176 THE ORIGIN OF SPECIES 



biT)Jken up, that is, which haye_as_yfit-Suffered least ex- 

 tinction, will, for a long period, continue- to. increage^ 

 But which groups will ultimately prevail, no man cun 

 predict; for we 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, an-^ leave no modified descendants; and 

 consequently that, of the species living at any one period, 

 extremely few will transmit descendants to a remote futu- 

 rity. I shall have to return to this subject in the chap- 

 ter on Classification, but I may add that as, according to 

 this view, extremely 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 exists so few classes in 

 each main division of the animal and vegetable king- 

 doms. Although few of the most ancient species have 

 left modified descendants, yet, at remote geological peri- 

 ods, 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 benehcial under 

 the organic and inorganic conditions to which each creat- 

 ure is exposed at all periods of life. The ultimate result 

 is that each creature tends to become more and more im- 

 i proved in relation to its conditions. This improvement 

 inevitably leads to the gradual advancement of the organ- 



