Chapter 17 Chapter 9 The Eclipse of Darwinism-1

In a book on evolution (new edition, Huxley, 1963), Julian Huxley used the phrase "the eclipse of Darwinism" to describe the time before genetics and selection combined into "modern synthesis" situation.Huxley was involved in this synthesis, and he was well aware of the precarious state Darwinism was in around 1900. Something similar was said by JBS Haldane, who at the beginning of a book on a genetic theory of selection (Haldane, 1932) chose an aphorism to illustrate the situation: "Darwinism is dead—it was didactic".But if preachers were ever to rejoice, it was scientists themselves who brought Darwinism into eclipse mode.From the 1870s and 1880s—the heyday of Darwinism, when Darwinism became almost synonymous with evolution—the theory of selection was so unpopular that by 1900, opponents of selection I am sure no one will advocate choice theory anymore.The theory of evolution itself has not been questioned, but a growing number of biologists prefer to use mechanisms other than selection to explain how evolution occurs.Classic studies of the situation, even by those writers sympathetic to Darwinism, admit that opposition to the theory of selection is strong (Romanes, 1892-97; Plate, 1900, 1903, 1913; Kellogg, 1907; Delages and Goldsmith, 1912).Those who do not sympathize with the theory of choice rejoice in the decline of Darwinism, and there is an offensive work, translated from German, with the triumphantly titled Dying Darwinism (Dennert, 1904).

Modern historians pay little attention to this rampant attack on Darwinism.Eiseley (1958) says that selection theory has had a decline, but he mentions only Hugo de Vries' catastrophe theory as an alternative theory.Philip Fothergill's lesser-known book (Fothergill, 1952) has an excellent treatment of this problem, Radl (English translation, Radl, 1930) and Nordskelter (English translation , Nordenski?ld, 1946) contains classic expositions in the history of biology.The latter, however, is a major secondary source, and at the time the book was written it was felt that Darwinism was dead.Later historians have focused more on those aspects of the post-Darwinian period that contributed to the rise of postmodern synthesis.However, they generally turn a deaf ear to theories that have been discarded by modern biology, dismissing them as a fork in the road ahead, and considering them unlikely to have had any impact on the development of modern evolution.As we move away from a historical approach apparently based on hindsight, it will become increasingly clear that non-Darwinism did play a role in determining evolutionary views in the late nineteenth and even twentieth centuries (Bowler, 1983, 1988).

Analyzing the theory of evolution in the 10 years around 1900 is a complex task, because there are indeed too many theories involved.Research sparked by Darwin's biography was underway at the time, and August Weissmann's neo-Darwinism saw natural selection as the only tenable mechanism of evolution.Far from bringing good fortune to Darwinism, Weissmann's dogma has alienated many biologists who have at least been inclined to advocate something that is not Darwinian.The rise of Neo-Lamarckism and Orthogenesis marked a shift towards more overtly anti-Darwinian forms of evolution.The apparent support for these theories is partly due to the fact that they seem to retain a teleological component as opposed to straightforward neo-Darwinian materialism.Naturalists who are unwilling to admit that evolution is an accidental, trial-and-error process propose that the development of life is limited to proceeding in a purposeful and regular manner by influencing the emergence of new mutations.They hold that the intellectual activity of the individual creature directs the variation, or that the forces inherent in the growth of the individual direct the variation.Such theories are a direct continuation of views advanced by Chambers in Traces of the Creation History of Nature and Mivart in The Occurrence of Species.The fact that many non-Darwinian paleontologists still use reenactment theory suggests that the idea that evolution was more or less akin to biological maturation was popular at the time.

This view of natural development collapsed in somewhat paradoxical ways.It is true not because of an attack on Darwinism that selection theory was at its lowest ebb during those critical years around 1900, when the plausibility of the reenactment theory was also shaken.Where Darwin failed, Mendelian genetics succeeded; Mendelian genetics proved that individual growth is not an appropriate way to explain evolution, thus undermining the direct evidence once used to support Lamarckism and Orthogenesis .At this time, it was believed that the evolutionary process could only be controlled by introducing new genetic elements into the population.Initially, geneticists did not recognize that selection effects of environmental adaptation could control the spread of "mutations".They believe that Lamarckism and Darwinism are unexperimental, outdated products of natural history.But there was not much hostility to Lamarckism, and it was the revolution based on heredity that finally established a new foundation for selection theory.

Neo-Darwinism The study of variation and geographic variation, among others, were areas that initially supported Darwinism.Research in these areas has continued, particularly with regard to the question of speciation, the question of how an original group diverges into many groups.It was eventually recognized that geographic isolation played an important role in speciation, although Darwin rejected the idea that geographic isolation was a fundamental factor in speciation.Those field naturalists who have continued to do this work have generally adhered to old-fashioned, flexible Darwinism, but some of them have taken a rigid approach, insisting that selection is the only mechanism of evolution.In England, the application of statistical techniques to the study of variation led to the creation of the "biostatistical school", whose proponents were also staunch defenders of Darwinism and were among the harshest critics of Mendelian genetics .But the hardest neo-Darwinist known was the German biologist August Weissmann.Weismann declared that Lamarckian exhaustive-regression inheritance was impossible because it was inconsistent with Weismann's theory of inheritance.Naturalists who hold that the mechanism of evolution is not selection but other do not share this extreme view.

