Chapter 22 Chapter 11 The Cause of Evolution: Natural Selection-2
The full title of the book is "Origin of Species by Natural Selection, or Preservation of Dominant Species in the Competition for Existence", which also gives people the wrong impression that it is just a theory.Darwin's discussion of speciation within natural selection in Chapter 4 also reinforces this view, but it is quite wrong.Let me give an example to illustrate that speciation and natural selection are two separate processes.It is possible for a population to form on an island and (theoretically) eventually become so different from the parent population simply due to random genetic processes (genetic drift) that it can no longer reproduce with the parent population, i.e. it has become Formation of new species (completely without the participation of natural selection process).Geographic distribution patterns are the same two practically independent evolutionary phenomena, mostly due to the accidental superimposition of dispersal and geographic or geological processes, independent of natural selection.It is quite misleading to think that natural selection explains distribution patterns, as Darwin did.
Table 3 Structure of some evolutionists' theories of evolution.
They all agree with the fifth component of the theory of evolution, which is to oppose the idea that the world is eternal and unchanging
[Agree, (+), Disagree, (-)]
Gradual Population Speciation by Common Ancestry Natural Selection
Lamarck (-) (+) (-) (-)
Darwin (+) (+) (+) (+)
Haeckel (+) (+) partly agrees
Neo-Lamarckist (+)(+)(+)(1)
Huxley (TH.) (+) (-) (-) (-)
Devry (+) (-) (-) (-)
Morgan (TH.) (+) (-) (1) not important
Let me now try to dissect the various theories out of which Darwin's model of evolution consists.
The world is not eternal but the product of continuous evolution. Of course, this theory did not start with Darwin.Yet by 1859, despite the work of Lamarck, Michael, and Chambers, the majority opinion was that the world was stable. Between 1800 and 1859 quite ad hoc compromises (e.g. Progressivism) were proposed in order not to accept evolution.But Darwin's profusion of evidence was so convincing that within a few years every biologist became an evolutionist, even the English Owens, Miffats, Butlers who opposed Darwin's other theories. The same goes for biologists.Agassi, a diehard who persisted to the end, also died in 1873.France is virtually the only country in which evolution itself has been contested (Conry, 1974; Boesiger, 1980).For many modern biologists, evolution is no longer a mere theory but an indisputable fact, evidenced by the generation-by-generation changes in the gene pools of species and by changes in the fossils of biota that are accurately dated by geological layers confirmed.The present resistance is entirely confined to religiously bound opponents.
Darwin is the founder of the theory that "all living things are descended from a common ancestor through a continuous branching process".When he has adopted the idea of the division of the parent species into several offspring species, the notion of common ancestry is necessarily brought to mind.When tracing ancestry to higher taxa he considers that all organisms "are direct descendants of a few organisms that lived long before the first Silurian deposits" (: 488), and that life "was originally infused into a few or one Biology" (p. 490).
The continual reproduction of species accounts for all the diversity of life.Reducing the origin of all species to a single common ancestor, the original origin of life, makes the theory of spontaneous generation (a natural process that contradicts Darwin's view of continuity) unnecessary or superfluous.Although this ultimate question was clearly beyond the reach of the scientific level at the time, Darwin could not help thinking about it.
The doctrine of common ancestry greatly facilitates the acceptance of the concept of evolution, as Darwin himself stated in , because it illuminates many previously unresolvable problems in comparative anatomy, biogeography, systematics, and other fields of biology.Even Leyle and the botanist Bentham, who originally opposed him, accepted the common ancestor theory in 1868.
It has become common practice to refer to the "Darwinian revolution" in the literature of the history of biology.Yet the connotation of this term (which I have used myself) is ambiguous, since Darwinian thought in general has been involved in several kinds of rational (intellectual) revolutions.Two interpretations are particularly appropriate.The first is to include humans in the family tree of common ancestors.Darwin stripped man of the privileged place in nature accorded to him by the Bible, and by nearly all the writings of philosophers.This can be said to be "deposed man".This is a truly revolutionary concept, very different from the view of man as the apex of the biological chain.Another revolution is natural selection (see below).
Darwin's insistence that evolution be gradual encountered almost as much resistance as his theory of natural selection.There are both practical and ideological reasons for this.Gradual change from one type (pattern) to another is simply inconceivable for an essentialist (patternist).Lyell and others have insisted that there are limits to a species' potential variation (ability) beyond which no selection can go.Each species is separated from the other by an unbridgeable gulf, and if evolution is to be claimed, it must be proposed that new forms arise suddenly by mutation.This is why Lyell argues that the "formation of new species" is a discontinuous process that often occurs continuously.The Darwinian doctrine that populations are the "action site" of speciation (speciation) and which allows for various degrees of intermediate forms between geographical varieties and species shatters the essentialist argument.
On the other hand, some actual (experimental) findings also seem to support essentialists.Comparative anatomists (with a few exceptions) emphasize fundamental differences between the structural schemes of higher taxa, which they say cannot be explained by gradual evolution.Likewise, paleontologists insist on the sudden appearance of new types in the fossil record (abrupt origin) and the complete absence of intermediate types.Look around the natural world, its outstanding feature is discontinuity.
Experimental biologists, who are staunch essentialists, have a particular difficulty understanding gradual evolution.Unaccustomed to thinking in terms of variable populations, they could not believe in the origin of any new species except by the generation of abnormal individuals by mutation (a hypothetical process later called macrogenesis).Negri, Sith, WH Harvey, Kolliker, Miffat, Galton and some other famous scholars all supported the occurrence of sudden change in the 1860s, 1970s and 1880s, but it was only a minority opinion in the Qing Dynasty.Catastrophe is clearly incompatible with gradual natural selection, and Darwin never used it.
Darwin understood better than any of his opponents that the observed discontinuities were like artifacts of history.He explained the divide between genus and taxa above genus through two processes of trait divergence and extinction, which is now generally accepted.Competition and encroachment into new habitats and areas of adaptation cause steady divergence, but extinction of intermediate types and linkers is more than any other factor responsible for the observed discontinuity between higher taxa.This break (chasm) is thus an indirect product and does not reflect the original process by which the taxon was formed.
What was the reason for Darwin's firm belief in the gradualness of evolution is not entirely clear.Some of this is apparently the result of direct observations, such as the gradual divergence between the Grapagos mockingjay and the Darwin's finches, and the continuity between the breeds of dogs, pigeons, and other domesticated animals that have been historically recorded.But as Gruber (1974) points out, there may also be a metaphysical element to Darwin's firm belief.After reading the works of the theologian Sumner (1824:20), Darwin came to the conclusion that all "natural" things evolved gradually from their predecessors (Precursors), and discontinuity (such as sudden mutation) Denotes a "supernatural" origin, that is, the intervention of the Creator.Darwin spent his life painstakingly reconstituting (reconstructing) the phenomenon of gradual evolution from what appeared at first glance to be the result of an apparently sudden origin.
