Dyson concludes therefore that, after Oparin’s metabolism stage, came Haldane’s replication stage, and his final scheme becomes: “metabolism-first, replication-second”. That RNAs could replicate themselves, within precellular systems, as viruses, is highly unlikely, but this point has nothing to do with Dyson’s mathematical model, and can be regarded as an unnecessary addition. If we stick only to the intrinsic characteristics of Dyson’s model, we have something very useful in our hands, because the scheme does give a valid answer to the main problem of chemical evolution: the problem of explaining how primitive systems made of proteins could be able to produce RNAs.
A somewhat parallel solution to the same problem has also been given by Wächtershäuser, with the description of an hypothetical, but plausible, sequence of chemical reactions that lead to the same final result. We have therefore both mathematical and chemical models that are capable, in principle, of explaining chemical evolution. This is only the first part of precellular evolution, and there still is a long way to go before the origin of the cell, but at least the metabolism paradigm does give us a good starting point.

The replication paradigm

The discovery of viruses made an enormous impression on biologists, because it was proving that something much smaller than a cell maintained the ability to replicate, the most quintessential of life’s properties. Haldane knew only too well that viruses are totally dependent on cells for their replication, and therefore that could have evolved only after cells, but those tiny proliferating crystals in the interior of huge cellular structures appeared to be claiming a deeper truth: that replication is simpler than metabolism. This was the concept that struck Haldane, and from that came the idea that everything started when the first molecular replicators appeared on the primitive Earth.
Today, replication is firmly based on nucleic acids, but the nucleotides that make up these molecules are much more complex than the amino acids which produce proteins, as can be clearly seen in Figure 5-6.