Some naturalists, before Darwin, did not think so high of the amount of variation in each species when they wished to establish a typical form.The theory of selection made them realize that generally each species is a population composed of more or less distinct varieties, each of which has the potential to become a new species.But how does one original group differentiate into several different new groups?What prevents the interbreeding and fusion between the two varieties, so that they are so differentiated that they cannot interbreed again?What is the relationship between two types with increasing degrees of divergence in physical characteristics?Are they still able to mate with each other?These problems are difficult to resolve mainly because Darwin and his followers did not adequately explore the implications of what Ernst Mayer called "groupthink."The inability of the naturalist to solve these problems in terms of a theory of choice must of course lower the standing of that theory in the scientific community.

Darwin found in the Galapagos Islands that geographical isolation favors the production of different types by preventing interbreeding, but that in other cases varieties of the same species co-exist in the same area.As Mayr (1959b) and Sulloway (1979) have pointed out, Darwin ultimately ignored isolation and instead believed that ecological specificity in the same area led to the production of different varieties.Wallace also accepted the idea of ​​sympatric speciation (speciation without geographical isolation), but he disagreed with Darwin on how different taxa acquired mutual sterility (Mayr, 1959b).George John Romanis argued that selection mechanisms can explain the origin of adaptations, but not the origin of species.In other words, selection theory can explain how a single group changes in response to environmental challenges, but cannot explain how a single group differentiates into several different types (Romanes, 1886; Lesch, 1975).He proposed a mechanism of "physiological selection", according to which, the phenomenon that the mutant cannot mate with the parent may be produced instantaneously.But this concession carries a fatal flaw: if it is admitted that mutations can produce sterility in addition to selection, why not admit the idea that mutation itself can produce all new traits without the action of selection?

As early as 1868, Moritz Wagner had proposed that the initiation of geographical separation was crucial for the establishment of mutual sterility (Wagner, English translation, 1873).Isolation prevents interbreeding that is still possible, so that separated populations may acquire different traits.If the difference is sufficient, even if the different forms recontact due to migration or changing geographical environment, they will not merge with each other.Unfortunately, selection was seen as a mechanism distinct from, rather than complementary to, selection, so Darwin and most of his followers rejected Wagner's view.In fact, neither side of the debate fully appreciates the implications of the concept of species in selection theory.At that time, people still defined species and varieties in terms of morphological differences (that is, differences in appearance), as if this difference was caused by God.But the real difference is whether the two populations can mate with each other, no matter how different the morphologies may be.Species and varieties are certainly groups that cannot interbreed, or they would fuse together and lose their uniqueness.Among the varieties, it is still theoretically possible to interbreed, and the barrier to interbreeding may be isolation, or the establishment of what is now called a "sequestration mechanism", that is, differences in behavior prevent mating .Isolation is necessary, not until sterility has been fully established, but until the isolation mechanism that actually prevents mutual mating is established.

It was only towards the end of the nineteenth century that views changed in favor of Wagner's initial view that isolation was necessary. In the 1880s, John Thomas Gulick, through his study of Hawaiian terrestrial snails, clarified the correlation between varieties and different geographical regions (Gulick, 1888; Addison Gulick, 1932; Lesch, 1975).At the end of the 19th century, Carl Jordan proposed the concept of species groups in the modern sense, and he also recognized the role of isolation (Mayr, 1955).Jordan went neither to extreme Darwinism nor to extreme Lamarckism, recognizing that whatever the mechanism of change, the more important work was to elucidate the fundamental nature of species.By 1905, American David S. Jordan admitted that most field naturalists at this time recognized the importance of isolation.He also laments the lack of interest in these developments among a new generation of biologists.

Another important Darwinist, Edward B. Poulton, also complained in his writings that experimentalists ignored the concerns of naturalists (Poulton, 1890, 1908).Bolton, a scholar of body color in animals, was convinced that animal camouflage and imitation had some adaptive value.Since animals have no control over their body colour, this cannot be explained using Lamarckianism, and it seems that only natural selection can explain the development of protective colouration.Bolton thinks it's easy for a biologist in the lab to dismiss the effect as a coincidence, because he knows nothing about the environments in which animals live in the wild.The fact that the adaptive significance of body color was widely challenged at the time shows how far anti-Darwinian sentiment had grown.Only field naturalists, like Bolton, refused to budge, believing that their observations had proved that, questionable or not, natural selection was plausible.