On the question of natural selection Darwin established (through) the theory of evolution It is certain that he enriched his theory of natural selection with many well-selected examples and impeccable arguments, and combined it closely with the equally well-demonstrated theory of evolution, which aroused the Western world. sensation.By explaining "design" in nature as the result of non-teleological, purely materialistic processes, the theory of natural selection rules out global teleology.Darwin's theory provides a causal account of the seemingly perfect order of the biological world, that is to say, the adaptation of organisms to each other and to the environment.The theory of natural selection is by far the most revolutionary concept put forward by Darwin.By providing a completely materialistic explanation of all phenomena in the biological world, the theory of natural selection is seen as having "deposed God".The theory of natural selection can rightly be called the second Darwinian revolution.
11.4 Resistance to the Theory of Natural Selection
If a modern biologist talks about Darwinism, he means in his mind natural selection, a component of the Darwinian model.Darwin recognized from the outset that this was the most revolutionary of his ideas; not surprisingly it was also the most strongly reacted by his opponents, who, from Herschel onwards, called it "a law of all sorts"; Sedgway Gram” called it “violating ethics.” Natural selection was the component of Darwinism that offended the most (“it dethroned God”), and even to this day that of natural selection is still most strongly opposed. Resist. Darwin's friend Asa Gray (a devout Christian) was one of the few Darwinists who managed to reconcile natural selection with the worship of a personal God. Not only theologians, philosophers and ordinary people opposed it, Until the Evolutionary Synthesis (Synthetic Evolution) of the 1930s and 1940s, even most biologists opposed it (MayrandProvine, 1980).
Even Darwin's friends and sympathizers expressed indifference to natural selection.None of the reviews of Approval published after 1859 emphasized natural selection (Hull, 1973).To the vast majority of Darwin's supporters, attempts to explain the world (including all living things) in a purely materialistic light were not to their liking.Lyell never accepted the theory of natural selection, and when he finally accepted the theory of evolution, he often referred to it as "Lamarckian," which particularly annoyed Darwin.
r. H．Huxley was Darwin's ally in the polemics and was a staunch defender of the theory of natural selection throughout Darwin's life, yet Poulton (1908) provides ample evidence that he was "never a true believer in the theory he defended" .Huxley was a morphologist, physiologist and embryologist, and in his view the evolution of the biological world was equivalent to the evolution of the chicken embryo in the egg (as he called it) (L.L.D., 11:202) .Natural selection does not fit very well with this concept; in an essay on Darwin (“The Coming of the Century of the Origin of Species”, 1893), he does not mention natural selection at all.When using the term "Darwinism," Huxley often meant more than the theory of evolution from a common ancestor.In a sign that he was not at all sure that the theory of natural selection would prove to be correct, it was implied in the following statement: "Whatever the ultimate fate of the unique theory proposed by Darwin may be . . . "
Huxley believed that sudden change could achieve what gradual evolution through natural selection could not.
The only serious support Darwin got for natural selection came from naturalists.First, of course, was his co-discoverer Wallace, who was even less conservative than Darwin in espousing selectionism.He restricts himself only as far as man and man's thoughts are concerned.Bates, Wallace's companion in South America, made important contributions to selectionism, as did another naturalist in Brazil, Fritz Muller (see below).On the whole, botanists were against natural selection, but Darwin's friend J.D. Hooker was on Darwin's side, and so was Thiselton-Dyer.Abroad, at least after 1880, no one was a more staunch selectionist than August Weismann.As will be discussed below, he was actually the first evolutionist to attribute evolutionary evolution to natural selection.It is clear from his biography and his work on butterflies that he was an avid naturalist throughout his life.
It is always said that Darwin-Wallace's theory of natural selection was initially completely ignored after it was published in 1858, which is not true.Ornithologist Alfred Newton once talked about how excited he was when he saw the Darwin-Wallace album published by the Linnean Society after years of arguing with his friends about the origin of species:
"I read it late that night...I fell asleep with the satisfaction of having found the answer" (1888:
241).He later referred the article to Canon Tristram, who, in his study of larks in desert regions, concluded that the bird's protective coloring was the result of natural selection, a month before publication (Tristram, 1859: 429).He elaborated on the conditions under which individuals with lighter colors and longer beaks would be selected for.Owen also referred favorably to Darwin-Wallace's article in an address to the Society's president in 1858, but he turned against the theory of natural selection after publication.
Perhaps the strongest support for selectionism came in the 1880s, when Weismann dismissed the inheritance of acquired traits and drew Lankester, Thiselton-Dyer, and others to it.It lost most of its support in the 1990s, and it was not until the 1930s and 1930s that the natural selection theory was finally adopted by almost all biologists after evolutionary synthesis occurred.Owing to the prevalence of the criticisms and censures of natural selection, it is impossible here to review them, but one must be introduced, because it has been held to be particularly sharp and powerful.
No attack on Darwin's theory has been more emphatic than that of the physical scientist and engineer Fleeming Jenkin (1867).This is partly due to Darwin's own opinion, "Jenkin has given me a lot of trouble, but has been more genuinely useful to me than other articles and reviews" (Letter to Hooker, 1869, M.L.D., 11 :
379).Modern readers will never be impressed by Jenkin's comments.This review is full of prejudices and misconceptions that physical scientists are accustomed to.Although Jenkin also admits that "one must admit that the process called natural selection is in general operation", what he understands by natural selection is actually the elimination process of essentialists.Had Jenkin understood that natural selection is a fundamental principle of reproductive success making offspring more adaptable to environmental changes, he would not have written the following passage: "Producing offspring more like their superior ancestors than their inferior ones This tendency in the parents is certainly not beneficial to any individual in the struggle for existence. On the contrary, the majority of individuals will benefit by producing defective offspring, who are at a disadvantage in competition with them."
Jenkin and Darwin, as well as most of their contemporaries, agreed that "there are two possible variations which must be considered separately: first, co-variations ... (referring to individual variations) ... and second, extremely rare variations, which may be simply called It is a 'distortion' (sport), for example a child is born with six fingers."
