62 THE EVOLUTION THEORY 



cases, the persecutors themselves are likewise adapted, and this need 

 not surprise us, when we remember that the very existence of a beast 

 of prey depends on its being able to gain possession of its victims, 

 and that therefore it must be of the greatest use to it to contrast as 

 little as possible with its surroundings, and thus be able to steal on 

 its quarry unperceived. Those that are best adapted in colour will 

 secure the most abundant food, and will reproduce most prolifically ; 

 and they will thus have a better prospect of transmitting their usual 

 colouring to their offspring. The Polar bear would starve if he were 

 brown or grey, like his relatives ; among the ice and snow of the 

 Polar regions his victims, the seals, would see him coming from afar. 



In the Arctic zone the adaptation of the colouring of the animals 

 to the white of the surroundings is particularly striking. Most of 

 the mammals there are pure white, or approximately white, at least 

 during the long winter : and it is easily understood that they must be 

 so if they are to survive in the midst of the snow and ice, — both 

 beasts of prey and their victims. For the latter the sympathetic 

 colouring is of ' protective ' value ; for the former, of ' aggressive ' 

 value (Poulton). Thus we find not only the Polar hare *and the 

 snow-bunting white, but also the Arctic fox, the Polar bear, and 

 the great snowy owl ; and though the brown sable is an exception, 

 that is intelligible enough, for he lives on trees, and is best concealed 

 when he cowers close to the dark trunk and branches. For him 

 there would be no advantage in being white, and therefore he has not 

 become so. 



Desert animals are also almost all sympathetically coloured, that 

 is, they are of a peculiarly sandy yellow, or yellowish-brown, or 

 clayey-yellow, or a mixture of all these colours ; and here again the 

 beasts of prey and their victims are similarly coloured. The lion 

 must be almost invisible from a short distance, when he steals along 

 towards his prey, crouching close to the ground ; but the camel too, the 

 various species of antelope, the giraffe, all the smaller mammals, and 

 also the horned viper (Vipera cerastes), the Egyptian spectacled snake 

 iX<ij<i haje), many lizards, geckos, and the great Varanus, numerous 

 birds, not a few insects, especially locusts, show the colours of the 

 desert. It is true that the birds often have very conspicuous colours, 

 such as white on breast and under parts, but the upper surface is 

 coloured like the desert, and conceals them from pursuers whenever 

 they cower close to the ground. It has even been observed that 

 a locust of the genus Tryxalis is of a light sand-colour in the sandy 

 part of the Libyan desert, but dark brown in its rocky parts, thus 

 illustrating a double adaptation in the same species. 



