Talk:Last Common Ancestor

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This is an old revision of this page, as edited by Fred Hsu (talk | contribs) at 12:31, 1 December 2007 (→‎Article should be restored for discussion: more). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Previous discussion

As for the cartoon, it was reinstated. It appropriately makes the point defined later in the text, ie., "...the LCA is the seminal individual that first coded the mutation..." That would be mom or dad, no way around it. I cannot believe someone would have a problem with that illustration in Wikipedia! And if he did this discussion page is the place to make the case, not with some hit and run on the article. Tom Schmal 02:48, 15 August 2007 (UTC) _____________________________________[reply]

Do not see much value for the reader in merging LCA and MRCA.

MRCA: "It is incorrect to assume that the MRCA passed all (or indeed any) of his genes down..." Contrast this concept to that of the LCA: "Every person on earth owes 100% of his genes to the LCA."

MRCA: "The existence of an MRCA does not imply existence of a first couple..." Contrast this to implication of the LCA, which is: "the LCA is seminal individual that first defined the new species."

One entry speaks to lineage and the other to evolution. Yes, both pages have something to do with heritage, as atoms and molecules have someting to do with matter, but it would be a stretch to say they should be defined together - especially given the different core meanings as seen above.

For the interested reader, the entries each have the other's links, which is appropriate. Tom Schmal 00:14, 24 July 2007 (UTC) _____________________________[reply]

And let me add that someone's sticking "MRCA" where it originally said "LCA" does not make the two terms identical! It was changed to read: "Proponents of the Multiregional hypothesis would place the "MRCA" of humankind two million years ago..." Which is ludricous, because the MRCA according to the entry itself is two thousand years old, not two million! jeez! Tom Schmal 00:26, 24 July 2007 (UTC)[reply]

Confusing article

This article is extremely confusing. It keeps flipping back and forth between defining the LCA as the species founder and as the most 'recent' common ancestor. These are two completely different concepts. If the article is not cleaned up, I am considering removing links to it from pages such as Mitochondrial Eve‎. See examples below. Fred Hsu 02:41, 2 November 2007 (UTC)[reply]

Last Common Ancestor (LCA) is the most recent common ancestor of two populations that came to be separated by a species barrier.

OK, so the above defines LCA as the most recent (closer to present time) organism which is an ancestor of at least two populations (or species or organisms).

Along the hominid line there have been many branches, leading for example, to Australopithecus africanus, Homo erectus and Homo neanderthalensis. Although every species has an LCA, recent discussion is...

A species does have a LCA; it is the MRCA of all living members of the species. This LCA is NOT the individual at the bifurcation point between two species (say between Neanderthals and other hominid species); that individual would be the LCA of Neanderthal and another hominid species.

Proponents of the Multiregional hypothesis would place the LCA of humankind two million years ago as an early form of Homo erectus

You mean the MRCA of living people today lived 2,000,000 years ago? See below.

Computer simulations suggest that every person living today could share a common ancestor who lived as few as 2,000 years ago

So the MRCA of living people today lived 2,000 years ago?

Sigh. Fred Hsu 02:41, 2 November 2007 (UTC)[reply]

_______________________________________


Thanks for coming to a discussion page Fred. Probably I could have done better keeping LCA and MRCA straight.

An LCA is in fact the individual (or founding group) at the bifurcation point between two species. For us, this individual, which lived between two million and 40,000 bce, and no others contributed ALL of the genes that make up humanity. If we could pin the date down more closely we could probably call it "The MRCA between modern man and XXX" but we don't know the XXX.

Now fast forward to 2007. You and I and every person on earth could trace our ancestries back to around 2,000 years ago and find a common grandparent, aka The MRCA of All Mankind. Unlike the LCA, the genetic contribution of this ancestor to any one person is extremely small. This is because some ten million of his contemporaries ultimately get into the action.

Obviously the MRCA of All Mankind cannot be both of these individuals. Chang, et al, call the individual of 2,000 years ago the MRCA of All Mankind. So we call the other guy, the individual that began the species, the LCA (of all mankind).

