This however does not authorize us to say that the same mechanisms also operated in the second phase of precellular evolution, the phase that went from the first mixed organic systems to the first cells. We conclude therefore that precellular evolution must be divided into two great stages: one before and one after the appearence of the first integrated systems made of both proteins and nucleic acids.
The first phase corresponds to classical chemical evolution, but the second one is more difficult to define, because it is no longer chemical evolution but not yet biological evolution. It is anyway necessary to characterize it, and to this purpose we can give it the name of postchemical evolution. Before the origin of life, in other words, there have been two evolutionary stages that were temporally and conceptually distinct: one of chemical evolution and the other of postchemical evolution.
Such a distinction is important because it gives us a criterion for a better evaluation of the origin-of-life theories. The solutions proposed by Sidney Fox or Wächtershäuser, for example, are exclusively theories of chemical evolution, and tell us nothing about postchemical evolution. It would be wrong to criticize them for this, but it would also be wrong to say that, if they explain chemical evolution, they also explain postchemical evolution and therefore the origin of the cell.
The concept of postchemical evolution, in conclusion, allows us to realize that there is another important dichotomy in the origin of life field. In addition to the distinction between metabolism-first and replication-first theories, it is necessary to distinguish clearly between theories of chemical evolution and theories of postchemical evolution.

The metabolism paradigm

We have seen that the sudden appearence on Earth of a system capable of both metabolism and replication is too unlikely to be taken seriously. All reasonable theories on the origin of life assume therefore that chemical evolution started from systems that could perform only one of those functions.