As far as individual variation is concerned, Jenkin, like Lyell, Owen, and other essentialists, asserts that natural selection will soon exhaust the available store of such variation.He also insisted that individual variation must never go beyond a certain "range" of variation, and must never stand out beyond a "pattern" (type).Selection can make a dog run faster or have a better sense of smell, but it can never make it something other than a dog: "No species can change beyond a certain limit," he repeated.
This widespread assumption is not only a corollary of essentialist thinking, but also expresses the experience of plant and animal breeders who have found that intensive artificial selection in a closed herd quickly eliminates effective variation. , which exhausts its available storage.
This view ignores that things are fundamentally different in nature, as the reservoir of variation is constantly being replenished by gene flow and mutation.In small, closed populations, continuous natural selection can only be achieved if the resulting new genetic variation is very rich.Like the early Mendelians, Jenkin proposed the so-called "mutational pressure"
(Mutation Pressure), in fact, makes natural selection have no effect on evolutionary evolution.Since he was utterly ignorant of natural selection, he repeatedly asserted dogmatically that its role was limited to "the case of a large number of individuals having the same variation . . . [it] does not play a role in producing new organs or new habits."
Jenkin gets close to the heart of his comment here.It would not help us even to admit that species selected for by individual variation were gradually improved, says Jenkin, "while the origin of species did not require the gradual improvement of animals retaining the same habits and structures, but those capable of such changes at will The habit and structure of the body can actually give rise to the formation of new organs." Like Miffat, Jenkin apparently found it particularly difficult to explain the origin of new organs.As an essentialist he could not imagine that this could be accomplished in any other way than by mutation, so he turned his attention to the second type of variation.
Darwin also occasionally referred to "aberrations," which he termed "single variations" because he thought they provided "so straightforward illustrations" (L.L.D., 11:
289).New structures that take species beyond their normal range of variation can be conceived to be the result of aberrations.Jenkin, however, argues that this is highly unlikely for a number of reasons, not least because when an aberration reproduces its "offspring will generally be intermediate between normal individuals and the aberration." In other words, Jenkin contends A phenomenon that was later termed "blending inheritance" in the genetics literature was widespread.This is all the more surprising in view of Jenkin's choice of a six-fingered individual as a typical example of the aberration, since polydactyly (to which six fingers also belong) has been known since Maupedet and Reaumur to have no intermediate form genetic.Darwin could have easily refuted Jenkin by pointing out that six-fingered individuals had no five-and-a-half-fingered offspring and 5.25-fingered offspring, nor had albino offspring half-coloured.Animal breeders have also faithfully reported many examples of this type of aberration returning to normal through backcrossing, such as the Ankang sheep mentioned by Darwin in .If the intermediate form mentioned by Jenkin is true, all these distortions will be quickly eliminated by backcrossing.
The fact that Darwin did not use these arguments against Jenkin demonstrates that Darwin himself was vague about the variation problem (see Chapter 16).Because of this, he honestly accepts Jenkin's fusion argument and makes him emphasize more than ever that aberrations are not important for evolution.Nor did Darwin understand that the convergence argument holds true for individual variation as long as it reflects real genetic variation. Vorzimmer (1963; 1970) has rightly pointed out that Jenkin's comments had only a very small influence on Darwin, although some earlier historians disagreed.To promote Jenkin's comments as an admirable and destructive critique of Darwin is, in my opinion, quite wrong.In fact it contains more false assumptions and misleading conclusions than those it attacks.What is particularly lame about Jenkin's arguments is his inappropriate comparison of biological processes with physical phenomena, such as comparing evolutionary evolution to the flight of a cannon ball.It is astonishing to a modern reader that physical scientists like Haughton, Hookins, and Jenkin imagine that by using ideas from the physical sciences, they can deal with phenomena as immensely complex as biological evolution, unparalleled in the nonliving world ( Hull, 1973).
Considering how quickly biologists embraced evolution and how slow they were to adopt the theory of natural selection, this is indeed a puzzling mystery.It was not until the "evolutionary synthesis" (see Chapter 12) in the 1930s that most biologists accepted it as the only directional mechanism for evolution.Even then, natural selection remained an alien concept to philosophers and non-evolutionists, and even now evolutionists have to go to great lengths to justify selection to non-evolutionists.
Of course, the opposition to the theory of natural selection is not absolute.Almost all opponents admit some degree of selection but argue that it cannot explain major evolutionary phenomena and processes.We know that Darwin himself accepted certain non-selective processes, such as the use-it-or-lose-it effect; yet natural selection was clearly the most important mechanism of evolutionary change for him.Most of his opponents believed that the importance of natural selection was not major, if not negligible.
What makes the anti-choiceist resistance so powerful?It does not appear to be attributable to any single factor but to a wide range of opposing arguments.No one has yet listed and analyzed all the objections raised, but the more important ones can be found in the following works: Kellogg (1907), Delage and Goldschmidt (1912), plate (1924), Hertwig (1927), Tschulok (1929), and certain French scholars such as Caullery, Cuenot, Vandel, Grasse; philosophers Cassirer (1950), Popper (1972) and others.
The following are some of the principal factors which constitute resistance to the acceptance of the theory of natural selection.
To explain the perfection of adaptation in terms of materialistic force (choice) excludes the Creator (God) from His creation.It knocks out the main arguments of natural theology, which some say died as a living concept on November 24, 1859.It is precisely this that deeply offends not only theologians but also those naturalists whose worldview is based on natural theology.From their point of view, the theory of natural selection is downright immoral.This is the state of mind expressed by Sedgwick when he exclaims at the top of his lungs, "The phony philosophy of physics of the present day deprives man of all moral character." The author presents an immoral heresy. What does it give us? A sense of right and wrong? A sense of law? A sense of duty?
(Hull, 1973).God assigns his purpose or will to the world, and the order of the moral world is also part of his will.To replace this will by the automatic process of natural selection would not only exclude the Creator from our conception of the world, but would also destroy the foundations of morality.
Thus, Sedgwick's outcry reveals more and more profound content than the denial of Paley's calculated adaptation shows.At this point, Von Baer (K.E. vonBaer, 1876)'s censure of Darwin is more obvious.Von Baer was a teleologist, and he believed that the biological world was not only adaptive (Zweckmsssig, Kant's usual term) but also goal-oriented (Zielstrebig).Being goal-oriented, he argued that adaptation preceded the formation of new structures, whereas, according to Darwin, adaptation was a consequence of the formation of structures (by natural selection) (1876:332).As far as teleologists are concerned, it is an inherent tendency in nature to tend to be more perfect and more harmonious.As L. Agassiz has repeatedly emphasized, symbols as the basis of design schemes can be seen everywhere.Such a design scheme can only realize its function through laws. Several such "laws" have been proposed before Darwin, such as MacLear's five-element theory as a basis for classification, Forbes' law of polarity in biological distribution, Agassiz's Triple parallel (correspondence) theory, that is, the parallel relationship among ontogenesis, fossil progress, and morphological progress (Bowler, 1977b).
