Sunday, July 15, 2012

Life: Hypercycles, Meaning, and Prebiotic Evolution

I'm posting some old notes (March 1988) as background to some of the pluralism posts I've been making. These notes are relevant to thinking about Realms of Being, in particular, the Realm of living things.

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Manfred Eigen, William Gardiner, Peter Schuster, Ruthild Winkler-Oswatitsch, "The Origin of Genetic Information," Scientific American 244, # 4: 88 - 118, April 1981.

p. 107:
Darwinian competition in a quasispecies distribution was based on selection according to the chemical kinetics of the sequences; what the sequences 'meant' played no role. The meaning of the message could not be ignored when hypercyclic organization of enzymes and RNS's came linto play, since the meaning governed the strength of the coupling. The one-directional character of the cyclic coupling, however, still excluded any feedback that would allow genetic meaning to be evaluated and so make possible selection of the best information.
To get feedback permitting the evaluation of genetic meaning Eigen et al. hypothesize that we get compartmentalization. A wall is built around a small volume of chemical soup in which a particular hypercycles is active. The genetic material in the soup codes the information necessary to build another enclosed volume (i.e. a cell). Now hypercycles can compete with one another. And genetic information can be evaluated. Now we have a meaningful genotype-phenotype distinction. In a way I don't really understand, that distinction is what allows us to talk properly genetic code, a physical structure which has a meaning.

Meaning–where meaning is 'information' about the environment 'stored in' a cell– arises from the interaction of these cells with their environment. Some cells will do better than others. Let us start with cell A0. It divides and becomes A1 and A2. A2 mutates and divides, producing A4 and A6. A1 one remains stable and divides, becoming A3 and A5. The mutation is favorable, making A4 and A6 more viable than A3 and A5 and so their descendants do better in future divisions, perhaps even eliminating the descendants of A3 and A5. That increment of improvement can be interpreted as information about something (either the environment or internal regulation), something which affects the viability of the cell. Under these conditions the structure of the DNA will begin encode information about the world, information which increases the likelihood of survival. The longer this goes on, the more information is encoded in the DNA strand.

Eigen et al. describe a sequence of steps which begins with the self-replicating chemical kinetics of RNA molecules and ends in something which can be meaningfully called the replication of a living cell. It seems to me that the genotype-phenotype is their boundary between the living and the prebiotic and that that distinction is closely related to the conception of coding (with the distinction between a physical substrate and meaning) which I've been dealing with. Information, as defined by information theory, has to do with the structure of the physical substrate. Meaning has to do with the overall operation of the system in which the information-bearing physical substrate functions.

The physical substrate always has its own structures and interactions, all of which are governed only by the appropriate physical laws. Because of this mutations are possible and the rate at which they occur depends only on the physical laws of the substrate, not on the laws governing the survival of the system in its environment. However, the results of these physical processes may well change the meaning of a particular message because one signifier will either be made meaningless or be transformed into another. The physical processes of the code are not dependent on the meanings of the code strings, but those processes may change meanings. Because of this some changes in the physical substrate will be favored over others (or over the absence of change).

Coding divides a system into a substrate and an environment, which gives that substrate meaning. The laws of the substrate are independent of the laws of the environment. But, because of the coding relationship, the events in one domain are not completely independent of the events in the other domain. There is a directed coupling. The environment determines the physical success of the substrate. Because that is so, random changes in the substrate (that is, random with respect to the meanings attached to the substrate items whose structure is altered) can "trap" information about the environment. The substrate, in conformity to its laws, changes. The environment, in conformity to its laws, says "yes" or "no." And so evolution can proceed. The substrate continues to generate changes and the environment continues to render verdicts. Over time, the structure of the substrate becomes more and more "adapted" to the structure of the environment.

The laws of the environment are physical laws. The organism is a physical system existing the environment. The laws of the physical substrate are physical laws (the same as the laws of the environment). The peculiar nature of the coding structure and process means, however, that the laws of the long-term interaction of the organism and its environment are not mere physical laws. They are informatic laws, or physical laws of a higher order -- whatever words and phrases you may choose, these laws are of a different realm of being.

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