Interesting article: Protein Superfamily Evolution and the Last Universal Common Ancestor (LUCA) Mmm, "Functional analysis of these ancestral domains reveals a genetically complex LUCA with practically all the essential functional systems present in extant organisms".... Let's see what they found: From the conclusion: What did this primitive clade of LUCAs have? What kind of machinery was present? 1) Replication, transcription, and translation 2) Repertoire of metabolic pathways coupled with the necessary machinery including; a) the use of glucose and other sugars b) the assimilation of amino acids and nucleosides/ base c) the synthesis of ATP both by substratelevel phosphorylation and through redox reactions coupled to membranes d) Signal transduction pathways controlling perception. e) These pathways are linked to gene regulation and protein modification, protein signal recognition, transport, and secretion, protein folding assistance f) And then of course the self-replication machinery. With all these present in the LUCA, all that is needed is a little time for functional diversification and genetic expansion. The inevitable and repeated emergence of eyes, body plans, toolkits for body plans etc. should not be a problem, even expected if the tape of life was to be replayed even if randomness was taken into consideration. But... it gets more interesting: A minimal estimate for the gene content of the last universal common ancestor—exobiology from a terrestrial perspective If you think the LUCA was just a simple self-replicator, think again: From the article the following conclusions were drawn: The gene content of LUCA with respect to A) DNA processing (replication, recombination, modification and repair) contains a wide range of functions including; DNA polymerase excinuclease ABC DNA gyrase topoisomerase NADdependent DNA ligase DNA helicases DNA mismatch repair MutS and MutT endonucleases RecA chromosome segregation SMC methyltransferase (Epigenetics related enzyme) methyladenine glycosylase and adenine glycosylase adenine phosphoribosyltransferase deoxyribodipyrimidine photolyase integrase HAM1 Sir2 involved invarious aspects of genomic stabilit) TatD—a recently discovered DNase histone deacetylase (More epigentically related enzymes) These are just replication related machinery. Next is: Transcription/regulation Translation/ribosome RNA processing (No, it is not junk DNA, RNA processing was there from the beginnig) Cellular processes (e.g. cell division control) Transport/membrane Electron transport Metabolism And several with unknown function... How deep does the rabbit hole go? Please Register or Log in to view the hidden image! Time will tell I guess....
It's fascinating stuff, and it's too bad you have chosen such a misleading term to label it. Most native English speakers familiar with the words regard preadaptation and exaptation to be directly opposed in their implications - almost opposites. (Bateson called it "abduction", from its logical structure: compare deduction, induction. I find that convenient and accurate)