Accepting the theory of evolution makes the question that the world is well-ordered particularly sensitive.If the world was created in a split second (or six days) and then remained constant, its harmony and order could be explained as the product of a well-conceived design scheme.But how to maintain order in an evolving and changing world has become a serious problem.Evolution was taken for granted as an "upward" movement by early evolutionists (e.g., Natural Philosophers, Lamarck, Chambers).Starting with raw materials and the simplest organisms (ciliates) there has been steady progress, and it all boils down to human evolution.Therefore, accepting the teleology of the universe is the inevitable result of adopting the theory of evolution.In order to be able to explain the natural ladder from the concept of time, the ultimate cause must be explained.The fact that the image of progressive evolution is so appealing, even after it has ceased to be a problem for those who accept natural selection, its reliability remains a question not only among a large segment of the biological community, but especially among laymen and theologians in general. question."Chance and Necessity" by Moreau
The main purpose of this book is to oppose the teleology of the universe ("necessity"), and all evolutionist treatises have the same purpose explicitly or implicitly when dealing with the problem of so-called progressive evolution (such as Simpson).Yet convincing someone ignorant of the mechanics of evolution that the world is not predetermined (destined) or programmed seems infinitely more difficult.
"How did man, dolphin, bird of paradise, or bee evolve by chance?" is a frequently asked question even today.
It is often asked, "Wouldn't a purposeless world render humans (humans) purposeless?" So accepting the theory of natural selection poses a metaphysical conundrum.
The situation in the 1860s and 1870s was exacerbated by liberal and conservative polemics among theologians (the liberals tried to adapt Darwinian ideas) and by struggles between church and state.For some evolutionists (especially Haeckel in Germany), the main significance of evolution theory and negative teleology is that it is the leader of materialism.As Weissman (1909) puts it, "The theory of selection solves the mystery of how adaptation (phenomenon) can be produced by intervention without identifying the target force."
So natural selection not only eliminates the need for a "designer" but also declares the bankruptcy of cosmic teleology.Finally it also became clear that the word "teleological" used to refer to a number of miscellaneous phenomena, some of which, besides cosmic teleology, were genuinely scientific processes (see Chapter 2).The demise of teleology has been slow even in evolutionary biology, revived by some post-Darwinian evolutionists under the name of the concept of orthogenesis (directed evolution) or related concepts (see below).
After its publication the relationship between science (biology) and religion changed decisively, especially in England. Before 1859 natural theology, the idealist morphology of the creationists, and some other theories in which God played an important role were considered orthodox scientific doctrines.In a debate it's scientist versus scientist.
After 1859, religious arguments quickly disappeared from the discourse of scientists, and the subsequent debate, as Gillipsie (1951) wisely pointed out, was between organized religion (the church) and scientists.
The theory of natural selection is meaningless to the essentialist because it never touches the essence that underlies things.Essentialists believe that natural selection is generally a negative process, which can eliminate unsuitable ones, but cannot play a constructive role.Lyell refers specifically to "the mere elimination power of natural selection" and argues that some truly creative force of nature was required to produce the highest animals, plants, and humans.
It has been said in the past that natural selection was rejected by vitalists (and it was true) but adopted by mechanists.The facts do not support this claim.Almost all experimental biologists are mechanistic, yet until recently, that is to say, until evolutionary synthesis, they were almost unanimous in their rejection of natural selection.Among experimental biologists only those who have adopted the population idea accept it.Embryologists in particular, who have always studied specific individual organisms and until recently never studied populations, have had the most difficulty understanding natural selection.This is from T. H．Morgan and E. B．It is clear from Wilson's writings that, according to Muller (1943:35), until the 1930s they "were not ready to admit that the 'laws of chaos' could provide a rational explanation for the phenomena of biological adaptation."
This is a very strange and paradoxical field in which some eminent experimental biologists who are very familiar with natural selection use the arguments of the essentialists in their evolutionary analyses.This is true, for example, of famous biologists like Waddington Moreau.This was also a feature of the arguments of physicists and mathematicians attending Wistar (Institute) conferences (Morehead and Kaplan, 1967).
Darwin himself was never entirely comfortable with the word "choice," neither did many of his supporters, and his opponents found fault with and ridiculed it.Darwin on September 28, 1838, called what came to be known as natural selection "wedging"
(wedging): "There is, so to speak, a force like a thousand wedges trying to drive every adapted structure into the cracks in the order of nature" (D: 135). He only used the word "selection" in the early 1840's when he compared artificial selection by breeders to natural selection (Ospovat, 1979).
Limoggs (1970) quite rightly points out that there are many doubts about the nature of natural selection in the post-Darwinian literature.Is it a cause, a process, or the result of a process?The biggest shortcoming of the word is that it implies who is choosing.Darwin's critics were annoyed by his unrestricted anthropomorphism of nature.Whenever a deist invokes God, Darwin appeals to nature: "Nature pays no attention to appearance, except that it may be useful to living beings. Nature is able to act on every internal organ, on the slightest difference in constitution, on the to the whole mechanism of life"
(:83). "Natural selection scrutinizes at every moment every variation, even the slightest, in the whole world" (p. 84).Didn't Darwin depose the God of the Bible in order to replace it with a new God, nature?
The dissatisfaction of Darwin's friends with the term "natural selection" prompted him to adopt Spenser's terse metaphor "survival of the fittest" in later editions.This he does is very bad, because it raises the objection that the whole theory of natural selection turns out to be based on tautology:
"Who survives? The fittest, who is the fittest? Survives".Darwin, of course, never said anything of the sort.Darwin only said that among the innumerable variations that arise in each species some "occur sometimes in the course of thousands of generations to the advantage of each being in one way or another in the acute and complicated struggle for existence" Individuals who have some advantage, however slight, over other individuals have a better chance of surviving and of reproducing their species” (p.These words are not in circles. Williams (1973b) and Mills and Beatty (1979) have analyzed the logical basis of Darwin's argument, and they have also concluded that there is no tautology (but see also Caplan, 1978).
Repeated attempts in the ensuing years to find a more appropriate term than "natural selection" or "survival of the fittest" were unsuccessful.Darwin himself had in mind "natural preservation" (or "natural preservation", naturalpreservation), but even this word does not show the creative component of natural selection.This creative component stems from the alternation between genetic recombination and reproductive success, is J.An aspect of natural selection emphasized by Huxley, Dubzansky, and other recent evolutionists.A new generation of biologists has become sufficiently accustomed to the term natural selection not to suffer from the troubles of Darwin's time.
