Chapter 14 Chapter 7 Darwinism: The Controversy in Science-2

In Haeckel's reconstructions, very little of the connections he posits is based on the fossil record; he therefore uses mostly circumstantial evidence.Anatomical similarities, he imagined, indicated a continuity of derivation.The reenactment theory he revived has aroused even greater controversy. The reenactment theory holds that individual development repeats phylogeny, that is, the embryonic growth of modern animals repeats key stages of the animal's past evolution.Haeckel disagreed with Agassiz's belief in the repetition of the divine plan in the successive sequences of the animal class and in the growth of the human embryo.He proposed that natural mechanisms would preserve the adult form of certain ancestral stages in the embryonic growth of their modern descendants.Although some types of evolution have been hindered, the naturalist can, if he is careful, identify those embryonic structures which represent past stages of evolution.Presumably it was Haeckel's misuse of this "law of biogenesis" that led to the widespread belief that the theory of evolution was limited to finding such embryological parallels.In fact, modern biologists do not accept this straightforward view of replayism, nor do their theories of evolution rest on such flimsy foundations.Haeckel's use of the embryo analogy shows that his thinking was heavily influenced by Lamarckian rather than Darwinian elements (Gould, 1977b).

Much of what biologists attempted in the 1870s and 1880s was to follow in Haeckel's footsteps.Other explanations for key stages of evolution have been proposed, with evidence of one kind or another.In the end, those scientists who were more concerned with experimental research began to doubt the value of doing the whole thing.Because there are only a few cases where theories can be tested with fossil evidence, they argue that this should be stopped in favor of more fruitful research.However, being against the establishment of a hypothetical genetics does not mean being against the basic idea of ​​evolution. , and paleontologists are still trying to find fossils that fit the theory of evolution.By the end of the century, Sir J. W. Dawson of Montreal was almost the only prominent paleontologist who still defended creation (Dawson, 1890; OBrien, 1971).Why did paleontologists later accept the theory of evolution?The answer seems to be that there is enough fossil evidence, if not evolution, to convince them of the absurdity of creationism.For example, an evolutionist might predict that if birds evolved from reptiles, there is hope of finding fossils of transitional types between the two classes.Creationists, on the contrary, are constrained by their insistence on sharp distinctions between existing groups and are reluctant to imagine intermediate transitional types from past groups.Once such an intermediate transition type is indeed discovered, by adding other miraculous events, the intermediate transition type may also fit the creationist theory, but only if the discovery prevents them from relying on any predictable Only then can they make a compromise.Thus, even though a complete sequence is still lacking, a single intermediate type supports the idea of ​​evolution.

Figure 20. Variation and recurrence theory Fritz Müller was the first to outline the circumstances under which reenactment could occur (Muller, English translation, 1869), whatever the mechanism of individual variation, but evolution involves the accumulation of individual variation.There are thought to be two ways in which an individual organism can vary the normal structure of a species.One pathway (left) is through divergence during growth, whereby adult types differ from other types that are end-products of normal growth.In this case it is impossible to preserve the original type in the embryonic growth of the mutant.So evolution cannot be repeated in embryonic development, there is only similar embryonic development towards a certain point.In the second mode of variation (right), new traits arise by adding additional stages to the original growth process.In the embryonic growth of the variety, therefore, the old adult form becomes a stage, and the embryonic development repeats the past stages of evolution.But this view of variation comes mainly from Lamarckism rather than from Darwinism. According to Lamarck, evolution occurs due to the efforts of adult organisms, while Darwin believed that it is easy to regard random variation as a tendency in the process of growth. different.

Not all fossils found have long-term significance.One of the biggest problems for evolutionists is the lack of fossils in Precambrian rocks, giving the impression that the earliest invertebrates arose suddenly at the beginning of the Cambrian period.Darwin and his followers rejoiced at the discovery in 1865 of a curious "fossil" in Precambrian rock in Canada.This stuff has been described as a huge relic of a foraminifera (a primitive marine organism) and has been named Eozo(n canadense, OBrien, 1970). For evolutionists, this " "Canadian primordial animals" are just one indication that evolved life was not entirely absent during the Precambrian period. Oddly enough, the discovery was also highly regarded by the creationist J.W. Dawson, who This finding is believed to support his view that the animal was more advanced than its modern relatives, indicating no evolutionary progress. Unfortunately, it was not long before this "fossil" was shown to be the product of pure mineral action. Only recently It took several decades to confirm the existence of true microfossils in Precambrian rocks, in which a large number of more complex types were found shortly before the Cambrian "big bang".

