Chapter 19 Chapter Ten Evidence for Darwin's Theory of Evolution and Common Ancestry-1

Darwin was aware at the time of the revolutionary nature of his work, and he also knew that he would encounter great resistance and resistance, and that in order to overcome it all, he would have to defeat or overwhelm his opponent.That is why he has spent 20 years gathering evidence and trying to make his arguments airtight.His strategy was to discuss the mechanisms of evolution first, and then only present the evidence in support of the theory of evolutionary evolution in the last few chapters; this approach may not be adopted by many modern textbook authors, but it was in line with the fashion at the time. The scientific tradition (Hodge, 1977).

Not everyone who has read it in the past realizes that it presents not a single theory of evolution but a whole set of more or less independent theories, each of which will be analyzed in detail below.These include Darwin's theories of speciation, common ancestry, gradual evolution and natural selection, together with the fundamental doctrine that the kingdom of life is not static but evolving and that the species that make up it are also evolving.Not only did Darwin have to provide evidence for each of these theories but he also had to argue against all alternative theories.Above all he had to refute the creationist ideology that still dominated Britain in the mid-nineteenth century, often in different guises.Thus, Darwin says in (459 pages); "This book is a long debate" (see also Gillespie, 1979).It is of course impossible to distill or summarize everything Darwin mentioned in his 490-page essay, but I will try to show what kind of evidence Darwin thought was presented in support of his contention, and which The evidence is again consistent with the level of biological knowledge in Darwin's day.I will start with the question of the evolving world.We know that Darwin was not the first to propose a theory of evolution, yet he not only was the first to propose a plausible mechanism, natural selection (see Chapter 11), but he synthesized such a body of evidence that in In the ten years since 1859 (published) not a single qualified biologist has ceased to accept the fact of evolution.

10.1 Evidence for biological evolution The basic, direct evidence for biological evolution has two parts: horizontal evolution, the inconsistency of species revealed by geographical research; and vertical evolution, the fossil record indicated by geological research.Having introduced and discussed Darwin's explanation of the problem of species inconsistency (multiplication) above, I shall now turn to the fossil record. Darwin was primarily a geologist during and after the voyage of the Beagle.He had read Leyle's "Principles of Geology" systematically and carefully, so he was very familiar with the geological problems of the earth's history.Geology, the most prosperous branch of natural history at that time, achieved rapid and important development in the first half of the 19th century.That the Earth is very old is no longer the next question, but is it old enough, as Darwin's theory requires, for the gradual evolution of life into a vast and unparalleled diversity?Do you still want to propose sudden evolution?

Fossils are two-faced. They are used by Cuvier, Agassiz, Bronn, and all the British geologists to deny the theory of evolution, and they are used by Chainbers and Wallace to support the theory of evolution.It was therefore natural for Darwin to devote two chapters to discussing the geological evidence in support of evolution.Darwin's strategy since he set out to write this book is to assess and answer all objections that may be raised against his theory, and to pre-empt them before they are raised.The objections to evolution raised by geologists are so numerous and so difficult to answer that Darwin devoted Chapter 9 to them.

Let me start with the question of the age of the Earth.Immediately after Hutton, Leyle proposed that the age of the earth is infinite, and Darwin believed that it was several billion years.In order to avoid circular reasoning, Darwin tried to prove his point with purely geological data.He came up with specific numbers, such as the unparalleled thickness of the geological layers, the slowness with which they were deposited, the slowness of erosion, etc., which provided impressive geological evidence for the unparalleled age of the Earth. Darwin was quite satisfied with his own conclusions, because there was enough time for any observed evolutionary phenomenon (even slow gradual evolution) to be realized.The actual figures he cites are large but of the correct order of magnitude.For example, he calculated that the denudation of the Weald zone in southeastern England may have gone through 300 million years (300 million years), and the current most accurate estimate is about 70-140 million years.

Although Darwin's numbers were at most only 2-4 times larger, the errors of contemporary physicists were several orders of magnitude. William Thomson (namely Sir Kelvin) calculated based on the cooling rate of an object the size of the earth (when receiving the radiant heat from the sun) that the age of the earth is at most no more than 100 million years, probably only 24 million years (Burchfield, 1975).Of course, this would hardly allow enough time for the gradual evolution of all known plants and animals. Kelvin's numbers are bound to prompt Darwin to abandon slow gradual evolution and adopt large-scale mutation (big mutation, "sports", macromutation) evolution.In fact Darwin was quite sure of his own opinion, and he responded to Jenkin's criticism.Later he paid less attention to large mutations than he did in 1859.There is an obvious contradiction between the biological evidence and the physical evidence here.As far as a physicist is concerned, it is completely unimaginable that he should ignore some important factors, so he flatly believes that biology is wrong.Although Darwin was also very annoyed by the discoveries of physicists, he was still very confident in the reliability of his biological discoveries and inferences. Finally, he concluded: "I am convinced that the world will be found to be much older than Thomson imagined. Much." Of course, the biologists were right.Regardless of the radioactivity that was not known at the time, the age of the earth estimated by physicists must be increased by two orders of magnitude, which is about 4.5 billion years, which is more than enough for the evolution of organisms. Darwin is often unfairly accused, saying that he is like Hutton Admit that the age of the earth is infinite, as Lyell did.He never said that.His proposed Earth age of several billion years turned out to be almost correct.

But there are still a few physicists and mathematicians who feel bad about the chronology adopted by the Darwinists.Some of the most eminent physicists in the world (including Bohr and Pauli) have shown to me that accidental processes of random variation and selection can form the biological world in less than 4 billion years. Diversity and the incomparable mutual adaptation of living things.When the reasons of a representative group of physicists and mathematicians were handed over to a group of evolutionists for careful analysis, it was found that physical scientists had an oversimplified understanding of the biological processes involved in evolution.As schematists, they did not give sufficient consideration to the uniqueness of recombination.Furthermore, they considered "tandem evolution," that is, evolution from one homozygous genotype to another, forgetting that genetic changes in evolving species can occur simultaneously in thousands of (not to mention millions) of loci. In short, Darwin's predictive estimates were confirmed again, while the criticism of physical scientists was based on some assumptions that are not suitable for biological systems (Moorhead and Kaplan, 1967).

