Search Results - The Complete Work of Charles Darwin Online

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

CHAPTER VI. DIFFICULTIES ON THEORY. Difficulties on the theory of descent with modification Transitions Absence or rarity of transitional varieties Transitions in habits of life Diversified habits in the same species Species with habits widely different from those of their allies Organs of extreme perfection Modes of transition Cases of difficulty Natura non facit saltum Organs of small importance Organs not in all cases absolutely perfect The law of Unity of Type and of the Conditions of

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

finishing this volume that large bodies of facts, otherwise inexplicable, can be explained by the theory of descent with modification, ought not to hesitate to go further, and to admit that a structure even as perfect as the eye of an eagle might have been formed by natural selection, although in this case he does not know the transitional steps. Even in the Vertebrata, so manifestly the most highly organized division of the animal kingdom, we can start, as in the former cases, from an eye, such as

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

how far these several facts and inferences accord with the theory of descent with modification. As the subject is somewhat complex, I must request the reader to turn to the diagram in the fourth chapter. We may suppose that the numbered letters represent [page] 39

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

the case. Thus, on the theory of descent with modification, the main facts with respect to the mutual affinities of the extinct forms of life to each other and to living forms, seem to me explained in a satisfactory manner. And they are wholly inexplicable on any other view. On this same theory, it is evident that the fauna of any great period in the earth's history will be intermediate in general character between that which preceded and that which succeeded it. Thus the species which lived at

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

half was formerly more closely allied, than it is at present, to the northern half. In a similar manner we know, from Falconer and Cautley's discoveries, that northern India was formerly more closely related in its mammals to Africa than it is at the present time. Analogous facts could be given in relation to the distribution of marine animals. On the theory of descent with modification, the great law of the long enduring, but not immutable, succession of the same types within the same areas, is at

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

difficulties, the other great leading facts in pal ontology seem to me simply to follow on the theory of descent with modification through natural selection. We can thus understand how it is that new species come in slowly and successively; how species of different classes do not necessarily change together, or at the same rate, or in the same degree; T 2 [page] 41

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

that towards the close of the Glacial period, icebergs, as suggested by Lyell, have been largely concerned in their dispersal. But the existence of several quite distinct species, belonging to genera exclusively confined to the south, at these and other distant points of the southern hemisphere, is, on the theory of descent with modification, a far more remarkable case of difficulty. For some of these species are so distinct, that we cannot suppose that there has been time since the

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

been nearly or quite joined to some continent. This view would remove many difficulties, but it would not explain all the facts in regard to insular productions. In the following remarks I shall not confine myself to the mere question of dispersal; but shall consider some other facts, which bear on the truth of the two theories of independent creation and of descent with modification. The species of all kinds which inhabit oceanic islands are few in number compared with those on equal continental

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

has been done, not because further research has detected important structural differences, at first overlooked, but because numerous allied species, with slightly different grades of difference, have been subsequently discovered. All the foregoing rules and aids and difficulties in classification are explained, if I do not greatly deceive myself, on the view that the natural system is founded on descent with modification; that the characters which naturalists consider as showing true affinity

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

laws of growth, but in order to excrete horny matter, as that the rudimentary nails on the fin of the manatee were formed for this purpose. On my view of descent with modification, the origin of rudimentary organs is simple. We have plenty of cases of rudimentary organs in our domestic productions, as the stump of a tail in tailless breeds, the vestige of an ear in earless breeds, the reappearance of minute dangling horns in hornless breeds of cattle, more especially, according to Youatt, in

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

as, or even sometimes more useful than, parts of high physiological importance. Rudimentary organs may be compared with the letters in a word, still retained in the spelling, but become useless in the pronunciation, but which serve as a clue in seeking for its derivation. On the view of descent with modification, we may conclude that the existence of organs in a rudimentary, imperfect, and useless condition, or quite aborted, far from presenting a strange difficulty, as they assuredly do on

