CHAP. XV.] RECAPITULATION. 385 



changed slowly and in a graduated manner. We clearly see this 

 in the fossil remains from consecutive formations invariably being 

 much more closely related to each other, than are the fossils from 

 widely separated formations. 



Such is the sum of the several chief objections and difficulties 

 which may be justly urged against the theory ; and I have now 

 briefly recapitulated the answers and explanations which, as far 

 as I can see, may be given. I have felt these difficulties far too 

 heavily during many years to doubt their weight. But it deserves 

 especial notice that the more important objections relate to ques- 

 tions on which we are confessedly ignorant ; nor do we know how 

 ignorant we are. We do not know all the possible transitional 

 gradations between the simplest and the most perfect organs; it 

 cannot be pretended that we know all the varied means of Distri- 

 bution during the long lapse of years, or that we know how im- 

 perfect is the Geological Record. Serious as these several objections 

 are, in my judgment they are by no means sufficient to overthrow 

 the theory of descent with subsequent modification. 



Now let us turn to the other side of the argument. Under 

 domestication we see much variability, caused, or at least excited, 

 by changed conditions of life ; but often in so obscure a manner, 

 that we are tempted to consider the variations as spontaneous. 

 Variability is governed by many complex laws, by correlated 

 growth, compensation, the increased use and disuse of parts, and 

 the definite action of the surrounding conditions. There is much 

 difficulty in ascertaining how largely our domestic productions have 

 been modified ; but we may safely infer that the amount has been 

 large, and that modification can be inherited for long periods. As 

 long as the conditions of life remain the same, we have reason to 

 believe that a modification, which has already been inherited for 

 many generations, may continue to be inherited for an almost 

 infinite number of generations. On the other hand, we have 

 evidence that variability when it has once come into play, does 

 not cease under domestication for a very long period ; nor do we 

 know that it ever ceases, for new varieties are still occasionally 

 produced by our oldest domesticated productions. 



Variability is not actually caused by man ; he only unintention- 

 ally exposes organic beings to new conditions of life, and then 

 nature acts on the organisation and causes it to vary. But man 

 can and does select the variations given to him by nature, and 

 thus accumulates them in any desired manner. He thus adapts 

 animals and plants for his own benefit or pleasure. He may do 

 this methodically, or he may do it unconsciously by preserving the 

 individuals most useful or pleasing to him without any intention 

 of altering the breed. It is certain that he can largely influence 



