Page - 468 - in The Origin of Species

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-