Stigmergy and a Persistent Multicellular "Self"

The biological "self" is not about the genetic identity of the cells, it's about the identity of the body. Many cells in the human body are not human at all, they are single-cell organisms such as bacteria or yeasts. Conversely, identical twins have the same genetic identity, but are different selves. Similar difficulties in defining "self" arise in multicellular computing systems.

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.

What is Self?

For a single-cell organism, the boundary of “self” is straightforward. It includes the outer cell wall and all the structures, e.g., organelles, that exist within the cell wall. Inside is “self” and outside is “other.”

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.

Genetic identity cannot determine self

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.

“It has been estimated that there are far more bacterial cells associated with the average human body than there are human ones and one of the most important functions of our normal flora is to protect us from highly pathogenic organisms. ... A few of our normal flora produce essential nutrients (e.g., vitamin K is produced by gut flora) and our normal flora may prevent pathogenic microorganisms from getting a foothold on our body surfaces. ... Like it or not, we have large amounts of many types of bacteria growing almost everywhere in and on our bodies. About 10 percent of human body weight and 50 percent of the content of the human colon is made up of bacteria, primarily the species known as Escherichia coli, or E. coli.” See here.

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 stigmergy 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