468 ORIGIN OF SPECIES 



Beings. — As the modified descendants of dominant species, 

 belonging to the larger genera, tend to inherit the advan- 

 tages 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 na- 

 ture. The larger and more dominant groups within each 

 class thus tend to go on increasing in size ; and they conse- 

 quently supplant many smaller and feebler groups. Thus we 

 can account for the fact that all organisms, recent and ex- 

 tinct, 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 proc- 

 ess of modification, how it is that the more ancient forms of 

 life often present characters in some degree intermediate 

 between exi.sting groups. As some few of the old and in- 

 termediate forms have transmitted to the present day de- 

 scendants 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 ex- 

 tremely few species; and such species as do occur are gen- 

 erally 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 favour- 

 able conditions. 



Mr. Waterhouse has remarked that^ when a member be- 



