CHAPTER 15 



Adaptation in Iterated and 

 Serial Systems 



15/1. The last three chapters have been concerned primarily 

 with technique, with the logic of mechanism, when the mechanism 

 shows partial, fluctuating and temporary divisions into sub- 

 systems within the whole ; they have considered specially the case 

 when the subsystems are rich in states of equilibrium. We can 

 now take up again the thread left at S. 11/13, and can go on to 

 consider the problem of how a large and complex organism can 

 adapt to a large and complex environment without taking the 

 almost infinite time suggested by S. 11/5. 



The remaining chapters will offer evidence that the facts are 

 as follows: 



(1) The ordinary terrestrial environment has a distribution of 

 properties very different from the distribution assumed when the 

 estimate of S. 11/2 came out so high. 



(2) Against the actual distribution of terrestrial environments 

 the process of ultrastability can often give adaptation in a reason- 

 ably short time. 



(3) When particular environments do get more complex, the 

 time of adaptation goes up, not only in theoretical ultrastable 

 systems but in real living ones. 



(4) When the environment is excessively complex and close- 

 knit, the theoretical ultrastable system and the real living fail 

 alike. 



In this chapter and the next we will examine environments of 

 gradually increasing complexity. (What is meant by 4 com- 

 plexity ' will appear as we proceed.) 



15/2. In S. 11/11 it was suggested that the Homeostat (i.e. the 

 two units or so marked off to represent ' environment ') is not 

 typical of the terrestrial environment because in the Homeostat 

 every variable is joined directly to every other variable, so that 



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