Mitochondrial Eve

Tim Robbins

Hi,
Just reading "River out of Eden" and a chapter is devoted to Mitochondrial Eve.
Basically, if you trace your maternal line, your Mother's, Mother's Mother's Mother's......Mother - sooner or later you will reach a singularity where every human alive today shares the same great great great......great grandmother.

Note it is strictly the maternal line, mother's mother's mother...
Not Mother's Father Mother.... Mother.

Now, because this is a singularity, it is popularly known as Mitochondrial Eve.

However, if homo erectus evolves, slowly and gradually to homo sapien surely it is possible for there to be no singularity i.e. no great great great...great grandmother in the maternal line that we all share.
Let me simplfy.

Suppose we have a large number of home erectus say 25,000.

After 10,000 years suppose the species is now:
90% home erectus, 10% homo sapien.

After 20,000 years suppose the species is now:
80% home erectus, 20% homo sapien.

After 30,000 years suppose the species is now:
70% home erectus, 30% homo sapien.

After 50,000 years suppose the species is now:
50% home erectus, 50% homo sapien.

After 70,000 years suppose the species is now:
30% home erectus, 70% homo sapien.

After 100,000 years suppose the species is now:
05% home erectus, 95% homo sapien.

After 120,000 years suppose the species is now:
00% home erectus, 100% homo sapien.

So where's the singularity?

Dawkins (and the wide Science community) seems adamant this singularity must exist.

What do you think?

robindch

Tim Robbins wrote: »

So where's the singularity?

Every child has one female mother, but not all women produce kids. Hence, the number of women in each previous 'generation' must be the same size, or smaller than, the number in the preceding generation. Carry this back to its logical conclusion and you'll eventually end up with one woman who's the most recent common female ancestor -- the woman whose descendant DNA is present in all living humans.

Similar logic indicates the existence of a Mitochondrial Adam, or most recent common male ancestor.

Two corollaries -- this lucky pair are separated by quite some time, as women and men pursue differing reproductive strategies. Also, as male and female lines die out, the MRCFA and MRCMA change from time to time.

Zombrex

Tim Robbins wrote: »

So where's the singularity?

It isn't really a singularity. Its just that this woman's DNA is found in all women. She wasn't the only woman around at the time or anything.

Tim Robbins

Wicknight wrote: »

It isn't really a singularity. Its just that this woman's DNA is found in all women. She wasn't the only woman around at the time or anything.

It is a singularity. She wasn't the only woman but she was the only women is the maternal great great ... grandmother of everyone alive today.

JC 2K3

Tim Robbins wrote: »

After 120,000 years suppose the species is now:
00% home erectus, 100% homo sapien.

You're making the assumption that humans can reach the point where they are 0% homo erectus.


What if the amount of our DNA which is derived from homo erectus tends towards zero as we evolve but never actually reaches it?

Tim Robbins

robindch wrote: »

Every child has one female mother, but not all women produce kids. Hence, the number of women in each previous 'generation' must be the same size, or smaller than, the number in the preceding generation.

The number of women that produce kids in each previous generation must be the same sice of less.

Carry this back to its logical conclusion and you'll eventually end up with one woman who's the most recent common female ancestor -- the woman whose descendant DNA is present in all living humans.

Yes but that woman may not be in the homo sapien species, it could much further back.
comments?





Similar logic indicates the existence of a Mitochondrial Adam, or most recent common male ancestor.

Two corollaries -- this lucky pair are separated by quite some time, as women and men pursue differing reproductive strategies. Also, as male and female lines die out, the MRCFA and MRCMA change from time to time.[/QUOTE]

Dades

I confused as to how this reconciles with evolution.

Surely there was never a "first" woman, just many female descendants at a similar stage in the evolutionary scale. And those many woman came from various other 'female' descendants right the way back to pond life...

I repeat again - I am confused!

Tim Robbins

JC 2K3 wrote: »

You're making the assumption that humans can reach the point where they are 0% homo erectus.


What if the amount of our DNA which is derived from homo erectus tends towards zero as we evolve but never actually reaches it?

