On the Origin of Species Darwin 1859
Darwins Buch On the Origin of Species. Sprache des Werks: English. Version: 1.
- On the Origin of Species The Voyage of the Beagle. The Origin of Species by means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life..
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The Voyage of the Beagle
The Origin of Species by means of Natural Selection;
Preservation of Favoured Races in the Struggle for Life.
By Charles Darwin, M.A., F.R.S., Author of "The Descent of Man," etc., etc.
Sixth London Edition, with all Additions and Corrections. The 6th Edition is often considered the definititive edition.
But with regard to the material world, we can at least go so far as this-- we can perceive that events are brought about not by insulated interpositions of Divine power, exerted in each particular case, but by the establishment of general laws.;--Whewell: Bridgewater Treatise.
The only distinct meaning of the word 'natural' is STATED, FIXED or SETTLED; since what is natural as much requires and presupposes an intelligent agent to render it so, i.e., to effect it continually or at stated times, as what is supernatural or miraculous does to effect it for once.--Butler: Analogy of Revealed Religion.
To conclude, therefore, let no man out of a weak conceit of sobriety, or an ill-applied moderation, think or maintain, that a man can search too far or be too well studied in the book of God's word, or in the book of God's works; divinity or philosophy; but rather let men endeavour an endless progress or proficience in both. --Bacon: Advancement of Learning.
AN HISTORICAL SKETCH
OF THE PROGRESS OF OPINION ON THE ORIGIN OF SPECIES,
PREVIOUSLY TO THE PUBLICATION OF THE FIRST EDITION OF THIS WORK.
I will here give a brief sketch of the progress of opinion on the Origin of Species. Until recently the great majority of naturalists believed that species were immutable productions, and had been separately created. This view has been ably maintained by many authors. Some few naturalists, on the other hand, have believed that species undergo modification, and that the existing forms of life are the descendants by true generation of pre existing forms. Passing over allusions to the subject in the classical writers (Aristotle, in his "Physicae Auscultationes" (lib.2, cap.8, s.2), after remarking that rain does not fall in order to make the corn grow, any more than it falls to spoil the farmer's corn when threshed out of doors, applies the same argument to organisation; and adds (as translated by Mr. Clair Grece, who first pointed out the passage to me), "So what hinders the different parts (of the body) from having this merely accidental relation in nature? as the teeth, for example, grow by necessity, the front ones sharp, adapted for dividing, and the grinders flat, and serviceable for masticating the food; since they were not made for the sake of this, but it was the result of accident. And in like manner as to other parts in which there appears to exist an adaptation to an end. Wheresoever, therefore, all things together (that is all the parts of one whole) happened like as if they were made for the sake of something, these were preserved, having been appropriately constituted by an internal spontaneity; and whatsoever things were not thus constituted, perished and still perish." We here see the principle of natural selection shadowed forth, but how little Aristotle fully comprehended the principle, is shown by his remarks on the formation of the teeth.), the first author who in modern times has treated it in a scientific spirit was Buffon. But as his opinions fluctuated greatly at different periods, and as he does not enter on the causes or means of the transformation of species, I need not here enter on details.
Lamarck was the first man whose conclusions on the subject excited much attention. This justly celebrated naturalist first published his views in 1801; he much enlarged them in 1809 in his Philosophie Zoologique, and subsequently, 1815, in the Introduction to his Hist. Nat. des Animaux sans Vertebres. In these works he up holds the doctrine that all species, including man, are descended from other species. He first did the eminent service of arousing attention to the probability of all change in the organic, as well as in the inorganic world, being the result of law, and not of miraculous interposition. Lamarck seems to have been chiefly led to his conclusion on the gradual change of species, by the difficulty of distinguishing species and varieties, by the almost perfect gradation of forms in certain groups, and by the analogy of domestic productions. With respect to the means of modification, he attributed something to the direct action of the physical conditions of life, something to the crossing of already existing forms, and much to use and disuse, that is, to the effects of habit. To this latter agency he seems to attribute all the beautiful adaptations in nature; such as the long neck of the giraffe for browsing on the branches of trees. But he likewise believed in a law of progressive development, and as all the forms of life thus tend to progress, in order to account for the existence at the present day of simple productions, he maintains that such forms are now spontaneously generated. (I have taken the date of the first publication of Lamarck from Isidore Geoffroy Saint- Hilaire's ("Hist. Nat. Generale", tom. ii. page 405, 1859) excellent history of opinion on this subject. In this work a full account is given of Buffon's conclusions on the same subject. It is curious how largely my grandfather, Dr. Erasmus Darwin, anticipated the views and erroneous grounds of opinion of Lamarck in his "Zoonomia" (vol. i. pages 500-510), published in 1794. According to Isid. Geoffroy there is no doubt that Goethe was an extreme partisan of similar views, as shown in the introduction to a work written in 1794 and 1795, but not published till long afterward; he has pointedly remarked ("Goethe als Naturforscher", von Dr. Karl Meding, s. 34) that the future question for naturalists will be how, for instance, cattle got their horns and not for what they are used. It is rather a singular instance of the manner in which similar views arise at about the same time, that Goethe in Germany, Dr. Darwin in England, and Geoffroy Saint-Hilaire (as we shall immediately see) in France, came to the same conclusion on the origin of species, in the years 1794-5.)
