Talk:Most recent common ancestor

From Wikipedia, the free encyclopedia

from VfD:

Keep. Nunh-huh's fix makes the page work for me. I am replacing the VfD with a "stub" to save everybody's time. If you think otherwise, then please replace the VfD notice on the Most recent common ancestor page and post your objections above. Thanks. ---Rednblu 20:22, 2 Oct 2004 (UTC)

Nonsense page currently. Possibly a valid topic combining general principles from both Mitochondrial Eve and Y-chromosomal Adam. New page by a new citizen, but this page may be part of a prank--see questions on bottom of Talk:Mitochondrial Eve. ---Rednblu 19:15, 2 Oct 2004 (UTC)

• keep. This is a well known topic in genetics, and it's distinct from "Mitochondrial Eve" and "Y-chromosomal Adam": the MRCA of present-day humanity is considerably more recent than either "Eve" or "Adam" - Nunh-huh 19:22, 2 Oct 2004 (UTC)

• Keep. I don't see why the current page is nonsense. It's a bit stubby. See also Genealogy (section The "Maximum Relationship"), which contains material that can put here (after it is corrected). Eugene van der Pijll 19:22, 2 Oct 2004 (UTC)

• Keep. Valid topic, well-written. RickK 19:40, Oct 2, 2004 (UTC)

• Keep. Notable concept, good article. — Gwalla | Talk 21:34, 2 Oct 2004 (UTC)

• Keep Looks like a good topic and article to me... --Asmodai 15:47, Oct 3, 2004 (UTC)

end moved discussion

Contents 1 Two meanings? 2 Time estimates 3 MRCA of different species 4 Descendents of Edward IV and Henry VII 5 Double meaning 6 Generations

[edit] Two meanings?

I believe that the MRCA is purely a mathematical model which accounts for mutation rates, migration, etc, but has nothing whatever to do with individuals taking genealogical DNA tests. If I'm correct then the second paragraph of this article should be revised.

One alternative might be the insertion of a new paragraph to distinguish between meanings. Here's a stab at it:

The term is used in two ways. In ordinary usage the most recent common ancestor refers to:

• An individual identified as the most recent ancestor of two persons -- by DNA testing of two males or two females, or by traditional genealogy.

In scholarly usage, however, it has another meaning:.

• An individual who lived at a time which has been estimated by a mathematical model accounting for the rate of mutation (and sometimes also the rates of migration, inbreeding, etc.) and who is the most recent ancestor of all males, all females, or all living persons.

Any comments, objections, etc.? AnonUser 14:49, 14 October 2005 (UTC)

The article, by focusing on the phrase "the MRCA of X", is better as is. You seem to be confusing "the MRCA of X" with "an estimate of when the MRCA of X lived". What does need emphasizing is that the MRCA of humans alive today may not have been the same individual as the MRCA of humans alive when (say) The Descent of Man and Selection in Relation to Sex was first published. Also some clarification about things like whether both parents of two siblings are regarded as the MRCA, or whether it is the younger of the two.Peak 16:38, 14 October 2005 (UTC)

I agree with the focus as is. The article is confusing, however, because it uses multiple definitions of MRCA. I propose that the article clearly distinguish among them up front. AnonUser 19:24, 14 October 2005 (UTC)

The article gives a definition in the very first sentence, and uses it consistently. I don't see a second definition, either explicitly or implicitly. Which sentence do you think is the source of confusion? Peak 22:08, 14 October 2005 (UTC)

Ah so -- you are correct. Perhaps its confusing because the examples are so dissimilar, without language tieing them together. If its confusing to me, its probably confusing to other readers too. Maybe a little tweaking would help. AnonUser 02:57, 15 October 2005 (UTC)

[edit] Time estimates

This section is based on a single study amongst a fairly large field of research, and the results of said study are patently false. Until someone can rewrite it with actual 'time estimates' that correspond to a older MRCA than 1000AD (which is obvious), I just going to comment it out. I hope this is not too presumptuous, but this section as it stands is only presenting known misinformation. Jodine Sparks 16:45, 29 January 2007 (UTC)

To: EamonnPKeane. Kindly state all your assumptions, including:

• the number of years between generations;
• the percentage of couples who were childless;
• the percentage of children who died before puberty; and
• the percentage of relatives (however distant) who married each other. AnonUser 03:47, 29 November 2005 (UTC)

The "historical times" estimate is patently ridiculous, imho; it seems they used some sort of diffusion to model human migration. The statement

The actual MRCA is farther back if one attempts to take into account long-isolated peoples, such as historical tribes in central Africa, Australia and remote islands in the South Pacific.

betrays the preceding estimate: We defined the MRCA as that of all humans alive today, so what do you mean "if one attempts to take into account tribes in Central Africa"? Unless you want to argue they are not human, you'll have no choice but to take them into account. I can easily believe the MRCA of Europeans (or even continental Eurasians) lived in the Common Era. It is inconceivable that the MRCA of all humans lived after 3000 BC: A single isolated tribe (Pygmies, Aboriginals, Indonesian bushmen, take your pick) pushes the MRCA back to the Paleolithic. I can easily imagine, even, that the MRCA of 99% of humans alive today lived in historical times, but it takes just a single surviving individual from an isolated lineage to render that calculation obsolete. dab (ᛏ) 09:56, 3 January 2006 (UTC)

I think that the suggestion of a human MRCA having lived from between 3000BC to 1000AD(!) is absolutely ridiculous. What kind of pseudo-science must this be? Think about it, if it were true, there would for example be no single 100% pure-blooded Native American alive today (since the Native Americans had reached and spread throughout the American continents well before 3000BC, a possible exception to this being the Eskimos) which, be they few, I think there are.

