RECAPITULATION. 483 



difficulties which may be justly urged against the theory; 

 and I have now briefly recapitulated the answers and ex- 

 planations 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 imijortaut objections relate to questions on 

 which we are confessedly ignorant; nor do we* know how 

 ignorant we are. We do not know all the possible transi- 

 tional gradations between the simplest and the most per- 

 fect organs; it cannot be pretended that we know all the 

 varied means of Distribution during the long lapse of 

 years, or that we know how imperfect is the Geological 

 Eecord. 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 Tariability, caused, or at 

 least excited, by changed conditions of life; but often in so 

 obscure a manner, that we are tempted to consider the varia- 

 tions as spontaneous. Variability is governed by many com- 

 plex laws, by correlated growth, compensation, the increased 

 use and disuse of parts, and the definite action of the sur- 

 rounding conditions. There is much difliculty in ascer- 

 taining 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 evidence that variability, when 

 it has once come into play, does not cease under domesti- 

 cation for a very long period ; nor do we know that it 

 ever ceases, for new varieties are still occasionally pro- 

 duced by our oldest domesticated productions. 



Variability is not actually caused by man ; the only 

 unintentionally exposes organic beings to new conditions 

 of life and then nature acts on the organization 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 



