Isolation. 5 



evolutionists have hitherto failed to perceive the full 

 importance of isolation, is because they have failed 

 to perceive the distinction which has now to be pointed 

 out. The distinction is, that isolation may be either 

 discriminate or indiscriminate. If it be discriminate, 

 the isolation has reference to the resemblance of the 

 separated individuals to one another; if it be indis- 

 criminate, it has no such reference. For example, if 

 a shepherd divides a flock of sheep without regard to 

 their characters, he is isolating one section from the 

 other indiscriminately ; but if he places all the white 

 sheep in one field, and all the black sheep in another 

 field, he is isolating one section from the other 

 discriminately. Or, if geological subsidence divides 

 a species into two parts, the isolation will be indis- 

 criminate ; but if the separation be due to one of 

 the sections developing, for example, a change of 

 instinct determining migration to another area, or 

 occupation of a different habitat on the same area, 

 then the isolation will be discriminate, so far as the 

 resemblance of instinct is concerned. 



With the exception of Mr. Gulick, I cannot find 

 that any other writer has hitherto stated this 

 supremely important distinction between isolation as 

 discriminate and indiscriminate. But he has fully 

 as well as independently stated it, and shown in 

 a masterly way its far-reaching consequences. Indis- 

 criminate isolation he calls Separate Breeding, while 

 discriminate isolation he calls Segregate Breeding. 

 For the sake, however, of securing more descriptive 

 terms, I will coin the words Apogamy and Homogamy. 

 Apogamy, of course, answers to indiscriminate isola- 

 tion, or separate breeding. Homogamy, on the other 



