DESIGN FOR A BRAIN 18/4 



18/4. What concerns us in this book is the fact that the active 

 defences can be direct or indirect. The direct were considered only 

 in S. 1/3. They include all the regulatory mechanisms that are 

 specified in detail by the gene-pattern. They are adapted because 

 the conditions that insisted on them have been constant over many 

 generations. 



The earlier forms of gene-pattern adapted in this way only. The 

 later forms, however, have developed a specialisation that can 

 give them a defence against a class of disturbances to which the 

 earlier were vulnerable. This class consists of those disturbances 

 that, though not constant over a span of many generations (and 

 thus not adaptable to by the gene-pattern, for the change is too 

 rapid) are none the less constant over a span of a single generation. 

 When disturbances of this class are frequent, there is advantage 

 in the development of an adapting mechanism that is (1) controlled 

 in its outlines by the gene-pattern (for the same outlines are 

 wanted over many generations), and (2) controlled in details by the 

 details applicable to that particular generation. 



This is the learning mechanism. Its peculiarity is that the 

 gene-pattern delegates part of its control over the organism to 

 the environment. Thus, it does not specify in detail how a kitten 

 shall catch a mouse, but provides a learning mechanism and a 

 tendency to play, so that it is the mouse which teaches the kitten 

 the finer points of how to catch mice. 



This is regulation, or adaptation, by the indirect method. The 

 gene-pattern does not, as it were, dictate, but puts the kitten into 

 the way of being able to form its own adaptation, guided in detail 

 by the environment. 



18/5. We can now answer the question raised in S. 17/12, and 

 can see how the law of requisite variety is to be applied to the 

 question of how the ancillary regulations are to be achieved, i.e. 

 how the necessary parameters are to be brought to their appro- 

 priate values. 



Some may be adjusted by the direct action of the gene-pattern, 

 so that the organism is born with the correct values. For this 

 to be possible, the environmental conditions must have been 

 constant for a sufficiently long time, and the processes of natural 

 selection must have been intense enough and endured long enough 

 for the total selection exerted to satisfy the law. 



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