From: dietz@cs.rochester.edu (Paul Dietz)
Newsgroups: sci.physics,sci.chem
Subject: Re: Entropy of the Universe, (was Re: Genesis - fact or fiction)
Date: 23 Aug 92 12:20:27 GMT
Distribution: na
Organization: Computer Science Department University of Rochester

In article <25681@dog.ee.lbl.gov> sichase@csa3.lbl.gov writes:
>In article <1992Aug21.231150.21126@cs.rochester.edu>, dietz@cs.rochester.edu (Paul Dietz) writes...

>>  Actually, only *some* of the molecules of life have been
>>shown to form naturally (specifically, some of the amino acids,
>>some bases, some sugars).  Unfortunately:  (a) they are formed
>>in very low concentrations, (b) they are mixed with large numbers
>>of other, biologically irrelevant isomers, (c) some of the experiments
>>showing their formation require unreasonable conditions (concentrated
>>formaldehyde, for example).
>
>You're a little behind on the literature here.  There are at least some
>credible models of chemical evolution which make use of the properties of 
>of bubbles - boundaries between air and water in the atmosphere and on 
>the ground, where chemicals can get highly concentrated and the thermodynamics

>can by favorable to otherwise difficult reactions.  It's new stuff, and
>certainly is open to criticism - but it at least addresses the concerns
>you list above.

No, it doesn't address the criticisms I've listed above.

I stand by the claim: no experiment with credible initial conditions
has produced anything like the mythical "prebiotic soup", nor produced
all the subunits needed for life, nor produced them in the absence of
large quantities of contaminants.

Remember that the Miller-Urey experiment is now widely viewed
as flawed, because the initial conditions (ammonia, methane, hydrogen)
are no longer viewed as credible for the initial terrestrial
atmosphere.  A slightly reducing atmosphere containing mostly
CO2 and N2 is much more plausible on geochemical grounds (ammonia,
in particular, is very unstable under UV irradiation, and hydrogen
escapes readily to space).  Under those conditions, M-U type
experiments produce a trace of glycine and not much else of
interest.

The existence of a "prebiotic soup" itself is also doubtful,
because the fate of small organic molecules is not to accumulate
for millions of years in the oceans, but rather to react to
form insoluble tars, or to be taken down into sediments.


>>4. "Natural selection gets around the combinatorial problem"
>> 
>>  This ignores the fact that natural selection can only occur in
>>systems that already can copy and express genetic information of some
>>kind.  Moreover, the requirements for copying accuracy are stringent.
>
>Natural selection doesn't require genetics.  It only requires each 
>"generation" to have variations whichaffect survival.  Any self-replicating
>molecule in which the duplication process is error-prone (all are to some
>extent) can have more successful variants selected.
>
>Genetics (DNA -> proteins -> traits) is only the modern version of heredity
>in complex organisms.  But simple molecules have all the information they need
>to carry built in to their own structure.


Wrong.  Natural selection requires *some kind* of stored, replicable
and expressible information.  Perhaps not as base pairs, and perhaps
not with today's separation of genotype and phenotype, but in some
form.  And unless this replication is quite accurate, the complexity
that can be built up by selection is limited.  Too much error
is fatal, because it destroys information faster than selection
can create it.

There have been recent experiments in which simple molecules catalyse
their own formation from rather complex initial reactants, perhaps
with a few mutations possible.  These experiments are cute, but
irrelevant to biogensis: the molecules are not plausible prebiological
molecules, nor is the amount of information they can carry
significant.  Most of the "information" in these experiments is input
when the experimenter prepares the mixture of purified reactants.

	Paul F. Dietz
	dietz@cs.rochester.edu