Talk:Last universal common ancestor

'all organisms', period?

seems like this isn't the place to argue that every organism in existence is on earth right now. we shouldn't use "all currently living organisms" to refer to the descendants of the LUA unless we're also going to say that there aren't any currently living organisms unrelated to life on earth. —The preceding unsigned comment was added by 69.181.232.197 (talk) 08:23, August 23, 2007 (UTC)

Along those same lines, perhaps drop the "living" as in the LUA being the "latest living organism?" Tom Schmal 15:35, 31 October 2007 (UTC)

Last or First?

If this is the "Last" common ancestor, what was the First one? Tom Schmal 13:00, 24 July 2007 (UTC)

The first sentence seems to be clear in that direction to me. First common ancestor is something really hypothetical (and a bit creationist, if you ask me). To put it simple, consider the LUCA as part of a wider group of people. He is the great-great-...-grandfather of everyone alive today, while none of the other people have any living descendants. » byeee 07:56, 27 July 2007 (UTC)

How many "universal" ancestors could there be? Wouldn't it be more correct if this ancestor were named the "First Common Ancestor?" So as between humans and chimps, for example, this would be the First Common Ancestor, then there would be millions of other common ancestors until finally five million years ago we would come to the Last Common Ancestor where the two species go their different ways.

Or maybe just the "Universal Ancestor." The "Last" seems redundant at best. Tom Schmal 15:06, 31 July 2007 (UTC)

If I don't reflect on it a whole bunch, it seems right. But if I start thinking whether Last or First is best, my head goes spinning. But, as you said the difference between the First and Last yourself, the Last seems much more important - and the scope of this article. » byeee 17:44, 31 July 2007 (UTC)

It's definitely last. There may have been earlier common ancestors, who may have had several descendant branches, but only one of these descendants is both LAST and COMMON. Draw a tree if you don't see it right away. Piet | Talk 20:31, 15 January 2008 (UTC)

I thought I'd add my two cents as I've referenced this section of talk below. As I see it there are three significant individual organisms related to the origins of life on Earth.

1. First Living Organism (FLO) - This is the first instance of life arising on Earth. It is not necessarily an ancestor of any life currently living as its entire line may have died out after another line (that line leading to all current life) independently came into existence.
2. First Universal Ancestor (FUA) - This is the first organism in the line leading to all life on Earth today. This organism would have no ancestors and would have arisen abiogenically as had the FLO above. The FUA would be the oldest ancestor of the LUA.
3. Last Universal Ancestor (LUA) - This is the organism that serves as common ancestor to all life today. It represents the only surviving branch of the FUA's line. The FUA's line may have had several other branches (none of which were ancestral to all current life) that have died out leaving only the LUA's descendents.

Hopefully that's fairly clear. I think it illustrates the difference between the Last Universal Ancestor and the First Universal Ancestor and explains why this article is called what it is.

Note: I think from what I'm seeing online that another name for the FUA is the Ur-organism (Emmanuelm explains below that this means original organism).

-Thibbs (talk) 17:49, 5 May 2008 (UTC)

(outdent) Unfortunately it seems that the subtleties of these concepts have proven more elusive than my basic explanations could compete with. To clarify the topic I will describe the terms FLO, FUA, and LUA in terms of the theoretical organisms given to us by Darwin in his Tree of Life (Note: although this link is accurate I would recommend finding a clearer copy to refer to the details).

edit: a clearer copy Thibbs (talk) 17:03, 6 May 2008 (UTC)

• Referring once more to the definitions for FLO, FUA, and LUA provided above, let us begin by imagining that the LUA is represented by organism a³ from Darwin's chart (let us extend the d-line to the 14th generation to represent bacteria, the f-line represent archaea, and the a⁵-a⁶-line represent eukaryota). If we now imagine that the m-line had ended at m⁸ and we ignore the F-, w-, and z-lines, then we can see that all living organisms at the current date (the 14th generation) descend from a³ (the LUA) and its ancestors.
• This then allows us to view A at the 0th generation (or more properly the common ancestor of A, B, C, and D at the -1st generation) as the FUA.
• The FLO is harder to illustrate. Let us begin by taking the same assumptions as we have for the LUA and the FLO. We now imagine that the common ancestor of A, B, C, and D is called α, the ancestor of E is ε, and the ancestor of F is φ. Let us for the moment ignore G, H, I, K, and L. Let us further imagine separate moments of abiogenesis for α, ε, and φ such that the order of their abiogenic development was first φ, second ε, and third α. The FLO, then, would be φ.

