Why do we all descend from one common Male and one common Female?

Discussion in 'Biology & Genetics' started by Unconcept, May 23, 2012.

  1. Unconcept Registered Senior Member

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    Within our species, we all descended from Y-chromosomal Adam and Mitochondrial Eve. I understand evolution as a variation of a population, from this I'd think we all should have descended from several ancestors of our species, but how come we only descended from two? Why did only these 2 survive?
    Are there other species with only one male and one female common ancestors too?
     
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  3. GeoffP Caput gerat lupinum Valued Senior Member

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    Well only those chromosomes survived. It might be that they don't mix well with other hominid chromosomes via haploid interactions or mtDNA-nuclear incompatibility, forcing the eventual survival of a single lineage on either side. I expect the nuclear contribution is generally more diverse, though, since the nuclear genome permits freer segregation and recombination. Both Y and mtDNA don't have recombination, the latter being complete and the former nearly so.
     
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  5. arauca Banned Banned

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    Interesting question >
    I suppose there is also that we are so drowned in a particular theory and we don't want to accept any other , even if it would be sugested.
     
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  7. GeoffP Caput gerat lupinum Valued Senior Member

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    So back your alternate.
     
  8. Aqueous Id flat Earth skeptic Valued Senior Member

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    For centuries some people were so drowned in a particular religious theory that when science came along, they simply didn't want to accept it.
     
  9. spidergoat Venued Serial Memberlist Valued Senior Member

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    Don't misunderstand, mitochondrial Eve was not a literal common ancestor. She had contemporaries that also had offspring. Also she was not the mate of Y-c Adam who could have lived thousands of years later.

    http://www.talkorigins.org/faqs/homs/mitoeve.html
     
  10. KilljoyKlown Whatever Valued Senior Member

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    I believe the current theory is that our ancestors were almost wiped out about 100,000 years ago due to some major disaster event and that the total human gene pool was reduced to as little as 2 or 3000 humans left to repopulate our species. That's far different than repopulating from just two. I've heard that just two is not enough gene diversity to be viable and our species would have died off. Adam & Eve scenario just doesn't make it.
     
  11. GeoffP Caput gerat lupinum Valued Senior Member

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    Quite. A simple drift to fixation followed by short term near-extinction.
     
  12. wellwisher Banned Banned

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    Not too long ago, it was taboo for different races to interbreed even though both had the same DNA and could breed. This resteaint was not because of genetic limitations but because of limitations created within the mind/brain due to bias.

    One way to come from one male and one female would be if there was something in two people and their descendants, analgous to separation of races. They could breed with others due to common human DNA, but will not.

    What then would need to happen is the separated race, from one male and one female, could be more advanced and might exterminate other pre-humans so all have a common mother-father, with human DNA.

    In modern times, the opposite can also form via the mind, where some humans will attempt to breed in situations where the DNA is not cooperative; animals and blowup dolls. That is not the DNA talking, but of the mind.
     
  13. iceaura Valued Senior Member

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    The point is not that we all descended from two people, but that interbreeding over the generations - and bottleneck events that weeded the outliers - have at some point in the generations mixed those two genetic lines into everybody's.

    It's not something that needs a "cause" - given enough generations and enough interbreeding, it's a likelihood approaching certainty on probability grounds alone. The question would be not whether, but when and where, the common genetic ancestor lived.

    There has never been any such time, for the human species overall.

    All assertions that confuse human genetics with sociological races are hopelessly screwed up anyway.
     
  14. Unconcept Registered Senior Member

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    I understand that they haven't lived together, I didn't bother to clarify it.

    The article you linked to was very useful, but this seems odd to me
    "she was by no means the only living woman on Earth during her lifetime. Many other women lived with her, but they either did not leave descendents or did not leave descendents via the matrilineal line, who are still alive today."
    and the analogy "Only this one woman and her daughters who were off in this Carribean island are safe from the viral plague..."
    It seems odd to me that only one woman left descendants via the matrilineal line, I need an explanation! And did this happen in other species too?
     
