THEORIES IN PRACTICE 363 



destroyed should the essential conditions of the 

 environment change. 



The great penalty of specialization is the 

 danger that attends it from this source. It is 

 held that the species that were eliminated when 

 the great climatic change occurred to which we 

 have more than once referred were those that 

 were the most highly specialized. 



But, on the other hand, a species that is able 

 to change in such a way as to adapt itself to new 

 conditions stands at least a chance of being pre- 

 served, however, widely the environment may be 

 altered. And, in fact, most species in a state of 

 nature have a considerable measure of adapta- 

 bility. Individual variation is the universal rule, 

 and such variations are accentuated by natural 

 selection very much as the plant developer accen- 

 tuates them by artificial selection. So the plants 

 and animals in a state of nature are plastic 

 material, and under changing conditions of 

 environment which represent probably the usual 

 and normal condition of things, they are con- 

 stantly, even if slowly, being modified. And of 

 course such modifications, when they have been 

 sufficiently added to, alter the character of the 

 species altogether. 



Which is only a detailed and roundabout way 

 of saying that species are evolved and trans- 