Perhaps the most important advances in geology in the half century preceding publication have been the identification, delimitation, and naming of geological ages, from the oldest—Sedgwick's Cambrian and Murchison's Silurian—to the Tertiary ( Lyell made a particularly important contribution to his Chronicle).These studies clearly show that each of the successive rock formations has its own distinct cluster of fossil species, and that the history of such series is essentially the same around the world.There was a heated debate about whether the fauna series represented some kind of progress (Progression), and it was finally clear that fish first appeared in the Silurian, reptiles-Carboniferous, mammals-Triassic, placental lactation species appeared in the most recent Cretaceous period.The general outline was clarified in the 1850s, and the more precise situation was after 1859.

The substitution of fauna and flora and the apparent progress of catastrophists such as Agassiz are explained from a non-evolutionary perspective.To an evolutionist like Wallace, these indicated "gradual change in organisms." He went on to recognize that "in each century there are only certain groups (fossils) of (organisms), often extending over several In rock formations, these groups are not found in other centuries... Species in genera or genera in families in the same geological century are more closely related in affinities than in different centuries... (All geographical and geological facts Both show that) no species or group has ever arisen twice.” The history of life on earth is not accidental, and has its own laws.

Yet it appears that only Chambers (whose knowledge was largely incomplete), Darwin, and Wallace were able to understand that fossils can serve as evidence for evolutionary history. Lovejoy (1959a) accused geologists of not knowing even this, but it must be understood that evolution before 1859 meant evolution of the Lamarckian and Chambersian model, i.e., naturally stepped, stable, mostly composed of "Raw" to more complex linear progression.Thus, the fact that placoderms, already known to be structurally very complex, or that some primitive (non-placental) mammals reappeared in the Jurassic (reptilian) period is considered a denial of evolution.Sometimes certain formations and certain creatures are misidentified to add to the confusion.Apart from referring to flora (there were no angiosperms before the Cretaceous) and fauna in general, the geologic record was far from being a useful help to the evolutionist, but almost a liability or a hindrance.If the major groups of plants and animals evolved slowly, links should be found between them.However, it was not found at the time.Even the nearly ideal link between reptiles and birds, Archaeopteryx, was discovered only two years after publication.Darwin's opponents posed other difficult questions: Why the sudden break between major geological centuries?Doesn't this situation support the theory of catastrophe rather than evolution?Why are most of the major phyla (phyla) fully formed in strata containing the lowest layers of fossils?Why do so many extinct species (eg, ichthyosaurs, pterodactyls, dinosaurs) and unusual types fail to fit nicely into any kind of reconstructed evolutionary sequence?

So it should come as no surprise that Chapter IX (in tone or tone) is defensive from start to finish. It begins by addressing the sharpest question posed by his opponent: "Why are particular types ... not blended together by innumerable transitional moments" (p. 279)? .Darwin thought this was because the geological record was too incomplete for the preservation of these particular types, and he produced evidence after evidence to support his thesis.Geological research over the past 100 years has fully proved that Darwin was right about the inadequacy of the geological record.Since these special types are preserved, it is a discontinuity problem.In Darwin's day, the geological record provided stronger support for the sudden emergence of new species and types (catastrophism) than for gradual evolution through natural selection.Although many "missing links" (miSSing links) have been discovered since Darwin, there are still too many gaps in the geological record, so in the 1940s some paleontologists (such as Schindewolf) and geneticists still Catastrophism in favor of large mutations; so do individual paleontologists to this day. Despite the lack of conclusive evidence, Darwin finally made the right answer because he consistently insisted on the origin of new species as the key to solving evolutionary problems.The reason why he insists on the above point of view is the result of the enlightenment of the experience of the Grapagos Islands; he "reverts" all macroevolutionary problems to the level of species, and "reverts" them to variation at