What really is under discussion here is the origin of self-replicating molecules. Once self-replicating molecules are in place, the process of biological evolution as described kicks off. The origin of these molecules is not really of any particular concern to evolutionary biologists, that being the discipline called primordial biochemistry. No theory, after all, explains everything. To evolutionary biology, the existence of such molecules is a priori.

On the other hand, I do have a short series of notes on the matter of the origin of self-replicating molecules, if you are interested.

 The process of formation of organic autocatalysis is time consuming. It begins with Piezoelectric systems on crystallien surfaces, which form the progenitors of ribozymes. The first biological molecules on Earth may have been formed by metal based catalysis on the crystalline surface of minerals.

In principle, an elaborate system of molecular synthesis and breakdown called metabolism could have existed as such long before the first cells. Life requires molecules which catalyze reactions hsih lead directly or indirectly to replication of more molecules like themselves. Catalysts with this self promoting propertycan use raw materials to reproduce themselves and therefore divert the same materials from the production of ther substances. In modern cells the most versatile catalysts are polypeptides. However, they cannot propogate self-replication, they do not replicate. There needs to be a molecule which can act as a catalyst and guide its own replication. Such a molecule does exist: RNA

 Polynucleotides Can Both Store Information and Catalyze Chemical Reactions. RNA can propagate itself by means of complementary base pairing. However, this process without catalysis is slow, error prone and inefficient. Today, such processes are catalyzed by a massive battery of complex interactions of RNA and proteins.

In the RNA world, the RNA molecules themselves would have acted as catalysts. A pre-RNA world probably Predates the RNA One. It is unlikely RNA was the first self-replicating propogater. It is difficult to imagine that they could form through nonenzymatic means. The ribonucleotides are hard to form enzymatically, also RNA polymers entail a 5 to 3 chain which must compete with other linkages that are possible including 2 to 5 and 5 to 5. It has been suggested that RNA was anteceteded by molecules with similar properties, but that were similar. Candidates for pre-RNA include p-RNA and PNA (peptide nucleic acid)

The transition from pre-RNA to RNA would have occurred through the synthesis of RNA via these simpler components as template and catalyst. Laboratory experiments demonstrate this as plausible. PNA can act as a template for RNA molecules. Once the first RNA molecules had been produced, they could have outphased their antecedents leading to the RNA world

Single-Stranded RNA molecules can fold into highly elaborate structures Comparisons between many RNA structures reveal conserved motifs, short structural elements used over and over again as part of larger structures. Common motifs include

Single strands, double strands, single nucleotide bulges, triple nucleotide bulges, hairpin loops, symmetric internal loops, asymmetric internall loops, two stem junction, three stem junctions and four stem junctions. RNA molecules can also form common conserved interactions such as psuedoknots and “kissing hairpins” and hairpin-loop bulge contacts.

-Protein catalysts require a surgace of unique countours. RNA molecules with appropriate folds can also served as enzyme. Many of the ribozymes work by positioning metal ions at the catalytic sites. Relatively few catalytic RNA exist in modern day cells, being the polypeptides work much better.

An example of In vitro selection of synthetic ribozymes:

-A large pool of dsDNA each with a randomly generated sequence. Transcription and folding into randomly generated RNA molecules. Addition of ATP derivative containing a sulfer in place of oxygen Only a rare RNA has the ability to phosphorylate itself. This is captured by elution of the phosphorylated material

These experiments and others like them have created RNAs that can catalyze a wide variety of reactions:

Peptide bond formation in protein synthesis, RNA cleavage and DNA ligation, DNA cleaving, RNA splicing, RNA polymerization, RNA and DNA phosphorylation, RNA aminoacylation, RAN alkylation, Amide bond formation, amide bond cleavage, glycosidic bond formation and porphyrin metalation, since, like proteins, ribozymes undero allosteric conformation change

Self-Replication Molecules Undergo Natural Selection

-he 3D structure is what gives the ribozyme chemical properties and abilities. Certain polynucleotides therefore will be especially successful at self-replication. Errors inevitably occur in such processes, and therefore variations will occur over time. Consider an RNA molecule that helps catalyze template polymerization, taking any RNA as a template

-This molecule can replicate. It can also promote the replication of other RNA. If some of the other RNA have catalytic activity that help the RNA to survive in other ways, a set of different typers of RNA may evolve into a complex system of mutual cooperation.

One of the crucial events leading to this must have been the development of compartments. A set of mutually beneficial RNA could replicate themselves only if the specialized others were to remain in proximity

Selelection of a set of RNA molecules according to the quality of replication could not occur efficiently until a compartment evolved to contain them and therefore make them available only to the RNA that had generated them. A crude form of this may have simly been simple absorption on surfaces or particles.

The need for more sophisticated containment fulfilled by chemicals with the simple physiochemical properties of ampipathism. The bilayers they form created closed vesicles to make a plasma membrane. In vitro RNA selection experiments produced RNA molecules that can tightly bind to amino acids. The nucleotide sequence of such RNA contains a disproportionate number of codons corresponding to the amino acid. This is not perfect for all amino acids, but it raises the possibility that a limited genetic code could have arised this way. Any RNA that guided the synthesis of a useful polypeptide would have a great advantage.