WE HAVE REACHED a point in our hypothetical reconstruction of the age of information where the first peptides began to be assembled by an RNA machinery. We know what came next: translation and the genetic code. Two questions challenge the historian. First, by what succession of steps did translation and the genetic code arise? Second, what was the driving force that propelled such an extraordinary development? The two questions are intimately related, since no pathway can be considered that does not entail an explanation of its spontaneous emergence. Before we try to answer these questions, a new element needs to be introduced, namely, the concept of a primeval cell.
The cell is the unit of life and figures at some stage in all attempted reconstructions of the origin of life. Some scenarios bring in cells early or, even, right at the start. Others begin with an unstructured soup and introduce cellularization later, sometimes postponing it to the last moment before it became indispensable for further progress. For reasons that will be explained in chapter 9, I have adopted the latter course. But a limit has been reached.
With the initiation of RNA-dependent peptide synthesis, if not before, emerging life had virtually exhausted the potential of molecular evolution. For further evolution to take place, less selfish criteria for selection--or, better said, less crudely selfish criteria--had to come into play. RNA molecules no longer had to be assessed solely on the strength of their intrinsic ability to survive and be replicated, but on the basis of their ability to do something that favored their survival and replication indirectly. But for this kind of selection to operate, the biogenic system needed to be parceled out into a number of discrete, semiautonomous, self-reproducing units--let us call them protocells--each containing its individual genome. Then, any useful