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PREFACE
INTRODUCTION
CHAPTER I VARIATION UNDER DOMESTICATIO
CAUSES OF VARIABILITY
EFFECTS OF HABIT AND OF 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
BREEDS OF THE DOMESTIC PIGEON，THEIR DIFFERENCES AND ORIGIN
PRINCIPLES OF SELECTION ANCIENTLY FOLLOWED，AND THEIR EFFECTS
UNCONSCIOUS SELECTION
CIRCUMSTANCES FAVOURABLE TO MAN’S POWER OF SELECTION
CHAPTER II VARIATION UNDER NATURE
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 INCLUDED WITHIN THE LARGER GENERA RESEMBLE VARIETIES IN BEING VERY CLOSELY，BUT UNEQUALLY，RELATED TO EACH OTHER，AND IN HAVING RESTRICTED RANGES
SUMMARY
CHAPTER III STRUGGLE FOR EXISTENCE
THE TERM，STRUGGLE FOR EXISTENCE，USED IN A LARGE SENSE
GEOMETRICAL RATIO OF INCREASE
NATURE OF THE CHECKS TO INCREASE
COMPLEX RELATIONS OF ALL ANIMALS AND PLANTS TO EACH OTHER IN THE STRUGGLE FOR EXISTENCE
STRUGGLE FOR LIFE MOST SEVERE BETWEEN INDIVIDUALS AND VARIETIES OF THE SAME SPECIES
CHAPTER IV NATURAL SELECTION; OR THE SURV OF THE FITTEST
SEXUAL SELECTION
ILLUSTRATIONS OF THE ACTION OF NATURAL SELECTION，OR THE SURVIVAL OF THE FITTEST
ON THE INTERCROSSING OF INDIVIDUALS
CIRCUMSTANCES FAVOURABLE FOR THE PRODUCTION OF NEW FORMS THROUGH NATURAL SELECTION
EXTINCTION CAUSED BY NATURAL SELECTION
DIVERGENCE OF CHARACTER
THE PROBABLE EFFECTS OF THE ACTION OF NATURAL SELECTION THROUGH DIVERGENCE OF CHARACTER AND EXTINCTION，ON THE DESCENDANTS OF A COMMON ANCESTOR
ON THE DEGREE TO WHICH ORGANISATION TENDS TO ADVANCE
CONVERGENCE OF CHARACTER
SUMMARY OF CHAPTER
CHAPTER V LAWS OF VARIATION
EFFECTS OF THE INCREASED USE AND DISUSE OF PARTS，AS CONTROLLED BY NATURAL SELECTION
ACCLIMATISATION
CORRELATED VARIATION
COMPENSATION AND ECONOMY OF GROWTH
MULTIPLE，RUDIMENTARY，AND LOWLY-ORGANISED STRUCTURES ARE VARIABLE
A PART DEVELOPED IN ANY SPECIES IN AN EXTRAORDINARY DEGREE OR MANNER，IN COMPARISON WITH THE SAME PART IN ALLIED SPECIES，TENDS TO BE HIGHLY VARIABLE
SPECIFIC CHARACTERS MORE VARIABLE THAN GENERIC CHARACTERS
SECONDARY SEXUAL CHARACTERS VARIABLE
DISTINCT SPECIES PRESENT ANALOGOUS VARIATIONS，SO THAT A VARIETY OF ONE SPECIES OFTEN ASSUMES A CHARACTER PROPER TO AN ALLIED SPECIES，OR REVERTS TO SOME OF THE CHARACTERS OF AN EARLY PROGENITOR
SUMMARY
CHAPTER VI DIFFICULTIES OF THE THEORY
ON THE ABSENCE OR RARITY OF TRANSITIONAL VARIETIES
ON THE ORIGIN AND TRANSITION OF ORGANIC BEINGS WITH PECULIAR HABITS AND STRUCTURE
ORGANS OF EXTREME PERFECTION AND COMPLICATION
MODES Of TRANSITION
SPECIAL DIFFICULTIES OF THE THEORY OF NATURAL SELECTION
ORGANS OF LITTLE APPARENT IMPORTANCE，AS AFFECTED BY NATURAL SELECTION
UTILITARIAN DOCTRINE，HOW FAR TRUE：BEAUTY，HOW ACQUIRED
SUMMARY：THE LAW OF UNITY OF TYPE AND OF THE CONDITIONS OF EXISTENCE EMBRACED BY THE THEORY OF NATURAL SELECTION