I agree that this is ludicrous. Are we talking about all humans or aren't we? Ancestors of Aborigines are believed to have arrived in Australia between 40k and 50k years ago: http://en.wikipedia.org/wiki/Indigenous_Australians I have a hard time believing that I, a white man, have a common ancestor with a black aborigine as recently as 4000 years ago. Who wrote this crap? Additionally, that time estimate 3000BC to 1000AD suspiciously encompasses when the Christian or Hebrew "creation" would have taken place. Zmbe 06:02, 11 March 2006 (UTC)

Now it does not: see Jewish calendar#Epoch or Ussher-Lightfoot Calendar#Ussher.27s history of the Earth, both of which suggest a date earlier than 3000 BC. --Henrygb 19:46, 11 March 2006 (UTC)

bad math on my part- however, i see from the ussher-lightfoot calendar that the time estimate DOES encompass the time of the 'great flood,' which may deserve suspicion. Zmbe 07:18, 12 March 2006 (UTC)

The whole concept of a purely mathematical MRCA is both unscientific and useless. It assumes the nonsensical notion that one's ancestors double with each generation backward, so that, for example, 20 generations ago I had a million (2^20) ancestors, or almost that many. But the human genome contains no more than 25,000 genes! In other words, no matter how many generations back I go, I cannot have any more than 25,000 genuine ancestors--i.e., ancestors who have actually contributed to my genome. All the other thousands or millions are ancestors on paper only, and have no scientific or practical significance.

Let's now even consider those 25,000 distant ancestors. Each contributed as little as a single gene to my genome. Big deal! Such an ancestor still has no practical significance to those living today, unless perchance that ancestor contributed a crucial improvement to humanity that we now all share. But I know of no such great improvement in the human genome within the last 70,000 years.

The bottom line here is that, beyond 20 generations, the ONLY ancestors that are of practical significance to humans living today are the two ancestors who contributed a SIGNIFICANT quantity of genetic material: the Y-chromosome ancestor and the mitochondrial DNA ancestor. Thus, it is for good reason that those interested in distant genealogy (beyond 20 generations) focus on the strict patrilineal and matrilineal lines.

i don't think the idea is that every person has one gene per ancestor. you might want to check your source on that one. anyway, please add your id and timestamp to all entries- it's easy to do by typing four tilda's ~ in a row after your entry.Zmbe 06:31, 3 August 2006 (UTC)

Well, arguably you don't know that your inherited Y-chromosome DNA (if you're male) and your mitochondrial DNA exceed the contribution of other genes. Other genes are subject to recombination, sure, but since the ancestral populations were incredibly small in some cases, most of our recombining DNA could be from a very small group of people. --Saforrest 06:25, 29 November 2006 (UTC)

[edit] MRCA of different species

I've added a section on MRCA of different species, and referenced Richard Dawkins' book, The Ancestor's Tale. I recommend it, especially to those who have contributed to the discussion above. He places a lower-bound of 13,000 years on the age of the MRCA of all humanity (with a rather sad proviso – see later). This is because it is known that the native population of Tasmania was physically separated from the rest of the world 13,000 years ago, and therefore we could not share a later ancestor with them. The only problem is that the Europeans who colonised Tasmania treated them as vermin and exterminated the whole lot by 1876. Also, FWIW, Dawkins reckons on an upper limit of 100,000 years as the age of the MRCA of all of us. --Portnadler 17:23, 8 May 2006 (UTC)

As I recall from the book, the point was that they exterminated all the "pure-blooded" ones. Presumably there are a few descendants still alive (as there are of the Beothuks, a similar sad story), but of course people of such recent mixed heritage would not preserve the 13,000-year genetic separation necessary to retain the MRCA figure. --Saforrest 06:03, 29 November 2006 (UTC)

[edit] Descendents of Edward IV and Henry VII

What sort of social rank would one have to bear in their family, in order to be a descendent of either?

How far up the totem pole, would you say?

This is intended to have broad answers and based on gradients of time and population, not going into specifics about exact descendents. About how common is their descent in the English or British genepool today?

I've noticed that American Presidents don't descend from either king, but the most common recent royal ancestor shared by many of us is Edward III. How common is it for anybody in the English or British genepool, to have a Protestant royal ancestor?

There is a general cutoff, isn't there?

Is it because of fratricide in the Wars of the Roses, the Tudors' "new men", or the Union of the Crowns, or the parliamentary union under Queen Anne (I can't think of any non-royal family descent from the Hanoverians within the UK)?

