I would say that complexity of the
molecule is not any simple function of its livingness. No matter how small a
structure you could produce that everyone would agree to be in some way a
reasonable example of a living organism, I could produce you a much larger one
that everyone would agree to be non-living.
Then again, consider some virus or
viroid molecules; would you call them living? One could make a good case
for it, but only if you supply them with a living organism as a host.
Your question raises some challenging
points that you need to address more clearly before we could give you a
definite reply, if at all.
You said: “Indeed does the question make
any sense.”
Sorta-kinda... yes. However, it is a
very begging question because it conflates or confuses (or both) several aspects.
The problem is to tease them out and deal with them in proper, meaningful
contexts. And if you think that we have the resources to do so properly, I
commend your optimism. Still if we avoided all questions that we were as yet
unable to formulate cogently, we would make miserably poor progress. So let’s
see whether we can make any sense of it at all. At the heart of the question is
possibly one (maybe more) of the most challenging and as yet barely engaged
open questions in science (or possibly proto-science?) Namely: what is life as
opposed to complexity and organisation and possibly in parallel or even as the
same matter, what is mind as opposed to computational power? I cannot answer
either, or to what extent they resemble, but...
You said: “My question is where do we
draw the line between life and non life?”
I say: I am not sure that it is a matter
of drawing a line. I am not at all sure that it is a matter of drawing a fuzzy,
twilit border region. I suspect that we are looking in the wrong dimension rather
than wrong direction. See the attached pictures by Escher for two analogies out
of many.
You said: “If we assume that more
primitive life forms get simpler and simpler until we reach the so called
building blocks of life, i.e. organic chemicals...”
I say: That is a biiig assumption! You
could make a reduced version of me by leaving off suitably selected molecules,
but only up to a point. Pretty soon you will get to the point where the reducee
is undebatably (and by some people unlamentably) not Jon, whether it is functionally
alive or not. You don’t get a smaller copy of me by splitting me down the
middle for example, an assertion that I firmly refuse to support by
demonstration, any more than by splitting your car down the midline would give
you two cars, no matter how well it might work with planarians. And yet, there
are undeniably independently living and viable creatures far smaller than the
split car, the split Jon, or the split planarian. A big assumption indeed in
more dimensions than one. It is not only whether you could do it, but why? Why should any of the building blocks of a
living thing be living, any more than the building blocks of my house are a
house, or the methyne groups of a benzene ring be miniature benzenes?
Fallacy of composition?
Not to put it too kindly, that is not so
much a reductio ad absurdum as a reductio ab absurdum... No?
But again, it becomes possible in
principle to reduce existing simple forms of life, such as large prokaryotes
into smaller prokaryotes, possibly with more constrained functions, beginning
with cells far smaller than any cell of yours or mine, and making them smaller
still. And yet we are still nowhere near Georg’s observation that we know of no
living molecule, even if that would be where any such process would (too late
for life) end.
Next we encounter another dimension. You
are living; so am I. So is my cat and my neighbouring mice and a rather
intriguing earwig I missed photographing up a mountain yesterday, and a
rotiferan in our neighbouring dam.
Yes?
Are you sure?
Without the wherewithal to support life?
I don’t think so, not for long.
If at all.
So what is all this about living things
and non-living things? Life obviously seems to require a system in which to
work, or it is hard to justify calling it life. You deny the validity of
calling an amoeba non-living if it has no droplet of water to live in and
bacteria to feed on? How about Legionella, that is a true bacterium, though it
needs a eukaryotic cell to survive in? Is it alive in the absence of a cell? Or
what about a mitochondrian, most of whose needs are supported in its enveloping
cell? Then who are you to forbid calling a viroid living, though it needs the
cells of say, a potato or a human for its reproduction? Even though it is a
single molecule, no proteins, just a ring of RNA?
But is the system the living thing? I
saw a tiny, immature toad grasshopper the same morning as I saw that earwig. It
looked pretty lively (though it did permit me a few photos!) Am I to deny that
it was alive any more than any of the mitochondria in one of its muscle cells
in isolation, or one of its protein molecules, because it was sitting on a rock
and not actually including any of the grass it might normally eat?
If so you may be right, but it LOOKED
pretty lively, and I think some people might beg to differ.
As Leonard Cohen said:
“A person who eats meat
wants to get his teeth into something
A person who does not eat meat
wants to get his teeth into something
else
If these thoughts interest you for even
a moment
you are lost"
You ask: “And since organic chemicals
can be made from inorganic ones do we have to assume that everything has a life
force? This may sound like a reducto ad absurdum argument but I am being
serious.”
RAA arguments are supposed to be serious
where I come from. If we could assume a life force abstracted from life, that
would solve a lot of problems, but I am not sure it wouldn’t create more than
it would solve. What life would a life force force when it wasn’t forcing life?
It would have a long, lonely time of it in the eight or ten billion years
before the right molecules began to fit together on a certain cloudy planet
some 3 to the 17 seconds ago!
You say: “Maybe by framing my question
in terms of a molecule I was being niave...”
Maybe.
“...it could be that life comes from a
cocktail of chemicals.”
No maybe about THAT being naïve!
Cocktail indeed! And a cocktail of bricks would be a house? Maybe?
You said to Georg: “...the link between
the two intrigues and interests me...”
Now, there we are at one!
Georg says: “...there is no example for
a living single molecule, all known living units consist of thousands, maybe
millions of molecules...”
This is true Georg, and I do not expect
us ever to find a counter-example on this planet or elsewhere, in spite of my
example of viroids. However, we know of no theoretical reason why no such molecule
could exist, at lest as alive as say, an Amoeba.
As you and
Mike agreed pretty well about: “In order
to provide an answer we need to know how you will distinguish when to recognize
something is living. Unless there are precise criteria then we will end up
debating whether or not something is living, rather than the point you are
asking.”
So do the rest of us, I bet.
