HISTORICAL SKETCH 17 



minating 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 organization progresses by 

 sudden leaps, but that the effects produced by the condi- 

 tions of life are gradual. He argues with much force on 

 general grounds that species are not immutable produc- 

 tions. But I cannot see how the two supposed "impulses" 

 account in a scientific sense for the numerous and beauti- 

 ful coadaptations which we see throughout nature; I can- 

 not 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, immedi- 

 ately had a very wide circulation. In my opinion it has 

 done excellent service in this country in calling attention 

 to the subject, in removing prejudice, and in thus prepar- 

 ing the ground for the reception of analogous views. 



In 1846 the veteran geologist M, J. d'Omalius d'Halloy 

 published in an excellent though short paper ("Bulletins 

 de I'Acad. Roy. Bruxelles," tom. xiii. page 581) his opin- 

 ion 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. 