I'm thinking that there is a big difference between Plantagenet and Tudor descents, that the commons in all likelihood have the former and the latter is held by the lords. (just generally speaking) Then again, Tudor descent in the Welsh must be higher in general. I am further curious about pre-Royal Tudor blood in Anglo-British people today, since the status and/or concept of Welsh royalty/nobility is rather hazy in my mind. I found the Blevins aka Ap Bleddyn family of Powys in my ancestry, but have no real idea on what to make of it--or any other Welsh "native aristocracy". I might be able to find Stewart descent somewhere, from way back when. What percentage of Hanoverian background do you think that German colonists had in America?

On the British side, I have to go as far back as Welf himself...but any recent genetic relationship with the Hanoverians or the counts of Nassau are completely obscure. How does one research those other colonial people, such as the Hessians?

UK genealogy is relatively easy when focusing on English (and French) ancestries. What would a "national person" of Jerusalem (or Antioch, for example) in Crusader times be known as?

We say "American" for those Founders, but was there such a nationality-term for the Crusaders in their own domains?

I guess the term is supposed to be Levantine/Outremer, or "Crusader" as our national heritage says "Colonist"...

IP Address 11:48, 9 May 2006 (UTC)

I have a question:

After reading the article I was happy to see how closely related we are. I would really appreciate it if someone has more detailed information on population. I just can't get past the fact that the article seems to focus on 6.5 billion people. Our ancestors came and went throughout history. From the point of our MRCA's existance to present more than 6.5 billion people have lived. The town where I lived has an approximate population of 100,000 but from the day the founder came and died to present I can't even fathom how many people have lived here. Can someone help me find the numbers I need to understand?

Approximate total of humans since time of our MRCA:???

83.219.199.121 00:38, 23 July 2006 (UTC)Leif

If anyone doesnt have a significant other because they have come to terms with the fact that we are all related let me put this into your heads. I am almost positive that somewhere out there in the universe that there is another species that are exactly like us, humonoid, but do not come from a genetic line that comes from this planet. It is an infinite universe. The distance between them (a mating partner not of our gentic line) and us is trillions of light years away.--RCJACOBS100 23:55, 16 September 2006 (UTC)Robert Curley Jacobs

If I understand you correctly, you're saying it's okay to breed with "relatives" because there must exist copies of them on this faraway planet to whom you are unrelated. First off, no, it's not at all clear that it's an infinite universe. Second, even if such a doppleganger species did exist, what does that matter, since we are probably millions of years apart? Anybody you could conceivably want to breed with is still related to you.

Lastly, if one uses this "infinite universe" argument in the manner you've described, one could just as easily argue that there must exist a person who's identical to your mother or father. Therefore, incest is justified since an "unrelated copy" exists.

Sorry if that came across as excessively harsh. It's an interesting thought experiment. --Saforrest 06:00, 29 November 2006 (UTC)

[edit] Double meaning

"This simple calculation does not take into account the fact that every marriage is really a marriage between distant cousins which include second cousins, fourth cousins, sixteenth cousins and so on. The ancestry tree is not really a tree, but a graph. One can place all living people at the bottom of the graph and ancestors above their descendants. As each generation of ancestor is added at the top of the graph, there will eventually be an MRCA from whom it is possible to trace a path of direct descendants all the way down to every living person at the bottom of the graph."

I thought this was meant to describe a graph? It clearly descibes a tree to me: "...there will eventually be an MRCA from whom it is possible to trace a path of direct descendants all the way down to every living person at the bottom..." - THAT is a tree. (by 90.242.58.236 on 06:44, February 19, 2007)

I modified this paragraph to make it more clear. The MRCA was only one of many top-level, contemporary ancestors. The MRCA is not the only 'node' at the top of a 'tree'. The MRCA is one of many top-level 'nodes' of a 'graph'. Notice that the subsequent paragraph makes this even more clear; it describes how contemporaries of the MRCA also pass down their genes onto descendents. Fred Hsu 16:09, 19 February 2007 (UTC)

[edit] Generations

User:Robin S added the following which I just removed:

Indeed, within twenty generations, most descendants of an individual will not have inherited any of their genes from a given ancestor since there will be far more ancestors than genes. Since considerably more than twenty generations have passed since the hypothesized date of the human MRCA, it is possible that not a single human gene present today was inherited from that individual.

It is not immediately clear that in 20 generations the number of ancestors will be greater than number of genes. Please see the other paragraphs in the same session where 'tree' vs. 'graph' was discussed. Note that many ancestors are shared. Also see the chapter 'All Africa and her progenies' in River out of Eden. But perhaps you are right. We just need to find a reference which shows this to be true, taking into account the graph nature of human ancestry. Fred Hsu 17:48, 21 March 2007 (UTC)

I had a feeling someone would bring that up. It is true that exponential growth fails as a model if taken indefinitely since, as mentioned, over 80 generations one would expect over a trillion trillion ancestors. However, expecting the number of ancestors over 20 generations to be of a significantly lower order of magnitude than the 27 000 (<2¹⁵) or so genes in the human genome seems to me to be unreasonable. For a start, wouldn't inbreeding pose a significant problem? Robin S 18:33, 21 March 2007 (UTC)