INDISCRIMINATE ELIMINATION. 209 
selection which is controlled by activities belonging to nature outside of the 
species. It is, therefore, clearly distinguished from active (or endonomic) selec- 
tion, which is controlled by differences of aptitudes or of habitudes in the different 
. groups for dealing with the environment, and not by exposure of the different 
groups to different environments. 
9. Indiscriminate Eliminational Intension. 
Eliminational intension is segregation and divergence produced by 
the indiscriminate destruction or failure to propagate of a part of the 
individuals of an intergenerating section of a species. “Though indis- 
criminate destruction can not be classed asa form of natural selection, 
it may nevertheless be the cause of transformation; and when a species 
is distributed in sections that are prevented from intergenerating, 
divergent evolution will often be hastened by the indiscriminate 
destruction of part of the members of one or more sections. Ifaspecies 
inhabiting a large island is divided by geological subsidence into two 
large sections, there may be a very close resemblance in the average 
character of the two sections; but if a subsequent eruption of hot ashes 
destroysa large portion of the individuals of one section, or of both, the 
probability of a close correspondence in the average character of the 
two sections will be very much less than before the eruption. 
Again, when the area occupied by a species is divided into two or 
more large districts, the occupants of which can have little or no 
opportunity for crossing, divergent evolution will arise in the different 
districts unless there is some constantly operating cause that insures 
that all the varieties surviving and propagating in any one district shall 
survive and propagate in all the districts. Nosuch cause has ever been 
pointed out, but, on the contrary, it can easily be shown that the prob- 
ability is very small that such a correspondence would occur, even if 
at the time of the division of the areas every individual in each district 
was represented by a completely similar individual in each of the 
other districts. Let us suppose a case: 
(1) Suppose the creatures under consideration to be a species of . 
mollusk, the sexual instincts of which act without any segregative 
tendency between the varieties of the same species, there being no 
aversion or other impediment that interferes with the free crossing 
of all the variations occurring within the limits of one district. 
(2) Suppose that the number of individuals in each district is 
10,000,000. 
(3) Suppose that one in a thousand of these has a tongue strong 
enough to feed on the bark of the tree the leaves of which are the ordi- 
nary food of the species, and that one in a thousand is capable of 
