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 