Even if Darwinists cannot find firm support from archaeologists, some interesting discoveries have been made in other fields.Attention initially focused on the reptile-bird connection. T.H. Huxley was the first to suggest that the legs and feet of some dinosaurs were not significantly different from those of birds (Rudwick, 1972; Bowler, 1976a; Desmond, 1976, 1982).For the first time, he claims, there have been signs of a "missing link" between two important classes.This was further confirmed by the later discovery of Archeopteryx; an animal with bird-like plumage, a body with many reptilian features, and a mouth with teeth instead of a beak. O. C. Marsh found some birds with more pronounced teeth in the United States, and named them Toothed Birds (Marsh, 1880).Exactly how the bird evolved from the dinosaurs remains a mystery, but this intermediate form doesn't fit the creationists' claim that recent classes all originated entirely independently.Possible connections between other classes have also been recognized, as in the case of 'mammaloid reptiles' (Desmond, 1982).In this case, however, it was the anti-Darwinian notion of evolution championed by Richard Owen and his followers that prompted the realization of the significance of this fossil.The spiritualist concept of orderly development, reinvented, became the basis for the view that mammals are not the descendants of a single evolutionary breakthrough, but rather organizational "levels" reached by the evolutionary paths of numerous reptiles.It has been argued, therefore, that it is not natural selection but some purposeful force that is at work in evolution.

People also found some small-scale evolutionary continuous sequences.The most striking example is the evolution of horses.The modern horse is highly specialized for running on the open plains, and its single toe has become a broad hoof.But if evolutionists are right, then modern horses must have descended from five-toed ancestors, the common five-toed mammal.Originally Huxley tried to link horses to some European fossils, which made sense since modern horses were brought to America by white people.But Marsh soon convinced him that horses migrated to Europe after they evolved in America.Marsh discovered a series of fossils that allowed modern horses to be linked to a small, polydactyl, Eocene ancestor that he named Eohippus.Huxley (1888) declared this fossil series to be "clear evidence of evolution".The true evolution of horses is more complex, with many fossils representing extinct offshoots rather than stages leading to modern horses.Still, the basic outline of the sequence of horse evolution fits well with Darwinian expectations.The more pronounced continuous sequence of fossils found in invertebrates undoubtedly led most paleontologists to think that the lines of evolution were too regular to be explained by the chaotic process of natural selection.Some Americans, such as Edward Drinker Cope and Alphonse Hyatt, described the evolution of adaptation as a sequence of lineage development leading to a directed goal by a Lamarckian mechanism (Bowler, 1977c, 1983).These views became the basis for the outburst of sentiment against Darwinism in the late nineteenth century (Chapter 9).

the age of the earth If paleontology posed no more challenges than Darwin had feared, geology posed his greatest headaches.Darwin, a follower of Ryle, had imagined that the history of life could be explained in terms of a perfectly infinite time.This assumption is crucial because he insists that evolution is a slow process.The accumulation of small variations caused by selection will take hundreds of millions, or even billions, of years to produce the diversity of life we ​​see today.According to Ryle's geology, life could develop in this way, but then the theory of uniformity would face new objections.A new attempt has been made to change the time scale of Earth's history, with the intention of challenging Darwin's theory of evolution.

The challenger was the physicist William Thomson, Lord Kelvin (Burchfield, 1975).Kelvin's basic point was that the steady-state geology advocated by Ryle was inconsistent with the laws of physics.This argument was obvious from the outset, and the reason it was not used against Ryle in the 1830s was because thermodynamic dynamics were still immature at that time.This is where Kelvin can combine arguments that are essentially commonsense with established scientific frameworks.All geologists admit that the volcanic activity is in fact caused by the high temperature of the earth's interior.But if the Earth is hot, it will cool down like all hot objects, and the heat will travel to the surface and radiate into space.Chemical reactions would generate heat to offset the cooling of the Earth, but Kelvin showed that the offsetting effect of chemical reactions was negligible for the final result.If the Earth is hot now, it was hotter in the past and cooled gradually to its present state.If we go all the way back in terms of cooling, we find that the planet Earth was once a gigantic molten rock, just as one would expect the Earth to begin with from the nebula hypothesis. In 1868, Kelvin pointed out based on careful calculations that the Earth existed for a much shorter time than predicted by the method of geological uniformity.He then declares that we have no reason to suppose that earlier processes of geological change were changing at the same rate as they are changing now.Cataclysms are right not only because they adopt a directional philosophy in their view of Earth's history, but because they assume that the factors at work in the past were far more dramatic than those at work in the present.