the species level.Thus in the chapter on the geological record surprisingly only briefly touches on speciation (pp. 297-298). What is most impressive about Darwin's approach to the chapter on the fossil record is that he was always thinking about things as a biologist.Whenever possible he followed Lyell's approach to provide ecological answers to complex phenomena in the geological record.His answer to the question of why large numbers of diverse taxa tend to appear suddenly in the fossil record is that this may not only be due to an incomplete fossil record, but may also be due to adaptive shifts: "It may take a long elbow for organisms to adapt to a new particular way of life, such as flight in the air; but when this is once achieved, and a few species thus have a greater advantage over the others, it is only necessary to compare Many types of divergence (divergence) can be produced in a short period of time, and these types of divergence will spread rapidly and widely throughout the world” (p. 303).The fossil history of birds, bats, or other organisms that ventured into differently adapted areas amply bears out Darwin's thesis. Darwin was particularly eager to find a plausible answer to the question of the sudden appearance of seemingly entirely new groups of organisms in geological sequences, a phenomenon cited by Agassiz, Sedgwick, and the Swiss paleontologist Pictet against the theory of gradual evolution .In addition to the shift of the adaptation zone, Darwin enumerates some other reasons why the geological record is so incomplete (pp. 287-302);For example, dead animals and plants in tropical forests decay rapidly and cannot form fossils, except in special cases buried by volcanic ash or magma.In continental areas with little erosion and deposition, there are often no fossil-bearing sedimentary deposits at all. For example, there are no Tertiary fossils in most parts of Africa, and there are no Triassic or Permian fossils in a certain period in many parts of the world.Another important reason for the absence of deposits that might contain fossils is the disappearance of continental shelves at moving plate fronts, as evidenced by the tectonic plate theory, which of course was unknown to Darwin. The fact that some extant organisms exist in little or no fossil form provides the strongest evidence that a group of organisms may have existed without leaving any trace in the fossil record.For example, the most primitive angnathians (lamprey and hagfish) were not found between the Paleozoic and modern times, and coelacanths flourished between the Devonian and early Mesozoic, and it is thought that in the Cretaceous (approximately 70 million years ago) became extinct until 1937 when one extant species (the lanceolata) was rediscovered in the Indian Ocean. Of all the sudden formation of fauna nothing annoyed Darwin more than the sudden appearance of some of the most important phyla of animals in the deepest fossil-bearing rock formations.Where do they come from? In the eighty years after 1859 the puzzle became even more obscure.Whenever new formations are discovered or carefully studied, the earliest types of animals are always found in the Cambrian period, and nothing is found in the pre-Cambrian formations.But the Cambrian period was about 600-650 million years ago, and the Earth as a whole is about 4.5 billion years old.Most of the geological columns are clearly much older than the Cambrian.The fact that there are large numbers of trilobites, brachiopods, and other fossils in the oldest fossil-bearing formations and no trace of their common ancestor in the older formations forced Darwin to admit that "the case is as yet unexplained." of" (p. 308).Darwin here (and always has) candidly acknowledged a difficulty which remains unresolved to this day.Thanks to the efforts of Barghoorn, Schopf, Cloud, and others, the fossil record has been stretched back to 3.5 billion years, but these older fossils are almost entirely microbial, protists in formations older than a billion years ( Schopf, 1978).We have to think that the wonderful radiation of invertebrates was indeed a relatively "sudden" event in the late Precambrian period (about 700-800 million years ago). There may be a range of factors contributing to this contingency: ocean chemistry may have changed, diploidy and genetic recombination may have been more frequent, and ecosystems such as the origin of predator types may have occurred changed and so on.It is also possible that we will never be able to solve this mystery. After Darwin attempted to answer all the hard questions his opponents might have in Chapter 9, he was free to apply the fossil record data to other questions of his own about biodiversity and adaptation in Chapter 10. : "Are some of the facts and laws relating to the geological order of living beings