To some extent, August Weismann's strict selection theory was destined to generate this wave of anti-Darwinian sentiment.The reason comes from Weissmann's new study of variation and heredity, which, however, must be carefully evaluated.Mayr (1985) regarded Weissmann as the most important evolutionist in the 19th century since Darwin, and his concept of "germplasm" as genetic material really helped to clarify the concept of natural selection in the modern sense.It should be noted, however, that Weissmann's work on genetic problems largely follows Darwin's own research program, according to which the study of genesis (the reproduction and growth of individuals) is an integral part of evolutionary theory (Hodge, 1985).Weissmann, like many at the time, did not believe in Darwin's theory of heredity, known as pangenesis, and he was looking for alternative models of how the continuation occurred between parents and offspring.To clarify this question, he set out to dabble in a new field of biology, cytology, or cell theory, in an attempt to understand how the genetic material of parents determines the cells of offspring (Robinson, 1979; Farley, 1972). Frederick Churchill (Churchill, 1986) found that Weismann's radical views on the nature of heredity follow a very traditional approach inspired by reenactmentism.When Weissmann applied this theory to the hydra, which he had studied earlier, he came to believe that all living things contained a latent, invariant essence of reproductive material that could be passed on to the next generation.Eye disease forced him to give up his research work under the microscope, but he had been convinced from the work he had done that the substances that transmit traits in reproduction were located on the chromosomes, which could be found by staining, which were tiny round substances in the nucleus.This important insight has been incorporated into the framework of modern genetics.Indeed, the notion that genetic material can encode the genetic information necessary for reproduction is important.Weissmann did not originate this concept; it exists in a very different form, in the form of the so-called "heteroplasm", in the theory proposed by Karl von Negri in 1884 (Gillis pie , 1960; Coleman, 1965), but in the 1880s, Weismann had been deliberating on the idea of ​​the basic nature of heredity, and founded the germplasm theory (Weismann, English translation, 1891-92, 1893a; Romanes, 1899) . Weisman proposed that the germplasm is completely incompatible with the organism that carries it.The structure of the body, the "soma", is built from information provided by parental germplasm cells.Afterwards, this structure carries the germplasm all the way to the next generation.Once the soma is formed, the soma acts like a "hotel host" holding the provenance material.The effects on the body are not passed on to the germplasm, so that what the organism passes on to the next generation is only what it has received from the parent.Enduring Weismann's germplasm theory is its "hard" genetic view, the view that the body's response to the environment cannot be inherited.In contrast, Darwin's pangenesis theory believes in soft inheritance, that is, the body's response to the environment can be inherited.Weisman proposed that the germplasm consists of units called "determinants," each of which is responsible for producing a certain part of the body.In sexual reproduction, determinants from both parents combine to provide the information the offspring uses to build its body. Weissmann's theory has a crucial significance for evolution: it makes Lamarckism impossible.The parental body doesn't produce germplasm; it just passes it on.Physical changes due to exhaustion are not reflected in the germplasm and therefore cannot be inherited.Weisman believes that the contrary belief held by the public is just a superstition.Normal variation in a population is due to recombination of determinants in sexual reproduction.Natural selection will favor those determinants that produce useful organs and suppress those that produce harmful organs.New mutations can be introduced only because of deformations in the determinant structure caused by accidental accidents in replication; but the body has no control over such accidents, so the generation of mutations is entirely random.Selection then becomes the only acceptable evolutionary mechanism. In one famous experiment, Weissmann amputated the tails of a nest of mice, and then continued to amputate the tails of the mice for many generations to come.Continuing tail clipping