A watershed differentiating between living and nonliving matter is that living matter is mediated. In fact, we can even argue that the qualitative difference between the two is evident whenever mediation enters the picture. This argument is far from clear or trivial, and its implications are even less trivial. What do we mean when we say that living matter is "mediated"? In a nutshell, the idea is that what characterizes living systems as a unique category of matter is that their behavior cannot be reduced to simple interactions between dyads. There is always a third party - a boundary condition, to use Michael Polanyi's term - whose description cannot be reduced to the language of the dyads. Whereas interactions between atoms are unmediated and occur through the direct exchange of electrons or through weak forces, the interactions that characterize living systems are always mediated by a third party. For example, the synthesis of proteins based on genes is not direct; mediation by RNA is a must.
The concept of mediation becomes more comprehensible if we explain it in terms of codes. A code is a set of rules of correspondence between two independent worlds (see Barbieri's editorial), and as such it prevails in both the organic and the mental realms. Codes are conventional in the sense that the correspondence between the realms is not established through rigid, universal, and transcendental laws but through
Ben-Gurion University of the Negev, Beer-Sheva, Israel, e-mail: [email protected]
M. Barbieri (ed.), The Codes of Life: The Rules of Macroevolution. © Springer 2008
convention (Barbieri, 2003): biological, psychological, or sociological. The "rules" that govern the codes of life are "rules" of coordination rather than the laws of logic or physics. Understanding living systems means understanding codes, from the organic codes that constitute the organism to the codes that constitute its mental life. It should be noted that the study of codes does not imply the study of simple rules of correspondence between different realms. Living organisms are paragons of complexity and studying biological complexity obliges us to move beyond simple models of coding to the way mediation constitutes the human organism.
The aim of this chapter is to illustrate this paradigmatic shift by dealing with a specific case - the immune self. My aim is to show how our understanding of the immune self can shift from simple rules of correspondence to the complexity of a meaning-making perspective on the immune self. This will be done in terms of the interrelations of two fields - semiotics and immunology - that have been following a similar trajectory from correspondence to complexity.
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