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eics 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 treated Psychology on the principle of the necessary acquirement of each mental power and capacity by gradation.

In 1852 (Revue Horticole, p. 102), M. Naudin, a distinguished botanist,* has expressly stated 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 can act under nature. He believes, like Dean Herbert, that species when nascent were more plastic He lays weight on what he calls the principle of finality, "puissance mystérieuse, indéterminée; fatalité pour les uns; pour les autres, volonté providentielle, dont l'action incessante sur les êtres vivants détermine, à toutes les époques de l'existence du monde, la forme, le volume et la durée de chacun d'eux, en raison de sa destinée dans l'ordre de choses dont il fait partie. C'est cette puissance qui harmonise chaque membre à l'ensemble en l'appropriant à la fonction qu'il doit remplir dans l'organisme général de la nature, fonction qui est pour lui sa raison d'être."

In 1853, a celebrated geologist, Count Keyserling (Bulletin de la Soc Geolog., 2d ser., tom, x., p. 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.

* M. Lecoq, another French botanist, entertains, I believe, analogous views on the modification and descent of Species.

The "Philosophy of Creation " has been treated in an admirable 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." I think this work can hardly have failed to have produced a great effect in every philosophical mind.

The third volume of the Journal of the Linnean Society (August, 1858) contains papers by Mr. Wallace and myself, in which, as stated in the introductory remarks to this volume, the theory of Natural Selection is promulgated.

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 dis tinct 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 tho whole series of changes which they have suffered."

In November, 1859, the first edition of this work was published. In December, 1859, Dr. Hooker published his Introduction to the Tasmanian Flora: in the first part of this admirable essay he admits the truth of the descent and modification of species; and supports this doctrine by many original and valuable observations.

Charles Darwtm

Down, Bromlet, Kent, Feb. 1860.

CONTENTS.

lmoDUCTion, ...... . Page I

CHAPTER I.

VARIATION UNDER DOMESTICATlON.

Causes of Variability—Effects of Habit—Correlation of Growth—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—Principle of Selection anciently followed, its Effects—Methodical and Unconscious Selection—Unknown Origin of our Domestic Productions—Circumstances favourable to Man's power of Selection, . 14

CHAPTER II.

VARIATION IIMI NATURE.

Variability-- Individual differences—Doubtful species—Wide ranging, much diffused, and common species vary most—Species of the larger genera in any country vary more 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 . . . . . .40

CHAPTER III.

STRUGGLE FOE EXISTENCE.

Bears on natural selection—The term used in a wide sense— Geometrical powers 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 speeies; often severe between species of the same genus—The relation of organism to organism the most important of all relations, . . . . .00

CHAPTER IV.

NATURAL SELECTION.

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—

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