ADAPTATION TO ENVIRONMENT 31 



a brown-and-green snake, head extended, fangs out, 

 ready to pounce upon its green victim, the frog ; behind 

 the snake and above it, the almost invisible snake- 

 eating bird is poised for her prey with the same calm 

 assurance that she herself is unseen. Sometimes the 

 protective coloring extends only to the offspring or to 

 the eggs, which are colored so as to match the leaves 

 among which they lie. The little chicks of the wild 

 turkey, herself more or less protectively colored, are 

 perfectly matched to the dry yellow leaves among 

 which lies the nest, from which the mother turkey may 

 depart and leave them in security. 



As we thus look out upon the vast array of life, 

 we see species that have made use of every possible 

 opportunity open to them. What one has not found 

 as a mode of defense, another seems to have hit upon 

 with a marvelous aptitude. Every form of diet, every 

 phase of environment, every device for capture or es- 

 cape has apparently been utilized. 



Throughout its whole course the process of evolu- 

 tion, where it is visible in the struggle of organisms, 

 has been marked by a progressive victory of brain 

 over brawn. And this, in turn, may be regarded as 

 but a manifestation of the process of survival by 

 lability rather than by stability. Everywhere the or- 

 ganism that exhibits the qualities of quick response, 

 of extreme sensibility to stimuli, of capacity to change, 

 is the individual that survives, " conquers," " ad- 

 vances." The quality most useful in nature, from the 

 point of view of the domination of a wider environ- 

 ment, is the quality of changeableness, plasticity, mo- 

 bility or versatility. Man's particular means of adapta- 