Kelvin's position was strong because he was basing it on the fundamental laws of physics, which to most scientists are far more reliable than the flimsy theories of geologists.If the earth is hot, then the laws of thermodynamics show that the earth will cool down after a certain period of time.Unless there is some factor that can ensure that the energy released by the earth into space is replenished, it is impossible for the planet earth to remain in a stable state indefinitely.Kelvin knew there was no such factor, so he simply thought his basic theoretical framework was sound, as did most of his contemporaries.Even though he admits that his estimates of the Earth's interior temperature and the rate at which it is cooling have some flaws, he still believes that the entire Earth cannot be older than hundreds of millions of years, far less than the time required for Darwinian evolution.Now that Kelvin was famous and his arguments seemed convincing, most geologists began to revise their theories to accommodate a much faster rate of change than Lyell had envisioned.

The retreat of geologists put Darwin in a difficult position, since he simply could not accept Kelvin's estimated age of the Earth to be only 100 million years (Burchfield, 1974).He could not react positively to the point of view from physics, but he insisted that the estimates he and Ryle had made were not wrong in magnitude.Darwin believed that Kelvin's calculations were wrong, but he had no evidence to support his belief.Even some evolutionists, such as Wallace and Huxley, came to believe that evolution must have happened more rapidly than they had originally thought.They argue that biological timescales come from geology, so if geologists believe Kelvin's estimate, evolution must occur on the same timescale.By the end of the century, a variety of evolutionary mechanisms had been proposed, at least some of which showed how the evolutionary process could proceed at a faster rate than could be caused by natural selection.Kelvin's arguments did not stop evolution, but they did play a large role in the fall of the natural selection mechanism from popularity in the late 19th century.

In the end, Kelvin's estimate of the Earth's age fell victim to the revolution in physics that occurred in 1900.The discovery of radioactivity introduced entirely new factors, making Kelvin's calculations no longer valid.Pierre Curie declared that the decay of radioactive elements such as radium can slowly and steadily release energy in the form of heat.Throughout the Earth, these elements are present in small amounts.By 1906, Lord Rayleigh showed that radioactivity generated deep within the Earth would balance the cooling envisioned by Kelvin.Moreover, the decay rate of these radioactive elements is so slow that this balance can be maintained for a long time, so the earth can remain in a stable state.Geologists soon realized that they could now go back to using Ryle's date; however, by the 1930s, the development of radioactive dating techniques had been able to show that the Cambrian was 500 million years ago.The modern synthesis of Darwinism and genetics will no longer have a problem with time. We tend to think of the 19th century as a time of optimism, and tend to think of evolution as a symbol of Victorian belief in the progress of the universe.Kelvin's view, however, showed the opposite tendency, a pessimistic view according to which the earth, and ultimately the entire universe, would decline and die.When Kelvin proposed that the Earth and Sun have a finite energy supply, he was actually predicting that eventually cold would wipe out all life on Earth.Physicist Rudolf Clausius predicted the "heat death" of the entire universe on a broader scale.Due to the difference in energy compensation, all natural processes will gain less and less energy, so at the end of the universe, all matter will have the same temperature, and there will be no natural fluctuations (Gillispie, 1960; Brush, 1978).According to this thoroughly pessimistic philosophy, all natural and human activity must eventually come to a halt by virtue of the relentless laws of physics.When discussing the intellectual characteristics of the nineteenth century, in addition to considering the optimism of the evolutionists, the existence of