# Talk:Last universal common ancestor

I have to say I'm slightly confused by the opening sentence, as to what this LUCA thing actually is. An individual, or a group of individuals? It's described as a "population" but then other parts of the article imply it was just a single bacterium or similar.  — Amakuru (talk) 22:52, 8 September 2023 (UTC)

It's spoken of in both ways. There was certainly a population of similar cells. However all living things come by definition from just one of these. Chiswick Chap (talk) 12:12, 9 September 2023 (UTC)
The Question from @Amakuru is concerning the “confusion”, I mentioned in my update from  20 September 2023. For example numerous authors use the term LUCA while it should be UCA. Maya Kandler (talk) 12:22, 23 September 2023 (UTC)
As you say, that has already been addressed; if more is really needed, then feel free to add and cite it (in the article body, not the lead, see below). But since this article is called "LUCA", and since as you rightly say many authors use the term, it is a "term of use" and we as an encyclopedia can properly have an article on it. It is fine to mention that "UCA" is an alternative, but it is not our job to say that a term in wide usage is "wrong", whatever that would mean. The other point is that we can't start talking about "UCA" in the lead: the lead is only a summary of the rest of the article, so there must be a discussion in the article body, presumably discussing the subtleties of UCA vs LUCA in terms everyone can understand, for the lead to summarize. Chiswick Chap (talk) 12:37, 23 September 2023 (UTC)
Plus, to add onto what you're saying, one must keep in mind that this LUCA specifically refers to the last universal common ancestor of our three main domains of life. LUCA itself would NOT have been a universal ancestor of all possible cellular life, as there could have been sister lineages that died out. Anything predating LUCA and the other forms of cellular life that existed alongside it, would be a true "UCA" in the sense that it would be a universal ancestor for ALL cells. 2600:1700:3D90:8860:81D:CF20:886A:D4AA (talk) 03:29, 16 December 2024 (UTC)
You could say a species, the only one at the time. But let's not forget, LUCA is a hypothesis. Archaea and bacteria are quite distinct. The evidence that they're derived from a common ancestor is, as things stand, not wholly conclusive. There's no spectrum of 'missing links' among known procaryotes. LUCA is more of an assumption: we kind of extrapolate to assume that archaea and bacteria are related because branching is how new species came to be, later on in the history of life. We may be wrong. If early planet Earth offered the conditions for life to develop once, why not twice? Magic77wand (talk) 20:15, 15 January 2024 (UTC)
You are getting confused. That all life on Earth is part of the same evolutionary tree is well-known and undisputed. DNA has all the required proof. We are not sure on the shape of that tree (is it how it has always been, are there missing branches, or even whole missing unrelated trees?), but the tree itself is out of the question. Cambalachero (talk) 19:20, 16 December 2024 (UTC)

This scheme is based on the cited original publication (Woese, Kandler, Wheelis 1990, Fig. 1, page 4578), called a “universal phylogenetic tree in rooted form, showing the three domains”. The term LUCA (last universal common ancestor) is not used.
The author of the file mentioned above should explain, that he has added the term LUCA.
In addition, Woese et al. proposed the new taxon Eucarya for the third domain (instead of the former terms Eubacteria, Archaebacteria, Eukaryota).
Please kindly use the designation of the original. Maya Kandler (talk) 12:29, 23 September 2023 (UTC)

I'm not at all sure what we should do here, as heading the LUCA article with a 1990 tree with obsolete nomenclature and without the label "LUCA" feels like a leap backwards in time, and it would certainly confuse readers. We may do better to drop the Woese et al. connection for the image caption and simply show the consensus arrangement of the domains, a far simpler diagram. Let's try that. Chiswick Chap (talk) 12:44, 23 September 2023 (UTC)
Eukarya is not obsolete, it is the current name for the domain.
Eukaryote(s) refers to the member(s) of this domain.
See Wikipedia-Article Domain, Textbook Brock or e.g. https://www.biologyonline.com/dictionary/eukarya ; https://www.biologyonline.com/dictionary/eukaryote

Current Textbook-Definitions of LUCA refer to the three domains, so it is important, to start the article with Woese et al. and add “LUCA” in the original scheme as you did (I just asked you to explain, that you added LUCA). So everyone can see the point/node of diversification.
The original scheme illustrates the diversity of organisms much better, than your new simpler scheme. Maya Kandler (talk) 14:05, 23 September 2023 (UTC)
It is "Eucarya" that I indicated was obsolete. I've tweaked the diagram for you and indicated that Woese et al did the tree but not the LUCA label. Chiswick Chap (talk) 14:33, 23 September 2023 (UTC)
Thank you! Maya Kandler (talk) 08:11, 24 September 2023 (UTC)

 This article was the subject of a Wiki Education Foundation-supported course assignment, between 30 September 2023 and 8 December 2023. Further details are available on the course page. Student editor(s): Gretashum (article contribs). Peer reviewers: Kcshaffman.
— Assignment last updated by Kcshaffman (talk) 01:10, 29 November 2023 (UTC)

Based on the text of the source, it appears to me that the hypothetical organism being described as the LUCA is actually the first universal common ancestor, as they state that their date reflects the common ancestor of all cellular life (not necessarily living cellular life) and even more tellingly that the archaea–bacteria split would only happen or hundreds of millions of years after the time of their "LUCA." This would explain why their date is far more ancient than any other given in the article, because our sources are talking about entirely distinct things. Could someone take a look at the source and confirm that I am not confused or misreading anything? I'm certainly not calling these experts wrong, I'm just saying that their terminology might not match the terminology we use in our articles. Anonymous 18:28, 16 June 2024 (UTC)

Not that, I think. Rather, it's that the paper isn't basically about the LUCA at all, and it really doesn't discuss the LUCA's age more than in passing, basing it only on the lack of more precise constraints. I've chopped one sentence from the rather over-bold discussion based on the paper. Chiswick Chap (talk) 14:12, 7 October 2024 (UTC)