in mice did not produce mice with shorter tails than normal.According to Lamarckians, this is not a reasonable experiment.They argue that inherited acquired traits are purposeful responses to the environment, rather than such accidental excisions.But Weissmann's experiment had a reasonable fulcrum, because Lamarckism had to be based on soft inheritance, while his experiment confirmed that inheritance is hard: the mice that lost their tails still carried the complete information of this trait.In fact, a small number of experiments supporting Lamarckism are also based on genetic effects caused by methods such as excision, because it is easier to produce and test such results in the laboratory. Figure 21. Pangenesis and germplasm theory. The two-line diagram illustrates Darwin's and Weissmann's concept of the relationship between the body (large circle) and the genetic material responsible for passing traits to the next generation (small circle).For reasons of brevity, the phenomenon of conjugation required in sexual reproduction is not represented.According to Darwin's theory of pangenesis (above), each part of the body produces buds that transmit traits.Bud bulbs pool in the reproductive system and are passed down to become the basis for building the next generation's body.According to Weismann's theory (below), the body develops from the germplasm, but the body does not cause any changes in the germplasm in the process of passing it on to the next generation.Because the body part does not generate its own genetic material, any changes due to exhaustion cannot be transmitted to the germplasm and therefore cannot be inherited. To those who generally believe, based on other experiments, that use and nonuse must have had an evolutionary effect, Weissmann's theory is nothing more than a symbol of neo-Darwinian dogma.If they must adopt a new attitude, it does not support selectionism.They claimed that the evidence for the germplasm theory was insufficient, so Weissmann's insistence on the "tonipotence of natural selection" was wrong.Herbert Spencer, who has always adhered to Lamarckism, also felt the need to challenge Weismann at this time and announced his departure from the Darwinist camp (Spencer, 1893; Weismann, 1893b).Some other Lamarckians launched a violent attack on the concept of germplasm, citing various evidences that were supposed to confirm the inheritance of exhaustion and obsolescence.Lamarckism was popular for a while, but the stubborn pushback against Weissmann at this time prompted Lamarckian supporters to openly break with Darwinism. Weissmann never subscribed to Lamarckism, but even then he had to make some concessions in some respects.To explain why vestigial organs became small, he proposed a mechanism called "embryonic selection" (Weismann, 1896, 1904; Bowler, 1979).This is selection occurring within the germplasm itself, where determinants for various traits compete for limited nutrient resources.Finally, Weissman even admitted that the mutations produced by embryo selection have a tendency to produce new organs.He conceded that, in most cases, such tendencies are only really important if the new organs can become useful and subject to the control of natural selection.To his opponents, this concession exposed the weakness of his absolute choice theory.Perhaps this internally oriented tendency automatically plays a role in evolution, which is the orthogenesis view.In any case, the theory of embryo selection is clearly an artificial development of the original theory, so that the whole theory seems to be the product of Weismann's rich imagination. To address the problem of variation and heredity, Weissmann had intended to build a model of the physical processes of variation and heredity, using this model to illustrate how traits are passed from one generation to another.The biostatistical school opened up another route to solve this problem: using statistical techniques to describe the distribution of variation in a population and the impact of selection on various variations.Keitel had pioneered the use of statistical techniques to study population issues earlier in the 19th century, but by this time statistical techniques were being used on a much wider scale.The theory of evolution has inspired people to search for more appropriate methods to try to understand those phenomena that are very important for the mechanism of selection. The founder of the biostatistics movement was Darwin's cousin, Francis Galton.Early in his career, Galton performed an experiment that disproved