Chapter 2 

 SYSTEM AND ENVIRONMENT 



The multiplicity of variables in biological systems is reflected by a correspond- 

 ing multiplicity of experimental disciplines, from biophysics to evolutionary 

 genetics. It would be extremely difficult to define explicitly the hne of demar- 

 cation between these different fields of study, for they all overlap at the edges; 

 and furthermore there is an undeniable unity in the biological sciences which 

 knits them together inextricably. However, in a study of the dynamic properties 

 of a certain class of biological phenomena such as we are attempting, it is 

 necessary to extract a manageable number of variables from the very large 

 array which occurs in any biological system. Is it ever possible to make such 

 an extraction or simplification without doing violence to the very basis of 

 biological organization, its inherent complexity ? There is certainly no a priori 

 answer to this question, and the only procedure is to try to find some set of 

 variables which appear to constitute a reasonably self-contained system and 

 see if one can get meaningful and useful results relating to its behaviour. In 

 order to do this, it is necessary to make some distinction between variables 

 which are major to the phenomena being investigated and those which are 

 minor. Having made the distinction, the former variables become the quan- 

 tities that define the system which one intends to study, while the latter become 

 either parameters of the system, thus defining its environment, or they are 

 relegated to that most useful of analytical categories: noise. Noise really 

 represents ignorance, and we will make much use of it in the present study. 



The analytical basis for distinctions between system and environment in 

 biological systems should be applicable throughout the whole range of pheno- 

 mena embraced by experimental biology. Perhaps the most obvious criterion 

 to use is the time scale on which a particular field of study operates, and this 

 has in fact been the most commonly used determinant for ordering the biolo- 

 gical sciences into a linear array. At the "bottom" comes biophysics, and at 

 the "top" is population genetics, to cover only the strictly experimental, not 

 the historical, disciplines. We find this ordering of biological processes in 

 time clearly drawn by C. H. Waddington (1957) in his " Strategy of the Genes", 

 where he observes that "the main respect in which the biological picture is 

 more complex than the physical one is the way time is involved in it". 

 Waddington distinguishes three levels of activity in time which are required for 

 the analysis of biological process : biochemical, developmental or epigenetic, 

 and evolutionary. It is precisely these categories which will form the basis for 

 a distinction between different systems and their environments in the present 

 study, and we will refer to them as the metabolic, the epigenetic, and the genetic 

 systems respectively. Since our main interest is in intracellular processes, these 



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