"Although I clearly observed Oliver's lips form the three syllables of his name, no sound could be heard to issue forth. Instead, from his mouth dropped what appeared to be a wooden ball of irregular, though roughly spherical, shape."

Sunday, May 15, 2005

On the Use of "Information Talk" in Biology - Introduction

[Note: This is clearly very much still a draft version. Very clearly, very drafty]

In biology, especially molecular biology and genetics, much use is made of the analogy between the structures and processes of genetics and those of the world of human artifacts such as computers and radios. Thus it is said that genes "carry information" about proteins and phenotypic traits, DNA is "read", translated, transcribed, and decoded; mutations arise by "copying errors", and are sometimes fixed during the duplication process by "proof-reading" mechanisms; and so on. Note that this is not merely a feature of popularizations of science, translating complex ideas into language more easily understood by the public; on the contrary, the information metaphor was vital to in developing the first understanding of how DNA functions. [\footnote{Quote JMS - no Rosetta stone; studying it just by chemistry would take forever.}]

However, the details of how good this analogy really is have come under considerable scrutiny by philosophers of science, with opinions varying widely as to whether such talk of "biological information carried in genes" is (at one extreme [JMS]) literally correct, and in need of precise fleshing out, or (on the other hand [Griffiths]) both imprecise and misleading.

The general question of what makes an analogy good or bad, useful or misleading,is obviously too large to be tackled within the scope of this essay [\footnote{Find some refs on goodness of analogies in the Phil Lang literature.}]; nor would it be appropriate to attempt to give a full account of how analogies are used and are understood, or how they inform, convey meaning, or provoke new ideas. Fortunately, such a detailed analysis of analogy and metaphor is unneccesary for the present case, and a few general remarks, outlined in the next section and developed elsewhere, will suffice.

Having set out some of this general background, we turn straight to the central disagreement between the two sides. Taking John Maynard Smith and Paul[?] Griffiths as representatives of the opposing camps, we find that the point of opposition is easily described. Maynard Smith thinks that the analogy with information storage and processing is a good one[\footnote{Indeed,good enough that such "information talk" should be taken as literal, not merely metaphorical - but this distinction goes beyond our present scope.}], while Griffiths claims that it is misguided, drawing from a too-limited stock of examples on the biological side, and therefore more misleading than useful.

To explore this disagreement, we will examine some of the ways JMS defines the analogy - the features of genetic systems that are analogous with conventional information processing technology - and defends it against some of the simpler objections of critics. We then consider some further objections by Griffiths, which seem to support a position that he calls "the Parity Principle", namely that 'there is no sense in which genes carry information about phenotypes that is not also exemplified by non-genetic factors'. Thus talk of "genes carrying information" (as distinct from non-genetic factors) implies a priviledged distinction where none exists, and so is misleading.

In the final section of the essay, we consider how a defender of the analogy such as JMS should respond to Griffiths' objections. Can his examples of non-genetic factors which meet JMS's definition of information-cariers be somehow excluded? Can this definition be further refined or re-worked in order to cover all and only the factors JMS requires for the information analogy to hold firm? To answer this question, we need to know what it is about the analogy that makes it worth defending. Why does JMS want to justify talk of "molecular biology as a branch of information theory"? It can only be that he thinks such a view will be useful in developing our understanding of biological systems. Bearing this in mind, we consider how an information analogy (refined to take account of all the relevant data about genetic and non-genetic factors etc.) could be useful in biology, and how it might be possible to establish such an analogy more rigorously.


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