this pessimism should not be ignored. Utility, Genetics, and Mutations Kelvin's calculations indirectly shook Darwin's assumption that the process of natural selection is very slow.But there were arguments against selection mechanisms specifically that required Darwin to rack his brains to defend the products he had conceived.With some fundamental questions, especially those related to understanding variation and inheritance, he, not surprisingly, found it difficult to face attacks from the field.This does not mean that the chosen basic idea has no value, but that some problems arose because Darwin was unable to come up with suitable ideas within the scope of his understanding at the time.The combination of selection and genetic modernity has resolved many of the earlier difficulties. Natural selection is an extremely pragmatic mechanism: selection can only develop those traits that are useful to the individual in the struggle for survival.If selection were the only mechanism of evolution, we should see every trait in every species, even subtle ones, subordinated to the purpose of adaptation.But is it always the case—are there no traits that are useless or even harmful to the species?For example, how to explain the bright colors of hummingbirds, isn't such body color necessarily easy to spot by predators?To explain this situation, Darwin made an important addition to his theory.This is the "sexual selection" he outlines in "The Descent of Man" (Darwin, 1871).He proposed that some traits are not used in the struggle for survival, but for individual mating.For example, if a male bird's particular color pattern is used to attract females in courtship rituals, males with more pronounced patterns will mate more and leave more offspring who inherit the pattern.Over many generations, an increase in coloration is promoted as females select males with more coloration.For the same reason, the horns of stags are well developed, as the purpose of the horns is to compete for more "wives" for mating.In each generation, only those stags with large horns are successful in courtship, so the average size of the horns gradually increases. The theory of sexual selection itself is not safe, either.Darwin and Wallace had a profound debate on this issue, and Wallace ultimately rejected the concept of female selection (Kottler, 1980).Some other naturalists believe that it is unlikely to explain the distribution of animal body color in terms of the usefulness of color to individuals. In 1864, the botanist Carl von Negri suggested that, in general, many types of traits are of little value and thus cannot be developed by selection.In particular, he argues that the subtle traits that naturalists use to distinguish closely related species have no practical value.By the end of the century, the belief that the constitution of nature was not entirely due to adaptation became the dominant view against Darwinism. Darwin took this objection seriously and admitted that selection cannot explain all non-adaptive traits.He does insist that Negri exaggerates how widespread the trait exists.It is difficult for the naturalist to determine which particular character has no purpose, usually because he knows so little about the way the species lives under wild conditions.But Darwin also had to admit that some traits could not have any practical purpose.The only hope of explaining this trait in terms of the theory of selection was a concept supplemented by Darwin called "correlated growth".If two characters are closely linked in the process of biological growth, then natural selection in favor of one of them will automatically promote the development of the other, whether it is valuable or not.Other naturalists, however, are inclined to think that there are some processes of life in living beings which are highly favorable to their variation in unadapted directions. This is the view held by St. George Jackson Mivart in The Occurrence of Species.Mivart was a Catholic who was deeply concerned with the implications of human evolution, and he was Darwin's staunchest critic (Gruber, 1960).He pointed out that even useful traits pass through an intermediate stage of little practical value in their full development.Darwinists later fired back at him by arguing that generally an organ did not