146 RESULTS OP THE ACTION OF [Chap. IV. 



most nearly related to each other in habits, constitution, 

 and structure. Hence all the intermediate forms be- 

 tween the earlier and later states, that is between tTie less 

 and more improved states of the same species, as well as 

 the original parent-species itself, will generally tend to 

 become extinct. So it probably will be with many whole 

 collateral lines of descent, which will be conquered by 

 later and improved lines. If, however, the modified 

 offspring of a species get into some distinct country, or 

 become quickly adapted to some quite new station, in 

 which offspring and progenitor do not come into com- 

 petition, both may continue to exist. 



If, then, our diagram be assumed to represent a con- 

 siderable amount of modification, species (A) and all the 

 earlier varieties will have become extinct, being replaced 

 by eight new species {a^* to m^*); and species (I) will 

 be replaced by six {n^* to z^*) new species. 



But we may go further than this. The original spe- 

 cies of our genus were supposed to resemble each other 

 in unequal degrees, as is so generally the case in nature; 

 species (A) being more nearly related to B, C, and D, 

 than to the other species; and species (I) more to G, 

 H, K, L, than to the others. These two species (A) and 

 (I) were also supposed to be very common and widely 

 diffused species, so that they must originally have had 

 some advantage over most of the other species of the 

 genus. Their modified descendants, fourteen in num- 

 ber at the fourteen-thousandth generation, will probably 

 have inherited some of the same advantages: they have 

 also been modified and improved in a diversified manner 

 at each stage of descent, so as to have become adapted 

 to many related places in the natural economy of their 

 country. It seems, therefore, extremely probable that 