Geoffroy Saint-Hilaire, as is stated in his Life, written by his son, suspected, as early as 1795, that what we call species are various degenerations of the same type. It was not until 1828 that he published his conviction that the same forms have not been perpetuated since the origin of all things. Geoffroy seems to have relied chiefly on the conditions of life, or the "monde ambiant" as the cause of change. He was cautious in drawing conclusions, and did not believe that existing species are now undergoing modification; and, as his son adds, "C'est donc un probleme a reserver entierement a l'avenir, suppose meme que l'avenir doive avoir prise sur lui."
In 1813 Dr. W.C. Wells read before the Royal Society An Account of a White Female, part of whose skin resembles that of a Negro; but his paper was not published until his famous Two Essays upon Dew and Single Vision appeared in 1818. In this paper he distinctly recognises the principle of natural selection, and this is the first recognition which has been indicated; but he applies it only to the races of man, and to certain characters alone. After remarking that negroes and mulattoes enjoy an immunity from certain tropical diseases, he observes, firstly, that all animals tend to vary in some degree, and, secondly, that agriculturists improve their domesticated animals by selection; and then, he adds, but what is done in this latter case "by art, seems to be done with equal efficacy, though more slowly, by nature, in the formation of varieties of mankind, fitted for the country which they inhabit. Of the accidental varieties of man, which would occur among the first few and scattered inhabitants of the middle regions of Africa, some one would be better fitted than others to bear the diseases of the country. This race would consequently multiply, while the others would decrease; not only from their in ability to sustain the attacks of disease, but from their incapacity of contending with their more vigorous neighbours. The colour of this vigorous race I take for granted, from what has been already said, would be dark. But the same disposition to form varieties still existing, a darker and a darker race would in the course of time occur: and as the darkest would be the best fitted for the climate, this would at length become the most prevalent, if not the only race, in the particular country in which it had originated." He then extends these same views to the white inhabitants of colder climates. I am indebted to Mr. Rowley, of the United States, for having called my attention, through Mr. Brace, to the above passage of Dr. Wells' work.
The Hon. and Rev. W. Herbert, afterward Dean of Manchester, in the fourth volume of the Horticultural Transactions, 1822, and in his work on the Amaryllidaceae (1837, pages 19, 339), declares that horticultural experiments have established, beyond the possibility of refutation, that botanical species are only a higher and more permanent class of varieties. He extends the same view to animals. The dean believes that single species of each genus were created in an originally highly plastic condition, and that these have produced, chiefly by inter-crossing, but likewise by variation, all our existing species.
In 1826 Professor Grant, in the concluding paragraph in his well-known paper (Edinburgh Philosophical Journal, vol. XIV, page 283) on the Spongilla, clearly declares his belief that species are descended from other species, and that they become improved in the course of modification. This same view was given in his Fifty-fifth Lecture, published in the "Lancet" in 1834.
In 1831 Mr. Patrick Matthew published his work on Naval Timber and Arboriculture, in which he gives precisely the same view on the origin of species as that (presently to be alluded to) propounded by Mr. Wallace and myself in the Linnean Journal, and as that enlarged in the present volume. Unfortunately the view was given by Mr. Matthew very briefly in scattered passages in an appendix to a work on a different subject, so that it remained unnoticed until Mr. Matthew himself drew attention to it in the Gardeners' Chronicle, on April 7, 1860. The differences of Mr. Matthew's views from mine are not of much importance: he seems to consider that the world was nearly depopulated at successive periods, and then restocked; and he gives as an alternative, that new forms may be generated without the presence of any mold or germ of former aggregates. I am not sure that I understand some passages; but it seems that he attributes much influence to the direct action of the conditions of life. He clearly saw, however, the full force of the principle of natural selection.
