THE SELECTING POWER OF ENEMIES 51 



tion or subtraction of one or more factors 

 to or from the specific environment. 



The subtraction of a factor may lead to 

 extinction of the species ; a food supply may 

 fail. Or if the species continues to thrive, 

 then those structures which were related to 

 the lost factor will degenerate. Those indi- 

 viduals who waste the least nourishment or 

 sustenance on a useless organ will have an 

 advantage over others in which this organ 

 is more developed. Degenerated organs are 

 found in species occupying degenerated en- 

 vironments. Degenerate structures will be 

 found to vary most because of the absence of 

 the fixing power of environmental selection. 



If a factor be subtracted locally, then a 

 local degenerate variety or sub-species will 

 be found. 



The addition of a new factor to the specific 

 environments may produce extinction. Short 

 of extinction, an added factor will prevent 

 a species fitting its environment perfectly ; 

 but sooner or later, as the result of variation 

 of the species and environmental selection, 

 new structures will arise which will enable 

 the species to perfectly fit the new environ- 

 ment. Further addition of factors will be 

 followed by the addition of new structures ; 