pangenesis; but soon he began to rely on his mathematical interests to produce accurate descriptions of the spread of variation in populations.Galton was an important inducing factor for the study of the genetic significance of the human race.He believed that the idea of ​​selection would lead social thinkers to see the prospect of racial improvement or racial degradation due to the different rates of reproduction of different classes.To win support for this "eugenic" policy of controlling human fertility, he pioneered techniques that his followers would use in animal populations to find experimental support for natural selection ( Galton, 1889, 1892; Pearson, 1914-30; Wilkie, 1955; Swinburne, 1965; Frog gatt and Nevin, 1971a; Provine, 1971; Cowan, 1972a, 1972b; De Marrais, 1974; Forrest, 1914; Mackenzie, 1982 ). The common way to describe the distribution of variation is to draw the frequency distribution curve of the proportion of each variation in the population.For most continuously variable traits, such as height in humans, the curve is a bell-shaped "normal" or "Gaussian" curve as drawn on a graph.But although Galton and his followers had developed techniques for expressing variation within a generation, what needed to be discovered was the change in the curve after selection had acted on a population for many generations.Galton proposed the "Law of Ancestral Inheritance" to describe the proportion of traits in a population that come from each ancestor: half from parents, quarter from grandparents, and so on.This law is wrong by modern standards, but many of his followers took it as the basis for measuring the effects of selection. Figure 22. Continuous mutation and selection The solid curve represents the normal distribution of a continuously varying trait, such as height in a population.This curve represents the proportion of each variation in a population when measuring a variable trait.So around the middle of the curve distribution (the average height of a human being) represents the largest proportion, while the proportions at the two extremes of the curve (the tallest or shortest people) are very small.For Darwinians, the key question is: what effect does selection have on this distribution?If an extreme variation (such as the tallest man) is advantageous in the struggle for existence, individuals at the extreme ends of the distribution will produce more offspring than the normal type; conversely, individuals at the opposite extreme will produce fewer offspring than the normal type. Types of.Dashed lines indicate the effect of this distribution.Is the movement of the whole population towards the median a constant movement in the direction of selection promotion?Weldon's experiments were designed to show that this permanent effect does indeed occur. Galton himself believed that his laws might lead people to think that selection has no lasting effect on species.To prove this, he introduced the concept of "regression".Imagine a quadrat of individuals with a particular distribution, such as a population of average heights.What happens after a few generations if mating is limited to this group of people?Galton believed that the mean of the trait for the quadrat would regress to the same state as the trait for the entire species.After many generations, the offspring of tall people will be the same height as the average height of people of normal height.Galton argued that if this were the natural tendency, selection could not have a lasting effect on a group.Regression places a bound on variation and always pushes a trait back to the mean, whether or not selection has had an effect.Selection can improve the health of a population, but it cannot permanently improve reproduction.Galton believed that species generally remain static over long periods of time, evolving through sudden mutations only when faced with major environmental challenges. Although Galton did not believe in the effects of selection, his followers in the biostatistical school believed that he had misinterpreted the laws of heredity from his own ancestors.Two in particular would later become prominent defenders of Darwinism, Carl Pearson and the biologist W. F. R. Weldon, famous for his treatises on the philosophy of science (Pearson, 1900) .Pearson pointed out that selection has lasting effects according to laws proposed by Galton himself (Pearson, 1896, 1898, 1900; Froggatt and Nevin, 1971a, Provine, 1971; Norton, 1973).The next step was to test this both theoretically and in nature, and Weldon took up this work.He set out, first with