Tom Schmal 05:59, 6 November 2007 (UTC)[reply]

Are you sure 'LCA of mankind' is defined in the academic circle in the way you define it? Without an additional XXX species to define two groups, LCA of mankind will automatically fall back to MRCA of mankind. How can you ever define LCA at a bifurcation point without at least two parties? This is the source of the confusion. Fred Hsu 13:05, 6 November 2007 (UTC)[reply]
To describe the bifurcation point, “MRCA" and "LCA" of Chimps and Humans, for example, are interchangeable. However you can't use the former term when you want to describe this individual as the seminal parent of one of the branches, eg, the humans, because is already taken. It’s Chang’s guy, the MRCA of all Mankind, who lived a few thousand years ago. So instead you use the LCA of all Mankind. This one name allows for both descriptions - as the bifurcation point and also as the parent of the species. That is why it is better to call him the LCA.
I am hopeful the X of the LCA of Mankind and species X will be clarified in the pretty near future, perhaps when the two parties sponsoring the two theories kiss and make up.
In the future Concestor may replace LCA but it is pretty new and for now all the literature is LCA.
This has really been an excellent exchange. I think the article's “Other Common Ancestor Titles” section, and maybe more – or maybe the MRCA article - could be clarified now. If no one takes a shot at it after a while, I will. Tom Schmal 17:09, 6 November 2007 (UTC)[reply]
The article states "Unlike the LCA, the genetic contribution of this ancestor (MRCA of humankind) to any one person is extremely small". Are you saying that LCA (as defined in one way in the article to have lived at 2,000,000 years ago) contributed even more significantly than MRCA at 2,000 years ago to human kind? The longer we go back the more contribution? How about the first bacteria? The LCA (as you define it) became ancestor to all humans and some unidentified XXX species. Are you saying that this LCA contributed more to both humans and XXX than human MRCA and XXX MRCA to each of their descendant groups?
This article looks more and more like a term seized by someone to explain an idea which the term does not originally represent. The article states, "Chang, et al, call the individual of 2,000 years ago the MRCA of All Mankind. So we call the other guy, the individual that began the species, the LCA (of all mankind)." Where is the source for this? I will check your sources and do research of my own. But it appears that you have arbitrarily chosen to use this term for your own purpose.
What exactly does 'last' in LCA mean? Does it mean 'last' in the sense that the 'last meal' I ate is later in time than the 'previous meal' I ate? If this is the case, the LCA means exactly the same thing as 'most recent' comment ancestor; they are really interchangeable. And you can't say that LCA of all humankind lived 2,000,000 years ago while MRCA of all humankind lived 2,000 years ago.
If by 'last' you mean the last ancestor you find by tracing ancestry backward starting at present time, then you can probably say, the individual who lived 2,000,000 years ago was the 'last' common ancestor' of all humankind who was NOT an ancestor of some other species XXX. You need to explicitly list two species in order to use this term, then. You can't just say the 'last common ancestor' of all humankind, because this organism is the first self-replicating RNA. You've got to stop tracing ancestry somewhere. If you don't identify a species to stop the back tracing, LCA of all any species will always be the first self-replicating RNA. Besides, I AM NOT SURE THE ACADEMIC CIRCLE ACTUALLY USES 'LCA' IN THIS SENSE. See the now-deleted 'most ancient common ancestor' article which I managed to delete via AfD; that articled attempted to invent a concept like this without any academic support. Fred Hsu 23:19, 6 November 2007 (UTC)[reply]
OK. I checked all references listed on the article, except the two books by Klein and Leakey respectively (I don't have these books). Not a single reference paper mentions LCA. They all talk about MRCA. Continue to look elsewhere online. Fred Hsu 23:45, 6 November 2007 (UTC)[reply]

Possible references for LCA

Here are some web pages I am looking at now. Unfortunately, some of these only show abstract. Fred Hsu 01:27, 7 November 2007 (UTC)[reply]

Papers

Abstract

It is clear from all papers that LCA is exactly MRCA. Not one paper uses LCA of group ABC to mean the individual at the bifurcation point of group ABC with some other unspecified group XYZ. In all cases I found, all occurances of LCA can be replaced by MRCA without altering the meaning of the paper. In a few instances, unqualified LCA (that is not LCA of something; simply LCA) is used to identify the last universal common ancestor, which makes perfect sense. Unqualified LCA is the LCA of all living organisms.

