WHAT ARE SPECIES 13 



find it to harmonise with the development hypothesis, that 

 Darwin devoted the whole of his life to collecting facts and 

 making experiments, the record of a portion of which he has 

 given us in a series of twelve masterly volumes. 



Proposed Mode of Treatment of the Subject. 



It is evidently of the most -vital importance to any theory 

 that its foundations should be absolutely secure. It is 

 therefore necessary to show, by a wide and comprehensive 

 array of facts, that animals and plants do perpetually vary in 

 the manner and to the amount requisite ; and that this takes 

 place in wild animals as well as in those which are domesti- 

 cated. It is necessary also to prove that all organisms do 

 tend to increase at the great rate alleged, and that this 

 increase actually occurs, under favourable conditions. We 

 have to prove, further, that variations of all kinds can be 

 increased and accumulated by selection ; and that the struggle 

 for existence to the extent here indicated actually occurs in 

 nature, and leads to the continued preservation of favourable 

 variations. 



These matters will be discussed in the four succeeding 

 chapters, though in a somewhat different order — the struggle 

 for existence and the power of rapid multiplication, which is 

 its cause, occupying the first place, as comprising those facts 

 which are the most fundamental and those which can be 

 perfectly explained without any reference to the less generally 

 understood facts of variation. These chapters will be followed 

 by a discussion of certain difficulties, and of the vexed question 

 of hybridity. Then will come a rather full account of the 

 more important of the complex relations of organisms to each 

 other and to the earth itself, which are either fully explained 

 or greatly elucidated by the theory. The concluding chapter 

 will treat of the origin of man and his relations to the lower 

 animals. 



