Recapitulation of the difficulties on the theory of Natural Selection. Recapitulation of the general and special circumstances in its favour. Causes of the general belief in the immutability1 of species. How far the theory of natural selection may be extended. Effects of its adoption2 on the study of Natural history. Concluding remarks.
As this whole volume is one long argument, it may be convenient to the reader to have the leading facts and inferences briefly3 recapitulated4.
That many and grave objections may be advanced against the theory of descent with modification5 through natural selection, I do not deny. I have endeavoured to give to them their full force. Nothing at first can appear more difficult to believe than that the more complex organs and instincts should have been perfected, not by means superior to, though analogous6 with, human reason, but by the accumulation of innumerable slight variations, each good for the individual possessor. Nevertheless, this difficulty, though appearing to our imagination insuperably great, cannot be considered real if we admit the following propositions, namely,--that gradations in the perfection of any organ or instinct, which we may consider, either do now exist or could have existed, each good of its kind,--that all organs and instincts are, in ever so slight a degree, variable,--and, lastly, that there is a struggle for existence leading to the preservation7 of each profitable deviation8 of structure or instinct. The truth of these propositions cannot, I think, be disputed.
It is, no doubt, extremely difficult even to conjecture9 by what gradations many structures have been perfected, more especially amongst broken and failing groups of organic beings; but we see so many strange gradations in nature, as is proclaimed by the canon, "Natura non facit saltum," that we ought to be extremely cautious in saying that any organ or instinct, or any whole being, could not have arrived at its present state by many graduated steps. There are, it must be admitted, cases of special difficulty on the theory of natural selection; and one of the most curious of these is the existence of two or three defined castes of workers or sterile12 females in the same community of ants; but I have attempted to show how this difficulty can be mastered.
With respect to the almost universal sterility14 of species when first crossed, which forms so remarkable15 a contrast with the almost universal fertility of varieties when crossed, I must refer the reader to the recapitulation of the facts given at the end of the eighth chapter, which seem to me conclusively16 to show that this sterility is no more a special endowment than is the incapacity of two trees to be grafted17 together, but that it is incidental on constitutional differences in the reproductive systems of the intercrossed species. We see the truth of this conclusion in the vast difference in the result, when the same two species are crossed reciprocally; that is, when one species is first used as the father and then as the mother.
The fertility of varieties when intercrossed and of their mongrel offspring cannot be considered as universal; nor is their very general fertility surprising when we remember that it is not likely that either their constitutions or their reproductive systems should have been profoundly modified. Moreover, most of the varieties which have been experimentised on have been produced under domestication18; and as domestication apparently19 tends to eliminate sterility, we ought not to expect it also to produce sterility.
The sterility of hybrids20 is a very different case from that of first crosses, for their reproductive organs are more or less functionally21 impotent; whereas in first crosses the organs on both sides are in a perfect condition. As we continually see that organisms of all kinds are rendered in some degree sterile from their constitutions having been disturbed by slightly different and new conditions of life, we need not feel surprise at hybrids being in some degree sterile, for their constitutions can hardly fail to have been disturbed from being compounded of two distinct organisations. This parallelism is supported by another parallel, but directly opposite, class of facts; namely, that the vigour24 and fertility of all organic beings are increased by slight changes in their conditions of life, and that the offspring of slightly modified forms or varieties acquire from being crossed increased vigour and fertility. So that, on the one hand, considerable changes in the conditions of life and crosses between greatly modified forms, lessen25 fertility; and on the other hand, lesser26 changes in the conditions of life and crosses between less modified forms, increase fertility.
Turning to geographical27 distribution, the difficulties encountered on the theory of descent with modification are grave enough. All the individuals of the same species, and all the species of the same genus, or even higher group, must have descended28 from common parents; and therefore, in however distant and isolated29 parts of the world they are now found, they must in the course of successive generations have passed from some one part to the others. We are often wholly unable even to conjecture how this could have been effected. Yet, as we have reason to believe that some species have retained the same specific form for very long periods, enormously long as measured by years, too much stress ought not to be laid on the occasional wide diffusion30 of the same species; for during very long periods of time there will always be a good chance for wide migration31 by many means. A broken or interrupted range may often be accounted for by the extinction32 of the species in the intermediate regions. It cannot be denied that we are as yet very ignorant of the full extent of the various climatal and geographical changes which have affected33 the earth during modern periods; and such changes will obviously have greatly facilitated migration. As an example, I have attempted to show how potent22 has been the influence of the Glacial period on the distribution both of the same and of representative species throughout the world. We are as yet profoundly ignorant of the many occasional means of transport. With respect to distinct species of the same genus inhabiting very distant and isolated regions, as the process of modification has necessarily been slow, all the means of migration will have been possible during a very long period; and consequently the difficulty of the wide diffusion of species of the same genus is in some degree lessened34.
As on the theory of natural selection an interminable number of intermediate forms must have existed, linking together all the species in each group by gradations as fine as our present varieties, it may be asked, Why do we not see these linking forms all around us? Why are not all organic beings blended together in an inextricable chaos35? With respect to existing forms, we should remember that we have no right to expect (excepting in rare cases) to discover DIRECTLY connecting links between them, but only between each and some extinct and supplanted37 form. Even on a wide area, which has during a long period remained continuous, and of which the climate and other conditions of life change insensibly in going from a district occupied by one species into another district occupied by a closely allied38 species, we have no just right to expect often to find intermediate varieties in the intermediate zone. For we have reason to believe that only a few species are undergoing change at any one period; and all changes are slowly effected. I have also shown that the intermediate varieties which will at first probably exist in the intermediate zones, will be liable to be supplanted by the allied forms on either hand; and the latter, from existing in greater numbers, will generally be modified and improved at a quicker rate than the intermediate varieties, which exist in lesser numbers; so that the intermediate varieties will, in the long run, be supplanted and exterminated39.
On this doctrine41 of the extermination42 of an infinitude of connecting links, between the living and extinct inhabitants of the world, and at each successive period between the extinct and still older species, why is not every geological formation charged with such links? Why does not every collection of fossil remains43 afford plain evidence of the gradation and mutation44 of the forms of life? We meet with no such evidence, and this is the most obvious and forcible of the many objections which may be urged against my theory. Why, again, do whole groups of allied species appear, though certainly they often falsely appear, to have come in suddenly on the several geological stages? Why do we not find great piles of strata45 beneath the Silurian system, stored with the remains of the progenitors47 of the Silurian groups of fossils? For certainly on my theory such strata must somewhere have been deposited at these ancient and utterly48 unknown epochs in the world's history.
