MMMIISM 



the maintenance of life? (2) What is the cause by which 

 adaptations are produced ? 



Every one knows that the theory of natural selection is 

 based upon the conception of adaptation. It insists upon the 

 observed facts of the small differences among individuals of 

 the same species, competition in the struggle for existence, 

 and individual heredity ; and draws the inference that among 

 a number of different and competing individuals, those which 

 are more perfectly adapted to the conditions succeed in 

 maintaining life, and producing offspring, while the rest fail. 

 But if there are diagnostic and hereditary peculiarities which 

 are in no way essential or advantageous to the maintenance 

 of life, then these remain untouched by the argument. 

 Weismann in constructing a theory of variation which ex- 

 cluded the inheritance of acquired characters, and attributed 

 all constant and hereditary structure to selection, maintained 

 that every detail of structure was adaptive, was, if not 

 essential, at any rate advantageous, to the maintenance of life 

 or the accomplishment of reproduction. He adduced the 

 peculiarities of the whale as an illustration of this. But 

 such an argument is quite inadequate. The whale is a 

 specialised animal maintaining its life under special conditions, 

 and it is by no means obvious that all the characters of other 

 animals are equally adaptive, and further, there is, properly 

 speaking, no animal which can be correctly called the whale 

 without further definition. There are many species of whale, 

 and the question of the adaptive importance of specific 

 peculiarities is not discussed by Weismann. We thus arrive 

 at a subject of enormous extent, namely the determination 

 of the significance, in relation to the maintenance of the 

 individual or of the race, of all the structural peculiarities by 

 which the subdivisions of the animal kingdom are dis- 

 tinguished from one another ; a subject which may be briefly 

 described as the extent of adaptation in diagnostic characters. 



