THE ORIGIN OF GROUSE. * 191 



parts of our island which lie furthest from the Conti- 

 nent, separated from Holland and Scandinavia by a 

 wide sea. Here it could not fail to be subjected to 

 special conditions, differing greatly from those of the 

 European mainland, partly in the equable insular cli- 

 mate, partly in the nature of the vegetation, and partly 

 in the absence of many mammalian foes or competitors. 

 These conditions would be likely first to affect the color- 

 ing and marking of the feathers, the spots on the bill, 

 the naked scarlet patch about the eye, and so forth ; for 

 we know that even freer-flying birds in the south, which 

 cross often with Continental varieties, tend slightly to 

 vary in such ornamental points ; and a very isolated 

 group like the red grouse would be far more likely to 

 vary in similar directions. Meanwhile, the main branch 

 of the family, separated on the great continents from 

 this slightly divergent group, would probably acquire 

 the habit of changing its plumage in winter among the 

 snows of the north, by stress of natural selection, just as 

 the Arctic fox and so many other northern animals have 

 done ; for in a uniform white surface any variation of 

 color is far more certain to be spotted and cut off than 

 in a many-colored and diversified environment. Thus it 

 would seem probable that the Scotch grouse has slowly 

 become accommodated to the heather, among which it is 

 so hard to discover it ; while the willow-grouse has 

 grown to resemble the snow in winter, and the barer 

 grounds of its northern feeding-places in the short Scan- 

 dinavian and Icelandic summer. 



If this be so, we must regard both birds as slightly 

 divergent descendants of a- common ancestor, from 

 which, however, our grouse has varied less than its Con- 

 tinental congener. Of course, it is just possible that the 

 common ancestor ha'd already acquired the habit of 



