Darwinian threshold

Before the Darwinian threshold

The Last Universal Common Ancestor is often considered to be an already complex organism with a DNA-based genome, a complex informational flow and an efficient metabolism, but some authors, like Carl Woese, believe instead that the LUCA was not a discrete entity but rather a diverse community of cells that survived and evolved as a biological unit.

Carl Woese indicated that most likely there existed high mutation rates and small genomes. Also present were small proteins and larger imprecisely translated "statistical proteins". Entities in which translation had not yet developed to the point that proteins of the modern type could arise, have been termed "progenotes," and the era during which these were the most advanced forms of life, the "progenote era".

These organisms or biological entities, these progenotes (or ribocytes), had RNA as informational molecule instead of DNA. RNA is capable of both catalysis and replication and could have been central to the origins of heredity and life itself. It has been proposed that the initial molecular events were carried out by transfer RNAs (tRNAs). It is hypothesized that structured tRNAs could have provided amino acids during a process called self-translation of a single extended tRNA strand.

It is hypothesized compartmentalization with membranes was not yet completed and translation of proteins was not precise. Likely not every progenote had its own metabolism; different metabolic steps may've been present in different progenotes. Therefore, it is thought that there existed a community of sub-systems that started to cooperate collectively and culminated in the LUCA.