originate from scratch but underwent a transition from one function to another before it was fully developed.Mivart also pointed out that there are a lot of strange coincidental connections among different evolutionary clades.For example, why do octopus eyes look so similar to ours?It is simply impossible for the selection of random variations to produce such a resemblance between two distinct types.Mivart proposes that the evolution of life must have proceeded in a definite way, according to certain tendencies, since the laws of optics determine the general structure of an effective eye, whereas the details of the actual formation of cephalopod and vertebrate eyes do differ slightly. different. An equally staunch objection focuses on the inner workings of the selection mechanism.We have already mentioned (in Chapter 6) that Darwin, like his contemporaries, believed in "confluent inheritance," the idea that the traits of the offspring incorporate or share the traits of the parents.It was known at the time that some traits were inherited in an all-or-nothing fashion, but such inheritance was thought to be the exception to the general rule.Darwin explained fusion inheritance in terms of his theory of pangenesis (published in Darwin, 1868; see Geison, 1969; Robinson, 1979; Farley, 1982; Hodge, 1985).This theory arose out of his earliest thoughts on the role of reproduction and growth in evolution.He believed that each part of the body produced something called a "bud", which was responsible for the reproduction of each part of the offspring.Buds travel through the bloodstream to the reproductive organs, and fertilization involves the union of parental buds.Because under normal circumstances each parent contributes buds that control one trait, although there are some exceptions where a trait is determined by buds from one parent, fusion will be the general rule.Today we believe that the all-or-none phenomenon articulates the fundamental genetic processes described by Mendelian genetics.Thus, by modern standards, Darwin's pangenesis and his understanding of heredity were clearly flawed.We have to remember, however, that pangenesis reflects mid-19th-century attitudes toward growth and reproduction.Despite the distinctly modern character of Darwin's study of biogeography, the foundations on which his ideas about the link between growth, heredity, and evolution were based were discarded with the advent of Mendelian genetics. To what extent does this error affect the plausibility of the selection mechanism?In fact, this problem can be illustrated by Darwin's response to the engineer Fleming Jenkin's comments on (Jenkin, 1867; reprinted in Hull, 1973b).Eiseley (1958) wrote that this comment might have convinced Darwin that selection was not well founded and forced him to turn to Lamarckism.He states (quite correctly) that pangenesis accommodates Lamarckism, since body parts make their own genetic material, structural changes through use and disuse will be reflected in the production of buds, and are heritable .But it would be a mistake to think that Darwin's pangenesis was a turn to the Lamarckian approach.Vorzimmer (1970) took the opposite view, arguing that Jenkin's comment had little impact and that it merely confirmed something Darwin had already thought of.A more plausible explanation for Darwin's apparent concern with Jenkin's comments in his letters is that he was forced to argue for the way he described choice without abandoning the idea of ​​choice entirely (Bowler, 1974b). Jenkin concedes that selection can work if we imagine that the object of selection is all the variations in a population.For example, if being taller was an advantage, then those individuals in a group who were taller than the group average would benefit in the struggle for survival.Likewise, many individuals of shorter than average height would have no advantage, and the next generation would have more offspring from taller than shorter parents.In this case, fusion inheritance does not interfere with natural selection, but spreads the benefit evenly to the offspring. However, Jenkin went on to suggest that selection acting on small variations that are common in a population does not cause large-scale evolution.He accepted the common-sense belief that ordinary variation