INTRODUCTION. 



simple being or a simple organ can be changed and perfected into 

 a highly developed being or into an elaborately constructed organ ; 

 secondly, the subject of Instinct, or the mental powers of animals : 

 thirdly, Hybridism, or the infertility of species and the fertility of 

 varieties when intercrossed ; and fourthly, the imperfection of the 

 Geological Record. In the next chapter I shall consider the geo- 

 logical succession of organic beings throughout time ; in the twelfth 

 and thirteenth, their geographical distribution throughout space ; in 

 the fourteenth, their classification or mutual affinities, both when 

 mature and in an embryonic condition. In the last chapter I shall 

 give a brief recapitulation of the whole work, and a few concluding 

 remarks. 



No one ought to feel surprise at much remaining as yet un- 

 explained in regard to the origin of species and varieties, if he make 

 due allowance for our profound ignorance in regard to the mutual 

 relations of the many beings which live around us. Who can ex- 

 plain why one species ranges widely and is very numerous, and 

 why another allied species has a narrow range and is rare? Yet 

 these relations are of the highest importance, for they determine the 

 present welfare and, as I believe, the future success and modification 

 of every inhabitant of this world. Still less do we know of the 

 mutual relations of the innumerable inhabitants of the world during 

 the many past geological epochs in its history. Although much 

 remains obscure, and will long remain obscure, I can entertain no 

 doubt, after the most deliberate study and dispassionate judgment 

 of which I am capable, that the view which most naturalists until 

 recently entertained, and which I formerly entertained — namely, 

 that each species has been independently created — is erroneous. 

 I am fully convinced that species are not immutable ; but that 

 those belonging to what are called the same genera are lineal 

 descendants of some other and generally extinct species, in the 

 same manner as the acknowledged varieties of any one species are 

 the descendants of that species. Furthermore, I am convinced 

 that Natural Selection has been the most important, but not the 

 exclusive, means of modification. 



