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

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

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

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

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

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

, 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

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

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

several lines of descent diverging from the parent-form A, will form an order; for all will have inherited something in common from their ancient and common progenitor. On the principle of the continued tendency to divergence of character, which was formerly illustrated by this diagram, the more recent any form is, the more it will generally differ from its ancient progenitor. Hence we can understand the rule that the most ancient fossils differ most from existing forms. We must not, however

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

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

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

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 conspicuous 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

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

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

F376    Book:     Darwin, C. R. 1860. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 2d ed., second 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

F376    Book:     Darwin, C. R. 1860. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 2d ed., second issue.   Text   Image   PDF

inferences briefly recapitulated. That many and serious 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

F376    Book:     Darwin, C. R. 1860. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 2d ed., second 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

F376    Book:     Darwin, C. R. 1860. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 2d ed., second issue.   Text   Image   PDF

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. It is

F376    Book:     Darwin, C. R. 1860. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 2d ed., second issue.   Text   Image   PDF

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 grave enough. All the

F376    Book:     Darwin, C. R. 1860. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 2d ed., second issue.   Text   Image   PDF

, 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 homologous organs, to whatever purpose applied, of the different species of a class; or to the homologous parts constructed on the same pattern in each individual animal and plant. On the principle of successive slight variations, not necessarily or generally supervening at a very early period of life, and being

F376    Book:     Darwin, C. R. 1860. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 2d ed., second 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] 12

F376    Book:     Darwin, C. R. 1860. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 2d ed., second issue.   Text   Image   PDF

several lines of descent diverging from the parent-form (A), will form an order; for all will have inherited something in common from their ancient and common progenitor. On the principle of the continued tendency to divergence of character, which was formerly illustrated by this diagram, the more recent any form is, the more it will generally differ from its ancient progenitor. Hence we can understand the rule that the most ancient fossils differ most from existing forms. We must not, however

F376    Book:     Darwin, C. R. 1860. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 2d ed., second 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

F376    Book:     Darwin, C. R. 1860. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 2d ed., second issue.   Text   Image   PDF

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 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

F376    Book:     Darwin, C. R. 1860. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 2d ed., second issue.   Text   Image   PDF

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

F381    Book:     Darwin, C. R. 1861. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 3d ed. Seventh 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 — 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

F381    Book:     Darwin, C. R. 1861. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 3d ed. Seventh thousand.   Text   Image   PDF

inferences briefly recapitulated. That many and serious 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

F381    Book:     Darwin, C. R. 1861. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 3d ed. Seventh thousand.   Text   Image   PDF

An organ, when rendered useless, may well be variable, for its variations cannot be checked by natural selection. At whatever period of life disuse or selection reduces an organ, and this will generally be when the being has come to maturity and to its full powers of action, the principle of inheritance at corresponding ages will reproduce the organ in its reduced state at the same age, and consequently will seldom affect or reduce it in the embryo. Thus we can understand the greater relative