[extropy-chat] HISTORY: Solved & Unsolved Riddles

[Rafal Smigrodzki]

----- Original Message ----- 
From: "The Avantguardian" <avantguardian2020 at yahoo.com>
To: "ExI chat list" <extropy-chat at lists.extropy.org>
Sent: Saturday, November 08, 2003 9:00 AM
Subject: Re: [extropy-chat] HISTORY: Solved & Unsolved Riddles


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> > > 3. Why is all life on earth asymmetric at a molecular level. The amino
> > > acids that make up proteins on earth all have a "left-handed"
> > > (levorotary) chirality and the sugars that make up carbohydrates are
> > > "right-handed" (dextrorotary). [snip]
> >
> Rafal Smigrodzki <rafal at smigrodzki.org> wrote:### Probably no need to
invoke the stellar dust, since the asymmetry is a
> direct consequence of the mechanics of biological macromolecule synthesis.
> An enzyme, ribosome or nucleic acid polymerase can recognize only a
limited
> number of molecular species (just like a lock can recognize only a limited
> number of keys, all of the same general symmetry), and the moiety that
forms
> the most rigid part in a polymer, the backbone, can only assume a limited
> number of conformations.
>
> *Correct- but you are putting the cart before the horse, unless you are
proposing that either enzymes or ribozymes came somehow into being
whole-cloth without some form of stochastic polymerization event from their
monomer constituents. Are you suggesting a Special Creation event? I would
not be terribly mortified if this is what you were suggesting since if I
walked into a room and saw thousands of coins all showing heads, despite
knowing that there is a finite none-zero probability that they fell that way
by pure chance, I would find the hypothesis that "someone" arranged them
that way to be the more probable hypothesis. Eleizer, what say you, oh
disciple of Bayes? *

### Of course ribozymes came into being whole-cloth by stochastic
polymerization (maybe with some help from montmorillonites), and once there
was a single self-replicating ribozyme (or even a pre-RNA molecule), all the
molecules derived from it had to have the same chirality.

The room with thousands of coins is an old creationist shtick, but
irrelevant here. Think about a room with thousands of high-energy entities
(like standing dominoes or abiotically produced nucleotide triphospates).
You need one event, a domino being flipped to the right or to the left or
polymerization of a single ribozyme, and you end up with thousands of
dominoes stacked in the same orientation, or with billions of macromolecules
of same chirality.

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>
> Using a standard conformation for the backbone of
> all monomers saves on the number of enzymes needed to make all the
> components, and the standard conformation for aminoacids just happened to
be
> the L-conformation.
>
> *Yes, and a standardized hardware configuration, operating system, and
programming language would save much money, time, and effort by IT
professionals the world over. But game theory predicts there will be two or
more standards, e.g. Macs vs. PCs or Unix vs. Windows vs Applesoft, that in
a competitive enviroment will reach a Nash equilibrium with one another
which incedently is the observed case. Note I would not be so surprised if
even a huge majority of life forms used one "chiral standard or the other"
but the fact that it is entirely a single standard strikes me as highly
improbable and wondrous.*

### No, not wondrous, but inevitable. If you have only one vendor and the
companies that split from it, because there was only one vendor in the
beginning, you will inevitably have identical standards for the basic
system.

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>
> Of course, if there were any imbalances in the concentration of one
> enantiomer in the primordial soup, that enantiomer would be much more
likely
> to become the standard...
>
> *ok, now both thermodynamically and game theory wise, it is easy to see
how a completely imbalanced asymmetric system might over time evolve into
either a chemical or a Nash equilibrium. For example it is easy to imagine a
perfectly ordered system of all reactants or all products becoming a
chemical equilibrium of both, even if products vastly outweigh the
reactants, but you would still have some reactant present at any given
temperature. Likewise lets say in game theory you have a system composed
entirely of doves, then hawks having such a huge advantage in such a
population would quite naturally evolve. Likewise doves will arise in a pure
population of hawks (since the hawks will kill one another while the doves
wont). Yet going the other way is much less credible. It is easier to
believe that Pepsi arose simply to compete with Coke's former monopoly and
stole market share from it, than to believe that if Coke and Pepsi started
out with equal market share that someday one !
> would buy
>  the other out and gain a monopoly.*
>
> one way or another, a standard had to choose itself.
> * Are you suggesting that in a former Spirit World Conference chaired by
the RNA Fairy the amino acid spirits got together and passed an unanimous
resolution calling for them to all become left-handed from that day forward?
Was the Esteemed Reverend Sun Yung Moon privy to those proceedings or is
that just hear-say?* <wicked grin>
>
### Wrong analogies.

Most likely there were never two populations. Being a D-aminoacid creature
in a world of L-aminoacid creatures would not give you an advantage of a
hawk over doves. Therefore there is no selective pressure to evolve
D-aminoacid proteins from scratch, like in founding a company to cash-in on
a monopoly.

The correct analogy is having two species of paramecium in the same tank -
no matter how closely matched their number in the beginning of an
experiment, one of the species dies out. Only one species can stably fill a
single ecological niche.

Rafal