The function of the organism hinges on the performance of itsinformation-processing networks, which convey information via molecularrecognition. Many paths within these networks utilize molecular codebooks, suchas the genetic code, to translate information written in one class of moleculesinto another molecular "language" . The present paper examines the emergenceand evolution of molecular codes in terms of rate-distortion theory and reviewsrecent results of this approach. We discuss how the biological problem ofmaximizing the fitness of an organism by optimizing its molecular codingmachinery is equivalent to the communication engineering problem of designingan optimal information channel. The fitness of a molecular code takes intoaccount the interplay between the quality of the channel and the cost ofresources which the organism needs to invest in its construction andmaintenance. We analyze the dynamics of a population of organisms that competeaccording to the fitness of their codes. The model suggests a generic mechanismfor the emergence of molecular codes as a phase transition in an informationchannel. This mechanism is put into biological context and demonstrated in asimple example.
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