Text 906, 67 rader
Skriven 2004-11-29 16:21:00 av Perplexed In Peoria (1:278/230)
Ärende: Re: No Grace Period for M
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"Catherine Woodgold" <an588@freenet.carleton.ca> wrote in message
news:coebn2$1m0h$1@darwin.ediacara.org...
> "Perplexed in Peoria" (jimmenegay@sbcglobal.net) writes:
> > But, if you have a kind of sludge composed of ten chemicals catalyzing
> > each others formation, and this gets replaced in part of its habitat by
> > a new eleven component sludge consisting of nine of the original chemicals
> > plus two new ones, then I don't think that there is anything wrong with
> > saying that the ten-component sludge is ancestral to the eleven-component
> > sludge.  And if this is then replaced by a twelve-component sludge where
> > the twelveth component is a nucleic acid capable of true heritable
variation,
> > then I don't see anything wrong with saying that the non-living (by
Catherine's
> > definition) sludge was ancestral to the living sludge.
>
> It depends on what you mean by "gets replaced by".  If the first
> sludge caused the formation of the second sludge that replaced it,
> then I'd call that a mutation -- well, at least if there was considerable
> similarity between the two.  But if the second sludge was
> going to come into existence anyway, perhaps it had nothing to
> do with the first sludge and I wouldn't call it a "mutation"
> but a second spontaneous generation of life (or of sludge).

Agreed.

> Another problem:  if the second catalytic loop has many of the
> same chemicals as the first catalytic loop, most likely both
> would head towards the same equilibrium and end up making
> all of the same chemicals.

Autocatalytic cycles don't go to equilibrium.  You probably mean to
say that they head to the same "steady state".  But I am not sure that
I would agree with this, either.

> I think you would need
> at least two new chemicals -- perhaps you're aware of this
> which is why you mentioned two -- and each of those two would
> have to be involved in the catalytic creation of the other.
> Otherwise the two sludges would not remain different.

I was unable to convince myself of this.  As a simple counter-example,
assume that the new chemical catalyzes its own formation directly (in
the context of the pre-existing cycle).  But I will agree that as a
general rule, autocats grow by the appearance of whole new pathways, involving
several chemical species, rather than by adding one chemical species at
a time.

But the sudden appearance of a new pathway is not necessarily
miraculous.  Suppose that an existing autocatalytic system includes a
multi-step pathway converting "Woodgoldate" into "Peoriate".  Assume that
a molecule of methyl-peoriate appears saltationally in the system and that
methyl-peoriate has the ability to catalyze the formation of methyl-woodgoldate
from ordinary woodgoldate.  Also assume that the catalysts for the original
pathway are also functional in converting methyl-woodgoldate to
methyl-peoriate.
Voila!  The flukish presence of a single chemical species is enough to cause
the persistent presence of a whole pathway of chemical species.
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