This covers the three most important players in the origin of life on earth (if we are to remain in the strictly scientific realm). It should be noted that a different table could be produced in which any two or all of the FLO, FUA, and LUA are the same organism.

• As a final note, and to explain my mysterious dismissal of G, H, I, K, and L (from Darwin's chart), I have recently considered that there is potentially one other interesting individual who could be discussed in the topic of the origin of life. The First Living Organism in the Universe (FLOU) could be described if we imagine G, H, I, K, and L on another planet. If their common ancestor is called γ and γ is contemporaneous with φ (Earth's FLO) in the same -1st generation, then we see that φ can remain as Earth's FLO despite the existence of other organisms (i.e. γ) in the same generation. If we now claim that the γ-line began much earlier we can postulate that if γ's ancestor, א (the only -2nd generation-member), was the first example of life in the universe/multiverse/reality of everything then א is the FLOU.

I hope this un-muddies the water a bit. -Thibbs (talk) 16:54, 6 May 2008 (UTC)

Source?

Does anyone have a citation for the claim that LUCA lived around 3.5 billion years ago? I'd like to use it for History of Earth. — Knowledge Seeker দ 00:07, 29 March 2006 (UTC)

"The Last Universal Ancestor hypothesis has since been refuted on many grounds[citation needed]. For example, it was once thought that the genetic code was universal (see: universal genetic code). Back in the early 1970s, evolutionary biologists thought that a given piece of DNA specified the same protein subunit in every living thing, and that the genetic code was thus universal. Since this is something unlikely happen by chance, it was interpreted as evidence that every organism had inherited its genetic code from a single common ancestor, aka. the "Last Universal Ancestor." In 1979, however, exceptions to the code were found in mitochondria, the tiny energy factories inside cells. Biologists subsequently found exceptions in bacteria and in the nuclei of algae and single-celled animals. It is now clear that the genetic code is not the same in all living things, and that it does not provide powerful evidence that all living things evolved on a single tree of life[citation needed]. Further support that there is no "Last Universal Ancestor" has been provided over the years by lateral gene transfer in both prokaryote and eukaryote single cell organisms. This is why phylogenetic trees cannot be rooted, why almost all phylogenetic trees have different branching structures, particularly near the base of the tree, and why many organisms have been found with codons and sections of their DNA sequence that are unrelated to any other species[citation needed]."

- I am very suspicious of this paragraph. It has no sources cited, and it does not match up at all with what I was taught in multiple University level Biology classes (Including Cellular, and Microbiology). I was taught that all known exceptions to the universality of the genetic code were believed to be acquired characteristics. Most of them are also attributable to post translational modification as well (such as the presence of Selenocysteine in mammals.Cadallin 20:50, 1 April 2007 (UTC)Cadallin

I have a page "Last Common Ancestor" so I put in a link to it, but no trail, so I will sign it here. Also whoever put in the text above about the refutation also put it in Last Common Ancestor reference section where I really don't think it belongs. Tom Schmal 22:54, 9 April 2007 (UTC)

Religious Bias

The information in the "Criticism" section can be broadly defined as "Creation Science." These are arguments commonly used to support the pre-conceived conclusion that humans evolved independently of all other organisms on earth. Basically, the author's position is that instead of there being ONE family tree for all life on earth, there are a bunch of different trees and that in some cases(particularly that of humans) the tree is simply linear. While the article should probably contain some general comment to the effect that there are some other non-trivial hypotheses about the exact path to our current biodiversity, it is NOT acceptable for non-NPOV theories outside sphere of accepted science to comrprise 60+% of the article. —The preceding unsigned comment was added by 167.83.10.20 (talk) 20:15, 11 April 2007 (UTC).