The celebrated geologist and naturalist, Von Buch, in his excellent Description Physique des Isles Canaries (1836, page 147), clearly expresses his belief that varieties slowly become changed into permanent species, which are no longer capable of intercrossing.
Rafinesque, in his New Flora of North America, published in 1836, wrote (page 6) as follows: All species might have been varieties once, and many varieties are gradually becoming species by assuming constant and peculiar characters;" but further on (page 18) he adds, "except the original types or ancestors of the genus.
In 1843-44 Professor Haldeman (Boston Journal of Nat. Hist. U. States, vol. iv, page 468) has ably given the arguments for and against the hypothesis of the development and modification of species: he seems to lean toward the side of change.
The Vestiges of Creation appeared in 1844. In the tenth and much improved edition (1853) the anonymous author says (page 155): The proposition determined on after much consideration is, that the several series of animated beings, from the simplest and oldest up to the highest and most recent, are, under the providence of God, the results, FIRST, of an impulse which has been imparted to the forms of life, advancing them, in definite times, by generation, through grades of organisation terminating in the highest dicotyledons and vertebrata, these grades being few in number, and generally marked by intervals of organic character, which we find to be a practical difficulty in ascertaining affinities; SECOND, of another impulse connected with the vital forces, tending, in the course of generations, to modify organic structures in accordance with external circumstances, as food, the nature of the habitat, and the meteoric agencies, these being the 'adaptations' of the natural theologian. The author apparently believes that organisation progresses by sudden leaps, but that the effects produced by the conditions of life are gradual. He argues with much force on general grounds that species are not immutable productions. But I cannot see how the two supposed impulses account in a scientific sense for the numerous and beautiful coadaptations which we see throughout nature; I cannot see that we thus gain any insight how, for instance, a woodpecker has become adapted to its peculiar habits of life. The work, from its powerful and brilliant style, though displaying in the early editions little accurate knowledge and a great want of scientific caution, immediately had a 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, page 581) his opinion that it is more probable that new species have been produced by descent with modification than that they have been separately created: the author first promulgated this opinion in 1831.
Professor Owen, in 1849 (Nature of Limbs, page 86), wrote as follows: The archetypal idea was manifested in the flesh under diverse such modifications, upon this planet, long prior to the existence of those animal species that actually exemplify it. To what natural laws or secondary causes the orderly succession and progression of such organic phenomena may have been committed, we, as yet, are ignorant. In his address to the British Association, in 1858, he speaks (page li) of the axiom of the continuous operation of creative power, or of the ordained becoming of living things. Further on (page xc), after referring to geographical distribution, he adds, These phenomena shake our confidence in the conclusion that the Apteryx of New Zealand and the Red Grouse of England were distinct creations in and for those islands respectively. Always, also, it may be well to bear in mind that by the word 'creation' the zoologist means 'a process he knows not what. He amplifies this idea by adding that when such cases as that of the Red Grouse are "enumerated by the zoologist as evidence of distinct creation of the bird in and for such islands, he chiefly expresses that he knows not how the Red Grouse came to be there, and there exclusively; signifying also, by this mode of expressing such ignorance, his belief that both the bird and the islands owed their origin to a great first Creative Cause." If we interpret these sentences given in the same address, one by the other, it appears that this eminent philosopher felt in 1858 his confidence shaken that the Apteryx and the Red Grouse first appeared in their respective homes "he knew not how, or by some process "he knew not what.
This address was delivered after the papers by Mr. Wallace and myself on the Origin of Species, presently to be referred to, had been read before the Linnean Society. When the first edition of this work was published, I was so completely deceived, as were many others, by such expressions as the continuous operation of creative power, that I included Professor Owen with other palaeontologists as being firmly convinced of the immutability of species; but it appears (Anat. of Vertebrates, vol. iii, page 796) that this was on my part a preposterous error. In the last edition of this work I inferred, and the inference still seems to me perfectly just, from a passage beginning with the words no doubt the type- form, etc.(Ibid., vol. i, page xxxv), that Professor Owen admitted that natural selection may have done something in the formation of a new species; but this it appears (Ibid., vol. iii. page 798) is inaccurate and without evidence. I also gave some extracts from a correspondence between Professor Owen and the editor of the London Review, from which it appeared manifest to the editor as well as to myself, that Professor Owen claimed to have promulgated the theory of natural selection before I had done so; and I expressed my surprise and satisfaction at this announcement; but as far as it is possible to understand certain recently published passages (Ibid., vol. iii. page 798) I have either partially or wholly again fallen into error. It is consolatory to me that others find Professor Owen's controversial writings as difficult to understand and to reconcile with each other, as I do. As far as the mere enunciation of the principle of natural selection is concerned, it is quite immaterial whether or not Professor Owen preceded me, for both of us, as shown in this historical sketch, were long ago preceded by Dr. Wells and Mr. Matthews.
