Biological and digital messages are transmitted by linear sequences of interchangeable elements - "alphabets" if you will. Cells use messenger molecules constructed of chains of simple chemical subunits called nucleotides, labeled in shorthand as A, C, T, G and U. Computers use messages composed of sequences of bytes.
Life has evolved two generic sorts of long-chain
molecules. One, molecules of DNA or RNA, are long chains
of nucleotides that primarily serve to carry the genetic
'program' of the cell. The others are proteins which are chains
of amino acids that fold tightly upon themselves to form complex
shapes that determine their functional/structural properties.
Protein chains tend to be from a few dozen to a few thousand
amino acids in length. Once folded, they become the "parts" that
make up most of the machinery of the cell. In contrast,
DNA when not active in its "code" role, is folded tightly so
that it cannot accidentally be "executed". Only when
playing its genetic coding role is it unfolded to expose its
coding sequence to the protein machinery that interprets its
execution. Chains of RNA can play both sorts of roles: they may
fold into functional shapes, much like a protein, to act as
"parts" in larger complexes, or their genetic sequence may be
interpreted programmatically (the details of the two roles of
RNA are beyond the scope of the current topic). In general,
however, transfer of messenger proteins cause the cell to select
behavior from its existing repertoire whereas transfer of
genetic material changes the repertoire itself. Metazoan cells
have predetermined functions and can seldom if ever tolerate
having their functional repertoire changed.
The distinction between the two kinds of message is central to communication strategies in biology and communication strategies in computing. The parallels between the two realms can help us to understand multicellular computing. Whereas single-cells and single computers can afford to exchange executable code, and often benefit by doing so, code exchange in multicellular systems is exceedingly dangerous -- it is all too often a vehicle for infection by a virus. That is why DNA exchange is taboo in multicellular life. In computing, we are learning the importance of that taboo the "hard way" as we cope with increasingly dangerous digital viruses and worms. Polymorphic non-executable messages are far better suited to communication in multicellular systems.