Volvox showed us something remarkable.
Cells can become differentiated components of a larger organism.
But that is not the only route to biological individuality.
There are organisms in which many bodies remain visibly distinct while becoming so tightly integrated that it becomes difficult to say where one organism ends and another begins.
This raises a more difficult question:
How many bodies can a single life contain?
The problem of the colony
A colony is not necessarily an individual.
Bacteria can form dense populations.
Cells can aggregate.
Organisms can cooperate.
None of this by itself means that a new individual has emerged.
The interesting question is what happens when the members of a collective become functionally dependent upon one another.
At some point, the distinction between:
many organisms
and:
one organised whole
becomes difficult to maintain.
Sponges at the boundary
Sponges provide a useful early example in animal evolution.
They contain several specialised cell types, and their bodies integrate activities involving feeding, internal transport, reproduction and environmental interaction. They are also especially informative for understanding the transition from unicellular relatives to multicellular animals.
Yet a sponge does not look much like the kind of individual we instinctively imagine.
There is no nervous system coordinating its activities.
Its organisation is distributed among cells embedded in a common structure.
The whole nevertheless has properties that cannot be understood simply by considering each cell separately.
Integration without centralisation
This gives us a recurring pattern.
We have already encountered distributed organisation in slime moulds.
We encountered differentiated organisation in Volvox.
Now we see those principles becoming more elaborate.
The body can be:
integrated without being centrally controlled.
The organism's organisation is distributed across many interacting processes.
There is no little executive sitting somewhere inside it.
The unity lies in the organisation of the relations.
Colonial organisms complicate things further
Siphonophores are an especially striking case.
They are colonial hydrozoans made up of specialised zooids attached to a common stem and connected by shared internal structures. Different zooids perform different functions, including feeding, locomotion and reproduction.
They can therefore look like collections of animals.
Yet the colony functions as an integrated whole.
A zooid is not simply an independent animal living beside another.
Its possibilities are defined partly by its role within the colony.
Many bodies, specialised roles
This takes us back to Volvox, but at a different level.
There, cells differentiated into somatic and reproductive roles.
In siphonophores, specialised zooids perform distinct functions within a larger colonial organisation.
The pattern is:
differentiation → interdependence → integration
The parts become more specialised.
The whole becomes more capable.
And the independence of the parts becomes correspondingly reduced.
The loss of independence creates the individual
This is one of the most interesting themes emerging from multicellular evolution.
An individual is not necessarily produced by adding things together.
It can be produced by making separation progressively less viable.
As functions become specialised, the lower-level units may lose the capacity to maintain an independent life.
Their fitness becomes increasingly tied to the success of the collective. Evolutionary studies of multicellularity describe this as a shift in individuality from lower-level units toward a higher-level individual.
In that sense:
individuation can emerge through interdependence.
What happens to biological value?
Now our original question returns.
A cell has its own organisation.
But its possibilities are altered when it becomes part of a larger whole.
Its immediate functioning contributes to the organism.
Its own fate becomes linked to the fate of the collective.
We therefore have nested forms of value:
cellular value
within:
organismic value.
The lower level has not necessarily ceased to matter.
But its organisation has become part of something larger.
Component or participant?
This raises an important distinction.
A component is something whose activity contributes to a larger system.
A participant is something that remains, in some meaningful sense, an independent locus of organisation while entering relations with others.
At the multicellular boundary, these categories become difficult to separate.
A cell may be a component of an organism while still retaining considerable autonomy.
A zooid may be highly specialised yet retain some distinct organisation.
Where the boundary lies is therefore not obvious.
Perhaps individuality is not a binary property.
Perhaps it is an organisational achievement that comes in degrees.
The same organism at different scales
Our topology now acquires another dimension.
At one scale:
cells matter to one another.
At another:
cells constitute tissues.
At another:
tissues constitute organisms.
At another:
organisms participate in populations and ecosystems.
A living system can therefore be simultaneously:
a whole at one level, and a participant or component at another.
There is no single privileged scale at which "the real organism" must exist.
This complicates our notion of sociality
It also warns us against calling every integrated collective social.
A human community is made of individuals who remain individuals.
A siphonophore colony contains specialised units whose individuality is profoundly altered by integration.
These are not the same kind of organisation.
So our distinction becomes increasingly useful:
integration is not sociality.
A new individual can emerge from the integration of lower-level individuals without those lower-level units becoming social participants.
And yet integration creates relations
Even where sociality has not appeared, relational significance has become much richer.
A component's condition affects the whole.
The whole affects the component.
The resulting feedback can be profound.
The organism therefore contains an internal topology of significance.
This topology is not social in the human sense.
But it demonstrates something important:
relational organisation can become constitutive of individuality without becoming social mattering.
The evolutionary threshold
This gives us a more nuanced sequence than the simple progression we began with:
individual value
↓
relational significance
↓
collective coordination
↓
integration
↓
differentiation
↓
higher-level individuality
And only after this do we need to ask about the emergence of something recognisably social.
That is exactly the question waiting for us.
The animal body was not inevitable
Multicellularity has evolved repeatedly in different lineages, and evolutionary transitions to multicellular individuality involve changes in adhesion, communication, differentiation and genetic regulation. The origins of animal multicellularity were particularly consequential because new cell types and coordinated developmental organisation had to arise.
There was therefore no single obvious route from cell to animal.
Different lineages explored different organisational possibilities.
That is important for our project.
We should think in terms of solutions to problems of organisation, not a ladder with humanity waiting at the top.
What multicellularity teaches us
Perhaps the deepest lesson is this:
A new level of individuality can emerge when the possibilities of lower-level participants become sufficiently interdependent that the collective acquires its own organisation.
The new whole is not simply the sum of its parts.
Nor does it replace them.
It reorganises them.
Their constraints become part of the conditions under which the new individual can exist.
The next question
We have now seen several ways of getting from many living units to a larger organised whole.
But none of these cases yet gives us the kind of social organisation we have been looking for.
For that, participants must remain distinct enough that their relations with one another become significant as relations among participants, rather than merely as parts of a single organism.
So we finally arrive at the threshold we have been approaching from the beginning:
When does biological value become social mattering?
No comments:
Post a Comment