DIFFERENTIATION OF INDIVIDUALS AND ADAPTATION I4I 



8. Animals become adapted to all the influences that tend to 

 make or mar their success in life. The more influential upon 

 living things the factor is the more certain the adaptation, 

 whatever may be the actual cause and origin of the adaptation, 

 because the destruction is the more certain in case of failure. 

 The principal classes of adaptations are,^ — those relating to the 

 using of the favorable and resisting the unfavorable features 

 of the inanimate environment ; those assisting in the obtaining of 

 food whether vegetable or animal; those of mating and care of 

 young; those of offense and defense, in predaceous animals 

 and their prey. The relations and adaptations range all the 

 way from indifference to friendship, and from feeding at the 

 same table on the one hand, to the utmost antagonism on the 

 other. 



9. Perhaps the most important and the least understood of 

 the series of adaptations which animals acquire are those con- 

 nected with the nervous system and its functions: — the in- 

 stincts, habits, and intelligence of animals. They are insepar- 

 able from those already enumerated, and yet in fundamental 

 importance they form a group of their own. They seem pri- 

 marily to depend upon the irritability of protoplasm which 

 enables it not merely to respond but to become permanently 

 changed by that response — a kind of organic memory. From 

 this fact acclimatization and adjustment become possible. 



10. In being scattered from their starting place, animals 

 with similar powers of response and adaptation come to be 

 located in the same kinds of conditions. This results in faunas 

 more or less characteristic of all the important kinds of en- 

 vironments: as marine, brackish water, fresh water, terrestrial, 

 aerial, cavern faunas, etc. 



11. The origin of animal life was in the ocean, and from 

 these marine types it is believed that all other forms of animal 

 life have come, by gradual adaptation to their present mode 

 of life. 



12. The various climatic zones of the earth and the principal 

 geographical regions are characterized by distinct forms of 

 life. For example, the lake life of Africa differs from that of 

 North America, and similarly for all the various types of 