I can answer these questions and grave objections only on the supposition that the geological record is far more imperfect than most geologists50 believe. It cannot be objected that there has not been time sufficient for any amount of organic change; for the lapse51 of time has been so great as to be utterly inappreciable by the human intellect. The number of specimens52 in all our museums is absolutely as nothing compared with the countless53 generations of countless species which certainly have existed. We should not be able to recognise a species as the parent of any one or more species if we were to examine them ever so closely, unless we likewise possessed54 many of the intermediate links between their past or parent and present states; and these many links we could hardly ever expect to discover, owing to the imperfection of the geological record. Numerous existing doubtful forms could be named which are probably varieties; but who will pretend that in future ages so many fossil links will be discovered, that naturalists55 will be able to decide, on the common view, whether or not these doubtful forms are varieties? As long as most of the links between any two species are unknown, if any one link or intermediate variety be discovered, it will simply be classed as another and distinct species. Only a small portion of the world has been geologically explored. Only organic beings of certain classes can be preserved in a fossil condition, at least in any great number. Widely ranging species vary most, and varieties are often at first local,--both causes rendering56 the discovery of intermediate links less likely. Local varieties will not spread into other and distant regions until they are considerably57 modified and improved; and when they do spread, if discovered in a geological formation, they will appear as if suddenly created there, and will be simply classed as new species. Most formations have been intermittent58 in their accumulation; and their duration, I am inclined to believe, has been shorter than the average duration of specific forms. Successive formations are separated from each other by enormous blank intervals59 of time; for fossiliferous formations, thick enough to resist future degradation60, can be accumulated only where much sediment61 is deposited on the subsiding62 bed of the sea. During the alternate periods of elevation63 and of stationary64 level the record will be blank. During these latter periods there will probably be more variability in the forms of life; during periods of subsidence, more extinction.
With respect to the absence of fossiliferous formations beneath the lowest Silurian strata, I can only recur65 to the hypothesis given in the ninth chapter. That the geological record is imperfect all will admit; but that it is imperfect to the degree which I require, few will be inclined to admit. If we look to long enough intervals of time, geology plainly declares that all species have changed; and they have changed in the manner which my theory requires, for they have changed slowly and in a graduated manner. We clearly see this in the fossil remains from consecutive66 formations invariably being much more closely related to each other, than are the fossils from formations distant from each other in time.
Such is the sum of the several chief objections and difficulties which may justly be urged against my theory; and I have now briefly recapitulated the answers and explanations which can be given to them. I have felt these difficulties far too heavily during many years to doubt their weight. But it deserves especial notice that the more important objections relate to questions on which we are confessedly ignorant; nor do we know how ignorant we are. We do not know all the possible transitional gradations between the simplest and the most perfect organs; it cannot be pretended that we know all the varied67 means of Distribution during the long lapse of years, or that we know how imperfect the Geological Record is. Grave as these several difficulties are, in my judgment68 they do not overthrow69 the theory of descent with modification.
Now let us turn to the other side of the argument. Under domestication we see much variability. This seems to be mainly due to the reproductive system being eminently71 susceptible72 to changes in the conditions of life; so that this system, when not rendered impotent, fails to reproduce offspring exactly like the parent-form. Variability is governed by many complex laws,--by correlation73 of growth, by use and disuse, and by the direct action of the physical conditions of life. There is much difficulty in ascertaining74 how much modification our domestic productions have undergone; but we may safely infer that the amount has been large, and that modifications75 can be inherited for long periods. As long as the conditions of life remain the same, we have reason to believe that a modification, which has already been inherited for many generations, may continue to be inherited for an almost infinite number of generations. On the other hand we have evidence that variability, when it has once come into play, does not wholly cease; for new varieties are still occasionally produced by our most anciently domesticated76 productions.
Man does not actually produce variability; he only unintentionally exposes organic beings to new conditions of life, and then nature acts on the organisation23, and causes variability. But man can and does select the variations given to him by nature, and thus accumulate them in any desired manner. He thus adapts animals and plants for his own benefit or pleasure. He may do this methodically, or he may do it unconsciously by preserving the individuals most useful to him at the time, without any thought of altering the breed. It is certain that he can largely influence the character of a breed by selecting, in each successive generation, individual differences so slight as to be quite inappreciable by an uneducated eye. This process of selection has been the great agency in the production of the most distinct and useful domestic breeds. That many of the breeds produced by man have to a large extent the character of natural species, is shown by the inextricable doubts whether very many of them are varieties or aboriginal77 species.
There is no obvious reason why the principles which have acted so efficiently78 under domestication should not have acted under nature. In the preservation of favoured individuals and races, during the constantly-recurrent Struggle for Existence, we see the most powerful and ever-acting79 means of selection. The struggle for existence inevitably80 follows from the high geometrical ratio of increase which is common to all organic beings. This high rate of increase is proved by calculation, by the effects of a succession of peculiar81 seasons, and by the results of naturalisation, as explained in the third chapter. More individuals are born than can possibly survive. A grain in the balance will determine which individual shall live and which shall die,--which variety or species shall increase in number, and which shall decrease, or finally become extinct. As the individuals of the same species come in all respects into the closest competition with each other, the struggle will generally be most severe between them; it will be almost equally severe between the varieties of the same species, and next in severity between the species of the same genus. But the struggle will often be very severe between beings most remote in the scale of nature. The slightest advantage in one being, at any age or during any season, over those with which it comes into competition, or better adaptation in however slight a degree to the surrounding physical conditions, will turn the balance.
With animals having separated sexes there will in most cases be a struggle between the males for possession of the females. The most vigorous individuals, or those which have most successfully struggled with their conditions of life, will generally leave most progeny83. But success will often depend on having special weapons or means of defence, or on the charms of the males; and the slightest advantage will lead to victory.
As geology plainly proclaims that each land has undergone great physical changes, we might have expected that organic beings would have varied under nature, in the same way as they generally have varied under the changed conditions of domestication. And if there be any variability under nature, it would be an unaccountable fact if natural selection had not come into play. It has often been asserted, but the assertion is quite incapable84 of proof, that the amount of variation under nature is a strictly85 limited quantity. Man, though acting on external characters alone and often capriciously, can produce within a short period a great result by adding up mere86 individual differences in his domestic productions; and every one admits that there are at least individual differences in species under nature. But, besides such differences, all naturalists have admitted the existence of varieties, which they think sufficiently87 distinct to be worthy88 of record in systematic89 works. No one can draw any clear distinction between individual differences and slight varieties; or between more plainly marked varieties and sub-species, and species. Let it be observed how naturalists differ in the rank which they assign to the many representative forms in Europe and North America.
If then we have under nature variability and a powerful agent always ready to act and select, why should we doubt that variations in any way useful to beings, under their excessively complex relations of life, would be preserved, accumulated, and inherited? Why, if man can by patience select variations most useful to himself, should nature fail in selecting variations useful, under changing conditions of life, to her living products? What limit can be put to this power, acting during long ages and rigidly90 scrutinising the whole constitution, structure, and habits of each creature,--favouring the good and rejecting the bad? I can see no limit to this power, in slowly and beautifully adapting each form to the most complex relations of life. The theory of natural selection, even if we looked no further than this, seems to me to be in itself probable. I have already recapitulated, as fairly as I could, the opposed difficulties and objections: now let us turn to the special facts and arguments in favour of the theory.
