Mitochondrial Eve

Jun 8, 2013


Discussion by: missbutton

Could an evolutionary biologist out there settle an argument for me? The other party in this dispute says that Mitochondrial Eve keeps changing because of 'broken lines'.  My position is that everyone alive today has a mother, and everyone's mother has a direct female line back to 'Eve'. As far as I can deduce, 'Eve' is not going to change unless there is another human bottleneck that wipes out most humans and brings about another 'Eve'. Is my opponent confusing Mitochondrial Eve with our Most Recent Common Ancestor (human)? Wikipedia seems to say the same thing as the other party. Am I missing something here? I'm probably not as confused as many people, so please don't be too withering. 

25 comments on “Mitochondrial Eve

  • 1
    mmurray says:

    What don’t you like about the wiki article.

    As ME is the most recent women from which everybody alive today is descended through the female line she can potentially change. I don’t think you need a dramatic extinction event to cause ME to move forward in time a bit. Yes if you want to move her forward to the present day but not if you want to move down a bit to one of her granddaughter say. That might only need a single person alive now to die.

    Michael



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  • 2
    missbutton says:

    I don’t see how a single person dying today could alter who ME is. Everyone has a mother, and every female line goes back to that one woman. Dammit, this is doing my head in. I really want to get it clear.
    In reply to #1 by mmurray:

    What don’t you like about the wiki article.

    As ME is the most recent women from which everybody alive today is descended through the female line she can potentially change. I don’t think you need a dramatic extinction event to cause ME to move forward in time a bit. Yes if you want to move her for…



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  • 3
    Jos Gibbons says:

    Here’s a simple way to look at it. Since everyone is connected to ME by an all-female line, everyone is connected to a daughter of ME by an all-female line, although we can’t all be connected to the same daughter, otherwise that daughter (or a female descendant thereof) would be ME instead. So there are all-female lines connecting everyone to ME, but via 2 or more of her daughters. We can then show that ME can move. To take an extreme example, if one person alive today is so connected to daughter B and everyone else is connected to daughter A, then that modern person’s death immediately makes daughter A the new ME.



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  • 4
    mmurray says:

    In reply to #2 by missbutton:

    I don’t see how a single person dying today could alter who ME is. Everyone has a mother, and every female line goes back to that one woman. Dammit, this is doing my head in. I really want to get it clear.

    Imagine ME has two daughters, A, B and a granddaughter C who is B’s daughter. Imagine all the lines in the world except mine go back through C -> B -> ME and mine goes back through A -> ME. Then I die. Suddenly everybody in the worlds line goes back through C -> B-> ME. So now the most recent female ancestor of everybody is C (or maybe some female descendant of C).

    Michael



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  • ME is the most recent common ancestor in the female line of everyone alive right now. Maybe a very simplified example, where A is Mitochondrial Eve, and other capital letters are her female (and only female) descendants:

    A -> B, C

    B -> E, F, G

    C -> H, I

    E -> J, K

    F -> (none)

    G -> L, M

    H -> (none)

    I -> N

    So now you have J, K, L, M, and N alive today, and A is the most recent common ancestor in the female line. Now N dies without female children. That leaves J, K, L, and M alive. They still all trace back to A, but they all hit B on the way there first. B has taken over as the most recent common ancestor in the female line.

    The current Eve, then, had at least two daughters, who each likewise had daughters, and so on down the line, all the way to the present. It’s possible for a single woman to be the last member of one of those chains. If she dies without having a daughter, the chain will be broken. If that leaves Eve with just the one daughter having an unbroken chain, then Eve is no longer Eve. Maybe her daughter takes up the role. Or, if her daughter only had one daughter, who herself only had one daughter, and so on, then the new Eve would be the old Eve’s great-great-[etc.]-granddaughter.

    It’s important to remember that we’re talking only about an unbroken female line. All it takes to break the chain is for a woman to have only sons.



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  • 6
    missbutton says:

    Are you saying that all women had at least two daughters in the last 200 thousand years? I know several who haven’t.In reply to #5 by Thanny:

    ME is the most recent common ancestor in the female line of everyone alive right now. Maybe a very simplified example, where A is Mitochondrial Eve, and other capital letters are her female (and only female) descendants:

    A -> B, C

    B -> E, F, G

    C -> H, I

    E -> J, K

    F -> (none)

    G -> L, M

    H -> (…



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  • 7
    Jos Gibbons says:

    ME has at least two daughters who each had a daughter who had a daughter… but only the first step requires two daughters. Certainly plenty of women have had no daughters, but they won’t be part of the ME-to-a-modern-person sequence (unless the modern person is a male who has no sister).



