Chapter 18 Chapter 9 The Eclipse of Darwinism-2

In the 20th century, Lamarckism quickly lost its reputation in experimental biology, especially in English-speaking countries.The inheritance theory of modern genetics makes the Lamarckian effect impossible, and biologists actively avoid exploring more variable genetic systems.No one dared to support the idea of ​​cytoplasmic transmission in addition to the nucleus (Sapp, 1987). Because of such obstacles in the process of exploring the mechanism, Lamarckism can prevail.Only in Germany, since genetics did not develop in a dogmatic form, there was an interactive relationship between experimental biologists and paleontologists exploring the mechanisms of non-Darwinian evolution (Reif, 1983, 1986).In the United States and Great Britain, paleontologists and field naturalists still supported neo-Lamarckism and Orozoism, but in doing so they further distanced themselves from the branch of experimental biology.It was not until the advent of modern synthesis in the 1930s and 1940s that the rift between the different disciplines was healed (Mayr and Provine, 1980).Occasionally, favorable evidence has been reported and has caused considerable controversy.Moreover, there are still many people who support Lamarckism outside the scientific community, including writers who support the theory because of its deep emotional appeal.In the first decade of the 20th century, Lamarckism was very popular among those who tried to broaden its meaning.

Among non-scientists, the playwright George Bernard Shaw was the most active proponent of Lamarckism (Smith, 1965).In Man and Superman in 1901, and especially in The Return of Methuselah in 1921, George Bernard Shaw declared that Lamarckism could save the evolution movement philosophically.Because the theory of choice explains everything as the accidental and meaningless product of a brutal struggle, George Bernard Shaw thinks otherwise.Lamarckism at least makes people feel that through their own efforts, life can hope to reach a higher form, so it is the philosophy of all normal thinking people.We will certainly benefit from this and continue to work to promote our own development, otherwise nature will give other species the opportunity to dominate the earth.George Bernard Shaw called the concept of life's inner purpose "creative evolution", which is similar to the name of the concept proposed by Bergson, but the philosophy it refers to is very different.While Shaw disapproved of the idea of ​​eliminating conscious thought in favor of instinct, he did agree with Samuel Butler's earlier critique of Darwin.Shaw believed he was running against the tide of Darwinism, but he was unaware that by this time scientists had ceased to support Lamarckism; it is not surprising that he was unaware of recent developments in biology.Unless he is wrong about the sentiments in the literary world, we can assume that the public supported Lamarckism to some degree long after Lamarckism was rejected by the scientific community.

In the scientific community, a few people still make a dying effort to find evidence in support of Lamarckism.Psychologist William McDougal did an experiment, which showed that after the rats were trained, they could pass on their knowledge of going through the maze to the next generation, as if going through the maze had become its inherent instinct (McDougall , 1927).It was later discovered that he hadn't realized that he had chosen the rat that was the best at running through the maze. Perhaps the most controversial episode of Lamarckism in the twentieth century was the experiment of the Austrian biologist Paul Kamal; the publication of Arthur Koestler's The Case of the Midwife Frog (Koestler, 1971) inspired another People's interest in this episode.Kamal's results are generally considered by the modern scientific community to be the product of forgery, but Koestler - who, like many early writers, hoped that Lamarckism would be a more promising philosophy of life - urges that the Consider this case.

Kamal's experiments were carried out before the First World War, when Lamarckism had not completely lost its market and was still attracting widespread attention.The famous "midwife frog" was carried out at this time, although this experiment is not the most important work of Kamal.Most frogs mate in water, with males grabbing females with special pads on their front paws.Midwifery frogs (Alytes obtetrican s) have adapted to mating on dry land, and males have lost their characteristic frog-like pads.Kamal, who has a remarkable skill at mating amphibians in captivity, claims to have obtained a midwife frog whose front paws have the mating pads found in other frog species.And this trait can be inherited.The war stalled Kamal's work, and in the 1920s, partly to secure more patronage, he revived interest in his work in Britain and the United States. In 1923, he visited both countries with his own breed of midwife frogs that presumably could inherit the mating mat.English translations of his work were also published (Kammerer, 1923, 1924).

By this time the scientific community had become increasingly skeptical of Lamarckism.Kamal was unable to come up with any plausible mechanism of soft inheritance, even borrowing Mendelian inheritance in his own writings.His views were welcomed by some skeptics, notably geneticist William Bateson.Fully aware of the broad implications of Lamarckism, Kamal paints a glorious picture of man for his own destiny.This has led to irresponsible publishing houses hyping Superman, and in doing so it has exaggerated the mistrust among the scientific community.After Kamal returned to Austria, Bateson demanded rigorous testing of the midwife frog specimens.Kamal refused to mail the midwife frog specimens, leading Bateson to publicly express doubts about the credibility of Kamal's experiments.No one can replicate this result, because these frogs are hardly able to mate.At this time, only a few scientists were still defending Kamal against Bateson's criticism; the leader of these scientists was E. W. McBride (MacBride, 1924), he was also the last supporter of the reenactment theory.Finally, when independent tests were made, it was confirmed that the midwife frog specimens used by Kamal had been marked with Indian ink.Kamal claims that he did not apply the ink on purpose in the first place, but that one of his assistants injected the ink after the original markings had faded due to manual preservation.Shortly after his suicide, most of the scientific community thought he was a big braggart.

