Chapter 24 Chapter 12 Diversity and Synthesis of Evolutionary Thought-2

The concept of evolution via mutational pressure, popular from Bateson, de Vry to Morgan, has lost momentum but not completely disappeared since 1910, and has recently been replaced by the concept of "non-Darwinian evolution". Supporters revived.The loss of the mutation pressure view was not only due to the growing support for natural selection (especially in the 1920s), but also due to the discovery of the phenomenon of reverse mutation.Stable evolutionary evolution through mutations is only possible if all mutations are in the same direction and cascaded.However, if the probability of mutation from a to a does not exceed the probability of back mutation from a to a, no evolutionary trend can be formed.Since Morgan discovered the formation of eosin eye by back mutation of white eye (drosophila) in 1913, more and more back mutations have been found. In many cases, the frequency from wild type to mutant type is not greater than that from mutant type to wild type The frequency, which has been determined by H. J．Confirmed by Muller and Timofeeff-Ressovsky (Muller, 1939).On the basis of these findings, the assumption that directed evolution (evolutionary tendencies) can be induced by mutational pressure is extremely unlikely.

Perhaps the most important contribution of the new genetics was the decisive rejection of soft inheritance.Such denials have been repeatedly postponed due to the frequent experimental confirmation of reports of acquired trait inheritance.Some of these reports are due to experimental error, while others are clearly fraudulent (Butkhardt, 1980).It is worth noting that some experimenters are often convinced that their experimental tests will produce the expected results, and thus "generate" data that cannot be obtained from their actual experiments.This psychological phenomenon has also been seen in other areas of experimental biology, such as cancer research and immunobiology.

Although the final negation of soft genetics must wait for the proof of molecular genetics, that is, the information obtained by proteins cannot be reversed to be transmitted to nucleic acids (it was not confirmed until the 1950s).However, geneticists point out that all the phenomena of gradual evolution and adaptive variation that have been used as evidence of heredity for traits in the past can be explained from the point of view of gene invariance (Sumner, Renxi, Meyer and other naturalists agree with this view).On the contrary, all attempts to demonstrate soft inheritance have failed (see Chapter 17).

Some geneticists focus on genetic mechanisms from the outset, while others are more interested in evolutionary issues.Geneticists wishing to understand the genetic basis of evolution have come to realize that evolution is a population (population) phenomenon and must be studied by population.Thus began a new branch of genetics, later called population genetics (population genetics).Geneticists interested in statistics such as Yule, Pearl, Norton, Jennings, Robbins, Weinbers, etc. made the first important contributions in this field.There is still a lack of a good history book to analyze this period, but these scholars seem to have reached some of the later conclusions of population genetics.Most of their discoveries are published in technical journals, so not many people know about them.Unfortunately, naturalists are mostly unaware of these research efforts.

Later, it was customary to refer to the genetics that studies the variation of gene frequency in a population as population genetics. The name "population genetics" is actually misleading because it encompasses two largely separate research programmes.One is mathematical population genetics, which is related to the research of Fisher, Haldane, and Wright (Sewall Wright).its "population" It is a group in statistics. Research work in this field can be done with paper and pen, later with a calculator, and now with a computer.Another form of population genetics is the study of actual populations of living organisms in the field and in the laboratory.There is no history of it yet.Active figures in this field are Schmidt, Goldschmidt, Sumner, Langlet, Baur, Chetverikov, Timofeeff-Ressovsky, Dobzhansky, Cain, Sheppard, Lamotte, Ford.

They mainly study the distribution of genes in natural populations, and changes over time.To distinguish it from mathematical genetics, Ford (1964) suggested calling it ecological genetics. Mathematical population genetics arose out of a debate between Mendelians (particularly Bateson) and biostatistics (Weldon, Pearson).The biostatistical school, while quite right in emphasizing the importance of continuous variation as the material of natural selection, also assumed heredity to be fusion.Early Mendelians recognized the granular nature of inheritance, emphasizing discrete variation.An important advance in evolutionary genetics was the demonstration that there is no contradiction between granular (non-fusion) inheritance, continuous variation, and natural selection.

The basis of all mathematical population genetics is the so-called Hardy-Weinberg equilibrium theorem (1908).This theorem states that the frequencies of two alleles (a and a) in a population will remain constant from one generation to another unless their frequencies are affected by immigration, mutation, selection, nonrandom mating, or sampling error and other reasons (for the discovery history of this theorem, please refer to Provine, 1971: 131-136).In the more than 30 years since the theorem was published, mathematical population genetics has focused on how different mutation rates, different selection pressures, and sampling errors affect the genetic composition of populations of different sizes.

