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
--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)