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In 1843-44, Prof. Haldeman in the Boston (U. S.) Journal of Nat. Hist., vol. iv., p. 468) has ably given the arguments for and against the hypothesis of the development and modification of species : he seems to me to lean towards the side of change.

The Vestiges of Creation appeared in 1844. In the last or tenth and much improved edition (1853, p. 155), the anonymous author says: “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. The author 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 earlier 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 calling in this country attention to the subject, and in removing prejudices.

In 1846, the veteran geologist, M. J. d'Omalius d'Halloz, published in an excellent, though short, paper (Bulletins de l'Acad. Roy. Bruxelles, tom. xiii., p. 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.

M. Isidore Geoffroy Saint Hilaire, in his Lectures delivered in 1850 (of which a Résumé appeared in the Revue et Mag. de Zoolog.,. Jan. 1851), briefly gives his reasons for believing that specific characters “sont fixes, pour chaque espèce, tant qu'elle se perpétue au milieu des mêmes circonstances, ils se modifient, si les circonstances ambiantes viennent à changer.” “En résumé, l'observation des animaux sauvages-démontre déjà la variabilité limitée des espèces. Les expériences sur les animaux sauvages devenus domestiques, et sur les animaux domestiques redevenus sauvages, la démontrent plus clairement encore. Ces mêmes expériences prouvent, de plus, que les differences produites peuvent être de valeur générique."

Mr. Herbert Spencer, in an Essay (originally published in the Leader, March, 1852, and republished in his Essays, 1858), has contrasted the theories of the creation and 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 treated Psychology on the principle of the necessary acquirement of each mental power and ca- . pacity 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 Esi says 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 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, 18 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 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 DARWIN Down, BROMLEY, KENT, Feb. 1860.

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