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

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

distinct genera, or even as distinct sub-families. Thus it is, as I believe, that two or more genera are produced by descent with modification, from two or more species of the same genus. And the two or more parent-species are supposed to have descended from some one species of an earlier genus. In our diagram, this is indicated by the broken lines, beneath the capital [page] 13

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 Nature non facit saltum Organs of small inportance Organs not in all cases absolutely perfect The law of Unity of Type and of the Conditions of

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

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

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

descended from I, also broken up into two families. Nor can the existing species, descended from A, be ranked in the same genus with the parent A; or those from I, with the parent I. But the existing genus F14 may be supposed to have been but slightly modified; and it will then rank with the parent-genus F; just as [page] 49

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

succession of the same types within the same areas Summary of preceding and present chapter. LET us now see whether the several facts and rules relating to the geological succession of organic beings, better accord with the common view of the immutability of species, or with that of their slow and gradual modification, through descent and natural selection. New species have appeared very slowly, one after another, both on the land and in the waters. Lyell has shown that it is hardly possible to

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

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

of species. If numerous species, belonging to the same genera or families, have really started into life at once, the fact would be fatal to the theory of descent with slow modification through natural selection. For the development of a group [page] 36

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

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

F3510    Book contribution:     Darwin, C. R. 1897. [Letters to Farrar, 1867, 1871 and recollection of Darwin]. In F. W. Farrar, Men I have known. New York: Crowell, pp. 140-9.   Text

weak; and now, after hearing what you say, I feel sure that this is the case, and that your cause will ultimately triumph. My indirect interest in your book has been increased from Mr. Hensleigh Wedgwood, whom you often quote, being my brother-in-law. No one could dissent from my views on the modification of species with more courtesy than you do. But from the tenor of your mind I feel an entire and comfortable conviction (and which cannot possibly be disturbed), that if your studies led you to

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

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

be that the inhabitants of the several islands had descended from each other, undergoing modification in the course of their descent; and that all the inhabitants of the archipelago had descended from those of the nearest land, namely America, whence colonists would naturally have been derived. But it long remained to me an inexplicable problem how the necessary degree of modification could have been effected, and it would have thus remained for ever, had I not studied domestic productions, and

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

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

be either artificial,—that is, founded on any arbitrary character,—or natural. With varieties a natural classification is certainly founded, and with species is apparently founded, on community of descent, together with the amount of modification which the forms have undergone. The characters by which domestic varieties differ from each other are more [page] 41

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

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

sides with equal ease; the pupil was small and oval, or rather a parallelogram with the ends cut off, and lying transversely across the ball. A new and strange breed might probably have been formed by careful breeding and selection from this animal. I have often speculated on the probable causes through which each separate district in Great Britain came to possess in former times its own peculiar breed of cattle; and the question is, perhaps, even more perplexing in the case of Southern Africa

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

sides with equal ease; the pupil was small and oval, or rather a parallelogram with the ends cut off, and lying transversely across the ball. A new and strange breed might probably have been formed by careful breeding and selection from this animal. I have often speculated on the probable causes through which each separate district in Great Britain came to possess in former times its own peculiar breed of cattle; and the question is, perhaps, even more perplexing in the case of Southern Africa

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

previously remarked, than the retention during many ages of rudimentary organs, or even only of a tendency to the production of a rudiment; but there is no reason to suppose that all dormant gemmules would be transmitted and propagated for ever. Excessively minute and numerous as they are believed to be, an infinite number derived, during a long course of modification and descent, from each cell of each progenitor, could not be supported or nourished by the organism. On the other hand, it does

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

were specifically different, though most closely related to each other. The archipelago. With its innumerable craters and bare streams of lava, appeared to be of recent origin; and thus I fancied myself brought near to the very act of creation. I often asked myself how these many peculiar animals and plants had been produced: the simplest answer seemed to be that the inhabitants of the several islands had descended from each other, undergoing modification in the course of their descent; and that

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

Product of variation, we can understand why they have not become feral, for the great amount of modification which they have undergone shows how long and how thoroughly they have been domesticated; and this would unfit them for a wild life. Fourthly. If it be assumed that the characteristic differences between the various domestic races are due to descent from several aboriginal species, we must conclude that man chose for domestication in ancient times, either intentionally or by chance, a

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

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

racters alone. This fact is explicable through the doctrine of natural selection; for each successive modification of structure in each natural species is preserved, solely because it is of service; and such modifications when largely accumulated imply a great change in the habits of life, and this will almost certainly lead to other changes of structure throughout the whole organisation. On the other hand, if the several races of the pigeon have been produced by man through selection and

F387    Book:     Darwin, C. R. 1869. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 5th ed. Tenth thousand.   Text   Image   PDF

other such cases, is intelligible, for generally within the same country, the existing and the extinct will be closely 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