When Does a Difference Make a Difference?: V. Being Sensitive to Difference

A difference can matter without being noticed.

Water can matter to a plant without the plant representing water.

Light can matter to an organism without the organism having a concept of light.

But living systems can do something more.

They can become sensitive to differences.

Sensitivity is not simply being affected.

Everything is affected by something.

A stone is warmed by the sun.

A leaf is moved by the wind.

A molecule responds to a change in its surroundings.

But sensitivity implies a particular kind of organisation.

A system responds differently because the difference is different.

The distinction is subtle.

A system can be changed by its environment without its subsequent activity depending systematically upon the character of the change.

Sensitivity begins when differences in the environment can produce differential responses.

A plant grows differently in different conditions of light.

A bacterium moves differently according to a chemical gradient.

An animal changes its behaviour according to changes in its surroundings.

The organism is not merely undergoing change.

Its organisation allows differences to become differences in what it does.

This gives sensitivity a history.

It does not appear from nowhere.

The organism already possesses capacities and internal organisation that make certain environmental differences consequential.

Sensitivity develops within those relations.

And this means that sensitivity is selective.

An organism cannot be equally sensitive to everything.

It is sensitive to some differences and relatively insensitive to others.

The world may contain an enormous number of physical differences.

Only some enter into the organism's organisation as differences to which it can respond.

This is another way of saying that an organism inhabits a particular world.

Not the whole physical world in its entirety, but a world structured by the differences that its organisation can make consequential.

A bird can detect differences in movement that matter for flight.

A plant can respond to differences in light.

A bacterium can respond to differences in chemical concentration.

Their worlds overlap.

But they are not identical.

The difference is not necessarily in what physically exists.

It is in what can enter into their organisation.

This is where perception begins to come into view.

But we should resist moving too quickly.

Sensitivity is not yet perception in the richer sense.

A system may be sensitive to a difference without constructing an internal representation of what that difference is.

The important point is more elementary.

The organism's activity is differentially organised by differences in its environment.

That is already a significant development in our story.

We began with differences that simply occur.

Then we saw that some differences alter what can happen.

Some become constraints.

With life, some differences can matter to the continuation of an organised system.

Now we have a system whose own organisation allows differences to produce different responses.

The relation has become reciprocal in a new sense.

The environment affects the organism.

But the organism's organisation determines which environmental differences can affect it in particular ways.

This is why sensitivity cannot be located entirely inside either side of the relation.

The environment supplies differences.

The organism supplies a capacity for differential response.

Sensitivity emerges from their encounter.

And once sensitivity exists, the organism's world becomes richer.

A difference in light can be distinguished from a difference in temperature.

A chemical gradient can be distinguished from a mechanical disturbance.

Not necessarily as concepts.

Not necessarily as representations.

But as differences that have different consequences for the organism's activity.

The world is beginning to become differentiated through the organism's responses.

This is an important threshold.

For once differences can be differentially registered in a system, the organism can begin to respond not merely to what happens, but to which difference has happened.

And that opens the possibility of anticipation.

A difference can become relevant before the consequences it predicts have fully arrived.

A gradient can be followed.

A signal can trigger a response.

A trace can guide behaviour.

The organism can become responsive to something that stands in a relation to something else.

Now we are approaching indication.

But indication is not yet meaning.

A difference can carry information about another state of affairs without becoming a sign.

The crucial question is therefore no longer simply whether an organism can be sensitive to difference.

It is:

When can one difference indicate another?

That is our next threshold.