Chapter 23 Chapter 12 Diversity and Synthesis of Evolutionary Thought-1

In the 80 years since its publication, differences of opinion among evolutionists have been stark.Every field of biology has its own traditions, as do every country.Germany embraced evolutionism quickly and quite comprehensively (LL.L.D:III:88).Haeckel, Germany's most ardent evolutionist, both facilitated and hindered the spread of Darwinism.He did a great deal of good work in popularizing Darwinism, and at the same time he used Darwinism as a weapon against all supernaturalism, especially Christianity, which in turn provoked a counterattack from the opposite side, who equated evolutionism with materialism and was immoral .Although this did not prevent the spread of evolutionism itself, it was nevertheless an important factor in the almost universal opposition to the theory of natural selection in Germany.

In the first decade or so after publication, the idea of ​​evolution by descent with modification has also been adopted more generally in England, at least in biology.Most people, however, are not interested in natural selection.It was accepted only by a few naturalists, such as Wallace, Bates, Hooker, and some of their friends and subsequently Poulton, Mendola, and some entomologists, but no experimental biologist recognized it.A decisive influence on the subsequent development of the theory of natural selection in Britain was the zoologist Ray Lankester (Ray Lankester, 1847-1929), who became a selectionist after reading some of Weissmann's papers.He actively supported the invitation of Weissman to give lectures in the UK, and established a school of selectionism at Oxford University, which has trained several generations, such as E. S． Goodrich, J. Huxley, G. de Beer, E. B． Ford．The University of Cambridge or University College London did not accept the theory of natural selection until R.A. Fisher and JBS Haldane began to publish articles.

Despite the strong support of Asa Gray, evolutionism is still suffering in the United States.At first, there were only a few professionals such as biologists and paleontologists in the United States, and the debate on evolutionism mainly occurred among writers, theologians and philosophers.Professional resistance to evolution came to an end, however, with Agassiz's death in 1873 and Dana's acceptance of evolution in 1874.However, the theory of natural selection is still criticized.The situation was further complicated by the vogue of Spencer's so-called Social Darwinism.As a reaction to social Darwinism on the one hand, and traditional American egalitarianism on the other, extreme environmentalism has developed in psychology and anthropology, which narrows, if not completely negates, the differences between individual human beings. genetic differences.This tradition has continued to some extent to the present day.Apart from chronological details, Germany, Britain, and the United States were basically similar in accepting Darwinism, that is, evolutionism was quickly accepted, but only a few people recognized the theory of natural selection at first.

Resistance to Darwinism was more tenacious in France than in other major Western countries. Not a single notable French biologist came out in favor of selection after 1859, and even evolutionism itself did not begin to circulate until the 1870s. It was not until 1888 that the Department of Evolutionary Biology was founded at the University of Paris (Sorbonne), with Giard as the first head of the department. In the 1880s and 1890s, when France finally adopted the theory of evolution, it was still in the form of neo-Lamarckism, and it was also quite popular in the United States and Germany at that time.Although the theory of natural selection was occasionally supported and adopted by Teissier and lHeritier in the 1930s, it was not generally accepted in France until after 1945 (Boesiger, 1980).

Strangely (given Lysenko's subsequent rise to power) no other country adopted Darwinism, including the theory of natural selection, more generally than the Soviet Union until the late 1920s.At first this was mainly due to political reasons, but partly due to the development of population systematics in Russia (Adams, 1968).The implications of this situation for the further development of population genetics will be presented later. Although Darwin was mainly a supporter of hard inheritance, he also made certain reservations about the use-it-out effect and some aspects of soft inheritance, which will be introduced separately in Chapter 16.

