66 GRAND STRATEGY OF EVOLUTION 



form a service for the other, and all together may 

 perform a common resultant service which man still 

 further supplements by using it in cooperation with his 

 organic mechanism, to enlarge his own life. 



Or it may be implied that fitness and adaptation is 

 the mutual moulding of one thing by the other, so that 

 each thereby becomes better fitted to act cooperatively 

 with the other and so acting produces something which 

 finds a place in the world where it may exist. 



In the case of the river and its bed, many creative 

 and cooperative factors are involved. On the one hand 

 there are the chemical and physical properties of water, 

 and the volume and rate of precipitation. On the 

 other hand, there are the physical and chemical char- 

 acters of the terrain, its elevation, slope, and vegetation. 

 And back of all these are the more fundamental cosmic 

 conditions of heat, light, gravity, daily, seasonal and 

 other periodic changes. All these factors acting to- 

 gether have produced, at a particular time and place, 

 a particular stream of water, in a particular channel, 

 each adapted to the other, and both, it may be, adapted 

 in a particular way to sustain life. In this case, while 

 the course of the current may be in part determined by 

 the terrain, and the terrain more or less sculptured by 

 the current, so far as we know, neither the attributes 

 of water, nor those of the constituents of the terrain 

 are modified, or moulded, in any way thereby. The 

 fitness of the river to its bed is chiefly and more imme- 

 diately due to the mutual influences of water and ter- 

 rain whereby both the direction of the stream and the 

 contours of its bed are modified or changed. This 

 process may be checked, or accelerated, extended or 

 diminished, by the cooperative action of many other 



