114 ON THE ORIGIN OF SPECIES 



form having some advantage over other forms in the 

 struggle for existence, it will chiefly act on those which 

 already have some advantage; and the largeness of any 

 group shows that its species have inherited from a 

 common ancestor some advantage in common. Hence, 

 the struggle for the production of new and 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 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. 

 Looking still more remotely to the future, we may 

 predict that, owing to the continued and steady in- 

 crease 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 vege- 

 table kingdoms. Although extremely few of the most 

 ancient species may now have living and modified 