crabs and later with snails, to demonstrate the correlation between variation and mortality (Weldon, 1894-95, 1898, 1901).The first attempts were unclear, but Weldon could clearly demonstrate the effect of selection in later experiments.In waters containing thick sediment layers, larger crabs are more likely to survive than smaller ones; the cumulative effect of selection has a persistent effect on the population over many generations. Many people object to the Darwinian view of the biostatistics school.Weldon's demonstration of the effect of selection is only at a small scale, and has little bearing on the idea that selection affects a limited range of species.Both Pearson and Weldon alienated most biologists by espousing more advanced philosophical views of science at the time (Norton, 1975a, 1975b).Because fitness is a function that cannot be determined objectively, Weldon simply linked mortality to some easily measurable trait, such as crab shell width.He argues that there is no need for a causal explanation of why larger shells are beneficial.In response to criticism, he later explained that the small crab gills tend to get clogged in silt-laden water, but his later work on snails, again, simply showed a correlation between snail shells and mortality, He did so based on imagining how these traits, which are not easily studied, could be used.Weldon's reluctance to study the nature of adaptation prevented him from gaining the approval of field naturalists who also supported Darwinism, or those who opposed the theory of selection at all. The most important obstacle to the success of biostatisticians is their conflict with the emerging Mendelian genetics.Even before Mendel's work was rediscovered, Weldon and Bateson had disputes over Bateson's claim that discrete variation was the true source of evolution.While biostatistical techniques are primarily used to study continuous variation, Bateson emphasizes traits that are inherited in an all-or-none manner and negates the role of selection.When Mendel's work on heredity was rediscovered in 1900, it was similar to the category of discrete variation, and in this way Bateson became a noted proponent of Mendelian genetics.The biostatisticians argue that, under normal circumstances, discontinuous factors are uncommon, so they object to new genetics.Therefore, the emerging Mendelianism is not the savior of Darwinism, but the theory that replaces Darwinism.Both sides quarreled and devalued each other, and in our present view, little progress was made, because each only grasped a part of the truth (Provine, 1971; Cock, 1973; Darden, 1977). The biostatisticians were wrong to oppose Mendelism, but they turned out to be right in favor of continuous variation as the mechanism of evolution.In fact, their most important innovation was the realization that variation and heredity are not opposing forces.Even Darwin saw heredity as a conservative force trying to preserve the original traits of a species.Galton and his followers at least recognized the fallacy of this paradoxical analogy.In fact, variation and inheritance are different manifestations of the same process, and the continuous flow of a large number of genetic factors in a population is the result of sexual reproduction.Their problem was that they didn't have a good theory to explain how inheritance works, and they couldn't support Darwinism by making the idea of ​​inheritance. Neo-Lamarckism The first important challenge to choice came not from Mendelism but from Lamarckism.During his lifetime Lamarck won little support for his mechanism of acquired inheritance.It was only after Darwin made people accept the basic ideas of evolution that it was possible to restore Lamarck's ideas.Those who acknowledged evolution but were unhappy with natural selection began to look for alternative mechanisms.Because Darwin's own theory was also in trouble at the time, acquired inheritance may have become an alternative mechanism of the past.Initially, it was not even recognized that Lamarck had first proposed the idea of ​​acquired inheritance, and it was not until the end of the 19th century that the name "Neo-Lamarckism" appeared (Packard, 1901).Even then, little attention was paid to Lamarck's obsolete writings.A full Lamarckian system is nothing like a post-Darwinian worldview.Neo-Lamarckism contains many basic concepts, some of which were developed by Lamarck but have been modified to accommodate evolutionary systems that were simply unimaginable at the beginning of the nineteenth century. According to its most prominent