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, their specialisation for different functions. 141. I believe in the doctrine of descent with modification, notwithstandg that this or that particular change of structure cannot be accounted for, because this doctrine groups together explains, many general phenomena of nature. [6
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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 — Means 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
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ORGANS. CLASSIFICATION, groups subordinate to groups — Natural system — Rules and difficulties in classification, explained on the theory of descent with modification — Classification of varieties — Descent always used in classification — Analogical or adaptive characters — Affinities, general, complex and radiating — Extinction separates and defines groups — MORPHOLOGY, between members of the same class, between parts of the same individual — EMBRYOLOGY, laws of, explained by variations not
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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 wh. naturalists consider as showing true affinity between any two or more species, are those which have been inherited from a common parent, , in so far, all true classification is genealogical; that community of descent is the hidden bond which naturalists have been unconsciously seeking, not some unknown plan of creation, or the enunciation of
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), extinct, and have left no descendants. Hence the six new species descended from (I), and the eight descended from (A), will have to be ranked as very 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 G 2 [page] 124 NATURAL SELECTION. CHAP. IV
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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 — Means 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
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Batrachians, the older Fish, the older Cephalopods, and the eocene Mammals, with the more recent members of the same classes, we must admit that there is some truth in the remark. Let us see 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 genera, and the dotted lines diverging from them the
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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 inter- [page] 334 GEOLOGICAL SUCCESSION. CHAP. X
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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 once explained; for the inhabitants of each quarter of the world will obviously tend to leave in that quarter, during the next succeeding period of time, closely allied though in some degree modified descendants. If the inhabitants of one continent formerly differed greatly from
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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; yet in the long run that all undergo modification to some extent. The extinction of old forms is the almost inevitable consequence of the production of new forms. We can understand why when a species has
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and other distant points of the southern hemisphere, is, on my 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 commencement of the Glacial period for their migration, and for their subsequent modification to the necessary degree. The facts seem to me to indicate that peculiar and very distinct species have migrated in radiating lines from some common centre; and I am
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the recent period all existing islands have been nearly or quite joined to some continent. This view would remove many difficulties, but it would not, I think, 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
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CHAPTER XIII. MUTUAL AFFINITIES OF ORGANIC BEINGS: MORPHOLOGY: EMBRYOLOGY: RUDIMENTARY ORGANS. CLASSIFICATION, groups subordinate to groups — Natural system — Rules and difficulties in classification, explained on the theory of descent with modification — Classification of varieties — Descent always used in classification — Analogical or adaptive characters — Affinities, general, complex and radiating — Extinction separates and defines groups — MORPHOLOGY, between members of the same class
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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 between any two or more species, are those which have been inherited from a common parent, and, in so far, all true classification is genealogical; that community of descent is the hidden bond which naturalists have been
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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 young
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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 [page] 456 SUMMARY. CHAP. XIII
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, together with their modification through natural selection, with its contingencies of extinction and divergence of character. In considering this view of classification, it should be borne in mind that the element of descent has been universally used in ranking together the sexes, ages, and acknowledged varieties of the same species, however different they may be in structure. If we extend the use of this element of descent,—the only certainly known cause of similarity in organic beings,—we shall
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inferences briefly recapitulated. That many and grave objections may be advanced against the theory of descent with modification 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 analogous with, human reason, but by the accumulation of innumerable slight variations, each good for the individual
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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, lessen fertility; and on the other hand, lesser changes in the conditions of life and crosses between less modified forms, increase fertility. Turning to geographical distribution, the difficulties encountered on the theory of descent with modification are
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judgment they do not overthrow 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 eminently susceptible 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 correlation of growth, by use and disuse, and by the
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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
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, 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 [page] 477 CHAP. XIV. RECAPITULATION
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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 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
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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 Y 2 [page] 484 CONCLUSION. CHAP. XIV
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embryo becomes at any period of life active and has to provide for itself;—of the embryo apparently having sometimes a higher organisation than the mature animal, into which it is developed. I believe that all these facts can be explained, 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
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F1577
Periodical contribution:
Barlow, Nora ed. 1963. Darwin's ornithological notes. Bulletin of the British Museum (Natural History). Historical Series 2 (7): 201-278. With introduction, notes and appendix by the editor.
