11/13 THE FULLY-JOINED SYSTEM 



other points. The two sets of facts were sometimes treated as 

 irreconcilable. 



Yet Sherrington in 1906 had shown by the spinal reflexes that 

 the nervous system was neither divided into permanently separated 

 parts nor so wholly joined that every event always influenced 

 every other. Rather, it showed a richer, and a more intricate 

 picture— one in which interactions and independencies fluctuated. 

 'Thus, a weak reflex may be excited from the tail of the spinal 

 dog without interference with the stepping-reflex '. . . . ' Two 

 reflexes may be neutral to each other when both are weak, but 

 may interfere when either or both are strong '. . . . * But to 

 show that reflexes may be neutral to each other in a spinal dog 

 is not evidence that they will be neutral in the animal with its 

 whole nervous system intact and unmutilated.' The separation 

 into many parts and the union into a single whole are simply the 

 two extremes on the scale of ' degree of connectedness '. 



Being chiefly concerned with the origin of adaptation and co- 

 ordination, I have tended so far to stress the connectedness of 

 the nervous system. Yet it must not be overlooked that adapta- 

 tion may demand independence as well as interaction. The 

 learner-driver of a motor-car, for instance, who can only just 

 keep the car in the centre of the road, may find that any attempt 

 at changing gear results in the car, apparently, trying to leave 

 the road. Later, when he is more skilled, the act of changing 

 gear will have no effect on the direction of the car's travel. Adap- 

 tation thus demands not only the integration of related activities 

 but the independence of unrelated activities. 



11/13. From now on, therefore, we'will no longer hold the implicit 

 assumption that all parts are richly joined. This freedom makes 

 possible various modifications that have not so far been explicitly 

 considered, and that give new forms of ultrastable system. These 

 forms are still ultrastable, for they conform to the definition 

 (which does not involve explicitly the amount of connexion), but 

 they will not be so excessively slow in becoming adapted as the 

 simple form of S. 11/2. They do this by developing partial, 

 fluctuating, and temporary independencies within the whole, so 

 that the whole becomes an assembly of subsystems within which 

 communication is rich and between which it is more restricted. 

 The study of such systems will occupy the remainder of the book. 



157 