If you are not satified, try searching at Blackwell Synergy or google scholar.

I am going to:

  • remove incorrect information from the LCA article (e.g. "the LCA is the seminal individual that first coded the mutation that created the characteristic that defined the new species", "Although every species has an LCA, recent discussion is", and "Proponents of the Multiregional hypothesis would place the LCA of humankind two million years ago")
  • remove redundant discussion on Multiregional hypothesis and dates; these have their own pages and are tangential to MRCA and LCA.
  • Add references I found to the article. Remove all existing references (except the two inline references) as they are irrelevant to LCA.
  • add a template to recommend that this article be merged into MRCA. The MRCA article already covers everything that LCA should cover. Since LCA is just another name for concestor (which is also covered in MRCA), it does not make sense to have a separate article for LCA.

Thanks. Fred Hsu 03:58, 7 November 2007 (UTC)[reply]

DONE. Fred Hsu 04:34, 7 November 2007 (UTC)[reply]

Removed content

I am removing the following content. For sake of fairness, I move them here. If anyone can find real references for these, feel free to move them back to the article, with proper inline citations. Fred Hsu 04:11, 7 November 2007 (UTC)[reply]

lead section

LCA of Humankind

(this complete section is wrong - as per research done as indicated in previous section on talk page)

The most famous LCA is the so-called “Missing Link”, the most recent common ancestor of the genera Pan and Homo, that is, of chimpanzees and humans.

Along the hominid line there have been many branches, leading for example, to Australopithecus africanus, Homo erectus and Homo neanderthalensis. Although every species has an LCA, recent discussion is often in reference to the branching of modern man from archaic Homo sapiens (now extinct).

Proponents of the Multiregional hypothesis would place the LCA of humankind two million years ago as an early form of Homo erectus. A larger consensus of opinion, however, is that the last common ancestor of all mankind was born much more recently, probably in Africa, between 100,000 and 40,000 years ago. Its descendants spread across the earth from there, replacing all other forms of hominid.

LCA of two species

(again, this is completely wrong)

While the new species will owe all its genes to its LCA, the LCA itself will be a member of the original line, not the new one. Its genetic contribution to that original line may be de minimis but as a convention the term LCA is often used as if it were the ancestor of both species.

LCA: a single organism?

‎At its most narrow definition, the LCA is the seminal individual that first coded the mutation that created the characteristic that defined the new species (see illustration). However, the defining mutation may be subtle and initially not a speciation event. In sexually-reproducing organisms, until the new species establishes itself there are going to be some, possibly many, generations of gene-swapping back to the parent branch.

Genetic evidence points to a long, perhaps a million year period before separation of the Pan and hominid lines was complete (see Patterson reference). Conversely, some experts believe that as recently as 40,000 years ago a non-anatomical trait, such as improved speech, suddenly emerged in archaic Homo sapiens (see Leakey reference). The individual first passing on this mutation would be the LCA of fully modern man.

Depending on the process that gives rise to the species, the LCA can sometimes be better described as the initial small breeding group or clan or founding population, all members of which carry a common species-defining mutation.

The Drosophila experiment conducted by Diane Dodd. Here, the LCAs may be best described as founding populations.

Other common ancestor titles

...It should be recognized, however, that every common structure in living people — from the makings of our mitochondria to our hair follicles — has an “Eve” that lived somewhere in the great distance between the LUA of three-plus billion years ago and the Last Common Ancestor of possibly 40,000 years ago. (what is this talking about?)

While each of us may have inherited genes from the MRCA of All Mankind, we have also inherited the genes from millions of his contemporaries. This case is different from that of the LCA, to whom every person on earth owes 100% of his genes, and to no other. (what?)