With the development of cytology, especially the growth of knowledge about chromosomes, many scholars began to doubt any acquired trait inheritance.However, such questions are only occasionally raised and have not attracted much attention.The denial of soft inheritance did not make real progress until Weismann published his theory of germplasm continuity in 1883 and 1884 and his claim for a complete and permanent separation of germplasm and constitution.The complete denial of any acquired trait inheritance means the denial of all so-called Lamarckism, Jeffreyism, or Neo-Lamarckism.That leaves only two conceivable mechanisms of evolution: catastrophe (evolution due to sudden and significant divergence from existing patterns) and selection among a few variants.Weissmann adopted an uncompromising selectionism, a theory of evolution that Romanes (1896) called neo-Darwinism.Neo-Darwinism can be said to be a Darwinian evolution theory that has nothing to do with any soft genetics.In fact Weissmann accepted most of the other components of Darwin's theory, with the exception of pangenesis.Nobody mentions pangenesis anymore.

Soft inheritance was considered at the time to be a major source of individual variability.Weisman argues that eliminating soft inheritance forces evolutionists "to search for new sources of this phenomenon, on which the selection process depends entirely." A specific process of genetic variability, which is now called "crossing over" (crossing over).If there is no such chromosomal recombination during gamete formation (meiosis), genetic variation (other than occasional new mutations) will be limited to reassignment of parental chromosomes.In contrast, the result of chromosomal recombination is that "in the second generation there will be no individuals identical to each other. (In each generation) there will be combinations which have never been before and never will occur again." No one before Weissmann understood This incomparable power of sexual recombination in generating genetic variability.

The importance of recombination in evolution was initially largely neglected in the genetics literature, which at the time was written in terms of "bean bag genetics" (see Chapter 13), which described evolution in terms of the "mutation and selection" formula .In fact, the selected target, the genotype, is the direct product of recombination rather than mutation.The evolutionary significance of recombination systems (genetic systems) until C. D． The articles of Darlington (1932, 1939) and Stebbins (1950: Chapter 5) were not fully recognized until they were published. Much has been written and written about Weissmann's theory of heredity and cell theory, but the development of his idea of ​​evolution has been fairly neglected by historians.Until such an analysis has been made, only tentative statements can be made. In 1872 Weismann intervened in the debate between Moritz Wagner and Darwin on the role of geographical isolation, showing a poor understanding of the issue. Some articles published in the late 1870s show that he still believed in soft inheritance at the time.It was not until 1883 that Weissmann explicitly disavowed it, and in the following years attached great importance to the role of recombination (the fusion of the sexes, amphimixis).It was also during this period of time that he put forward the theory that is now almost universally accepted, that is, the selective advantage of sex (gender) lies in the rapid proliferation and expansion of genetic variability, thus providing more abundant raw materials for selection.Weismann was the first to address the issue of natural selection's control of lifespan (see also Korschelt, 1922).

More specifically, he takes a completely new way of looking at the meaning (i.e., choice value) of aspects of a creature (morphological and otherwise).In his view, everything in the biological world is the expression of Allmacht der Naturuzchtunn (Allmacht der Naturuzchtunn). However, after the age of 60, Weisman began to doubt the ability of natural selection itself to dominate the evolutionary trend without external forces, and admitted that it is impossible for "the adaptation necessary for the survival of organisms to originate from accidental variation", and proposed "species Qualitative selection" theory (principle of germinal selection).Thus he held that the emergence "towards variation ... is caused and directed by the living conditions of living beings" (1896: IV).Weismann categorically denied any inner (orthogenetic) impulse, and maintained that selection for certain traits, such as the trait of longer tail feathers in birds, favored in selection all genotypes altering the length of the tail feathers.Weismann distinguished hereditary variation from the ability of organisms to produce variations of specific traits and pointed out that both can be subject to selection.However, his thinking sometimes contradicts himself. He admits that the model of some butterflies is very similar to the mimic (mimic), "it cannot be due to chance, but must be due to the directional variation caused by the utility itself" (1896: 45).Weisman then admitted that "the Lamarckists are correct in insisting that only selection (individual choice) is not enough to explain all phenomena until now" (1896: 59).

