194 THEORY OF EVOLUTION 



to new characters we do not know, although 

 we have no reason for supposing that they are 

 due to other than natural processes. 



Evolution has taken place t)y the incorpora- 

 tion into the race of those mutations that are 

 beneficial to the life and reproduction of the 

 organism. Natural selection as here defined 

 means both the increase in the number of 

 individuals that results after a beneficial muta- 

 tion has occurred (owing to the ability of living 

 matter to propagate )_and also that this prepon- 

 derance of certain kinds of individuals in a 

 population makes some further results more 

 probable than others. More than this, natural 

 selection can not mean, if factors are fixed and 

 are not changed by selection. 



