ADAPTATION TO ENVmONMENT WARDLAW 403 



conditions, these two classes of mechanism had at least ono feature 

 in common. They owe their effectiveness to the fact that barriers 

 are placed between the organism and unfavorable conditions. In 

 the first instance cited, the barrier is composed of the substance of 

 the organism. The surface of contact between the organism and 

 its environment is rather sharply defined. In the second instance, 

 the barrier is composed of a part of the environment, which the 

 organism places between itself and the unfavorable conditions. 

 The change which takes place is not in the organism, but in the 

 distribution of its enWronment about it. In neither instance, how- 

 ever, does the environment itself undergo any perceptible modifica- 

 tion, nor does the organism itself appear to undergo further change. 



As our definition of the term adaptation is the power to remain 

 essentiall}^ unchanged in spite of external changes, it might be sup- 

 posed that, as adaptive mechanisms increased in efficiency, they would 

 bring about an ever sharper differentiation between the organism 

 and its environment. An examination of the relevant data shows 

 that what actually happens is just the reverse of this. Far from 

 tending to isolate themselves more completely from their surround- 

 ings, the most perfectly adapted organisms are those in which the 

 freest interchange is allowed with the environment. 



Although the effect of each increase in the complexity of the 

 mechanism of adaptation is to place additional barriers between the 

 essential living unit, at the same time it extends further the range 

 over which the organism is able to modify or, as it were, overlap its 

 environment. Each adaptation, by increasing the intimacy of the 

 relations between the organism as a whole and its external surround- 

 ings, protects the cell itself still more effectively from variations in 

 the medium in which it lives. 



One of the most important factors in the environment of an organ- 

 ism is the supply of available food materials which it contains. The 

 ability favorabl}^ to control this supply nnjst therefore be of great 

 assistance to an organism to maintain itself in that uniform state 

 which we have conceived as one of the principal aims of adaptive 

 processes. This ability is possessed by man in an outstanding degree, 

 but many organisms possess this power to a greater or less extent. 

 It is seen more especially in the provision which they nuikc for the 

 nutrition of their young. 



In oviparous animals and in many plants the young organism, 

 when it leaves the body of its parent, is enclosed in a more or less 

 impervious membrane which contains a supply of food material. By 

 this means the young organism is able to pass through certain stages 

 of its development in an environment which is entirely independent 

 of outside fluctuations of food supply. In organisms of this kind, 

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