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  • 8
    God fearing Atheist says:

    By definition ME must have had at least two daughters, and descendants of at least two daughters must be alive today.

    If “ME” only had one daughter, or if only the descendants of one daughter were alive today, then the daughter would be the real ME.

    Think of a dying tree, where most of the leaves are brown and dead, but some are green and alive. Suppose you trace life back down the branches to the root. At some point all “live” branches will converge at a single “live” branch. That is “ME”. Now suppose one branch (daughter A) above ME only has three living leaves, and those leaves now die. If ME only has two daughters, now all living leaves converge at daughter B who becomes the new ME.

    If there were three daughters, and daughter A’s descendants all die, then ME stays the same. It is only when either all B’s or C’s descendants die that the other inherits the ME title.



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  • 9
    mmurray says:

    Imagine you have a single grandmother, mother and aunt. Assume some cousins alive and some siblings. Then in your family your grandmother is ME. Now assume your cousins die. Then your mother is ME. Assume your siblings die. Then you are ME!

    Michael



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  • How would you be able to tell that something like this did not happen. Protohumans are evolving away. A group gets isolated on Madagascar. They continue evolving in a convergent evolutionary way toward modern humans. They get back together, and eventually interbreed.

    Could you tell just from DNA that happened? In other words, we have two Eves. Or would you need the fossil evidence too? or is such a scenario for some reason impossible?



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  • 11
    Pabmusic says:

    In reply to #10 by Roedy:

    How would you be able to tell that something like this did not happen. Protohumans are evolving away. A group gets isolated on Madagascar. They continue evolving in a convergent evolutionary way toward modern humans. They get back together, and eventually interbreed.

    Could you tell just from DNA…

    The problem with your scenario (if I’ve understood it correctly) is that the Madagascan group gets back together (with the rest of humanity, I presume) and starts interbreeding. If that did happen, the Madagascan group did not become a new species and therefore none of them would take over as ME. ME would still have been very distant and common to all humans (actually, we’re not really talking about humans here).

    If the Madagascan group did continue to evolve separately, they would eventually lose the desire and ability to interbreed with humans and would eventually become a new species.



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  • 12
    Cairsley says:

    Hello, Miss Button!

    I wonder whether you are understanding ‘Eve’ in a different sense from the sense in which others here are using the name. As M. Murray succinctly put it: “ME is the most recent woman from which everybody alive today is descended through the female line.” You, however, may be understanding ‘Eve’ in the time-honored (and very biblical) sense of ‘first woman’. I trust you can see the difference.



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  • 13
    steve_hopker says:

    What about, dare I ask, the status of Mr Eve, so to speak, ie MEs other half. Of course, she could have had children by several men either serially or simultaneously. But I’d there was just one “Mr Eve’, he would surely also be the most recent common ancestor?

    On the first woman question, well that is as I suspect all or most here would agree, is a mythic idea from Genesis of species creation out of the blue, so to speak. There is no first example of a species, so far as I know.

    However, I am vague on how species do arise. I presume they emerge, so to speak, within a population. So while ME debunks the multi origin theory, the existence of a, or several, ‘Mr Eve(s)” must mean the human species arose from a group.



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  • 14
    God fearing Atheist says:

    In reply to #13 by steve_hopker:

    , ie MEs other half. Of course, she could have had children by several men either serially or simultaneously. But I’d there was just one “Mr Eve’, he would surely also be the most recent common ancestor?

    Not necessarily. Suppose all but one male of a species died, and then that one male mated with many females. The last common male ancestor could be much more recent than ME. It is unlikely, but males do tend to have either many children or none. The male equivalent of ME is Y Chromosome Adam. Genghis Khan made a pretty good attempt at the title.

    Secondly, there are a whole set of individuals who are the MRCA of the current individuals in a species. Consider an absurdly mathematical species of 4 males and 4 females. They pair up, and have 2 kids. The 8 kids of the next generation pair up without incest, and each pair has 2 kids. The grandkids pair up (without cousin incest) and each have 2 kids. The 8 kids of that generation have 8 greatgrandparents who are the original 8. Therefore the original 8 are all the MRCA of the current generation.