better suited to the view of invariant species, or to that of gradual and slow change by heredity and natural selection?" (p. 312) In fact Darwin Sticking to one's own theory is not only to oppose the argument of species invariance, but also to oppose Lamarck's orthogenesis (directed evolution theory) and catastrophe theory (or sudden change theory).In this chapter Darwin used the hypothetical-deductive method with particular skill. He not only presented geological evidence but also developed some general principles of evolution.He emphasized that "the variability of each species is independent of the variability of all other species." For this reason and some other factors, each species has its own rate of evolution, which may be slow or rapid .The same holds true for higher taxa. "Generuses and families follow the same general laws in their appearance and disappearance as do individual species" (p. 316).Such an emphasis on the individuality of taxa and the uniqueness of each taxon's evolutionary behavior was clearly unorthodox in an era dominated by the thinking of physical scientists.These physical scientists believed only in general laws that could be expressed with mathematical precision, and they assumed that all evolving organisms evolved at the same rate.Darwin emphatically rejected this argument: "I do not believe in dead laws of development, which cause the inhabitants of a country to change suddenly, or at the same time, or to the same degree" (p. 314). Extinction No other aspect of the geological record fits Darwin better than extinction.We also remember that Lamarck thought extinction was impossible.Since Cuvier, the continual extinction of species and whole higher taxa has become undeniable, not even by those geologists who do not support extinction (via catastrophe).Yet if evolution is denied, extinction is a vexing problem.Why did Creation primarily create so many vulnerable species?Why did the Creator have to try to replace them?By what process did the Creator introduce many new species to fill their spaces? As far as Darwin is concerned, extinction is an inevitable accompaniment of evolution, which is inseparable from each other.Since the world is constantly changing, some species will find that the environmental conditions are no longer suitable, so "species and groups of species will gradually disappear one by one, first from one place and then from another. One place, and finally disappear from the world” (p. 317).But biological factors are more important than physical factors. Darwin pointed out: "The improved and modified descendants of a species will generally promote the extinction of the parent species (p. 321). When a major group disappears entirely, such as trilobites or ammonites (nautilus fossils), the extinction is a slow gradual process, culminating in the extinction of the last surviving species. Darwin also Says: "We needn't be surprised by extinction because it fits the theory of natural selection" (p. 322). For Lyell, however, it fits a very emotional theory. It is only in the last 12 pages of Chapter 10 that Darwin presents the crucial evidence for evolution shown by the study of the fossil record.His conclusions can be summarized as follows: (1) All fossil forms (forms) can be arranged into a perfect natural system, even some types like ammonites (cephalopods) and trilobites (arthropods). (2) As a general rule, the older a fossil species is, the more it differs from extant species. (3) Fossils in two consecutive rock formations are much more closely related to each other than in rock formations that are far apart. (4) The genetic relationship between the extinct species on any continent and the existing species on the nuclear continent is closer. For example, the extinct Tertiary mammals in Australia are similar to the existing mammals, and most of them are kangaroo marsupials ; in South America, the extinct Quaternary fauna mainly includes armadillos, sloths, and modern fauna are similar.Darwin named this phenomenon the "law of succession of types". The evidence Darwin mentioned in Chapters 9 and 10 he sums up in the following words: "Therefore, it seems to me, that the theory of descent with modification has no relation to each other of extinct species. The principal facts of the affinities of the species and of their affinities with extant species are satisfactorily explained, which, from any other point of view, are inexplicable" (p. 333). Since paleontology is the only biological science that can directly study macroevolutionary phenomena, the theory of evolution is a great boon to paleontology.The idea that nature evolves and that groups of related taxa derive from a common ancestor has been almost universally accepted by paleontologists since 1859.In contrast, Darwin's other two theories, gradual evolution and natural selection, are opposed by almost all paleontologists, which will be introduced later. 