I want to start with living, not existing.
Sure we exist, things exist, but we do so in a living way.
Whatever existence we have, even if you think it could be all a dream, is nothing is not living.
Whatever we are, whatever we are doing, we are living.

And other things are living too, not just humans.
The animals, plants and bacteria.
But think of all the things that have a beginning, middle and end.
Which is to say: all the things that are born, grow and die, and in doing so undergo continual, though not necessarily predictable, change.
Think of, be with, feel... the things that change, or rather, the things that grow, are alive, are living.
Anything growing is living.
This gives us a handle on things that the biologists would not want to call living (they are into cells that metabolise). 
You can handle this. Think about the existence of growing things.

What is living?
We take a trip through the physical material, the bio-material, and the thought-material, of our existing.
Galaxies. And within them also stars (planets, comets).
Fire events.
The stock market.
Rivers. And other geological features.
And more. And more.
And plants, animals and humans.


But what is this living, which I'm saying is a growing (and withering/dying)?

Living is growing, but more than just the exterior/observable state of change. 
How do things get into the condition of growth? What is the condition of being able to grow?

* Living is the opening up of further possibilities within current limitations – whatever the materials and conditions. (Dying is the closing down of further possibilities.)
Living is opening up possibilities, through the specific materials available.
Life opens up further possibility within current limitation.

* Living is growth, of possibilities which open up (rather than growth of quantity alone)
* A type of growth that is what Fritjof Capra describes as "qualitative growth" (some economists want to call this a 'qualitative development' as opposed to 'quantitative growth').


I'd like to think about how planets-stars-galaxies, sand-rocks-mountains-continents, rain-streams-rivers-oceans and wind-clouds-cyclones-weather are minimally living in some way. Then plants some more, and animals even more, and then humans.

But what is this 'more' to living systems that seem more detailed, complex, intricate than other living systems? Wilber distinguishes between 'significant' and 'fundamental'. Basic things, underwriting other systems, are more fundamental and widespread, but more intricate living things are less widespread but involve what is fundamental in more significant ways. 


Thus, living systems.

A living system is a system that does this - a system/network/cluster/assemblage that opens up further possibilities within current limits (and thus it will be an open, complex, emergent, relational, living system).