InterJournal Complex Systems, 425
Status: Accepted
Manuscript Number: [425]
Submission Date: 719
Revised On: 10206
Language as a Model of Biocomplexity
Author(s): Sungchul Ji

Subject(s): CX.3, CX.07, CX.41

Category: Article


Biocomplexity is simply defined as the property of living systems that cannot be completely accounted for in terms of the properties of their components and their interactions. To understand biocomplexity, it is proposed that natural (or human) language be adopted as a convenient model, language being one of the most complex systems ever to have evolved or been invented by human society. Such a proposal gains some support from the recent finding that living cells use a language whose properties are similar in principle to those of human language (S. Ji, BioSystems 44:17-39 (1997); Ann. N. Y. Acad. Sci. 870:411-417 (1999) ). One of such principles is the so-called 'rule-governed creativity,' according to which the human brain (the cell) can produce an almost infinite number of meaningful sentences (protein-protein interactions) based on a finite set of words or the lexicon (proteins) and grammatical rules (specificity of molecular interactions). Material systems that exhibit rule-governed creativity are referred to as 'creatons,' examples of which include biopolymers, metabolic networks (metabolons), cells, multicellular organisms, groups of organisms, and the biosphere. A creaton embodies two kinds of information -- i) the internal information, Ii, originating from inside of system, and ii) the external information, Ie, derived from factors external to the system. We may represent this idea as Ic = Ii + Ie = Ii ( 1 + C), where Ic stands for the information of a creaton (i.e., the information required to completely specify a creaton), and C is the ratio, Ie/Ii , called the 'creativity' index, and the equation itself may be referred to as the 'complexity equation.' It is further proposed that the Ii term in the complexity equation corresponds to the rule-governed aspect of a creaton, while the Ie term reflects the creative aspect engendered by the interaction between a creaton and its environment. The former aspect is in principle predictable from the component properties of a creaton, whereas the latter is unpredictable because of the history of the interactions between a creaton and its environment. As a specific example, we can consider an enzyme viewed as a creaton. An enzyme embodies two kinds of information -- Ii such as its secondary structure mostly predicable from its primary amino acid sequence, and Ie such as its tertiary and quaternary structures which are unpredictable from its primary structure because their folding patterns are extremely sensitive to microenvironmental factors (pH, ionic composition, local electric fields, presence or absence of other proteins, etc.) inside the cell during their genesis. Three main conclusions have been drawn: (i) All biocomplex systems can be viewed as creatons. (ii) Biocomplex systems embody two kinds of information, internal information, Ii , and external information, Ie. (iii) The cause of complexity in biocomplex systems is attributed largely to Ie, which can be viewed as a memory of the interaction between a biocomplex system ( a creaton) and its environment encoded in the material structure of biocomplex systems.

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