INTRODUCTION. 5 



able to variation. In the next chapter the Struggle for 

 Existence amongst all organic beings throughout the 

 world, which inevitably follows from the high geo- 

 metrical ratio of their increase, will be considered. 

 This is the doctrine of Malthus, applied to the whole 

 animal and vegetable kingdoms. As many more in- 

 dividuals of each species are born than can possibly 

 survive; and as, consequently, there is a frequently 

 recurring struggle for existence, 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 in- 

 evitably causes much Extinction of the less improved 

 forms of life, and leads to what I have called Diver- 

 gence 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 transitions, 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 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 im- 

 perfection of the Geological Eecord. In the next 

 chapter I shall consider the geological succession of 