References

(done) Fred Hsu 04:34, 7 November 2007 (UTC)[reply]

Article should be restored for discussion

Mr. Hsu, you have just gone too far. Chopping up this article on the strength of your own personal misunderstanding of it is not right. I am obviously not a wiz at manipulating the Wikipedia but from what I have read here about how differences of opinion should be handled I can say absolutely that your sudden attack is not at all in the spirit of what we are trying to build.

This article made the Wikiedia better, your removing it made the Wikipdia worse.

You say you are proposing a "Merge" of this article with another one, one that you yourself have heavily edited. You ask for discussion but all that you left for this discussion is dismembered. Why did you do that? And you did it he day after I responded to you! What was the rush?

I have tried to explain to you the difference between the LCA of Mankind and the MRCA of Mankind and have obviously failed - but we and others can discuss the science later. What is needed now is that you reassemble the article to the way it was somewhere around November 5th. That way the evidence will be available in continunity and the issues, if any, can be addressed by interested parties and experts. Perhaps all it needs is more clarity around your issue and it will be fine.

So would you do that please? And <smile> don't forget the cartoon Tom Schmal 04:42, 16 November 2007 (UTC)[reply]

The revision before I started to clean up can be accessed here. Your explanation of 'your view' on LCA was expressed on the article itself. It was very confusing, as I discussed earlier on this talk page. So, I had to dive into the actual references, all references you have listed on the article. Absolutely NONE supported your theory, as I also explained on this talk page later.
Wikipedia tries to be neutral, by presenting all sides WITH ACTUAL SCHOLARLY REFERENCES, not just whims. Please check out the URLs I provided earlier on the 'most ancient common ancestor' article which I managed to delete via AfD (Article for Deletion). Your personal theories do not count as a 'side'. If you can provide references to back up your second definition of LCA, of course we will be happy to have it on wikipedia. I beg you to actually read what I wrote on this talk page.
I beg you to read what I wrote on this talk page carefully. I started with questions. Then I listed confusing points. Then I follow up on your references. I understood your references. I concluded that none supported your theory. All papers used LCA interchangeably with MRCA. So I delete all incorrect paragraphs from the article. All steps are faithfully laid out on this talk page. I even included deleted content here for future refrences. What more do you ask of me? Fred Hsu 06:00, 16 November 2007 (UTC)[reply]
Thank you for putting the page back together again. Maybe the key to unconfusing you is to demonstrate the the difference in the two ancestors with an example.

As a first step, without going into other issues, can you see that the same name cannot be used for the two persons in this chart? They are separated by thousands, maybe millions of years. Tom Schmal (talk) 19:00, 19 November 2007 (UTC)[reply]
I understood your point since my first comment on this talk page. Please check what I wrote. You do not understand what I have been trying to tell you. Please re-read what I wrote on this talk page. Your definition of LCA has NO backing from any paper. Please tell me which book or paper gave you this idea about this particular definition of LCA. If you cannot cite a paper or a book, your ideas are NOT fit for wikipedia. Wikipedia is not a soapbox. Fred Hsu (talk) 01:40, 20 November 2007 (UTC)[reply]


From your first comment to me you state that my LCA and your MRCA of All Living Humans should be the same. For example, you state: "A species does have a LCA; it is the MRCA of all living members of the species." Later you state: "You can't say that LCA of all humankind lived 2,000,000 years ago while MRCA of all humankind lived 2,000 years ago." Yet this is exactly what I am saying! Look again at my chart. You tell me, what is the correct name for the individual on it, the founder of the species, entitled "LCA of all living humans?" I await your response.

Yes you have back-up issues such as non neutral PoV, lack of references, making up the term "LCA" and etc. We can discuss those in due course. I think the best way to move forward is for you to state that you either agree or disagree that the two individuals on my chart - whatever their names - must be different and *can not* have the same name. Do you agree or do you disagree? How can we move forward unless you clearly state your position? —Preceding unsigned comment added by Tom Schmal (talk • contribs) 03:37, 20 November 2007 (UTC)[reply]