The first question to investigate is whether or how effective selection is when a new allele is introduced into the population when the selective advantage (selective advantage) is small.British mathematician H. T． J． Norton has studied this problem for genes that occur at different frequencies under different selection intensities.Surprisingly, he went so far as to demonstrate that small (less than 10%) selection benefits (or selection losses) can cause drastic genetic changes in a few generations.This discovery deeply touched Haldane (who published a series of articles on selected mathematical problems in the 1920s) and Soviet naturalist and geneticist Chetvenikov (SS Chetverikov).The conclusion that alleles with small differences in selection value can replace each other very quickly in evolution has prompted some neo-Lamarckians (such as Renxi and Meier) to abandon soft inheritance, because it was already clear that things like climate Species (clans) and other environment-related adaptation phenomena can be explained by selection acting on multiple alleles and genes.

Beginning in 1918, Fisher (R.A. Fisher, 1890-1962) published a series of articles on the mathematics of gene distribution in populations.These studies involve the division of genetic differences into additive parts (caused by alleles or independent genes with similar effects) and non-additive parts (epistasis, dominance, etc.), and the conditions under which polymorphisms are maintained in balance, dominant role.The rate of dispersal of favorable genes in populations of different sizes.Some of his discoveries, such as equilibrium polymorphism, are now so certain that it is almost impossible to understand how he could have studied it in the first place.His other research conclusions are also substantial and credible, but they have only been fully utilized in the last ten years.

Fisher's most important conclusion was that most continuous variation, at least in humans, is due to the action of multiple Mendelian factors rather than environmental influences.His emphasis on genes that have little effect on phenotype has gone a long way toward dispelling the rift between geneticists and naturalists.Like most mathematical geneticists, Fisher also tends to try to minimize the effects of genetic locus (loci) interactions. Fischer has always focused on large populations. Although he is fully aware of the existence of sampling errors, he believes that due to differential selection and recurrent mutations of competing genes, such selection errors will eventually have little effect on evolution. This is indeed the case for large populations.Another geneticist, Sewall Wrisht, disagreed with Fischer on this point, sparking a debate that is still unresolved.It was J.T. Gulick who first (1872) advanced the contention that most evolutionary changes are simply the result of random variation.This argument was prompted by his observations of local snail populations in Hawaii, where they observed a great variety (diversity) and occasional variations in appearance in the absence of exact differences in environmental factors.Since then, the argument that most variation is neutral in selection has been repeatedly advanced.Fischer (1922: 328) called this random variation the Hagedoorn effect, after the names of two scientists who had collected a large amount of evidence to support this view.Their argument (similar to Gulick's) is based on the assumption that most of this variation is actually neutral with respect to selection.In contrast, Fisher argued that most allelic polymorphisms in a population are due to heterozygosity.

Wright, a student of W.E. Castle, began to study the genetics of skin color and inbreeding effects in guinea pigs in 1914.This study led him to realize that "effective breeding populations" (later called congeneric or mixed taxa, demes) are generally small even in wild animals, making sampling error a non-negligible factor. Of course, gene flow from adjacent populations can generally prevent random fixation of genes, but there is enough "genetic drift" (genetic drift) to favor gene combination, which is unlikely to occur in large populations.In his first major paper (193la) the formulation gives the impression that he advocated genetic drift as an alternative mechanism of natural selection, which caused some confusion.Wright's views became widely known among evolutionists through Dubzhansky's Genetics and the Origin of Species (1937), and in the 1940s and 1950s a tendency emerged to convert almost everything Evolutionary phenomena are all attributed to genetic drift.In both Dubzhansky's work and