India ink injected by someone else who wanted to preserve the original mark?Or do you do it consciously?Perhaps the Nazis provided evidence against those who opposed their racial theories?Koestler certainly believed that Kamal's experiment was a genuinely successful experiment, although others believed that Kamal was cheating (Aronson, 1975).Even those scientists who did not think there was falsification believed that Kamal had misinterpreted the results of the experiment (Waddington, 1975).As has been encountered in other cases, initially Lamarckianism seems to be confirmed, but other interpretations of the results are possible.We probably won't know what's really going on in this story.

When Kamal committed suicide in 1926, he was about to find a new position in Moscow.That was no coincidence, because a few years later, under the leadership of TD Lysenko, Lamarckism achieved its greatest success in Russia.Kamal is said to have deliberately led Russian biology along the Lamarckian path, a movement that was delayed by his suicide until another leader could be found (Zirkle, 1949, 1959b).Earlier efforts to introduce Lamarckism to Russia were attempted, but failed (Gaissinovitch, 1980).In fact, Darwinism did not hold water in Russia (Rogers, 1974), and the revolutionary philosophy of Marxism was in conflict with the theory of natural selection understood from the perspective of capitalism.Lamarckism was clearly available as an alternative theory, and Lysenko, in the 1930s, successfully combined Lamarckism with official communist philosophy.Was his rise to positions of power merely a crude attempt to impose ideology on science, or was it the result of political support he gained by promising to end years of poor wheat harvests in Russia (Medvedev, 1969; Joravsky, 1970)?

Lysenko became famous for his discovery of "vernalization" of wheat, a process in which wheat is frozen so that it germinates quickly in the spring.This process has long been known in the West, but Lysenko claimed that the phenomenon is hereditary, that is to say as Lamarckism says.Once the wheat has undergone the vernalization process, it germinates earlier in subsequent generations.This is of great value in areas where crops can only be grown for a short season.Before long, Lysenko had strong political support to openly attack genetics and the theory of selection.Thus, genetics was dismissed as idealistic nonsense, and the selection mechanism was regarded as a reduction to chance.Lysenko's rhetoric, however, was similar to that used by earlier Lamarckists who sought to foresee improvements in the human race by manipulating the evolutionary process.Marxism predicted that a perfect society could be built without genetic changes in human nature.However, the rights that Lysenko acquired were meant to be used to solve food shortages, but instead he used them to weed out accomplished geneticists.All these geneticists either abandoned their "bourgeois" Mendelism or were exiled to Siberia, some of whom were never heard from again.

It was only in the 1950s that Russian biology awoke from this nightmare.Clearly, Lysenko did nothing to end food shortages. Instead, he underestimated the use of Mendelian genetics so that Soviet agriculture could not keep pace with Western agricultural reforms.This strange episode also leaves many unanswered questions.What role does ideology play in science?What role did ideology play in Lysenko's rise?He just acted as an adventurer to make Stalin credulous?Or did he really want to create a Marxist science?If Marxist science really exists, then it should obviously pay more attention to refined experiments, rather than arbitrarily judging problematic experiments in the name of dialectical materialism.Marxists are now trying to realize that the mistakes made by the Lysenko case might help them do their research in a better way (Lewontin and Levin, 1976; Lecourt, 1977).Of course, Lysenko's failure will not lead us to blindly and automatically assume that Western science has nothing to do with ideology. 

Orthogenesis Another mechanism that was closely related to Lamarckism, in the view of many naturalists at the turn of the 20th century, was Orthogenesis.The term "Heogenesis" was popularized by Theodora Emmer, originally a Lamarckian, and the term was later used by American school paleontologists to describe phylogenetic trends.Strictly speaking, the term connotes a linear process of evolution, generally considered to be a regular process in which internal forces drive an organism to take place.Orthogenesis assumes that mutations do not occur randomly, but point to fixed targets.Selection thus plays no role, and species arise automatically in the direction chosen by the internal forces controlling variation.From the point of view that evolutionary dynamics and development have rules, Orthogenesis is obviously very similar to American Lamarckism.The key difference between the two is that Orthogenesis holds that the tendency of evolution is non-adaptive.Orthogenesis argues that species do not respond passively to their environment, but instead represent a non-utilitarian force that can, in some cases, lead to extinction.In this respect, Orthogenesis is very similar to Hyatt's principle of racial aging.