Tom, I am afraid you completely miss my point. I know the concept you are trying to convey. But its name IS NOT Last Common Ancestor. Perhaps there are other names you can find from papers and books. But until you find them, your theory is not worthy of a place in wikipedia. Please see Wikipedia:No original research. "LCA" is used by researchers to mean exactly MRCA. See real references I added to the article. You cannot hijack a phrase used by researchers to mean something completely different that you cook up.
I beg you, read my previous words on this talk page. Pay special attention to the 'most ancient common ancestor' article which I managed to delete via the deletion process. Please click on the URL in the following quote to see for yourself. I understand your idea; it's exactly like what Robert tried to present in the now-defunct 'most ancient common ancestor'. Fred Hsu (talk) 05:28, 20 November 2007 (UTC)[reply]

See the now-deleted 'most ancient common ancestor' article which I managed to delete via AfD; that articled attempted to invent a concept like this without any academic support.

You say you "know" the concept - but can't state whether you agree or disagree with the it? Fred, this is not new stuff. We must have two individuals here, not one (please review the chart), do you agree or don't you? Tom Schmal (talk) 15:12, 20 November 2007 (UTC)[reply]

You are trying to sidetrack the issue here. If I say I agree that there is a individual who first had some sort of mutation, you will simply take my answer and spin it as if I agreed to your interpretation of LCA. For the record, I disagree with your interpretation of LCA.
Now, answer my question. I will repeat it here to save you time. Where did you read about this definition of LCA that you use to mark your 'seminal' individual? Please, give me a straightforward answer. Did you read about it, or did you just seize LCA and use it to mean what you believe needs to be named?
If you did not read it on a paper or a book, then please stop arguing. Fred Hsu (talk) 00:50, 21 November 2007 (UTC)[reply]

LOL, okay I will take that for a "Yes" you agree there is a seminal individual (or founding population) that cannot be or be called the MRCA of All Mankind - that name already being taken by your very own article. As for sources for the name of this fellow, there are lots - but you don't have to look any further than your own reference, the very one you put in the article! It is a good one!

"Recent African Origin of Modern Humans Revealed by Complete Sequences of Hominoid Mitochondrial DNAs" Here are some findings by these esteemed scientists:

"The main controversy, therefore, has centered around the estimated age of the LCA and the reliability of the mitochondral clock on which it is based... the upper 95% confidence limit of the age of the LCA is as low as 179,000 years.

"While such an estimated age of the LCA by no means implies that modern humans emerged at that time, the age expected according to the mltitregional hypothesis should be as old as 1 Myr if gene exchanges among local populations were limited... A more likely explanation is that the age of the LCA indicates that modern humans originated much less than 1 Myr ago without integrating the substantial diverged H. erectus genes."

What say you, my friend? Ready to smoke the peace pipe? Tom Schmal (talk) 01:54, 21 November 2007 (UTC)[reply]

______________________

You were confused, maybe others were also. However, you have shed some good light on how to present the article. The First Definition of LCA was originally "The parent of a new species." Another contributor changed that to "The MRCA of two populations." This I believe led to the the confusion. So my plan from here is to restore a "parent" type idea as the First Definition and the bifrucation definition (which, as you point out, it shares with MRCA) as a secondary. Hopefully that will resolve the issue Tom Schmal (talk) 14:49, 21 November 2007 (UTC)[reply]

Tom, do you really understand this paper? It does not use LCA the way you use it. You look at the number of years and automatically assume they are talking about the same 'seminal individual' as in your mind. From your reply, I conclude that you invented the meaning of this term and that you have no source to cite.
I replaced the reference with the same paper in PDF format, so you can read the whole article. Please read it and tell me where it uses LCA to mean the individual at a bifurcation point of human and some unknown XYZ humanoid species. For your edification, I'll try to summarize the paper for you. The paper selects among a dozen humans 3 people: one European, one Japanese and one African. They then use mtDNA of apes and these 3 people to try to estimate the LCA of all human kind, that is, the most recent common ancestor of these 3 people, in the hope that this MRCA estimate is representative of that of MRCA of all humankind. The fact that the paper comes up with a wildly different (farther in the past) time estimate for MRCA compared to the 3,000 years ago estimate of Chang, et al is tangential to our discussion here. These researchers are trying to disprove multiregional hypothesis. The differences in time estimate between Chang and them is relatively small, if you compare both numbers of the supposedly >1 million year estimate for LCA if multiregional hypothesis were true.
Pay attention to the abstract and to the phylogenetic trees on page 535. Compare the 4.9 million year estimate for common ancestor between human and chimps to 143,000-18,000 years for LCA amongst all humans. Then look at the phylogenetic trees on page 535. See how the bifurcation (branching) point into humans and chimps represents the last common ancestor of all humand and chimp? See how the most recent branching point into all three humans represents LCA of all humankind. Please point out where your idea of the 'seminal' individual is on these trees. Fred Hsu (talk) 01:55, 22 November 2007 (UTC)[reply]