On the view that species are only strongly marked and permanent varieties, and that each species first existed as a variety, we can see why it is that no line of demarcation can be drawn91 between species, commonly supposed to have been produced by special acts of creation, and varieties which are acknowledged to have been produced by secondary laws. On this same view we can understand how it is that in each region where many species of a genus have been produced, and where they now flourish, these same species should present many varieties; for where the manufactory of species has been active, we might expect, as a general rule, to find it still in action; and this is the case if varieties be incipient92 species. Moreover, the species of the larger genera, which afford the greater number of varieties or incipient species, retain to a certain degree the character of varieties; for they differ from each other by a less amount of difference than do the species of smaller genera. The closely allied species also of the larger genera apparently have restricted ranges, and they are clustered in little groups round other species--in which respects they resemble varieties. These are strange relations on the view of each species having been independently created, but are intelligible93 if all species first existed as varieties.
As each species tends by its geometrical ratio of reproduction to increase inordinately94 in number; and as the modified descendants of each species will be enabled to increase by so much the more as they become more diversified95 in habits and structure, so as to be enabled to seize on many and widely different places in the economy of nature, there will be a constant tendency in natural selection to preserve the most divergent offspring of any one species. Hence during a long-continued course of modification, the slight differences, characteristic of varieties of the same species, tend to be augmented96 into the greater differences characteristic of species of the same genus. New and improved varieties will inevitably supplant36 and exterminate40 the older, less improved and intermediate varieties; and thus species are rendered to a large extent defined and distinct objects. Dominant97 species belonging to the larger groups tend to give birth to new and dominant forms; so that each large group tends to become still larger, and at the same time more divergent in character. But as all groups cannot thus succeed in increasing in size, for the world would not hold them, the more dominant groups beat the less dominant. This tendency in the large groups to go on increasing in size and diverging98 in character, together with the almost inevitable99 contingency100 of much extinction, explains the arrangement of all the forms of life, in groups subordinate to groups, all within a few great classes, which we now see everywhere around us, and which has prevailed throughout all time. This grand fact of the grouping of all organic beings seems to me utterly inexplicable101 on the theory of creation.
As natural selection acts solely102 by accumulating slight, successive, favourable103 variations, it can produce no great or sudden modification; it can act only by very short and slow steps. Hence the canon of "Natura non facit saltum," which every fresh addition to our knowledge tends to make more strictly correct, is on this theory simply intelligible. We can plainly see why nature is prodigal104 in variety, though niggard in innovation. But why this should be a law of nature if each species has been independently created, no man can explain.
Many other facts are, as it seems to me, explicable on this theory. How strange it is that a bird, under the form of woodpecker, should have been created to prey105 on insects on the ground; that upland geese, which never or rarely swim, should have been created with webbed feet; that a thrush should have been created to dive and feed on sub-aquatic insects; and that a petrel should have been created with habits and structure fitting it for the life of an auk or grebe! and so on in endless other cases. But on the view of each species constantly trying to increase in number, with natural selection always ready to adapt the slowly varying descendants of each to any unoccupied or ill-occupied place in nature, these facts cease to be strange, or perhaps might even have been anticipated.
As natural selection acts by competition, it adapts the inhabitants of each country only in relation to the degree of perfection of their associates; so that we need feel no surprise at the inhabitants of any one country, although on the ordinary view supposed to have been specially10 created and adapted for that country, being beaten and supplanted by the naturalised productions from another land. Nor ought we to marvel106 if all the contrivances in nature be not, as far as we can judge, absolutely perfect; and if some of them be abhorrent107 to our ideas of fitness. We need not marvel at the sting of the bee causing the bee's own death; at drones being produced in such vast numbers for one single act, and being then slaughtered108 by their sterile sisters; at the astonishing waste of pollen109 by our fir-trees; at the instinctive110 hatred111 of the queen bee for her own fertile daughters; at ichneumonidae feeding within the live bodies of caterpillars112; and at other such cases. The wonder indeed is, on the theory of natural selection, that more cases of the want of absolute perfection have not been observed.
The complex and little known laws governing variation are the same, as far as we can see, with the laws which have governed the production of so-called specific forms. In both cases physical conditions seem to have produced but little direct effect; yet when varieties enter any zone, they occasionally assume some of the characters of the species proper to that zone. In both varieties and species, use and disuse seem to have produced some effect; for it is difficult to resist this conclusion when we look, for instance, at the logger-headed duck, which has wings incapable of flight, in nearly the same condition as in the domestic duck; or when we look at the burrowing113 tucutucu, which is occasionally blind, and then at certain moles114, which are habitually115 blind and have their eyes covered with skin; or when we look at the blind animals inhabiting the dark caves of America and Europe. In both varieties and species correlation of growth seems to have played a most important part, so that when one part has been modified other parts are necessarily modified. In both varieties and species reversions to long-lost characters occur. How inexplicable on the theory of creation is the occasional appearance of stripes on the shoulder and legs of the several species of the horse-genus and in their hybrids! How simply is this fact explained if we believe that these species have descended from a striped progenitor46, in the same manner as the several domestic breeds of pigeon have descended from the blue and barred rock-pigeon!
On the ordinary view of each species having been independently created, why should the specific characters, or those by which the species of the same genus differ from each other, be more variable than the generic116 characters in which they all agree? Why, for instance, should the colour of a flower be more likely to vary in any one species of a genus, if the other species, supposed to have been created independently, have differently coloured flowers, than if all the species of the genus have the same coloured flowers? If species are only well-marked varieties, of which the characters have become in a high degree permanent, we can understand this fact; for they have already varied since they branched off from a common progenitor in certain characters, by which they have come to be specifically distinct from each other; and therefore these same characters would be more likely still to be variable than the generic characters which have been inherited without change for an enormous period. It is inexplicable on the theory of creation why a part developed in a very unusual manner in any one species of a genus, and therefore, as we may naturally infer, of great importance to the species, should be eminently liable to variation; but, on my view, this part has undergone, since the several species branched off from a common progenitor, an unusual amount of variability and modification, and therefore we might expect this part generally to be still variable. But a part may be developed in the most unusual manner, like the wing of a bat, and yet not be more variable than any other structure, if the part be common to many subordinate forms, that is, if it has been inherited for a very long period; for in this case it will have been rendered constant by long-continued natural selection.
Glancing at instincts, marvellous as some are, they offer no greater difficulty than does corporeal117 structure on the theory of the natural selection of successive, slight, but profitable modifications. We can thus understand why nature moves by graduated steps in endowing different animals of the same class with their several instincts. I have attempted to show how much light the principle of gradation throws on the admirable architectural powers of the hive-bee. Habit no doubt sometimes comes into play in modifying instincts; but it certainly is not indispensable, as we see, in the case of neuter insects, which leave no progeny to inherit the effects of long-continued habit. On the view of all the species of the same genus having descended from a common parent, and having inherited much in common, we can understand how it is that allied species, when placed under considerably different conditions of life, yet should follow nearly the same instincts; why the thrush of South America, for instance, lines her nest with mud like our British species. On the view of instincts having been slowly acquired through natural selection we need not marvel at some instincts being apparently not perfect and liable to mistakes, and at many instincts causing other animals to suffer.
