IIG RESULTS OF THE ACTION OF C'kap. TV. 



than one modified descendant; for nalural selection Avill al- 

 ways act according to the nature of the places which arc either 

 unoccupied or not perfectly occupied by other beings ; and 

 this will depend on infinitely-complex relations. But, as a 

 general ruh>, the more diversified in structure tlic descendants 

 from any one species can be rendered, the more places they 

 will be enabled to seize on, and the more their modified pro- 

 geny will increase. In our diagram the line of succession is 

 liroken at regular intervals by small numbered letters marking 

 the succ(>ssivc forms which have become sufficiently distinct to 

 be recorded as varieties. But these breaks are imaginary, and 

 might have been inserted an^^vhere, after intervals long 

 enough to have allowed the accumulation of a considerable 

 amount of divergent variation. 



As all the modified descendants from a common and wide- 

 ly-diffused species, belonging to a large genus, Avill tend to 

 partake of the same advantages which made their parent suc- 

 cessful in life, they will generally go on multiplying in number 

 as well as diverging in character: this is represented in the 

 diagram by the several divergent branches proceeding from 

 (A). The modified offspring from the latter and more highly- 

 improved branches in the lines of descent, will, it is probable, 

 often take the place of, and so destroy, the earlier and less im- 

 j)i(ived branches : this is represented in the diagram by some 

 of the lower branches not reaching to the upper horizontal 

 lines. In some cases I do not doubt that the jirocess of modi- 

 fication will be confined to a single line of descent, and the 

 ntunber of the descendants Mill not be increased; althouglithe 

 amount of divergent modification may have been increased in 

 the successive generations. This case would be represented in 

 tlic diagram, if all the lines proceeding from (A) Avere removed, 

 excepting that from «* to rt'°. In the same way, for instance, the 

 English race-horse and English pointer have apparently both 

 gone on slowly diverging in character from their original stocks, 

 Mithout either having given oft' any fresh branches or races. 



After ten thousand generations, species (A) is sujiposed to 

 liave produced three forms, «",/'", and wi", which, from hav- 

 ing diverged in character during the successive generations, 

 will have come to differ largely, but jicrhaps unequally, from 

 each other and from their common jvarcnt. If we suppose the 

 amount of change between each horizontid line in our diagram 

 to be excessively small, these three forms may still be only 

 w('ll-mark,Ml varieties ; but we have only to suppose the steps 



