Re: Evolution does not get started until there are replicators.


"Primary AL" <aavery6801@xxxxxxxxx> wrote in message news:6a7944b4-d6e7-4550-baa7-9f495d6b2b55@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
An origin of life, anywhere, consists of the chance arising of a self-
replicating entity. Nowadays, the replicator that matters on Earth is
the DNA molecule, but the original replicator probably was not DNA.
We don't know what it was. Unlike DNA, the original replicating
molecules cannot have relied upon complicated machinery to duplicate
them. Although, in some sense, they must have been equivalent to
"Duplicate me" instructions, the "language" in which the instructions
were written was not a highly formalized language such that only a
complicated machine could obey them. The original replicator cannot
have needed elaborate decoding, as DNA instructions... do today. Self-
duplication was an inherent property of the entity's structure just
as, say, hardness is an inherent property of a diamond... the original
replicators, unlike their later successors the DNA molecules, did not
have complicated decoding and instruction-obeying machinery, because
complicated machinery is the kind of thing that arises in the world
only after many generations of evolution. And evolution does not get
started until there are replicators.

I think that this is pretty accurate, but I want to add one quibble or
clarification. The functionality of replicating or building a new DNA
molecule has two parts. The first part is chemical - it says, in effect,
"You need to build or find these monomers, and then you need to
string them together by tieing together sugars and phosphates in
a particular way. Oh, and by the way, these reactions are
thermodynamically 'uphill', so you will also need a source of energy".
This chemical part of the function is indeed specified and implemented
using 'complicated decoding and instruction-obeying machinery', just
as you say.

The second part is informational - it says, in effect, "As you string those
nucleotides together, here is the sequence you should produce". But
this part isn't complicated at all, and it may well have arisen without
any evolution at all - the information carrying capabilities of nucleic
acids are 'built in'. Though whether that information 'means something'
is a different story.

In the teeth of the so-called
"Catch-22 of the origin of life"... the original self-duplicating
entities must have been simple enough to arise by the spontaneous
accidents of chemistry

I agree, though I would point out that we are talking about rather a
lot of time and space available for us to 'wait for' that accident.
But, my intuition is that we would have to wait far too long for
a nucleic acid to appear carrying the instructions that I described
above as the 'chemical' part of replicator functionality. That is why
I favor hypotheses of abiogenesis in which the specification of
the 'chemical' part was provided by a simpler lifeform which used
something like nucleic acids for a non-informational purpose - maybe
something structural - cell wall construction, maybe. Then, the fluke
was simply that one cell happened to make its nucleic-acid-like
polymer out of honest-to-goodness nucleic-acid monomers, and
the natural information transmission capabilities of the molecule
cause it to 'take over' - eventually learning to do the 'chemical'
part of the act itself.

.

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