194 REV. J. T. aULICK ON DIVERaEJiTT EVOLTJTIOTT 



neutralized" (p. 74). Natural Selectiou is not in itself an 

 unconditional necessity, but is dependent on migration and 

 geographical isolation during a long period, together with altered 

 conditions of life " (p. 57). " Where there is no migration, that 

 is where no isolated colony is founded, natural selection cannot 

 take place " (p. 59). 



A comparison of his paper with my two papers published in 

 1872, already referred to, will show several fundamental dif- 

 ferences in the two theories. He maintains that : — 



(1) The separation of a few individuals from the rest of the 

 species is absolutely necessary for the operation of Natural 

 Selection, and therefore for any transformation of the species, 

 no matter how great the change of conditions may be in the 

 original home of the species. 



(2) Migration and geographical barriers are the only effectual 

 causes, independent of human action, by which a few individuals 

 can be separated from the rest of the species, and are, therefore, 

 necessary to the transformation of species. 



(3) Exposure to a new form of Natural Selection is a necessary 

 condition for any transformation of a species. 



(4) Difference of external conditions is necessary to difference 

 of Natural Selection, and therefore necessary to any transforma- 

 tion of species. 



(5) Greographical isolation and altered conditions of life are 

 necessary conditions for Natural Selection, as that is for the 

 modification of species. 



(6) The separation of which he speaks is the entering of a few 

 individuals into a new territory, where the conditions are dif- 

 ferent from those in the old habitat, and where the body of the 

 species fail of reaching them. 



My chief positions were the following, in strong contrast with 

 the foregoing : — 



(1) Separate generation is a necessary condition for divergent 

 evolution ; but not for the transformation of all the survivors of 

 a species in one way. 



(2) " Separation does not necessarily imply any external 

 barriers, or even the occupation of separate districts." 



(3) Diversity of Natural Selection is not necessary to diversity 

 of evolution. 



(4) Difference of external conditions is not necessary to di- 

 versity of evolution. 



