As multicellular computing becomes more and more complex, we face an increasingly difficult problem of protecting large diverse systems, such as corporate IT systems, from intruders, viruses, worms, denial-of-service attacks, and other tricks used by cyber-warriors, cyber-criminals, rogue employees and hobbiest hackers. One idea that comes up periodically is to somehow mimic an immune system that distinguishes between self and non-self, protecting the one and killing the other. Yet that's not as straightforward as people often assume. The underlying assumption in the immune system metaphor is that a biological "self" is a collection of cells with the right genetic IDs. Therefore, determining self is just a matter of "checking the IDs" of all the cells. In the case of multicellular computing, this would perhaps be done via certificates or other nominally incorruptible and unforgeable tokens. However, that is a misreading of what "self" versus "other" means in the biological world. It turns out that a healthy organism often includes cells other than those directly related to the metazoan's "own" cells. A Metazoan must distinguish its own cells from dangerous bacteria or virus infected cells, it must not kill its beneficial single-cell partners. Termites and cows, for example, absolutely require gut bacteria to digest their cellulose-laden diets and those bacteria depend upon their host to provide the cellulose they live on.
For multicellular organisms, the answer is more complicated but it comes down to one simple fact: the cells in a multicellular organism share a physically co-located structure – for animals, it is their “body.” The body constituting a multicellular “self” is a stigmergy structure that is created by the body's cells. The cells build the body as the organism grows and the body, in turn, does much to coordinate the actions of the cells as they cooperate over their lifetime and even as they build the body. The organism begins with a fertilized egg that divides repeatedly according to its developmental program. In the process, the living cells create or assemble nonliving structures that provide form, cohesion, containment, stiffness, moving parts and protection. These structures include bone, sinew, connective tissue, fur, shell, scales, chitin, bark, wood, and all manner of other non-living extracellular material. That is, Metazoan cells construct and continually maintain the very bones, sinews, etc. that help to protect, organize and provide the physical structure of the multicellular body. This body is a stigmergy structure that, together with all the cells that live within it, defines the self. Therefore, a multicellular self is a unit of benefit in the competition for survival of the fittest. Although only the germ line is passed on when an individual survives long enough to reproduce, all the cells in a multicellular organism, together with their non-living constructs, compete as a unit and therefore live or die as a unit. Evolutionary processes select for the fitness of the whole organism, i.e., the whole stigmergy structure.
The collection of Metazoan cells that descend from the fertilized egg is only part of the genetic identity of the organism. Complex multicellular organisms are ecologies in which many various species of single-cell organisms play vital cooperative roles. In humans, more than ten thousand species of bacteria and yeasts cohabit with us and play beneficial roles.
Upwards of 500 species live on our skin, others in our mouths, still
others in our urogenital tracts. And each persons complement of
bacteria is different. These single-cell partners are
often the first line of defense
against infection by less friendly bacteria. Our formal immune system
only comes into
action when the first line fails. An
immune system that insisted upon
destroying these symbiotic organisms would destroy itself.
Nor does the genetic identity of the Metazoans cells necessarily distinguish one self from another. Starfish generate new selves from pieces of themselves when dismembered. Many plants generate new selves from cuttings. And human identical twins have identical genetic makeup. In all these cases, multiple distinct selves share the same DNA. That is, each of these genetically identical selves benefits separately from surviving long enough to pass on their genes to the next generation.
So, what determines "self"? The body, not the identity of any or
all of its cells. Similarly, in multicellular computing, self is
far more determined by the computing
structure (body) it participates
in than by some magic "identity"of the
individual computers, e.g., encrypted certificates.
Contact: sburbeck at mindspring.com
Last revised 6/13/2012