Re: Las universal common ancestor

On 13/07/2024 23:03, William Hyde wrote:

erik simpson wrote:

The nature of the last universal common ancestor and its impact on the early Earth system
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Abstract
The nature of the last universal common ancestor (LUCA), its age and its impact on the Earth system have been the subject of vigorous debate across diverse disciplines, often based on disparate data and methods. Age estimates for LUCA are usually based on the fossil record, varying with every reinterpretation. The nature of LUCA’s metabolism has proven equally contentious, with some attributing all core metabolisms to LUCA, whereas others reconstruct a simpler life form dependent on geochemistry. Here we infer that LUCA lived ~4.2 Ga (4.09–4.33 Ga) through divergence time analysis of pre-LUCA gene duplicates, calibrated using microbial fossils and isotope records under a new cross-bracing implementation. Phylogenetic reconciliation suggests that LUCA had a genome of at least 2.5 Mb (2.49–2.99 Mb), encoding around 2,600 proteins, comparable to modern prokaryotes. Our results suggest LUCA was a prokaryote-grade anaerobic acetogen that possessed an early immune system. Although LUCA is sometimes perceived as living in isolation, we infer LUCA to have been part of an established ecological system. The metabolism of LUCA would have provided a niche for other microbial community members and hydrogen recycling by atmospheric photochemistry could have supported a modestly productive early ecosystem.
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https://www.nature.com/articles/s41559-024-02461-1

 Does not the existence of the immune system itself imply the existence of other life forms?  Smaller, parasitic or infectious?  But since this is LUCA they themselves cannot have left descendants.
  So if they were virus-like they went extinct and the virus form evolved again.
 Corrections and comment welcome, as ever.

You might think of this as LUCCA - last universal cellular common ancestor. Coeval viruses might have "living" descendants.
When I read that this LUCA has an immune system I made the assumption that this implied the existence of coeval viruses. But I now realise that there are other alternatives, such as a prokaryote that injects a copy of DNA into other cells, or still existing categories such as viroids and plasmids.
I used to be agnostic between the 3 major hypotheses for viral origins, but I am becoming increasingly convinced that at least some viral groups are ancient. Viruses are now classified into 6 realms (and more than 2 dozen incertae sedae groups). One realm - the Adnaviria - seems to be as old as the Archaea.

 William Hyde
 

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alias Ernest Major