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three and a half years, which I believe made him a confirmed believer in descent with modification. In his wanderings he had become physically and mentally aware of the biological barriers of sea, sterile plain and the Cordillera Range, and the part they played in geographical isolation; the succession of forms was there before his eyes, but he had not yet found his working model of Natural Selection. VI. Sixthly and finally follows the Zoology of the Beagle, Vol. II, 4to, published with the
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F1577
Periodical contribution:
Barlow, Nora ed. 1963. Darwin's ornithological notes. Bulletin of the British Museum (Natural History). Historical Series 2 (7): 201-278. With introduction, notes and appendix by the editor.
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should have been created. We can see this in the light of later knowledge as a very transparent curtain to evolutionary views far advanced. But I believe that already by 1834-35 there were questions being asked in the O.N.s that could only have been based on a groping belief in some form of descent with modification. I have looked up the equivalent passage in the early draft in Vol. 31 i, C.U.L. Handlist p. 277, reverse, Wilmot paper, 1828. Darwin writes from Valparaiso, dated Aug.-Sep. 1834: It
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F1574a
Pamphlet:
de Beer, Gavin ed. 1960. Darwin's notebooks on transmutation of species. Part I. First notebook [B] (July 1837-February 1838). Bulletin of the British Museum (Natural History). Historical Series 2 (2) (January): 23-73.
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arises how this is to be reconciled with Darwin's statement2 written in 1876 referring to the Essay of 1844: But at that time I overlooked one problem of great importance. This problem is the tendency in organic beings descended from the same stock to diverge in character as they become modified . In trying to explain this discrepancy, Sir Francis Darwin3 was mistaken in thinking that descent with modification necessarily implies divergence; evolution might take place along single lines without
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F1574c
Pamphlet:
de Beer, Gavin ed. 1960. Darwin's notebooks on transmutation of species. Part III. Third notebook [D] (July 15 to October 2nd 1838). Bulletin of the British Museum (Natural History). Historical Series 2 (4) (July):119-150.
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wolf-like Fox of East and West Falkland Islands. If there is the slightest foundation for these remarks, the Zoology of Archipelagoes will be well worth examining; for such facts would undermine the stability of species. The problem presented to Darwin did not admit of many degrees of freedom in its solution. If the various species had not all been specially created with the observed differences between them ready-made, then they must have been produced by descent with modification from their
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F1555
Book:
Darwin, Francis ed. 1909. The foundations of The origin of species, a sketch written in 1842. Cambridge: University Press.
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original creations. But if the descendants of A have peopled the earth by beating out other forms, they must have diverged in occupying the innumerable diverse modes of life from which they expelled their predecessors. What I wrote2 on this subject in 1887 is I think true: Descent with modification implies divergence, and we become so habituated to a belief in descent, and therefore in divergence, that we do not notice the absence of proof that divergence is in itself an advantage. I have called
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F1556
Book:
Darwin, Francis ed. 1909. The foundations of The origin of species. Two essays written in 1842 and 1844. Cambridge: University Press.