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

extend the use of this element of descent, the only certainly known cause of similarity in organic beings, we shall understand what is meant by the natural system: it is genealogical in its attempted arrangement, and the grades of acquired difference are marked by the terms varieties, species, genera, families, orders, and classes. On this same view of descent with modification, all the great facts in Morphology become intelligible, whether we look to the same pattern displayed in the

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

encountered on the theory of descent with modification are serious enough. All the individuals of the same species, and all the species of the same genus, or even higher group, must have descended from common parents; and therefore, in however distant and isolated parts of the world they may now be found, they must in the course of successive generations have passed from some one point to all the others. We are often wholly unable even to conjecture how this could have been effected. Yet, as

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

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 the facts, which the record does give, strongly 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

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

, 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

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

The existence of closely allied or representative species in any two areas, implies, on the theory of descent with modification, that the same parents formerly 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 there. Wherever many closely allied yet distinct species occur, doubtful forms and varieties of the same species like-wise occur. It is a rule of high generality that the

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

within each great class have been created with plain, but deceptive, marks of descent from a single parent. 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

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

plained, as follows, on the view of descent with modification. It is commonly assumed, perhaps from monstrosities often affecting the embryo at a very early period, that slight variations necessarily appear at an equally early period. But we have little evidence on this head indeed the evidence rather points the other way; for it is notorious that breeders of cattle, horses, and various fancy animals, cannot positively tell, until some time after the animal has been born, what its merits or

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F385 Book: Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th ed. 8th thousand. Text Image PDF

very wide circulation. In my opinion it has done excellent service in this country in calling attention to the subject, in removing prejudice, and in thus preparing the ground for the reception of analogous views. In 1846 the veteran geologist M. J. d'Omalius d'Halloy published in an excellent, though short paper ('Bulletins de l'Acad. Roy. Bruxelles,' tom. xiii. p. 581), his opinion that it is more probable that new species have been produced by descent with modification, than that they have been

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F879.1 Book: Darwin, C. R. [1868]. The variation of animals and plants under domestication. With a preface by Asa Gray. New York: Orange Judd and Co. vol. 1. Text Image PDF

), that most wonderful fact in the whole round of natural history, namely, the similarity of members of the same great class in their embryonic condition, the embryo, for instance, of a mammal, bird, reptile, and fish being barely distinguishable, becomes simply intelligible. It is the consideration and explanation of such facts as these which has convinced me that the theory of descent with modification by means of natural selection is in the main true. These facts have as yet received no

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F877.1 Book: Darwin, C. R. 1868. The variation of animals and plants under domestication. London: John Murray. 1st ed., first issue. vol. 1. Text Image PDF

unbroken or continuous. New species come in gradually one by one. Ancient and extinct forms of life often show combined or intermediate characters, like the words of a dead language with respect to its several offshoots or living tongues. All these and other such facts seemed to me to point to descent with modification as the method of production of new groups of species. The innumerable past and present inhabitants of the world are connected together by the most singular and complex affinities, and

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F877.1 Book: Darwin, C. R. 1868. The variation of animals and plants under domestication. London: John Murray. 1st ed., first issue. vol. 1. Text Image PDF

embryonic growth (and both these principles can be shown to be probable from direct evidence), that most wonderful fact in the whole round of natural history, namely, the similarity of members of the same great class in their embryonic condition,—the embryo, for instance, of a mammal, bird, reptile, and fish being barely distinguishable,—becomes simply intelligible. It is the consideration and explanation of such facts as these which has convinced me that the theory of descent with modification by

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F877.2 Book: Darwin, C. R. 1868. The variation of animals and plants under domestication. London: John Murray. 1st ed., first issue. vol. 2. Text Image PDF

fail to retain their primordial state,—are the same with the parts which differ in the natural species of the same genus. As, on the theory of descent with modification, the species of the same genus have been modified since they branched off from a common progenitor, it follows that the characters by which they differ from each other have varied whilst other parts of the organisation have remained unchanged; and it might be argued that [page] 6