I am removing the "LUCA is refuted" paragraph, it's thinly disguised creationism. The somewhat relevant parts of it, about problems rooting the tree of life, are already addressed in the article via the section on gene transfer.

-Blueshifter 15:26, 29 April 2007 (UTC)

The criticism section smacks of creationist nonsense right from the first sentance. — Preceding unsigned comment added by 12.33.211.29 (talk • contribs) 09:56, 20 June 2007 (UTC)

Removed unsourced, weasely criticism section. There is no doubt some published scientific criticism - so find and cite it if the section is to be re-written. Vsmith 11:28, 20 June 2007 (UTC)

"What we know" section created

I created a paragraph that attempts to list all the properties shared by all independently living organisms (not viruses), based on the assumption that the LUA must also have had these properties. I had lots of fun doing this. It is clearly incomplete; be bold, improve it. Emmanuelm (talk) 16:15, 11 January 2008 (UTC)

It's very interesting, nice work. It would be better if you had a source, but I won't touch it. One thing struck me however: "almost all independently living organisms". Considering the scope of the LUA concept, "almost" has no place there. I've removed it, at the risk of being less exact(?) In this place however "almost" is a weasel word. But again, nice work. Piet | Talk 20:37, 15 January 2008 (UTC)

Thanks Piet. I added two references only; they were surprisingly difficult to find. Please help by finding more. Emmanuelm (talk) 17:00, 18 January 2008 (UTC)

"Darwin's black box and the LUA" section created

I added this paragraph. A bit weak, but I think it is interesting. If you delete it, I will not revert. Emmanuelm (talk) 17:08, 11 January 2008 (UTC)

Microtubule-based locomotion?

What source - or for that matter, what line of reasoning - advocates microtubule-based locomotion in the last universal ancestor, as currently purported by this article? MicroProf (talk) 02:46, 27 February 2008 (UTC)

I guess you are right; the line is removed. Emmanuelm (talk) 00:47, 16 March 2008 (UTC)

Merger proposal

According to the definition of Ur-organism found in its article, there seems to be no need for both articles on "ur-organism" and "LUCA". I am not familiar with the ur-organism concept, but it also seems possible to me that it actually refers to the first instance of life or even the First Common Ancestor (as discussed above), and that the definition listed at Ur-organism is incorrect. Does anyone know anything more about this? Should the two be merged and disambiguation be set up or should the definition of ur-organism simply be rewritten accurately? -Thibbs (talk) 21:58, 3 May 2008 (UTC)

In Google scholar, a search for "ur-organism" returned 8 hits, only one article using this term in its title. A search for "last universal common ancestor" return 53,000 hits. As per WP:Fringe, I vote we kill the Ur-organism article and redirect it to this one. Emmanuelm (talk) 20:18, 4 May 2008 (UTC)

Sounds good to me unless as I suggested earlier ur-organism actually means something different than it purports to in the ur-organism article. I'll try to do a little follow up on this. -Thibbs (talk) 23:36, 4 May 2008 (UTC)

OK, well this is proving to be more of a challenge than I'd thought. There seems to be much confusion of language online about what the term means. Harold J. Morowitz' book, Beginnings of Cellular Life: Metabolism Recapitulates Biogenesis (1993, Yale University Press) suggests that

"We envision the Ur-cells as being very simple, whereas the universal ancestor must—by comparison to these—have been quite complex. Thus, the gap between the approach from above and the approach from below must be filled by an evolutionary path from the ur-organism to the universal ancestor. The problem is not simply the origin of life, it is the physical formation of the the Ur-organism and a subsequent evolutionary epoch giving rise to the universal ancestor."