I mean 0% more in terms of ability to reproduce with them.

Tim Robbins

Dades wrote: »

I confused as to how this reconciles with evolution.

Surely there was never a "first" woman, just many female descendants at a similar stage in the evolutionary scale. And those many woman came from various other 'female' descendants right the way back to pond life...

I repeat again - I am confused!

+1

Zombrex

Tim Robbins wrote: »

It is a singularity. She wasn't the only woman but she was the only women is the maternal great great ... grandmother of everyone alive today.

Well no not exactly. She is just the most recent.

But don't forget that you have 2 grandmothers, 4 great grandmothers, 8 great great grandmothers, 16 great great grandmothers, 32 great great great grandmothers etc etc

Going back 140,000 years it is not hard to imagine that some where in the mass of great great great ... great grandmothers is one that is shared by all of female kind.

And there are plenty of others that are nearly shared by all of female kind, but due to creating lineages that end due to death before reproduction, or simply having only sons, don't quite make it.

cavedave

Just some biology points.
1. Very little mitocondria comes from the male so there is really no mitocondrial Adam. A Y-chromosome Adam there is.

2. Two different species cannot interbreed and have fertile offspring. So a horse and donkeys child cannot have children itself (except in rare cases). This means that man was not half homo erectus half homo sapien.

Correct me if i am wrong

robindch

Tim Robbins wrote: »

Yes but that woman may not be in the homo sapien species, it could much further back.

I'd imagine that she may well be of the same "species" (in that she could reproduce with today's males), but that does depend somewhat on your definition of species. Perhaps she could also exist at one end of a ring-species-like chain of human and human-like creatures, each one of which can mate with others close in time, but not necessarily able to mate with those who are not.

But so what? The MRCFA and MRCMA are artifacts of how the system works; speciation is an unrelated issue, so to speak.

robindch

cavedave wrote: »

1. Very little mitocondria comes from the male so there is really no mitocondrial Adam. A Y-chromosome Adam there is.

Yes, you're quite right. I should have stuck to the unwieldy MRCMA terminology

Tim Robbins

Wicknight wrote: »

Well no not exactly. She is just the most recent.

But don't forget that you have 2 grandmothers, 4 great grandmothers, 8 great great grandmothers, 16 great great grandmothers, 32 great great great grandmothers etc etc

Going back 140,000 years it is not hard to imagine that some where in the mass of great great great ... great grandmothers is one that is shared by all of female kind.

And there are plenty of others that are nearly shared by all of female kind, but due to creating lineages that end due to death before reproduction, or simply having only sons, don't quite make it.

No, in any one generation you only have one great, great, great...grand mother which is in the maternal line.
i.e. mothe's mother's, mother's, mother's, mother's,...,mother

I see no mathematical reason we should shard all the same maternal mother, that must be in the homo sapient species, it could be a fish, but I see not reason why she must be a human.

Tim Robbins

cavedave wrote: »

2. Two different species cannot interbreed and have fertile offspring. So a horse and donkeys child cannot have children itself (except in rare cases). This means that man was not half homo erectus half homo sapien.

Correct me if i am wrong

Correct that is the definition of a species.

Dades

Tim Robbins wrote: »

I see no mathematical reason we should shard all the same maternal mother, that must be in the homo sapient species, it could be a fish, but I see not reason why she must be a human.

Exactly what I can't help thinking.

Until one starts drawing arbitrary lines (on what criteria?) how can any one member of any one species in the chain be singled out as a descendant of all?

Tim Robbins

But so what? The MRCFA and MRCMA are artifacts of how the system works; speciation is an unrelated issue, so to speak.

Dawkins is adamant MRCFA is a human. My opinion is that it is logically possible for MRCFA to be homo erectus.

It must be that the actual differences between mitochondrial DNA in women today and then the known rate of change of mitochondrial DNA indicate that MRFCA lived at a certain time and must have been a women.

i.e.

Let Rate of Change be R,
Let average difference be D,

R * D probably indicates when MRCFA is, not sure just guessing.