Simpson's (1944) quantum evolution, genetic drift plays an important role in the "non-adaptive phase" concept.The backlash against the abuse of genetic drift was finally triggered, as described by Mayer (1963: 204-214). As a student of Kessel, Wright had certain contacts with naturalists and was particularly interested in the research of F.B. Sumner in the 1920s (Provine, 1979).Wright therefore tends to think in terms of natural populations and recognizes that genetic fitness values ​​are not fixed but changing. "Genes that favor one kind of combination . . . are likely to be unfavorable for another" (1931: 153).Unfortunately, he rarely applies this insight to his equations and graphs; he does so almost exclusively with single genes and fixed fitness values.Wright, like Chetvinikov, was particularly impressed by the pleiotropic effects of genes: "Because genes often have multiple effects . 1931a:105).Because of his background, among the mathematical geneticists his thinking is closest to that of the naturalist.Wright's view of species as groups of populations (aggregates) was a prerequisite for his later collaboration with Dubzhansky. Population genetics, which originated in the Soviet Union, mainly through the work of Sergei S. Chetvegikov (1880-1959) and his students, represents another school of very different temperament.Russia is traditionally very different not only from the United States but also from Western Europe.Before the 1920s, the theory of natural selection was more popular in Russia than in other countries, and natural history enjoyed a higher prestige and influence in Russian universities.Even today most students studying zoology, such as Moscow University, spend their summers doing fieldwork at biological field stations or elsewhere. There were several institutes of genetics in the USSR (two in Leningrad and one in Moscow), and in the 1920s there seemed to be as many geneticists in the USSR as there were in all the rest of continental Europe combined.From 1924 to 1929 Chetvinikov was director of the Genetics Laboratory at the Kotsov Institute of Experimental Biology in Moscow.He is a keen expert on butterflies, and at the age of 76 he also described a new species of butterfly from the Ural Mountains.He also paid close attention to evolutionary issues. In 1906, he published an important paper on the growth and decline of populations. The importance of population growth and decline (especially its key links) in evolution was not fully realized before.He has taught genetics since the early 1920s and was the leader of a sizable research group of genetics enthusiasts.He was forced to leave Moscow in 1929 for political reasons and could no longer pursue genetics research (Adams, 1968; 1970; 1980a). Since he was a naturalist himself, this background allowed Chetvinikov to answer the questions and criticisms of opponents of Mendelism far more eloquently and convincingly than Morgan or mathematicians.In one of the most important works in the entire history of evolutionary biology (1926) he set himself the task of "clarifying certain evolutionary problems with our present concepts of genetics" (p. 169).First, he points out that there is a complete, almost "imperceptible transition from a fully normal viable mutation" to a less viable or even lethal mutation.The idea that all mutations are harmful is incorrect.In fact, as Dubzhansky and others have pointed out, there may be mutations with higher fitness than wild type.Chetvinikov clearly understood (as did Fischer and others before him) that a new mutant always begins as a heterozygote, and that if it is recessive it can remain hidden in a population for a long time (unless lost due to sampling error), since only heterozygotes are available for selection.He thus concludes that "species are like sponges, sucking up heterozygous mutations and remaining outwardly (phenotypically) homozygous" (p. 178).A large amount of cryptic genetic variability should therefore exist in each species.To test this idea, he collected 239 wild-type female fruit flies near Moscow and sib-mated among their offspring. In this small number of samples, he found that no less than 32 loci (sites) were segregated to become visible and recessive, thus confirming his hypothesis.No one before him had guessed that there were such a number of cryptic variations in a wild population.His students, especially N. V． Timofeeff-Ressovsky, BLA Staurov, N. P． Dubinin, D． D． Romashov began by rigorously analyzing genetic variation in wild populations and combining it with experimental studies in the laboratory.Dubzhansky, although not a member of this research