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 problème àréserver entièrement à l'avenir, supposé 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 resembled 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 the others to bear the diseases of the country. This race would consequently multiply, while the others would decrease; not only from their inability 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 in Dr Wells' work.
The Hon. and Rev. W. Herbert, afterwards Dean of Manchester, in the fourth volume of the 'Horticultural Transactions,' 1822, and in his work on the 'Amaryllidaceae' (1837, pp. 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 intercrossing, 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. p. 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 55th 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 'Gardener's Chronicle,'
on April 7th, 1860. The differences of Mr Matthew's view from mine are not of much importance; he seems to consider that the world was nearly depopulated at successive periods, and then re-stocked; and he gives as an alternative, that new forms may be generated ' without the presence of any mould 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, p. 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 (p. 6) as follows:- 'All species might have been varieties once, and many varieties are gradually becoming species by assuming constant and peculiar characters'; but farther on (p. 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. p. 468) has ably given the arguments for and against the hypothesis of the development and modification of species: he seems to lean towards the side of change.