134 ORIGIN OF SPECIES 



modified descendants will mainly lie between the larger 

 groups which are all trying to increase in number. One 

 large group will slowly conquer another large group, reduce 

 its numbers, and thus lessen its chance of further variation 

 and improvement. Within the same large 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 disappear. Looking to the future, we can 

 predict that the groups of organic beings which are now 

 large and triumphant, and which are least broken up, that 

 is, which have as yet suffered least extinction, will, for a long 

 period, continue to increase. But which groups will ulti- 

 mately prevail, no man can predict; for we know that many 

 groups, formerly most extensively developed, have now be- 

 come extinct. Looking 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 Classi- 

 fication, but I may add that as, according to this view, ex- 

 tremely few of the more ancient species have transmitted 

 descendants to the present day, and, as all the descendants 

 of the same species form a class, we can understand how it 

 is that there exist so few classes in each main division of 

 the animal and vegetable kingdoms. Although few of the 

 most ancient species have left modified descendants, yet, at 

 remote geological periods, the earth may have been almost 

 as well peopled with species of many genera, families, orders, 

 and classes, as at the present time. 



ON THE DEGREE TO WHICH ORGANIZATION TENDS TO ADVANCE 



Natural Selection acts exclusively by the preservation and 

 accumulation of variations, which are beneficial under the 

 organic and inorganic conditions to which each creature is 

 exposed at all periods of life. The ultimate result is that each 



