We have now seen several ways in which biological organisation can become more than the sum of its parts.
Organisms can signal to one another.
Formerly independent organisms can become integrated into a new individual.
Distributed processes can coordinate without a centre.
But multicellularity introduces another possibility.
What happens when living cells become differentiated components of a larger organised body?
Volvox gives us a remarkably clear case.
From colony to organism
Volvox carteri belongs to a group of green algae containing unicellular, colonial and multicellular forms, making the group particularly useful for studying the transition to multicellularity.
An adult Volvox spheroid contains thousands of small somatic cells and a much smaller number of larger reproductive cells called gonidia. The somatic cells occupy the surface and provide coordinated motility; the gonidia reproduce.
The cells have therefore become differentiated.
They no longer all do the same thing.
Their differences are part of the organisation of the whole.
Division of labour
The somatic cells have flagella and contribute to the movement of the spheroid.
The gonidia are specialised for reproduction.
Somatic cells are terminally differentiated and do not reproduce; the gonidia generate the next generation.
This creates something very different from a loose collection of cells.
The capabilities of the whole depend upon different kinds of cells performing complementary functions.
The organisation has become differentiated.
But what is the participant?
This raises a question that is particularly important for our project.
The individual cells remain living systems.
They have their own metabolic organisation.
But the Volvox individual's possibilities depend upon the coordinated organisation of all its cells.
The somatic cell contributes to the life of the spheroid.
The gonidium contributes to its continuation across generations.
So who is the participant?
The cell, the colony, or both?
Perhaps the answer is that we have encountered a new level of organisation in which the cell remains a biological individual while also becoming a component of another individual.
Value becomes nested
This recalls the lesson of endosymbiosis.
There too, one living system became part of a larger organisation.
But Volvox adds something new.
The constituent cells are not merely incorporated.
They become differentiated according to roles within the larger system.
Their own organisation is nested within another organisation.
We might therefore say:
biological value has become hierarchically organised.
What matters for one cell's immediate activity is now connected to what the larger body requires.
Sacrifice is not necessarily suffering
The somatic cells provide motility but are terminally differentiated and ultimately die without reproducing themselves.
It would be tempting to describe this as sacrifice.
But that would import human moral and psychological categories too quickly.
The more interesting fact is structural.
A component's reproductive possibilities have become subordinated to the organisation of the larger life cycle.
The transition to multicellularity therefore involves not merely cooperation, but reorganisation of what the parts can do.
From collective to individual
This complicates our earlier distinction between collective and individual.
A collection of bacteria can coordinate while remaining a population.
A Volvox spheroid has a much stronger claim to being an individual organism because its differentiated cells are integrated into a common developmental and functional organisation.
Its cells are not simply collaborating.
They are constituting the body.
This suggests another distinction:
collective coordination → integrated individuality
The transition is not simply a matter of greater complexity.
It changes what counts as the relevant unit of organisation.
The cells become participants in another level
This is why "participant" is useful, even if we use it carefully.
The cells are not social participants in our sense.
But their activity has become organised within the possibilities of a larger participant.
The cell's role cannot be fully understood without the spheroid.
And the spheroid cannot exist without the differentiated cells.
We therefore have a reciprocal dependence between levels:
cellular organisation ↔ organismic organisation
Each level constrains and enables the other.
The topology has acquired layers
Our topology can now become hierarchical.
At one level:
cells interact with their immediate environment.
At another:
cells participate in the organisation of the spheroid.
At another:
the spheroid interacts with its environment.
The same cell can therefore occupy different relational positions at different scales.
This is important because it suggests that biological organisation is not one topology placed upon another.
It is a set of nested relational organisations.
The repertoire changes too
A cell in a multicellular organism does not have the same repertoire as its unicellular ancestor.
Its possibilities have changed.
Some have been lost.
Others have become specialised.
A somatic cell can contribute to motility but no longer reproduce.
A gonidium can reproduce but does not provide motility.
The larger organism therefore creates differentiated repertoires by restricting and redistributing possibilities.
This is a powerful form of organisation.
Individuation through limitation
There is a paradox here.
Multicellularity gives the larger organism more possibilities.
But it does so partly by giving individual cells fewer possibilities.
Specialisation requires constraint.
The cell becomes less generally capable while the organism becomes more capable as a whole.
So biological individuation can proceed through:
differentiation → restriction → integration → expanded collective possibility.
That principle will become increasingly important as we approach more complex organisms.
The emerging pattern
Our sequence has now become richer:
biological value
↓
relational significance
↓
collective coordination
↓
integration
↓
differentiation
↓
nested individuality
We are still below social mattering.
But we are getting closer to a world in which the activities of distinct living units are organised into persistent relations that cannot be understood adequately at the level of the units alone.
What Volvox teaches us
The importance of Volvox is not simply that it is "a simple multicellular organism".
It shows us that becoming multicellular can involve a profound reorganisation of who does what, what remains possible, and at what level biological value is organised.
The larger organism becomes a new unit of organisation without erasing the living organisation of its cells.
That is a remarkable solution to the problem of individuation.
The next question
But Volvox is still a relatively simple case.
What happens when multicellularity becomes more elaborate?
When organisms consist of many differentiated cell types, tissues and organs?
When some organisms live in permanent colonies without becoming fully integrated individuals?
And when the boundary between one organism and many organisms becomes genuinely difficult to draw?
Many Bodies, One Life?
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