Weissmann no longer believed that random random variation, codified by selection, was sufficient for evolution. Evolutionary phenomena that once puzzled Weissman, such as the similar tendency of variation in many species of the same genus, or the gradual degeneration of useless and residual organs (such as the loss of vision in cave animals), no longer are modern evolutionary geneticists. Serious Problem.The fact that the coherent integration of genotypes imposes certain constraints on possible genetic variation, together with the selection for or against certain regulatory 'genes', accounts for all the observed 'orthogenetic tendencies'. ".These modern notions of constraint and regulation correspond to Weismann's germplasm selection.

Weissmann had a profound impact on evolutionary biology.He forced every biologist to take an attitude toward the inheritance of acquired traits.He insisted (albeit watered down by his outdated theory of germplasm selection) that there is only one directional force in evolution, namely selection, and thus forced his opponents to present evidence in support of their opposing theory.Most debates about evolution in the ensuing 50 years have involved issues that Weissmann had articulated so unequivocally.Moreover, thanks to his imaginative theories of genetics, he opened the way to the rediscovery of Mendel, a state of affairs that finally solved the evolutionary problems that had stumped Weissmann. 12.1 The Growing Difference Among Evolutionists Evolutionists formed a united front when it was still necessary to bring the phenomenon of evolution to the world's awareness and understanding, and this continued roughly until 1882, the year of Darwin's death.Over the next 20 years, however, a growing number of developments sowed discord among evolutionists.The first is Weismann's categorical denial of any kind of inheritance of acquired traits.This provoked the neo-Lamarckists to step up their counterattack. More importantly, the increasingly obvious differentiation of various disciplines in biology may not have been fully recognized at the time. The rise of evolutionism after 1859 was accompanied by the increasing differentiation of zoology and botany into specialized fields (disciplines), such as embryology, cytology, genetics, behavioral biology, ecology, and so on.Many of these new disciplines of biology were primarily experimental, thus making experimental biologists and others who trained as naturalists and studied whole organisms (most zoologists, botanists, paleontologists) scholars) the gap between them is widening.Experimentalists and naturalists differ not only in their research methods, but also in the questions they ask.Both types of scholars are interested in evolution, but the research lines are divergent and the aspects of evolution are different.Experimental evolutionists, most of whom were originally embryologists, entered the newly pioneering field of genetics with an interest in the study of recent causes, with particular emphasis on the behavior of genetic factors and their origins.Bateson, de Vry, Johannsen, Morgan are typical representatives of this camp.Some of them have a strong interest in or training in the physical sciences and mathematics.By contrast, the naturalist is concerned with ultimate causes; tends to study evolutionary phenomena in nature or in the wild and places particular emphasis on diversity.Paleontologists, taxonomists, naturalists and geneticists speak different languages ​​and find it increasingly difficult to communicate with each other. From the beginning naturalists have been particularly fascinated by diversity, its origin and meaning.Taxonomists are primarily concerned with species issues, while evolutionary trends and origins of higher taxa attract paleontologists and comparative anatomists.In contrast, prior to evolutionary synthesis, geneticists had almost completely disregarded diversity when discussing evolution. They focused only on transformational evolution, and the focus of attention was all on genes, traits, and their changes over time ( change).They write as if completely unaware that there are taxa, and that these taxa (eg different populations, species, etc.) are the real actors in the evolutionary arena.Even a phenomenon such as adaptive radiation, as Eldredge points out (1979: 7), "is seen as a matter of divergent anatomical specialization among a range of closely