is strictly confined within the range of variation within species, but that new species cannot be produced by variation, since variation itself cannot cross species boundaries.Domestic species demonstrate the existence of such boundaries.For example, hundreds of years of selection in dogs has produced a large number of strains with very different traits, yet all dogs belong to the same species.Darwin, of course, did not admit the existence of such a limit, but instead believed that, given enough time, mutations could cross this apparent limit.On this assumption, he has no reason to abandon the theory of choice, and even Jenkin concedes that choice can work.So why did Darwin admit that Jenkin's comments made him think so carefully about the problems of variation and heredity? The answer lies in Jenkin's second argument.He has already shown that he does not disagree with the view that selection acts on normal variation within a limited range, and he further proposes that the only way of crossing the boundaries of species is by selection acting on those individuals born with an apparently abnormal structure, i.e. Acts on deformities, or what came to be called "nature's teasing" products.The products of this teasing will exceed the limits of normal variation, and it is possible that occasionally one of the types will employ the deformity it possesses in the struggle for existence.Can selection make this "promising deformity" useful?It is already known that artificial selection can take advantage of a person born with a desired trait to produce a new strain.In the case of the Ankang sheep, a farmer noticed that one of his male lambs was born with abnormally short legs, and he realized that if the whole flock had this trait, it would prevent the sheep from jumping out. lock up.Through careful selection of the descendants of this original ram, he was able to produce this line, which became more and more numerous.Jenkin believes that this phenomenon cannot occur in nature, and there is no way to ensure that offspring can be produced between deformities, and after several generations, through mixing with a large number of individuals in the same population, the effects of deformities may disappear.Even if deformities, because of their advantages in the struggle for survival, have more chances of mating than normal individuals, it will have no effect in the long run.It's a lot like putting a drop of black paint in a pinch of white paint, and you won't see it when you stir it. If Darwin based his idea of ​​selection on this hopeful monstrosity, it would be understandable why Jenkin's comments caused such a jolt.Instead, he insisted that "nature makes no leaps" and that evolution proceeds through the accumulation of small changes.The problem is, sometimes, he writes, even small favorable mutations occur in only a few individuals.Instead of advocating the idea of ​​widespread variation among whole populations, he suggested that only slight, favorable changes in traits occur in a small number of individuals.If there is a distribution of variation for a trait like height, then by definition half the individuals in the population are taller than the mean and half are taller than the mean, then selection will play a role even in the case of fusion inheritance effect.But if the favorable variant (small or large) is a small number of individuals, then Jenkin's elimination argument can be applied. So the effect of Jenkin's comments was not to make Darwin abandon the idea of ​​selection, but to make him describe variation in populations in a different way.Darwin would no longer think of varieties as individual individuals, but instead adopted the concept of a distribution of variations.The role of choice can only be explained if the meaning of "groupthink" is fully explored. AR Wallace, in particular, insisted that Darwin recognized this, and Wallace, in his own later work, devoted considerable effort to showing that in many populations there are markedly variable distributions of traits (e.g., Wallace , 1889).So, by adopting a population description of the variation, the selection mechanism is maintained.The reason why Darwin had planned to abandon the group description of variation was because he was pessimistic about the extent of variation in the wild. Another