So IMO what's missing in Dawkins explaination is that it is logically possible for MRFCA to be homo erectus, egaster or habiilus or even a fish but maths and genetics indicate she is actually a human.

If he included the actual maths it would make sense, but it's pop science so that means no maths unfortunately.

robindch

Dades wrote: »

Surely there was never a "first" woman, just many female descendants at a similar stage in the evolutionary scale.

At any one point in time, there were many women who produced offspring, but for any given population at a point in time, there is an MRCFA. But this MRCFA had a mum who would have been closer to the "first" woman, but not necessarily the first woman of the species herself (see the comment about ring-species above).

Dades

robindch wrote: »

At any one point in time, there were many women who produced offspring, but for any given population at a point in time, there is an MRCFA. But this MRCFA had a mum who would have been closer to the "first" woman, but not necessarily the first woman of the species herself (see the comment about ring-species above).

Thanks Robin.

What is clearer now is that there are terms being bandied about that makes this "woman" sound like something less "sciencey". Misleading, but no doubt a better way to sell a few books.

Zombrex

Tim Robbins wrote: »

No, in any one generation you only have one great, great, great...grand mother which is in the maternal line.
i.e. mothe's mother's, mother's, mother's, mother's,...,mother

Yes but that is when you are just picking the line. The line is mother mother mother, but in each generation you can pick from all your great ... grand mothers.

For example

M-F    M-F  M-F   M-F   M-F   M-F
  |      |   |     |    |     |
  F  -  M   F  - M   M -  F
     |           |         |
     M    -   F          M
            |
            F

The line comes down from the 3rd female, to the second female, to the first female ...

But that doesn't mean there was only one woman alive in the first generation. There were 6 alive. And in this example they only produce one child. In reality they could produce many.

Perhaps I'm not following exactly what is troubling you about this?

robindch

Tim Robbins wrote: »

Dawkins is admanat MRCFA is a human.

hmmm... it's not immediately clear to me that she should have distinctively 'human' genes, but I can't quite put my finger on why. Before disagreeing with Dawkins on a matter of biology, I'll ask my resident geneticist over lunch at 2 and make sure I'm right (or wrong )

pH

Tim Robbins wrote: »

Yes but that woman may not be in the homo sapien species, it could much further back.
comments?

I'm trying to understand what you're asking. You are agreeing that logically a mitochondrial DNA MRCA exists just questioning if she was H.sapiens?

Given that dating for H.sapiens is circa 200,000 BP and the dating for mitochondrial Eve measuring molecular drift in mitochondrial DNA is 140,000 years BP it looks likely she was, though other estimates (170,000 years +/- 50,000) make it a possibility that she was a little earlier.

Dades wrote: »

I confused as to how this reconciles with evolution.

Surely there was never a "first" woman, just many female descendants at a similar stage in the evolutionary scale. And those many woman came from various other 'female' descendants right the way back to pond life...

I repeat again - I am confused!

Bloody creationists!

Rev Hellfire

I'm curious as to what people think is the significance of such a singularity? Keeping in mind this eve also would have had a line of mitochondrial decent also.
It seems like a fancy game of degree's of bacon to me.

Zombrex

Rev Hellfire wrote: »

I'm curious as to what people think is the significance of such a singularity?

Significant in what way?

Zombrex

pH wrote: »

I'm trying to understand what you're asking. You are agreeing that logically a mitochondrial DNA MRCA exists just questioning if she was H.sapiens?

Oh right, is the the issue.

Well TR the dating suggests that she was Homo Sapien.

What did Dawkins actually say?

Tim Robbins

Wicknight wrote: »

Yes but that is when you are just picking the line. The line is mother mother mother, but in each generation you can pick from all your great ... grand mothers.

For example

M-F    M-F  M-F   M-F   M-F   M-F
  |      |   |     |    |     |
  F  -  M   F  - M   M -  F
     |           |         |
     M    -   F          M
            |
            F

The line comes down from the 3rd female, to the second female, to the first female ...

But that doesn't mean there was only one woman alive in the first generation. There were 6 alive. And in this example they only produce one child. In reality they could produce many.

