THE MACHINE WITH INPUT 4/24 



is shown, for instance, in a piece of pitchblende, by the number of 

 atoms that are of radium. It is also shown by the number in a 

 species when the species is tending to extinction. 



(2) k = \. In this case the number tends to stay constant. An 

 example is given by the number of molecules dissociated when the 

 percentage dissociated is at the equilibrial value for the conditions 

 obtaining. (Since the slightest deviation of k from 1 will take the 

 system into one of the other two cases it is of httle interest.) 



(3) /: >> 1 . This case is of great interest and profound importance. 

 The property is one whose presence increases the chance of its 

 further occurrence elsewhere. The property "breeds", and the 

 system is, in this respect, potentially explosive, either dramatically, 

 as in an atom bomb, or insidiously, as in a growing epidemic. A 

 well known example is autocatalysis. Thus if ethyl acetate has 

 been mixed with water, the chance that a particular molecule of 

 ethyl acetate will turn, in the next interval, to water and acetic acid 

 depends on how many acetate molecules already have the property 

 of being in the acid form. Other examples are commonly given by 

 combustion, by the spread of a fashion, the growth of an avalanche, 

 and the breeding of rabbits. 



It is at this point that the majestic development of life by Dar- 

 winian evolution shows its relation to the theory developed here of 

 dynamic systems. The biological world, as noticed in S.4/21, is a 

 system with something like the homogeneity and the fewness of 

 immediate effects considered in this chapter. In the early days of 

 the world there were various properties with various ^''s. Some 

 had k less than 1 — they disappeared steadily. Some had k equal 

 to 1 — they would have remained. And there were some with k 

 greater than 1 — they developed like an avalanche, came into 

 conflict with one another, commenced the interaction we call 

 "competition", and generated a process that dominated all other 

 events in the world and that still goes on. 



Whether such properties, with k greater than 1, exist or can exist 

 in the cerebral cortex is unknown. We can be sure, however, that 

 if such do exist they will be of importance, imposing outstanding 

 characteristics on the cortex's behaviour. It is important to notice 

 that this prediction can be made without any reference to the par- 

 ticular details of what happens in the mammalian brain, for it is 

 true of all systems of the type described. 



4/24. The remarks made in the last few sections can only illustrate, 

 in the briefest way, the main properties of the very large system. 

 Enough has been said, however, to show that the very large system 



71 



