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Shadowkiller00 t1_j2ce2ap wrote

We know how fast genetic changes occur. If we look at all mitochondrial dna and count the number of genetic differences between all we have cataloged, we can follow backwards to they would all effectively be the same. Depending on fastest estimates and slowest estimates of genetic drift, it's roughly 150k-170k years ago.

And basically this means that we only know of one female at that point. We can see nobody else beyond her because we have no mitochondria that show genetic differences that come out older than that. Either they all died out, or they were bred out of the population.

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JonesP77 t1_j2f6kq0 wrote

I dont understand. I dont get the connection between differences in our mitochondrial DNA and the time we can follow it back. How do we get to that number? I really seem to miss something because i have no clue what youre saying.

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VoilaVoilaWashington t1_j2fkhph wrote

Say you have an heirloom poem that each member of your family has to transcribe. It's in Latin, so you have no idea what it says.

Even with all the checking, we know that every new generation makes minor mistakes transcribing it, which build up over time. The same poem has somehow spread all over the world because your family is all over.

How do you find out when it was written?

Well, you compare the last few generations' worth of poems and realize it's on average 1.75 mistakes each time it's transcribed. Now you compare your family's to another one elsewhere on earth, and there are 500 differences - how many generations ago did they branch off?

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jamesj t1_j2fc6c2 wrote

Differences in DNA that are neutral with respect to their effect on function accumulate at a roughly constant rate. This is genetic drift. So, by looking at the number of changes between two sets of DNA you can calculate roughly how long they've been drifting apart.

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jayhovian OP t1_j2bas9k wrote

I understand that "she" is our maternal common ancestor. But why do we place her at 150,000 years ago? What about HER mother? Or greatgreatgreat...grand mother?

What is it that makes 150,000 years the cut off for mtDNA and not, say a million years?

mtEve's mother had the same mtDNA did she not?

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Calth1405 t1_j2cdmb4 wrote

Because you are missing part of the definition. Mitochondrial Eve is defined as the most recent maternal common ancestor.

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Pegajace t1_j2cd5zl wrote

The title of "Mitochondrial Eve" is defined as the most recent matrilineal common ancestor of all living humans. If we trace the ancestry of all living humans through their mother's side, all lineages pass through M.E. before they get to any generations further back, and once you're past M.E. all the lineages look identical.

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NakoL1 t1_j2cgxum wrote

the others have given you the answer but I just wanted to point out that your logic is absolutely correct

that's why all the ancestor-related stuff always specifies "most recent". Otherwise you'd have to enumerate all the ancestors of the ancestors every single time

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jayhovian OP t1_j2dylsb wrote

Thats it! Like others pointed out I missed part of the definition.

Thanks for making it clear!

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bullevard t1_j2eiukk wrote

It is also worth noting that mitochondrial eve can change over time. Say this person had 2 daughters and at some point it just so happens that all of those descended from daughter 2 die out. Then daughter 1 now becomes mitochondrial eve, since that is now the most recent common ancestor.

Obviously our math isn't getting us precise enough to detect that single generational change. But recognizing mitochondrial eve is a concept (whoever the current most recent common female ancestor is) rather than a person (that gal named Ugh Ugh who lived in that cave over there) is helpful. It is pointing at an individual at a time, but that individual can change as human populations change and matrilineal lines die out.

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Busterwasmycat t1_j2e2dnc wrote

which makes it so you have to go back to the very first life form (if there was such a thing), if you take it to the logical conclusion. There are some things that all life shares. We are not so much interested in that stuff, because it does not tell us anything we don't already know (that all life appears to have come from a common origin). We are interested in when the things that make us different came into existence, when we "separated" from the other life that is not like us.

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S1rmunchalot t1_j2ckkxr wrote

She was the only female to pass on mitochondrial DNA, not necessarily the only female to exist at the time.

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mouse_8b t1_j2fs6yz wrote

Slight tweak to this, she was the only one whose mtDNA is still around. The other women of her generation would have also been passing on their mtDNA at the time. However, those other lines didn't make it to the present, for whatever reason.

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skrybll t1_j2d83m9 wrote

She is everyone’s great100x grandmother. Everything else after that is everyone else’s great great100x grandmother

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ajovialmolecule t1_j2eheo5 wrote

So, I understand that this is a simplified example, but I’ll ask anyway. Is it know how many daughters mitochondrial Eve would have had? Everyone can trace back to her, which means not everyone can trace back to her daughters — right?

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OlyScott t1_j2ey78p wrote

You only get mitochondria from your mother, never your father. Your biological mother got her mitochondrial DNA from her biological mother, and so on and so on back to Mitochondrial Eve. Yes, everyone's matrilineal line goes back to one of her daughters.