group (he worked with Filipshchenko in Leningrad), followed these studies keenly, which is one of the reasons why he later worked on fruit flies . In Chetvinikov's view, population changes are not the result of mutational pressure but the product of selection.Based on Norton's statistical tables (1915), he refined his arguments and finally concluded that "even if the biological improvement is insignificant (slightly superior to a certain gene), it still has a certain probability of constituting all the individuals of the free-breeding population (species) spread out” (1961: 183).Whether the new gene is dominant or recessive, it doesn't matter whether its selective effect is 50% or just 1%; "the complete replacement of a gene by a more adaptive gene always goes to the end." Whereas Fischer and Haldane expended their main energy on proving the validity of choice, Chetvinikov, following the Russian tradition, took choice for granted, which led him to turn his attention to other issues. Many of Chetvinikov's conclusions were finally made independently by Fischer, Haldane, and Wright, and these conclusions entered the western evolutionary literature through them.Chetvinikov is far ahead of the Western genetics because he has a clearer understanding of the importance of gene interaction in evolution.He categorically rejected "the previous notion of a mosaic of independent genes" and concluded that "each hereditary trait...is not determined by a single gene alone, but by a whole The complex determines." No gene has a constant fitness value because "the same gene behaves differently because of the relationship of other genes in the complex in which it is found" (p. 190). Each gene is phenotypically expressed depending on its "genotypic background". Chetvinikov bases his conclusions on the discovery (particularly by Morgan's group) of pleiotropic effects of gene action; pleiotropic effects of genes on several components of the phenotype (see Chapter 17).His student Timofeeff-Ressovsky once discovered the important performance of pleiotropy (1925).In contrast, mathematical population geneticists, notably Fisher and Haldane, focused on the behavior of individual genes for the sake of simplicity.What is described in their equations and graphs is only the increase or decrease in frequency of individual genes under the influence of selection, mutation, sampling error, etc.Genetics textbooks in the 1940s and 1950s all included experimental exercises, in which genes were represented by beans of different colors, packed in pockets, and mixed and picked according to certain experimental rules as the representation of each generation.Mayer (1959d) coined the nickname "bean-bag genetics" for genetics that disregards gene interactions because of the complete exclusion of gene-to-gene interactions in this type of exercise.Unfortunately, most of the mathematical population genetics at the time was "bean bag genetics".Even a scholar like Wright, who is well aware of the significance of gene interactions, considers the behavior of individual genes almost exclusively in his mathematical calculations and expositions.It was thus not until the 1950s and later that Chetvinikov's concept of genotypic background fully penetrated the minds of evolutionary biologists. Although Russian publications were hardly read outside the Soviet Union, the writings of the Chetvinikov school were not entirely unknown in Britain and the United States.At least three of Chetvinikov's 1927 articles and Timofeeff-Ressovsky's papers have been translated into English or German and published in relevant publications, and the Reerdan Laboratory also has a full translation of Chetvinikov's 1926 papers .Since Timofeeff-Ressovsky and Dubzhansky left the Soviet Union at the end of the era, they are still working hard to spread the ideas of Chetvini's school of thought.This undoubtedly made an important contribution to evolutionary synthesis. Together, Chetvinikov and mathematical population geneticists were on a mission to defeat the Mendelian theory of evolutionary genetics.They demonstrated the importance of selection and the absence of mutational pressure; they established the genetic basis of Darwinian evolution and demonstrated the absence of soft inheritance.In the end they revealed that there is no contradiction between discontinuity in genes and continuity in individual variation.They laid an important foundation for a bridge to the camp of naturalists who had been opposed to the de Vryian's large mutations and mutational pressures, but who also emphasized the importance of gradual evolutionary evolution and natural selection. 