Re: Last universal but not universal common ancestor of life

On 6/7/2025 12:24 PM, JTEM wrote:

On 6/7/25 9:53 AM, RonO wrote:
 

The last universal common ancestor discussed in the PNAS article that is discussed in the Popular Mechanics article is just the last common ancestor (LUCA) of all extant life on earth.

 Yes. Which was one of my complaints. Language matters.
 

  The PNAS article thinks that they can acquire information about life that existed before LUCA by looking at the amino acids used in protein domains that would have existed in pre LUCA lifeforms.  They tried to figure out the amino acid composition of the protein domains that have likely existed since the first proteins were evolving to be functional.

 They are operating on the assumption that they know the "How" life
first began. If their assumptions are wrong, everything is wrong.
 

  They claim to have estimated the frequency of use of each of the 20 amino acids before and after LUCA.

 Cart. Horse. Before. Put.
 I suppose you could argue that it's a round about way to getting to the
creation of non life under laboratory conditions. But it is representing
itself as knowing answers it does not know.

They are only talking about evolution of the genetic code.  The original lifeform that arose by abiogenesis did not have a genetic code for the production of polypeptides.  It may not have used amino acids in reproducing itself.  We do not know what the first simple self replicators were made of.  It looks like the RNA world evolved the genetic code, so early lifeforms would have evolved RNA nucleotide polymers before they could have made polypeptide polymers using a genetic code.
Ron Okimoto