Text 1052, 103 rader
Skriven 2004-12-16 22:33:00 av Tim Tyler (1:278/230)
Ärende: Re: Biochemical evolution
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Perplexed in Peoria <jimmenegay@sbcglobal.net> wrote or quoted:

> There are basically three possibilities:
> (1).  If genetics arose early and easily, as in the theory of Cairns-Smith,
> then no new principles are needed.  Just some clever ideas, most of which
> Cairns-Smith has already provided.  Personally, though, I find this idea
> unconvincing.
> (2).  There may have been some not-yet-appreciated self-organization
principle
> at work.  Perhaps it was based on non-equilibrium thermodynamics as the
> Brussels school proclaims.  Or perhaps it is based on complex systems
> theory as Stuart Kauffman seems to think.  Again, I am unconvinced.
> (3).  Or perhaps there is no over-arching principle to explain the apparent
> "progress".  Perhaps life arose "by accident" or as a result of a series of
> accidents.  This idea is unsatisfying to the scientifically inclined, but,
> IMHO, it is probably correct.  (Yes, Mr. Hendricks, I know you disagree.)

How can one distinguish the hypothesis that there's a "pressure"
that drove the OOL from the hypothesis that it was an accident?

The only way I can think of is to ask how probable the OOL was -
and if it was a difficult, or rare process, the origin deserves to
be described as accidental.

One experimental data point bears fairly directly on the issue: the early 
origin of life.

The early origin of life on the planet suggests life forms pretty easily - 
at least if you accept:

  http://en.wikipedia.org/wiki/Mediocrity_principle

On the other hand, the absence of extraterrestrials - and the lack of
obvious signs of life on nearby planets are data-points that suggest
that life may not be /that/ common elsewhere.

I favour the idea that the OOL was rather easy, and that the universe
is rather full of life.

Consequently, describing life as "accidental" doesn't strike me as
appropriate.

I favour the second option - that the laws of physics naturally promote
the formation of complex systems - which tend to culminate in living 
systems after a bit of complexification has gone on.

This notion is rather in constrast with the ideas of Cairns-Smith - who 
rejected the whole notion of pre-biotic evolution, claiming that chemical 
evolution was impossible without some sort of heredity.

While he's right there, complex systems *do* preserve and transmit 
information over time - and that counts as a sort of heredity.

As simple examples, whirlpools remember which way around they are 
rotating - and streams remember the path along which they are flowing.

While in such systems there's no reproduction, something like
a river system can come to consist of a large, complex object which
preserves and transmits a large volume of information about where
it is flowing over an extended period of time.  There's even something
akin to natural selection going on - in that some streams can invade
and displace other ones.

There are other types of self-organising system - and at least one of
them produced such a complex object with such a large volume of stored 
information that the result qualified as an ecosystem.

> But regardless of what "drove" the origin of life, we still have to work out
> the path that was followed.  And until we have a theory that describes that
> path in detail, and draws on supporting evidence ("molecular fossils") in
> present-day life, then no one's opinion is going to convince anybody.

Looking for molecular fossils is likely to be hopeless - the path 
backwards seems likely to get pretty muddy much beyond RNA - and 
is unlikely to lead anywhere near as far back as life's origin.

IMO, the only approach that is likely to convince anyone is a synthetic
one - we should create living systems from plausible inorganic
components - and then explore the most plausible synthesis routes.

> The origin is a tough problem, and an unsolved problem.  Francis Crick, a
> fairly militant atheist, is quoted to the effect that the problems with a
> mechanistic origin are so great that an honest man would have to say that
> it would almost require a miracle.  I think that is still true today.  But
> I expect that the problem will be solved sometime during this century.

I too expect that the problem will be solved sometime during this century.

Actually, I think the problem was solved before I was born - way back in 
the 1960s - but this century there's fairly likely to arise a consensus 
about how life started that is shared by most scientists.
-- 
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