RECAPITULATION AND CONCLUSION 419 



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 Dis- 

 tribution 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 do- 

 mestication 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. Varia- 

 bility 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 diffi- 

 culty in ascertaining how largely our domestic productions have 

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

 large, and that modifications 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 evi- 

 dence 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 uninten- 

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

 nature acts on the organization and causes it to vary. But man C2in 

 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 me- 

 thodically, or he may do it unconsciously by preserving the indi- 

 viduals most useful or pleasing to him without any intention of 



