126 CONCLUDING EE1TAEKS. Chap. XXYIII, 



all the descendants of one common progenitor, and we must 

 admit that the whole vast amount of difference "between 

 these forms has primarily arisen from simple variability. 

 To consider the subject under this point of view is enough to 

 strike one dumb with amazement. But our amazement ought 

 to he lessened when we reflect that beings almost infinite in 

 number, during an almost infinite lapse of time, have often 

 had their whole organisation rendered in some degree 

 plastic, and that each slight modification of structure which 

 was in any way beneficial under excessively complex con- 

 ditions of life has been preserved, whilst each which was in 

 any way injurious has been rigorously destroyed. And the 

 long-continued accumulation of beneficial variations will 

 infallibly have led to structures as diversified, as beautifully 

 adapted for various purposes and as excellently co-ordinated, 

 as we see in the animals and plants around us. Hence I 

 have spoken of selection as the paramount power, whether 

 applied by man to the formation of domestic breeds, or by 

 nature to the production of species. I may recur to the 

 metaphor given in a former chapter : if an architect were 

 to rear a noble and commodious edifice, without the use of cut 

 stone, by selecting from the fragments at the base of a preci- 

 pice wedge-formed stones for his arches, elongated stones for 

 his lintels, and flat stones for his roof, we should admire his 

 skill and regard him as the paramount power. Now, the 

 fragments of stone, though indispensable to the architect, 

 bear to the edifice built by him the same relation which the 

 fluctuating variations of organic beings bear to the varied 

 and admirable structures ultimately acquired by their modified 

 descendants. 



Some authors have declared that natural selection explains 

 nothing, unless the precise cause of each slight individual 

 difference be made clear. If it were explained to a savage 

 utterly ignorant of the art of building, how the edifice had 

 been raised stone upon stone, and why wedge-formed frag- 

 ments were used for the arches, flat stones for the roof, &c. ; and 

 if the use of each part and of the whole building were pointed 

 out, it would be unreasonable if he declared that nothing had 

 been made char to him, because the precise cause of the shapa 



