4 INTRODUCTION. 



in any manner profitable to itself, under the complex and 

 sometimes varying conditions of life, will have a better 

 chance of surviving, and thus be naturally selected. From 

 the strong principle of inheritance, any selected variety 

 will tend to propagate its new and modified form. 



This fundamental subject of natural selection will be 

 treated at some length in the fourth chapter ; and we shall 

 then see how natural selection almost inevitably causes 

 much extension of the less improved forms of life, and 

 leads to what I have called divergence of character. In the 

 next chapter I shall discuss the complex and little known laws 

 of variation. In the five succeeding chapters, the most appar- 

 ent and gravest difficulties in accepting the theory will be 

 given ; namely, first, the difficulties of transitions, or how a 

 simple being or a simple organ can be changed and perfected 

 into a highly developed being or into an elaborately con- 

 structed 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 geological 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 

 unexplained 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 explain 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 wel- 

 fare 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 enter- 

 tained, and which I formerly entertained — namely, that 



