304 Evolution and Adaptation 



on mountains." Other cases also are on record in which the 

 colors of a plant are dependent on external conditions. 



The sizes of plants and animals are also often directly trace- 

 able to certain external conditions ; the change is generally- 

 connected with the amount of food obtainable. " Generally- 

 speaking," De Varigny says, " insular animals are smaller 

 than their continental congeners. In the Canary Islands 

 the oxen of one of the smallest islands are smaller than 

 those on the others, although all belong to the same breed, 

 and the horses are also smaller, and the indigenous inhabitants 

 are in the same case, although belonging to a tall race. It 

 would seem that in Malta elephants were very small, — fossil 

 elephants, of course, — and that during the Roman period 

 the island was noted for a dwarf breed of dogs, which was 

 named after its birthplace, according to Strabo. In Corsica, 

 also, horses and oxen are very small, and Cervus corsicanus, 

 the indigenous deer, is quite reduced in dimensions; . . . 

 and lastly, the small dimensions of the Falkland horses — 

 imported from Spain in 1764 — are familiar to all. The 

 dwarf rabbits of Porto Santo described by Darwin may also 

 be cited as a case in point." 



These facts, interesting as they are, will, no doubt, have to 

 be more carefully examined before the evidence can have 

 great value, for it is not clear what factor or factors have 

 produced the decrease in size of these animals. 



The following cases show more clearly the immediate 

 effect of the environment : " Many animals, when trans- 

 ferred to warm climates, lose their wool, or their hairy cover- 

 ing is much reduced. In some parts of the warmer regions 

 of the earth, sheep have no wool, but merely hairs like those 

 of dogs. Similarly, as Roulin notices, poultry have, in 

 Columbia, lost their feathers, and while the young are at first 

 covered with a black and delicate down, they lose it in great 

 part as they grow, and the adult fowls nearly realize Plato's 

 realistic description of man — a biped without feathers. 



