506 ORIGIN OF SPECIES 



manner. We clearly see this in the fossil remains from con- 

 secutive formations invariably being much more closely re- 

 lated to each other, than are the fossils from widely separated 

 formations. 



Such is the sum of the several chief objections and diffi- 

 culties 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 im- 

 portant objections relate to questions on which we are con- 

 fessedly ignorant; nor do we know how ignorant we are. 

 We do not know all the possible transitional gradations be- 

 tween the simplest and the most perfect 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 imper- 

 fect is the Geological Record. Serious as these several ob- 

 jections 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. 