Darwin's uncompromising rejection of any teleological factor in the causes of evolutionary change has drawn even more vehement criticism from many opponents of natural selection.他的同时代人只懂得除了目的论以外只有另一种选择或解释，那便是偶然。确实，一直到近代很多科学家和哲学家拒绝自然选择学说，他们的理由是“生物界奇妙的和谐”竟然完全出于偶然简直是不可思议。提出这种反对意见的人不了解自然选择是一种两步过程。第一步产生遗传变异性；在这一步中偶然确实具有绝对权威。第二步是遗传变异性通过选择加以整理或安顿，这就决不是机遇过程。
自然选择也绝非偶然与必然之间的某种过渡，而是完全新式的、避开了只能在这两者（偶然与必然）之中作抉择的困境的某种事态。赖特（Wright，1967：117）对这一点讲得再好不过：“达尔文的偶然过程与选择过程不断交相作用的历程并不是纯粹机遇与纯粹必然之间的中间状态，但其结果在性质上却和两者完全不同。”
值得注意的是一般都忽视了这样一种情况，即达尔文由于自然选择介绍了一种完全新的革命性原则，这一原则对于那些认为他的学说完全基于偶然的反对意见来说是根本无懈可击的。达尔文本人有时也忘记了这一点，因为他一度也承认对“这广阔无垠、奇妙无比的宇宙…竟然是盲目的机遇或必然的产物感到非常难于甚至无法理解”而十分苦恼，似乎只有这两者可供选择。
物理科学家特别对自然选择感到莫明其妙，因为它和物理学说或定律大不相同，它既不是严格的决定论的，又不是预测性的，而是具有浓厚随机意味的概率性的。喜不喜欢这样一种无纪律的过程都无关紧要，事实是它出现在自然界，而且对遗传型的命运或前途来说极端重要。
对自然选择学说并不是只有科学上的论战，应当记住进化生物学的原理和方法在中是第一次宣告于世界。达尔文的对手几乎全是数学家、工程师、物理学家、哲学家、神学家和其他类型的学者，他们的生物学知识少得可怜。然而他们认为进化是一个相当重要的论题来证明任何人参与讨论都是合理的。既然无法提出科学论据，他们就转而声称达尔文破坏了正确科学方法的规矩。（Hull，1973）。他们声言达尔文的工作是臆测性的，假定性的，推论性的，未成熟的。他们还批评他的结论或根据，而这些都是他们按地们称之为“唯一正确的科学方法”归纳法所未曾取得的。此外，他们还一再扬言不能接受进化学说，因为没有实验根据（迟至1922年贝特森尚如此说）。他们认为比较一观察证据缺乏科学性，必须是实验证据才是科学的。
这些批评全都是根据现在已被彻底否定的这样一种假定，即含有由时间变化而产生信息的现象和过程必须按研究纯粹功能性过程的方法来研究。更露骨地说就是物理科学（其现象领域非常有限）中有用的方法对全部科学都是充分够用的。指责达尔文没有遵循正规的科学方法和没有提供确切无疑证据的评论，没有认识到在19世纪中叶科学发生了一场方法论革命。达尔文一贯运用假说-演绎法（Ghiselin，1969）大大有利于确立这一方法的声誉并对确定某一学说的可靠性的标准作了修订（见第二章）。正是达尔文揭示了生物学说的形成在很多方面都和传统物理学说的形成有多么大的不同（Hull，1973；Hodge，1977；1981）。
历史陈述能用实验来检验的非常之少。然而就像达尔文所说的那样可以“推测”，也就是说可以根据观察构成假说，然后再用进一步观察来检验这一假说，这就是达尔文所不断进行的。达尔文的推测是一种按部就班的程序，他运用这种程序（现代的每一位科学家都是印此）为进一步观察所进行的检验发出指示，如果可能，还设计实验。
达尔文的方法论中尤其不同一般的是他论证了为什么问题（Why－questions）的合理性。进化原因只能通过提问为什么问题来分析。“为什么食叶昆虫是绿色的？”这个问题并不是探索最后（终极）原因而寻求过去（或当前）的选择压力。“为什么格拉帕戈斯群岛上的动物和南美动物的亲缘关系比之其他太平洋岛屿动物的更接近？”也是一个完全合理的科学问题。动物区系一定是通过跨越海洋的移殖到达海岛的这一假定的答案就容许有各种各样的预测，例如这一动物区系很可能来自最邻近的来源地区（南美），或者不能飞的动物（除非它们具有特殊的扩散方式）比能飞的动物更难到达海岛；事实上真正海岛没有或很少有陆栖哺乳类，但是蝙蝠则能到达绝大多数海岛。
达尔文通过新的方法论将终极原因的整个领域从神学转移到科学。他充分意识到他在干什么。因为他对一连串现象都问，“是用特创论还是用共同祖先的进化结果来解释更恰当？”（Gillespie，1979）。
甚至达尔文的一些最热心的支持者也承认自然选择学说几乎完全是根据演绎推理。
他的反对者将这种方法称之为纯粹臆测并要求提出归纳性的或实验证据。达尔文唯一能作的就是和人工选择作类比。但是T． H．赫胥黎又承认动物育种家从来没有经由选择培育出一种生殖隔离的新物种。瑞士生物学家Kolliker将极不正常的狗和鸽的品种称为“病态的”，他十分正确地坚持这样的动物在自然界中决不能生存。
贝茨（H．W．Bates）发现拟态现象（1862）就正好是天锡良机，达尔文兴高采烈马上就此写了一篇高度赞扬的评论。贝茨观察到在不可食（如果不是有毒的话）的螺状花纹蝴蝶中，每个种或地理宗（geogratoic race）常在其出没处和一种或几种模拟其色彩的可食蝴蝶（贝茨氏拟态）群聚在一起。甚至还不止于此，如果螺状花纹种的蝴蝶由于地理分布而发生变化（大都如此，而且变化很显着），则模拟它的伴随种也发生完全相同的变化。贝茨（1862：512）指出这种类型的变异只能是出于“自然选择，选择者是捕食昆虫的动物，后者将那些与原种不十分像的畸变或变种逐渐消灭。”蝴蝶的地理性变异（有些变异的发展是渐进性的）进一步揭示拟态现象并不是来自骤变而是由自然选择逐渐产生的。后来通过基因分析也证实了这一结论。