If species be only well-marked and permanent varieties, we can at once see why their crossed offspring should follow the same complex laws in their degrees and kinds of resemblance to their parents,--in being absorbed into each other by successive crosses, and in other such points,--as do the crossed offspring of acknowledged varieties. On the other hand, these would be strange facts if species have been independently created, and varieties have been produced by secondary laws.
If we admit that the geological record is imperfect in an extreme degree, then such facts as the record gives, support the theory of descent with modification. New species have come on the stage slowly and at successive intervals; and the amount of change, after equal intervals of time, is widely different in different groups. The extinction of species and of whole groups of species, which has played so conspicuous118 a part in the history of the organic world, almost inevitably follows on the principle of natural selection; for old forms will be supplanted by new and improved forms. Neither single species nor groups of species reappear when the chain of ordinary generation has once been broken. The gradual diffusion of dominant forms, with the slow modification of their descendants, causes the forms of life, after long intervals of time, to appear as if they had changed simultaneously119 throughout the world. The fact of the fossil remains of each formation being in some degree intermediate in character between the fossils in the formations above and below, is simply explained by their intermediate position in the chain of descent. The grand fact that all extinct organic beings belong to the same system with recent beings, falling either into the same or into intermediate groups, follows from the living and the extinct being the offspring of common parents. As the groups which have descended from an ancient progenitor have generally diverged120 in character, the progenitor with its early descendants will often be intermediate in character in comparison with its later descendants; and thus we can see why the more ancient a fossil is, the oftener it stands in some degree intermediate between existing and allied groups. Recent forms are generally looked at as being, in some vague sense, higher than ancient and extinct forms; and they are in so far higher as the later and more improved forms have conquered the older and less improved organic beings in the struggle for life. Lastly, the law of the long endurance of allied forms on the same continent,--of marsupials in Australia, of edentata in America, and other such cases,--is intelligible, for within a confined country, the recent and the extinct will naturally be allied by descent.
Looking to geographical distribution, if we admit that there has been during the long course of ages much migration from one part of the world to another, owing to former climatal and geographical changes and to the many occasional and unknown means of dispersal, then we can understand, on the theory of descent with modification, most of the great leading facts in Distribution. We can see why there should be so striking a parallelism in the distribution of organic beings throughout space, and in their geological succession throughout time; for in both cases the beings have been connected by the bond of ordinary generation, and the means of modification have been the same. We see the full meaning of the wonderful fact, which must have struck every traveller, namely, that on the same continent, under the most diverse conditions, under heat and cold, on mountain and lowland, on deserts and marshes121, most of the inhabitants within each great class are plainly related; for they will generally be descendants of the same progenitors and early colonists122. On this same principle of former migration, combined in most cases with modification, we can understand, by the aid of the Glacial period, the identity of some few plants, and the close alliance of many others, on the most distant mountains, under the most different climates; and likewise the close alliance of some of the inhabitants of the sea in the northern and southern temperate123 zones, though separated by the whole intertropical ocean. Although two areas may present the same physical conditions of life, we need feel no surprise at their inhabitants being widely different, if they have been for a long period completely separated from each other; for as the relation of organism to organism is the most important of all relations, and as the two areas will have received colonists from some third source or from each other, at various periods and in different proportions, the course of modification in the two areas will inevitably be different.
On this view of migration, with subsequent modification, we can see why oceanic islands should be inhabited by few species, but of these, that many should be peculiar. We can clearly see why those animals which cannot cross wide spaces of ocean, as frogs and terrestrial mammals, should not inhabit oceanic islands; and why, on the other hand, new and peculiar species of bats, which can traverse the ocean, should so often be found on islands far distant from any continent. Such facts as the presence of peculiar species of bats, and the absence of all other mammals, on oceanic islands, are utterly inexplicable on the theory of independent acts of creation.
The existence of closely allied or representative species in any two areas, implies, on the theory of descent with modification, that the same parents formerly124 inhabited both areas; and we almost invariably find that wherever many closely allied species inhabit two areas, some identical species common to both still exist. Wherever many closely allied yet distinct species occur, many doubtful forms and varieties of the same species likewise occur. It is a rule of high generality that the inhabitants of each area are related to the inhabitants of the nearest source whence immigrants might have been derived125. We see this in nearly all the plants and animals of the Galapagos archipelago, of Juan Fernandez, and of the other American islands being related in the most striking manner to the plants and animals of the neighbouring American mainland; and those of the Cape126 de Verde archipelago and other African islands to the African mainland. It must be admitted that these facts receive no explanation on the theory of creation.
The fact, as we have seen, that all past and present organic beings constitute one grand natural system, with group subordinate to group, and with extinct groups often falling in between recent groups, is intelligible on the theory of natural selection with its contingencies127 of extinction and divergence128 of character. On these same principles we see how it is, that the mutual129 affinities130 of the species and genera within each class are so complex and circuitous131. We see why certain characters are far more serviceable than others for classification;--why adaptive characters, though of paramount132 importance to the being, are of hardly any importance in classification; why characters derived from rudimentary parts, though of no service to the being, are often of high classificatory value; and why embryological characters are the most valuable of all. The real affinities of all organic beings are due to inheritance or community of descent. The natural system is a genealogical arrangement, in which we have to discover the lines of descent by the most permanent characters, however slight their vital importance may be.
The framework of bones being the same in the hand of a man, wing of a bat, fin11 of the porpoise134, and leg of the horse,--the same number of vertebrae forming the neck of the giraffe and of the elephant,--and innumerable other such facts, at once explain themselves on the theory of descent with slow and slight successive modifications. The similarity of pattern in the wing and leg of a bat, though used for such different purpose,--in the jaws136 and legs of a crab,--in the petals137, stamens, and pistils of a flower, is likewise intelligible on the view of the gradual modification of parts or organs, which were alike in the early progenitor of each class. On the principle of successive variations not always supervening at an early age, and being inherited at a corresponding not early period of life, we can clearly see why the embryos138 of mammals, birds, reptiles139, and fishes should be so closely alike, and should be so unlike the adult forms. We may cease marvelling140 at the embryo133 of an air-breathing mammal or bird having branchial slits141 and arteries142 running in loops, like those in a fish which has to breathe the air dissolved in water, by the aid of well-developed branchiae.
Disuse, aided sometimes by natural selection, will often tend to reduce an organ, when it has become useless by changed habits or under changed conditions of life; and we can clearly understand on this view the meaning of rudimentary organs. But disuse and selection will generally act on each creature, when it has come to maturity143 and has to play its full part in the struggle for existence, and will thus have little power of acting on an organ during early life; hence the organ will not be much reduced or rendered rudimentary at this early age. The calf144, for instance, has inherited teeth, which never cut through the gums of the upper jaw135, from an early progenitor having well-developed teeth; and we may believe, that the teeth in the mature animal were reduced, during successive generations, by disuse or by the tongue and palate having been fitted by natural selection to browse145 without their aid; whereas in the calf, the teeth have been left untouched by selection or disuse, and on the principle of inheritance at corresponding ages have been inherited from a remote period to the present day. On the view of each organic being and each separate organ having been specially created, how utterly inexplicable it is that parts, like the teeth in the embryonic146 calf or like the shrivelled wings under the soldered147 wing-covers of some beetles148, should thus so frequently bear the plain stamp of inutility! Nature may be said to have taken pains to reveal, by rudimentary organs and by homologous structures, her scheme of modification, which it seems that we wilfully149 will not understand.
