igO THE DOCTRINE OF DESCENT. 



Artificial selection — and here we may speak of design 

 — produces perfection when, by mechanical and physio- 

 logical labour (the latter especially by means of suit- 

 able nutriment), it exercises the particular parts which 

 are to be perfected, and propagates the advantages 

 obtained. What we term natural selection is the epitome 

 of the improvements acquired by specialization in the 

 process of adaptation. The most faithful image of this 

 gradually acquired specialization is afforded by the 

 development of the individual, where from the undif- 

 ferentiated, by constantly increasing differentiation, the 

 mature animal is evolved in the plenitude of its ph\sio- 

 logical functions. That in the various animal groups 

 certain grades of perfection are attained, is an uncon- 

 troverted fact ; but every closer investigation shatters 

 the idol of design. The organism of the bird might 

 induce us to consider it, in the abstract, as modified 

 for the purpose of flight. But if design be allowed to 

 watch over the good flyers, the idea of design must be 

 abandoned with respect to the non-flyers, and, if some 

 idea is indispensable, adaptation must have its due. 

 Herewith the whole theory is broken down, and it will 

 be the same in every other case. 



How organic perfection stands with reference to the 

 idea of design, has been acutely and clearly expressed 

 by the author of the " Unconscious" {" Unbcvvussten"). 

 The theory of descent teaches that there is no inde- 

 pendence of the conditions co-operating in an organic 

 phenomenon ; rather that its increasing divergence from 

 a common neutral point was an effect of the same causes. 

 The theory of selection makes us acquainted with one 

 of these causes, and unquestionably the most important 



