Stigmergy Organizes the Multicellular "Self"

"Self" in living organisms refers to the identity of the body rather than the identity of its cells. Our bodies contain many non-human single-cell bacteria or yeasts. Conversely, identical twins have the same genetic identity but are different selves. Similar issues arise in defining and protecting the integrity of multicellular computing systems.

As multicellular computing becomes more and more complex, we face an increasingly difficult problem of protecting large diverse systems. Corporate IT systems for example face attacks by intruders, viruses, worms, distributed denial-of-service (DDoS) attacks, and other tricks used by cyber-warriors, cyber-criminals, rogue employees and hobbyist hackers.

One oft proposed idea for defending such systems is to somehow mimic the way a biological immune system distinguishes between self and non-self, protecting the one and killing the other. 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. But that's not as straightforward as people often assume.

Genetic identity does not determine self

The collection of Metazoan cells that descend from a fertilized egg is only part of the genetic identity of the organism. 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 feed on. So the genetic identity of cows must also include their gut bacteria. A Metazoan therefore needs to distinguish its own cells from dangerous bacteria or virus infected cells, but it must not eliminate the beneficial single-cell partners it relies upon.

Multicellular organisms are ecologies in which many various species of single-cell organisms play vital cooperative roles. The ecology of various microbial species living in or on a multicellular organism is called it's microbiome. The human microbiome contains more than ten thousand species of bacteria and yeasts that cohabit our bodies and play beneficial roles. The body contains trillions of microorganisms-outnumbering human cells by 10 to 1. It now is clear that "...microbes contribute more genes responsible for human survival than do our parents genomes."

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 5000 species live on our skin, others in our mouths, others in our gut, and still others in our urogenital tracts. And each person's complement of bacteria is different; men's differ from women's, and the bacterial complement of one hand differs from the other! 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 that first line fails. An immune system that insisted upon destroying these symbiotic single cell 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 human genetic makeup although not necessarily identical microbiomes.

What is Self?

For a single-cell organism, the boundary of “self” is straightforward. It is defined by the cell wall. It includes all the structures within the cell such as the cytoskeleton, organelles, and genetic structures that exist within the cell plus sensory molecules and motile structures (flagella and cillia) that span the cell wall to import information about its surroundings and to move about in its environment. In computing terms, those are the input and output functions (I/O). Inside the cell wall 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 build the body and then cooperate over their lifetime.

The organism begins with a fertilized egg that divides repeatedly according to its developmental program and environmental factors that help to steer that 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.

So, what determines "self" in multicellular computing? It is not the identity of any or all of the various digital devices interconnected, perhaps intermittently, by the corporate networks. The multicellular computing self is far more determined by the computing stigmergy structure (body) that it participates in than by some magic "identity"of the individual computers, smart-phones, routers, firewalls, thumb-drives, and even printers.

Last revised 3/14/2015