Perhaps I'm not following exactly what is troubling you about this?

I think you are misunderstanding me. I know there could have been (most likely were) other women alive at the sametime as the singularity. That's quite easy to understand. But my question is specific, is it logically possible for the MRCFA for the human species not to be a human? It seems to me it is, but it is evidence and theory which suggest it is not.

Rev Hellfire

I'm asking why you think such an entity is important. What does its existence actually prove. For example its certainly not the origin of Homo Sapien.

Tim Robbins

pH wrote: »

I'm trying to understand what you're asking. You are agreeing that logically a mitochondrial DNA MRCA exists just questioning if she was H.sapiens?

Basically, yes.

Given that dating for H.sapiens is circa 200,000 BP and the dating for mitochondrial Eve measuring molecular drift in mitochondrial DNA is 140,000 years BP it looks likely she was, though other estimates (170,000 years +/- 50,000) make it a possibility that she was a little earlier.

This would be the same as what I was saying in Today 12:45.

Tim Robbins

Rev Hellfire wrote: »

I'm asking why you think such an entity is important. What does its existence actually prove. For example its certainly not the origin of Homo Sapien.

I find it fascinating that the MCRFA was a human.

Dades

pH wrote: »

Bloody creationists!

I'd say using all my knowledge of DNA there must have been one single descendant.
And she probably lived in a garden.

Rev Hellfire

I'm sure I'm missing something important here but it is just degree's of bacon we're talking about. We are not talking about a common singular ancestor for everyone, but rather the most common one (ie. highest bacon factor) ?
I mean its cool in a that's cool sort of way but beyond that how ? Bear with me I'm stupid.

Zombrex

Tim Robbins wrote: »

But my question is specific, is it logically possible for the MRCFA for the human species not to be a human? It seems to me it is, but it is evidence and theory which suggest it is not.

Well the MRCFA changes from time to time based on the current population, so it is logically possible that it is anyone.

The current one probably was a human based on the time scale.

Zombrex

Rev Hellfire wrote: »

I'm sure I'm missing something important here but it is just degree's of bacon we're talking about. We are not talking about a common singular ancestor for everyone, but rather the most common one (ie. highest bacon factor) ?
I mean its cool in a that's cool sort of way but beyond that how ? Bear with me I'm stupid.

The most recent common ancestor (an ancestor shared by all living humans) was alive approx 3,000 years ago.

What Eve is is the most recent common anscestor on the material line, so mother's mother's .... mother's mother

Because of that you need to go back much much further than the most recent common ancestor.

It is not really the 6 degress of seperation thing, though that shares similar mathematical properties.

Rev Hellfire

But Mitochondrial Eve is not a fix entity it can and does shift, the most obvious one is the Mitochondrial Eve of the our current Mitochondrial Eve, who may herself get usurped by another.

All it is a genetic game with the same rules as degree's of bacon. My under standing of it is she is not the common ancestor of all humans alive today, but rather the one to which the largest number of people can link back to.

I guess we'll have to wait until robin gets to talk to someone who actually knows and works in the relevant field to get the true low down.

Zombrex

Rev Hellfire wrote: »

But Mitochondrial Eve is not a fix entity it can and does shift, the most obvious one is the Mitochondrial Eve of the our current Mitochondrial Eve, who may herself get usurped by another.

Yes

Rev Hellfire wrote: »

All it is a genetic game with the same rules as degree's of bacon.

Well the degree's of bacon game you have to work if you know someone who knows someone who knows someone etc etc who knows Kevin Bacon. So it isn't exactly the same :-)

As you say the Mit Eve can shift around over the generations.

Rev Hellfire wrote: »

My under standing of it is she is not the common ancestor of all humans alive today, but rather the one to which the largest number of people can link back to.

No she is the common ancestor of all females alive today. There are other more recent common ancestors of a large number of females alive today, but to find the woman that every woman on Earth through the material lineage you need to go back 140,000 years. That is because you can't have a daughter-son-daughter link, it has to be daughter-daughter-daughter all the way back.