10.2 Evidence for the Common Ancestry Theory Once Darwin abandoned the notion of the immutability of species, there was no longer any obstacle on the way to the doctrine of common ancestry.If the ancestral line of cats gave rise to several species, it would be plausible (and indeed logical) that all cats could have descended from a common ancestor.Since cats, weasels, dogs, and cats share many similarities, it would be plausible to hypothesize that they arose from a common ancestor that led to all carnivores.So consistent adherence to the concept of common ancestry from beginning to end binds the entire biological world together.The infinite diversity of animals and plants seems so chaotic and completely inconceivable, but as long as we use the concept of common ancestor to investigate, it will suddenly become clear and understand everything.At the same time, this idea is so seamless and exciting that Darwin expressed it as the capstone of his pyramid in the last paragraph of his book: "This life now has a grandeur, which at first only gave to few. Or even the only species, but with its multiple magnification, it has evolved from such a simple beginning to a magnificent and colorful world composed of endless species." Lamarck, Chambers, and some other early evolutionists did not focus specifically on species, which prevented them from discovering the concept of a common ancestor.Apart from the theory of natural selection, this is perhaps the most instructive concept that Darwin proposed and developed.Before 1869, most phenomena in the biological world were regarded as random and changeable. However, it is logical and logical to explain them with the concept of common ancestor.Chapter VI, Chapters 10 to 13 are mostly arguments aimed at proving that some phenomena are much easier to explain using the concept of common ancestry than creationism. Darwin admired the philosopher John F. W． Herschel and William Whewell, both of their scientific philosophy and methodology originated from Newton.Darwin applied their principles or principles in his writings whenever possible.This includes the search for regularities in natural phenomena, especially to explore the mechanisms or causes of phenomena that can explain phenomena in a wide variety of fields (Ruse, 1975b, Hodge, 1977).In this respect the theory of common ancestry must have satisfied him more than any other theories advanced by Darwin, since it explained more phenomena.These include Linnaeus' hierarchical structure, distributional patterns, some facts in comparative anatomy, and almost everything that is currently cited in support of evolution.Even cytology gained new meaning from it, for it showed that animals and plants, though otherwise very different, were made of the same basic unit (the cell) as the heritage of their common ancestor. Advocates of the concept of the ladder of nature (the world) see a steady progression from the simplest to the most perfect organisms.Much of Lamarck's theory of evolution rests on this concept.However, as people learned more about plants and animals, the discovery of differences and similarities (differences and similarities) between organisms became less and less consistent with this pattern.Organisms are usually divided into very clear and often independent groups, such as mammals, birds, and reptiles, and cannot be placed into a linear sequence from simple to complete.On the other hand, almost all taxa are remarkably similar to some taxa.Naturalists since Aristotle have classified creatures according to this principle of similarity, and Linnaeus' hierarchical structure has been formed since the seventeenth and eighteenth centuries (see Part I).As Darwin said: "Since life arose on earth, all living beings have gradually become less similar to each other, so that they can be divided into subclasses. This classification is obviously not as arbitrary as the classification of stars in constellations" (: 411 ).But what is the reason for this classification surface format?What is the nature of its limiting factors?To say that this reflects the Creator's plan, as Agassiz did, is to leave no answer, to say nothing. But when it is supposed that all the members of a taxon are descended from a common ancestor, everything becomes clear.Darwin indicated this with the diagram opposite on page 116.This doctrine of common origin explains why "species descended from a single progenitor are grouped into genera; genera in turn include, or belong to, subfamilies, families, and orders, all of which unite into classes. The fact that there are categories...is fully explained as far as I am concerned" (413 pages).And it is true. However, two points must be emphasized here.The first point is that when Darwin proposed the