Re: OOL III - Connecting the Blocks
From: Tim Tyler (tim_at_tt1lock.org)
Date: 03/11/05
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Date: Thu, 10 Mar 2005 20:47:11 -0500 (EST)
Perplexed in Peoria <jimmenegay@sbcglobal.net> wrote or quoted:
> "Tim Tyler" <tim@tt1lock.org> wrote in message news:d0on9t$gvl$1@darwin.ediacara.org...
> > Carbon compounds are practically all too reactive and "sticky" to
> > self-organise into aperiodic crystals without a fair bit of orchestration.
> >
> > By constrast, clay minerals are much more inert - and as a consequence,
> > don't get so easily stuck together and tangled up. They readily form
> > self-organising structures all over the place with no assistance
> > whatsoever - and best of all - have been observed to form long-distance
> > repeating patterns - i.e. aperiodic crystals - via a growth mechainsm
> > involving screw dislocations.
> >
> > Repeated patterns with a period in excess of 100 layers have been
> > observed [as reported in M. CZANK, 1986, Proc IMA Meeting 86, p.85,
> > Stanford University, Stanford, CA].
> >
> > It seems pretty obvious to me which type of system is more likely to
> > form primitive self-replicating organisms. Why would anyone in their
> > right mind be looking at systems based on carbon - when clay-based
> > systems so clearly exhibit the required self-organising properties
> > so much more easily than their carbon-based equivalents?
>
> Perhaps because modern life is based on carbon rather than silicates?
That's a *dreadful* reason! ;-)
Modern life is based on carbon rather than silicon because carbon
is *vastly* superior at building complex life-forms.
Clays self-assemble easily - but self-disassemble almost as easily. They
are very literally constantly prone to falling to bits.
Carbon-based compounds don't do that - once assembled, they stay
assembled. That's bad in the context of origin of life scenarios -
since there are so many ways of coming together in a tangle - but
it's good for high-tech life, provided it has developed adaptations
to make sure everything comes together in the right configurations
and otherwise deal with the problem.
> If you or some other Cairns-Smith fans can come up with a plausible
> "just-so saga" for the transition from silicate crystals to organic
> lifeforms with nucleic acid genetics, then people will sit up and notice.
The main answer to this is that once you have a process capable of
supporting biological *evolution*, all the big problems associated
with the origin of life are over.
Natural selection is master at locating what would otherwise be highly
unlikely patterns. If you have a system of inheritance and can
employ adaptations in your explanations, then the difficulties
associated with the origin of life evaporate.
Once you can say - "that happened as a result of natural selection",
difficulties associated with purifying reactants, employing
unnatural catalysts, and so on are over.
> Last I heard, your plan for making the transition was to have your clay
> genes adsorb organics. Ok. You dip your crystals in tar. Then what?
My "just-so" story about the origin of organic replicators is known as
the "Sweet Crystal hypothesis":
http://originoflife.net/sweet_crystal/
I start out by saying:
``When Cairns-Smith formulated his theory of crystalline ancestry - which
accounts for the main mechanism by which life can form from inorganic
precursors - he was percieved as not having provided a very detailed
scenario for the introduction of organic material. Rather he showed how
life can form, demonstrated that genetic takeovers were possible,
illustrated that there would be selection pressure for carbon-based
systems once they arose, and then suggested that the rest of the story
was simply a matter for natural selection.
This state of affairs apparently left some of those who had not read
Genetic Takeover [1] unsatisfied. They felt as though the origin of
their sort of life had not /really/ been explained at all. They did not
see where nucleic acid came from - and the origin of cell walls was
still a mystery.
While some of the details have no-doubt been lost to history, it seems
that some of the subsequent paths in the early evolution of organisms
can be identified with a reasonable level of confidence. Even where
this is not the case, it may prove helpful to identify in some detail
at least one plausible scenario by which evolution can lead away from
crystalline organisms, towards ones more easily recognisable as our
ancestors.
We'll try to be more specific - at least in some areas - than
Cairns-Smith was in chapter 9 of Genetic Takeover [1]. [...]''
- http://originoflife.net/sweet_crystal/
As a one-sentence summary:
The Sweet Crystal hypothesis proposes that the first organic replicators
formed in parallel grooves in the surfaces of self-replicating crystals
"designed" to hold them - and were "unzipped" from their partner molecules
by the process of the crystals breaking under their own weight - ripping
the adjacent strands of the organic molecules apart in the process.
Though no-doubt only one of many possible just-so stories, I *really*
like the idea. It seems to be that it simultaneously resolves several
puzzles - in particular it provides a catalytic mechanism for positioning
complementary organic units adjacent to one another in the correct
orientation, and also provides a force capable of regularly mechainically
unzipping them once they had become zipped up.
Once you can invoke natural selection as an explanatory force in your
explanations, many things become possible, just as Cairns-Smith hinted
they would.
At this stage, my hypothesis is just that. However, I propose that
it's possible that both the mineral origin and the sweet crystal
hypothesis might actually be virtually inevitable stages in the origin
of life - wherever it takes place in the universe.
It is not that no other routes are possible - but rather that these
two stages are so much more probable than all the other pathways - as
respectively, the origins of the first replicators, and the first
organic replicators.
-- __________ |im |yler http://timtyler.org/ tim@tt1lock.org Remove lock to reply.
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