    Species do arise from populations. Consider a population as a cloth woven through time. Each individual is a thread, who can fuse with another thread (mate), and produce new threads (children). There is a tendency to mate with threads nearby. Assume we start with a 1,000 threads and start weaving, over tens of generations even the descendent threads of the left most thread could drift right meet and mate with a descendent of the threads on the right. That pattern would be repeated down the generations so the species as a whole would weave a tight cloth of interrelatedness down the generations. That cloth is a branch on the tree of life. Now suppose a geological event happens like a huge river cutting through the middle of the species’ territory that makes it impossible for those in the West (the left of the cloth), to mate with those in the East (right of the cloth). Over the generations a fault appears in the weave of the cloth where there are no more cross-links. If, after a hundred thousand generations the river disappears and the two populations meet but don’t or can’t mate then they are two species. One great woven branch of the tree of life has split into two great woven branches.

    The above is implied by straight forward logic. I don’t know where a biologist would say the speciation event occurred. The start of the tear is a well defined point, but for generations the two branches would be able to interbreed if they had the opportunity, they just don’t. The point they are no longer able to breed is a hypothetical point that never gets tested.

    Another interesting point is that the individuals who are the MCRA of both species may have lived many generations before the start of the fault.

    When a palaeontologist finds a fossil that appears to be an intermediate there is no way to tell of the individual lived a few (hundred) thousand generations before or after the tear.



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  • 15
    missbutton says:

    I’m not that stupid. In reply to #12 by Cairsley:

    Hello, Miss Button!

    I wonder whether you are understanding ‘Eve’ in a different sense from the sense in which others here are using the name. As M. Murray succinctly put it: “ME is the most recent woman from which everybody alive today is descended through the female line.” You, however, may be und…



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  • 16
    Alan4discussion says:

    Just for the record!

    http://en.wikipedia.org/wiki/Y-chromosomal-Adam

    In human genetics, Y-chromosomal Adam (Y-MRCA) is the name given to the most recent common ancestor (MRCA) from whom all currently living people are descended patrilineally (tracing back only along the paternal or male lines of their family tree). However, the title is not permanently fixed on a single individual (see “Variable Adam”).

    Y-chromosomal Adam is named after the biblical Adam, but the bearer of the chromosome was not the only human male alive during his time.[1] Some of his male contemporaries have descendants alive today.

    A paper published in March 2013 determined that, with 95% confidence and that provided there are no systematic errors in the study’s data, Y-chromosomal Adam lived between 237,000 and 581,000 years ago.[2] Earlier studies have estimated the date for Y-MRCA as between 60,000[3] and 142,000 years ago.[4]

    Analogous to Y-chromosomal Adam, Mitochondrial Eve is the woman from whom all living humans are descended matrilineally. The inherited DNA in the female case is her mtDNA, rather than his nuclear Y chromosome. There is no reason to suggest that Y-chromosomal Adam and Mitochondrial Eve should have lived at the same time[5] and Mitochondrial Eve is estimated to have lived approximately 200,000 years ago.



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  • 17
    Pabmusic says:

    In reply to #13 by steve_hopker:

    However, I am vague on how species do arise. I presume they emerge, so to speak, within a population. So while ME debunks the multi origin theory, the existence of a, or several, ‘Mr Eve(s)” must mean the human species arose from a group.

    It’s difficult to know what you mean by ‘within a group’. Different species arise when part of a group (a ‘species’) becomes separated from the rest so that interbreeding with the original group cannot occur. The two groups continue to adapt to their different environments until they have grown sufficiently far apart for them no longer to be able to mate with each other (if they met again). At that point they are regarded as being of different species. Humans arise from a small group of ‘common ancestors’ (the Great Rift Valley is the likely culprit) but for many thousands of years were simply a group of ‘common ancestors’ who did not live in the forest. It was not until many milennia had passed that they were sufficiently different that the two groups could no longer interbreed. The main group continued to evolve and became chimpanzees and banobos, the other group were widely dispersed and gave rise to perhaps seven different species of homonid, only one of which did not go extinct – us.



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  • 18
    missbutton says:

    Thanks for the great explanations. It’s a lot clearer now, but I still think my opponent has it wrong too. Here’s what he says:

    “Mitochondrial Eve is a person who continues to change, as the mitochondrial lines die out, which they do very rapidly. The mitochondrial DNA can only be passed by a mother to her children. A mother who has a son, has her mitochondrial DNA line die out with him. A mother who has two daughters, who then produce only sons, has her line die out as well. At every generation, a daughter must produce a daughter of her own for the line to continue.”