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the earth by beating out other forms, they must have diverged in occupying the innumerable diverse modes of life from which they expelled their predecessors. What I wrote2 on this subject in 1887 is I think true: Descent with modification implies divergence, and we become so habituated to a belief in descent, and therefore in divergence, that we do not notice the absence of proof that divergence is in itself an advantage. The fact that there is no set discussion on the principle of divergence in
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CUL-DAR185.109a
Figure:
[[1858--1882.04.19]]
`christstmas piece', watercolour drawings, some on reverse of drafts and old notes by Darwin Charles Robert
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, generally, but not universally, resembling each other;—of the structure of the embryo not being closely related to its conditions of existence, except when the embryo becomes at any period of life active and has to provide for itself;—of the embryo apparently having sometimes a higher organisation than the mature animal, into which it is developed. I believe that all these facts can be explained, as follows, on the view of descent with modification.] [left side and bottom of page excised] '48'
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different species within the same class, generally, but not universally, resembling each other;—of the structure of the embryo not being closely related to its conditions of existence, except when the embryo becomes at any period of life active and has to provide for itself;—of the embryo apparently having sometimes a higher organisation than the mature animal, into which it is developed. I believe that all these facts can be explained, as follows, on the view of descent with modification.] [48v
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F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
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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 — Means 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
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F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
Text
Image
PDF
ORGANS. CLASSIFICATION, groups subordinate to groups — Natural system — Rules and difficulties in classification, explained on the theory of descent with modification — Classification of varieties — Descent always used in classification — Analogical or adaptive characters — Affinities, general, complex and radiating — Extinction separates and defines groups — MORPHOLOGY, between members of the same class, between parts of the same individual — EMBRYOLOGY, laws of, explained by variations not
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F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
Text
Image
PDF
), extinct, and have left no descendants. Hence the six new species descended from (I), and the eight descended from (A), will have to be ranked as very 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 G 2 [page] 124 NATURAL SELECTION. CHAP. IV
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F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
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 — Means 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
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F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
Text
Image
PDF
Batrachians, the older Fish, the older Cephalopods, and the eocene Mammals, with the more recent members of the same classes, we must admit that there is some truth in the remark. Let us see 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 genera, and the dotted lines diverging from them the
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F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
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 inter- [page] 334 GEOLOGICAL SUCCESSION. CHAP. X
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F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
Text
Image
PDF
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 once explained; for the inhabitants of each quarter of the world will obviously tend to leave in that quarter, during the next succeeding period of time, closely allied though in some degree modified descendants. If the inhabitants of one continent formerly differed greatly from
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F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
Text
Image
PDF
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; yet in the long run that all undergo modification to some extent. The extinction of old forms is the almost inevitable consequence of the production of new forms. We can understand why when a species has
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F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
Text
Image
PDF
and other distant points of the southern hemisphere, is, on my 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 commencement of the Glacial period for their migration, and for their subsequent modification to the necessary degree. The facts seem to me to indicate that peculiar and very distinct species have migrated in radiating lines from some common centre; and I am
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F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
Text
Image
PDF
the recent period all existing islands have been nearly or quite joined to some continent. This view would remove many difficulties, but it would not, I think, 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
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| 61% |
F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
Text
Image
PDF
CHAPTER XIII. MUTUAL AFFINITIES OF ORGANIC BEINGS: MORPHOLOGY: EMBRYOLOGY: RUDIMENTARY ORGANS. CLASSIFICATION, groups subordinate to groups — Natural system — Rules and difficulties in classification, explained on the theory of descent with modification — Classification of varieties — Descent always used in classification — Analogical or adaptive characters — Affinities, general, complex and radiating — Extinction separates and defines groups — MORPHOLOGY, between members of the same class
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F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
Text
Image
PDF
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 between any two or more species, are those which have been inherited from a common parent, and, in so far, all true classification is genealogical; that community of descent is the hidden bond which naturalists have been
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F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
Text
Image
PDF
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 young
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| 61% |
F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
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PDF
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 [page] 456 SUMMARY. CHAP. XIII
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F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
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Image
PDF
, together with their modification through natural selection, with its contingencies of extinction and divergence of character. In considering this view of classification, it should be borne in mind that the element of descent has been universally used in ranking together the sexes, ages, and acknowledged varieties of the same species, however different they may be in structure. If we extend the use of this element of descent,—the only certainly known cause of similarity in organic beings,—we shall
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| 61% |
F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
Text
Image
PDF
inferences briefly recapitulated. That many and grave objections may be advanced against the theory of descent with modification 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 analogous with, human reason, but by the accumulation of innumerable slight variations, each good for the individual
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| 61% |
F373
Book:
Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st ed., 1st issue.
Text
Image
PDF
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, lessen fertility; and on the other hand, lesser changes in the conditions of life and crosses between less modified forms, increase fertility. Turning to geographical distribution, the difficulties encountered on the theory of descent with modification are
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