INTRODUCTION. 9 



The most interesting and important question in the science 

 of life is, as I have already remarked, that of the Origin The origin 

 of Species ; and this is an historical problem, or problem ° ^P^^ies. 

 of origin, in exactly the same sense as the problems of 

 geology, or that of the origin of the solar system. 



All problems concerning the development of living 

 beings are, by their definition, problems of origin : this 

 is true alike of the development of the individual and of 

 that of the species. The problems of geology, also, as we 

 have seen, are problems of origin. In one word, both of 

 these two classes of problems are historical. But there is 

 an important difference between them. The problems of The pro- 

 vital development are not only historical but genetic.^ vital de- 

 By this distinction I mean that the visible facts of geology velopment 

 are the results of causes acting from without and uncon- Explana-^°' 

 nected with each other ; but the facts of organization and tion of this 

 vital development are the results of causes which have 

 their seat in the nature of the living organism itself. This 

 distinction may perhaps not be quite intelligible without 

 further explanation. In vital development, every stage is History of 

 determined by that which has gone next before it. The ^gj^p^''' 

 egg of an insect gives origin to a worm-like larva ; this is ment. 

 transformed into a chrysalis, and the chrysalis into a 

 winged insect resembling the parent. These changes 

 follow each other in a fixed order, which depends, not on 

 any external agency, but on the mysterious laws of life 

 belonging to the species ; and the same laws determine the 

 result of the developing process — whether, for instance, its 

 laltimate product is to be a fly or a beetle. External 

 agencies may hinder these formative laws from coming into 

 action ; that is to say, they may destroy the life of the 

 larva, and so prevent the development of the mature form ; 

 but they cannot modify their action, except within very 

 narrow limits ; they cannot cause one species to be hatched 

 out of the eggs of another. I shall have to show, in the 

 chapters on the Origin of Species, how I believe this truth 

 to be quite reconcilable with the theory of the origin of 



1 Genetic, from genesis, " original production." 



