190 
DARWINISM 
CHA1’. 
great variability. We see this in our horses and cattle, our 
dogs and cats, our pigeons and poultry. Now, the essential 
difference between the conditions of life of domesticated and 
wild animals is, that the former are protected by man, while 
the latter have to protect themselves. The extreme variations 
in colour that immediately arise under domestication indicate 
a tendency to vary in this way, and the occasional occurrence 
of white or piebald or other exceptionally coloured individuals 
of many species in a state of nature, shows that this tendency 
exists there also; and, as these exceptionally coloured in¬ 
dividuals rarely or never increase, there must be some con¬ 
stant power at work to keep it in check. This power can 
only be natural selection or the survival of the fittest, which 
again implies that some colours are useful, some injurious, in 
each particular case. With this principle as our guide, let 
us see how far Ave can account both for the general and 
special colours of the animal world. 
Colour and Environment. 
The fact that first strikes us in our examination of the 
colours of animals as a whole, is the close relation that exists 
between these colours and the general environment. Thus, 
white prevails among arctic animals ; yelloAv or brown in desert 
species; Avhile green is oidy a common colour in tropical ever¬ 
green forests. If we consider these cases somewhat carefully 
Ave shall find, that they afford us excellent materials for forming 
a judgment on the various theories that have been suggested 
to account for the colours of the animal Avorld. 
In the arctic regions there are a number of animals which are 
Avholly white all the year round, or which only turn Avhite in 
Avinter. Among the former are the polar bear and the American 
polar hare, the snowy oavI and the Greenland falcon ; among 
the latter the arctic fox, the arctic hare, the ermine, and the 
ptarmigan. Those which are permanently Avhite remain among 
the snow nearly all the year round, while those Avhich change 
their colour inhabit regions which are free from shoav in 
summer. The obvious explanation of this style of coloration 
is, that it is protective, serving to conceal the herbivorous species 
from their enemies, and enablingcarnivorous animals to approach 
their prey unperceived. Two other explanations have, Iioav- 