To assume that directed variation can cause evolution to proceed along non-adaptive trends would undermine the most fundamental tenets of Darwinism.Both acquired inheritance and selection assume that adaptation to the environment is the main factor in species change.That's why Lamarckian paleontologists like Cope are also able to contribute to our modern understanding of how evolution occurs.Of course, the regularity of direct generation does not depend on the environment.The extinction of a species due to its inability to adapt to a changed environment is an integral part of the Darwinian argument; but the idea that the species itself becomes extinct is the exact opposite of Darwin's typical view.At the expense of utilitarian factors, proponents of Zhishengism are obsessed with the laws of evolution, which embodies the remnants of idealism's influence on modern biology. Carl von Negeli's theory that the "principle of internal perfection" drives evolution towards non-adaptive goals is an example of what came to be known as Orthogenesis (N?geli, English translation, 1898).But, in fact, Emmer popularized the idea in the 1890s (Bowler, 1979, 1983).Emer studied body color variation in animals, first in lizards and later in insects.Originally a Lamarckian (Eimer, English translation, 1890), he soon became convinced that some evolutionary scenarios had little adaptive significance, which he called "orthogenesis" (Eimer , English translation, 1898).For example, he divided butterflies into families that, assuming they represented evolution, each changed wing color in the same order.This parallel relationship explains the consistency that exists between structurally unrelated organisms, a consistency that Darwinists have attributed to mimicry.Emer claims that this sequential color change is ubiquitous in the animal kingdom, a clear indication that evolutionary patterns are inherent in life itself.Of course, this model cannot be used to account for all living organisms, and Emmer does not affirm that the various modern forms correspond chronologically to different stages [of evolution]. Only fossils can definitively demonstrate regularity over time (Rainger, 1981).Hyatt's concept of human degeneration already explored evidence for the existence of maladaptive tendencies, and examples of this kind became the main evidence for Orthogenesis.Orthogenetic tendencies are generally thought to arise from forces within species which drive variation in directions which lead to the extinction of the species.A famous example is the recently extinct 'Irish elk', which is thought to have been extinct due to the excessive size of its horns due to its intrinsic strength (Gould, 1974b).The tendency that initially led to such large horns seemed to have some practicality, but its own drive made the horns grow far beyond practicality.This "overdevelopment" extinction theory was very popular among non-Darwinian paleontologists in the early 20th century. The Russian biologist Leo S. Berg (Berg, English translation, 1926) was a staunch supporter of the theory, but perhaps the best-known exponent of the theory was the American paleontologist Henry Fairfield Oss Book.As a student of popular science, Osborne was at first a neo-Darwinian, but he soon became dissatisfied with this line of thinking.Together with Baldwin and Morgan, he proposed the mechanism of organic selection, which holds that animals can make conscious choices that direct the direction of the natural selection process. At the beginning of the 20th century, he began to develop the straight generation view, and eventually used his own coined term "aristogenesis" (Osborn, 1908, 1912, 1917, 1929, 1934).He knew, of course, that basic evolution of any kind must be a branching process, with diverging lines of descent from a common ancestor.Osborne coined the term, "adaptive radiation", to describe the process by which species diverge from one class into different types, but he believed that once distinct orders were established within a class, their subsequent evolution was a stable , linear process, without the small-scale continuous branching process assumed by Darwinism.His evidence came from the seemingly regular lines of evolution revealed by fossils, especially in the horns and teeth of certain mammalian species.Even if these organs are ultimately