INTRODUCTION 3 



requiring the agency of certain insects to bring pollen from one 

 flower to the other, it is equally preposterous to account for the 

 structure of this parasite, with its relations to several distinct 

 organic beings, by the effects of external conditions, or of habit, 

 or of the volition of the plant itself. 



It is, therefore, of the highest importance to gain a clear insight 

 into the means of modification and coadaptation. At the com- 

 mencement of my observations it seemed to me probable that a 

 careful study of domesticated animals and of cultivated plants 

 would offer the best chance of making out this obscure problem. 

 Nor have I been disappointed; in this and in all other perplexing 

 cases I have invariably found that our knowledge, imperfect 

 though it be, of variation under domestication, afforded the best 

 and safest clew. I may venture to express my conviction of the 

 high value of such studies, although they have been very com- 

 monly neglected by naturalists. 



From these considerations, I shall devote the first chapter of 

 this abstract to variation under domestication. We shall thus see 

 that a large amount of hereditary modification is at least possible ; 

 and, what is equally or more important, we shall see how great 

 is the power of man in accumulating by his selection successive 

 slight variations. I will then pass on to the variability of species 

 in a state of nature; but I shall, unfortunately, be compelled to 

 treat this subject far too briefly, as it can be treated properly only 

 by giving long catalogues of facts. We shall, however, be enabled 

 to discuss what circumstances are most favorable to variation. In 

 the next chapter the struggle for existence among all organic be- 

 ings throughout the world, which inevitably follows from the 

 high geometrical ratio of their increase, will be considered. This 

 is the doctrine of Malthus, applied to the whole animal and vege- 

 table kingdoms. As many more individuals of each species are born 

 than can possibly survive; and as, consequently, there is a fre- 

 quently 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 inevitably causes much extension 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 com- 