related organisms, rather than as a matter of individual distinct species occupying a range of different habitats. Range or range of related species.” The emphasis is on transformation rather than diversity.Precisely because of this complete neglect of diversity, or at best no more than de Vryian mutations or what the geneticist Goldschmidt called "promising monsters" (hopeful monsters) such panacea to explain, so that the naturalist is very dissatisfied. Disagreements among evolutionists affect the interpretation of nearly every aspect of evolution.The most intensely debated questions at the time were the following three questions: (1) whether all heredity was hard (as Weissmann believed) or some soft; (2) whether the main directing factor of evolution was mutation , selection, environmental mutagenesis, or intrinsic tendency; (3) whether evolution is gradual or sudden. Kellogg (1907) has described it in terms of many different combinations of opposing views held by different evolutionists. The rediscovery of Mendel's laws in 1900 brought the disagreement among evolutionists to a head.These laws prompted the early Mendelians to use the granularity (discontinuity) of genetic elements as evidence for the important role of catastrophic processes in evolution, especially in the origin of species.Since then, two camps have formed among evolutionists: the Mendelians and the naturalists (Mayr and Provine, 1980). Both camps' explanations of evolution are an equally unlucky mixture of right thinking and wrong ideas.Naturalists have misconceptions about the nature of heredity and variation, while experimental geneticists, dominated by schema thinking, ignore the existence of populations and focus only on gene frequencies in closed gene pools; they do not consider the reproduction of species, the origin of higher taxa And questions like the source of evolutionary miracles.The two camps don't quite understand each other's arguments and are therefore unable to mount effective rebuttals. The two camps also represent different research traditions.Naturalists, following in much of the original Darwinian tradition, study natural populations and pay special attention to the origin of diversity.Most importantly, they carried on the Darwinian tradition of asking ultimate causes.Before Darwin the answer to the "why" question of adaptation, and of any other biological phenomenon, was always "It is by design," or "It is the result of natural laws prescribed or designed by the Creator." Exclude said natural phenomena from scientific analysis.For the first time, Darwin's theory of natural selection provided a reasonable research route or plan for the study of the ultimate cause, and this type of cause is the first concern of naturalists. Experimental geneticists, by contrast, draw most of their methods and ideas from the physical sciences.They are convinced that their method is more objective, more scientific, and therefore superior to the "speculative" methods of evolutionary naturalists.For example T. H．Morgan (1932) believed that only by using the experimental method can "the theory of evolution be discussed objectively, which is obviously different from the old speculative method of treating evolution as a historical problem." The inability to understand each other's arguments is exacerbated by the fact that experimental biologists and naturalists, in general, work at different levels in the hierarchy of natural phenomena.Geneticists deal with genes, while naturalists deal with populations, species, and higher taxa.Only in recent years has it been fully appreciated how difficult it is to transfer findings and conclusions from one level of hierarchy to another, especially higher levels (Pattee, 1973).Furthermore, geneticists generally study a single-dimensional (single-dimensional) system of a single gene pool, while naturalists consider multidimensional systems of geographic space and time.The fundamental question that separates the two camps, however, is whether evolution is gradual or sudden. Any group of individuals of a species (from the simplest sexually reproducing organisms to humans) that exhibits individual variation (differences).This refers to how individuals differ from one another in size, proportion, shade of coloration, and other traits that can be quantified or graded.This variation is again classified as continuous variation because, if the number of