326 EEV. J. T. GULICK ON 



variations in instinct may lead to different habits o£ sustentation, 

 and it is evident that, as soon as the qualities that win success 

 in the different sectioDs differ, the Natural Selection must 

 differ. 



It should be remembered, however, that the meaning of 

 anyone's statements on this subject will depend on his definitions 

 of the words used. What is meant by environment, external 

 conditions, and other similar terms ? Until we define we shall 

 only beat the air, however exact our statements may be. I 

 therefore repeat what I have elsewhere stated, that, according to 

 my definition, change in the environment is always change in 

 activities that lie outside of the species, or of the segregated 

 group of individuals that is under consideration. In Darwin's 

 usage, the phrase " Change in external conditions " seems to 

 carry the same meaning ; but in some places this can hardly be 

 the case, and accordingly great obscurity hangs over some of his 

 statements on the most important subjects. 



Diversity in the uses to which different sections of one species 

 put their powers, when appropriating resources from the same 

 environment, must produce diversity in the forms of variation 

 that are most successful in the different sections. This I call 

 Active Natural Selection as contrasted with Passive Natural 

 Selection, which varies according to difTerences in the environ- 

 ment. All diversities of Natural Selection that do not vary 

 according to differences in the environment must be classed as 

 diversities of Active Natural Selection, for they must have 

 originated in some variation in the powers of the organism, or in 

 the diversity of uses to which it has put its powers. Diversity 

 in the successful use of the powers of the species, whether ini- 

 tiated by diversity in the action of the species in its different 

 sections, or by diversity in the activities of the different environ- 

 ments, necessarily introduces diversity of Natural Selection. 

 This principle may be expressed as the Dependence of Diversity 

 of Adaptational Selection on Diversity of Successful Use. 



(5) Now diversity in the successful use of its powers in the 

 different sections of a species cannot be maintained and accumu- 

 lated without some degree of Segregation between the different 

 sections, for within one intergenerating group every initial 

 divergence is speedily merged in the general character of the 

 group. This law may be briefly defined as the Dependence of 