M. Isidore Geoffroy Saint-Hilaire, in his lectures delivered in 1850 (of which a Resume appeared in the Revue et Mag. de Zoolog., Jan., 1851), briefly gives his reason for believing that specific characters sont fixes, pour chaque espece, tant qu'elle se perpetue au milieu des memes circonstances: ils se modifient, si les circonstances ambiantes viennent a changer. En resume, L'OBSERVATION des animaux sauvages demontre deja la variabilite LIMITEE des especes. Les EXPERIENCES sur les animaux sauvages devenus domestiques, et sur les animaux domestiques redevenus sauvages, la demontrent plus clairment encore. Ces memes experiences prouvent, de plus, que les differences produites peuvent etre de VALEUR GENERIQUE. In his Hist. Nat. Generale (tom. ii, page 430, 1859) he amplifies analogous conclusions.
From a circular lately issued it appears that Dr. Freke, in 1851 (Dublin Medical Press, page 322), propounded the doctrine that all organic beings have descended from one primordial form. His grounds of belief and treatment of the subject are wholly different from mine; but as Dr. Freke has now (1861) published his Essay on the Origin of Species by means of Organic Affinity, the difficult attempt to give any idea of his views would be superfluous on my part.
Mr. Herbert Spencer, in an Essay (originally published in the Leader, March, 1852, and republished in his Essays, in 1858), has contrasted the theories of the Creation and the Development of organic beings with remarkable skill and force. He argues from the analogy of domestic productions, from the changes which the embryos of many species undergo, from the difficulty of distinguishing species and varieties, and from the principle of general gradation, that species have been modified; and he attributes the modification to the change of circumstances. The author (1855) has also treated Psychology on the principle of the necessary acquirement of each mental power and capacity by gradation.
In 1852 M. Naudin, a distinguished botanist, expressly stated, in an admirable paper on the Origin of Species (Revue Horticole, page 102; since partly republished in the Nouvelles Archives du Museum, tom. i, page 171), his belief that species are formed in an analogous manner as varieties are under cultivation; and the latter process he attributes to man's power of selection. But he does not show how selection acts under nature. He believes, like Dean Herbert, that species, when nascent, were more plastic than at present. He lays weight on what he calls the principle of finality, puissance mysterieuse, indeterminee; fatalite pour les uns; pour les autres volonte providentielle, dont l'action incessante sur les etres vivantes determine, a toutes les epoques de l'existence du monde, la forme, le volume, et la duree de chacun d'eux, en raison de sa destinee dans l'ordre de choses dont il fait partie. C'est cette puissance qui harmonise chaque membre a l'ensemble, en l'appropriant a la fonction qu'il doit remplir dans l'organisme general de la nature, fonction qui est pour lui sa raison d'etre. (From references in Bronn's Untersuchungen uber die Entwickelungs-Gesetze, it appears that the celebrated botanist and palaeontologist Unger published, in 1852, his belief that species undergo development and modification. Dalton, likewise, in Pander and Dalton's work on Fossil Sloths, expressed, in 1821, a similar belief. Similar views have, as is well known, been maintained by Oken in his mystical Natur-Philosophie. From other references in Godron's work Sur l'Espece, it seems that Bory St. Vincent, Burdach, Poiret and Fries, have all admitted that new species are continually being produced. I may add, that of the thirty-four authors named in this Historical Sketch, who believe in the modification of species, or at least disbelieve in separate acts of creation, twenty-seven have written on special branches of natural history or geology.)
In 1853 a celebrated geologist, Count Keyserling (Bulletin de la Soc. Geolog., 2nd Ser., tom. x, page 357), suggested that as new diseases, supposed to have been caused by some miasma have arisen and spread over the world, so at certain periods the germs of existing species may have been chemically affected by circumambient molecules of a particular nature, and thus have given rise to new forms.
