276 RECAPITULATION. [Chap. XV.. 



that species have all changed; and the;}i have changer^ 

 in the manner required by the theory, I'or. they havp 

 changed slowly and in a graduated manner. W. ^ clearl^ 

 see this in the fossil remains from consecutive foruidtions 

 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 Distribution dur- 

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

 perfect is the Geological Eecord. Serious as these sev- 

 eral objections are, in my judgment they are by no means 

 sufficient to overthrow the theory of descent with sub- 

 sequent 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, compen- 

 sation, 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 



