第岛上（McKinney，1972）。他根据这种思想写成了一篇短文，并寄给他认为最有资格评价这篇文章的博物学家——达尔文。 华莱士像达尔文一样，去南美时随身带着赖尔的《地质学原理》。他接受了逐渐变化的地质学体系，不过不久就对赖尔的物种固定不变的假设提出了质疑。他开始对地理障碍是如何将物种限定在一定区域的问题感兴趣，并且得出的结论与达尔文受加拉帕格斯群岛影响得出的结论类似。华莱士开始感到特创论需要太多的人为假设来解释生物分布的事实。他对钱伯斯的《自然创造史的痕迹》有很深的印象，通过这部书，他开始关注生物转变的问题。到了19世纪50年代，华莱士虽然还不理解变化的机制，但是他已经确信分支进化的发生。他开始计划写一部关于物种问题的书，1855年，他发表了一篇重要的文章，文章的开头便说道“每一个物种从时间和空间上来自原先相近的物种”（Wallace，1855；重印在Wallace，1870，1891）。他开始和达尔文通信，达尔文曾对他的文章给予很高的评价。然而，达尔文并没有同他讨论自己的理论，导致华莱士认为他首先想到了这种含有重要新见解的思想。 华莱士那篇1858年文章的标题是《论变种无限地离开原始模式的倾向》（重印在Wall ace，1870，1891；Darwin and Wallace，1958）。人们通常认为，虽然这两个博物学家是通过实际上不同的方式得出进化思想的，但是华莱士的文章中包含了达尔文已经得出的理论的实质。华莱士对赖尔论述的物种之间的“自然战争”有很深的影响，而且他也正是在这个层次上理解生存斗争的。像达尔文一样，他也读了马尔萨斯的书，因为他对人类的进化很感兴趣。但是华莱士似乎以不同的方式在运用斗争概念，因而有些评论者怀疑他是否可以被当作达尔文自然选择学说的共同发现者（关于对这种观点的评价，见Kottler，1985）。 A·J·尼克尔森（Nicholson，1960）指出，华莱士倾向于认为环境确立了绝对的适应值衡量标准，一个物种中的所有成员都要接受检验。凡是不能通过这种标准检验的就要被淘汰，只有在环境发生变化的情况下，才可以发生进化。与达尔文的概念相比，这个概念远算不上严格的选择概念，按照达尔文的选择概念，无论环境状况如何，群体中的成员总是在相互竞争，两个人之间最明显的差异或许体现在华莱士对“变种”一词的用法上（Bowler，1976c）。有可能认为，在华莱士1858年文章的大部分地方，他所强调的是已经成为变种或亚种之间的竞争，而不是个体变异之间的竞争。达尔文一直认为竞争是在个体水平，并将其作为选择学说的基础。华莱士坚持认为选择作用于变种上，淘汰那些不同适应物种分布范围内环境条件的变种。他认识到，为了使这个机制自恰，物种必须不断地形成新的变种，但是他并没有很清楚地提到这是在更基本水平上自然选择作用于个体变异引起的。因此华莱士1858年文章主要涉及次一级水平的选择，而达尔文最终认识到变种的选择只是歧化的原因。 如果注意到华莱士与达尔文作出发现的道路有明显的不同，便可以理解为什么华莱士观点得出了这些不同的解释。达尔文在岁贝格尔号航行期间便相信了进化，但是但是回国后，他通过研究人工驯化，想到了变化的机制。从而使他关注群体内的变化过程，并强调选择是作用于个体差异上的。华莱士也是按照同样的途径相信进化的，但是并没有对人工驯化感兴趣；实际上他否认人工选择可以很好地与自然过程作类比。由于思想上未受到人工选择模式的影响，华莱士不可能关注个体竞争。进而，他对生物地理分布的兴趣可能导致从以群体为判定单位的适应值的绝对标准来思考。 无论他们的研究方式有何不同，华莱士的文章使达尔文确信他自己的观点现在已经有人在很大程度想到了。一个不诚实的人可能会销毁这篇文章并对华莱士置之不理。达尔文并没有考虑这样做，然而，同时他也不想使自己二十年的优先权付诸东流。他求助于赖尔和胡克的帮助，他们安排宣读了华莱士的文章，从达尔文正在写作的书中摘出的两篇简短的梗概和一封给阿沙·格雷的信，这封信可以证实他率先认识到歧化原理。这些文章是在林奈学会上宣读的，后来又发表在学会的刊物上。奇怪的是，文章宣读后没有引起什么争论，文章发表后也没有引起什么反映。这样简短的说明未能使公众关注这样一个重大的问题。但是这时达尔文认识到，他不能再迟疑了，必须写出一部可以很快发表的包括他的理论的实质内容的书。发表于1859年底，引起了很大的争议。