118 ANALYSIS OF THE FOUR PRINCIPLES (CONTINUED). 
case of the snails just considered some of them are brought to groves 
on the northeast side of the mountain range, they will be exposed to a 
somewhat greater rainfall, and will probably be subjected to some 
change through the resulting selection. Again, suppose a colony is 
planted on either side of the range, in a valley where but one kind of 
shade trees is found, and this a kind that has never before been occu- 
pied by the species. In both these cases we should have heteronomic 
selection of the form that has been called natural selection. If any 
of these snails should be discovered by man to be good for food or 
medicine, and should be subjected to selection for the purpose of 
improving the qualities sought, the result would be heteronomic 
selection of the artificial form. 
Environal election corresponds with environal selection in the 
general influences by which it is shaped; but it differs in the results 
produced, for it relatesto the intensifying of habitudes and acquired 
characters within the associating group. The higher the grade of 
intelligence the more marked are the changes and divergences intro- 
duced by acquired habitudes and characters, and accordingly, in such 
cases, endonomic election becomes the leading factor by which some 
new adjustment to the environment is developed into an established 
method of sustaining life; and if the inherited endowments are not in 
complete accord with the new life, coincident selection carries the 
adjustment to higher degrees; for variations favoring the conditions 
imposed by the new tradition will have the advantage. Examples of 
endonomic election preceding and introducing coincident selection 
are seen in the tree-climbing rats mentioned above,* and in the cats 
that have taken to wading and fishing.t Heteronomic election is 
either natural or artificial. Avtzficral election is seen in dogs and other 
domestic animals that have been subjected to training. Natural 
election is seen in the case of the chimney swift, which, in a large meas- 
ure, having lost the hollow trees in which it used to build its nests, 
has been forced to find a substitute in the chimneys built by the 
intruders who cut down its trees. The new habit is undoubtedly 
being reinforced by instincts gradually established by coincident 
natural selection. 
2. The Methods of Environal Isolation. 
Endonomic tsolation.—It is evident that, when varieties of the same 
species of plant occupying the same areas are prevented from crossing 
by flowering at different seasons, the process which I call seasonal 
isolation is rightly classed as a form of endonomic isolation. The 
* See page 101. + See pages 67-68. 
