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 oj the Segregative Principles. 



Again, let us consider what the results are when the action of these 

 principles is indiscriminate. Indiscriminate survival takes place in 

 regard to any given character of a species when the presence or absence 

 of the character has no effect on the adaptation of the individual. 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 a race or species. 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 isolation 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. If a 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 

 ever occur. 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 

 be in part the explanation of Wallace's position ; for in enumerating the 