theory of common ancestor, he found the answer to the important question of "natural system" that has puzzled systematicians for more than a hundred years.If species are derived from a common ancestor, an inclusive hierarchy classification system with classes under classes must be formed. In turn, as Darwin then emphasized, the fact of biological hierarchy is very strong evidence in support of his theory.There is simply no other possible explanation for the hierarchical structure than the wish for an extremely fickle creator.Darwin concludes by repeating that "the descent is the hidden bond of relation which the naturalist seeks under the name 'natural systems'" (p. 433).Indeed, every systematicist since Darwin has admitted (or at least paid lip service) that any taxonomic system must be consistent with the theory of evolution, that is, that every recognized taxon must have been descended from some common ancestor. business composition. The question is often raised, did Darwin become an evolutionist because he had to explain Linnaeus' hierarchical structure?Or to put it more bluntly, what is the causal relationship between evolution and classification?Answers to these questions can be found by looking at Lamarck or Cuvier. The excellent classifications of Pallas, Latreille, Ehrenberg, or Leuckart, etc. do not lead to a theory of evolution, nor did Cuvier or Agassiz.They all take Linnaeus' hierarchical structure for granted, yet explain it from a static point of view, since the most complete "natural" classifications can be explained in terms of essentialism.Nor does acknowledging evolution necessarily provide a causal explanation for Linnaeus' hierarchical structure.Many early evolutionists (such as Lamarck) attempted to arrange higher taxa in order of increasing sophistication based on the natural ladder view.A tentative answer to the above question is that knowledge of the Linnaean hierarchy alone does not automatically lead to the notion of a theory of evolution through a common ) without a full understanding of Linnaeus' hierarchical structure will not succeed.Darwin succeeded precisely because he had both. Unite all animals into a single hierarchical structure (phylogenetic tree) descended from a common ancestor.Immediately the question of the place of the human being arises.Linnaeus (1758) quietly included man in the primate order of mammals, and in some of his articles made it clear how closely he was related to the great apes.Owing to space limitations it is not possible to list here the evidence gathered since then—especially the evidence via comparative anatomy that humans and great apes are fundamentally similar.Everyone knows how proud Goethe was when he discovered the intergnathus in Homo, whose absence had hitherto been considered a distinguishing feature of the genus Homo.However, Darwin only said in the book (page 488): "The origin and history of man will be explained in the future." It was not until 1871 that he was willing to say without reservation that man originated from an orangutan-like ancestor.Huxley and Haeckel formally stated this as early as the 1860s and it was immediately accepted by most informed biologists and anthropologists. The claim (and more correctly confirmed by science) that human beings are no special creation, but part of the mainstream of life, caused a great deal of shock.Not only does it contradict the generally accepted teachings of the Christian Church, but it is even incompatible with the tenets of many schools of philosophy, ending the domination of an anthropocentric worldview and calling for a reordering of man's place in nature.At least in principle it colonized new grounds for ethics, especially conservation ethics (White, 1967).The shock wave of mankind being "deposed" has not disappeared.The disenfranchisement of humanity's privileged status required by the doctrine of common ancestry was the first Darwinian revolution.Like most revolutions, it went too far at first, which was reflected in some extremist claims that humans were "nothing more than" animals.This is of course imprecise.Zoologically speaking, humans are indeed animals.Yet man is a unique animal, so different from other animals in so many fundamental respects that it is entirely justified to be studied by a separate branch of anthropology.Knowing this, it must never be forgotten that man has revealed his ancestry in many and often unsuspected ways.At the same time, human uniqueness (within certain limits) justifies anthropocentric value systems and ethics.In this sense, a strictly modified anthropocentrism is still legitimate. The opening sentences are, "When I was aboard the HMS Beagle as a naturalist, I was struck by certain aspects of the distribution of South American flora and fauna . . . may explain the mystery of the mystery of the origin of the