On the other hand the common ancestor of all humans lived only 3,000 years ago. That is because you can have daughter-son-daughter chain, so you don't need to go back as far.

pH

Rev Hellfire wrote: »

But Mitochondrial Eve is not a fix entity it can and does shift, the most obvious one is the Mitochondrial Eve of the our current Mitochondrial Eve, who may herself get usurped by another.

All it is a genetic game with the same rules as degree's of bacon. My under standing of it is she is not the common ancestor of all humans alive today, but rather the one to which the largest number of people can link back to.

Not sure it really matters, but it's not "the largest number", it's "all people can link back to on their maternal line". She is the Mitochondrial DNA Most Recent Common Ancestor, so she is not the most recent common ancestor (he or she is thought to have lived about 3,000 years ago) but is definitely a common ancestor (the most recent by maternal descent).

As for her importance or otherwise, you're correct it's just a term, she existed, and locating here in time/place is a challenge to which people have risen.

Wicknight wrote:

No she is the common ancestor of all females alive today.

No she is the most recent ancestor on the maternal line of everyone (male and female) alive today.

sdep

I'll throw in 'coalescent theory', which models this. It's an application of population genetics that models how, going back through generations, all current copies of a gene coalesce to a single common ancestor.

Going in the forwards direction, starting in mtEve's generation, you get sampling effects occurring in each generation, as not every female has offspring - or more specifically female offspring who will continue her line. As time rolls on, the population has fewer and fewer matrilines from the starting generation. Eventually you reach a point where only one is present - mtEve's.

Of course, the 'starting generation' mentioned above is nothing special. Every generation has its own mtEve, so in Eve's own generation the MRCFA would have dated to much earlier, and as time progressed, the MRCFA of each generation will have dated more and more recently.

As to mtEve being human, that's just a consequence of figuring out when she lived, looking at fossils from around then and deciding if they were human or not.

Applying the same method to human and Neanderthal mtDNA sequences gives a much older MRCFA, of the order of 750,000 years, so non-human.

Rev Hellfire

So hows does paternal mtDNA effect the concept of the Mitochondrial Eve, or does it at all ?

Johnmb

Rev Hellfire wrote: »

So hows does paternal mtDNA effect the concept of the Mitochondrial Eve, or does it at all ?

It doesn't effect the concept. You get your mtDNA from your mother, so there is no paternal mtDNA to trace back. You get the Y-chromosome from your father, and that is what is traced back along the paternal line (father's father's father's......father). He dates to about 60,000 year ago if I remember correctly, and is referred to as Y-Chromosomal Adam.

Rev Hellfire

Johnmb wrote: »

It doesn't effect the concept. You get your mtDNA from your mother, so there is no paternal mtDNA to trace back. You get the Y-chromosome from your father, and that is what is traced back along the paternal line (father's father's father's......father). He dates to about 60,000 year ago if I remember correctly, and is referred to as Y-Chromosomal Adam.

As far as I'm aware there is evidence of paternal mtDNA been passed on, so this must have some bearing on the eve theory since its basic idea was that it can only be passed on the female line.

Johnmb

Rev Hellfire wrote: »

As far as I'm aware there is evidence of paternal mtDNA been passed on, so this must have some bearing on the eve theory since its basic idea was that it can only be passed on the female line.

All mtDNA actually passed on seems to be from the mother. There is a theoretical possibility that up to 0.1% could come from the father, but that is a theoretical maximum and, as far as I know, has never been observed in reality.

Zombrex

pH wrote: »

No she is the most recent ancestor on the maternal line of everyone (male and female) alive today.

That is a good point, the current generation the males are also included, everyone after all has a mother.

Rev Hellfire

Johnmb wrote: »

All mtDNA actually passed on seems to be from the mother. There is a theoretical possibility that up to 0.1% could come from the father, but that is a theoretical maximum and, as far as I know, has never been observed in reality.

There are a good few articles on the subject of paternal mtDNA and recombination on nature.com along with links to the relevant studies, so its not exactly a theoretical possibility. I'm not saying that it rules out the existence of an eve, but it does muddy the pool somewhat.

