SUMMARY AND PREFACE 



The work also in a sense develops a theory of the ' natural 

 selection ' of behaviour-patterns. Just as, in the species, the 

 truism that the dead cannot breed implies that there is a funda- 

 mental tendency for the successful to replace the unsuccessful, 

 so in the nervous system does the truism that the unstable tends 

 to destroy itself imply that there is a fundamental tendency for 

 the stable to replace the unstable. Just as the gene-pattern, in 

 its encounters with the environment, tends towards ever better 

 adaptation of the inherited form and function, so does a system 

 of step- and part-functions tend towards ever better adaptation 

 of learned behaviour. 



These remarks give an impressionist picture of the work's 

 nature ; but a description in these terms is not well suited to 

 systematic exposition. The book therefore presents the evidence 

 in rather different order. The first five chapters are concerned 

 with foundations : with the accurate definition of concepts, with 

 basic methods, and especially with the establishing of exact 

 equivalences between the necessary physical, physiological, and 

 psychological concepts. After the development of more advanced 

 concepts in the next two chapters, the exposition arrives at its 

 point : the principle of ultrastability, which in Chapter 8 is defined 

 and described. The next two chapters apply it to the nervous 

 system and show how it explains the organism's basic power of 

 adaptation. The remainder of the book studies its developments : 

 Chapters 11 to 13 show the inadequacy of the principle in systems 

 that lack part-functions, Chapters 14 to 16 develop the properties 

 of systems that contain them, and Chapters 17 and 18 offer 

 evidence that the principle's power to develop adaptation is 

 unlimited. 



The thesis is stated twice : at first in plain words and then in 

 mathematical form. Having experienced the confusion that 

 tends to arise whenever we try to relate cerebral mechanisms to 

 psychological phenomena, I made it my aim to accept nothing 

 that could not be stated in mathematical form, for only in this 

 language can one be sure, during one's progress, that one is not 

 unconsciously changing the meaning of terms, or adding assump- 

 tions, or otherwise drifting towards confusion. The aim proved 

 achievable. The concepts of organisation, behaviour, change of 

 behaviour, part, whole, dynamic system, co-ordination, etc. — 

 notoriously elusive but essential — were successfully given rigorous 

 definition and welded into a coherent whole. But the rigour 

 and coherence depended on the mathematical form, which is not 

 read with ease by everybody. As the basic thesis, however, 

 rested on essentially common-sense reasoning, I have been able to 

 divide the account into two parts. The main account (Chapters 

 1-18) is non-mathematical and is complete in itself. The Appen- 

 dix (Chapters 19-24) contains the definitive theory in mathema- 



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