i82 ANIMAL ECOLOGY 



until we are led by an apparently unassailable chain of reasoning 

 to the existence of adaptations everywhere in nature. We 

 must now leave arguments for a moment, and start at the other 

 end by reviewing a few of the facts. In the front court of the 

 British Museum of Natural History there are two cases which 

 illustrate the beautiful colour adaptations of arctic animals to 

 their surroundings, and will also serve to illustrate what we 

 wish to point out here. There is in one case a group showing an 

 arctic fox (Vulpes lagopus), some ptarmigan, and some ermine, 

 in their summer dress of browns and greys, which match the 

 surrounding vegetation with great exactness. In the other 

 case the animals are shown in their winter dress of pure white, 

 which makes them invisible against the snow. So far, so good. 

 But further study of what is known about the field natural 

 history of the arctic fox begins to reveal awkward facts, which 

 do not fit in easily with this scheme of protective coloration, 

 and in fact reveal a number of creaking joints in its harness. 

 All over the arctic regions the arctic fox possesses two colour 

 phases, one of which is brown in summer and white in winter, 

 while the other is grey or black in summer, and " blue " — 

 often quite black — ^in winter. The writer has seen a " blue " fox 

 in summer which was the colour of a black cat, and startlingly 

 visible against rocks and vegetation at a distance of a quarter 

 of a mile. The blue and white phases occur equally in males 

 and females, and interbreed freely, and in different parts of 

 the arctic regions are found in various proportions in the 

 population. In Iceland only the blue phase is found, while 

 in Labrador it is rare. In Greenland, Alaska, and Spitsbergen 

 both are common.ios if the whiteness in winter is an adapta- 

 tion, the blackness of the other phase cannot also be advantage- 

 ous. If the black colour is not adaptive, how did it evolve ? 

 If the white colour is adaptive, how does the black survive? 

 We have in addition to reckon with the fact that in many parts 

 of the arctic, the fox can have no possible use for its colour 

 in winter, because it subsists at that season upon carrion left 

 by bears, out on the frozen sea-ice, or if it is on land, it depends 

 almost entirely on caches of animals collected and stored up 

 in the autumn. 



