THE ORIGIN OF GROUSE. 201 



other northern animals have done ; for in a uniform 

 white surface any variation of colour is far more certain 

 to be spotted and cut off than in a many-coloured 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 Scandinavian 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 

 Continental congener. Of course, it is just possible that 

 the common ancestor had already acquired the habit of 

 changing its coat in winter before the divergence took 

 place ; and if so, then it is the Scotch grouse which has 

 altered most : but this is less probable, because the use- 

 fulness of the change would certainly be felt even in a 

 Scotch winter, and the white suit is not, therefore, likely 

 ever to have been lost when once acquired. Though 

 the winter is not severe enough in Scotland to make 

 such a change of coat inevitable where it does not 

 already exist, it is yet' quite severe enough to preserve 

 the habit in animals which have once acquired it, as we 

 see in the case of the varying hare, a creature which in 

 colder ages spread over the whole of northern Europe, 

 and which still holds its own among the chillier portions 

 of the Scotch Highlands. Hence we may reasonably 

 infer that if our grouse had ever possessed a winter coat 

 it would have always retained it for an alternative dress, 

 as the ptarmigan still does in the self-same latitudes. 

 Accordingly, analogy seems to point to the conclusion 



