The Mechanism of Adaptation 337 



Zealand, which was originally an insect-eating and fruit-eat- 

 ing bird, but which has become more or less carnivorous 

 since r the introduction of sheep into that country; it was 

 evidently well fitted, or preadapted, for this new kind of 

 food even before the food appeared. All such fitnesses were 

 developed without regard to their later use ; they are there- 

 fore preadaptations. 



Cuenot further points out that such preadaptations, or 

 fortuitous conjunctions of favorable environment and char- 

 acters preadapted to this environment, have been an impor- 

 tant factor in progressive evolution. For example, the ap- 

 pearance of several great classes of the animal kingdom has 

 followed the occupation of a place, either unoccupied or 

 peopled by an inferior group not able to resist the invasion. 

 Thus shallow-water fishes have given birth by mutation to 

 amphibians capable of living in a merely humid environment, 

 thanks to their aerial respiration and walking limbs. From 

 these issued reptiles which occupied dry regions; their hard 

 skin, digits armed with claws, internal fecundation and large 

 eggs, capable of direct development, permitting the omission 

 of an aquatic stage, were preadaptations necessary to this 

 change of habitat. Birds, derived from reptiles, peopled 

 the unoccupied realms of the air owing to their preadapta- 

 tions for flight. Mammals derived from primitive reptiles 

 were able to replace these because of their intra-uterine 

 development, maternal protection of the young and constant 

 temperature. Man has been able to prevail over preceding 

 forms because of his superior brain all these fitnesses being 

 preadaptations. 



This theory of preadaptation is evidently a modification 

 and extension of the Darwinian doctrine to the origin of ad- 

 aptations, as the mutation theory is an extension of that doc- 

 trine to species formation; it is merely a variant on the 

 theme of natural selection. 



