RECAPITULATION AND CONCLUSION 419 



all species have changed ; and they have changed in 

 the manner which my theory requires, for they have 

 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 formations dis- 

 tant from each other in time. 



Such is the sum of the several chief objections and 

 difficulties which may justly be urged against my 

 theory ; and I have now briefly recapitulated the 

 answers and explanations which can be given to 

 them. I have felt these difficulties far too heavily 

 during many years to doubt their weight. But it de- 

 serves especial notice that the more important objec- 

 tions relate to questions 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 during the long lapse of years, or that 

 we know how imperfect the Geological Record is. 

 Grave as these several difficulties are, in my judgment 

 they do not overthrow the theory of descent from a few 

 created forms with subsequent modification. 



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

 Under domestication we see much variability. This 

 seems to be mainly due to the reproductive system 

 being eminently susceptible to changes in the condi- 

 tions of life ; so that this system, when not rendered 

 impotent, fails to reproduce oifspring exactly like the 

 parent-form. Variability is governed by many complex 

 laws, — by correlation of growth, by use and disuse, and 

 by the direct action of the physical conditions of life. 

 There is much difficulty in ascertaining how much 

 modification our domestic productions have undergone; 

 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, 



