From: rwallace@unix1.tcd.ie (russell wallace)
Subject: Re: ETs and Radio
Organization: Trinity College, Dublin
Date: Wed, 29 Jul 1992 12:09:56 GMT

In <Bs4744.3I8@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes:

>In article <rwallace.712328556@unix1.tcd.ie> rwallace@unix1.tcd.ie (russell wallace) writes:
>>Given that for evolution of life to start, a simple living organism must
>>come together from amino acids etc. by accident; and that for any
>>complex structure to fall together by accident is extremely improbable...

>Try applying the same argument to crystals, or even atoms.  These things
>may come together by accident, but they're found together because that's
>the more stable state for them to be in.  Sure, it's improbable for complex
>structures to come together all at once, but it doesn't happen that way --
>complex stable structures evolve from simpler ones.  A crystal doesn't
>form out of its component subatomic particles all at once.

Sure, a collection of amino acids could quite easily fall together by
accident, in the same way a crystal can.

However, one crystal is pretty much the same as another; none of them
actually do anything (in the absence of humans to make use of them).

The situation is completely different with self-replicating collections
of organic molecules, where only a tiny fraction of all the possible
collections of the organic molecules present on the primitive Earth
would be self-replicating; such a tiny fraction that if all the planets
in the visible universe were trying combinations for the age of the
universe, there is hardly any chance of even one of them stumbling on a
self-replicating system (though, as you point out, collections of
organic molecules that are not self-replicating will form many times).

>There are still fuzzy spots in our understanding of the evolution of life,
>but they're shrinking steadily.  Nothing that is *understood* about the
>way it happened looks particularly unlikely.  The biggest question mark
>at the moment is not the development of self-reproducing, evolving
>molecules, but the development of the cell (which drastically speeds
>up evolution, because then molecules not involved in producing better
>machinery don't benefit from it).

Not so. You actually need something like a cell to have
self-reproduction at all, where by "self-reproduction", I mean
non-trivial self-reproduction, not things like crystal growth. For
non-trivial self-reproduction to occur, the following must be present:

An information storage unit which stores information on how to build the
organism.

Some machinery to construct a new organism.

Reproduction works when the machinery builds a new set of machinery and
a new information storage unit according to the blueprint, and copies
the information from the old blueprint into the new one by regarding the
old blueprint as data rather than instructions (see William Poundstone's
"The Recursive Universe" for an excellent explanation of this).

In organic life forms, DNA is the blueprint, which is interpreted by the
transcription process, and copied by splitting the strands and adding
matching nucleotides to each. The enzymes are the machinery, and there
is a cell membrane around the whole thing (which is needed, otherwise
the enzymes will float away and be lost).

The point is that you do actually need all this for non-trivial
self-reproduction; and furthermore, you need it all to fall together by
accident, since evolution (which can produce complex organisms from
simpler ones) by definition cannot start to operate until you have
non-trivial self-reproduction. It doesn't matter that the accidental
falling together of the first life-form need not be all in one instant,
and that instead the enzyme molecules, cell membrane and DNA can form
separately and then come together; the point is that since there are
10^(many thousands, maybe millions) of different ways for that many
amino acids etc. to be arranged, that only one in 10^(probably several
thousand) of these is a self-replicator, and that there is no way for
natural processes to home in on the self-replicators, but must try
combinations at random until one fits; then the probability that life
will appear anywhere in the visible universe is one in 10^(thousands).

--
"To summarize the summary of the summary: people are a problem"
Russell Wallace, Trinity College, Dublin
rwallace@unix1.tcd.ie