species." These distributions are mentioned again and again in chapters eleven and twelve, as well as in his autobiography.Two phenomena in particular attracted Darwin's attention; first, that the fauna of the temperate regions of South America contain species more closely related to those of the tropical regions of South America than with those of other continents; Falklands, Grapagos, Giro) and the fauna of the adjacent South American continent are more closely related than those of other islands.Thus, the history of the "introduction" of these flora appears to be more important than the ecology of their distribution areas.The distribution of species is clearly not random, but what factors determine it? Of course, this is not a new problem.A brief introduction to the history of biogeography is necessary in order to understand why Darwin posed such questions in his work.With the help of our modern understanding of these issues, we can speak more accurately and realistically about the distributional problems that were of particular concern to the naturalists of the eighteenth and nineteenth centuries.In a regional fauna (eg monkeys in the tropics, bears in the temperate zone) is this apparent kinship facilitated by environment or by shared history?Was the discontinuous distribution the result of multiple creations or a second separation of previously continuous territories or colonization over long distances? 古代人早就知道动植物分布有地区性差异，并且认为某些物种的出现是由于气候影响，分布的不连续性（例如印度和非洲的大象）是由于过去是联结在一起的（希波格拉底，亚里斯多德等等）。当地球是球形而不是平底的观点传播开来后又引起了新的问题，例如在地球的另一面可能存在正相反的人类的问题。自从宗教教会篡夺了西方思想的领导权后，对这类问题的自由探讨就不再可能，动物地理问题也以圣经的言辞来陈述。这就使得不同动植物区系的问题更加难于解决。因为依照圣经一切生命都来自伊甸（乐）园的主人，或者更准确地说，来自诺亚洪水的幸存者，他们的后裔必然是在方舟靠岸的地方（一般认为是阿拉拉山）扩散开来。这个解释便排除了分布格局的纯粹静止概念，因为这解释的依据是发生了扩散和迁移。 如果只是欧洲和毗邻的非洲和亚洲部分的动物区系，则从阿拉拉山向外扩散还似乎是可信的。后来发现了完全陌生的美洲并在几世纪末了解到这新大陆有极其丰富的、与旧大陆完全不同的动物区系；这些情况引起了极大的震动。继此之后又发现了中非、南非和东印度的动物区系最后还有更独特的澳大利亚动物区系，这些都向探索不倦的生物地理学家提出了更难于解答的问题。从一个唯一的创造中心将永远不变的动物生命向全世界扩散越来越成为逻辑上不可能的事情。 植物学家J． G． Gmelin（1747）首先提出物种的创造是在全世界普遍发生的，并不限于一地。伊甸乐园和诺亚方舟的圣经故事已悄悄地被一些“创造中心”学说所取代。 有些学者仍然主张由单独一对动物形成的单一起源说，另一些学者则认为每个物种是在它现在分布的地区起源的，有多少物种就有多少个起源。 在18世纪中布丰对生物地理学的发展影响最大，因此他被称为动物地理学之父。他在和林奈的对垒交锋中不同意按共同性状而是根据它们的来源地这种“实用”系统将动物分类。换句话说，他将动物归类为动物区系。他由此作出的动物区系一览表使他能得出各种结论，例如北美洲的动物区系导源于欧洲。 布丰（1779）提出了历史的和生态的这两种原动力（Roger，1962）。当地球开始冷却时，生命首先出现于很远的北方，因为这时靠近热带的地区仍然太热不适于动物生存。当地球逐渐冷却时，北方的动物区系随着温度降低便朝热带移动，新的北方区系便又形成，很可能在西伯利亚出现。已经占据南美的动物区系由于巴拿马地峡山脉的保护从而没有遭到北方新区系的侵犯，这就是为什么“在美洲南部找不到任何一种欧洲南部动物”（176页）的原因。在旧大陆“没有一种热带的主要物种原先不是存在于北方的” （177页）。由于布丰深信动物区系是地区性产物，他对两洲（欧洲、美洲）热带动物区系竟然很不相同感到很惊讶，因为“由欧洲南部地区的创造力所产生的物种应当和其它洲南部地区的动物相似”，然而正如前面已经谈到过的，这两个热带地区并没有一个物种相同。 布丰所提出的是当“出生”时动物区系是其来源地区的产物，但是随着气候条件的变化，它能够而且将会扩散。当出生时，物种是遵照一定的规律被创造的，每个物种适应于它的气候区，这就是为什么能有热带、沙漠、北极等等动物区系的原因。布丰曾说过，由于自然为物种造就了气候，所以自然也为气候造就了物种：“大地造就了植物；大地和植物随后造就了动物”（Buffon，1756，VI）。 化石和半化石长鼻类动物以及其它分布资料对布丰学说中的历史性部分具有重要影响。他的“地区性产物”的想法的来源也并不清楚，然而我怀疑这和他遵奉牛顿哲学有关。起源必然是由于某种力（的作用）。 布丰着作中解释上的矛盾一直延续到1859年。虽然每一位旅行家都描叙了各地动植物区系之间的明显差异，但是对那些认为分布应当像上帝所创造的世界中的每件事物那样夸耀了设计的人来说在下意识中是无法接受的。因此，不同的洲或不同海岛的热带动物区系，像布丰所说的“应当相似”，然而实际上它们却并不相似。在进化论以前的时代对这种期望与实际不相符合的事是无法解释的。 在强调历史因素上，布丰并不是唯一的一个人。林奈在1744年从一个热带海岛山地上收集到各类植物，这些植物从这海岛已扩散到全世界（Hofsten，1916）。动物学家EAWZimmermann于1778－1783年间发表了在当时是十分先进的观点。他证明哺乳类的分布并不能用气候充分说明而是明显地受到地球历史的影响。动物的分布确实提供了地球表面气候变化的证据。当目前被海洋分隔开的两个地区虽然气候相同却具有不同的哺乳类区系时，那末这两个地区一定是一直被分隔开的。然而当这样的地区拥有相似或相同的物种时，他说那就可以合理地推论以前这两个地区是联结在一起的。他列举了一些海岛，如英伦三岛，西西里岛，锡兰（斯里兰卡），大巽它群岛，在以前一定是和大陆联在一起，并提出北美和北亚以往也是相联的。有些学者认为Zimmermann是历史生物地理学的创始人是有一定道理的。 C． F． Willdenow（1798）是解释物种的不连续分布区是由于原先的连续区被第二位原因阻断的结果的第一位植物学家。 亨波特（Alexander von Humboldt）在年轻时曾经想写一本“植物的历史和地理成植物逐渐扩散到全世界的历史资料”（1805）。但是最后他出版了《植物地理论》，这本书几乎完全讲的是植物地理分布学和植物生态学。他的兴趣显然是植物的现行分布及其对环境物理因素的依赖性。那时他认为起源问题是无法解决的。 生物地理学在18世纪末和19世纪初的迅速发展又提出了一些新的难题。有一些亲缘相近的物种（例如欧亚大陆和北美的海狸）的分布区虽旗相邻但被分隔开，而同一物种却分布在分隔得很远的地区，如亚尔卑斯山脉的植物也出现在比利牛斯山脉，斯堪的那维亚山区、甚至北极低地。怎样解释这种不连续分布的情况成为了19世纪前半期生物地理学的主要问题（Hofsten，1916）。 当福斯特父子随柯克第二次远航在南美南端火地岛（Tierradel Fuego）发现了欧洲的植物后，他们立即推断这是由于相似的气候产生相似的物种的结果（1778），然而达尔文却将这种情况看作是植物具有非凡扩散能力的极好例证。 对历史因素如此强调在布丰，Zimmermann，Willdenow以及其它的18世纪学者的着作中常可见到，但在19世纪早期的生物地理学家的着作中却不再发现。当人们对动植物区系了解得更多，尤其是自从发现了澳洲（澳大利亚）的生物区系（生物相，biota）非常奇特之后，人们的注意力便又转向到不同地区的生物区系的独特性方面（Engler，1899，1914）。每一种植物和动物区系都是在一定的创造中心（center or focus ofcreation）引入的。德坎多尔（de Candolle，1855，1862）确认了20个植物区（不包括海岛上的分隔开的植物区系），每个植物区可能就是一个单独的创造中心。 某些人，例如阿伽西（1857），深信世界是完全静止的、上帝的创造能力是无限的因而主张物种是在其每个不连续的分布区中分别被创造的，这样一来就把多重创造中心论拽到了它的逻辑极限。当阿伽西在19世纪50年代撰写有关生物地理着作时，他的不妥协的原教旨主义者的解说就好像是退回到过去很久远的时代去了。 在莱伊尔的着作中也很强调地区差别和创造中心的思想，达尔文在生物地理方面的观点很多都得自莱伊尔（Hodge，1981）。当达尔文在贝格尔号上时对物种分布仍然坚持神创论观点是不足为怪的。当他在研究某些海岸阶丘的动物艰难生存状况时，他曾说过：“看来这并不是一种不可能的猜想，即这些动物的贫困很可能是由于当这种地区从海底冒出来时还没有动物（被创造出来）（达尔文，1933）。达尔文在当时的看法是，局部地区的创造受局部地区环境（特别是气候）的影响。 从达尔文自贝格尔号归来到出版的23年间事态发展对生物地理学说发生了深刻影响。一些所谓的灾变论者，不管他们在其它多数方面是多么错误，然而他们却强调地球表面经历了十分激烈的变化，如果认为生物区系和它们的环境是协调一致的，那末这种变化就必然要大大影响分布。这种情况很明显而又出人意料的由阿伽西的冰期学说证实。当北欧大部分地区被冰雪覆盖而其它部分的气候深受这冰冠影响时，植被区及其中的栖息者势必要发生急剧的移动或变化。有两位植物学家运用这种新见解将静态的生物地理学转变成动态的，发展的科学；他们就是福布斯（Edward Forbes）和德坎多尔（Alphonse de Candolle）。