I have now recapitulated the chief facts and considerations which have thoroughly150 convinced me that species have changed, and are still slowly changing by the preservation and accumulation of successive slight favourable variations. Why, it may be asked, have all the most eminent70 living naturalists and geologists rejected this view of the mutability of species? It cannot be asserted that organic beings in a state of nature are subject to no variation; it cannot be proved that the amount of variation in the course of long ages is a limited quantity; no clear distinction has been, or can be, drawn between species and well-marked varieties. It cannot be maintained that species when intercrossed are invariably sterile, and varieties invariably fertile; or that sterility is a special endowment and sign of creation. The belief that species were immutable151 productions was almost unavoidable as long as the history of the world was thought to be of short duration; and now that we have acquired some idea of the lapse of time, we are too apt to assume, without proof, that the geological record is so perfect that it would have afforded us plain evidence of the mutation of species, if they had undergone mutation.
But the chief cause of our natural unwillingness152 to admit that one species has given birth to other and distinct species, is that we are always slow in admitting any great change of which we do not see the intermediate steps. The difficulty is the same as that felt by so many geologists, when Lyell first insisted that long lines of inland cliffs had been formed, and great valleys excavated153, by the slow action of the coast-waves. The mind cannot possibly grasp the full meaning of the term of a hundred million years; it cannot add up and perceive the full effects of many slight variations, accumulated during an almost infinite number of generations.
Although I am fully82 convinced of the truth of the views given in this volume under the form of an abstract, I by no means expect to convince experienced naturalists whose minds are stocked with a multitude of facts all viewed, during a long course of years, from a point of view directly opposite to mine. It is so easy to hide our ignorance under such expressions as the "plan of creation," "unity13 of design," etc., and to think that we give an explanation when we only restate a fact. Any one whose disposition154 leads him to attach more weight to unexplained difficulties than to the explanation of a certain number of facts will certainly reject my theory. A few naturalists, endowed with much flexibility155 of mind, and who have already begun to doubt on the immutability of species, may be influenced by this volume; but I look with confidence to the future, to young and rising naturalists, who will be able to view both sides of the question with impartiality156. Whoever is led to believe that species are mutable will do good service by conscientiously157 expressing his conviction; for only thus can the load of prejudice by which this subject is overwhelmed be removed.
Several eminent naturalists have of late published their belief that a multitude of reputed species in each genus are not real species; but that other species are real, that is, have been independently created. This seems to me a strange conclusion to arrive at. They admit that a multitude of forms, which till lately they themselves thought were special creations, and which are still thus looked at by the majority of naturalists, and which consequently have every external characteristic feature of true species,--they admit that these have been produced by variation, but they refuse to extend the same view to other and very slightly different forms. Nevertheless they do not pretend that they can define, or even conjecture, which are the created forms of life, and which are those produced by secondary laws. They admit variation as a vera causa in one case, they arbitrarily reject it in another, without assigning any distinction in the two cases. The day will come when this will be given as a curious illustration of the blindness of preconceived opinion. These authors seem no more startled at a miraculous158 act of creation than at an ordinary birth. But do they really believe that at innumerable periods in the earth's history certain elemental atoms have been commanded suddenly to flash into living tissues? Do they believe that at each supposed act of creation one individual or many were produced? Were all the infinitely159 numerous kinds of animals and plants created as eggs or seed, or as full grown? and in the case of mammals, were they created bearing the false marks of nourishment160 from the mother's womb? Although naturalists very properly demand a full explanation of every difficulty from those who believe in the mutability of species, on their own side they ignore the whole subject of the first appearance of species in what they consider reverent161 silence.
It may be asked how far I extend the doctrine of the modification of species. The question is difficult to answer, because the more distinct the forms are which we may consider, by so much the arguments fall away in force. But some arguments of the greatest weight extend very far. All the members of whole classes can be connected together by chains of affinities, and all can be classified on the same principle, in groups subordinate to groups. Fossil remains sometimes tend to fill up very wide intervals between existing orders. Organs in a rudimentary condition plainly show that an early progenitor had the organ in a fully developed state; and this in some instances necessarily implies an enormous amount of modification in the descendants. Throughout whole classes various structures are formed on the same pattern, and at an embryonic age the species closely resemble each other. Therefore I cannot doubt that the theory of descent with modification embraces all the members of the same class. I believe that animals have descended from at most only four or five progenitors, and plants from an equal or lesser number.
Analogy would lead me one step further, namely, to the belief that all animals and plants have descended from some one prototype. But analogy may be a deceitful guide. Nevertheless all living things have much in common, in their chemical composition, their germinal vesicles, their cellular162 structure, and their laws of growth and reproduction. We see this even in so trifling163 a circumstance as that the same poison often similarly affects plants and animals; or that the poison secreted164 by the gall-fly produces monstrous165 growths on the wild rose or oak-tree. Therefore I should infer from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial166 form, into which life was first breathed. When the views entertained in this volume on the origin of species, or when analogous views are generally admitted, we can dimly foresee that there will be a considerable revolution in natural history. Systematists will be able to pursue their labours as at present; but they will not be incessantly167 haunted by the shadowy doubt whether this or that form be in essence a species. This I feel sure, and I speak after experience, will be no slight relief. The endless disputes whether or not some fifty species of British brambles are true species will cease. Systematists will have only to decide (not that this will be easy) whether any form be sufficiently constant and distinct from other forms, to be capable of definition; and if definable, whether the differences be sufficiently important to deserve a specific name. This latter point will become a far more essential consideration than it is at present; for differences, however slight, between any two forms, if not blended by intermediate gradations, are looked at by most naturalists as sufficient to raise both forms to the rank of species. Hereafter we shall be compelled to acknowledge that the only distinction between species and well-marked varieties is, that the latter are known, or believed, to be connected at the present day by intermediate gradations, whereas species were formerly thus connected. Hence, without quite rejecting the consideration of the present existence of intermediate gradations between any two forms, we shall be led to weigh more carefully and to value higher the actual amount of difference between them. It is quite possible that forms now generally acknowledged to be merely varieties may hereafter be thought worthy of specific names, as with the primrose168 and cowslip; and in this case scientific and common language will come into accordance. In short, we shall have to treat species in the same manner as those naturalists treat genera, who admit that genera are merely artificial combinations made for convenience. This may not be a cheering prospect169; but we shall at least be freed from the vain search for the undiscovered and undiscoverable essence of the term species.