samples is large enough, there is usually an imperceptible gradual shift from one extreme of the variation curve to the other, for example from the smallest to the largest individual. If by chance in the population of a species an individual exceeds the normal standard of variation, this appears to be a variation of quite a different kind.Is such an individual a new species?According to the view of creationists who prevailed from the 16th century to the 18th century, all new species were created by God "in the beginning", that is to say, in the original creation of the world recorded in Genesis in the Bible. created by god.It is puzzling that the occasional spontaneous occurrence of individuals outside the normal range of variation of a species is to be regarded as discrete variation.Is this evidence of continual creation as claimed by St. Augustine, or a sign that the nature of species is more malleable than previously thought? Darwin paid little attention to the importance of discrete variation in evolution.He only occasionally mentions mutant individuals who are very different from other members of the same population (including parents, siblings) in certain traits.When Jenkin criticized him in 1867 he mentioned such variants even less.In his letter to Wallace (L.L.D, III: 108) wrote, "I always thought that individual differences were more important; but I was wrong and thought it possible that single variations (discontinuous variations) were preserved more often than I now realize..., I think I am mainly I've been duped for providing such a simple and clear illustration of single mutations under artificial selection." A man who was as inquisitive as Darwin was obviously dissatisfied with such rare mutations.They appear to be accidents of nature, and most scholars who write about them never attempt to explain them. In reading Darwin's treatise on variation, one gets the impression that he thought it easier to explain normal continuous variation. His theory of natural selection was based on the assumption of endless individual variation, which in turn was based on his observation that each individual was slightly and uniquely different from the other.He repeatedly refers to this mutant individual: "We found many small differences, which can be called individual differences, which are often seen in the offspring of the same parent..., and this individual difference is very important for us. , because they furnish material for natural selection . . . I think individual differences alone are sufficient." Darwin's argument that natural selection gradually accumulates variants as a mechanism of evolutionary change was not very popular among his contemporaries.Some people criticized him for not explaining the reasons for this continuous variation, and some criticized him for ignoring or underestimating the importance of discontinuous variation that was widely circulated at that time.T. H. Huxley, who spent his life dissociated from essentialism, disagreed with Darwin's indifference to sudden change, writing in a famous review in The Times (April 1860): "We argues that Mr. Darwin would have been stronger if he had not been squirmed by the recurring aphorism 'Nature makes no leaps' which often occurs between the lines of his writing. We believe that...nature does sometimes make leaps, and acknowledging this fact is not Irrelevant." On this point Huxley was not alone.Many of those who acknowledged the idea of ​​evolution after 1859 valued mutation more than Darwin did.Botanists and horticulturists in particular cite a number of instances to illustrate this situation, which belong more or less to the same category as Linnaeus' Peloria (see Chapter 6), namely, the sudden appearance of particularly abnormal mode (type).Yet Darwin and his friends (such as Asa Gray) still denied the evolutionary importance of such anomalous types. This opinion clearly prevailed in the late 1880s.Darwin's equating of discontinuous variation with the formation of monstrous monstrosities and his thesis that new complex adaptations (phenomena) cannot be achieved overnight seem to have gained acceptance.Weismann, like Darwin, was a gradualist, and he once said: "The sudden transformation of species is inconceivable, because it would make the species impossible to survive" (1892: 271).But a growing number of other evolutionists argue that gradual variation is insufficient to explain