I looked and I understood. Now you look Fred - look at the title: "Origin of Modern Humans." This paper calls it the LCA. Get it? Origin = LCA. It just doesn't get any plainer than that. Tom Schmal (talk) 14:43, 25 November 2007 (UTC)[reply]

The term LCA is ubiquitous, what do you mean "invented" the usage?

http://www.itee.uq.edu.au/~listarch/fod/archive/2006/05/msg00003.html Prof Bernard Degnan, University of Queensland Any meaningful reconstruction of the last common ancestor (LCA) to all living metazoans through comparative analyses of extant taxa requires input from the most ancient body plans

http://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2006/11/16/MNGMFMDVG31.DTL&type=printable According to their DNA analysis, the last common ancestor of Neanderthals and humans lived about 700,000 years ago, and the ancestral populations of humans and Neanderthals diverged and split into distinct species about 370,000 years ago -- well before the evolution of anatomically modern humans

http://www.palaeos.com/Vertebrates/Lists/Glossary/GlossaryJL.html From the glossary of Palaeos,a reference frequently cited in Science Online. LCA: (abbr.) last common ancestor (and all descendants of that ancestor).

http://www.everything-science.com/sci/Forum/topic,1753.0 Earliest Primate May Have Pre-Dated some Dinosaurs (Nature) "We present a new statistical method that suggests a Cretaceous last common ancestor of primates, approximately 81.5 Myr ago, close to the initial divergence time inferred from molecular data.

http://johnhawks.net/weblog/reviews/genetics/genetics_mre_aapa_2005.html analytical papers by Hey and separately by Alan Rogers and colleagues The "ancestral allele" at a given locus is the allele thought to have been carried by the last common ancestor (LCA) of all humans.

http://discovermagazine.com/2005/feb/new-limb-on-family-tree New Limb on Family Tree 02.06.2005 The creature, known scientifically as Pierolapithecus catalaunicus, may be the last common ancestor of the great ape family: gorillas, chimps, orangutans, and humans.

http://www.talkorigins.org/faqs/homs/mtDNA.html Fossil Hominids: mitochondrial DNA However, using the genetic difference to estimate the time of the last common ancestor is difficult, for a couple of reasons. One is that the rate at which mtDNA mutates is poorly measured.

http://www.geocities.com/CapeCanaveral/Lab/2948/tree.html The British biologist Richard Dawkins points out some interesting dates about this. The last common ancestor between men and chimpanzees lived as recently as five million years ago. Our last common ancestor with the carnivores (cats, dogs) lived some 60 million years ago. The last common ancestor between a whale and a pea lived about 2 billion years ago.

Fred, which of these meanings am I "inventing?" 98.196.237.162 (talk) 18:09, 25 November 2007 (UTC)[reply]

Tom, these uses of the term LCA mean exactly MRCA. None of these use the term to mean the bifurcation point of modern human and some unspecified XYZ species. You seize LCA and define it in your own way. Let me give you an analogy. Let's say I take the term, the Last Emperor of China of the Qing Dynasty, and I define it as "the person who sat on the throne who was founder of the Qing dynasty, marking the end of some unspecified previous dynasty". Do you think it makes sense? I can google for the term and come up with more than 23,000 pages. Does it mean my definition is correct? Think about it.
If you are not happy with the situation, raise an issue following Wikipedia:Dispute resolution. Be prepare to back up your claim, however. Merely goggling for the term does not automatically give you claims to your own definition of the term. It is clearly from our long exchange here that you do not understand the issue at all. Have you actually read the page I included twice on the deletion of the most ancient common ancestor. Please read this page, and write a few sentences indicating your understanding of why this article was deleted. If you can articulate why that article was deleted, then you can truly claim to have understood what I said. That article tried to define the exact same idea you are vouching for. Are you another Sockpuppet of Robert Young? Fred Hsu (talk) 22:42, 25 November 2007 (UTC)[reply]