Johnmb

Rev Hellfire wrote: »

There are a good few articles on the subject of paternal mtDNA and recombination on nature.com along with links to the relevant studies, so its not exactly a theoretical possibility. I'm not saying that it rules out the existence of an eve, but it does muddy the pool somewhat.

Not really. The amount in minuscule, and even if you have a tiny bit of mtDNA from your father, he got it from his mother, and she from her mother etc, bringing you back into the female line. The chances of having a line of people where the males passed on their maximum amount (0.1%) of mtDNA consistently enough to effect Eve is so slim as to be statistically unimportant.

Zillah

Rev Hellfire wrote: »

I'm asking why you think such an entity is important. What does its existence actually prove. For example its certainly not the origin of Homo Sapien.

Don't you think its cool that there was a single woman who's offspring would eventually take over the planet?

Imagine her, a couple hundred thousand years ago. There's probably only a few tens of thousands of humans alive across the whole globe. She lives in a small travelling tribe of perhaps fifty people. That one woman is the mother of every human being on the planet today.

I think thats cool.

Rev Hellfire

Ohh I agree its cool, but what's the practical benefit of it ?

Johnmb

Rev Hellfire wrote: »

Ohh I agree its cool, but what's the practical benefit of it ?

Eve isn't particularly important. Finding her is just a side effect of the study. The practical benefit of the study is to trace human ancestry.

bleg

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

sdep

Rev Hellfire wrote: »

There are a good few articles on the subject of paternal mtDNA and recombination on nature.com along with links to the relevant studies, so its not exactly a theoretical possibility. I'm not saying that it rules out the existence of an eve, but it does muddy the pool somewhat.

Initial evidence was indirect - looking for the tell-tale traces left by recombination - splicing between different versions of the mtDNA sequence that had to be present together in the cell. People challenged this indirect evidence, but it wasn't demolished.

More recently, a patient apparently inherited a mitochondrial disease from his father, and about 90% of mitochondria in his muscle tissue turned out to be paternal. Apart from this case, though, direct sequencing methods show paternal inheritance to be very rare. Paternal mitochondria are swamped by maternal ones in the fertilised egg, and they're also selectively destroyed. A breakdown of this elimination might mean more paternal mitochondria survive.

So many things have to happen to get inheritance of paternal-maternal recombinant mitochondria. The father's mitochondria have to get into the egg, survive there, not get diluted out in subsequent cell divisions, fuse with and recombine their DNA with the maternal mitochondria, get into the germline for the next generation, all in a woman, who has to have children (ideally daughters). So things are stacked against it.

Alternative possibilities are recombination with mitochondrial genes that have transferred over evolutionary time into the 'conventional' nuclear genome (though there are similar problems with this) or, more likely, recombination between different maternal mtDNA molecules inherited from the same egg.

What does all this mean for mtDNA Eve?

Well, the link between matrilineal Eve and the most recent mtDNA ancestor would be broken. Go back far enough and there'll still be a single matrilineal ancestor, but her line won't be perfectly associated with the mitochondrial DNA molecule. The date at which the most recent common mtDNA ancestor lived will change; most authors suggest a more ancient date. More significantly than Eve herself, some of the mtDNA-inferred dates of human population origin, expansion and migration might have to be reassessed. I wouldn't expect the dates to change too radically though.

Rev Hellfire

bleg wrote: »

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

Lets all link to our favorite school year book

Akrasia

cavedave wrote: »

Just some biology points.
1. Very little mitocondria comes from the male so there is really no mitocondrial Adam. A Y-chromosome Adam there is.

2. Two different species cannot interbreed and have fertile offspring. So a horse and donkeys child cannot have children itself (except in rare cases). This means that man was not half homo erectus half homo sapien.

Correct me if i am wrong

There was one divergent colony/family of homo erectus where due to a mutation and natural selection, over a few generations of interbreeding, the genetic differences became so great that this colony could no longer breed with homo erectus and became homo sapien. That was colony zero of humanity.

There were probably lots of other similar divergent mutations over time that were unsuccessful and died out.