The second of the four principles of multicellular systems is that the receiver, not the sender, of messages must determine the meaning of the message. That principle is known in computing as polymorphic messaging -- different receiving cells (or computers) may interpret the message differently according to their different specialized function.
Both living and computing systems are about information processing. Necessarily, then, they must export and import information. Living organisms import information about their environment to find food or avoid danger. And their unavoidable need to export biochemical by-products of their metabolism provides information to surrounding organisms. Computers likewise must import and export information. Because multicellular organisms and computers are specialized, their cooperative behavior requires more orchestration. So the way they exchange information becomes far more important. Cooperation between specialized elements requires complex and selective messages.
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. Computers use messages that are sequences of bytes.
Life has evolved two sorts of chain molecules: proteins, which are chains of amino acids, and DNA or RNA, which are chains of nucleotides that carry the genetic 'program' of the cell. Protein chains tend to be from a few dozen to a few thousand amino acids in length. Functional RNA chains can be as short as 10-20 units or as long as a million units. Bacterial DNA molecules are a few million units long. Human chromosomes, each of which is one contiguous chain of paired nucleotides, range in length from 50 million base pairs to about 250 million base pairs. DNA/RNA differ from messenger proteins in their relationship to the cellular CPU (its nucleus in which complex control mechanisms determine which chunks of genetic material will be expressed). DNA and RNA are “executable” by the cellular machinery whereas proteins are not. Transfer of messenger proteins causes the cell to select behavior from its existing repertoire whereas transfer of genetic material changes the repertoire itself.
Digital messages in computing are strings of bytes that range from idiosyncratic binary codes to highly structured XML messages such as SOAP or other Web Services messages. Some strings are executable and some are not depending on the computer’s CPU (or interpreters for scripting languages such as Javascript or ActiveX). Thus, both life and computing have evolved two forms of complex information media: one executable and the other not.
The distinction between the two kinds of message is central to communication strategies in biology and communication strategies in computing. The parallels can help us understand multicellular computing. Whereas single-cells and single computers 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.
Contact: sburbeck at mindspring.com
Last revised 5/29/2010