feature, Lamarckism is based on the assumption that structural changes produced by the activities of adult organisms can be reflected in the genetic material and can be transmitted to the next generation.We know that exercise, with and without use, can affect the size of organs: weightlifters have thicker arms, and giraffes hypothetically elongate their necks to eat leaves.The change is a response to new habits, and is generally adaptive, so that regressive inheritance can be used as a substitute for natural selection.But the assumption that such acquisitions could be inherited has been controversial.Did a Weightlifter's Son Inherit His Father's Muscles?According to Weismann's germplasm theory, this theory cannot be established, and although the neo-Lamarckists expressed contempt for Lamarck's system, they did not propose their own satisfactory model of soft inheritance.Most people simply think that soft inheritance is possible because they can support their theory with other arguments. However, it must be emphasized that Lamarckism is not a unified theory.Those who consider themselves followers of Lamarck do not merely see exhaustive regressive inheritance as the only mechanism proposed by Lamarck.Other naturalists have also suggested that the environment can directly affect (that is, without a perceptible response) the growth of plants and animals, and that changes can be inherited.For example, plants grown in dry environments develop traits that help them retain water.Another group of Lamarckists pushed Lamarckism in a completely different direction.In the United States, some students of Luis Agassiz became interested in embryology and believed that the promotion of individual growth could lead to evolution.They then saw that exhaustive regressive inheritance could explain why this growth-promoting phase of an individual occurred at a certain time in material history.American neo-Lamarckians differ from other neo-Lamarckians in that they have always maintained a certain interest, in particular their belief that evolution occurs in regular ways, with occasional sudden changes. Why was Lamarckism so popular at the turn of the 19th and 20th centuries, when acquired inheritance was not supported by experimental evidence?The answer should be found from the broad philosophical meaning contained in it.It has been suggested that American neo-Lamarckism is a direct continuation of natural theology (Pfeifer, 1965).Some neo-Lamarckians have adopted exhaustive regressive inheritance, of course, because it seems to be more consistent with the idea of ​​God being benevolent than natural selection.However, neither Lamarckism nor Darwinism can confirm God's design, since both theories hold that species were formed in a natural way rather than according to God's command.Some neo-Lamarckians are not interested in religious questions, so their motives must lie elsewhere.The point is that, according to Lamarckism, it seems that life itself is purposeful and creative.Life forms direct their own evolution: they selectively respond to the challenges of their environment, and thus, through their own efforts, determine the direction of evolution.Philosophical or not, this view is clearly more promising than Darwinism.生命成了自然中的一种主动的力量，而不止是仅仅以被动的方式对环境的压力作出反应。因此，新拉马克主义者所渴望的东西与柏格森在创造进化论中所表达的东西之间是有联系的。 有一种拉马克主义的成分已经存在于达尔文主义者的最初观点中。达尔文直到晚年仍然承认用尽废退式遗传起到了一定的作用。他的一些追随者，尤其是德国的海克尔，更加强调拉马克主义的作用。赫伯特·斯宾塞在一些著作中，比如他的《生物学原理》（Spencer ，1864），也支持将选择与拉马克主义结合起来。只是在魏斯曼的绝对选择论出现之后，新达尔文主义与新拉马克主义之间的分歧才公开化。在德国，西奥多·埃默尔等博物学家，开始在适应产生的问题上，以牺牲选择的作用为代价，支持用尽废退（Eimer，英译本，1890）。这时，斯宾塞写文章攻击魏斯曼，并宣扬拉马克主义的重要性。到了19世纪结束时，很多博物学家开始支持拉马克主义，更常见的是，他们倡导以拉马克主义来代替选择学说，而不止是作为选择论的补充（Packard，1901年的论述；Kellogg，1907；见Churchill，1976；Limoges，1976；Bowler，1983）。 达尔文本人在同作家萨缪尔·巴特勒的争论中，首次尝到了［拉马克主义的］利害（Wi lley，1960；Pauly，1982）。巴特勒最初相信的是达尔文主义，在读罢米伐特的《物种的创生》后，转而相信非达尔文主义的机制更可能成立。随着愈加关注使进化中含有目的的含义，巴特勒开始从拉马克主义中看到间接保留上帝设计形式的前景。上帝不再是从一无所有中创造了世界，相反，上帝可能就存在于生命的发展过程中，在这个过程中，从一开始就包含了上帝的创造力。巴特勒主要关心的是动物和人类的心智生活，不过他和其他一些拉马克主义者不同，他并没有认为意识是生命活动的最高形式。他认为，本能是充分发展了的心智活动，而且他将这种观点融入到他的拉马克主义中。有意识的选择先是指导着动物对新的情况作出反应，在此之后，首先是习性，然后是本能，相继作出适当的变动，这些都根本不需要意识。通过用尽废退式遗传，身体的结构不久也将适应新的本能。巴特勒提出，如果人类本身可以祛除一切有意识的思想，完全根据本能去生活的话，人类会更加幸福。当他确立了这些观点后，他确信达尔文在其添加在后来版本中的历史回顾中，故意地贬低了拉马克等早期进化论者思想的意义。巴特勒在《进化论，旧与新的学说》一书中，批驳了达尔文，强调了拉马克主义的重要性，而且他在后来出版的一个以《幸运还是机敏？》为题的丛书中，继续发展了这种观点。 直到19世纪末，非常成熟的新拉马克主义出现之后，巴特勒的书籍才流行开来。在斯宾塞对魏斯曼所宣称的自然选择具有全能性的观点的批评中，可以看到拉马克主义者在后期阶段所使用的一个有代表性的论点（Spencer，1893）。斯宾塞在批评魏斯曼时声称，“如果获得性不能遗传，那也就没有进化。”他提出这个论点有两个目的：动摇选择和种质学说，其次是表明拉马克主义的优越性。在反对选择本身时，斯宾塞使用了一个论点，如果按照遗传学出现之前的标准看，他的这个论点是比较尖锐的（Ridley，1982a）。