贝茨的工作是一项非常出色的博物学研究，很快就由其他的研究者加以证实。华莱士在新几内亚的杂色蝴蝶中也发现了类似情况，而且每年都相继发现各种类型的拟态新事例。研究拟态现象最重要的发展是缪勒（Fritz Muller，1879）指陈彼此互相模拟也可以出现在不可食的、有毒的或具有毒腺的动物如黄蜂、蛇中（缪勒氏拟态）。由于这类动物的捕食者显然必须学会（至少是部分地学会）应当避免捕食哪一种色彩模式的被捕食者，这就使具有警戒色的动物集群在某个地区采用单一的色彩类型作为代价。对该集群的每个成员来说拥有这种警戒色彩模式对选择是有利的。因此，配合自然选择的需要属于某种缪勒氏拟态复合体中的一切物种以平行对应的方式随地理分布而变化，也就不足为怪了。（Turner，1977）。
进化生物学的大多数研究工作特别是在1930年以后都侧重于确定动植物各种不同特征的选择值（selective value）（见第十二章）。
按哲学家Popper的意见，只有能够“反证”的学说才是科学的学说，有些反对自然选择的哲学家声称无法反证自然选择学说所说的一切。在这个问题上必须分清自然选择学说本身和将自然选择运用于某一特殊事例之间的区别，一旦涉及特殊事例就可以进行预测，这类预测在原则上是能够通过某些假定的检验来反证的。当然也有一些当代哲学家对完全依靠反证提出了怀疑。最后，由于新达尔文主义者很少提到表现型的每个组分和每种进化演变是特别选择（ad hoe selection）的结果，所以不能反证即不科学的论点并没有多大影响力。
自然选择概念最终不可避免地要引用于人类。这不仅导致某些极端（如种族主义）而且也产生了针锋相对的主张，即认为在人类中具有选择意义的遗传差异这一假定和平等原则背道而驰。极端的平等主义促使强大的环境主义学派迅速发展，特别是在美国的人类学界和行为心理学界中。尽管这类动向在其基本意识形态上是高尚的，而且在和种族主义以及社会偏见的斗争中可能是必要的，然而这些学派的主要主张却并没有得到任何具体证据的支持。它们所依据的只是一种非生物学的平等概念。当李森科主义在苏联抬头、当西方国家某些组织决定对遗传学发动攻击并推行环境主义时，情况就变得更糟。
近年来对社会生物学所发起的某些攻击也是出于同样的意识形态。把达尔文的名字和斯宾塞的社会达尔文主义联在一起，也妨碍人们接受自然选择学说。（Freeman，1974；Nichols，1974;Hertwig，1921；Greene，1977;Bannister，1979）。
研究生物多样性的学者根据观察结果也对自然选择学说提出了异议。他们声称，根据优秀个体存活与种群逐渐变化的论点，自然界应当是完全连续的；但实际上所见到的却只是不连续性。一切物种都被无法联接的裂缝将被此分隔开；物种之间的中间型从来没有观察到。物种之间的不育性障碍，怎样可能会是由逐步选择而形成？在高级阶元层次，这问题就更加严重。怀疑者认为，高级分类单位，如鸟类和哺乳类，或者甲虫与蝴蝶，彼此相差是如此悬殊，它们的起源是无法用自然选择的渐进进化来解释的。此外，选择又怎样能说明像翼这样的一些新器官的起源，尤其是当起初的新器官并不具备选择值一直要等到长大才能充分发挥功能？最后，一切渐进进化（包括地理变异）中所见到的种群中个体之间的极小差异起什么作用（有人说这类差异区别太小，并没有选择意义）？渐进进化的辩护者必须能够反驳这些反对意见并为支持这些学说的前提条件提供有力的证据；这些前提条件可列举如下：
（1）拥有用之不尽的个体变异的来源。
（2）个体变异的遗传力。
（3）即使最细微变异的选择优势也具有进化意义。
（4）对选择的反应是没有限制的。
（5）对主要的进化奇迹的逐渐变化和高级分类单位的起源作出说明。
达尔文和他的支持者起初都不能提供这类证据。因此，一直到现代传统性的反对意见一再被提出，其中最强硬的是Schindewolf（1936），Goldschmidt（194o），以及某些法国的动物学家。（Boesiger，1980）。直到新系统学时期，壬席，迈尔和其他人论证了不连续性的种群起源，（Mayr，1942；1963），遗传学家则提供了有关变异的证据，这些变异是自然选择发挥作用所必需的。
11．5其他的进化学说
对否定达尔文的自然选择学说的人来说接受进化论就又使他们处于进退两难的尴尬境地。支配或控制进化的因素如果不是自然选择那又是什么别的因素（或许多因素）？
1859年以后的80年间，先后提出了许多其他学说而且实际上在那一段时间里比自然选择流传更广。为了不致曲解当时的舆论气氛，我必须强调当时并不是彻底否定自然选择。
许多生物学家都承认，“当然，自然选择是存在的，但它不是进化的唯一动因，因为有很多很多的进化现象它无法解释。”因此必须记住，仅仅接受选择的一部分而同时却又承认还有支配进化的其他因素，就不是一个达尔文主义者。反达尔文主义者所特别不能接受的达尔文主义和新达尔文主义者的三个论点是渐进主义，否定软式遗传，否定目的论。因此可以将反对达尔文的各种学说，按所反对的是上述三个论点中的哪一个来区分。
下面就按下述三个题目来介绍：（1）骤变学说，（2）新拉马克学说，（3）直生论（Kellogg，1907；Mayr and Provine，1980）。
反对达尔文渐进主义的早期学说（His，Kolliker及其他）前面已介绍过。在19世纪60年代到80年代，这些学说只有少数支持者，但在1894年以后骤变学说很快就流行了起来并在本世纪初以“突变论（或突变主义）”（mutationism）的名义占居支配地位。
这些学说在20世纪的大辩论中所起的作用将在第十二章介绍。
对达尔文主义反对最坚决和最富成效的有好几种学说，一般统称为“新拉马克主义”。这一名称的自相矛盾的一面是拉马克学说的最根本的组成部分（进化中的目的论因素将生物的种系序列导向愈益完善或完备）并不是新拉马克主义的主要论点。然而不可否认新拉马克主义和拉马克在两个主要概念上是一致的进化是“纵向”进化，其实质是适应能力的提高（忽视或完全不考虑多样性的起源），另一个概念是个体的获得性状能够遗传软式遗传，（soft inheritance）。因此与其把新拉马克主义当作进化学说倒不如把它看作是遗传学说。软式遗传将在第十六章介绍。