In this same year, 1853, Dr. Schaaffhausen published an excellent pamphlet (Verhand. des Naturhist. Vereins der Preuss. Rheinlands', etc.), in which he maintains the development of organic forms on the earth. He infers that many species have kept true for long periods, whereas a few have become modified. The distinction of species he explains by the destruction of intermediate graduated forms. Thus living plants and animals are not separated from the extinct by new creations, but are to be regarded as their descendants through continued reproduction.
A well-known French botanist, M. Lecoq, writes in 1854 (Etudes sur Geograph. Bot. tom. i, page 250), On voit que nos recherches sur la fixite ou la variation de l'espece, nous conduisent directement aux idees emises par deux hommes justement celebres, Geoffroy Saint-Hilaire et Goethe. Some other passages scattered through M. Lecoq's large work make it a little doubtful how far he extends his views on the modification of species.
The Philosophy of Creation has been treated in a masterly manner by the Rev. Baden Powell, in his Essays on the Unity of Worlds, 1855. Nothing can be more striking than the manner in which he shows that the introduction of new species is a regular, not a casual phenomenon, or, as Sir John Herschel expresses it, a natural in contradistinction to a miraculous process.
The third volume of the Journal of the Linnean Society contains papers, read July 1, 1858, by Mr. Wallace and myself, in which, as stated in the introductory remarks to this volume, the theory of Natural Selection is promulgated by Mr. Wallace with admirable force and clearness.
Von Baer, toward whom all zoologists feel so profound a respect, expressed about the year 1859 (see Prof. Rudolph Wagner, Zoologisch-Anthropologische Untersuchungen, 1861, s. 51) his conviction, chiefly grounded on the laws of geographical distribution, that forms now perfectly distinct have descended from a single parent-form.
In June, 1859, Professor Huxley gave a lecture before the Royal Institution on the Persistent Types of Animal Life. Referring to such cases, he remarks, It is difficult to comprehend the meaning of such facts as these, if we suppose that each species of animal and plant, or each great type of organisation, was formed and placed upon the surface of the globe at long intervals by a distinct act of creative power; and it is well to recollect that such an assumption is as unsupported by tradition or revelation as it is opposed to the general analogy of nature. If, on the other hand, we view Persistent Types in relation to that hypothesis which supposes the species living at any time to be the result of the gradual modification of pre-existing species, a hypothesis which, though unproven, and sadly damaged by some of its supporters, is yet the only one to which physiology lends any countenance; their existence would seem to show that the amount of modification which living beings have undergone during geological time is but very small in relation to the whole series of changes which they have suffered.
In December, 1859, Dr. Hooker published his Introduction to the Australian Flora. In the first part of this great work he admits the truth of the descent and modification of species, and supports this doctrine by many original observations.
The first edition of this work was published on November 24, 1859, and the second edition on January 7, 1860.
VARIATION UNDER DOMESTICATION.
Causes of Variability -- Effects of Habit and the use or disuse of Parts -- Correlated Variation -- Inheritance -- Character of Domestic Varieties -- Difficulty of distinguishing between Varieties and Species -- Origin of Domestic Varieties from one or more Species -- Domestic Pigeons, their Differences and Origin -- Principles of Selection, anciently followed, their Effects -- Methodical and Unconscious Selection -- Unknown Origin of our Domestic Productions -- Circumstances favourable to Man's power of Selection.
Variability -- Individual Differences -- Doubtful species -- Wide ranging, much diffused, and common species, vary most -- Species of the larger genera in each country vary more frequently than the species of the smaller genera -- Many of the species of the larger genera resemble varieties in being very closely, but unequally, related to each other, and in having restricted ranges.
Its bearing on natural selection -- The term used in a wide sense -- Geometrical ratio of increase -- Rapid increase of naturalised animals and plants -- Nature of the checks to increase -- Competition universal -- Effects of climate -- Protection from the number of individuals -- Complex relations of all animals and plants throughout nature -- Struggle for life most severe between individuals and varieties of the same species; often severe between species of the same genus -- The relation of organism to organism the most important of all relations.
NATURAL SELECTION; OR THE SURVIVAL OF THE FITTEST.
Natural Selection -- its power compared with man's selection -- its power on characters of trifling importance -- its power at all ages and on both sexes -- Sexual Selection -- On the generality of intercrosses between individuals of the same species -- Circumstances favourable and unfavourable to the results of Natural Selection, namely, intercrossing, isolation, number of individuals -- Slow action -- Extinction caused by Natural Selection -- Divergence of Character, related to the diversity of inhabitants of any small area and to naturalisation -- Action of Natural Selection, through Divergence of Character and Extinction, on the descendants from a common parent -- Explains the Grouping of all organic beings -- Advance in organisation -- Low forms preserved -- Convergence of character -- Indefinite multiplication of species -- Summary.
