Reflexions sur l'usage,en biologie,de la theorie de l'information

For living beings, information is as fundamental as matter or energy. In this paper we show: a) inadequacies of quantitative theories of information, b) how a qualitative analysis leads to a classification of information systems and to a modelling of intercellular communication. From a quantitative point of view, the application in biology of information theories borrowed from communication techniques proved to be disappointing. These theories ignore deliberately the significance of messages, and do not give any definition of information. They refer to quantities, based upon arbitrarily defined probabilistic events. Probability is subjective. The receiver of the message needs to have ‘meta-knowledge’ of the events. The quantity of information depends on language, coding, and arbitrary definition of disorder. The suggested objectivity is fallacious. In common language, the word ‘information’ is synonymous with knowledge of order. Following common sense a message (letters, coded signals, etc.) is information just in case it is interpretable, i.e.if it fits to a previously acquired meaning (the words of an available language, etc.). The consequence is that calculation of quantities in the sense of Shannon can be used for transmissions, but it is itself meaningless (has no significance). In linguistics and semantics, information is composed of a ‘signifier’, a physical medium (letters, coded signals, etc.), and a ‘signified’ or significance. The nature of information is complex. The laws of linguistics and semantics are valid not only at the human, organismic level, but also at the cellular and molecular level. The physiology of sensations gives us many examples for application of a concept of information An electromagnetic wave of 0,7% give us the sensation of a red colour. Sensations have no physical reality. They are purely subjective. At the cellular level communication operates by means of chemical messengers (first messengers), which generally do not penetrate the plasmic membrane. Specific captors operate as transductors: external factors are converted into secondary messengers (cyclic AMP, Ca ion, etc.). Sometimes, electric signals (like depolarization waves) may also play a part in the intercellular communication. Such processes are characterized by changes in a sequence of different molecules carried by a physical signal. What is transmitted is themeaning of the message (significance) which can be memorized by the cell, providing a possible following use. At the molecular level one can find also the processes of linguistic nature. We know that the significance of a word is changed with changing the order of letters (ADD→DAD, etc.). In the same way bases C and U are coding for serine (UCC), leucine (CUC) or proline (CCU). Here, amino-acids express the significance. In spite of the fact that this key-lock mechanism may explain many reactions, the examples prove that other elements are necessary for understanding the information. The living cell is the receiver. The message actualizes only previously learned and memorized significances or actions (trigger effect). Significance is not an emergent property of the shape of the message. It depends on the receiver and the transmitter. A word can have more than one meaning. Similarly, a messenger can order different physiological responses: muscular tension, hormonal secretion, etc.. Thus a chemical messenger is a signal which is identified and interpreted by the receiver, depending upon specific languages and previous learning. These views are in harmony with immunological and Jerne's theory (of idiotypical net). The above mentioned considerations led the author to propose thetheory of data transfer, which takes into account significance. In this theory the quantity of information is the product of the probabilistic recognition of message and the value of significance as determined by its semantic level. (See: Acta biotheoretica vol. 41 No 1/2 June 1993.) The complex nature of information asks to propose a qualitative classification with respect to thematerial support and thesignificance.

1. The material support may be linear in time (sequential reading, ADN translation)-The material support may be referred to non-temporally (drawings, logos, holograms) (Reading is instantaneous)-The material support may be in circulation, or in stock.
2. The significance may be local (tissues, organs) or general (organisms). Asignificance may be a command to be executed (imperative, conditional order) or knowledge to bememorized. The purpose of significance may be a coding for space (for morphology) or for time (ontogeny, ageing).

Conclusion: Information cannot any longer be regarded as an object. Its nature is complex, at all levels of a living being. At the molecular level to memorize an information by modification of a molecule is comparable with writing words on a diary. The key-lock process does not suppress the question of the interpretation, i.e. relations existing between the shape of a microscopic element as a molecule, and its macroscopic effect, as an antenna or a leg. There are still many unclear points in these relations, e.g. the sweet taste of molecules of tomatine and monelline. The abstract nature of significance which at the human level is concerned to mental processes, is not only a philosophical problem. In fact, there is a hypothesis based on quantum mechanics which allows to consider a physical nature of significance. In any case, the important conclusion is that significance in bio-information must be considered in relation to the message-receiver. The receiver must no longer be considered a passive one. The qualitative classification of information will allow an understanding of circulation of information in organisms and between cells.