环境对生物性状具有决定性影响的观念可以远溯到古代民间传说。它在哲学家之间，尤其是在启蒙运动之前和运动期间非常流行（洛克，康迪乃克）。在英国作家中哈特莱（David Hartley）是极端环境主义者的典型例子。他认为“生活条件的变化”严重影响“生物的变异”，布丰、林奈，拉马克和布鲁门巴赫都接受他的这一观点，他们还在不同程度上也都承认获得性状可以遗传。例如布鲁门巴赫认为黑色人种是由于热带的强烈阳光作用于浅色人种的肝脏而来。达尔文也不例外（见第十六章），他一直相信用进废退的某些效应及其遗传。他为了说明这种情况还采纳了泛生论，不过他认为和自然选择比较起来它的作用很小而已。
“新拉马克主义”包罗了一大堆杂七杂八的观点。从来没有两个新拉马克主义者具有相同的观点，不过要详细介绍这些观点或学说就离题太远。其中有一种被称为杰弗莱主义（Geoffroyism）的，将进化演变的原因归之于环境的直接影响。虽然拉马克曾公开地驳斥过这种环境直接诱变的看法，但是19世纪晚期一些承认这种观点的人也被列为新拉马克主义者。很多博物学家认为这是一种和自然选择共存的过程。例如他们深信除非通过环境的诱变作用否则渐进的地理变异就无法解释。杰弗莱主义有很多追随者，特别是在20世纪早期，他们形成了与突变主义相对抗的“反对派”，突变主义认为进化演变的唯一原因是不连续的骤变。环境诱变似乎是解释博物学家随处都可观察到的渐进变异现象的唯一途径。
获得性状遗传和用进废退有关的概念相结合在各种新拉马克学说中占有主要地位。
科普的“生长与效应定律”（law ofgrowth and effort）就是如此。某一器官如果在一新环境中变得更加有用，那么它的生长在每个世代中将会被促进，从而能更好地适应环境。这显然和拉马克的某些观点非常相似。他为这样一种过程所提出的运行机制是“生殖细胞具有对生长力过去工作效应的记录，就像和记忆相类似的情况”（Bowler，1977a：260）。Cope的这种机制将会自然地产生适应（现象）而无需借助于设计或超自然力。绝大多数美国的进化主义者在1900年以前都是新拉马克主义者。
许多新拉马克主义者求助于智力（mental forces）。这开始于拉马克本人“致力于”满足“需要”的进化（被错误地解释为“按志愿”产生新结构）；科普和其他新拉马克主义者曾提到“意识”，而在保利（Panly）的心理拉马克主义（Psycho－Lamarckism）中达到了极点，它对Boveri及Spemann都产生了相当影响（Hamburger，1980）。一切新拉马克主义者的学说的共同特点是都主张某一世代的阅历可以传递给下一代而且成为它的遗传性的一部分。因此，所有的新拉马克主义者都支持获得性状遗传。
在遗传物质的本质没有研究清楚之前，新拉马克主义对适应现象的解释远比用偶然变异和选择的随意过程来解释更使人满意。一旦发现微突变（基因突变，minimutation）及重组是进化的遗传物质基础以及软式遗传被否定后，年轻的新拉马克主义者很快就转向达尔文主义。
这第三组反对达尔文主义的学说也有很悠久的历史，它们的依据是进化是由于包含有某种目的论成分的概念。虽然“自然界阶梯”是静止的，虽然“创世纪”的作者有了上帝在第六天创造人类的设想而根本不会想到进化，但在这两种情况下都暗示了从低等到高等的必然序列。实际上在哲学家和许多宗教中某种形式宇宙目的论的假定很普遍。
Erasmus Darwin认为“不断改进的能力。是生命本身的基本性质之一：“不妨大胆设想很久以前，自从地球开始存在，也许是人类历史发端之前几百万年，所有的温血动物都来自活的细丝，这活的细丝是由'第一原因'赋以动物性具有取得新结构的能力，伴有新的习性，由刺激、感觉、意志、联想等引导；从而具有经由其本身固有的活动而产生的不断改进的能力，并通过生育将这些改进传递给后代，世代相传，一至无穷！ "
（1796，I：509）。
就拉马克看来进化显然是趋于更加完善的运动，地质学家中的进步主义者在每一新的动植物区系形成中也发现有某种向上的趋向，某种使生物能圆满适应大地环境变化的趋向（Agassiz，1857；Bowler，1974b）。无论所设想的机制是会自动保证完全适应的一套“定律”还是造物主不断的直接关注，结果都相同：一种趋向于完美无缺（完备）的不可抗拒的运动。
目的论思想在19世纪前半期非常流行。就阿加西和其他进步主义者看来化石动物区系序列的确反映了在造物主的构思中创造方案的成熟程度。有神论者和自然神论者的哲学家都需要最终原因在自然界普遍运行，因为这是造物主存在的最重要的证据之一（如果不是唯一的证据）。有神论者如塞吉威克，冯贝尔在自然界的各个角落都能发现目的。
冯贝尔在一篇评论时文章中写道，“我的目标是保卫目的论”，因为“自然力必须是协调的和取向的。未取向的力（所谓的盲目力）决不能产生秩序…如果高等动物与低等动物之间有因果关系，是由低等动物发展而成的，那么我们怎么能否认自然界是有目的的？”阿伽西也同样讽刺过盲目力的效力。甚至达尔文起初也接受过目的论，因而有过这样不平常的言论：“如果所有的人都死了，猴子就成为人——人就成为神”
（《笔记》，169页）。Herbert（1977）指出，地理变异的研究使达尔文很快放弃了任何直生论观念。将替代种加以比较，他并没有发现必然的和内在固有的进步趋势的任何证据。自从他采纳了自然选择之后，便再也不需要任何目的论原则。
在为进化的目的论原则做辩护的人之中，内格里（1865；1884）和Elmer（1888）提出了最为精心构思的学说。这些学说的根据或者是假定一切生物都具有内在的完善化因素或者假定遗传结构对一切生物加以控制使进化只能按多少是直线方向进行。 Eimer采用了海克尔最先提出的一个词将完善化因素称为直生因素，他的学说便被称为直生论；其他的生物学家和哲学家也为基本相似的进化力量制订了不同的名称，如Berg的“循规进化说”（nomogenesis）；H． F． Osborn的“芒状发生说”（arhosenesis），Teilhard de Chardin的“阿米加原则”（Omega Principle）。古生物学家特别相信某种内在的定向力，因为他们随处都观察到千百万年的进化趋向。在人类学家中广泛流传的、人类进化必然通过一系列阶段的观点也属于这一类（White，1949）。