Effects of changed conditions -- Use and disuse, combined with natural selection; organs of flight and of vision -- Acclimatisation -- Correlated variation -- Compensation and economy of growth -- False correlations -- Multiple, rudimentary, and lowly organised structures variable -- Parts developed in an unusual manner are highly variable; specific characters more variable than generic; secondary sexual characters variable -- Species of the same genus vary in an analogous manner -- Reversions to long-lost characters -- Summary.
Difficulties of the theory of descent with modification -- 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 Existence embraced by the theory of Natural Selection.
MISCELLANEOUS OBJECTIONS TO THE THEORY OF NATURAL SELECTION.
Longevity -- Modifications not necessarily simultaneous -- Modifications apparently of no direct service -- Progressive development -- Characters of small functional importance, the most constant -- Supposed incompetence of natural selection to account for the incipient stages of useful structures -- Causes which interfere with the acquisition through natural selection of useful structures -- Gradations of structure with changed functions -- Widely different organs in members of the same class, developed from one and the same source -- Reasons for disbelieving in great and abrupt modifications.
Instincts comparable with habits, but different in their origin -- Instincts graduated -- Aphides and ants -- Instincts variable -- Domestic instincts, their origin -- Natural instincts of the cuckoo, molothrus, ostrich, and parasitic bees -- Slave-making ants -- Hive-bee, its cell- making instinct -- Changes of instinct and structure not necessarily simultaneous -- Difficulties on the theory of the Natural Selection of instincts -- Neuter or sterile insects -- Summary.
Distinction between the sterility of first crosses and of hybrids -- Sterility various in degree, not universal, affected by close interbreeding, removed by domestication -- Laws governing the sterility of hybrids -- Sterility not a special endowment, but incidental on other differences, not accumulated by natural selection -- Causes of the sterility of first crosses and of hybrids -- Parallelism between the effects of changed conditions of life and of crossing -- Dimorphism and Trimorphism -- Fertility of varieties when crossed and of their mongrel offspring not universal -- Hybrids and mongrels compared independently of their fertility -- Summary.
ON THE IMPERFECTION OF THE GEOLOGICAL RECORD.
On the absence of intermediate varieties at the present day -- On the nature of extinct intermediate varieties; on their number -- On the lapse of time, as inferred from the rate of denudation and of deposition -- On the lapse of time as estimated in years -- On the poorness of our palaeontological collections -- On the intermittence of geological formations -- On the denudation of granitic areas -- On the absence of intermediate varieties in any one formation -- On the sudden appearance of groups of species -- On their sudden appearance in the lowest known fossiliferous strata -- Antiquity of the habitable earth.
ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS.
On the slow and successive appearance of new species -- On their different rates of change -- Species once lost do not reappear -- Groups of species follow the same general rules in their appearance and disappearance as do single species -- On extinction -- On simultaneous changes in the forms of life throughout the world -- On the affinities of extinct species to each other and to living species -- On the state of development of ancient forms -- On the succession of the same types within the same areas -- Summary of preceding and present chapter.
Present distribution cannot be accounted for by differences in physical conditions -- Importance of barriers -- Affinity of the productions of the same continent -- Centres of creation -- Means of dispersal by changes of climate and of the level of the land, and by occasional means -- Dispersal during the Glacial period -- Alternate Glacial periods in the north and south.
GEOGRAPHICAL DISTRIBUTION -- CONTINUED.
Distribution of fresh-water productions -- On the inhabitants of oceanic islands -- Absence of Batrachians and of terrestrial Mammals -- On the relation of the inhabitants of islands to those of the nearest mainland -- On colonisation from the nearest source with subsequent modification -- Summary of the last and present chapter.
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, between parts of the same individual -- Embryology, laws of, explained by variations not supervening at an early age, and being inherited at a corresponding age -- Rudimentary Organs; their origin explained -- Summary.
RECAPITULATION AND CONCLUSION.
Recapitulation of the objections to the theory of Natural Selection -- Recapitulation of the general and special circumstances in its favour -- Causes of the general belief in the immutability of species -- How far the theory of Natural Selection may be extended -- Effects of its adoption on the study of Natural history -- Concluding remarks.