176 GRAND STRATEGY OF EVOLUTION 



provides, in due season, for life's usage. And today 

 life still bides its time and awaits the performances of 

 specific social services. 



IV. Reciprocal Relations Between the Architecture 



of the Individual and Its Response to 



Its Environment 



But how is it possible for such a great variety of 

 living things to exist side by side in what appears to 

 be the same external environment? Why is it that 

 many of them live on the same structural level in dif- 

 ferent environments; and again, why do some advance 

 in structure, others fall to lower levels, and still others 

 remain practically stationary for indefinite periods? 

 It will help us to answer these questions if we bear in 

 mind the difference between the nominal habitat of the 

 individual and the real one ; between the architectural 

 materials which are utilized, and the structural plans 

 which have been adopted in each particular organism. 



The environment of any living thing, using the term 

 in its commonly accepted meaning, does not represent 

 the whole content of the place wherein it exists. It com- 

 prises only those parts of it to which the living thing 

 responds, and with which it comes into constructive 

 relations. In this sense, two things may live side by 

 side in the same habitat, and yet have their being in 

 different environments because they do not react to the 

 same agencies in them, and because they are not active 

 parts of the same system. The tree does not live in the 

 same environment as the bird that nests in its branches ; 

 nor does the dog live in the same environment as his 

 master, even though he lives in companionship with 