The other and more general departments of natural history will rise greatly in interest. The terms used by naturalists of affinity170, relationship, community of type, paternity, morphology, adaptive characters, rudimentary and aborted171 organs, etc., will cease to be metaphorical172, and will have a plain signification. When we no longer look at an organic being as a savage173 looks at a ship, as at something wholly beyond his comprehension; when we regard every production of nature as one which has had a history; when we contemplate174 every complex structure and instinct as the summing up of many contrivances, each useful to the possessor, nearly in the same way as when we look at any great mechanical invention as the summing up of the labour, the experience, the reason, and even the blunders of numerous workmen; when we thus view each organic being, how far more interesting, I speak from experience, will the study of natural history become!
A grand and almost untrodden field of inquiry175 will be opened, on the causes and laws of variation, on correlation of growth, on the effects of use and disuse, on the direct action of external conditions, and so forth176. The study of domestic productions will rise immensely in value. A new variety raised by man will be a far more important and interesting subject for study than one more species added to the infinitude of already recorded species. Our classifications will come to be, as far as they can be so made, genealogies177; and will then truly give what may be called the plan of creation. The rules for classifying will no doubt become simpler when we have a definite object in view. We possess no pedigrees or armorial bearings; and we have to discover and trace the many diverging lines of descent in our natural genealogies, by characters of any kind which have long been inherited. Rudimentary organs will speak infallibly with respect to the nature of long-lost structures. Species and groups of species, which are called aberrant178, and which may fancifully be called living fossils, will aid us in forming a picture of the ancient forms of life. Embryology will reveal to us the structure, in some degree obscured, of the prototypes of each great class.
When we can feel assured that all the individuals of the same species, and all the closely allied species of most genera, have within a not very remote period descended from one parent, and have migrated from some one birthplace; and when we better know the many means of migration, then, by the light which geology now throws, and will continue to throw, on former changes of climate and of the level of the land, we shall surely be enabled to trace in an admirable manner the former migrations179 of the inhabitants of the whole world. Even at present, by comparing the differences of the inhabitants of the sea on the opposite sides of a continent, and the nature of the various inhabitants of that continent in relation to their apparent means of immigration, some light can be thrown on ancient geography.
The noble science of Geology loses glory from the extreme imperfection of the record. The crust of the earth with its embedded180 remains must not be looked at as a well-filled museum, but as a poor collection made at hazard and at rare intervals. The accumulation of each great fossiliferous formation will be recognised as having depended on an unusual concurrence181 of circumstances, and the blank intervals between the successive stages as having been of vast duration. But we shall be able to gauge182 with some security the duration of these intervals by a comparison of the preceding and succeeding organic forms. We must be cautious in attempting to correlate as strictly contemporaneous two formations, which include few identical species, by the general succession of their forms of life. As species are produced and exterminated by slowly acting and still existing causes, and not by miraculous acts of creation and by catastrophes183; and as the most important of all causes of organic change is one which is almost independent of altered and perhaps suddenly altered physical conditions, namely, the mutual relation of organism to organism,--the improvement of one being entailing184 the improvement or the extermination of others; it follows, that the amount of organic change in the fossils of consecutive formations probably serves as a fair measure of the lapse of actual time. A number of species, however, keeping in a body might remain for a long period unchanged, whilst within this same period, several of these species, by migrating into new countries and coming into competition with foreign associates, might become modified; so that we must not overrate the accuracy of organic change as a measure of time. During early periods of the earth's history, when the forms of life were probably fewer and simpler, the rate of change was probably slower; and at the first dawn of life, when very few forms of the simplest structure existed, the rate of change may have been slow in an extreme degree. The whole history of the world, as at present known, although of a length quite incomprehensible by us, will hereafter be recognised as a mere fragment of time, compared with the ages which have elapsed since the first creature, the progenitor of innumerable extinct and living descendants, was created.
In the distant future I see open fields for far more important researches. Psychology185 will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Light will be thrown on the origin of man and his history.
Authors of the highest eminence186 seem to be fully satisfied with the view that each species has been independently created. To my mind it accords better with what we know of the laws impressed on matter by the Creator, that the production and extinction of the past and present inhabitants of the world should have been due to secondary causes, like those determining the birth and death of the individual. When I view all beings not as special creations, but as the lineal descendants of some few beings which lived long before the first bed of the Silurian system was deposited, they seem to me to become ennobled. Judging from the past, we may safely infer that not one living species will transmit its unaltered likeness187 to a distant futurity. And of the species now living very few will transmit progeny of any kind to a far distant futurity; for the manner in which all organic beings are grouped, shows that the greater number of species of each genus, and all the species of many genera, have left no descendants, but have become utterly extinct. We can so far take a prophetic glance into futurity as to foretel that it will be the common and widely-spread species, belonging to the larger and dominant groups, which will ultimately prevail and procreate new and dominant species. As all the living forms of life are the lineal descendants of those which lived long before the Silurian epoch49, we may feel certain that the ordinary succession by generation has never once been broken, and that no cataclysm188 has desolated189 the whole world. Hence we may look with some confidence to a secure future of equally inappreciable length. And as natural selection works solely by and for the good of each being, all corporeal and mental endowments will tend to progress towards perfection.
It is interesting to contemplate an entangled190 bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with Reproduction; Inheritance which is almost implied by reproduction; Variability from the indirect and direct action of the external conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the Extinction of less-improved forms. Thus, from the war of nature, from famine and death, the most exalted191 object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur192 in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed193 law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.
