Dear Nigel Stobbs:
The question of what is life has probably puzzled humans since they first
evolved and will probably keep puzzling us for eons to come. Indeed, I've
heard that the trait that separates humans from animals is that we
concern ourselves about such questions.
I think you are tackling it in a logical concrete manner by posing "What
is it that a biologically living thing has that no purely artificial thing can
ever have?" and also "How can one distinguish between things which are
biologically alive and things which are functionally alive?" For a paper,
academics usually look for a logical theme that strings a multitude of
references together ("synthesis"). The more you can dig up the better.
As every one of us probably wrestles with this question in one way or
another, you'll get as many answers as you'll get responders.
"If it looks like a cigar, and smells like a cigar and tastes like a
cigar, it probably is a cigar." Hence if an artificial system is made to mimic
a biological system in every way then it will be a biological system, much
like the anderoid Data in Star Trek, the Next Generation.
There is a concept, though, of multi-functionality and networking. In the
first case, some viral proteins are not only used as structural components,
but also have enzymic properties and also have immuno-modulation properties,
etc. Even some viral RNA genomes may be read forward, backward, or
staggered so that there is not only information, but hidden
information. Recently microtubules, believed to be the skeleton of a cell,
have been speculated as also micro-computers, each protein capable of "on-off"
information storage. Each tiny cell would have far greater computing power
than a Cray super-computer.
For the second concept, you can have a DNA sequence and protein
expression, but for the latter there are several permutations for folding,
some taking form because the cell does so. In the absence of other systems,
the specific system doesn't get done correctly. Think of it as a goseling that
has the instinct to migrate, but needs its parents to show where it must
migrate to.
You may get several definitions of life in that it is a collection of
self-replicating organic molecules (unlikely as our own systems depend on
nitrogen, metals, etc.), it is a dimension (where dimension is a description
like length and width) or bundles of catalytic entropy, but try to limit the
paper to the key questions you have already stated.
Good luck...John