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  • 19
    SaganTheCat says:

    As far as I can deduce, ‘Eve’ is not going to change unless there is another human bottleneck that wipes out most humans and brings about another ‘Eve’.

    no that’s not right, another bottlneck will not change the human ME. Eve was not a modern human, I think she lived about 3M years ago and her descendants most likely included neanderthals and “hobbits” and all apes of the homo sub-species. for ME to change through an extinction event, you’d be looking at all humans alive now dying out and another class of apes taking over the role of humans. they would have a different ME, but they would also share an ancestor with modern humans, albeit one that goes back much further, to before the shared ancestor of chimps and humans (most likely) so at least 7MY in my reckoning.

    your friend may be confused over the term “Eve”. I read the 7 daughters of eve some time ago, which gave an estimate of a particular “Eve” (can’t remember now but i’m guessing somewhere between 50-100 thousand years). However, this was the ancestor of european humans, as each of the 7 women identified (varying from 10,000-50,000 years ago) was located in europe and the middle east, dispite many humans remaining in africa.

    not sure what they mean by broken lines though. if a line is broken, that’s it. no one has a broken line in their ancestry



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  • 20
    mmurray says:

    In reply to #19 by SaganTheCat:

    As far as I can deduce, ‘Eve’ is not going to change unless there is another human bottleneck that wipes out most humans and brings about another ‘Eve’.

    no that’s not right, another bottlneck will not change the human ME. Eve was not a modern human, I think she lived about 3M years ago and her desc…

    That’s not right. ME can change. She is the most recent ancestor of all living humans through the female line. Change the living humans and you can change ME. At least theoretically.

    Michael



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  • 21
    mmurray says:

    In reply to #18 by missbutton:

    Thanks for the great explanations. It’s a lot clearer now, but I still think my opponent has it wrong too. Here’s what he says:

    “Mitochondrial Eve is a person who continues to change, as the mitochondrial lines die out, which they do very rapidly. The mitochondrial DNA can only be passed by a moth…

    Sounds like your opponent is trying to argue that ME does actually change rather than could theoretically change. That’s a more tricky question. I would have thought with billions of people currently alive the probability of change has got to be low but that’s just a feeling it’s not an area I have any expertise in. It would be interesting to know what is known.

    Michael



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  • 22
    God fearing Atheist says:

    In reply to #18 by missbutton:

    Thanks for the great explanations. It’s a lot clearer now, but I still think my opponent has it wrong too. Here’s what he says:

    “Mitochondrial Eve is a person who continues to change, as the mitochondrial lines die out, which they do very rapidly. The mitochondrial DNA can only be passed by a moth…

    What science will settle your dispute?

    Mitochondrial Eve exists, and therefore there is a single branching tree of mDNA. If mDNA is randomly sampled from a million+ people the mutations can be mapped, and the mutation tree of mDNA reconstructed. The number of living humans in each branch of the mDNA tree can also be estimated. Starting at the present, history can be traced back down the tree, and the number of living descendants at every mutation point calculated. Find the branch just above ME. If the count is 7 billion to 1 million, then if the 1 million die, ME moves. But ME moves to a mutation point, which might be several human generations, so the probability of ME moving should be calculated from the probability of the 1 million descendants dying, factored by the probability they descendants of each of the possible MEs up to the mutation point.

    You may have to wait a long time before someone does the analysis and writes a paper on that. Make a bet with your friend, keep your eye on the literature, and wait.

    The alternative is a computer simulation. But that requires an accurate model of a distribution of breeding daughters since ME.



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  • 23
    SaganTheCat says:

    In reply to #20 by mmurray:

    In reply to #19 by SaganTheCat:

    That’s not right. ME can change. She is the most recent ancestor of all living humans through the female line. Change the living humans and you can change ME. At least theoretically.

    Michael

    Thanks. seeing your other response I understand. ME could become a more recent ancestor, in theory. although i suspect it’s statistically unlikely



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  • 24
    SirCrispin says:

    It’s also worth remembering that Mitochondrial Eve is almost certainly not our MRCA. She is only the MRCA through the all female line. The true MRCA probably lived much later and we are all decended from this individual through mixed male/female lines



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  • 25
    Pabmusic says:

    In reply to #25 by SirCrispin:

    It’s also worth remembering that Mitochondrial Eve is almost certainly not our MRCA. She is only the MRCA through the all female line. The true MRCA probably lived much later and we are all decended from this individual through mixed male/female lines

    Yes. This blog contains some interesting thoughts on this:

    http://freethoughtblogs.com/singham/2006/10/02/realistic-calculation-of-the-date-of-our-most-recent-common-ancestor/



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