Indiscriminate Isolation 
happen to be a very large number, sooner or 
later their progeny will come to differ from that 
of the parent type, or unisolated portion of the 
parent stock. And, of course, as soon as this 
change of type begins, the isolation ceases to be 
indiscriminate ; the previous apogamy has been 
converted into homogamy, with the usual result 
of causing a divergence of type. The reason 
why progeny of an indiscriminately isolated 
section of an originally uniform stock—e.g. of a 
species—will eventually deviate from the original 
type is, to quote Mr Gulick, as follows :—‘ No 
two portions of a species possess exactly the 
same average character, and the initial differ- 
ences are for ever reacting on the environment 
and on each other, in such a way as to ensure 
increasing divergence as long as the individuals 
of the two groups are kept from _ inter- 
generating.’ ” 
The words of Mr Gulick require close scrutiny. 
We may admit that “no two portions of a species 
possess exactly the same average character,” but 
why should the two, if prevented from inter- 
breeding yet subjected to similar climatic and 
other conditions, present the phenomenon of 
“increasing divergence?” The reason assigned 
by Romanes is the “ Law” of Delbceuf, which 
runs :—‘‘ A constant cause of variation, however 
insignificant it may be, changes the uniformity of 
type little by little, and diversifies it ad i- 
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