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immutability
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| n.不变(性) | |
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adoption
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| n.采用，采纳，通过；收养 | |
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briefly
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| adv.简单地，简短地 | |
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recapitulated
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| v.总结，扼要重述( recapitulate的过去式和过去分词 ) | |
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modification
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| n.修改，改进，缓和，减轻 | |
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analogous
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| adj.相似的；类似的 | |
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preservation
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| n.保护，维护，保存，保留，保持 | |
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deviation
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| n.背离，偏离；偏差，偏向；离题 | |
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conjecture
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| n./v.推测，猜测 | |
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specially
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| adv.特定地；特殊地；明确地 | |
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fin
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| n.鳍；(飞机的)安定翼 | |
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sterile
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| adj.不毛的，不孕的，无菌的，枯燥的，贫瘠的 | |
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unity
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| n.团结，联合，统一；和睦，协调 | |
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sterility
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| n.不生育，不结果，贫瘠，消毒，无菌 | |
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remarkable
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| adj.显著的，异常的，非凡的，值得注意的 | |
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conclusively
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| adv.令人信服地，确凿地 | |
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grafted
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| 移植( graft的过去式和过去分词 )； 嫁接； 使（思想、制度等）成为（…的一部份）； 植根 | |
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domestication
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| n.驯养，驯化 | |
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apparently
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| adv.显然地；表面上，似乎 | |
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hybrids
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| n.杂交生成的生物体( hybrid的名词复数 )；杂交植物（或动物）；杂种；（不同事物的）混合物 | |
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functionally
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| adv.机能上地，官能地 | |
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potent
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| adj.强有力的，有权势的；有效力的 | |
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organisation
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| n.组织，安排，团体，有机休 | |
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vigour
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| （=vigor）n.智力，体力，精力 | |
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lessen
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| vt.减少，减轻；缩小 | |
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lesser
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| adj.次要的，较小的；adv.较小地，较少地 | |
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geographical
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| adj.地理的；地区(性)的 | |
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descended
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| a.为...后裔的，出身于...的 | |
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isolated
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| adj.与世隔绝的 | |
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diffusion
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| n.流布；普及；散漫 | |
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migration
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| n.迁移，移居，（鸟类等的）迁徙 | |
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extinction
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| n.熄灭，消亡，消灭，灭绝，绝种 | |
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affected
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| adj.不自然的，假装的 | |
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lessened
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| 减少的，减弱的 | |
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chaos
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| n.混乱，无秩序 | |
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supplant
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| vt.排挤；取代 | |
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supplanted
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| 把…排挤掉，取代( supplant的过去式和过去分词 ) | |
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allied
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| adj.协约国的；同盟国的 | |
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exterminated
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| v.消灭，根绝( exterminate的过去式和过去分词 ) | |
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exterminate
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| v.扑灭，消灭，根绝 | |
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doctrine
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| n.教义；主义；学说 | |
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extermination
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| n.消灭，根绝 | |
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remains
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| n.剩余物，残留物；遗体，遗迹 | |
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mutation
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| n.变化，变异，转变 | |
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strata
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| n.地层（复数）；社会阶层 | |
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progenitor
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| n.祖先，先驱 | |
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progenitors
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| n.祖先( progenitor的名词复数 )；先驱；前辈；原本 | |
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utterly
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| adv.完全地，绝对地 | |
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epoch
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| n.(新)时代；历元 | |
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geologists
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| 地质学家，地质学者( geologist的名词复数 ) | |
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lapse
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| n.过失，流逝，失效，抛弃信仰，间隔；vi.堕落，停止，失效，流逝；vt.使失效 | |
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specimens
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| n.样品( specimen的名词复数 )；范例；（化验的）抽样；某种类型的人 | |
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countless
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| adj.无数的，多得不计其数的 | |
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possessed
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| adj.疯狂的；拥有的，占有的 | |
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naturalists
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| n.博物学家( naturalist的名词复数 )；（文学艺术的）自然主义者 | |
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rendering
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| n.表现，描写 | |
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considerably
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| adv.极大地；相当大地；在很大程度上 | |
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intermittent
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| adj.间歇的，断断续续的 | |
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intervals
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| n.[军事]间隔( interval的名词复数 )；间隔时间；[数学]区间；（戏剧、电影或音乐会的）幕间休息 | |
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degradation
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| n.降级；低落；退化；陵削；降解；衰变 | |
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sediment
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| n.沉淀，沉渣，沉积(物) | |
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subsiding
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| v.（土地）下陷（因在地下采矿）( subside的现在分词 )；减弱；下降至较低或正常水平；一下子坐在椅子等上 | |
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elevation
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| n.高度；海拔；高地；上升；提高 | |
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stationary
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| adj.固定的，静止不动的 | |
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recur
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| vi.复发，重现，再发生 | |
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consecutive
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| adj.连续的，联贯的，始终一贯的 | |
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varied
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| adj.多样的，多变化的 | |
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judgment
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| n.审判；判断力，识别力，看法，意见 | |
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overthrow
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| v.推翻，打倒，颠覆；n.推翻，瓦解，颠覆 | |
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eminent
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| adj.显赫的，杰出的，有名的，优良的 | |
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eminently
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| adv.突出地；显著地；不寻常地 | |
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72
susceptible
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| adj.过敏的，敏感的；易动感情的，易受感动的 | |
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73
correlation
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| n.相互关系，相关，关连 | |
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74
ascertaining
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| v.弄清，确定，查明( ascertain的现在分词 ) | |
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75
modifications
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| n.缓和( modification的名词复数 )；限制；更改；改变 | |
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76
domesticated
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| adj.喜欢家庭生活的；（指动物）被驯养了的v.驯化( domesticate的过去式和过去分词 ) | |
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77
aboriginal
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| adj.（指动植物）土生的，原产地的，土著的 | |
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78
efficiently
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| adv.高效率地，有能力地 | |
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79
acting
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| n.演戏，行为，假装；adj.代理的，临时的，演出用的 | |
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80
inevitably
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| adv.不可避免地；必然发生地 | |
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81
peculiar
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| adj.古怪的，异常的；特殊的，特有的 | |
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82
fully
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| adv.完全地，全部地，彻底地；充分地 | |
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83
progeny
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| n.后代，子孙；结果 | |
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84
incapable
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| adj.无能力的，不能做某事的 | |
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85
strictly
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| adv.严厉地，严格地；严密地 | |
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86
mere
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| adj.纯粹的；仅仅，只不过 | |
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87
sufficiently
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| adv.足够地，充分地 | |
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88
worthy
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| adj.(of)值得的，配得上的；有价值的 | |
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89
systematic
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| adj.有系统的，有计划的，有方法的 | |
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90
rigidly
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| adv.刻板地，僵化地 | |
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91
drawn
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| v.拖，拉，拔出；adj.憔悴的，紧张的 | |
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92
incipient
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| adj.起初的，发端的，初期的 | |
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93
intelligible
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| adj.可理解的，明白易懂的，清楚的 | |
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94
inordinately
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| adv.无度地，非常地 | |
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95
diversified
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| adj.多样化的，多种经营的v.使多样化，多样化( diversify的过去式和过去分词 )；进入新的商业领域 | |
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96
Augmented
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| adj.增音的 动词augment的过去式和过去分词形式 | |
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97
dominant
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| adj.支配的，统治的；占优势的；显性的；n.主因，要素，主要的人(或物)；显性基因 | |
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98
diverging
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| 分开( diverge的现在分词 )； 偏离； 分歧； 分道扬镳 | |
