[…]
>>>DNAunion: Second, you have glazed over some of the most important steps
on the way to
life: how the first self-replicators arose.
>>>Chris: Actually, I've dealt with this in previous posts…
**************************
DNAunion: Okay, but not in the one to which I was replying. In addition, if
I remember correctly now, your explanations were similar to those you present
in this post of yours - which are still vague in that they deal with
nameless, hypothetical entities that might do this or that. For example:
"A simple A-B template molecule such that A attracts and holds another B, and
the B attracts and holds another A, until there is *both* another A and B,
which then join and break free from the original molecule will work."
"I don't actually know, of course, how the original replicator molecules
might have occurred, or even what they might have been"
"However, I'd bet that a good chemistry-simulating program could find a fair
number of them quite rapidly."
You later state in your most-recent post that you know that more was
obviously needed to generate life than mere energy flowing though the
prebiotic "biosphere", but you still omitted that fact from your post to
which I was replying: you mentioned only the open-system thermodynamics part.
Okay, I promise to be more amiable in the rest of my post.
******************
>>>Chris: … though by no means exhaustively. Self-replicating molecules are
not exactly uncommon.
******************
DNAunion: I am unaware of any known natural self-replicating molecule (they
are very uncommon in nature, if they exist at all). Note the even DNA is not
self-replicating (I bring this up because it is sometimes incorrectly stated
that DNA replicates itself).
******************
>>>Chris: Even slightly *evolving* self-replicating molecules have been
observed (in laboratory research, admittedly).
******************
DNAunion: I would like more details. The main in vitro ("test tube")
evolution experiments I am familiar with use PCR to amplify the selected
molecules. That is "cheating": the molecules being studied in such
experiments do not qualify as self-replicating. (I will briefly address the
32-amino-acid "self-replicating" peptide in response to your next statement).
******************
>>>Chris: A simple A-B template molecule such that A attracts and holds
another B, and the B attracts and holds another A, until there is *both*
another A and B, which then join and break free from the original molecule
will work.
******************
DNAunion: This sounds exactly like the 32-aa "self-replicating" peptide that
a fair amount of people bring up (A could be the 15-aa "half", B the 17-aa
"half", and AB the full 32-aa peptide). I won't repeat all the points I
brought up in another post, but suffice it to say that the full 32-aa peptide
(AB) was powerless to create the two halves (A and B) it was made from: the
researches had to continually produce and feed the full 32-aa peptide (AB)
the 15-aa (A) and 17-aa (B) halves that it would then pair with and bond
together. This is not self-replication.
*******************
>>>Chris: I don't actually know, of course, how the original replicator
molecules might have occurred, or even what they might have been.
*******************
DNAunion: No one knows how they could have occurred (you are in good company
there!). From what I have read, it basically comes down to chance: for
example, trillions of trillions of randomly-generated RNA molecules were
somehow "pumped out" by some "prebiotic RNA manufacturing plant" until two
that could function as RNA replicases arose, close enough in space and time
to find each other, and one copied the other, and one of the then 3 copies
copied one of the others producing 4 RNA replicases, etc.
What the first self-replicators *might have* been include (1) RNA replicases
(probably the predominant school of thought, but it *might* be slipping a
bit), (2) PNA replicators (since RNA itself does not look very prebiotic, OOL
researchers have started looking for simpler backbone systems), (3) pRNA
replicators (the pyranosyl - 5 carbons in the ring - form of ribose is
apparently easier to make prebiotically than the furanosyl - 4 carbons in the
ring - kind found in RNA), (4) peptide replicators (though it would then
become difficult to explain the reverse flow of information, from protein
into nucleic acids), or (5) inroganic replicators (such as Cairns-Smith's
"clays", but they have largely been ignored and considered irrelevant).
*******************
>>>Chris: However, I'd bet that a good chemistry-simulating program could
find a fair number of them quite rapidly (to be followed by real-world
testing, of course).
*******************
DNAunion: I am glad to hear you say that they should go past mere
simulations: that they need to actually do something in the lab to try to
confirm their model instead of simply assuming it is an accurate
representation of the real world. Many people I have debated (for example,
in relation to the "lipid world" computer model) seem to feel confident that
if a computer model shows X can happen, well then by golly it obviously can;
and if the computer model shows that Y cannot happen, well then by golly Y
obviously can't. As someone who has programmed computers for years (as you,
Chris, appear possibly to be also), I am aware of discrepancies that commonly
exist between reality and computer models. In fact, something I just posted
here today about near-zero gravity allowing for heat to flow from cold to hot
was not allowed by computer models - but it actually occurred in nature. The
Science article I quoted went on to say that when the programmer made
adjustments to his code, by figuratively canceling out gravity in the
computer model to match the "absence" of gravity (microgravity) in the Mir
space station, that it THEN gave the correct result.
********************
>>>Chris Cogan: (I understand that one such program has recently been
written in the programming language Prolog, which is a remarkable tool in
itself, aside from the power of some of the programs written in it).
********************
DNAunion: As I expressed above, I will wait until the actual lab work is
done to validate such a model.
Second, even if it does generate self-replicators, we would still need to ask
whether of not they were prebiotically-plausible. It would do OOL
researchers no good at all if all the computer program came up with were
things like multimeric proteins consisting of three dissimilar subunits, each
400 or 500 amino acids in size.
********************
[…]
**********************
DNAunion: NEW STUFF.
Since we are discussing origin of life stuff again, I recently read something
I would like to point out and comment on.
In the chapter being quoted from, David Deamer has just presented several
paragraphs of detail concerning the following summary. This detail material
has been omitted for brevity's sake.
"To summarize, an abundant source of long-chain hydrocarbon components of
prebiotic membranes is not obvious. On the other hand, one might argue that
because the origin of cellular life absolutely requires lipidlike hydrocarbon
derivatives, such molecules must have been available on the early Earth from
a yet unknown source." (David Deamer, Membrane Compartments in Prebiotic
Evolution, Chapter 8 of The Molecular Origins of Life: Assembling Pieces of
the Puzzle, edited by Andre Brack, Cambridge University Press, 1998, p194)
Can anyone else see the circular reasoning in this? If not, let me give you
an analogy.
PROSECUTOR: Ladies and gentlemen of the jury, the state believes that Mrs.
Jones' disappearance is not due to her being abducted by a stranger, but
rather is due to her husband's discarding her body after he savagely killed
her. Let it first be noted that the state can't present any actual evidence
that shows Mrs. Jones is dead, but we strongly suspect so: call it a working
assumption. In addition, we don't have a murder weapon with Mr. Jones'
fingerprints on it, despite our best searches. But we argue that since Mrs.
Jones could not have been murdered by her elderly husband without a murder
weapon being involved, then we can assume that the murder weapon with his
fingerprints does exist somewhere, and that we just haven't come across it
yet. The state asks that you sentence Mr. Jones to life in prison without
the opportunity for parole for his committing of such a brutal and
unthinkable act."
Okay, a bit over-dramatic (to say the least), but I think everyone gets the
point. Take away the preexisting assumption that Mrs. Jones was murdered (or
analogously, that life arose here on Earth) and the assumption based on it -
that a murder weapon with Mr. Jones' fingerprints on it must exist (or
analogously, that an abundant source of long-chain hydrocarbon components
must have existed) is unfounded, meaningless, and bankrupt. If one is trying
to demonstrate a basic, underlying assumption, then one shouldn't use
assumptions drawn solely from that final underlying assumption that he or she
is trying to validate to argue into existence, from thin air, evidence that
supports any part of that final underlying assumption.
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