INDISCRIMINATE ACTION OF THE PRINCIPLES. 133 
changes are sometimes experienced in temperature; or in the salinity 
of the water, in the case of water plants and animals. 
2. Indiscriminate Action of the Segregative Principles. 
Again, let us consider what the results are when the action of these 
principles is indiscriminate. IJndiscriminate survival takes place in 
regard toany given character of aspecies when the presence or absence 
of the character has no effect on the adaptation of theindividual. For 
Anglo-Saxons the possession of blue eyes or gray eyes is a matter of 
non-selective importance, and selection does not determine which shall 
prevail. There is, however, another form of indiscriminate survival 
which may have definite influence in determining the subsequent form 
of araceorspecies. I refer to the indiscriminate destruction of all but 
a small portion of the intergenerating group. Against heavy volcanic 
convulsions the varying endowments of different individuals of any 
one species usually count for nothing, and therefore the destruction 
falling upon them is indiscriminate; but if only a pair or two are left to 
propagate the species, the probability is that the type will be more or 
less changed in one or more of its characters. 
Indiscriminate vsolation of only a small fragment of a species is liable 
to result in important divergence in one or more of the characters of 
the species. Ifa single gravid individual, of a variable species of 
Hawaiian tree snails, is carried for a mile or two from its native val- 
ley while clinging to a leaf borne by a bird or a strong wind, it may 
fall in a neighboring valley, among groves and thickets of the same 
trees and shrubs that furnished its natural station in its original 
home. Is there now any probability that the colony descending 
from this individual, completely isolated from the original stock, but 
living in a valley with the same climate, and vegetation, and birds, 
and insects as are found surrounding their relatives in the original 
valley, will, by any chance, reproduce all the variations and varie- 
ties of the original species, and in the same proportions, and at the 
same time avoid producing any new varieties? My knowlege of var- 
iable animals in general, and my observations on Hawaiian snails in 
particular, make it impossible for me to believe that such a case could 
everoccur. If anyone says that an isolated portion of a species under 
absolutely the same environment as the original stock must produce the 
same varieties, as Wallace maintains in his volume entitled ‘‘ Darwin- 
ism,’’ I suspect he is using the word “‘ environment ”’ as equivalent for 
all the conditions that may cause divergence, whether they lie within 
- the species or belong to what lies outside of the species. This seems to 
bein part the explanation of Wallace’s position ; for in enumerating the 