Later in the chapter he refers to the ur-organism as "a protobiotic form." This source, then, clearly supports the idea that "ur-organism" is a term for the First Universal Ancestor (not to be confused with the First Living Organism) rather than the Last Universal Ancestor. There are a few corroboratory sources from the social sciences or religious scholarship which I would hesitate to rely upon (eg. Rist's paper and Unger's article which was referenced in Google Scholar...). There are also an irritating number of folks online who employ the term "ur organism" to mean "your organism" as in "u take ur organism and put it undr teh microscope." The wiki article, Ur-organism, references Darwin as the originator of the term and I have run text searches on online versions of Origin of Species to no avail. I have not yet run tests on Descent of Man or his other works. I notice that Oparin has also been referenced but I have not yet examined his use of the term (if indeed he has used it at all). Before doing difficult-to-reverse changes to wiki, though, it seems to me that we need more authority than the unreferenced definition found in the ur-organism article. If anyone can find any information on the use of this term it would be very helpful. -Thibbs (talk) 00:37, 5 May 2008 (UTC)

Another option, incidentally, is to simply merge "ur-organism" with "abiogenesis" somehow. Prior to any merge, though, we need to get consensus on the definition of the term "ur-organism." -Thibbs (talk) 00:41, 5 May 2008 (UTC)

Another search at Google Books found two mentions in the context of evolution. No Darwin, no Oparin. Fringe comes to mind once more.

BTW, I'll bet (less than a dollar) that this weird word comes from Ur, the birth city of Abraham, the founder of all monotheistic religions. Emmanuelm (talk) 03:23, 5 May 2008 (UTC)

I lost my cheap bet with myself. From Audi Quattro the "Ur-" prefix is a German augmentative used, in this case, to mean "original" . Emmanuelm (talk) 03:30, 5 May 2008 (UTC)

Wow, Thibbs, the LUCA concept is a theoretical construct based on analogy (genetic and others) between currently living organisms. The adjective "last" is used to mean "most recent". It refers to the fact that this bug was most certainly not the first living organism but was itself the result of a long evolution. This evolution is, unfortunately, locked in a blackbox that may never be cracked by science. This is briefly explained in the article. You may expand it if you have time. Emmanuelm (talk) 13:53, 6 May 2008 (UTC)

Emmanuelm, you are incorrect that the term LUCA requires that "this bug was most certainly not the first living organism but was itself the result of a long evolution." It is possible that LUCA could be the same as the first instance of life in the universe, although this is more unlikely than your guess. I am very cognizant of the fact that this article is about the "last" (meaning "most recent") ancestor common to all life and I don't believe I've made any claims to the contrary. You must recognize, however, that there is a small chance that the last common ancestor to all current life is also the last common ancestor to all life that ever lived. I don't propose here to change the article to focus on this, but I certainly object to the assertion that this LUCA "bug" was most certainly not the first living organism when in fact it may well have been. (Incidentally I would also caution against using the term "bug" to describe the LUCA as bugs are, in fact, orders of magnitude more complex than the LUCA organism would statistically certainly have been). Perhaps to clarify I should mention that the FUA discussed above would also be a theoretical concept based on genetic analogy between organisms, however the scope of its analogical pool would include organisms (non-extant) that are not included in the line of the LUCA's ancestry. I will add a quick example to better explain this tricky concept above.

I think we have drifted away from the main topic of this thread, however. My question, to reiterate, was: Does the term "ur-organism" mean "LUCA," "First Universal Ancestor," or "First Living Organism?"

PS - Thanks for your contributions so far, Emmanuelm. I am glad at least someone else is aware of this corner of wiki. If there is anyone else out there who knows anything about the issue at hand or can help in any way please feel free to chime in. -Thibbs (talk) 15:52, 6 May 2008 (UTC)

Once this merge dispute is resolved, can someone fix cenancestor to point to the best article describing it? Thanks. StevePrutz (talk) 04:37, 22 May 2008 (UTC)

After a quick Google, I conclude that cenancestor is a synonym of LUCA. I changed the redirection of cenancestor to reflect this. I still think that ur-organism is different and should probably be redirected to origin of life. Emmanuelm (talk) 21:22, 23 May 2008 (UTC)

I agree with Emmanuelm that ur-organism is most likely different from LUCA. I had written to the creator of the article on "ur-organism" and he has not responded. I will go ahead and remove the redirect tags for ur-organism->LUCA and rewrite the lead for ur-organism so that it can no longer be confused with the LUCA. -Thibbs (talk) 21:36, 24 May 2008 (UTC)

Misconceptions

This section needs to be expanded, or better yet scrapped completely with the information being redistributed throughout the article. Phoenix1304 (talk) 08:35, 28 May 2008 (UTC)