358 THE EVOLUTION OF LIFE. 



well as Latin and Greek and certain extinct and spoken 

 languages of the East, are shown to have traits in 

 common, which, notwithstanding the wide gaps between 

 them, unite them together as one great class of Aryan lan- 

 guages; radically distinguished from the classes of lan- 

 guages spoken by the other great divisions of the human 

 race. 



§ 123. Now this kind of subordination of groups, which 

 we see arises in the course of continuous descent, multiplica- 

 tion, and divergence, is just the kind of subordination of 

 groups which plants and animals exhibit : it is just this 

 kind of subordination which has thrust itself on the attention 

 of naturalists, in spite of pre- conceptions. 



The original idea was that of arrangement in linear order. 

 We saw that even after a considerable acquaintance with the 

 structures of organisms had been acquired, naturalists con- 

 tinued their efforts to reconcile the facts with the notion of a 

 uni- serial succession. The accumulation of evidence necessi- 

 tated the breaking up of the imagined chain into groups 

 and sub-groups. Gradually there arose the conviction that 

 these groups do not admit of being placed in a line. And the 

 conception finally arrived at, is, that of certain great sub- 

 kingdoms, very widely divergent, each made up of classes 

 much less widely divergent, severally containing orders still 

 less divergent; and so on with genera and species. The 

 diagram on page 303, shows the general relations of these 

 divisions in their degrees of subordination. 



Hence this "grand fact in natural history of the subordina- 

 tion of group under group, which from its familiarity does 

 not always sufficiently strike us," is perfectly in harmony 

 with the hypothesis of evolution. The extreme significance 

 of this kind of relation among organic forms, is dwelt on by 

 Mr Dai win ; who shows how an ordinary genealogical tree 

 represents, on a small scale, a system of grouping analogous to 

 that which exists among organisms in general, and which is 



