INTRODUCTION 23 



account for the structure of this parasite, with its relations to 

 several distinct organic beings, by the effects of external condi- 

 tions, or of habit, or of the volition of the plant itself. 



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

 sight into the means of modification and coadaptation. At the 

 commencement 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 clue. 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 pos- 

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

 great is the power of man in accumulating by his Selection suc- 

 cessive slight variations. I will then pass on 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, how- 

 ever, be enabled to discuss what circumstances are most favour- 

 able to variation. In the next chapter the Struggle for Existence 

 amongst all organic beings 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 vegetable kingdoms. As many more individuals of 

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

 quently, there is a frequently recurrent 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 con- 

 ditions 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 Diver- 



