Seite - 13 - in The Origin of Species

HISTORICAL SKETCH 13 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 be- come changed into permanent species, which arc no longer capable of intercrossing. Rafinesque, in his 'New Flora of North America,' pub- lished 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 charac- ters;" 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 modi- fication of species : he seems to lean towards the side of change. The 'Vestiges of Creation' appeared in 1844. In the tenth and much improved edition (1853) the anonymous author says (p. 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 re- cent, are, under the providence of God, the results, first, of an impulse which has been imparted to the forms of life, ad- vancing 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 ap- parently 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 co-adaptations which we see throughout nature; I cannot see that we thus gain