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F878.1 Book: Darwin, C. R. 1868. The variation of animals and plants under domestication. London: John Murray. 1st ed., second issue. vol. 1. Text Image PDF

unbroken or continuous. New species come in gradually one by one. Ancient and extinct forms of life often show combined or intermediate characters, like the words of a dead language with respect to its several offshoots or living tongues. All these and other such facts seemed to me to point to descent with modification as the method of production of new groups of species. The innumerable past and present inhabitants of the world are connected together by the most singular and complex affinities, and

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F878.1 Book: Darwin, C. R. 1868. The variation of animals and plants under domestication. London: John Murray. 1st ed., second issue. vol. 1. Text Image PDF

embryonic growth (and both these principles can be shown to be probable from direct evidence), that most wonderful fact in the whole round of natural history, namely, the similarity of members of the same great class in their embryonic condition, the embryo, for instance, of a mammal, bird, reptile, and fish being barely distinguishable, becomes simply inintelligible. It is the consideration and explanation of such facts as these which has convinced me that the theory of descent with modification by

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F878.2 Book: Darwin, C. R. 1868. The variation of animals and plants under domestication. London: John Murray. 1st ed., second issue. vol. 2. Text Image PDF

fail to retain their primordial state, are the same with the parts which differ in the natural species of the same genus. As, on the theory of descent with modification, the species of the same genus have been modified since they branched off from a common progenitor, it follows that the characters by which they differ from each other have varied whilst other parts of the organisation have remained unchanged; and it might be argued that [page] 6

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F879.1 Book: Darwin, C. R. [1868]. The variation of animals and plants under domestication. With a preface by Asa Gray. New York: Orange Judd and Co. vol. 1. Text Image PDF

The succession of the many distinct species of the same genus throughout the long series geological formations seems to have been unbroken or continuous. New species come in gradually one by one. Ancient and extinct forms of life often show combined or intermediate characters, like the words of a dead language with respect to its several offshoots or living tongues. All these and other such facts seemed to me point to descent with modification as the method of production of new groups of

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F877.1 Book: Darwin, C. R. 1868. The variation of animals and plants under domestication. London: John Murray. 1st ed., first issue. vol. 1. Text Image PDF

parallel manner,—in the seed being downy or glabrous, and in colour,—and in the florets being barbed or not barbed, c. Those who believe that all the kinds are descended from a single wild species may account for this parallel variation by the inheritance of a similar constitution, and a consequent tendency to vary in the same manner; and those who believe in the general theory of descent with modification may extend this view to the several species of wheat, if such ever existed in a state of

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F878.1 Book: Darwin, C. R. 1868. The variation of animals and plants under domestication. London: John Murray. 1st ed., second issue. vol. 1. Text Image PDF

parallel manner, in the seed being downy or glabrous, and in colour, and in the florets being barbed or not barbed, c. Those who believe that all the kinds are descended from a single wild species may account for this parallel variation by the inheritance of a similar constitution, and a consequent tendency to vary in the same manner; and those who believe in the general theory of descent with modification may extend this view to the several species of wheat, if such ever existed in a state of

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F879.1 Book: Darwin, C. R. [1868]. The variation of animals and plants under domestication. With a preface by Asa Gray. New York: Orange Judd and Co. vol. 1. Text Image PDF

they contain. Nearly all the races or species of wheat vary, as Godron29 has remarked, in an exactly parallel manner, in the seed being downy or glabrous, and in colour, and in the florets being barbed or not barbed, c. Those who believe that all the kinds are descended from a single wild species may account for this parallel variation by the inheritance of a similar constitution, and a consequent tendency to vary in the same manner; and those who believe in the general theory of descent with

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A610 Review: Anon. 1868. [Review of] Variation of animals and plants under domestication. Gardeners' Chronicle and Agricultural Gazette (22 February): 184. Text Image

discoveries, aud sagacious observations, that have lent so great a charm to his Journal, and made him as famous as a traveller, discoverer, and collector, as he now is as an experimenter and thinker. Nor can we conclude this preliminary sketch of his labours better than by the following quotation: It is the consideration and explanation of such facts as these, which has convinced me that the theory of descent with modification by means of Natural Selection is in the main true. These facts have as

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