12.3 Advances in evolutionary systematics The rapid progress made in evolutionary genetics has been paralleled by great advances in systematics (and more specifically, naturalists' understanding of biological diversity).In fact, the kind of population genetics that Chetvinikov understood was nothing more than the transfer of concepts and methods that had existed in systematics for more than a hundred years to genetics.I refer to the study of the different geography of a species, which has been casually discussed by Buffon (in North American fauna) and Ballas (in Siberian fauna).And fully extended by KDG (Gloser).Henceforth, wiser taxonomists have paid more attention to the inherent differences among different groups, especially among species geography. Such population differences have been mentioned successively by Linnaeus (1739), Buffon (1756), Blumenbach (1775), Ballas (1811), von Buch (1825), and Kroger (1827, 1833). been.This has also been generally known to foresters in Sweden, Germany and France since the mid-18th century (Langlet, 1971).Hooker found that the hardiness of pine trees and stone barrels at different heights in the Himalayas varied greatly, and Darwin had cited this information (1859: 140).It was soon realized that this variation is closely related to the environment, and the term climate family (climate family) was created in the middle of the 19th century.In botany also extended to the study of soil factors.The combination of soil factors and climate factors will develop into an ecotype (Turesson, 1922).Among the studies that emphasize the geographical aspect are Baur's studies on Spanish snapdragon populations (Schiemann, 1935; Stubbe, 1966).Zoologically related are such studies by Schmdt (1917) on fish, Goldschmidt on diabolism moths, and Sumner on North American white-footed mice. But none of these experimental materials are as amenable to detailed genetic analysis as fruit flies.It is worth noting that most of Chetvinikov's research work is to bring classic and ancient problems to a new and particularly appropriate research material. The development of population systematics so that it could be easily transformed into population genetics was one of the great contributions of naturalists.They (Darwin himself was one of them) carried on a tradition of studying natural populations, variation within populations, and variation between populations along geographical gradients.They take the population as the unit of evolution rather than the phylogenetic lines that comparative anatomists and paleontologists value.Naturalists are the only biologists who study isolation as well as geographic and individual variation.In addition to animal breeders, naturalists first recognize individual (individual) and formulate their methodologies accordingly, and thus oppose "mass collection" or "serial" collection.This inevitably leads to the use of statistics, but Galtonian statistics (Galtonian statistics) emphasizes the variance rather than the mean.A proper history of evolutionary natural history is unfortunately lacking, although some developments are described in Stremsman's Ornithology (1975) and in Meyer's Historical Review (1963). The most important contributions made by naturalists are conceptual.A true understanding of natural selection, speciation and adaptation was only possible after population thinking replaced pattern (type) thinking.The population thought of naturalists had a particularly important influence on Chetvinikov and his school.Naturalists were not the only ones who helped spread the concept, however. Another source of population thinking comes from animal and plant breeders, as Darwin did.Certain geneticists who were closely associated with breeders, such as Castle, East, Emerson, and Wright, were also very successful in avoiding the quagmire of model thinking.Population thinking led among naturalists to the new concept of "clans" as variable populations, each with its own distinct geographical (sexual) history. The concept of "Zong" leads to the concept of biological species, which finally comes down to the so-called new systematics, more correctly, it should be called population systematics (see Chapter 6). It is the naturalist who solves the great species questions, questions that the geneticist avoids altogether or cannot answer well with pattern thinking.The naturalist points out that species are not essentialist entities, not characterized by form, but collections of natural populations which are reproductively isolated from one another and possess species specificity (species specificity) in nature. ) ecological