  15. Aqueous Id flat Earth skeptic Valued Senior Member

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    Maybe it will help to distinguish between the genealogical and evolutionary differences in the term common ancestor.

    http://tedlab.mit.edu/~dr/Papers/Rohde-MRCA-two.pdf

    It's lengthy and detailed but maybe the first few pages will suffice. Spidergoat's cite was more concise.

    As for evolution by common descent, the "common ancestor" takes on an entirely different meaning.

    Suppose we declare that humans popped into existence upon the birth of the first mutant apelike ancestor in which apelike ancestral chomosomes 2a and 2b fused into the human chromosome 2.

    http://en.wikipedia.org/wiki/Chromosome_2_(human)

    I suppose we would only need to figure out what happened after the birth of that individual. The first assumption is that is was one of a kind, relegated to mating with an individual of the 2a/2b apelike-ancestor genotype.
     
    Last edited: May 24, 2012
  16. Aqueous Id flat Earth skeptic Valued Senior Member

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    One interpretation is that this was a near-extinction episode. It may have taken many generations to wipe out the other families. Some severe stress would probably be the cause.

    http://en.wikipedia.org/wiki/Toba_catastrophe_theory


    There probably is no way to know since genealogical studies require the use of a #2 pencil.

    Please Register or Log in to view the hidden image!

     
  17. Asguard Kiss my dark side Valued Senior Member

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    err no, from what i remember the bottle neck out of africa (and it ONLY relates to non african humans) was 10 women not 1 and also it doesnt dispute the possiblity of more who only happened to have male offspring. mitochondrial DNA is ONLY pased from mother to who children which means if she has only sons then this marker will disapear. The same is true of the Y chromosone, it is only passed male to male so when a male has a daughter only the Y disapears
     
  18. Neverfly Banned Banned

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    Misconception:
    M.E. points to a Lone Ancestor.

    Concept:
    M.E. points to the most recent Common Ancenstor

    Maybe this graph will help:

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  19. Asguard Kiss my dark side Valued Senior Member

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    Never fly there is one mestake in your piture. At the very end you only have the MDNA going to the daughter, thats wrong. It goes to the sons as well it just doesnt get passed ON from them. Ie you can trace a mans female linage as well, you just cant trace his fathers mothers linage
     
  20. Neverfly Banned Banned

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    The picture shows the tracing back in the pink ( I didn't make it) bands and the passing on with the yellow arrows.
    So, yes, the mitochondria is passed on to both, but you can only trace it back through the direct mothers side.

    Technically, not a mistake but a poor graph- or at least poor wording on its caption.
    Thanks for bringing it up- always is good to question everything.
     
  21. iceaura Valued Senior Member

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    Humans gone through many thousands of generations of stable or decreasing population growth, including at least one serious bottleneck event.

    In these generations, each woman left on average one reproductive female child - 25% 2, 25% 0. In the solitary female child one of her two grandmothers contributes no mitochondrial DNA - she got one of the X strands and the egg mitochondria from a maternal grandmother, one of the X only from a paternal grandmother.

    So tracing any given maternal lineage, we see in each independent - unduplicated - generation a 25% chance of losing a given maternal ancestor from that line.

    But as some disappear, duplicates of others - women with two daughters - fill in. Now the odds are different - extinction is not as likely with a larger population.

    And so it goes, with early advantage likely to be reinforced and amplified. In the end, those choosing mates are most likely to choose from one of the duplicated mitochondrial lines (there are many more individuals in them), and if duplicated themselves are now certain to redouble the duplications.

    After a while of this there are likely to be only one or two truly numerous lines,

    and then come the bottleneck events, or the migration, or the geological isolation vents, or a disease, or the like.
     
  22. Asguard Kiss my dark side Valued Senior Member

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    The same is shown in surnames. For instance my partners surname is about to disapear compleatly because ALL of her relitives (who have that surname) have daughters. So when we have kids they will have my surname and not hers and so forth for all of them
     
  23. Hercules Rockefeller Beatings will continue until morale improves. Moderator

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    Mod note: Posts that unnecessarily bring religion into this thread, where it is neither required nor wanted, have been and will be deleted.
     
    Last edited: May 25, 2012

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