What is Self?

For multicellular organisms, the answer is more complicated but it comes down to one simple fact: the organisms, including biofilms, share a physically co-located structure – their “body.”  Such a multicellular “self”  is a stigmergy structure that is created by the body's cells. That is, the cells build the body and the body, in turn, helps to coordinate the actions of the cells.

The organism begins with a fertilized egg.  As this single cell divides repeatedly according to its developmental program, the organism grows.  In the process, the living cells create or assemble nonliving structures that provide form, cohesion, containment, stiffness, moving parts and protection.  Examples include bone, sinew, connective tissue, fur, shell, skin, 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 clearly 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 is neither necessary nor sufficient to determine self

Genetic identity is not necessary nor even desirable within a multicellular organism because most multicellular organisms benefit from symbiotic relationships with a wide variety of single cell organisms that live within them.  Complex organisms are typically ecologies in which many various species of single-cell organisms play vital cooperative roles.  In humans, at least a thousand species of bacteria and yeasts cohabit with us and play beneficial roles.

These single-cell protectors are often the first line of defense against infection.  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 is the genetic identity of cells in Metazoans sufficient to determine self.  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.