378 Classification. Chap. xiv. 



that of the other members of the family to which it belonged. 

 There is, however, some difficulty on this head, for it is necessary 

 to suppose in some cases that ancient members belonging to several 

 distinct groups, before they had diverged to their present extent 

 accidentally resembled a member of another and protected group 

 in a sufficient degree to afford some slight protection ; this havino- 

 given the basis for the subsequent acquisition of the most perfect 

 resemblance. 



On the Nature of the Affinities connecting Organic Beings. — As 

 the modified descendants of dominant species, belonging to the 

 larger genera, tend to inherit the advantages which made the groups 

 to which they belong large and their parents dominant, they are 

 almost sure to spread widely, and to seize on more and more places 

 in the economy of nature. The larger and more dominant groups 

 within each class thus tend to go on increasing in size ; and they 

 consequently supplant many smaller and feebler groups. Thus we 

 can account for the fact that all organisms, recent and extinct, are 

 included under a few great orders, and under still fewer classes. As 

 showing how few the higher groups are in number, and how widely 

 they are spread throughout the world, the fact is striking that the 

 discovery of Australia has not added an insect belonging to a new 

 class ; and that in the vegetable kingdom, as I learn from Dr. Hooker, 

 it has added only two or three families of small size. 



In the chapter on Geological Succession I attempted to show, on 

 the principle of each group having generally diverged much in 

 character during the long-continued process of modification, how it 

 is that the more ancient forms of life often present characters in 

 some degree intermediate between existing groups. As some few of 

 the old and intermediate forms have transmitted to the present day 

 descendants but little modified, these constitute our so-called 

 osculant or aberrant species. The more aberrant any form is, the 

 greater must be the number of connecting forms which have been 

 exterminated and utterly lost. And we have some evidence of 

 aberrant groups having suffered severely from extinction, for they 

 are almost always represented by extremely few species ; and such 

 species as do occur are generally very distinct from each other, 

 which again implies extinction. The genera Ornithorhynchus and 

 Lepidosiren, for example, would not have been less aberrant had 

 each been represented by a dozen species, instead of as at present 

 by a single one, or by two or three. We can, I think, account for 

 this fact only by looking at aberrant groups as forms which have 

 been conquered by more successful competitors, with a few members 

 still preserved under unusually favourable conditions. 



