194 REV. J. T. GULICK ON DIVERGENT EVOLUTION 
neutralized” (p. 74). “Natural Selection 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 
1S72, 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) Gfeographical 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. 