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99
inevitable
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| adj.不可避免的，必然发生的 | |
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100
contingency
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| n.意外事件，可能性 | |
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101
inexplicable
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| adj.无法解释的，难理解的 | |
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102
solely
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| adv.仅仅，唯一地 | |
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103
favourable
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| adj.赞成的，称赞的，有利的，良好的，顺利的 | |
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104
prodigal
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| adj.浪费的，挥霍的，放荡的 | |
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105
prey
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| n.被掠食者，牺牲者，掠食；v.捕食，掠夺，折磨 | |
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106
marvel
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| vi.(at)惊叹vt.感到惊异；n.令人惊异的事 | |
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107
abhorrent
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| adj.可恶的，可恨的，讨厌的 | |
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108
slaughtered
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| v.屠杀，杀戮，屠宰( slaughter的过去式和过去分词 ) | |
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109
pollen
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| n.[植]花粉 | |
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110
instinctive
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| adj.(出于)本能的；直觉的；(出于)天性的 | |
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111
hatred
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| n.憎恶，憎恨，仇恨 | |
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112
caterpillars
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| n.毛虫( caterpillar的名词复数 )；履带 | |
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113
burrowing
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| v.挖掘（洞穴），挖洞( burrow的现在分词 )；翻寻 | |
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114
moles
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| 防波堤( mole的名词复数 )； 鼹鼠； 痣； 间谍 | |
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115
habitually
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| ad.习惯地，通常地 | |
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116
generic
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| adj.一般的，普通的，共有的 | |
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117
corporeal
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| adj.肉体的，身体的；物质的 | |
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118
conspicuous
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| adj.明眼的，惹人注目的；炫耀的，摆阔气的 | |
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119
simultaneously
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| adv.同时发生地，同时进行地 | |
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120
diverged
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| 分开( diverge的过去式和过去分词 )； 偏离； 分歧； 分道扬镳 | |
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121
marshes
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| n.沼泽，湿地( marsh的名词复数 ) | |
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122
colonists
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| n.殖民地开拓者，移民，殖民地居民( colonist的名词复数 ) | |
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123
temperate
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| adj.温和的，温带的，自我克制的，不过分的 | |
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124
formerly
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| adv.从前，以前 | |
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125
derived
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| vi.起源；由来；衍生；导出v.得到( derive的过去式和过去分词 )；（从…中）得到获得；源于；（从…中）提取 | |
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126
cape
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| n.海角，岬；披肩，短披风 | |
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127
contingencies
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| n.偶然发生的事故，意外事故( contingency的名词复数 )；以备万一 | |
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128
divergence
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| n.分歧，岔开 | |
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129
mutual
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| adj.相互的，彼此的；共同的，共有的 | |
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130
affinities
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| n.密切关系( affinity的名词复数 )；亲近；（生性）喜爱；类同 | |
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131
circuitous
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| adj.迂回的路的，迂曲的，绕行的 | |
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132
paramount
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| a.最重要的，最高权力的 | |
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133
embryo
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| n.胚胎，萌芽的事物 | |
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134
porpoise
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| n.鼠海豚 | |
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135
jaw
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| n.颚，颌，说教，流言蜚语；v.喋喋不休，教训 | |
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136
jaws
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| n.口部；嘴 | |
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137
petals
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| n.花瓣( petal的名词复数 ) | |
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138
embryos
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| n.晶胚；胚，胚胎( embryo的名词复数 ) | |
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139
reptiles
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| n.爬行动物，爬虫( reptile的名词复数 ) | |
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140
marvelling
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| v.惊奇，对…感到惊奇( marvel的现在分词 ) | |
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141
slits
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| n.狭长的口子，裂缝( slit的名词复数 )v.切开，撕开( slit的第三人称单数 )；在…上开狭长口子 | |
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142
arteries
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| n.动脉( artery的名词复数 )；干线，要道 | |
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143
maturity
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| n.成熟；完成；(支票、债券等)到期 | |
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144
calf
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| n.小牛，犊，幼仔，小牛皮 | |
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145
browse
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| vi.随意翻阅，浏览；(牛、羊等)吃草 | |
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146
embryonic
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| adj.胚胎的 | |
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147
soldered
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| v.（使）焊接，焊合( solder的过去式和过去分词 ) | |
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148
beetles
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| n.甲虫( beetle的名词复数 ) | |
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149
wilfully
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| adv.任性固执地；蓄意地 | |
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150
thoroughly
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| adv.完全地，彻底地，十足地 | |
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151
immutable
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| adj.不可改变的，永恒的 | |
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152
unwillingness
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| n. 不愿意，不情愿 | |
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153
excavated
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| v.挖掘( excavate的过去式和过去分词 )；开凿；挖出；发掘 | |
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154
disposition
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| n.性情，性格；意向，倾向；排列，部署 | |
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155
flexibility
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| n.柔韧性，弹性，（光的）折射性，灵活性 | |
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156
impartiality
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| n. 公平, 无私, 不偏 | |
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157
conscientiously
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| adv.凭良心地；认真地，负责尽职地；老老实实 | |
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158
miraculous
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| adj.像奇迹一样的，不可思议的 | |
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159
infinitely
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| adv.无限地，无穷地 | |
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160
nourishment
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| n.食物，营养品；营养情况 | |
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161
reverent
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| adj.恭敬的，虔诚的 | |
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162
cellular
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| adj.移动的；细胞的，由细胞组成的 | |
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163
trifling
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| adj.微不足道的；没什么价值的 | |
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164
secreted
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| v.（尤指动物或植物器官）分泌( secrete的过去式和过去分词 )；隐匿，隐藏 | |
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165
monstrous
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| adj.巨大的；恐怖的；可耻的，丢脸的 | |
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166
primordial
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| adj.原始的；最初的 | |
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167
incessantly
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| ad.不停地 | |
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168
primrose
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| n.樱草，最佳部分， | |
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169
prospect
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| n.前景，前途；景色，视野 | |
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170
affinity
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| n.亲和力，密切关系 | |
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171
aborted
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| adj.流产的，失败的v.（使）流产( abort的过去式和过去分词 )；（使）（某事物）中止；（因故障等而）（使）（飞机、宇宙飞船、导弹等）中断飞行；（使）（飞行任务等）中途失败 | |
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172
metaphorical
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| a.隐喻的，比喻的 | |
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173
savage
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| adj.野蛮的；凶恶的，残暴的；n.未开化的人 | |
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174
contemplate
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| vt.盘算，计议；周密考虑；注视，凝视 | |
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175
inquiry
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| n.打听，询问，调查，查问 | |
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176
forth
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| adv.向前；向外，往外 | |
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177
genealogies
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| n.系谱，家系，宗谱( genealogy的名词复数 ) | |
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178
aberrant
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| adj.畸变的，异常的，脱离常轨的 | |
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179
migrations
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| n.迁移，移居( migration的名词复数 ) | |
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180
embedded
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| a.扎牢的 | |
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181
concurrence
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| n.同意；并发 | |
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182
gauge
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| v.精确计量；估计；n.标准度量；计量器 | |
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183
catastrophes
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| n.灾祸( catastrophe的名词复数 )；灾难；不幸事件；困难 | |
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184
entailing
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| 使…成为必要( entail的现在分词 )； 需要； 限定继承； 使必需 | |
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185
psychology
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| n.心理，心理学，心理状态 | |
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186
eminence
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| n.卓越，显赫；高地，高处；名家 | |
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187
likeness
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| n.相像，相似（之处） | |
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188
cataclysm
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| n.洪水，剧变，大灾难 | |
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189
desolated
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| adj.荒凉的，荒废的 | |
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190
entangled
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| adj.卷入的；陷入的；被缠住的；缠在一起的v.使某人（某物/自己）缠绕，纠缠于（某物中），使某人（自己）陷入（困难或复杂的环境中）( entangle的过去式和过去分词 ) | |
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191
exalted
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| adj.(地位等)高的，崇高的；尊贵的，高尚的 | |
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192
grandeur
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| n.伟大，崇高，宏伟，庄严，豪华 | |
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193
fixed
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| adj.固定的，不变的，准备好的；(计算机)固定的 | |
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