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THE AMERICAN NATURALIST [Vol. XLII 



regation," read before the Linnean Society in 1887 and 

 1889, and published in their Journal, the subject was more 

 fully discussed, and since then in my volume on "Evolu- 

 tion, Racial and Habitudinal," published by the Carnegie 

 Institution, my view of the factors of organic evolution 

 has been presented, with special relation to their inter- 

 action on each other, and the close correlation between 

 the evolution of habits and the evolution of racial charac- 

 ters. It is to this last-mentioned phase of the subject that 

 I have hoped that I might call special attention. I regard 

 this influence of acquired habits in the control of the 

 forms of selection as of great importance, especially in 

 the evolution of the higher classes of animals, and in the 

 races of mankind. 



Meaning of the Term Environment 

 In all my discussions, I have been careful to give a 

 uniform meaning to the term environment. When treat- 

 ing the evolution of species, or of smaller groups of in- 

 tergenerating organisms, the environment is, in my lan- 

 guage, always the set of influences lying outside of the 

 group under discussion, and is never used to designate the 

 influence of one part of the group upon another part, as, 

 for example, the influence of parents upon offspring, of 

 males upon females, of the strong upon the weak. In the 

 generalizations made by some writers, it is impossible to 

 decide whether the environments referred to are intended 

 to include these reflexive influences or not, But even with 

 the broadest interpretation of the term environment, I 

 can not accept the statement often made that there is no 

 divergence in branches of the same species unless they are 

 exposed to different environments. 



fails to recognize the fact that isolated groups of indi- 

 viduals of the same variety, exposed to the same external 