当解释直生论的原因时，在其支持者之间也众说不一，而且都很含糊。其中有些人把进化仅仅看作是某种基本不变的本质潜势的显示，这也就是“进化”的本义。可以说这是把胚胎学中的先成论应用于进化。这基本上就是阿伽西的思想并为遗传学家贝特森（Bateon）所赞同（1914）。另有些人则将促使直生论进化发生的原因归之于神秘定律：
“生物的进化是生物固有的某些过程的结果，这些过程所依据的是定律。因此，有目的的结构和动作是生物的基本特性”（Berg，1926：8）。这些话当然等于白说，什么也没有解释。Eimer后来又提出环境定向的变异企图避开内在的目的论因素，但是生物对环境的恰当反应仍然是以内在的具有目的性的能力为基础。
达尔文主义者之所以抵制或否定任何内在的走向机制或有目的的因素有许多理由。
首先，因为直生论的拥护者提不出任何符合于物理化学原则的合理机制，其次，因为详细研究这样的趋势一定会暴露出许多不正常甚至有时完全相反的情况（Simpson，1953）。最后，因为当进化序列分叉时，子序列可能具有极不相同的趋向，偶尔还会和原来的趋向相反。再者，这和一个整合（集成）的机制不相容。对变态昆虫和海洋生物幼虫期和成虫期的观察往往显示了完全不同的趋向，这已经由魏斯曼和缪勒作为进一步反驳直生论的例证指出过。
支持直生论的所有学说到了适当的时候全被否定，但这并不能作为忽视这类文献的理由。直生论的主要代表，无论是古生物学家还是其他类型的博物学家都是敏锐的观察者，他们为进化趋向和进化过程中的遗传控制收集了不少令人深感兴趣的证据。他们坚持大量的进化现象是“直线式”的（至少从表面上看）是正确的。就马来说，趾骨缩小和牙齿变化就是着名的例子。事实上对几乎所有长时期的化石系列进行研究的结果都显示出进化趋向的例证。这样的趋向对进化论者很重要，因为这趋向表明连续性存在，值得研究，因此在当前的关于进化的文献中倍受重视。
进化趋向的形成可能有两层原因。一方面这趋向可能是由于环境的一贯变化所引起，例如第三纪时亚热带和温带气候日益干旱，这就促成了不断的选择压力使马的趾骨和牙齿进化。对这样不断的选择压力的反应Plate（1903）称之为“直向选择”（定向选择，orthoselection）另一方面，进化趋向可能是遗传型的内聚性所必需的，这种内聚性对可能发生的形态变化施加严格的约束（控制）。因此，进化趋向在达尔文学说的理论框架之内很容易解释，并不需要任何单独的“定律”或因素、原则。
达尔文主义者要向其对手讲清楚否定某种内在的完善化因素并不等于否定所观察到的进化性进步确实相当困难。否定从纤毛虫进步到被子植物和脊椎动物就可能意味着完全否定进化。达尔文由于充分认识到进化的不可预测性和机遇性方面，所以他只是反对“从较不完善的到较完善的”这种定律式的进步。正是在这种意义上他曾提醒过自己“决不要说高等的、低等的。”
当然，达尔文也并没有按照他所说的去做，在中他经常提到进化性进步（149，336－338，388，406，441，489页）。这样做是必要的，不仅为的是反驳莱伊尔的稳定态世界概念，也是为了和一种新发展起来的、否定最简单和最复杂生物之间在完善程度上有任何区别的新学派相抗衡。例如爱仑堡（Ehrenberg）就声称从最低等生物纤毛虫到最高等生物脊椎动物在结构上并没有前进（advance）。它们全都有执行动物全部一功能所必需的结构，因而全都是“完备的”（“完善的”）。这种奇怪议论完全忽视了下面的事实：从腔肠动物的扩散式神经纤维到高度发展的鲸类或灵长类的中枢神经系统之间确实是巨大前进。爱仑堡的言论当然具有强烈的反对进化论的含意。莱伊尔也同样试图否定从最底层化石矿床到现代在动物区系系列上的任何进步（除了人类最晚出现以外）。上述言论显然都含蓄地否定了通过自然选择的进步。达尔文认识到“博物学家还未能就高等低等作出彼此都满意的定义，”然而他接着说，“按我的学说，最新近的类型一定比那些较古老的类型更高级，因为每一新物种是在生存竞争中由于比其他的和原先的类型具有某些优点或长处而形成的”（：337）。
事实上在进化进程中出现的形态上和生理上的一系列改进很难说不是进步。我想到的一些现象如光合作用，真核性（eukaryoty，构成细胞核），多细胞性（多细胞动物，多细胞植物），二倍性，恒温性，捕食，抚幼等等，这些仅仅是从第一个原核生物出现后三十亿年过程中进化性进步的几个例子。无论用什么尺度衡量，一个乌贼，一个蜜蜂或一个灵长类动物怎样也比一个原生生物进步得多，然而“进步”这个词含有直线性的意思，而这在生物进化中是找不到的。在生物进化中也没有单一序列，因为在植物，节肢动物，鱼类，哺乳类以及几乎所有类群的生物中都有进步性进化，每一系谱的进步表现方式却又非常不同。
对达尔文关于进化性进步所写下的一切材料加以仔细分析后发现他并不自相矛盾。
他所反对的是目的论，目的论也就是对由“自然”定律支配的、趋向于完美无缺的内在冲动的一种信念。达尔文每当在进化过程中遇到进步现象时，他发现这些现象很容易用变异和自然选择的结果归纳推理来解释。进化性进步一经出现，它就不是目的性过程；达尔文的这个结论是一切进化生物学家都同意的。
达尔文主义的反对派所提出的主要反对意见总是针对这样一个问题：生物界充满了进步趋向，但这类进步趋向竟然是由偶然性的变异和自然选择引起的却怎样也无法令人相信。达尔文学派的回答是，为什么不行？每一种进步，在每个基因库中产生的每一种结构上、生理上和行为上的创新终究会对进化有利，也就是引起习惯上所说的进步。这正是达尔文已充分了解的。
一个更尖锐的问题是怎样给进步下定义。学者们对这个问题的意见极不一致，甚至没有两个人的意见是相同的。复杂性决不一定是衡量进步的尺度，因为在很多进化序列中最古老的倒是最复杂的，而进步却在于简（单）化。几乎没有人能够完全避开拉马克的衡量进步标准，即与人类作比较。当J．赫胥黎（1942）提出以“控制环境”作为衡量尺度时，无疑就把人远远置于其他生物之