Biochemical ‘Cambrian’ explosion-implosions: the generation and pruning of genetic codes

Tlusty's topological analysis of the genetic code suggests ecosystem changes in available metabolic free energy that predated the aerobic transition enabled a punctuated sequence of increasingly complex genetic codes and protein translators. These coevolved via a `Cambrian explosion' until, very early on, the ancestor of the present narrow spectrum of protein machineries became evolutionarily locked in at a modest level of fitness reflecting a modest embedding metabolic free energy ecology. Similar biochemical `Cambrian singularities' must have occurred at different scales and levels of organization on Earth, with competition or chance-selected outcomes frozen at a far earlier period than the physical bauplan Cambrian explosion. Other examples might include explosive variations in mechanisms of photosynthesis and subsequent oxygen metabolisms. Intermediate between Cambrian bauplan and genetic code, variants of both remain today, even after evolutionary pruning, often protected in specialized ecological niches. This suggests that, under less energetic astrobiological ecologies, a spectrum of less complicated reproductive codes may also survive in specialized niches.