Text 858, 124 rader
Skriven 2004-11-18 07:39:00 av Tinyurl.Com/uh3t (1:278/230)
Ärende: Re: First Mutation Was Bi
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> From: an588@freenet.carleton.ca (Catherine Woodgold)
> Well, what exactly do you mean by "capable"?

Any replicator with fecundity greater than 1.0, regardless of whether
it gets bad luck and dies out the first one or two times around the
loop, or whether it gets good luck and grows to sufficient numbers that
it will never die out.

The number of ways of linking carbon molecules into branching chains,
and adding other atoms somewhere in or attached to the chains, is
surely larger than not only the number of grains of sand on all the
beaches but the number of ways of arranging all those grains of sand
into different patterns.

Among all of those potential molecular species, there are probably
billions of different species that would be good catalysts,
where if somebody invented such a molecule and manufactured fifty or a
hundred molecules of it and dropped them into a Miller-Urey situation,
they'd immediately start catalyzing reactions. Among those billions of
potential catalysts, there are probably millions that actually can be
created by chemical cascades starting with basic chemicals and
high-energy source, and most of them have probably in fact been created
one time or another, and among those millions there are probably
thousands that are part of potential catalytic loops with once-around
fecundity greater than one hence a potential replicator. (Note I
thought of a few days ago but didn't find a good place to mention until
now, except a few minutes ago when I should have included it but didn't
remember it until just after I posted: In a catalytic loop where one of
the catalysts has very high fecundity, like thousands, and the rest
have very low fecundity, much less than 1.0, so the product once around
the loop has fecundity greater than 1.0, all those much-less-than-1.0
links in the cycle don't actually have to be catalysts. They could be
just ordinary reactive chemicals that are consumed whenever they react.
It's only the one link with fecundity greater than one where a catalyst
must be involved. So in the third example of my few-minutes-ago post:
  C1 --(0.07)-> C2 --(0.03)-> C3 --(9742)-> C4 --(0.055)-> C1
C1 C2 and C4 don't need to be catalysts at all, only C3 must really be
a catalyst.) So thousands of replicators probably formed during the
first several hundred million years of Earth's pre-life time, but only
the very first few had a chance to grow exponentially, of which the
last of those first few in fact did, all later ones quenched by that
first successful one.

(Regarding my wild speculation that maybe in the original Miller-Urey
experiment a replicator already formed and succeeded at taking over the
experiment, but nobody had any idea to look for it, so Miller and Urey
and later similar experimenters never checked for that possibility, so
none of them has yet discovered it:)

> If new replicators
> are really created that often, then there would almost
> certainly be competition among them for resources,

Yes, although they'd have wildly different fecundities, so they'd each
grow exponentially until their various replicator-foods started to
become exhausted, at which point for each particular scarce
replicator-food only one replicator needing that food would retain
fecundity greater than one, so all the rest needing that particular
food would decline to extinction, leaving just one replicator to
consume all of that one scarce food. But then it's possible that waste
products from the various replicators would interfere with each other,
reducing the fecundities of some of the remaining replicators to less
than one, causing those to go to extinction too. The end result, when
equilibrium is reached, could either be a single surviving replicator,
or more than one which eat different food and don't poison each other
badly enough to kill off any one species of replicator.

If that happened, with more than one surviving replicator, it'd greatly
speed up my scenerio for multiple replicators forming symbiotic
relationships such as on lipid bubbles. But that's a long shot. I think
we really need to study the Miller-Urey chemistry to find out whether a
replicator formed so quickly or not, per the multi-generation infection
experiments I proposed a few days ago. Chances are the result will be
negative, but I think we need to find out for sure. (The logic is the
same as the SETI experiments, where we listen to radio signals from
deep space on the off chance that somebody out there is transmitting
radio signals strong enough for us to receive here. There's very little
chance of any particular frequency being used by anyone in any
particular place of the Galaxy, but we ought to listen to all the
frequencies from all places just in case.)

> and as a result of that competition their individual
> fecundities would each be less than 1, until that
> "biggish" mutation I've been talking about

No, just one, or a few, each consuming a different scarce food, would
survive the initial years. But if new capable replictors formed every
few minutes, with wildly different fecundities, then it's completely
possible that one of the new replicators would have fecundity much
greater than the established replicator which consumed the same food,
so that even with food diminished to where the established replicator
has fecundity exactly one, the new replicator would have fecundity
greater than one in that food-depleted environment, so it'd grow
exponentially to replace the established replicator. There might be
several such replacements, occurring at longer and longer intervals
because such much-higher fecundity occurs much less often. (As I
pointed out before, I wouldn't consider such a replacement to be a
"mutation", but I don't want to argue about usage of that word in this
case.)

There's one possible factor that might make such replacements more
common: If the first replicator produces waste product that consists of
very complicated molecules, and if that waste product gets involved in
chemical cascades to produce a whole new distribution of random
chemicals including random new catalysts, then there's a good chance
those more complicated catalysts would be better catalysts than the
first catalyst, hence more likely to form catalytic loops with
fecundity much greater than the original replicator, and replace it. If
in turn the replacement replicator produces waste even more complicated
than the first produced, the same process might occur again. Here's
another wild speculation, brand new tonight: Maybe this kind of more
complicated replacement was a "runaway" process, whereby the complexity
of the successive replacement replicators increased faster and faster,
rapidly exploding into something as complicated as a RNA replicator you
are so fond for.
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