the general discontinuity seen between species and between higher taxa. A particularly bitter view of the role of gradual change in evolution was the British zoologist Bateson, who later played a decisive role in the rise of genetics.His first important paper was the embryology study of Balanoglossus (Balanoglossus, hemicordia), which was published by American zoologist W. K． Completed in Brooks' laboratory.There Bateson developed a keen interest in the problems of evolution, especially the role of variation (without which natural selection would be meaningless).He once said: "Variation, no matter what its cause is,...provides the essential phenomenon of evolution. In fact, variation is evolution. Therefore, the easiest way to solve the problem of evolution is to study the reality of variation." (1894: 6).With regard to Darwin's thesis that continuous variation was the basis of evolution, Bateson, like Huxley before him, expressed displeasure at "unnecessary troubles arising from this assumption" (p. 15). "Since species are discontinuous, are the variations from which species are also discontinuous?" (p. 18). He reiterated this argument in his conclusion: "The discontinuity...is not due to the environment, nor to any adaptation, but to the intrinsic nature of the organism itself, expressed in the original discontinuity of variation. on” (p. 567). Oddly enough, Bateson's focus on variation at the time was purely evolutionary rather than genetic.in his.Compilation of Variation Research Materials.In one book, he collected a large amount of variation data in natural populations (598 pages in total) and pointed out the possible role of these variations in speciation. Many variants are indeed deformities.But Bateson pays special attention to variants outside the normal range of variation that are significant in species differences.From such evidence, Bateson draws the following conclusion: "The discontinuity exhibited by species . Sex arises from discontinuities of variation." Bateson thought in terms of individual types (patterns) rather than populations and did not change his views throughout his life (cf. his lecture in Toronto in 1922).Discontinuous variation was therefore for him the key to evolution, which is why he turned to heredity (see Chapter 16). Developments in the ensuing years showed that Bateson's arguments had a decisive influence on the thinking of many of his contemporaries. At the turn of the 19th and 20th centuries, two works gave even stronger impetus to the idea that new species originated from sudden mutations.In 1899 and 1901, the Russian botanist Korschinsky (S. Korschinsky) further developed the argument put forward by Kolliker in 1864, insisting that all living things have occasional discontinuities different from other members of their own species. The ability of the offspring ("heterosenesis", "heterosenesis").Darwin (1868) has reported many of these cases in cultivated plants; Koskinski goes far beyond Darwin in emphasizing that the differences from the type species are not always sharp, and may show differences of various degrees .Such anomalous individuals arise not because of circumstances but because of inherent potential. Catastrophism gained its greatest support due to de Vry's catastrophe theory (1901; 1903).Like Bateson, de Vrij starts with the fact that there are two types of variation.where "normal or so-called individual variability cannot ... lead, even under the most harsh and constant selection, beyond species boundaries" (1901: 4).Speciation must therefore be the spontaneous formation of new species by the sudden generation of discrete variants. "New species thus arise suddenly, arising from existing species, without observable preparatory stages or transitions" (p. 3). Unfortunately, de Vry's argument is entirely circular: he calls any discontinuous variant a species, and thus a species originates from any single step that gives rise to the discontinuity.The origin of species, he says, is the origin of its characters (p. 131).De Vry had no concept of populations or of species as breeding groups; he was a modelist through and through. His theory of evolution was thus based on the following three assumptions: (1) as far as evolution is concerned, continuous individual variation has nothing to do with evolution, (2) natural selection is irrelevant, and (3) all evolutionary changes are due to sudden large