INTRODUCTION. 3 



let this opportunity pass without expressing my deep 

 obligations to Dr. Hooker, who for the last fifteen years 

 has aided me in every possible way by his large stores 

 of knowledge and his excellent judgment. 



In considering the Origin of Species, it is quite con- 

 ceivable that a naturalist, reflecting on the mutual 

 affinities of organic beings, on their embryological rela- 

 tions, their geographical distribution, geological succes- 

 sion, and other such facts, might come to the conclusion 

 that each species had not been independently created, 

 but had descended, like varieties, from other species. 

 Nevertheless, such a conclusion, even if well founded, 

 would be unsatisfactory, until it could be shown how 

 the innumerable species inhabiting this world have been 

 modified, so as to acquire that perfection of structure 

 and coadaptation which most justly excites our admi- 

 ration. Naturalists continually refer to external con- 

 ditions, such as climate, food, &c, as the only possible 

 cause of variation. In one very limited sense, as we 

 shall hereafter see, this may be true ; but it is pre- 

 posterous to attribute to mere external conditions, the 

 structure, for instance, of the woodpecker, with its feet, 

 tail, beak, and tongue, so admirably adapted to catch 

 insects under the bark of trees. In the case of the 

 misseltoe, which draws its nourishment from certain 

 trees, which has seeds that must be transported by 

 certain birds,. and which has flowers with separate sexes 

 absolutely requiring the agency of certain insects to 

 bring pollen from one flower to the other, it is equally 

 preposterous to account for the structure of this parasite, 

 with its relations to several distinct organic beings, by 

 the effects of external conditions, or of habit, or of the 

 volition of the plant itself. 



The author of the * Vestiges of Creation ' would, I 

 presume, say that, after a certain unknown number of 



b2 