useful, Osborn insists that they have little adaptive value at an early age and that their development must be driven by forces other than selection.Ultimately, this direct force caused these structures to grow so large that they became an obvious hindrance, and thus perhaps enough to cause extinction. The vast majority of proponents of Orthogenesis make no effort to explain why this tendency occurs, and are resigned to apparently mysterious forces.Perhaps this is unfair—their theories run counter to the more hopeful philosophies embodied in creative evolution.But Osborn was troubled by the inability to come up with any natural explanation, and first tried to propose one.He points out that the interplay of energy within an organism can lead to a tendency for variation to become fixed in the germplasm.In fact, many early geneticists believed that mutations were generally directional, but they could not conceive of any mechanism by which usable traits would arise.Soon after, Osborn himself admitted that his explanation was unsatisfactory, since it implied that evolutionists might have to abandon the search for material explanations in favor of the abstract tendencies uncovered by paleontologists.At this point, the geneticist T. H. Morgan accused him of mysticism (see Allen, 1969a).Osborne's dilemma can be seen as the dilemma of idealism in the era of experimental science. Most of the fossil evidence used to support Orthogenesis in the past can now be reinterpreted in terms of modern selectionism.For example, the horns of Irish elk may have had positive uses.When modern synthesis emerged, it was also suggested that selection theory could explain some apparent maladaptive tendencies through correlated growth rates or allometric phenomena (Huxley, 1932).But in most cases, further discoveries have shown that so-called linear trends are simply paleontological oversimplifications based on incomplete evidence.It's easy to draw a straight line connecting some samples, but more information usually reveals that, in fact, evolution is branched and irregular.Orthogenetic tendencies exist more in the minds of their proponents than in nature itself (Simpson, 1944, 1953b). Mendelianism and Catastrophe Theory The modern theory of natural selection genetics arose out of some curious events.Mendel's genetic work was neglected for 35 years, and the author only became famous after his death.When a new emphasis on the study of genetics led to the rediscovery of his work in 1900, the potential of Mendel's ideas for the study of mechanisms of selection was not well understood.Mendel's theory was not presented as the savior of Darwinism; quite the contrary, it was an option for those who clashed with the ideas of the biostatistical school because of their emphasis on discrete variation.When the concept of "mutation" was introduced to explain the production of new genetic traits, it was thought that this would make selection redundant, and it was only in the 1920s that it was realized that this new genetic approach could be used to explain selection Problems in the theory's original form (for a general history of genetics, see Dunn, 1965; Sturtevant, 1965; Carlson, 1966; Stern and Sherwood, 1966; and Stubbe, 1972; for twentieth-century biology, see Allen, 1975a) . Interpretation of Mendel's own contribution is complicated by the fact that Mendel's followers interpreted Mendel's writings in terms of their own ideas.It has also been suggested recently that Mendel was not a pioneer, but in fact attempted to follow the tradition started by Linnaeus (Olby, 1979).This tradition believes that new species can be produced by hybridization between two existing species, so Mendelianism can obviously be regarded as an alternative to Darwinism.His famous laws of heredity were to him only insofar as they prompted him to consider the possibility of successive crosses in the production of new species.Nor was he clear about his own thinking about genetic elements—what modern genetics calls alleles.The mathematical rigor of Mendel's work was refreshing, and it was precisely what his rediscoverers were after.Admittedly, it was the post-Darwinian debate about whether heredity was continuous or discontinuous that shaped their thinking, so it was natural for them to understand Mendel's paper in this light.For convenience, in the ensuing