The three domains concept has been a goldmine for molecular biologists and evolutionists alike. The unique features of Archaea, as well as the close similarities between many archaeal and eukaryal versions of fundamental molecular processes, has led to several unexpected discoveries, either relevant for the history of Archaea themselves, or for the functionning of the eukaryotic cell.
I will give a few examples from work in our laboratory. On the other hand, working on Archaea press you to think about origin and early evolution of life. Building upon the three domains concept, new and sometimes provocative evolutionary hypotheses have been proposed by various authors. I will then briefly discuss some ideas and speculations on the nature of LUCA and the origin of the three domains. Recently, the problem of the origin and nature of viruses (and their evolutionary relationships with ther cellular hosts) has been also revisited in the light of the three domain concept (enriched with new data from virus sampling, comparative genomic and structural analyses). Didier Raoult and myself have suggested a new (provisional) dichotomic division of the living world (!) ....no more between prokaryotes and eukaryotes, but between ribosomes-harboring organisms and capsid-harboring organisms.