mutations, and the species has a mutatable phase and a non-mutatable phase.De Vrij describes how he began studying species near Rotterdam in 1886 in order to find a truly variable species. "I have bred more than a hundred of these species over many years, but only one has survived as I wished" (p. 151).All other species, he says, are in the non-mutatable stage.The only mutatable species is Lamarckian primrose (Oenothera lamarckiana). One can only shake their heads and sigh when they read de Vry's Die Mutationstheorie. The eminent physiologist and geneticist (whose 1889 book on pangenesis in cells was the most visionary and illuminating work on heredity until 1900) wrote in his Theory of Mutations " violates all principles of science.Not only did he adopt a circular argument on most of his conclusions, but he also based his entire theory on a single anomalous species, arguing without a shred of evidence that "a hundred or more other species" different from evening primrose happened to be In the "non-mutatable phase".His final conclusion was that species did not "originate" in the struggle for existence and natural selection, but were "eliminated" by these factors. Although de Vry's work had obvious shortcomings and was strongly opposed by leading naturalists of the time (such as Poulton, 1908), it still dominated biological thought from 1900 to 1910.As Dunn (1965a: 59) rightly points out, "De Vry's famous first volume, published in 1901, had in one sense a much greater impact on biology than the rediscovery of Mendel's laws. A well-known textbook of genetics at the time (Lock, 1906) summed up the Mendelian view as follows: "Species arise by mutation, in which a single trait or a whole set of traits changes by a sudden step." Morgan was initially (1903) enthusiastic about de Vry's teachings.This Mendelian view of evolution by mutation negates Darwin's theory of gradual evolution by selection.Thus, Bateson asserts that "the claim that large groups of people vary by imperceptible steps directed by choice is so untrue as it now appears to most of us, that we cannot fail to appreciate the To be amazed at their lack of insight, and at the same time unable to fail to marvel at their eloquent skill, is what makes their arguments seem admissible, if only temporarily (1913: 248)".Johansen even objected to any role for selection in evolution. To show how he totally rejected Darwin's theory of natural selection, Bateson also, with grace, claimed: "We support Darwin's incomparable efforts to gather facts (but ignore his theoretical preaching)...he can no longer speak to us with philosophical authority. We read his evolutionary scheme as we read Lucret the same scheme as that of Thompson (ancient Roman philosopher) or Lamarck" (1914:8).In denying Darwin, Bateson goes far beyond de Vry, who has repeatedly stated that his theory is merely a modification of Darwin's, not a replacement for it. The geneticist R.A. Fisher once said, "The early proponents of Mendel's theory almost completely misunderstood the relation of Mendel's discoveries . . . to the process of evolution.They believed that Mendelianism defeated the theory of choice.The granular theory of heredity meant, in their view, a corresponding discontinuity in evolution" (1959; 16). He was quite right in his assessment of the prevailing sentiment. The prevailing opinion was therefore that Darwinism was dead. This situation made In his otherwise authoritative History of Biology (1920-1924), Nordenskiold wrote: "The most important aspects of Darwin's theory were rejected long ago...and the objections that were raised when it was first published are essentially the same as those that contributed to its demise much later." Many scholars who opposed Darwin's theory at the time Among them, Morgan argues that mutational pressure alone is sufficient to do all that Darwin entrusted to natural selection. What upsets naturalists most is the lack of hereditary basis for so-called individual or fluctuating variation, often proposed by Mendelians such as de Vry.This is of decisive significance in the determination of geographical sects (geographically isolated species), and the Darwinian school regards certain geographical sects as primitive species.De Vry had to object to the concept of geographic speciation because it was in direct conflict with his mutation theory (species formed from genetically distinct individuals).He makes