From Molecules to Metabolism — I. When Chemistry Began to Take Care of Itself

Life did not begin with an organism.

Or at least, we need not begin the story there.

Before there could be a cell, there had to be chemistry capable of sustaining a sufficiently organised pattern of activity. The interesting question is not exactly which molecules appeared first, but how molecular processes could begin to form a system whose present activity helped make its future activity possible.

A molecule reacts.

Another molecule reacts with it.

Products become reactants for other processes.

Energy enters.

Some reactions promote others.

Some pathways become more likely because the processes that preceded them have changed the conditions in which subsequent processes occur.

Nothing here is alive.

But something important is beginning to happen.

Chemistry is acquiring organisation.

The distinction matters because a collection of reactions is not yet a metabolism. Metabolism is not simply chemistry happening inside a boundary. It is a network of transformations in which material and energy flow through processes that collectively sustain the organisation of the network.

The crucial word is collectively.

A reaction does not need to preserve itself. A network can.

This introduces a strange possibility.

Perhaps the transition towards life did not begin when a molecule acquired some mysterious property called life. Perhaps it began when chemical processes became organised so that the continuation of one process helped make possible the continuation of others.

A reaction produces a substance.

That substance enables another reaction.

The second reaction changes the conditions for the first.

The system begins to participate in its own continuation.

We are still not entitled to call it an organism.

But we can now ask a new question:

What happens when chemistry becomes capable of making more chemistry possible?

That question takes us beyond individual molecules.

It takes us towards networks, cycles, boundaries, energy flows and eventually metabolism.

Life may not begin with a thing.

It may begin with a relation that becomes organised enough to persist.

And perhaps the first step towards life was therefore not the appearance of a special molecule, but the moment when chemistry began, in some primitive sense, to take care of its own continuation.