You say I am self-defining the name. You ask "Where did you read about this definition of LCA that you use to mark your 'seminal' individual?" So I provide several references (including one of your own) naming LCA as the origin of modern humans and then I show papers naming an LCA of primates, an LCA of metazoans, etc. It is a very common way of naming the originator of a species (and all descendants). Why do you keep questioning it? Is it because you still think (very incorrectly) that the LCA of all mankind, ie., the originator of the species, was born a mere 2,000 years ago? And he is the same individual Chang calls the MRCA of all mankind? You have got to get that thought out of your head Fred or you will never be able to move forward. Go back and look at the line chart I drew for you and tell me what you think is wrong with it. Tom Schmal (talk) 04:43, 28 November 2007 (UTC)[reply]

Please find in one published article a chart like the one you drew. You misunderstand these papers. They are not talking about founders of species. They are talking about the very last common ancestor shared by a set of animals!!! The very last common ancestor shared by all humans alive today is calculated to have lived not too long ago, because of persistent genetic mixing between geographical areas.
Did you understand the phylogenetic tree I pointed out to you earlier? Do you know what a phylogenetic tree is? Any any branching point, where a single line diverges into two lines leading to species A and B, you are not talking about LCA of A or LCA of B. The branching point defines the LCA (aka MRCA) of all members of A and B, combined. We are talking about the LCA of A and B. By LCA of humans, we mean, find the branching point leading to n number of lines leading to all living individual where n is the number of people alive today. Sigh. Fred Hsu (talk) 08:12, 28 November 2007 (UTC)[reply]

Hey, despite your continual <sighs>, I just found another reference. You are going to love this one: "MRCA is now more frequently used to describe common ancestors within a species. On the other hand, LCA now describes the common ancestor between two species."

Fred, you yourself typed those words into your Wikipedia article MRCA on Juy 24th. It is exactly what I am saying is correct! Common ancestor between two species is exactly my definition of LCA! Obviously you are not an expert, but when I see you are saying it too - man I have to ask: why are you going on and on with me? What is your point? Tom Schmal 01:40, 1 December 2007 (UTC)[reply]

Sigh. And I am not joking here. That definition is NOT the founder of a species. Let me see if I can get this point through to you, again. What the above quote says is: MRCA and LCA are synonyms; both terms are applied to a SET OF THINGS. You need to explicitly list THESE THINGS, either by specifying two or more species, or specify a group such as "all humans". Now, the way to compute either MRCA and LCA is exactly the same; you simply find the last common ancestor of all these THINGS.
Now, let's examine the two points in your Eiffel Tower chart. There is "MRCA of all living humans at 2K" and "LCA of all living humans at 2M". Do you see where the problem is now? Sigh. The LCA you are trying to pinpoint here is probably MRCA of human and other apes. But the caption should have read "MRCA of human and chimp" or "LCA of human and chimp".
I did not point out all problems with your original article. Let me illustrate a few more. Take this one for instance: "While the new species will owe all its genes to its LCA, the LCA itself will be a member of the original line, not the new one" (emphasis mine). How can all living human owe all its genes to a single person? Do you think your LCA cloned itself? This is simply wrong. Please read on up how inheritance actually works.
Take another one: "‎At its most narrow definition, the LCA is the seminal individual that first coded the mutation that created the characteristic that defined the new species". There is no magical mutation that defines a new species. At the MRCA point, individuals from two future branches can continue to breed. Species are defined in retrospect, after a long time have passed, and two groups of animals continued to be able to interbreed after some form of sepration. Again, please read up on the topic of species. Fred Hsu 12:24, 1 December 2007 (UTC)[reply]
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