Talk:Last universal common ancestor/Archives/2008/May

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)

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)

Phoenix, be bold, do it. Emmanuelm (talk) 12:54, 28 May 2008 (UTC)