DESIGN FOR A BRAIN 16/12 



S. 15/6, and the whole will progress to adaptation similarly. In 

 this case the time taken to reach adaptation will be the moderate 

 time of T 3 , rather than the excessive time of T v 



As the connexions become richer, whether by more basic joins 

 or by the subsystems having fewer states of equilibrium, so will 

 the system move towards the richly-connected type of S. 16/4; 

 and so will the time required for adaptation increase towards 

 that of T v % 



Summary. We are now in a position to summarise the answer, 

 given by the intervening chapters, to the objection, raised in 

 S. 11/2, that ultrastability cannot be the mode of adaptation used 

 by living organisms because it would take too long. We can now 

 appreciate that the objection was unwittingly using the assumption 

 that the organism and the environment were richly joined both 

 within themselves and to each other. Evidence has been given, 

 in S. 15/2, that the actual richness is by no means high. Then 

 Chapters 15 and 16 have shown that when it is not high, adaptation 

 by ultrastability can occur in a time that is no longer impossibly 

 long. Thus the objection has been answered, at least in outline. 

 There we must leave the matter, for a closer examination would 

 have to depend on measurements of actual brains adapting to 

 actual environments. The study of the matter should not be 

 beyond the powers of the present-day experimenter. 



Retroactive inhibition 



16/12. The suggestion now before the reader is that the system 

 of Figure 7/5/1, when looked at more closely in the forms in 

 which it occurs in actual organisms and environments, will be 

 found to break up into parts more like those of Figure 16/6/1 — 

 the multistable system. Let us trace out some of the properties 

 of this system — extra to those it possesses by being basically 

 ultrastable and only a particular form of Figure 7/5/1 — and see 

 how they accord with what is known of the living organism. 



A first question to be asked about the multistable system is 

 whether it can take advantage of the recurrent situation, a matter 

 considered earlier in Chapter 10. Thus, after a multistable system 

 has adapted to a parameter's taking the value P 2 > then to its 

 value P 8 , will it, when given P 2 again, retain anything of its first 

 adaptation ? 



214 