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jayhovian OP t1_j2eyk05 wrote

As i understand it she must have had atleast 2 daughters.

How many she really had cannot be known.

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mouse_8b t1_j2fstp7 wrote

Mostly right. Realistically, her daughters and further lineage were all the same for a few generations until a new mutation occurred.

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whippoorwillhunter t1_j2eqo5x wrote

The most DISTANT common maternal ancestor would be something like an invertebrate.

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jayhovian OP t1_j2er7rv wrote

Or even further back, like when the first mitochondria got gobbled up thru endosymbiosis

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NeighborhoodNorth249 t1_j2d9dex wrote

This is the answer to " the chicken or the egg " question. The 1st "chicken" was a hybrid of two non-chicken species. The sperm cell is made up of DNA of the male and the egg " shell" is made up solely of the DNA of the female. Eve's the first nobe on a new vector.

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FeloranMe t1_j2dyq46 wrote

Mitochondrial Eve is the most recent ancestor who had an unbroken line of daughters to the present day. She also had to have had two daughters. If she had one that woman would be Mitochondrial Eve.

Eve's daughters passed on the mitochondrial line that are present today in every human on Earth. So she was the many times great grandmother of every human on Earth.

She was not a new species. She might not have had any advantageous characteristics. There is likely nothing special about her mitochondria. There were many other human beings living alongside her and long, long before her. What was significant was that her descendants included an unbroken line of daughters.

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tossedmoose t1_j2e0hpl wrote

I cannot comprehend how there is one... I just cannot wrap my head around it to make it make sense. Is it that there were obviously many other women alive at the time and their offspring all mingled with mito-eve's?

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Routine-Prize-1782 t1_j2exwhz wrote

Here’s a thought experiment to help you understand:

Let’s say ten unrelated couples, with different last names, land on an island with no other people. They follow the custom of the family’s name being the father’s name.

Each couple has two children. To make it simpler, we’ll say each child survives, is fertile, etc., no uncles marry nieces, and for the purpose of this example are heterosexual, etc.

Half the new children are males, half are females. So the next generation has the same ratio of ten males and ten females.

Now let’s say the sex of their children are randomly assigned.
Some couples will have one son and one daughter.
Some couples will have two daughters.
Some couples will have two sons.

The men with only daughters have just as many children, but they don’t pass on their last names nor their Y-chromosomes. Likewise the women with only sons will not pass on their mitochondria.

In both cases, the number of offspring is the same, every member of the population has descendants, but this one trait could be lost for each person.

If one family had two daughters, and one had two sons, but all the rest had one of each, then that next generation would have lost one mitochondrial line, leaving 9, and one Y-chromosome, again leaving 9.

You could repeat this, and with random distribution of sons and daughters there would be additional losses in both of these over the generations, even though everyone has the same number of living descendants. Eventually there would just be one. That one is the one that is the mitochondrial Eve. And there is a similar Y-chromosomal Adam.

Of course, this example is flawed by starting with a tiny population which would eventually be forced to marry/mate with cousins or other relatives, which would then complicate the math. In fact, there is a branch of math that deals with the complex nature of populations.

But this gives you the tools to understand the concept of mitochondrial Eve.

(It isn’t true, by the way, that there is a 100% chance that the mitochondria always vary measurably from mothers to daughters, hence the oft-repeated statement that “she had to have had at least two daughters, because if there was one one, then she would be mitochondrial Eve” is not absolutely correct.)

This is called the founder effect.

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OlyScott t1_j2f0tq9 wrote

I don't follow your reasoning to support the idea that her only daughter wouldn't be Mightochondrial Eve. Everyone in the world would be descendants of that one daughter.

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Kailaylia t1_j2faxjw wrote

You're correct. If mitochondrial Eve only had one daughter, she would not be mitochondrial Eve, her daughter wold be.

However science is not talking about an individual whom they have identified. Science is talking about a time in history when the woman from whom we inherited our mitochondria must have lived.

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Kailaylia t1_j2fahw0 wrote

Mitochondria don't combine. They are inherited directly from, and only from, the mother.

Perhaps there was a disaster that wiped out other women, or perhaps other human groups failed to survive to pass their mitochondria on to the present day. For whatever reason, mitochondrial Eve is the original source of the mitochondria all of us share.

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[deleted] t1_j2ex3i9 wrote

[removed]

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Kailaylia t1_j2fbe7i wrote

Some people believe the Earth is flat and contains an advanced civilization hidden deep in its centre, accessible only through a hole in the antarctic. .

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Conundrum1859 t1_j2fc3y7 wrote

Some people believe Phobos is that shape and density because it was mined by aliens. Also others who believe that the Moon is an alien megastructure.

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