William Morse  wrote or quoted:
> Guy Hoelzer  wrote in
> > Tim Tyler at tim{at}tt1lock.org wrote on 8/10/04 9:10 AM:
> >> Guy Hoelzer  wrote or quoted:
> >>> Tim Tyler at tim{at}tt1lock.org wrote on 8/8/04 3:22 PM:

> >> Even raindrops have inheritance - when they split their offspring
> >> definitely share a number of their qualities.
> >> 
> >> My preferred metric for dealing with such things involves the
> >> quantity of heritable information involved.  I would dismiss
> >> prospective organisms with not very much heritable information as not
> >> /really/ being alive. 
> > 
> > AMOUNT of something seems like a pretty tenuous way to distinguish
> > natural categories (e.g., living vs. non-living).  How much is enough?
> 
> I think the definition of life has to encompass the use of fuel, but it 
> should be something like "the ability to maintain a structure against an 
> energy gradient by using an available energy source."

Practically any self-organising system does that.

Look at a whirlpool - for example.

> This gets around the crystal question because their structure is the 
> lowest energy solution, not a structure maintained against a gradient.

Don't get me going on the crystal subject.  Crystals can be *extremely*
complex.  One of the main reasons is that they are *not* normally at the
lowest energy level for such a structure.

Their energy is usually at a local minima - not a global one.

The imperfections are manifested as fault structures within the crystal.
These are ubiquitous.  The faster crystals grow, the more faults and
dislocations they exhibit.

Out of all the natural but non-biological self-organising systems I am 
aware of, I classify crystals as the most life life.  Indeed, there's
a whole theory of the origin of life that says that life came from
clay crystals.

One of my web pages on the subject: http://originoflife.net/cairns_smith/

> Flames utilize an energy source but do not maintain a structure.

Unless they are at the top of a candle ;-)

> Tornados might qualify as alive under this definition - I don't really 
> know whether their structure is a lowest energy solution but I suspect 
> it is not.

The "lowest possible energy" wasn't part of your definition of life anyway.

Tornadoes and whirlpools *do* seem to qualify under your definition -
as do fractal drainage systems, waterfalls, sand dunes - and all manner
of other things.

However, I reckon most people would agree that such things are not alive.

> The definition could be qualified further by requiring the use of electron 
> transport for energy - I hesitate to do this because it might eliminate 
> non-earth life that should still qualify. But perhaps electron transport 
> is in fact a requirement for any true life?

Definitions of life should not make any mention of electron transport -
IMHO.
-- 
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