DESIGN FOR A BRAIN 17/8 



balance, but what we have seen is sufficient to show that richness 

 of corwcr ion between the parts in the brain has both advantages and 

 disadvantages. Clearly the organism must develop so that its 

 brain finds, in this respect, an optimum. 



It is not suggested that what is wanted is the optimum in the 

 strict sense. Finding an optimum is a much more complex 

 operation than finding a value that is acceptable (according to a 

 given criterion). Thus, suppose a man comes to a foreign market 

 containing a hundred kinds of fruit that are quite new to him. 

 To find the optimum for his palate he must (1) taste all the hundred, 

 (2) make at least ninety-nine comparisons, and (3) remember the 

 results so that he can finally go back to the optimal form. On 

 the other hand, to find a fruit that is acceptable he need merely 

 try them in succession or at random (taking no trouble to remember 

 the past), stopping only at the first that passes the test. To 

 demand the optimum, then, may be excessive; all that is required 

 in biological systems is that the organism finds a state or value 

 between given limits. 



Thus, for the organism to adapt with some efficiency against 

 the terrestrial environment, it is necessary that the degree of 

 connexion between the reacting parts lie between certain limits. 



Ancillary regulations 

 17/8. ' Between certain limits ' — we have heard that phrase 

 before ! Are we arguing in a circle ? Not really, for two different 

 adaptations are involved, of two types or levels or orders. 



To see the two adaptations and their relation, recall that we 

 started (S. 3/14) by assuming that certain essential variables were 

 to be kept within limits. Call them E v E 2 , E 3 , and 22 4 ; in Figure 

 8/2/1 they are clearly evident; keeping them within limits is one 

 adaptation. In Chapter 11 we added another essential variable 

 F: the time taken by the four E's to get stable within their limits; 

 keeping it within limits is another adaptation. This F is quite 

 distinct from a fifth E, which would enter the system in quite a 

 different way. Yet F does come to the whole as an essential 

 variable, for from S. 11/2 onwards we have consistently discussed 

 the case in which it has certain limits which we do not want it 

 to exceed. (The possibility of various classes of essential variables 

 was mentioned in S. 3/15.) 



The 25' s — the four relays on the Homeostat say — are clearly 



224 



