RESPONSIVE LIFE OF ORGANISMS 497 



exchange, replacing the barter of products that was charac- 

 teristic of the pastoral stage. Men began to gather into 

 cities. In preceding stages all men were engaged in much 

 the same pursuits, but now they differentiated, one man 

 producing articles for the use of the others, and receiving 

 the products of the others in exchange. 



Finally, came the inventor stage. The forces of nature were 

 harnessed to do men's work. Artisans largely gave place to 

 operators of machines. Production was vastly increased; 

 population grew apace. The exigencies of commerce de- 

 mand the centralization of lines of communication and of 

 transportation and thus cities grow. And the end of this is 

 not yet. 



Doubtless the earliest of these periods was most extensive; 

 the night of savagery was long and the dawn broke slowly. 

 But it was a period of physical perfecting and of sound 

 beginnings of mental improvement. During the long 

 struggle with animals, better equipped by nature for fight- 

 ing, man had to match their strength and cunning with his 

 wit. Thus he gained good eyes and ears, a supple frame, 

 quick muscles and strong sinews, hands that could control 

 weapons with deftness and precision, and above all, a brain 

 that could turn to advantage the circumstances of his en- 

 vironment. The elimination of the unfit was then most 

 rigorous. The savages of all dominant tribes are fine 

 physical specimens, and it is not too much to say that on 

 this basis of physical fitness all subsequent history is built. 

 The foresight that would put a stick of wood on a fire to keep 

 it going, that would shape a stone for hitting, or that would 

 improve its efficiency by the addition of a handle, marked an 

 enormous psychological departure from the status of the 

 brute. The native taste that shaped an arrow head with 

 symmetry and beauty, or that traced with flint its crude 

 fancy in a picture on bone, had in it the germ of art. Given 

 these, all language, all subsequent history was possible. 