this very clear with regard to the geography of mankind: The variability exhibited by man is fluctuating variation, whereas species are formed by mutation.The two phenomena are fundamentally different. The assumption that human variability is related to variation and that variation must or is supposed to have caused the origin of species seems to me absolutely unreasonable... Favorable or unfavorable conditions of life, migration to different climatic zones, etc. traits have little effect.But this effect is only temporary, and once the interfering factors are eliminated, the effect it produces will disappear.On the other hand, the morphological traits (characteristics) of Zong are not affected by these factors at all.New variants do not arise this way.Humans have not formed new sects or types since the Pluviocene (Pleistocene).Humans are in fact nonmutatable, albeit highly mutable (1901, I: 155-156). (De Vry has another argument that is not at all factual!) The early Mendelian explanation of evolution can be summarized as follows: (1) Every change in evolution is due to the emergence of a new mutation, that is, the emergence or occurrence of a new genetic discontinuity.The driving force behind evolution is therefore mutation pressure. (2) Selection is an insignificant force in evolution, at best playing a role in weeding out deleterious mutations. (3) Because mutation can explain all evolutionary phenomena; and individual variation and recombination cannot produce any new state of affairs, so it can be ignored.Most continuous individual variation is not inherited. Naturalists were dismayed that all their discoveries and accounts since Wallace's pioneering article in 1855 had been ignored by experimental biologists.As Rothschild-Jordan said (1903: 492) "whoever has studied in detail and extensively the differences between geographical varieties laughs at the notion that species have arisen by mutation." Everywhere the naturalist sees Graduality and both believe (at least to some extent) in natural selection. Poulton (1908) not unreasonably scoffed at the catastrophists when he said, "Mutation without selection is reserved only for those who desire to revive Creationism (Creationism) under another name." However, naturalists also have some misconceptions.For example they are so obsessed with gradualness that they downplay Mendelian inheritance.的确，他们承认不连续性状可能遵从孟德尔定律，但是这样的一些性状终究没有什么进化上的重要意义。博物学家声称，渐进的数量性状才在进化上具有重要价值；但这些性状又不遵照德弗里和贝特森制定的孟德尔规律，因此就必须寻找另外的出路。 他们所能找到的解决办法只有两条，或者是新拉马克主义，或者是进化中的某种直生论。 虽然他们之中的大多数人都承认自然选择是一种进化力量，但并不是进化中的主要因素。 相反，博物学家倒仍然相信用进废退，环境的直接诱导作用或者软式遗传的其他表现。 直到本世纪20年代和30年代实际上所有的关于进化的主要着作在不同程度上都是坚决反对达尔文主义的，例如Berg，Bertalanffy，Beurkn，Boker，Goldschmidt，Robsonand Richards，Schindewolf，Wiills以及法国的所有进化主义者，包括Cuenot，Caullery，Vandel，Guyenot，Rostand等人的着作。在非生物学家中达尔文主义则更不怎样受欢迎。特别是哲学家几乎一致反对它，而且这种抵制一直持续到晚近（Cassirer，1950；Grene，1959；Popper 1972）。大多数历史学家同样也反对自然选择学说（如Radl，Nordenskiold，Barzun，Himmelfarb）。 在这两个阵营的某些直接对抗中根本看不出有妥协和解的愿望；所有的论据都是企图证明对方阵营是错误的。1929年在德国吞平根城举行的一次遗传学家与古生物学爱会议上，古生物学家采取了一种最愚蠢的策略。（Weidenreich，1929）。他们不去集中精力提出遗传学家（尤其是孟德尔学派）所不能解释的进化现象，反而集中力量试图证明获得性状遗传的存在，这个论题是他们无论如何也没有资格讨论的。可是还有极多进化问题是当时遗传学家的“基因频率变化”的进化概念所完全无法解释的，诸如相差悬殊的进化速度，主要结构类型的基本稳定性、主要结构类型之间的绝对不连续性以及物种的繁衍问题等等。 当这两个阵营的论战一旦开始（19世纪末与20世纪初），双方的思想概念互不相容。 更重要的是各自支持的某些解释又能被对方加以否定。但是只有在双方各自澄清了或部分地修正了自己的观点之后才能认清这一点。为了能够理解这两个阵营之间的矛盾是怎样解决的，就有必要对两个阵营在进化遗传学（约在1906年以后）和进化系统学（从达尔文以后一直到30年代）的进展情况加以介绍。这些进展最终促使这两个敌对阵营的和解成为可能并将这两种研究传统的正确成分加以综合。 12．2进化遗传学的进展 德弗里、贝特森、约翰森只代表了进化遗传学的一个流派，这个流派到本世纪的头十年即已消失。贝特森的对手生物统计学派（Provine，1971；见第十六章）则更加短命。上述这些进化遗传学先驱的过分简化的思想观点遭到新一代遗传学家的彻底修正。 源于实验动物学的一个学派（如哥伦比亚大学的摩根）和孟德尔学派原来的进化思想最接近，强调突变和个别基因不连续的独立性（Allen，1968）。但是从博物学或动植物育种学转入遗传学的其他遗传学家，例如瑞典的Nilsson－Ehle，美国的East，Jones，Castle，Jenninns，Panne，德国的Baur等通过实验研究发现遗传学证据和自然选择，进化的渐进性、种群思想之间并没有矛盾。 这些发现的详细历史将在第十七章介绍。其中对解释进化最为重要的可归纳如下： （1）只有一种变异，大突变和非常细微的个体变异（体）代表了同一梯度的两个极端。 （2）一切突变并不全是有害的；有些是中性的，还有一些肯定是有利的。 （3）遗传物质本身是不变的（稳定的），也就是说，没有软式遗传。 （4）重组是种群中遗传变异的最重要源泉。 （5）连续的表现型变异可以由多个因素（多基因）作用连同上位性相互作用的结果来解释，和颗粒遗传并不矛盾。 （6）一个基因可以影响表现型的几个性状（多效性，pleiotroPy）。 （7）实验数据以及观察资料都表明选择是有效的。 这些发现彻底驳斥了反选择主义者并完全否定了德弗里和贝特森的骤变进化学说。 奇怪的是这并没有招致骤变主义的消亡，它还持续了几十年并得到相当多的支持，例如遗传学家Goldschmidt（1940），古生物学家Schindewolf（195O）以及其他（特别是德国的）古生物学家，植物学家WilliS（1922；1940），还有一些哲学家。最后，除了多倍性（主要在植物中）外，人们普遍承认经由个体的物种起源和高级分类单位起源并不存在。骤变式发生的拥护者用来支持他们论点的一些现象现在很容易按渐进进化的观点来解释。对两个阵营的和解特别重要的是认识到前此一直被忽略的两种进化过程的重要意义。这两种进化过程是：不同生物和种群中进化速度非常不同（差别悬殊）；被隔离的小种群的进化演变。直到40年代和50年代进化综合开始时，为骤变式发生辩护的文章才从有关进化的文献中消失。