4 CONTROLLED NATURAL SELECTION 



On these three facts the theory may be said 

 to rest : 



1. Within a species, individuals differ in 

 value. 



2. Within a species, individuals differ in 

 structure. 



3. Within a species, individuals form socie- 

 ties. 



Further, there is a correlation between these 

 facts, in that the differences in value are 

 associated with the differences in structure. 

 Females are more valuable than males ; females 

 differ in structure from males other than in 

 their sexual organs. Young are more valuable 

 than old, and they too are different in structure. 

 The third fact is also correlated, in that differ- 

 ence in structure between male and female 

 and between young and old are especially to 

 be found in those animals which are closely 

 united socially, either sexually or into families. 



The theory can now be stated under four 

 headings : 



1. Natural Selection appreciates the differ- 

 ences in character which distinguish male from 

 female, young from old. 



2. Natural Selection must treat associations 

 of individuals as units, just as it does single 

 individuals. 