niche (niche).Certain further knowledge is necessary to fully understand the nature of species, such as the distinction between taxa and (taxonomic) levels, and the recognition that the word "species" is a word of mutual relation (like the word "brother") , and philosophically speaking, a species taxonomic unit is an individual, and members of a species are "components" of this individual.Nowhere is this more true than when we consider that the genes of all members of a species are part of the same gene pool (Ghiselin, 1974b; Hull, 1975; see also Chapter 6). New insights into the nature of populations and species have allowed naturalists to solve the age-old problem of speciation, a problem that had been elusive to those who had sought answers at the level of genes or genotypes.The only solution to the above-mentioned level can only be the instantaneous speciation through violent mutation or through other unknown processes.As de Vry (1906) once said, "The theory of mutation presupposes the emergence of new species and varieties by definite leaps from existing forms." Or, as Goldschmidt (1940: 183), "the evolution The decisive step towards macroevolution, that is, the step from one species to another, requires another mode of evolution than the mere accumulation of small mutations (that is, the hopeful deformity The emergence of organisms).” The naturalist recognized that the essential factor in the speciation process was not the physiological mechanism involved (genes or chromosomes) but the phoenix, a certain population. Meyer therefore defines geographic speciation (effect) by population as follows: "If a population is geographically separated from its parent species and acquires during the of the relevant characters, a new species is formed" (Mayr, 1942: 155). The most important conceptual advances are the systematic and precise formulation of the problem.It is not enough to explain the origin of variation or the beginning of evolutionary evolution within populations in order to explain speciation.What must be explained is the origin of reproductive isolation between populations.Speciation is thus not so much the initiation of new types (patterns) as the origin of effective means of preventing the influx of heterologous genes into the gene pool. This insight is more than a hundred years old.It was von Buch (L. von Buch, 825) who first proposed that speciation is geographical in most cases.This concept is evident in Darwin's 1837-38 notebooks and 1842 and 1844 papers (Kottler, 1978; Sulloway, 1979), as well as Wallace's 1855 essay.But later this view gradually weakened.Beginning in the early 19th century, Darwin argued that speciation, especially on continents, could occur without strict geographical isolation, which brought him into a bitter debate with Moritz Wagner . Wagler (1813-1887) was a famous explorer, collector and geographer. He spent three years (1836-1838) exploring in Algeria, North Africa.He found there that each species of the wingless beetle (pimelia and melasonma) was invariably distributed on the northern slopes of the zone between the two rivers that flow down from the Atlas Mountains.Once across the river, another beetle appears. (Wagner, 1841:199-200).Wagler's later travels in West Asia also confirmed the isolation of rivers; and through the comparison of fauna on both sides of mountain ranges (such as the Caucasus Mountains), or in terms of mountain animals and plants, the main peaks separated by basins (such as South American Anders Dashan), he believes that this is also geographical segregation, and draws the following conclusions from it: True varieties (referred to by Darwin as holospecies) can form in nature only when a few individuals have transcended the limits of their range and been separated in space for a long period of time from the other members of their species... In my opinion, if alien The formation of new sects is by no means possible without long periods of continuous isolation from other members of its species. ...unrestricted interbreeding, the unrestricted cross-fertility of all individuals of the species will produce uniformity, and any variety whose character has been fixed at the end of many generations will revert to its original state. The above passage seems to give a very reasonable account of the process of geographic speciation.Unfortunately, Wagler combined this with some strange variations and selection views.He believed that the isolation of the founder population (founder population) would cause increased variability, and he also believed that only in such isolated populations could natural selection really