It seems that this is serving to be an extremely huge enigma for evolutionists.
An enigma for
abiogenesists to figure out.
Evolution only acts on existing life, and the theory of evolution says nothing at all about the origin of life.
in 1994, Leslie Orgel observes, "Because synthesizing nucleotides and achieving replication of RNA under plausible prebiotic conditions have proved so challenging,
This was over ten years ago, an enormous amount of RNA-enzyme and RNA-replicator work has been done in that time. As part of that work, it has been discovered that
short RNAs are capable of synthesizing nucleotides , and that
short RNAs are capable of efficiently and accurately catalyzing RNA replication - thus the two problems Orgel states as "so challenging" have since been solved. In fact the
first paper (I think) describing self-replicating RNAs came out just two years after Orgel's comment.
Scientists produced these enzymatic RNAs NOT by designing them, but by selecting for enzymatic activity from a few million randomly and chemically assembled RNAs. Absolutely no DNA or protein is required for any of this to occur.
There is no evidence in life today of anything that produces huge quantities of new, random strings of nucleotides or amino acids, some of which are advantageous.
The conditions of primitive Earth were quite unlike "life today", so looking for evidence of abiogenesis based on current conditions is a fallacy.
Also, "huge quantities" is a bit misleading. Only a single (or few)
self-replicating RNAs would need to arise to allow evolution to begin (mutation and selection could act upon the replicator). Efficient replicators as described above are less than thirty bases long, if I remember correctly, so there is no "impossible" probability associated with it arising. Also, the smallest RNAs with enzymatic activity are only seven bases long.
After making some helpful assumptions we can get the ratio of actual, useful proteins to all possible random proteins up to something like one in 10^500 (ten to the 500th power).
Those "helpful assumptions" are only helpful if one is trying to boost the improbability of abiogenesis "up to" something seemingly impossible; see -
Lies, Damned Lies, Statistics, and Probability of Abiogenesis Calculations. Does your source provide the calculations so that we might check them, and their underlying "helpful assumptions"?
Also, it is unlikely that life began with protein, yet those arguing against a naturalistic origin of life use protein "occurring" for calculations since it gives much lower probabilities of randomly happening (that are flawed in any case).
More informed models of early RNA evolution show the evolution of essential ribozymes to be quite plausible.
Ribozymes are an intricate part of cellular biology, they are still essential for human life. The same
small RNAs required for vertebrate life are found conserved in the kingdom Archea, suggesting a quite "primordial" evolutionary origin.
Hopefully I've showed that the gaps you've described in the RNA-world hypothesis have been filled. (To some extent "RNA"-world is a bit misleading - it was likely a "nucleotide"-world made up of RNA, RNA-analogs, and/or DNA; and at some later point protein.)
However, I realize that the point of the thread is to get at the origins of DNA polymerase.
RNA likely begat DNA, which is a simple chemical difference resulting in a great improvement in stability. Initial DNA may not have coded for protein, but may itself been active in catalysis, as part of
chimeric DNA-RNA-zymes, or it may have been
an inert byproduct of RNA transcriptase until ribosomal RNA appeared. Once ribosomes were in the picture, DNA-coded protein became a possibility, and thus the evolution of a DNA polymerase.
A major point to realize is that chemical abiogenesis was a historical event that happened under unknown conditions. Abiogenesis research will never be able to "prove" exactly how it happened; but it can demonstrate ways it
could have occurred.
The chance of random, natural, processes is extremely unlikely. While this does not completely rule out evolution, I think this is convincing evidence that there had to be a Creator to have started it all.
The "unlikelihood" of the process cannot be known, since the conditions of abiogenesis are unknown - for all you or I know, chemical conditions may have been absolutely perfect, essentially guaranteeing the arisal of life.
It seems to me that you see two possibilities for the origins of life - a Creator or a Chemical Reaction. Personally, I see the catalysis of nucleotide polymers on a clay substrate under varying temperature conditions to be
much more probable than an eternally-existing, omnipotent, deceitful intelligence. A lack of evidence for the chemical origins is not evidence for a Creator as you imply. Thus; we have some evidence for chemical origins, while we have no evidence for the other option you present.
References:
Ekland EH, Bartel DP. 1996 RNA-catalysed RNA polymerization using nucleoside triphosphates. Nature. Jul 25;382(6589):373-6.
Chapple KE, Bartel DP, Unrau PJ. 2003 Combinatorial minimization and secondary structure determination of a nucleotide synthase ribozyme. RNA. Oct;9(10):1208-20.
Johnston WK, Unrau PJ, Lawrence MS, Glasner ME, Bartel DP. 2001 RNA-catalyzed RNA polymerization: accurate and general RNA-templated primer extension. Science. May 18;292(5520):1319-25.
McGinness KE, Wright MC, Joyce GF. 2002 Continuous in vitro evolution of a ribozyme that catalyzes three successive nucleotidyl addition reactions. Chem Biol. May;9(5):585-96.
Szabo P, Scheuring I, Czaran T, Szathmary E. Nature. 2002 In silico simulations reveal that replicators with limited dispersal evolve towards higher efficiency and fidelity. Nov 21;420(6913):340-3.
Leon PE. 1998 Inhibition of ribozymes by deoxyribonucleotides and the origin of DNA.J Mol Evol. Aug;47(2):122-6.
Frimerman A, Welch PJ, Jin X, Eigler N, Yei S, Forrester J, Honda H, Makkar R, Barber J, Litvack F. 1999 Chimeric DNA-RNA hammerhead ribozyme to proliferating cell nuclear antigen reduces stent-induced stenosis in a porcine coronary model. Circulation. Feb 9;99(5):697-703.
Terns MP, Terns RM. 2002 Small nucleolar RNAs: versatile trans-acting molecules of ancient evolutionary origin. Gene Expr. 10(1-2):17-39.
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