  The function of the organism hinges on the performance of its
information-processing networks, which convey information via molecular
recognition. Many paths within these networks utilize molecular codebooks, such
as the genetic code, to translate information written in one class of molecules
into another molecular "language" . The present paper examines the emergence
and evolution of molecular codes in terms of rate-distortion theory and reviews
recent results of this approach. We discuss how the biological problem of
maximizing the fitness of an organism by optimizing its molecular coding
machinery is equivalent to the communication engineering problem of designing
an optimal information channel. The fitness of a molecular code takes into
account the interplay between the quality of the channel and the cost of
resources which the organism needs to invest in its construction and
maintenance. We analyze the dynamics of a population of organisms that compete
according to the fitness of their codes. The model suggests a generic mechanism
for the emergence of molecular codes as a phase transition in an information
channel. This mechanism is put into biological context and demonstrated in a
simple example.
