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From: Ernest Major <{$to$}@meden.demon.co.uk>
Newsgroups: talk.origins
Subject: Re: Las universal common ancestor
Date: Sun, 14 Jul 2024 09:20:03 +0100
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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
>>
>> 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.
>>
>> 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
> 

-- 
alias Ernest Major