EVOLUTION MADE PLAIN 25 
highly developed trait would be most useful 
while in another some other character or set 
of characters wouid be the saving factor, be¬ 
cause a change of environment means a change 
of weather conditions, of the food supply and 
the means of getting it, of enemies, etc. 
From the foregoing brief outline it would 
seem that only a little exercise of reason is 
required of any one to see that natural selec¬ 
tion operating in unlike environments would, 
in the course of many generations, produce 
from the same species types of animals (or 
plants) very unlike—not only unlike each 
other but unlike their parent species. At first 
these types derived from a common ancestor 
would be only varieties, but varieties are in¬ 
cipient species. Given sufficient time, and the 
intervention of natural barriers to prevent the 
crossing of extremes, and the creation of new 
species would be the natural result. 
As a vivid illustration of how the law of 
natural selection works, and of how great is 
the sum of the results of its operation accumu¬ 
lated through many generations, let us observe 
one of many modifications an animal under¬ 
goes in its struggle for existence. To the ques¬ 
tion, “Why are animals of the arctic regions 
white?” we ought to be able, with what we al¬ 
ready know of natural selection, to give the 
answer. Imagine those lands of snow and ice 
originally inhabited by animals of all colors 
from white to black, or even of all shades of 
one color, brown. The animals of what colors 
or shades, among the flesh-eaters, would have 
the least difficulty in stealthily approaching 