福布斯在一篇重要论文中试图说明英伦三岛的动植物区系分布是近期地质历史的产物。他主张每个物种只有一个起源中心，不连续的分布区是原先的连续（分布）区遭到第二位破坏（secondary disruptions）的结果。他认为英伦诸岛生物区系的组成是由于更新世确规东部和南部区系成分（elements）移殖而成。 除了纯粹的物理障碍（如海洋、山脉）之外，他还强调了气候和植被障碍，例如将欧洲山地的阿尔卑斯植物区系和亲缘很近的北极植物区系分隔开的那些障碍。达尔文也在其手稿中作出了相似的结论，但一直到十三年之后才发表。 福布斯和达尔文在两个重要方面不相同。福布斯对地质变化的印象很深但对动植物的扩散能力又估计过低，他以构想大陆桥（land—bridse）而闻名，特别是传说中位于直布罗陀以西的大西洋中的一个洲——阿特兰提斯洲（传说后因地震而沉没）的积极支持者。更重要的是，福布斯坚信物种不变，当他发现亲缘相关的物种在不同地区出现肘，他将之归于各自单独的创造而不是隔离现象中的进化分化（evolutionarydifferentiation）。这正是Thomas Kuhn所说的要放弃一个久已熟悉的模式是多么困难的典型例子。 植物学家德坎多尔（1806-1893）是达尔文以前最重视“间断物种（disjunctSpecies）”这个问题的学者。他首创的“间断”物种这个词指的是分布在被分隔开地区的植物由于被隔离（isolated）很充分因而目前要从一个地区扩散到另一地区似乎是不可能的。在一篇较早的文章（1835）中他还肯定间断物种的多重创造，但是在他所写的着名的《植物地理学原理》一书中他已坚决地转向根据历史解释被分隔的分布区，着重说明当前的地理和气候条件只起第二位作用”。更确切地说这和以前各个时期中的散布机会不同有关。虽然德坎多尔的植物地理学对分布不连续的起源。了非常出色的分析，而且是一位植物地理学家第一次一贯试图说明当前的分布是历史的产物，然而他还没有接受进化观点，所以不能对动植物区系的历史作出全面性的解释。在出版以后，他建议可以将“由以往物种的变异所形成的物种连续学说”看作是解释间断（物种）的“最自然（不过）的假说”（1862）。 正是达尔文采取了决定性步骤才使生物地理学摆脱了神创论的羁绊。在1859年以前关于生物区系的起源（在这里暂不考虑随后的迁移）问题基本有两种学说。有神论者认为每一物种是经由创造分别引人并且在原则上有多少个物种或不相连物种区就有多少个创造中心。这种学说意味着有一个极其善变的造物主，只有极端的原教旨主义者才能接受。自然神论者和自然神学家深信世界是由神设计的，并认为创造和引入新种是由特定的力促使并必须遵从一定的规律。因此他们认为在一切热带地区，一切干旱的沙漠地区，一切山地或海岛都能找到相似（“亲缘相关”）的物种。当然，这正像达尔文一再指出的那样，完全不是生物地理学家所见到的情况。这两种学说的破产促使达尔文提出了第三种学说，即分布是共同祖先现象的产物。 达尔文提出亲缘有关物种的以及同一高级分类单位成员的共同祖先，使他对饥往的分布和这些分类单位的迁移作出意义深远的结论。他在的十一章和十二章中提出了他的证据，这两章由于方法论严密，论断的逻辑性强，很值得一读。达尔文在这里已不再必须提出这样的问题：这一物种分布在此是不是因为造物主将它安顿在这里？ 由于他摆脱了宗教羁绊所以他才能够提出像下面这样一些问题：为什么某一地区的动植物区系具有特殊的组成结构？为什么某些地区的生物区系相似而其它地区的又并不相似？ 海岛的动物区系结构是由什么决定的？分布的不连续格局原因是什么的？ 达尔文通过提出这些问题而成为原因生物地理学（causalbioseography）的创始人。 的确，他的全部兴趣都集中在问题的原因上，在这两章里只有很少的叙述性生物地理学内容。根据现实主义传统，达尔文坚持按照大陆的现有结构解释分布问题，反对任何轻率构思大陆桥的观点，这和福布斯以及随后80年的大多数生物地理学家是不同的。在这方面和其它许多方面达尔文都比他的同时代人或其早期的追随者更接近于现代思想。 达尔文的议论基本上是针对两方面的。一方面他试图去否定原先错误的或无用的观点，另一方面又试图介绍新的关于事物的原因的学说。他在文章开头就支持“每个物种起初是在一个地区引入的观点…反对这观点的…概要求助于奇迹”（，352页），这正是Asa Gray在谈到阿伽西的多重创造学说时所说的。英伦三岛和欧洲大陆有很多物种相同而欧洲却没有一种哺乳类和南美洲或者澳洲的相同，达尔文认为这一事实符合动态生物地理学的规律而是特创论（神创论）所不能解释的。 按照神创论学说，生物区系就是当地气候的直接产物。达尔文彻底地否定了这一学说：无论是将欧洲和北美气候相同的地区加以比较，或者“在南半球将纬度25”和35” 之间的澳洲，南非和南美西部的广大地区加以比较，就可以发现有些地区在一切环境条件上都非常相似，然而却无法找到更加完全不同的三种动植物区系”（347页）。森林地带、海岛、海洋的情况也与此相同。因此没有任何迹象表明是按照特定定律引进任何一种固定不变的物种的。 按照达尔文的原因生物地理学学说，分布格局，尤其是不连续性，通过下面的两个可能假定中的任何一个就能很容易地加以解释：（1）所研究的分类单位具有超越障碍的扩散能力，例如能够越过低地的山区物种移居到另一山地分布区，或者（2）不连续分布区是原先的连续分布区的残迹。有了共同祖先学说和上述两个假定就能够解释任何分布格局而勿需借助于任何超自然力量。这样一来，生物地理学者的主要任务就是研究障碍的本质以及动植物的扩散能力。“任何形式的障碍或阻止自由移动的障碍物都和不同地区生物之间的差异密切有关”（347页）。达尔文并不把障碍仅仅看作是物理性的障碍物，因为在物种的扩散能力和障碍的效率之间呈反比例关系，另外，他还认为竞争性物种的分布区也构成强有力的扩散障碍．达尔文清楚地知道正确评价扩散是解释分布格局的关键问题（356—365页）。他是运用巧妙的实验来研究这类问题的第一个博物学家；这些实验表明生物的扩散能力，尤其是植物种子的扩散能力要比以往所想像的强大得多，并没有什么特殊要求需要借助于大陆桥来解释跨越海洋的扩散。他却全然低估了的一个因素是风和气流的运送能力，它不仅能散布种子，而且还能运送小动物。 达尔文和福布斯（虽然他也独立地作出了这一结论）相仿，很重视冰河期对当前物种分布的影响（365—382页）。他从全世界范围来研究这一点，试图解释北方物种在南半球和热带山区出现的问题。当他运用类比的方法从同一物种的不相连种群的分布到同一个属亲缘有关的种的分布，再进而到分类阶元等级结构的推理过程中，不相连分布在他的思绪中具有极为关键的作用。 第十二章的绝大部分用于讨论海洋岛屿上的动植物分布。达尔文指出神创论者完全无法解释为什么海祥岛屿上的物种那么少，为什么在海岛上一直没有某些类群的动物，如陆居哺乳类，有尾两栖类以及真正的淡水鱼。海洋岛屿生物相的奇特不平衡性以及大陆和海洋岛屿动物区系的明显差异是“按创造的独立行动观点”所无法解释的，而“就我看来倒更符合运输的偶然方式这一观点”（396页）。这也说明了为什么海洋岛屿的动植物总是和最邻近的大陆上的劫植物亲缘关系最密切，这些情况促使达尔文向神创论者发起了挑战：“为什么被认为是在格拉帕戈斯群岛（而不是在别的什么地方）由神创造的物种应当和在美洲由神创造的物种盖有如此明显的亲缘关系标记？” （398页）。 一直用生物学观点来看待博物学现象的达尔文充分意识到成功的扩散包含两种能力： 到达新地区的能力和成功地占有它的能力。“我们应当永远也不要忘记分布很广意味着不仅要具有超越障碍的能力；而且更重要的是在遥远地区和外来者的生存竞争中具有取胜的能力”（405页）。最后他以典型的维多利亚时代的间接语气将他的发现归结加下： “同一物种的所有个体，不论它们分布在什么地方，都是来自共同祖先，要承认这一点是有困难的，我想这困难并不是不能克服的”（407页）。 在生物地理学方面，正像在很多其它研究工作方面一样，达尔文一直远远走在同时代人之前，生物地理学一直到本世纪40年代并没有真正追上他，虽然在这中间的年代里也有少数真正的达尔文学派的生物地理学者。 现代科学的生物地理学是从的第十一章和第十一二章肇始的。由于篇幅限制这里不可能对其后120年的历史作详尽阐述，只就其某些主要趋势予以论列。 区域性生物地理学对不同地区动植物区系的比较研究可以追溯到17世纪。就布丰和林奈而言这是他们的主要研究内容，对19世纪前半期的生物地理学家诸如德坎多尔，Swainson，Schmarda来说也是如此。 P． L． Sclater根据鸟类分布（1858）将全世界分为（六个）动物地理区可以说是一个新时期的开始。 达尔文从来没有特别注重区域性生物地理学。他显然认为这种研究分布现象的方法是静态的而且侧重描述性分类。然而《物，种起源》出版后的头60年中，绝大多数生物地理学者的主要精力都花在区域性研究上。这一学派的“圣经”就是华莱士的权威性两卷本《动物的地理分布》（1876）。虽然每个人都同意主要的动物地理区多少和大陆的大陆块（land masses）相一致，但是以生物类群为依据结合地理区划形成的“区域” 方案却有不少。研究哺乳动物的学者对欧亚大陆和北美的哺乳类区系十分相似这一点印象很深，并将之合并为全北区（Holarctie Region）。与之相对应，研究鸟类的学者发现北美和南美鸟类的亲缘关系很相近，因此他们之中有些人提议从旧大陆（旧界，Paleosaea）分出一个新界（Neooaea）（见Mayr，1946a）。对植物学家来说，还有一些其它的划分显得更自然。例如从马来半岛到新几内亚和太平洋岛屿这整个区域的植物属于单一的植物区系，而就动物而言则在西面的印度-马来亚区系和东面的澳大利亚-巴布亚区系之间有一明显的断裂，由新几内亚和大巽它之间的一条南北走向的线将两者分隔开。对这条线的确切位置一直争论了几乎八十年，最后才认识到婆罗洲（加里曼丹）与西里伯岛之间的“华莱士线”反映了亚洲大陆架的边缘，而西里伯岛与摩鹿加群岛之间的“魏伯线”则是植物区系的均势线或平衡线（Mayr,1944b）。 区域性生物地理学者不满足于这种粗糙的分析，由德坎多尔开始试图努力将区域（region）精细划分成亚区（subregions）和生物区（biotic districts），这种努力一直持续到今天。总的来说，这一类的研究还处在描述水平，还无助于作出概括性结论。 E． R． Dunn（1922）首先起来反对这种静态方法而代之以动物区系的原因分析（causal analysis）。辛普森（G．G．Simpson，1940；1943；1947）后来成为这一新倾向的领导人物，特别是在哺乳类方面，鸟类方面则是迈尔。辛普森指出，联结大陆块的大陆桥有不少种，例如“走廊”，“渗入桥”等。他在考虑跨越水域扩散的可能性时特别强调统计因素。这实际上是返回到被华莱士及其学派忽视了的达尔文的原因生物地理学框架结构。在这种研究方法中扩散是一个关键问题。 大陆的历史和扩出方式就达尔文学派的生物地理学而言，有两个问题一直存在着争议：一个是大陆过去的历史以及它们之间的联结，另一个是不同类群动物的主动和被动扩散方式。 就大陆间的联结来说存在着三个主要学派。一个学派继承了福布斯的传统，偏重于寻思大陆桥和以前存在的海岛以及沉浸的大陆。分布的不连续性是由于在欧洲和北美之间，非洲和南美之间，南美和澳洲（大洋洲）之间，马达加斯加与印度之间，夏威夷和萨摩亚之间等等过去都有大陆桥存在。在这个学派鼎盛时期每个海洋都有其大陆桥联贯。