他指出，当一个新的结构进化出来后，身体的其他所有部分都必须适应这种新的发展。于是要求通过一系列变异来调节整个结构，以便与这种新的器官相契合。存在这种在一定的时间同时发生所有这些变异的机会吗？利用选择可以解释单个器官的变化，但是无法解释整个身体的整体转变。此外，由于习性变化，不使用所导致的器官消失也会带来一个问题。选择可以解释器官的缩小，但是很难解释器官的完全消失，后来魏斯曼也承认这一点。拉马克主义在解释这种发展时并没有遇到困难。如果面临复杂的变化，整个身体会以新的方式活动，因此这种获得的性状本身整体上就必然是契合的。同样，不用器官之所以消失，是这些器官在实际中不使用的直接结果。 斯宾塞将拉马克主义设想为一种功利主义的机制，按照这种机制，通过用尽废退，一个物种可以调节结构，使其具有适应环境的功能。实际上，用尽废退式遗传当然最适合从动物主动性行为的角度来解释适应。但是正如乔治·亨斯罗的著作中所表明的那样，也不是没有可能用拉马克主义来解释植物的进化（Henslow，1888，1895）。亨斯罗相信，所有的自然变异都是向着一定的目标进行的，自然变异通常是对环境的适应性反应。当一种植物生长在异常的条件中时，结构会自动地发生适当的变化。虽然亨斯罗清楚地认识到可以将此现象作为证明造物主智慧的证据，但是他并没有打算解释为什么植物的这种变化是适应的。尽管他的主要工作就是要证实确实发生了这样的反应，但是他并没有想到需要表明它们是以符合真正的拉马克主义要求的方式遗传的。如果植物能够在新的环境条件下生存下去，这显然将对后来的每一代都造成影响。判决性实验将表明它们在回到对它们来说是正常的环境后，经过许多代后，还保留着异常的性状。亨斯罗未能认识到，需要通过证明这一点来说明拉马克主义论点中的共同弱点：证实获得性的存在，然后再认为它们是遗传的。 亨斯罗还观察到花的形状是如何与昆虫进入花的路径相互关联的。他提出，通过这一现象再次证明了植物对于外界的刺激可以作出直接的反应。在每一代中，昆虫都对花施加了压力，这种扭曲性的效果经过积累，便决定了花的进化。他的论点中再次包含了拉马克主义者中常见的谬见。花的形状适应于昆虫并不能证明是植物作出的直接反应。如果花的形状可以用于促进昆虫为植物授粉，通过对随机变异的选择，也可以产生出同样的效果，如果在每一代中这些花都是偶然更好地适应了昆虫的需要，那么这些花就更容易授粉，因此就会产生出更多的种子。 在美国，阿尔丰斯·帕卡德之所以支持用尽废退式遗传，根据的是昆虫学和对生活在洞穴中的盲鱼的研究，他认为盲鱼失去视觉的原因是因为不使用视觉（Packard，1889，1894）。然而，独具特色的美国式的新拉马克主义的起源则可以追溯到19世纪60年代早期许多博物学家对选择学说的不满（Pfeifer，1965，1974；Dexter，1979）。特别是通过古生物学家爱德华·德林克·科普和阿尔丰斯·海厄特，发展出一种根据重演论研究进化的特殊方式。 科普因为与O·C·马什之间就美国西部丰富的化石层问题上所发生的争论而出名（Osbo rn，1931；Schuchert and Levene，1940；Plate，1964；Lanham，1973；Shor，1974）。虽然科普和海厄特从19世纪60年代开始相信进化论，但是他们发现自然选择是无法接受的。更值得一提的是，在他们的早期生涯中，他们都和阿加西有过接触，海厄特在哈佛时是阿加西的学生。他们俩人最初都不是拉马克主义者；事实上，他们一直在探讨如何将阿加西关于胚胎学的唯心论模式与新的进化论结合起来（Bowler，1977b，1983；Gould，1977b）。关键是重演论，即相信胚胎的生长重复着物种的进化史。在阿加西本人看来，这两种发展模式的平行表明，上帝有意地创造了具有等级序列的、和谐的发展模式，在这个序列中，人成了创世的目的。科普和海厄特作为新一代人，无法接受创世有一个单独目标的见解。他们认识到，进化一定是不断分支的过程，但是他们认为，各个主要类群的进化可能是在重演的指导下进行的。于是他们提出了一个理论，这个理论忽视了达尔文主义的自然史概念，而是侧重于将生命的发展表现为化石的规则顺序，以及相平行的胚胎有目标的发育过程。科普和海厄特虽然抛弃了创生完全是和谐的观点，但是他们在每一个生命类群的进化观中保留了规则性的成分。 “生长加速律”首次发表在科普1867年的文章“论属的起源”中（重印于Cope，1887），海厄特也提出过这种观点（Hyatt，1866）。按照这个定律，生物通过个体生长中的一系列加速而发生进步式进化。在某一时间段，一个物种中的每个个体都会表现出新的生长时期，从而超越了其他物种，形成新的物种。为了给这种加速发展腾出空间，成体类型压缩成生长的早期阶段，这样，在成熟之前便多了一个阶段。科普否定小尺度的进化是分支化的过程，相反，他提出，一个属代表着已经在其发展的历史上达到某个阶段的一个物种类群。生物之间具有密切的关系并不表明它们有着共同的祖先，而是表明它们在发展的过程中达到同样的位置。因此，一个类群的进化中包含了许多按照同样模式发展的平行路线，胚胎生长中展示出所有模式的生物表明它们距现代最近。 是什么决定了下一个发展阶段的方向？当然不是随机变异与选择，因为科普和海厄特提出每一步是按照预定方向的累计式进步。科普甚至否定任何新形状的适应值，他声称，新的形状只不过是造物主设计的规则模式中的一个阶段。海厄特虽然不是出于宗教的企图，但是他在他的第一篇文章中提出，进化是预定顺序的展示。不久，他们俩人都意识到未能清楚地说明新形状是如何在某一特定时刻添加进去的，于是他们无法通过自然的因果关系来说明进化问题。科普这时不再反对功利主义的原则，并且承认多数变化都有适应的目的。他和海厄特开始将拉马克的用尽废退式遗传作为他们正在寻找的导向力量。拉马克主义很适合重演的概念，因为拉马克主义要求新的阶段是由成体发展出来的，尔后压缩到胚胎发育中，这样新的阶段才可以遗传。科普假设了一种生长力，叫做“沐浴子”；沐浴子集中作用于身体中最常用的部分，从而使这些部分得到发展，而其他部分则得到了抑制。到了19世纪最后一个十年，这种拉马克主义的理论已经发展到相当程度（Cope，1887，1896；Hyatt，1880，1884，1889）。 具有深厚宗教情感的科普进一步提出，根据拉马克主义，仍然可以认为意识是进化中起导向作用的力量。按照这种观点，物种并不是由外在的造物主设计的，而是通过自身的设计，在生物界逐渐地拓展自己的表现。因此进化要实现最终的目的需要精神的特征，于是出现了心灵的作用（Moore，1979）。动物控制着自己的进化，因为它们在有意识地对环境作出反应的过程中，通过用尽废退式遗传，决定了它们身体的形态。而且心灵本身将推动心智更发达类型的进化，而人类就是这种趋势的最终体现。不过，海厄特倒是怀疑这种形而上学的精心说明，他想如果认为他曾经研究过的头足类动物中含有意识的驱动力，那太荒谬了。 尽管有海厄特的怀疑，拉马克主义还是能给人一种生命决定自己命运的印象，而且这种观点成了受人欢迎的道德观念。不少人都很热心于表明根据选择理论也能说明进化按照一定的有意识的方向进行，以避免想到物种是由不遂人愿的环境力量所驱动。19世纪80年代，古生物学家HF奥斯本和生理学家詹姆斯·马克·鲍德温及C·劳埃德·摩尔根分别提出了“有机选择”机制，后来叫做“鲍德温效应”（Baldwin，1902；RJRichards，1987）。按照这个理论，生物面对环境的挑战会挑选最合适的反映，而它们的身体则通过使用会获得最适合新行为模式的形状。但是，获得的这些新形状只是使物种具有足够的易变性，可以在短时间内适应环境的变化，没有必要认为这些获得的形状可以遗传。最终，随机变异也许会产生出可遗传的同样形状，自然选择则能够使物种向着已经由新行为适应的方向变化。作为科普的学生，奥斯本将鲍德温效应机制视为选择论与拉马克主义之间的一种妥协，但是鲍德温和摩尔根非常敏锐地认识到这种观点对达尔文很有利。有机选择否定了获得性的遗传，同时又利用获得性遗传来表明通过生物对其环境的积极反应如何激发了选择。 美国学派的明显特点在于其坚持每一个进化分支中发展的规则性。拉马克主义并不一定要求这一点，因为在多数欧洲人看来，用尽废退式遗传取代的只是在达尔文模式中作为不规则分支过程驱动力的自然选择。但是科普和海厄特开始时就设想进化中存在着规则性，只是在后来他们才用拉马克主义来解释这种规则性。用这种思路很适合解释海厄特所研究的头足类动物，因为它们的进化所表现出来的模式曾经使后来的许多达尔文主义者感到迷惑不解。科普利用同一种思路来解释无脊椎动物，例如，他提出，现代马的进化沿着单一的方向经历了规则的历程，对此无法用随机变异来解释。几乎可以肯定的是，这种对规则性的强调，是当初由阿加西引入到美国的唯心论的迟到的表达。 科普之所以打算维护物种的独特性，正是由于受到了同样的影响。最初，他坚持认为进化的发生是通过一系列生长的突然加速，每一次加速都使得物种与其祖先有了明显的区别。只是当科普转而相信拉马克主义之后，他才提出物种会抵抗施加给物种的压力，直至物种达到“显现点”，这时会很快产生出一种形态。这当然不是通过突然的突变产生的进化，但是这种思想使得博物学家将物种视为在逐渐进化过程中不能与其他物种混合的明确实体。 进化规则性信念中最吸引人的表述就是海厄特的“族衰老”概念。他相信一个类群，比如说头足类动物，开始时的形态比较简单，在条件适宜期间，进入规则发展阶段，产生出许多先进的形态。然后便开始了退化：条件变得不适宜，类群中的许多成员不能应付环境条件的挑战，于是失去了它们先进的特性，重又退回到原来的水平。在灭绝前的最后一个阶段，与最初形态非常简单的阶段很相似。这是一种形式的拉马克主义，即衰退是对外界因素的直接反应，这时生物对环境挑战的反应是盲目的，并不是由于适应力量的影响。海厄特的这个理论是将类群的发展类比成生命的成长、衰老和死亡，这个理论以更加复杂的形式表达了个体生物的生命周期是说明进化最好模式的观点。直生论的倡导者们充分地解释过所有进化的分支最终都会发展到尽头，面临衰退和灭绝的境况。 如果美国新拉马克主义精髓最终可以表述为直生论，那么这种结构并不严密的替代选择的理论便直到20世纪一直受到一些人的欢迎。不足的是，获得性遗传的观点缺乏实验的证据，随着新的向着实验生物学发展的趋势逐渐成为主要的潮流，这个缺陷便显得愈加突出。法国生理学家布朗塞加尔报道过通过切除天竺鼠的脑引发的癫痫病可以遗传这一支持获得性遗传的结果（例如见Romanes，1892-97），但是未能证实这一结果是由于遗传传递的。也有可能切除脑后产生的毒素通过子宫由母亲传给了下一代。这种替代式的解释常常妨碍了那些成功地证实拉马克主义合理性的少数努力。在20世纪早期，多少实验生物学家逐渐失去了耐心。1900年，由于重新发现了孟德尔遗传定律和新遗传学的出现，开始引入一种新的因素。随着新遗传学的发展，最终动摇了对拉马克主义的理论支持，反之，支持了魏斯曼所宣称的种质不受携带它的身体的直接影响。