From Molecules to Metabolism — IV. When the Boundary Became Part of the Metabolism

A chemical network needs an environment.

But once it begins to regulate its exchanges with that environment, something changes.

The boundary is no longer merely around the chemistry.

It becomes part of the chemistry's organisation.

A membrane can retain some substances and exclude others. It can maintain concentrations and gradients. It can make certain reactions possible that would otherwise be too unlikely or too dispersed.

But the membrane itself also has to be maintained.

Its components must be produced, repaired or replaced.

The network must therefore contribute to the continuation of the boundary that helps sustain the network.

A loop has closed.

Metabolism maintains the boundary; the boundary makes metabolism possible.

This is a deeper kind of organisation than either component possesses alone.

The membrane is not simply a container.

The metabolism is not simply a collection of reactions.

Together they form a system in which each contributes to the continuation of the other.

This is where the idea of an organism begins to become difficult to avoid.

Not because a particular molecule has suddenly become alive, but because a network of processes has acquired a degree of organisational closure.

The system depends on its surroundings, but some of the relations that determine how it survives are generated within the system itself.

It has become a centre of activity.

And now the distinction between inside and outside has acquired a new significance.

Outside conditions affect the system.

Inside processes alter how those conditions affect it.

The system is no longer simply subject to its environment. It participates in determining the terms on which the environment can affect it.

That is a profound shift.

A chemical system has become capable of regulating the conditions of its own continuation.

We still do not need consciousness.

We do not even need a fully formed cell.

We need only a network in which the organisation that sustains the processes is itself sustained by those processes.

Perhaps this is one of the crucial thresholds on the road from chemistry to life.

The boundary is no longer just a difference between two regions.

It has become part of a cycle through which the system maintains itself.

Chemistry has acquired an inside.

And the inside has begun to take responsibility for its own existence.