126 NATURAL SELECTION. Chap. IV. 



group, the later and more highly perfected sub-groups, 

 from branching out and seizing on many new places 

 in the polity of Nature, will constantly tend to supplant 

 and destroy the earlier and less improved sub-groups. 

 Small and broken groups and sub-groups will finally 

 tend to disappear. Looking to the future, we can pre- 

 dict that the groups of organic beings which are now 

 large and triumphant, and which are least broken up, 

 that is, which as yet have suffered least extinction, 

 will for a long period continue to increase. But which 

 groups will ultimately prevail, no man can predict; 

 for we well know that many groups, formerly most 

 extensively developed, have now become extinct. Look- 

 ing still more remotely to the future, we may predict 

 that, owing to the continued and steady increase of the 

 larger groups, a multitude of smaller groups will become 

 utterly extinct, and leave no modified descendants ; and 

 consequently that of the species living at any one period, 

 extremely few will transmit descendants to a remote 

 futurity. I shall have to return to this subject in the 

 chapter on Classification, but I may add that on this 

 view of extremely few of the more ancient species 

 having transmitted descendants, and on the view of all 

 the descendants of the same species making a class, 

 we can understand how it is that there exist but very 

 few classes in each main division of the animal and 

 vegetable kingdoms. Although extremely few of the 

 most ancient species may now have living and modified 

 descendants, yet at the most remote geological period, 

 the earth may have been as well peopled with many 

 species of many genera, families, orders, and classes, as 

 at the present day. 



Summary of Chapter. — If during the long course of 

 ages and under varying conditions of life, organic beings 