account of Mendel's work, we will use it as it was understood in 1900. Gregor Johann Mendel was not a brilliant student and had only a limited science education (Iltis, 1932; Stern and Sherwood, 1966; Orel, 1984).He later entered the monastery of Bruno (now Borno, Czechoslovakia) in the Moravian region of Austria, and eventually became abbot.His work on plant hybridization was carried out in the Abbey gardens, and the results of the experiments were published in the journal of the local naturalist society in 1865 (Mendel, English translation, 1863; see also Bateson, 1902; Stern and Sherwood, 1966).He received no support from the scientific community, and the church was rather disappointed in him.Exhausted by his tireless efforts to prevent the Austrian government from taxing the monastery, he died in 1884. Mendel focused his attention on discrete variation, on traits inherited in an all-or-none manner, which he felt would simplify the problem of identification after crosses.The literature on interbreeding is plentiful, and there are occasional references to the phenomenon of hereditary segregation (Robert, 1929; Zirkle, 1951; Olby, 1966), but no one has ever paid attention to whether the regular mathematical laws can be applied here.Mendel apparently did know what he was looking for, and he chose an appropriate test material—peas.It has been suggested that the results he obtained were too good to be true, perhaps improved by an assistant who knew of Mendel's attempts (Fisher, 1936; Wright, 1966; Waerden, 1968). Mendel singled out seven traits in peas, the maximum number he could have selected for a desired outcome, including plant size, flower color, shriveled seeds, and so on.For example, in terms of height, peas exhibit two well-defined traits: tall or short.The experiment starts with the selection of plants homozygous for each trait, that is, those plants that retain the original trait after passage.The first step is to cross plants with opposite traits, tall pea homozygotes crossed with dwarf pea homozygotes, and so on.When the planted seeds grew into plants, Mendel was able to see how traits were inherited from heterozygotes.In each experiment, there was no 〖HT H〗fusion phenomenon; heterozygotes exhibited only one of the two hybrid traits.Heterozygous offspring of tall and short pea crosses are all tall peas—the mid-height fusion trait never occurs.The heterozygotes are then selfed and the seeds grow into plants.In the second generation of heterozygotes, Mendel discovered his famous 3:1 ratio.There is still no fusion, but in the first-generation heterozygotes, the lost trait appears in the second-generation heterozygotes in a ratio of 1/3.On average, there is one short plant for every three tall plants. To Mendel's later followers, these cases clearly indicated the existence of a mechanism of granule inheritance; granules or units in the germplasm responsible for the transmission of traits from one generation to the next.It is also evident that this unit necessarily exists in two forms, each responsible for one of the two characters (tall or short).We call this unit today a "gene," and another form of it is its "allele."Two decisive hypotheses are needed to complete the theory.First, each organism must carry two units of a certain trait.This is determined by the nature of sexual reproduction in nature; if the offspring receives part of the germplasm from each parent separately, it must acquire one unit of the trait from the father and another unit from the mother, the second key The hypothesis is that two units of opposite shape that determine a character are combined in the same individual and that their actions are not fused.In other words, one is "dominant" and the other is "recessive"—one that completely controls the development of the trait in new organisms, and the other that remains dormant in the germplasm.Only when both units are recessive does the trait arise in the mature organism. We can now understand the results of Mendel's experiments.The two homozygous (tall and short) individuals he began to study carry a pair of units that determine their respective traits. If we use the letter "T" to represent the high allele and "S" to represent the short allele, The genetic forms of the two homozygous plants are definitely TT and SS.A heterozygote obtained by crossing these