CHAPTER VII MISCELLANEOUS OBJECTIONS TO THE THEORY OF NATURAL SELECTION
CHAPTER VIII INSTINCT
INHERITED CHANGES OF HABIT OR INSTINCT IN DOMESTICATED ANIMALS
SPECIAL INSTINCTS
INSTINCTS OF THE CUCKOO
SLAVE-MAKING INSTINCT
CELL-MAKING INSTINCT OF THE HIVE-BEE
OBJECTIONS TO THE THEORY OF NATURAL SELECTION AS APPLIED TO INSTINCTS：NEUTER AND STERILE INSECTS
SUMMARY
CHAPTER IX HYBRIDISM
DEGREES OF STERILITY
LAWS GOVERNING THE STERILITY OF FIRST CROSSES AND OF HYBRIDS
ORIGIN AND CAUSES OF THE STERILITY OF FIRST CROSSES AND OF HYBRIDS
RECIPROCAL DIMORPHISM AND TRIMORPHISM
FERTILITY OF VARIETIES WHEN CROSSED，AND OF THEIR MONGREL OFFSPRING，NOT UNIVERSAL
HYBRIDS AND MONGRELS COMPARED，INDEPENDENTLY OF THEIR FERTILITY
SUMMARY OF CHAPTER
CHAPTER X ON THE IMPERFECTION OF TH GEOLOGICAL RECORD
ON THE LAPSE OF TIME，AS INFERRED FROM THE RATE OF DEPOSITION AND EXTENT OF DENUDATION
ON THE POORNESS OF PALAEONTOLOGICAL COLLECTIONS
ON THE ABSENCE OF NUMEROUS INTERMEDIATE VARIETIES IN ANY SINGLE FORMATION
ON THE SUDDEN APPEARANCE OF WHOLE GROUPS OF ALLIED SPECIES
ON THE SUDDEN APPEARANCE OF GROUPS OF ALLIED SPECIES IN THE LOWEST KNOWN FOSSILIFEROUS STRATA
CHAPTER XI ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS
ON EXTINCTION
ON THE FORMS OF LIFE CHANGING ALMOST SIMULTANEOUSLY THROUGHOUT THE WORLD
ON THE AFFINITIES OF EXTINCT SPECIES TO EACH OTHER，AND TO LIVING FORMS
ON THE STATE OF DEVELOPMENT OF ANCIENT COMPARED WITH LIVING FORMS
ON THE SUCCESSION OF THE SAME TYPES WITHIN THE SAME AREAS，DURING THE LATER TERTIARY PERIODS
SUMMARY OF THE PRECEDING AND PRESENT CHAPTERS
CHAPTER XII GEOGRAPHICAL DISTRIBUTION
SINGLE CENTRES OF SUPPOSED CREATION
MEANS OF DISPERSAL
DISPERSAL DURING THE GLACIAL PERIOD
ALTERNATE GLACIAL PERIODS IN THE NORTH AND SOUTH
CHAPTER XIII GEOGRAPHICAL DISTRIBUTION? CONTINUED
FRESH-WATER PRODUCTIONS
ON THE INHABITANTS OF OCEANIC ISLANDS
ABSENCE OF BATRACHIANS AND TERRESTRIAL MAMMALS ON OCEANIC ISLANDS
ON THE RELATIONS OF THE INHABITANTS OF ISLANDS TO THOSE OF THE NEAREST MAINLAND
SUMMARY OF THE LAST AND PRESENT CHAPTERS
CHAPTER XIV MUTUAL AFFINITIES OF ORGANIC BEING MORPHOLOGY—EMBRYOLOGY—RUDIMENTAR ORGANS
CLASSIFICATION
ANALOGICAL RESEMBLANCES
ON THE NATURE OF THE AFFINITIES CONNECTING ORGANIC BEINGS
MORPHOLOGY
DEVELOPMENT AND EMBRYOLOGY
RUDIMENTARY，ATROPHIED，AND ABORTED ORGANS
SUMMARY
CHAPTER XV RECAPITULATION AND CONCLUSION
APPENDIX GLOSSARY OF THE PRINCIPA SCIENTIFIC TERMS USED IN THE PRESEN VOLUME

　　PREFACE
　　—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 of “the axiom of the continuous operation of creative power, or of the ordained becoming of living things.” Further on, 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.

