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CONTRIBUTED BY THE AUTHOR TO THIS AMERICAN EDITION.
I WILL here attempt to give a brief, but I fear imperfect, sketch of the progress of opinion on the Origin of Species. The great majority of naturalists have believed that species were immutable productions and have been separately created: this view has been ably maintained by many authors. A few naturalists, and several who have not particularly studied natural history, believe, on the other hand, that species undergo modification, and that the existing forms of life have descended by true generation from pre-existing forms. Passing over authors of the classical period, and likewise Demaillet and Buffon, with whose writings I am not familiar, Lamarck was the first man, whose view that species undergo change excited much attention. This justly celebrated naturalist published his Philosophie Zoologique in 1809, and his Introduction to his Hist. Nat. des animaux sans Vertèbres in 1815, in which works he upholds the doctrine that species are descended from each other. He seems to have been chiefly led to this conclusion by the difficulty of distinguishing species and varieties,—by the almost perfect gradation of the forms in certain groups, and by the analogy of domestic productions. With respect to the means of modification, he attributed something to the action of
external conditions, something to the crossing of already existing forms, and much to use and disuse or 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 tended to progress, in order to account for the presence of very simple productions at the present day, he maintained that such forms were now spontaneously generated.
Geoffroy Saint Hilaire, as is stated in his Life by his Son, as early as 1795, suspected 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; but he was cautious, and, as his son says, "C'est donc un problème à reserver entièrement a l'avenir, supposé même que l'avenir doive avoir prise sur lui.”
In England, the Hon. and Rev. W. Herbert, afterwards Dean of Manchester, in his work on the Amaryllidaceae (1837, p. 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 by intercrossing and by variation have produced all our existing species.
*It is curious how completely my grandfather, Dr. Erasmus Darwin, anticipated these erroneous views in his Zoonomia (vol. i. pp. 500–510), published in 1794,
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 spe