ULTRA STABILITY IN THE LIVING ORGANISM 9/10 



From these basic rules, an ultrastable system of any size can 

 be generated by mere repetition of parts. Thus each critical 

 state is to have a value related to the limits of the essential vari- 

 ables ; but this requirement applies to all other critical states 

 by mere repetition. The repetition needs fewer genes than would 

 be necessary for independent specification. 



It is not possible to give an exact estimate of the number of 

 genes necessary to determine the development of an ultrastable 

 system. But the number of items listed above is only six ; and 

 though the number of genes required is probably a larger number, 

 it may well be less than the number known to be available. It 

 seems, therefore, that the requirement of S. 1/9 has been met 

 satisfactorily. 



9/10. If the higher animals are made ultrastable by their genetic 

 inheritance, the gene-pattern must have been shaped by natural 

 selection. Could an ultrastable system be developed by natural 

 selection ? 



Suppose the original organism had no step-functions ; such an 

 organism would have a permanent, invariable set of reactions. 

 If a mutation should lead to the formation of a single step-func- 

 tion whose critical states were such that, when the organism 

 became distressed, it changed value before the essential variables 

 transgressed their limits, and if the step-function affected in any 

 way the reaction between the organism and the environment, 

 then such a step-function might increase the organism's chance 

 of survival. A single mutation causing a single step-function 

 might therefore prove advantageous ; and this advantage, though 

 slight, might be sufficient to establish the mutation as a species 

 characteristic. Then a second mutation might continue the pro- 

 cess. The change from the original system to the ultrastable 

 can therefore be made by a long series of small changes, each 

 of Avhich improves the chance of survival. The change is thus 

 possible under the action of natural selection. 



References 



Culler, E., Finch, G., Girden, E., and Brogden, W. Measurements of 

 acuity by the conditioned-response technique. Journal of General 

 Psychology, 12, 223 ; 1935. 



123 