problem posed by fusion inheritance concerns the process of speciation, the divergence of one species into distinct species.The original example of the Galapagos Islands convinced Darwin that the divergence of species was essentially due to geographical isolation.If the population is not physically isolated, continuous interbreeding will cause the traits of individuals in the population to merge, thereby preventing the fundamental differentiation of species.It should be possible to circumvent the problem Jenkin raised, since in small island populations a single variant will not completely eliminate it.Darwin had abandoned this view when he wrote, as we saw in Chapter 6, when he believed that natural selection was sufficiently capable of making an initial succession of species by adapting extreme forms in groups to different forms of life. groups separate.He argues that because the population is not too large, it is sufficient to ensure the survival of favorable variants, even if such mutant individuals arise very slowly.Extreme isolation can also hamper this process, since in small groups the emergence of the most favorable individual can be a very rare event.Jenkin convinced Darwin that he must regard favorable varieties as individual individuals: any population, even a small one living only on islands, must exhibit a distribution of variation across all its traits.Nevertheless, Darwin did not reconsider his views on segregation, because he still felt that intense competition in a contiguous geographical area would promote divergence more effectively.He refutes the assertion by Moritz Wagner (Wagner, English translation, 1873) that geographic variation is a necessary prerequisite for speciation (Mayr, 1959b; Sulloway, 1979).But this brought him to the second problem of fusion inheritance: what caused the original variety to become infertile and lose its distinctive characteristics?The search for mechanisms that made the idea of ​​sympatric speciation (speciation without isolation) likely survived the rest of the century, and the failure to discover such a mechanism prompted many naturalists to turn against selection theory .In the end, Wagner's position was upheld as most naturalists accepted that geographical isolation was a necessary prerequisite for the first stage of speciation. The difficulty in explaining speciation arose from the failure of most early Darwinists to distinguish between geographic and reproductive isolation.This makes them reluctant to accept a conception of the nature of species that is entirely group.No intermediate stage can be identified between the "variety" which is still interferable, and the original species, which is genetically incompatible.Modern biologists realize that the important thing is that the "segregation mechanism" is not so much genetic as it is behavioral: individuals from two populations may be genetically able to mate with each other, but they do not mate, which is Because their mating behavior is different.Once such an isolation mechanism is established, the two populations occupy the same area, but they will not mix with each other, and will continue to separate until they form genetically distinct true species.The crux of the problem is how to keep separate from each other until the isolation mechanism is established.The prevailing thinking is that the initial phase of geographic segregation is crucial.Darwin did not have such a view, so he could not explain how selection divided previously continuous populations until genetic sterility was established. This question is related to the question of sterility across species.Why do crosses between different varieties of the same species produce normal offspring, while crossing definite boundaries of species either fail or produce sterile hybrids like mules?Opponents of evolution use this sterility as evidence that species have unique properties.Darwin proposed that there were no clear dividing lines between species, but that the degree of sterility increased as the constitutional traits of the two types became more and more distinct.The example of the mule illustrates that the boundary between two parental species is not as absolute as it should be.Seeing it this way still raises the question of how evolution established levels of