706 THE RELATION OF INSTITUTIONS TO ENVIRONMENT. 



Manifold results flow from the strife of the desert. Since only a few 

 organisms can be maintained, eacli strives to perpetuate its kind, not 

 by multiplying' progeny as amid softer surroundings, but by prolong- 

 ing the life of the individual and economizing in reproductive energy. 

 Thus plants and animals live long and leave scant offspring. Since 

 the organisms are few, species can be perpetuated only through indi- 

 vidual vigor, and each strives for this and other qualities of individu- 

 ality, so that the plants and animals are strong and hardy. Since the 

 organisms are molded by interaction with the same physical agencies, 

 they grow toward likeness in form and function to the extent that 

 unrelated organisms assume similar characters. Finally, since the 

 organisms are engaged in common strife, they spontaneously fall into 

 a cooperation through which each assists alien neighbors in such 

 manner that all are united against the common enemies of sun and 

 sand. 



There are many grades of cooperation depending on the number of 

 species engaged therein. The shrub shelters the field mouse irom the 

 sun and the hawk, and the field mouse loosens and fertilizes the soil 

 about the roots of the shrub, and the two dwell together in mutual 

 tolerance, without enmity or intimate union. The insect comes to feast 

 on the flowers and fruit of the shrub, and incidentally to spread pollen 

 and to be devoured by the mouse, and thus plant and animal are linked 

 in more intimate union by tbe mediate insect, the despoiler of one and 

 the prey of the other, yet the benefactor of both. Then the grass 

 springs about the burrows in the shelter of the shrub, and incidentally 

 retains the scant moisture; the herbivore arises to consume the grass, 

 but incidentally to spread the seeds of the shrub; birds gather to 

 devour insects and fruits, and incidentally fertilize the soil and distrib- 

 ute seeds; and the carnivore comes to feast on flesh, yet incidentally to 

 protect the shrub and grass by decimating the herbivores; and in this 

 way the shrub and the mouse and all the other organisms are brought 

 into an intimate union in which every habit, even individual enmity, 

 makes for the common good. Thus the cooperation among the living 

 things of the desert begins in tolerance and ends in solidarity — a soli- 

 darity so perfect and far-reaching that no organism exists beyond it, 

 that every organism within its bounds is directly or indirectly depend- 

 ent on its advantages, and that the sum of life is multiplied through 

 its beneficence. 



There are also several kinds of cooperation depending on intimacy 

 of union. The shrub and the mouse and the insect are loosely linked, 

 and each is free to come and go and reproduce after its kind, yet they 

 spontaneously gather into colonies or communities to the extent that 

 the prevailing life of the desert is communal. The farmer ant fertilizes 

 the silver grass in an unknown way, and the grass flourishes and the 

 ant subsists on its seeds, so that each furnishes food for the other and 

 both increase and multiply apace; thus, although free to come and go 

 and to reproduce each after its kind, the ant and grass are commensal, 



