Text 1106, 120 rader
Skriven 2004-12-20 06:18:00 av Tim Tyler (1:278/230)
Ärende: Re: Biochemical evolution
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Perplexed in Peoria <jimmenegay@sbcglobal.net> wrote or quoted:
> "Tim Tyler" <tim@tt1lock.org> wrote in message
news:cpt9hl$tbe$1@darwin.ediacara.org...
> > Perplexed in Peoria <jimmenegay@sbcglobal.net> wrote or quoted:

> > > There are basically three possibilities:
> > > (1).  If genetics arose early and easily, as in the theory of
Cairns-Smith,
> > > then no new principles are needed.  Just some clever ideas, most of which
> > > Cairns-Smith has already provided.  Personally, though, I find this idea
> > > unconvincing.
> > > (2).  There may have been some not-yet-appreciated self-organization
principle
> > > at work.  Perhaps it was based on non-equilibrium thermodynamics as the
> > > Brussels school proclaims.  Or perhaps it is based on complex systems
> > > theory as Stuart Kauffman seems to think.  Again, I am unconvinced.
> > > (3).  Or perhaps there is no over-arching principle to explain the
apparent
> > > "progress".  Perhaps life arose "by accident" or as a result of a series
of
> > > accidents.  This idea is unsatisfying to the scientifically inclined,
but,
> > > IMHO, it is probably correct.  (Yes, Mr. Hendricks, I know you disagree.)
> >
> > How can one distinguish the hypothesis that there's a "pressure"
> > that drove the OOL from the hypothesis that it was an accident?
> 
> The word "accident" means different things to different people at different
> times.  Perhaps I should apologize for using it here.  The method I
> would prefer for verifying or refuting my hypothesis that the origin was
> largely accidental is to wait until we have a full account of the whole
> sequence of events that constitutes the origin.  Then ask whether all of the
> steps in that sequence have some common causal pattern, or whether each
> step occurred for its own idiosyncratic reason.  If there is a pattern, then
> it was not an "accident".

I can't say I like using the word "accident" there.

I'm not sure I like the subjective element, that could creep in 
there either.  Who gets to choose what qualifies as a step - or
whether the steps form some sort of pattern?  Aren't these points
that could be contraversial?

For instance, "A" might argue that photosynthesis, sex and
the nuclear cell have nothing to do with each other - and do
not form a pattern - while "B" might argue that they all
represent technological advances which advance life on its
path from dust towards angeldom.  Who is right there?

> > One experimental data point bears fairly directly on the issue: the early
> > origin of life.
> >
> > The early origin of life on the planet suggests life forms pretty easily -
> > at least if you accept:
> >
> >   http://en.wikipedia.org/wiki/Mediocrity_principle
> >
> > On the other hand, the absence of extraterrestrials - and the lack of
> > obvious signs of life on nearby planets are data-points that suggest
> > that life may not be /that/ common elsewhere.
> >
> > I favour the idea that the OOL was rather easy, and that the universe
> > is rather full of life.
> >
> > Consequently, describing life as "accidental" doesn't strike me as
> > appropriate.
> 
> I agree with the logic of your analysis, though I remain unconvinced that
> life is ubiquitous in the universe.  So the early origin may still be
> simply a symptom of some kind of "anthropic principle".  If, after exploring
> and sampling the galaxy, we find that life is only moderately common,
> that it has a variety of dates of origin, and that those planets with the
> most advanced life are those where life arose earliest, then your argument
> collapses.

The mediocrity principle isn't foolproof.  However it is worth *something*.

> Another issue is that we don't really know whether "life", by your favorite
> definition, really arose early on earth.

I'm fairly agnostic about that.  If anything I think the odds are good 
that Mars was inhabited before the earth was.

> AFAIK, there is no evidence bearing directly on when genetics arose.  
> What we have is some debatable evidence that cellular morphologies 
> arose early and some even more debatable evidence that biology-like 
> carbon fixation arose early.  It is only an assumption, based IMHO on 
> lack of imagination, that these morphologies and metabolic processes 
> must have been driven by genetics.

Bear in mind that I practically define genetics in terms of
information about how to persist being preserved over time.

I don't insist that such information is preserved using
template replication - or any other mechanism really.

As I may have mentioned, even dynamic systems such as rivers show this 
sort of "inheritance" - in that information about where the ravines
are on the lanscape is preserved over time - and that information
pertains to the persistence of such systems in the face of
environmental perturbations.

It is true that my favoured OOL scenario puts template replication
- based on "aperiodic crystals" - bang at the start of life.

IMO, that makes it a lot less speculative than many "autocatalytic set"
theories.  We /know/ template replication of aperiodic crystals
works as a /practical/ basis of living systems.
-- 
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