Re: Las universal common ancestor

On 7/13/24 3:03 PM, 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.
 William Hyde
 

I'm not sure what "ancestral" means to a virus.  Can someone with better chops than I comment on that?  I've never seen a phylogenetic tree for viruses, or how that could be incorporated into a bacterial tree.  The authors mention "horizontal transfer awareness".