4 INTRODUCTION. 



the doctrine of Malthns, applied to the whole animal and 

 vegetable kingdoms. As many more individuals of each 

 species are born than can possibly survive; and as, conse- 

 quently, there is a frequently recurring struggle for exist- 

 ence, it follows that any being, if it vary however slightly 

 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 extinction 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 apparent and gravest difficulties in accepting the 

 theory will be given: namely, first, the difficulties of tran- 

 sitions, or how a simple being or a simple organ can be 

 changed and perfected into a highly developed being or 

 into an elaborately constructed organ; secondly, the sub- 

 ject 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 con- 

 sider the geological succession of organic beings through- 

 out time; in the twelfth and thirteenth, their geogi'aphical 

 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 ransre 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 modifica- 