two plants will definitely get one unit from each parent, which can only be a TS structure.In this example, the tall gene is dominant and the dwarf gene plays no role in heterozygotes. TT×SS (Tall) (Short) Pure Line The first generation of TS hybrids (high) When the first generation of heterozygotes selfed, the genetic units redistributed independently so that the number of T and S had approximately the same four possible combinations.Considering the dominant-recessive relationship, 1/3 of the recessive traits will appear in the second generation of heterozygotes. The first generation of TS×TS cross (High)(High)TT TS ST SS The second generation of (tall)(tall)(tall)(short) cross Therefore, a two-unit gene theory of inheritance, coupled with a dominant-recessive relationship, can explain the experimental results of discontinuous variation.In addition, Mendel was able to show that his seven different traits were genetically independent of other traits.This was not always the case, as Mendel failed to detect what is now known as a "chain-on" effect (Blixt, 1975). It is sometimes surprising to think that Mendel's work was buried for 35 years.Although the journal of the Bloom Natural Society is not very prestigious, it is still available in the UK, and Mendel's papers are occasionally cited in some later literature (Olby and Gautry, 1968, Weintein, 1977).Mendel kept in touch with a prominent biologist, Karl von Negri, who told him his results were meaningless, causing him to turn to other objects whose complexity was his. Insurmountable by the technology of the times.In fact, the scientific community in the 1960s was not equipped to apply this work (Gasking, 1959; Posner and Skutil, 1968).The experiment might be seen as a contribution to what now appears to be an obsolete debate about interbreeding to produce new species.Discontinuous variation within species is thought to be generally an exception to the rule of convergence.In fact, most genetic events are far more complex than Mendel's well-chosen simple examples.The same rule does not apply unless the detection technique for this event is far more sophisticated than Mendel was able to use.What is needed is an atmosphere in which scientists are convinced that a conventional view of genetics is wrong and have a way to do new research. By the end of the 19th century, advances in the study of genetics created a new environment in which Mendel's results could be interpreted in a modern way.Weissmann defined the concept of hard inheritance by assuming that traits are determined by the composition of the germplasm.He insisted that the germ plasm in the nucleus absolutely controls the growth of organisms.Environmental factors are not important for any changes in the growth process of organisms and have no evolutionary significance.At first, this "nuclear determination" theory was hotly debated because it violated the prevailing hypothesis that the environment could influence the growth of organisms (Gilbert, 1978, Maiensc hein, 1978, 1984).Even Weissmann, in the traditional fashion, studied heredity and growth simultaneously as interrelated biological processes.At this time, some biologists tried to apply experimental methods to the study of growth. They tried to establish a "developmental mechanics" to explain how the fertilized egg produced the growing structure of the embryo.But this was far beyond the capabilities of nineteenth-century science, and the focus gradually turned to the question of how traits are passed from parent to offspring.Before long a group of scientists was actively looking for examples to trace the inheritance of different traits through generations. Thereafter, the emergence of what became known as "Mendelism" or "genetics" marked a break with the past.At this time, the traditional view that growth and inheritance are two aspects of the same process began to decline (Horder et al, 1986).When one studies heredity, one does not have to worry about how traits arise in a growing organism.By the standards of this emerging science, growth has nothing to do with evolution: only the introduction of new genetic traits can change a population, and the process cannot be explained by its resemblance to growth.At this point, Lamarckism, recurrence theory, and evolutionary models can all be discarded as vestiges of an outdated conceptual