AN UNWARRANTED ASSUMPTION. 1 45 



group. In the second place, it ignores the fact that diversity of envi- 

 ronal selection may be brought about either by diversity in the activ- 

 ities of the environment (that is by heteronomic selection), or by 

 diversity in the organism determining its methods of dealing with 

 the environment (that is, by endonomic selection). 



Small differences may of course be found in the conditions presented 

 in any two isolated positions ; but when the divergence in the groups 

 of organisms is not in accord with nor in proportion to these, it can not 

 be attributed to them. If, however, we find that the form of selec- 

 tion is determined by the methods of using the environment adopted 

 by the group, and that this is determined by the innate aptitudes of 

 the individuals that founded the colony, I call the principle aptitudinal 

 selection. If again, the method of using the environment, and so the 

 form of selection, is determined by the training and acquired habits 

 of those founding the group, I call the principle habitudinal selection. 



Still further, there are strong reasons for believing that divergent 

 forms of survival may arise in isolated groups, not only when the envi- 

 ronment surrounding each group is the same, but when the habitudes 

 and aptitudes of the individuals establishing the groups are the same. 

 If we select two islands as completely alike in climate and resources 

 as can be found, and plant upon the same two colonies of a few 

 families each, selected in such a way that the average character of 

 the colonies, in both innate and acquired characteristics, shall be as 

 much alike as possible, and if we then subject them to complete iso- 

 lation from each other and from the rest of the world, will they not in 

 a few generations become divergent in language, in dress, in customs, 

 in industries, and, if the experiment is continued through scores of gen- 

 erations, even in race characters? This might be called spontaneous 

 diversity of election in partitioned groups, producing divergence 

 of habitudes, and finally divergence of habitudinal selection, and so 

 divergence in race characters. 



In Professor Conn's Methods of Evolution, 1900, will be found a 

 very lucid statement of the importance of isolation as a primal factor 

 in all divergent evolution ; but his plan of exposition aims at giving 

 in broad outlines the main factors, rather than a complete analysis 

 of the influences producing each. 



