Help understanding Mitochondrial Eve

[Kaldanis]

Earlier, I brought up in a discussion with a friend the concept of Mitochondrial Eve. I tried to explain it based on my limited knowledge which was basically as follows: All mitochondria are passed down from mother to their offspring, if you keep tracing back the mother of every person alive then eventually they will converge on one common source. My friends reaction to this was pretty violent, saying people are idiots if they believe this and it's not possible (that's the nice way of putting what she said). She had a hard time believing that 1 woman could have a daughter and that daughter would have a daughter, and always end up having a daughter for thousands of years to modern times. I also have some questions so I was hoping someone could clear it up.

1. Is this absolutely 100% fact? Is there evidence?
2. Does that mean all women alive today have exactly the same mitochondria, and if they do, then how do we know that they came from one person? (if it's always all the same throughout history then how can we say it came from 1 person?)
3. If I have it wrong can you try and explain it to me?

Thanks!

 

[Ygggdrasil]

Well, think of the converse situation. Everyone has a mother. Everyone's mother has a mother. Everyone's grandmother has a mother, etc. Therefore, everyone can trace back their lineage to a woman whose lineage kept having daughters for however long you trace back to until modern times. Unless someone was somehow born without a mother, such an individual must exist.

 

[phinds]

Ygggdrasil has it spot on; I would just add that your friend's confusion likely stems from the correct assumption that not all women have female babies COMBINED with her not having realized what Ygggdrasil point out which is "yes, but all children have mothers, so there IS a female lineage for everyone.

 

[Kaldanis]

Thank you, I keep thinking "but what if..." then I think about it more and it makes sense that everyone had to have come from the same mother if you go back far enough. But surely that means that the mitochondria in all living women are all basically the same?

 

[Ygggdrasil]

Not exactly. While all the mitochondria descend from the same mitochondrial eve, mitochondrial DNA can undergo mutations which will create differences between different lineages. In fact, tracking the different mutations in mitochondrial DNA is a useful tool for studying the human population genetics.

 

[Ryan_m_b]

One of the biggest points with mitochondrial eve is that it does not mean that there was just one woman we all descended from, rather there is one woman from whom all our mitochondria descend from. This is because some women would only have sons (or only have sons that reproduce), because men do not pass on their mitochondria these mothers pass on no mtDNA to the next generation but they do pass on nuclear DNA.

When explaining this to people it is always important to mention it. Personally I think using the term Eve was a bit stupid because it immediately conjures up connotations in laypeople of just one woman period.

 

[Pythagorean]

One of the biggest points with mitochondrial eve is that it does not mean that there was just one woman we all descended from, rather there is one woman from whom all our mitochondria descend from. This is because some women would only have sons (or only have sons that reproduce), because men do not pass on their mitochondria these mothers pass on no mtDNA to the next generation but they do pass on nuclear DNA.

Err.. if any of those males reproduce, they reproduce with a woman who descended from mitochondrial eve though, correct? So a strain that didn't come from mito-eve isn't going to live very long without introducing mito-eve?

 

[Ryan_m_b]

Err.. if any of those males reproduce, they reproduce with a woman who descended from mitochondrial eve though, correct? So a strain that didn't come from mito-eve isn't going to live very long without introducing mito-eve?

Sorry I'm not sure what the question is? When a non mito-eve woman has sons she is effectively removed from the lineage.

 

[Pythagorean]

Wait, where does a non mito eve woman come from?

 

[Ryan_m_b]

Wait, where does a non mito eve woman come from?

The same place every other woman came from, they evolved. The complicated thing is that one of these women had a more successful mitochondrial lineage;

 

[Pythagorean]

The same place every other woman came from, they evolved. The complicated thing is that one of these women had a more successful mitochondrial lineage;

alright, back to my question then:

So a strain that didn't come from mito-eve isn't going to live very long without introducing mito-eve?

i.e. any non-mito-eve strains alive today are likely only recently mutated strains? I mean, your pic matches my imagination: all the non-eve's are wiped out at the end of the time series. So essentially, everyone alive today does all come from the same mito-eve? But you are saying they actually don't, so I am having a conflict.

 

[Ryan_m_b]

i.e. any non-mito-eve strains alive today are likely only recently mutated strains? I mean, your pic matches my imagination: all the non-eve's are wiped out at the end of the time series. So essentially, everyone alive today does all come from the same mito-eve? But you are saying they actually don't, so I am having a conflict.

(Emphasis mine) No I wasn't you've got it right. Sorry if that's how it seemed

I was saying that they didn't come from one woman, a common confusion is that mt-eve is the sole woman we are descended from. Wikipedia covers this well;

Not the only woman
One of the misconceptions of mitochondrial Eve is that since all women alive today descended in a direct unbroken female line from her that she was the only woman alive at the time. Nuclear DNA studies indicate that the size of the ancient human population never dropped below tens of thousands. There may be many other women around at Eve's time with descendants alive today, but sometime in the past, those lines of descent included at least one male, who do not pass on their mother's mitochondrial DNA, thereby breaking the line of descent. By contrast, Eve's lines of descent to each person alive today includes precisely one purely matrilineal line.

 

[Ygggdrasil]

Here's a useful example. You have four grandparents, two sets of grandmothers and two sets of grandfathers. Your genomic DNA has contributions from all four individuals: 1/4 from your maternal grandmother, 1/4 from your maternal grandfather, 1/4 from your paternal grandmother, and 1/4 from your paternal grandfather. Despite your maternal grandmother and your paternal grandmother contributing equally to your genomic DNA, only your maternal grandmother contributes to your mitochondrial DNA.

If you are male, a similar situation occurs with your Y-chromosome. Despite your paternal grandfather and maternal grandfather contributing equally to your autosomal DNA, only your Y-chromosome is inherited solely from your paternal grandfather.

Therefore, most of our DNA descends from many thousands of women who existed in the past. It is only our mitochondrial DNA that we can trace back to descending from only one sole individual.

 

[Pythagorean]

Oh gotcha, you're saying as well as mito-eve. Whew, ok, catastrophic retooling of world model has been temporarily diverted.

 

[Ryan_m_b]

Here's a useful example. You have four grandparents, two sets of grandmothers and two sets of grandfathers. Your genomic DNA has contributions from all four individuals: 1/4 from your maternal grandmother, 1/4 from your maternal grandfather, 1/4 from your paternal grandmother, and 1/4 from your paternal grandfather. Despite your maternal grandmother and your paternal grandmother contributing equally to your genomic DNA, only your maternal grandmother contributes to your mitochondrial DNA.

If you are male, a similar situation occurs with your Y-chromosome. Despite your paternal grandfather and maternal grandfather contributing equally to your autosomal DNA, only your Y-chromosome is inherited solely from your paternal grandfather.

Therefore, most of our DNA descends from many thousands of women who existed in the past. It is only our mitochondrial DNA that we can trace back to descending from only one sole individual.

Great explanation!

Oh gotcha, you're saying as well as mito-eve. Whew, ok, catastrophic retooling of world model has been temporarily diverted.

You stoke my ego by suggesting that I'm a key factor in your world model