　　auses of variability—Effects of habit and the use and disuse of arts—Correlated variation—Inheritance—Character of domestic arieties—Difficulty of distinguishing between varieties and pecies—Origin of domestic darieties from one or more species—omestic pigeons, their differences and origin—Principles of election, anciently followed, their effects—Methodical and nconscious selection—Unknown origin of our domestic roductions—Circumstances favorable to man’s power of selection
　　WHEN WE compare the individuals of the same variety or sub-variety of our older cultivated plants and animals, one of the first points which strikes us is, that they generally differ more from each other than do the individuals of any one species or variety in a state of nature. And if we reflect on the vast diversity of the plants and animals which have been cultivated, and which have varied during all ages under the most different climates and treatment, we are driven to conclude that this great variability is due to our domestic productions having been raised under conditions of life not so uniform as, and somewhat different from, those to which the parent species had been exposed under nature. There is, also, some probability in the view propounded by Andrew Knight, that this variability may be partly connected with excess of food. It seems clear that organic beings must be exposed during several generations to new conditions to cause any great amount of variation; and that, when the organisation has once begun to vary, it generally continues varying for many generations. No case is on record of a variable organism ceasing to vary under cultivation. Our oldest cultivated plants, such as wheat, still yield new varieties: our oldest domesticated animals are still capable of rapid improvement or modification.
　　As far as I am able to judge, after long attending to the subject, the conditions of life appear to act in two ways—directly on the whole organisation or on certain parts alone and in directly by affecting the reproductive system. With respect to the direct action, we must bear in mind that in every case, as Professor Weismann has lately insisted, and as I have incidently shown in my work on “Variation under Domestication,” there are two factors: namely, the nature of the organism and the nature of the conditions. The former seems to be much the more important; for nearly similar variations sometimes arise under, as far as we can judge, dissimilar conditions; and, on the other hand, dissimilar variations arise under conditions which appear to be nearly uniform. The effects on the offspring are either definite or in definite. They may be considered as definite when all or nearly all the offspring of individuals exposed to certain conditions during several generations are modified in the same manner. It is extremely difficult to come to any conclusion in regard to the extent of the changes which have been thus definitely induced. There can, however, be little doubt about many slight changes, such as size from the amount of food, colour from the nature of the food, thickness of the skin and hair from climate, etc. Each of the endless variations which we see in the plumage of our fowls must have had some efficient cause; and if the same cause were to act uniformly during a long series of generations on many individuals, all probably would be modified in the same manner. Such facts as the complex and extraordinary out growths which variably follow from the insertion of a minute drop of poison by a gall-producing insect, shows us what singular modifications might result in the case of plants from a chemical change in the nature of the sap.
　　In definite variability is a much more common result of changed conditions than definite variability, and has probably played a more important part in the formation of our domestic races. We see in definite variability in the endless slight peculiarities which distinguish the individuals of the same species, and which cannot be accounted for by inheritance from either parent or from some more remote ancestor. Even strongly-marked differences occasionally appear in the young of the same litter, and in seedlings from the same seed-capsule. At long intervals of time, out of millions of individuals reared in the same country and fed on nearly the same food, deviations of structure so strongly pronounced as to deserve to be called monstrosities arise; but monstrosities cannot be separated by any distinct line from slighter variations. All such changes of structure, whether extremely slight or strongly marked, which appear among many individuals living together, may be considered as the in definite effects of the conditions of life on each individual organism, in nearly the same manner as the chill effects different men in an in definite manner, according to their state of body or constitution, causing coughs or colds, rheumatism, or inflammation of various organs.