system.Where Darwinism touches, genetics finally triumphs, and genetics does away with the teleological approach that compares evolution to growth. The new science was not immediately hailed as the savior of Darwinism, though, and early Mendelians tended to dismiss selection theory as another outdated artifact of old-fashioned natural history.In principle, genetics solved some of Darwin's problems, notably Jenkin's claim that fusion inheritance would eliminate new traits, whatever their selective advantage (De Beer, 1964; Vorzimmer, 1968).If traits are predetermined in the nucleus and passed unchanged from parent to offspring, then selection can always increase the proportion of a favorable trait in a population.But the new science was started by biologists who believed that only discrete variations were heritable and evolutionarily significant.They proposed that evolution would proceed through the emergence of different new traits, a process that would soon be called "mutation."The continuous variation in some traits observed by proponents of the biostatistical school does not have any real meaning.Geneticists are skeptical that the external environment can determine new traits. By 1900, Mendel's work was being repeated in a thoroughly modern way in the search for discrete patterns of inheritance.Two biologists, Carl Currens and Hugo de Vries, "rediscovered" Mendel's laws and claimed that they held the key to a new theory of heredity (Wilkie, 1962; Zirkle, 1964).Some people do not accept that EV. Churchmark was also a rediscoverer, and even dispute the role of de Vries (Zirkle, 1968; Koler, 1979).Whatever the circumstances, by this time Mendel had been hailed as a hero of the emerging science, and his experiments were seen as classic examples of genetic disfusion and discontinuity. In Britain, the most famous Mendelian proponent was William Bateson (Beatrice Bateson, 1928).Beginning as a morphologist in the Haeckel tradition, Bateson turned zealously to the experimental study of heredity, hoping that this new direction would rid Darwinism of its fantasies.The work of Francis Galton and American biologist W. K. Brooks convinced him that evolution occurs suddenly and that discontinuous variation is far more meaningful than continuous variation. In 1894, he emphasized in "Materials for the Study of Variation" that there are far more traits of discrete variation than Darwinists admit.This inevitably led to arguments between him and the biostatists, and brought to a head a personal conflict between Bateson and Weldon.Bateson wanted to find out how discontinuous factors were inherited, so he started his own hybridization experiments and soon learned that Mendel had been rediscovered.It was he who first published the English translation of Mendel's articles (see Bateson, 1902) and saw Mendel's theory as the key to revolutionizing the entire science of genetics (Coleman, 1970; Provine, 1971; Cock, 1973; Darden, 1977 ). Since biostatisticians had already quarreled with Bateson about the significance of variation in evolution, it was clear that they would have to object to Mendel's theory; Reconcile understanding of evolutionary mechanisms.Mendel's laws involved the transmission of existing traits, not the creation of new ones, and Bateson began to doubt the idea that new heritable traits could be produced through mutation.He was convinced that mutations are always regressive, including the extinction of existing traits.So how does forward evolution come about, Bateson notes, that genetic elements are sometimes shielded by suppressor genes, which block the expression of traits.If the suppressor is eliminated by degenerative mutations, the masked factor will apparently manifest a new trait.Bateson failed to notice the implication in the view that all the traits that developed throughout evolutionary history, once confined to the genes of the first organism, were masked by a series of suppressor genes that have now disappeared ( Bowler, 1983), who came close to developing this idea into a general theory of evolution (Bateson, 1914). 无论贝特森是否怀疑，关心进化机制的大多数生物学家还是开始明白经常有新的遗传因子引入。从荷兰植物学家雨果·德弗里斯提出的“突变论”中，最终产生出一些类似现代的观点。1889年，德弗里斯根据不连续的单位控制每个性状的观点，发表了“细胞内泛生论”理论（De Vries ，英译本，1910a；Darden，1976）。在深入研究这个理论时，他偶然见到了孟德尔的工作，并因此成为一位“重新发现者”。不久之后，德弗里斯在发展突变概念时，对孟德尔定律失去了兴趣。