DESIGN FOR A BRAIN 1/9 



The genetic control of cerebral function 



1/9. In rejecting the genetic control of the details of cerebral 

 function (in adaptation, S. 1/4) we must be careful not to reject 

 too much. The gene-pattern certainly plays some part in the 

 development of adaptive behaviour, for the various species, 

 differing essentially only in their gene-patterns, show character- 

 istic differences in their powers of developing it; the insects, for 

 instance, typically show little power while Man shows a great deal. 



One difficulty in accounting for a new-born baby's capacity for 

 developing adaptations is that the gene-pattern that makes the 

 baby what it is has about 50,000 genes available for control of 

 the form, while the baby's brain has about 10,000,000,000 neurons 

 to be controlled (and the number of terminals may be 10 to 100 

 times as great). Clearly the set of genes cannot determine the 

 details of the set of neurons. Evidently the gene-pattern deter- 

 mines a relatively small number of factors, and then these factors 

 work actively to develop co-ordination in a much larger number 

 of neurons. 



This formulation of how the gene-pattern comes into the picture 

 will perhaps suffice for the moment; it will be resumed in S. 18/6. 

 (/. to C, S. 14/6, also discusses the topic.) 



Restrictions on the concepts to be used 



1/10. Throughout the book I shall adhere to certain basic 

 assumptions and to certain principles of method. 



I shall hold the biologist's point of view. To him, the most 

 fundamental facts are that the earth is over 2,000,000,000 years 

 old and that natural selection has been winnowing the living 

 organisms incessantly. As a result they are today highly special- 

 ised in the arts of survival, and among these arts has been the 

 development of a brain. Throughout this book the brain will be 

 treated simply as an organ that has been developed in evolution 

 as a specialised means to survival. 



1/11. Conformably with this point of view, the nervous system, 

 and living matter in general, will be assumed to be essentially 

 similar to all other matter. So no use of any ' vital ' property 

 or tendency will be made, and no Deus ex machina will be invoked. 



8 