sterility.Mutual sterility is valuable for both groups because mutual sterility contributes to divergence and thus reduces competition between groups.However, mutual sterility is of no value to the individual, because the individual seeks to maximize the number of offspring produced by mating with a wide range of mates.Darwin's belief that sterility was a by-product of divergence is the essence of the modern view.Wallace, on the other hand, insisted that natural selection actually worked to cause sterility, although he seemed to think that selection was acting between groups rather than individuals.Darwin did not accept the idea of ​​"group selection" (Ruse, 1980), and most modern biologists agree that selection occurs purely at the individual level.The debate in sociobiology is essentially the result of attempts to explain what are in fact purely selection effects on the reproductive success of individuals into traits that appear to be beneficial to the population as a whole (Chapter 11).在不育的案例中，不存在是否对个体有利的问题，因此不育性状的产生肯定只是趋异的副产品，即使这种不育可能对整个群体有利。 方法问题 除了生物学上的反对意见，达尔文还发现人们对于他的科学方法的合理性提出了质疑。他曾经希望他的工作被当作纯粹的科学工作来接受，所以他失望地看到有人批评中有大量的臆想得不到他所提供的证据的支持。有人认为，他并没有选择归纳科学的道路，而是沉湎于更加随意的假说法，从而完全超出了科学的限定的范围（Elleg？rd，1957，1958；Hull，1973a，1973b）。 确定假说在科学中作用的问题，使得当时的许多哲学家都感到困惑。一些重要的人物，比如K·F·W·赫歇尔——他的著作曾经使早期的达尔文产生了对科学的兴趣，承认在发现的过程中假说或有限制的臆想起到过一定的作用。简单的培根归纳法，即随机地收集事实并期望分辨出最后的图景，在面对大量的可以获得的数据情况下，常常无所适从。科学家只有根据所获得的事实发明一种合理的假说，并且经常利用这个假说来指导以后的研究。这种方法在今天叫做假说演绎法（Hempel，1966）。根据假说推导出经验性的结果，然后再用事实来检验。如果得不到验证，便否定了这个假说，并且要去探讨新的假说。如果最初的检验是成功的，那就要继续检验，结果或者是该假说得到了更多的支持，或者是最后该假说的弱点暴露了出来。 毫无疑问，达尔文在确立他的理论时使用了这种方法（Ghiselin，1969）。那么为什么科学哲学家会认为他的理论不坚实呢？部分原因是一般人感到科学家在构想假说时不应该超出人们已经接受的准则。达尔文逾越了人们已经接受的所有自然史教义，提出了超出了限制的猜想。而且19世纪的哲学家相信，真正富有成果的科学假说必须道出自然的真理。最后，这个假说的推论要符合基于事实的推理逻辑链，并能够提供可以检验的证据。对此，现代的科学哲学家无法接受，因为根据这样的标准，任何理论都不会合格。人们不可能证实一种理论在任何情况中都是正确的，因为情况的复杂性使得人们无法作出完整的推论。科学家只能提出证据支持他的理论，因为他认识到这个理论总会由于缺乏绝对的证据而失败，而且一种理论只能暂时被接受。 达尔文当然提出了支持他的假说的证据，他表明，在许多领域中，对于一些事实，如果不根据进化来解释，就无法理解。他认识到，如果要求他的理论有可证实的证据，结果就会妨碍限定在科学的范围来研究整个进化问题；无论是他的理论，还是其他构想出的理论，都不能提供这样的证据。但是他的许多同代人却相信，一个理论首先必须是可以证实的，然后才能成为人们接受的科学知识。有些很重要的理论在提出时都曾经过激烈的争论，但是后来却被遗忘了。赫胥黎就曾落入这个陷井，他承认，除非通过人工选择可以从一个种源中产生出两个不育的物种，否则就无法证实达尔文的理论，这对于相信进化过程非常缓慢的达尔文来说，是一个不合理的要求。至少赫胥黎认识到进化论是真正的科学理论，它能够经受事实的检验，因此只要有证据就能获得支持。那些否定这个理论人，指责达尔文提出的只不过是得不到支持的猜想，因为他不能提供有关的绝对证据。还应该指出的是，现代的特创论者依然使用这种伎俩。 另一个有关的问题涉及选择作为真正原因的价值，即作为可以被科学所接受的一种“真正原因”。这个问题产生于人们关于科学定律和原因概念的争论。参加争论的主角是威廉·休厄尔，他的《归纳科学的哲学》出版于1837年，再就是约翰·斯图亚特·穆勒，他的经典之作《逻辑系统》出版于1834年。穆勒坚持传统的英国经验主义，即所有的知识都来源于感知，而“原因”只不过是由于一种事件与另一种事件之间有着固定的联系。休厄尔试图使康德的唯心论适应于英国的习惯，他提出，直觉提供的知识源泉独立于感知，从而能够使得科学家根据直觉构想出自然的法则，然后再将事实与该法则联系起来。而且根据直觉的认识，原因是自然中作用力，导致的事件以符合自然法则的方式发生。 达尔文的支持者来自经验主义阵营。穆勒本人则陷入了一种困境，他无法分辨发现的过程和证据的逻辑关系，因而提出，一种理论只有在具有了绝对证据的条件下才能被真正接受。他至少证实了，事实上按照经验主义的标准，自然选择是真正的原因。其中所含的所有因素（随机变异、生存斗争等），从经验的角度看，是有合理效应的。这些因素合起来是否能够产生出达尔文所宣称的结果，还要去证实，但是至少这个理论的基础是牢靠的。达尔文所不满的是，赫胥黎和穆勒要求一种按照定义这个理论无法提供的证据，但是他比其他人都更清楚地知道他的思想在多大程度上根据的是纯粹可以观察到的原因。 然而，对于唯心论者来说，达尔文在提供一种真正的原因方面，并没有满足要求。他们相信，他们凭借直觉可以获得的关于自然的真理，要比达尔文浅薄的理论框架坚实得多。这些真理包括物种固定不变的性状以及控制物种结构及其相互之间关系的一个目的。科学家一般研究的次级自然原因最终涉及第一原因、即上帝本身的力量控制之外的范围。因为唯心论者根据直觉确信第一原因的存在及其对自然的直接控制，所以唯心论者认为，当次级原因表现出不正确时，应该求助于第一原因。于是休厄尔会提出凭借已知的自然原因不可能解释物种的起源，在这个问题上科学家应该放弃研究，以确保这个问题直接包含在第一原因的知识中。即使承认基于进化的“创生法则”有可能存在，这也能说明自然的目的性而且依然要求第一原因作智力指导。 达尔文的机制所遇到的问题是它未能将这些目的性的因素包括进去。达尔文未能完备地描述变异产生的原因，而且产生变异的原因并非与物种必备的条件相关。选择所起到的是一种糟糕的作用，因为它只是不淘汰那些碰巧在生存斗争中占据优势的个体。达尔文未能指明变异，这一事实正好表现出他的理论中弱点：如果他不能说明变异的起源，他怎么能够宣称解释了建立在变异基础上的进化呢？对于唯心论者来说，一种真正的进化原因应该能够说明变异的产生，而且说明的方式应该符合博物学家在建立生命历史时所具有的直觉性感知。赫歇尔将自然选择称作乱七八糟的法则，表达了他对于一种将生命的发展归因于偶然事件偶然结合机制的鄙薄。真实的情况是，比较保守的思想家想要坚持物种固定不变的旧思想和有利于设计的论点。唯心论使得他们可以追求一种有关自然目的的直觉性知识，因此也就可以贬低达尔文的理论不正确，因为这个理论不支持他们的直觉。如果进化发生的话，那么也一定是揭示出神的计划，而不是偶然的结果。因此唯心论者对于选择的批判引发出这个理论所导致的宗教和道德问题。 通过总结一下各种科学争论可以看出，达尔文使多数追随他的博物学家都转变了观念，开始相信进化论，但是他的选择机制却没有成功地推广开。有些保守的思想家不相信任何形式的进化论，因为进化论与他们所相信的神缔造了自然规则的信念相矛盾。不过达尔文却表明，人们在很多领域都可以对于事实至少大致作出自然的解释，而迄今为止这些事实都被归因于上帝的作用。越来越多的生物学家开始接受自然进化的观点，只不过是因为他们认为物种起源的问题肯定不可能永远游离于科学研究的范围之外。这其中选择机制所起到的确切作用是：选择机制表明对于进化的自然解释并不是完全无法想象的。但是选择机制是否是一种正确的解释则仍然是一个可以商榷的问题。达尔文及其追随者发展选择理论，但是一旦有可能，他们宁愿利用传统的机制来解决困难的问题。他们曾经提出选择是科学进化论的中心原理，但不是唯一的原理。然而那些反对任何形式自然进化理论的人最先对于选择机制提出了坚实的反对意见。随着时间的推移和这些反对意见对达尔文主义者的影响，越来越多的博物学家也不再看重选择。虽然没有引起他们完全放弃进化论，但是他们在继续寻找替代选择的机制，而且在这个世纪末期，人们对于选择论愈发的反感了（见第九章）。因为提出来的替代机制保留了达尔文之前有关自然发展的典型的目的论进步观，所以给人一种印象，好象达尔文主义革命的影响远不及人们通常认为的那样大。这个关于自然发展理论的胜利，并没有带来达尔文的批评者所预想的悲惨结果，因为他的理论中最激进的部分在他那个时代并没有被人们所接受。