这种观点发表在1901-1903年的《突变论》中（De Vries ，英译本，1910b）和在加利福尼亚大学发表的一系列有关演说中（De Vries，1904；Allen，1969b；Bowler，1978，1983）。对于厌倦了达尔文论者和拉马克论者之间争执的许多博物学家来说，突变论似乎包含了所有的答案。突变论解释了新性状的起源和新变异及物种的分离，而无需达尔文主义的复杂的隔离机制。而且，突变论看来是建立于坚实的实验基础上，这符合新兴科学的传统。 德弗里斯并没有赋予术语“突变”完全现代的意义。对他来说，突变并没有将一个新的因子引入到现存群体中；相反，突变是新形态形成中的一个阶段，这种新形态会继续成为一种不同的繁殖群体。按照达尔文主义的看法，突变的类型是一个新变种，但是看起来是由一定数量的个体突然突变为一个新性状，而不是由亲代通过微小变异的积累而逐渐形成的。因此，突变提供了一个毋需隔离即形成物种的理想解释，因为新类型是如此独特，以至于从一开始它就只能在本类型内部繁殖。德弗里斯坚持认为存在着正向突变，这样就可以解释进化历程中新性状的引入。他相信物种会偶然来一阵儿快速突变，于是便可以解释化石记录中的缺环，还能说明整个过程的速度，从而符合开尔文对地球年龄的限定。 德弗里斯的证据来自他对月见草(Oenothera lamarckiena)的研究。他在荷兰的野外发现了这个物种，并亲眼看到它产生出明显的变异类型。他主张，每个新类型从一出现起就是真实传代的，因而形成了一个特异的变种。事实上，他给最重要的变异分别起了各自的名称，意味着变异之间存在很大程度的不同。到了1910年，才有人首次提出，德弗里斯的理论依据有错误，只是在1920年才最后发现，月见草有一套异常复杂的遗传结构，与起初对它的解释并不相符。月见草其实是一个杂合体，因此，它的“突变”更多地是由于现存因子的重组，而不是由于存在新的因子。 而且，德弗里斯的理论之所以广为流行，是因为人们把它作为了替代达尔文主义的理论。不过德弗里斯自己倒坚持认为，他并没有打算挑战达尔文理论的整体框架，仅仅是将它换了一个形式。当然，他沉重打击了生物统计学派的选择理论，因为，他宣称只有突变才能产生有意义的遗传性改变。个体变异的自然选择是无力的。这意味着没有必需去假定一个物种的所有性状都有适应的价值，因为突变性状由种质中的随机改变所产生。但是，德弗里斯宣称，作为一名出色的达尔文论者，他所依据的基础是愿意承认自然选择在较高级的水平发挥作用，突变则包含在其中。在突变阶段，在一个物种中将会有大量新变种产生，其中绝大部分都将是非适应性的。这些变异品种之间将竞争有限的食物或空间，较弱的品种会因此而灭绝。突变迟早将创造出一个比亲代更适应现存条件的变种，它将淘汰其它所有竞争对手。从长远角度看，适应确实决定了进化的进程，德弗里斯利用这个信念来抵御神秘论或生机论的复苏。 德弗里斯的许多追随者认为，他没有必要努力去维护选择理论。就拿托马斯·亨特·摩尔根来说，突变理论是攻击达尔文主义整体哲学思想的基础（Allen，1968，1978；Bowler，1978，1983）。虽然摩尔根赞成遗传学与选择理论相结合，但他开始从事研究工作时，或许是出于道德上的原因，他强烈地反对达尔文建立在竞争基础上的自然观。他的《进化和适应》（Morgan，1903）一书，不仅攻击了选择机制，而且也攻击了整个功利主义自然观。他利用德弗里斯的突变的产生不是出于任何适应的目的的观点，接着他又提出，根本没必要去想象选择会在任何水平起作用。他相信，任何突变体只要不与环境明显不相容，就可以生存和繁殖。环境并不有效地控制进化：进化的历程完全由各种突变来决定。 也是这时，丹麦生物学家威廉·约翰森刚刚发表关于大豆“纯系”繁殖的试验工作（Johann sen，英译本，1955）。人们普遍认为，他的工作是对选择的进一步反证，而且是一个极端的突变理论的例子。然而，约翰森并不关心进化这样的大问题，他只研究发生在种群内部的选择作用。他挑选的是可以进行自交繁殖的物种。约翰森所谓的“纯系”是指从单个个体产生出的后代。在他研究的大豆中，变异体现出在两极之间的连续分布；当分析在这个范围内构成各种变异的纯系时，约翰森表明，每个变异都是真实繁衍的。事实上，连续的变异分布由一组重叠但又互不相同的变异单元组成，这些单元并不融合在一起，并且经过了多次世代传递依然保持原样。在这个基础上，约翰森断言，仅仅当选择能够剔除存在于变异范围内的一个极端纯系时，选择它才是有效的。一旦一个极端纯系被分离出来，它就不能再受选择的影响，因为任何现存的变异体都是纯合型的，也就是说，外部的因子不会对其生长产生重大的、可遗传的影响。因此，选择一定会达到一个不能逾越的极限——就象詹金及其他反对达尔文的人很久以前所宣称的那样。约翰森相信，将一个真正的新因子引入物种遗传构成的唯一途径，是通过突变改变现存纯系的性状。 生物统计学派表明，约翰森得出的结果并不象他坚持的那么清楚，但他们的反对只是使他们没有妨碍人们热情地接受了不连续进化的新“证据”。随着孟德尔论者用“突变”这个术语去称呼繁殖种群中自发出现的新遗传因子，德弗里斯关于这个词的最初定义也被人们遗忘了。约翰森本人接着提出，他的原理依然适用于普通的有性生殖。根据孟德尔定律，因子的分离很复杂，但是选择的作用远不是仅仅隔离开负责产生极端变异类型的基因。只有当突变增加了一个新因子时，才会发生正向进化，因此进化的原因是突变，而不是选择。为了阐明有性生殖中的有关情况，约翰森首次以现代的方式区出了个体的“基因型”和“表现型”（Ch urchill，1974）。基因型是有机体的遗传组成，表现型是基因型的外在表现。由于显性作用，基因型和表现型可能不同。所以，在孟德尔的原来的试验中，高的亲本与第一代杂合子具有同样的表现型（都是高的），但是基因型却不一样（TT和TS）。 证明突变将新遗传特征引入现存群体的最好证据来自摩尔根及其同事所做的果蝇(Drosophil a melanogaster)实验（Shine and Wrobel，1976；Allen，1978）。他们在实验群体中鉴别了出大量不同的突变，从而证明突变增加了物种的变异范围。最初时，摩尔根怀疑孟德尔学说，但通过果蝇染色体的研究，使他确信某种机制可以解释为什么遗传按照这些定律起进行。这时，已经确定魏斯曼宣称的种质存在于染色体上。只有贝特森还在拒绝接受赞同这种对孟德尔学说的机械论解释（Coleman，1965，1970）。这种解释表明，当减数分裂产生卵子或精子时，生殖细胞或配子仅仅得到了体细胞一对同源染色体中的一条。受精卵分别从卵子和精子中各获得一条同源染色体，从而使两个亲代向子代提供了同等数量的遗传物质。当时甚至能够确定相应于不同性状的基因在染色体上的相对位置。经典著作《孟德尔遗传机制》（Morgan et al.，1915）利用全新的证据，建立了新的遗传理论。 至少在英美，摩尔根的工作标志着拉马克思想在实验生物学中的终结。即使起初还有一些异议，但是这时这门新兴的遗传学宣称染色体是遗传的主要载体，从而消除了这些异议（Sapp ，1987）。这时可能人们会反对细胞核外的胞质也能影响性状的传递。既然染色体是传递遗传性状的固定单位，不能被外界因子所改变，这样就使拉马克主义失去了立足之地。奇怪的是，德国遗传学界并没有普遍坚持核决定论。在德国，遗传学这门新的学科并没有为学术界所接受，从而使细胞质遗传为拉马克主义和直生论等非达尔文因素的继续存在留下余地（Ha rwood，1984，1985；Reif，1983，1986）。因此，不将生长和进化进行类比，最初主要是英语国家生物学的一个特征。 这时，在这种对于遗传学的严格研究中，突变似乎成了新性状的唯一来源。人们相信，依照孟德尔定律而结合在一起的一小部分不同的遗传因子，导致了物种中全部有意义的变异。这些因子决定了变异的极限，即选择的极限。真正的进化并非依赖于对现存因子的选择，而是依赖于引入通过突变产生的新因子。突变的原因还不知晓，但人们相信突变是基因内部的自发改变。突变并不受身体施加的任何有目的作用的影响，因此，拉马克主义错了。到了20世纪10年代，人们逐渐开始认识到，利用孟德尔因子的一套复杂体系，也可以说明生物统计学家所研究的效应。实验工作也表明，在选择过程中，遗传重组自身就能导致新性状的出现，从而突破了约翰森确定的变异极限。最后，突变的确使群体增加了新性状，但这并不是短期进化绝对需要的，而且其效应也并不总是像早期的孟德尔主义者所预计的那样明显。 孟德尔主义也许有助于摧毁拉马克学说，但贝特森与生物统计学派之间的冲突妨碍了孟德尔学说与选择理论的结合。由于这场冲突，孟德尔主义者夸大了不连续变异的影响，因而他们看不到，这些概念本来能够以一种更富于弹性的方式与生物统计学派的原理综合起来。而且，绝对的孟德尔主义者由于只注意实验室工作，这样使得他们疏离了传统的博物学问题，并使他们把复杂的适应与物种形成问题简单化。进化曾被想象成一种高度人工的方式，而没有考虑到真实生命的复杂性。很多遗传学家以为，导致进化的是突变本身，而不是选择，突变倾向于以某一特定方向，系统地产生出新的性状。实际上，“突变压力”驱使进化向非适应性方向进行的见解，成了直生论的另一种解释。T·H·摩尔根本人在早期的反达尔文主义时期，就提出了这种可能性，而且一些孟德尔主义者一直笃信此意。至少有一些反对达尔文主义的孟德尔主义者，遵循的路数与传统的由拉马克主义和直生论的支持者奉行的一样。突变被视为一个体内过程，受纯生物学定律控制，可以产生更加有规律的进化，该进化历程不受环境偶然变化的影响。 孟德尔主义与达尔文主义的两极分化一直持续到1920年才开始降温。实验室生物学家和野外博物学家开始意识到他们彼此隔离的程度，并且更加广泛地理解了建立真正综合性进化理论所涉及的有关问题。这时看来，这样一个理论最可靠的来源，将是对选择理论和最成熟孟德尔理论的综合。20世纪30年代，一少部分不受正统观点限制的遗传学家，还是支持通过不连续突变导致进化的观点（比如Goldschmidt，1940；见Allen，1974）。到了这时，大多数遗传学家都接受了实验室所提供的突变以多方向发生的证据；当时的形势要求科学家采纳某种形式的选择理论，以便保持整个进化论的连贯性。人们这时已经认识到，大多数突变仅仅对表现型产生很小的影响，而且同一性状常常受不同基因的影响。由此必然可以得出一个结论，遗传变异提供了生物统计学派所研究的持续变异的范围；环境剔出那些不利于生物体适应值的遗传组合。这时是遗传学与达尔文主义完全结合的时期。