work (Sulloway, 1979). From Darwin's point of view, this was going too far.Not only was Darwin right in insisting that natural selection and evolution could proceed without isolation, but he also clearly argued that isolation is not a necessary condition for speciation.Darwin concluded his refutation of Wagler's argument with the following emphasis: "My strongest objection to your (geographic speciation) theory is that it does not account for the structurally diverse adaptations of each organism ( phenomenon)" (L.L.D, III: 158), it seems that speciation and adaptation are mutually exclusive phenomena.Perhaps Darwin was compelled to take this hard stand by the following statement by Wagler; Wagler said: "Organisms which never leave their ancient ranges never change" (1889:82), which is certainly not quite true, but it may be closer to the truth than it has been believed to be for more than half a century. After a while Weissman also got involved in the controversy.He published his Reply to Wagler (1872), perhaps the worst of the many excellent articles he published.Wagler's original question, "Can species reproduce without geographical isolation?" was changed to the following questions: "Is isolation itself the cause of changes in isolated populations?" and "Is isolation necessary for varieties to cease to change?" of?" The question of attaining reproductive isolation is never mentioned in Darwin's writings, the emphasis is on the degree of morphological difference.How superficially Weismann and his contemporaries understood what the essence of the problem of reproduction of species really was can be illustrated by quoting Weismann, "How in this respect did they (endemic species present in isolated areas) originate? Whether it is mutual infertility (amixia) during the mutation stage or due to natural selection, these are attempts to adjust the relationship between the immigrant and the new environmental conditions of the quarantine area. Effects that are completely unrelated to the quarantine, such as Changes can also be brought about by the direct influence of the physical environment, or by the process of sexual selection" (1872: 107). Wagler has been insular in his insistence on the importance of geographic separation.Wallace squarely sided with Darwin and concluded: "Geographic or local isolation is of no importance in the divergence of species, since the same result would have been obtained by initial species which acquired different habits or frequented different habitats; the same The different varieties of a species will be willing to mate with like-like counterparts, so that the most efficient forms of physiological isolation will do the same." Needless to say, Wallace has produced no proof for these assertions. One of the ironic aspects of the Darwin-Wagler polemic is that each side consistently eluded the other.Wagler insisted that reproductive segregation is generally impossible without geographic segregation.Darwin, fascinated by the principle of divergence at the time, replied that "neither isolation nor time in itself has any effect on the modification of species" (L.L.D., II: 335-336), it seems that Wagler denied that phylogenetic evolution occurred.In all his correspondence with Wagler, Semper, and Weissmann it is evident that Darwin did not understand how intractable a problem it was to achieve reproductive isolation. A major difficulty is that most of those involved in the debate in subsequent years—Romans, Gulick, and even Wallace (Lesch, 1975)—did not distinguish between geographic and reproductive isolation, between individual variation and Geographic variation, and is often equated with natural selection in discussions of speciation.What makes this confusion particularly irritating is that in Romance's writings he coined the misleading term "physiological selection" in place of reproductive isolation.There has been no comprehensive critical analysis of the literature of this period, but in general there are two camps, and those who followed Darwin did not make a clear distinction between the two types of segregation (among them Weismann, Simper, Romance, Gulick and Wallace); those who support Wagler believe that geographical isolation is a special factor necessary for speciation (eg Seebohm, K. Jordan, D. S. Jordan, Grinnell. Many entomologists such as H.W. Bates, and possibly Meldola, Poulton, Kerner, Wettstein among botanists). The theory of speciation by geographic isolation after 1900 was almost completely eclipsed because isolation was no longer considered necessary in the mutationalism developed by Bateson and de Vry.Because of D． S． Jordon K． The importance of geographic isolation in speciation has not been entirely forgotten by the efforts of Jordon, Streathman, Renxi, Mertens, and other taxonomists.However, as late as 1937, Dubzhansky included both internal genetic factors and external geographical barriers in the isolation mechanisms he enumerated.One of the main arguments in Meier's Systematics and the Origin of Species (1942) is that there is a fundamental distinction between these two classes of isolating factors, and (as Wagler and K. ) Geographical isolation is a prerequisite for building an internal isolation mechanism.