72S 



THE AMERICAN NATURALIST 



[Vol. XLII 



changes go on of themselves, without the need of environmental 

 interference. 



If we advance with sufficient confidence in isolation we event- 

 ually come through to the realization that our alleged environ- 

 mental factors are unnecessary as causes, because evolution is 

 spontaneous. This approximation of views has been recognized 

 by Dr. John T. Gulick who states in the January number of 

 the American Naturalist that our interpretations differ only 

 in the meaning attached to the word evolution. 1 



I am naturally very much pleased to agree with Dr. Gulick, 

 for no other student of isolation has given the subject such 

 extensive and thorough study. I subscribe to Dr. Gulick 's state- 

 ment that there does not seem to be any essential difference 

 between us regarding facts. The difference is that the facts 

 appear to me as of more significance than Dr. Gulick has repre- 

 sented. In attempting to point out this greater significance I 

 have used a different method of expression. 



To say that isolation and selection are factors of evolution 

 should mean, in simpler English, that they cause evolution, or 

 at least help it along, whereas they do neither. They appear 

 to cause or to conduce to evolution only so long as we take it for 

 granted that changes in the characters of species are dependent 

 upon the subdivision of species, to form additional species. 



The separation of a species into two or more parts allows the 

 parts to become different, but there is every reason to believe 

 that evolutionary changes of the same kind would take place if 

 the species were not divided. That the isolated groups become 

 different does not indicate that isolation assists in the process 

 of change. It gives the contrary indication that changes are 

 restricted by isolation. If isolation did not confine the new 

 characters to the groups in which they arise, the groups would 

 remain alike, instead of becoming different. Thus it appears 

 to me that the danger of confusing the issues is much greater 

 when we say that isolation and selection are factors of evolu- 

 tion, than when we say that they are not factors of evolution, 

 however important they may he in multiplying and differentiat- 



Sulficiently narrow forms of isolation no doubt affect plants 

 and animals m nature in the same way as the "intensive segre- 