在澄清概念上另一项是按种群观点给隔离机制下定义（Mayr，1970：56）。然而甚至在今天还有不少学者混淆了物种形成机制（基因，染色体等等）和物种形成中所涉及的种群所处的位置（即种群是同域的还是异域的），不认识这两个方面是彼此独立而又是必然同时涉及的。从1942年起（由博物学家努力解决的）地理物种形成的重要意义并没有被否定。仍有争议的主要问题是两种可选择的过程，如瞬时成种（通过多倍性或其他的染色体再组成）和同域成种的相对重要性。 博物学家对进化思想所作出的另一贡献是他们认识到物种内地理变异的适应性质。 这大大加强了渐进进化的信念。远见卓识的博物学家早在1859以前就观察到不仅很多物种的不同种群彼此不同（地理变异），而且多数这种变异是渐进的并且和环境因素有关，也就是说它是适应性的（Gloser，1833；Bersmann，1847）。由Allen（19世纪70年代），Sumner（萨姆纳）（20世纪20年代），壬席（二三十年代）深入细致地研究这类气候变异为达尔文的进化演变的渐进性以及环境的重要性论点提供了有力的支持（Mayr，1963：309－333）。对植物也进行了类似的但不够系统的研究，特别是通过将北方树种的个体移植到南方纬度，这种实验证实了与气候有关的地理变异（Langlet，1971；Stebbins，1979）。然而在早期孟德尔学派坚持遗传变异是急剧的和不连续的那个阶段，这类适应性变异被大多数博物学家（30年代早期）认为是有利于软式遗传的重要证据（Rensch，1929）。 12．4进化综合 20世纪的头30多年实验遗传学家和博物学家之间的鸿沟是如此之深广似乎没有办法弥合。德国着名生物学家Buddenbrock在30年代曾说过：“争论…在今天就和70年前一样仍然没有解决…双方都不能否定对方的论点，看来这种局面将不会很快改变”（86页）。这两个阵营的成员仍然说不同的话，提出不同的问题，依从不同的概念，这从当时的文献中可以充分看出。（Mayr and Provine，198O）。 怎样才能打破这种僵局？怎样才能说服双方承认他们的某些假定是错误的或者（尤其是实验遗传学家方面）他们的解释忽略了某些重要方面？这两个阵营要能联合必须在事前满足两个条件： （1）对多样性和种群进化都感兴趣的年轻一代遗传学家必须成长起来。 （2）博物学家必须认清这新一代的遗传学家对进化的遗传解释不再反对渐进性和自然选择。 这种局面一旦出现，思想的融合在1936年到1947年这短短的12年中就很快而且彻底地实现了。在这些年中进化生物学的绝大多数分支领域的生物学家以及很多国家的生物学家都接受了两项主要结论：（1）进化是渐进的，这是按小的遗传变化与重组的观点以及通过自然选择将这类遗传变异加以整理的观点来说明；（2）由于运用了种群概念，将物种看作是种群生殖隔离的集群，并通过分析生态因素（占有生境，竞争，适应辐射）对多样性的高级分类单位起源所产生的影响，就能够用既符合已知的遗传机制又符合博物学家的观察证据的方式来解释一切进化现象。JulianHuxlev（1942）将对上述几点取得一致意见的重大成就称为“进化综合”（或综合进化论，the evolutionarysynthesis）。进化综合要求博物学家放弃他们对软式遗传的崇拜，要求实验生物学家戒除模式思想并乐意将多样性起源列入他们的研究计划。进化综合使“突变压力”概念式微衰退并用深信自然选择的威力和对自然种群具有无穷无尽的遗传变异的新认识来代替它。 上面只是说明了在综合过程中发生了一些什么事态，并没有提到综合是怎样实现的。 现在普遍认为两个阵营的和解是通过为数不多的进化主义者的努力才实现的，这些进化主义者既能在不同学术领域之间架起桥梁，又能消除阵营之间的误解。 一个进化主义者应当具备什么条件才能成为一个搭桥者？首先他必须高出于狭隘的专家。他必须乐干熟悉他自己专业领域之外的生物学其他领域，了解其他领域的新发现。 他必须具有灵活性，能够放弃原先的旧观念，接受新观念。例如萨姆纳、壬席、迈尔起初相信软式遗传，在熟悉了遗传学新发现后才采取了严格的新达尔文主义观点。对进化综合的建筑师们的着作现在仍然缺乏批判性的分析。他们的新观点（如果有的话）是什么？它是不是收集了大量的有决定性影响的事实？它所注意的焦点是不是特别有影响的一些具体进化现象（物种形成，适应辐射，进化趋向等等）？哪一些新的遗传见解最有利于消除误解？每一位综合建筑师的特殊作用是什么？这些问题（以及很多其他问题）都没有取得完满的答案。对进化综合的研究显然还只是刚刚开始（Mayrand Provine，1980）。 如果我们把综合的建筑师看作是他们的主要着作实际上在不同的领域之间构筑了沟通桥梁，那么特别是有六位学者的名字闪入我们的脑海，他们是：杜布赞斯基（1937），赫胥黎（1942），迈尔（1942），辛普森（1944；1953），壬席（1947），史太宾斯（Stebbins，1950）。必须强调的是还有许多许多进化论者协助“清理岩层”从而使桥梁得以建成而且还提供了重要的建筑材料。这些人中首先是苏联的切特维尼可夫和季米费叶夫雷索夫斯基；英国的菲舍、霍尔丹、达林顿（Darlington）、福特（Ford）；美国的萨姆勒、戴斯（Dice）、斯特体范特（Sturtevant）赖特；德国的鲍尔（Baur）、卢德维希（Ludwig）、斯垂思曼（Stresemann）、齐默曼（Zimmermann）；法国的台斯尔（Teissier）和莱赫雷梯（lHeritier）；意大利的布扎提特拉维索（Buzzati－Traverso）；另外，Heberer主编的《生物的进化》（1943）和赫胥黎的《新系统学》 （1940）也对进化综合作出了贡献。 在对进化综合最积极的十来个学者中，他们每个人都有自己的专业领域。只要提起杜布赞斯基、辛普森、迈尔、壬席、赫胥黎和史太宾斯这几个人对这一点就很明显。然而他们又都有一个共同点：他们都认识到各个进化学派之间的信息沟并企图通过协调摩根、菲舍等的基因频率观点和博物学家的种群思想来填平这一鸿沟。 和进化综合的突然来临令人感到同样惊讶的是，它在进化生物学界传播之迅速。 1947年1月2日至4日在美国普林斯顿举行的一次国际学术会议上，生物学大多数领域和学派（死硬派的拉马克主义者除外）的代表都一致同意综合的结论。所有与会者都赞同进化的渐进性，自然选择的突出重要性以及多样性起源的种群观。（Jepsen，Mayr andSimpson，1949）。然而也并不是所有其他的生物学家都是如此，这可以从菲舍、霍尔丹、穆勒（Muller）迟至四五十年代还一再努力反复提出支持自然选择普遍性的证据这件事看出；另外，从少数着名生物学家（如MaxHartmann）对进化的一些合理怀疑言论也可以察觉。 凡是参与进化综合的学者以及某些历史学家都完全同意有一份特别重要的着作宣告了综合的发端，而且事实上它比任何其它着作更是促成综合的契机，这就是杜布赞斯基的《遗传学与物种起源》。正如邓恩（L．C．Dunn）在该书的序言中正确指出的，这本书象征了“某种只能称之为回到自然的运动。”该书开头第一章是讨论生物的多样性，其它各章涉及自然种群的变异，选择，隔离机制，以及作为自然单位的物种。杜布赞斯基在该书中顺理成章地将博物学家对进化问题洞察入微的深刻了解和他前此12年作为一个实验遗传学家的深湛学识密切地结合起来。他才是第一个真正在实验生物学家和博物学家两个阵营之间架起牢固桥梁的人。 进化综合一劳永逸地断然结束了无数的古老争论，从而为讨论全新的问题开拓了道路。这无疑是1859年出版后进化生物学历史上最有决定性意义的事态。然而科学史家和科学哲学家对进化综合究竟是怎样切合科学进展学说的却迷惑不解。它肯定不是一次科学革命，因为它显然只是达尔文进化学说的最终成熟。但是它是否配称为“综合”？对这个问题我是断然作出肯定回答的。 我在上面介绍了进化生物学家两大阵营，即实验遗传学家阵营与种群博物学家阵营的根本不同观点和专心致志的工作。它们就像Laudan（1977）所说的真正代表了两种十分不同的“研究传统”。Laudan指出“有时当两个或更多的研究传统，彼此不是互相拆台，可以融合起来，产生综合，这综合比前此的两个或更多的研究传统都更进步” （103页）。从1936年到1947年在进化生物学中所发生的恰恰就是两种研究传统（以前彼此不可能交流信息）的这种综合。这里并没有一种模式战胜另一种模式的情形，就像Kuhn的科学革命学说那样，而是前此彼此竞争的两种研究传统“交换”彼此最有生命力的组份。由于这个原因，说综合仅仅是博物学家接受了遗传学的新发现显然是不正确的。 这样就会忽略博物学家所提供的许多概念：种群思想，多型种的多维性（multldimensionality of the Polytypic species），生物学种概念（将物种定义为生殖的和生态的自主实体），行为的作用以及功能变化在进化奇迹起源中的作用，以及全面强调多样性的进化。所有这些概念都是充分理解进化所不能缺少的，然而在实验遗传学家的概念结构中却几乎并不存在。 在短时期里，对进化生物学影响最大的也许是否定了一些错误概念。这包括软式遗传、骤变、进化本质论、自然发生学说。进化综合着重证实了自然选择的无比威力，进化的渐进性，进化的两重性（适应与多样化），物种的种群结构，物种的进化功能，硬式遗传。虽然这意味着进化主义者所能选择的余地大大缩小，但是它仍然留下许多问题没有解决。这些问题分为两类，由下面的两个问题表示：（1）某一现象（选择，渐进进化，生物学种等等）的意义是什么？（2）某一进化原理或进化现象怎样在个别情况下实际起作用并且又会引出什么新问题（例如将之运用于选择、隔离、产生变异、随机过程等等）？