Freethought & Rationalism Archive

B. H. Manners · 09-30-2002, 06:56 PM

I have a woman over at a Christian board saying that mitochondrial DNA shows that all humankind has descended from one woman. What is the truth on this?

Doubting Didymus · 09-30-2002, 07:05 PM

If you think about it from an evolutionary perspective it should be obvious that all humans are descended from the same couple, if you go back far enough. The 'woman' part is due to the fact that what we use to determine the phylogeny in this case is the DNA from the mitochondria, which everyone inherits only from the female.

However, recent results have suggested that it is possible to inherit them from your father, as well. I am not sure what impact (if any) this discovery has on the mitochondrial eve hypothesis.

What should be noted is that 'eve' was not the first woman. She was simply the human races most recent common ancestor, and she was certainly just one of a large population of humans. The only thing that makes her special is that, eventually, only her descendants made it, eventually trumping everyone else.

I have gone and forgotten the date she was supposed to have lived at.

Dr Rick · 09-30-2002, 07:13 PM

It has been widely asserted that all mammalian mitochodrial DNA is maternally inherited, but evidence to the contrary has recently been published:

The New England Journal of Medicine
Volume 347:576-580 August 22, 2002 Number 8

Paternal Inheritance of Mitochondrial DNA
Marianne Schwartz, Ph.D., and John Vissing, M.D., Ph.D.

Quote:

Mammalian mitochondrial DNA (mtDNA) is thought to be strictly maternally inherited. Sperm mitochondria disappear in early embryogenesis by selective destruction, inactivation, or simple dilution by the vast surplus of oocyte mitochondria.

Very small amounts of paternally inherited mtDNA have been detected by the polymerase chain reaction (PCR) in mice after several generations of interspecific backcrosses.4 Studies of such hybrids and of mouse oocytes microinjected with sperm support the hypothesis that sperm mitochondria are targeted for destruction by nuclear-encoded proteins. We report the case of a 28-year-old man with mitochondrial myopathy due to a novel 2-bp mtDNA deletion in the ND2 gene (also known as MTND2), which encodes a subunit of the enzyme complex I of the mitochondrial respiratory chain. We determined that the mtDNA harboring the mutation was paternal in origin and accounted for 90 percent of the patient's muscle mtDNA.

Rick

Liquidrage · 09-30-2002, 07:19 PM

Quote:

Originally posted by BH:
<strong>I have a woman over at a Christian board saying that mitochondrial DNA shows that all humankind has descended from one woman. What is the truth on this?</strong>

It may very well be true.

However, I think it should be noted that this is said to have occured about 80K years ago.

It should also be noted that there were humans before this. The reason were all seem to have DNA from the same woman is that there appears to be a bottle kneck in population at this time (80K YA).
The human species may have been down to a few 1000 (at least what I have read on this theory). The decendants of 1 woman all lived or at least mated with all the decendants that have come since.

The theory itself does nothing to create a true Eve. It's just another case os someone taking a decent scientific theory and using only small portion of it to try and support their personal agendas, meanwhile they ignore the other details that contradict their personal agendas.

The Lone Ranger · 09-30-2002, 07:20 PM

The phylogenetic evidence suggests that "Mitochondrial Eve" lived about 200,000 years ago, probably in Africa.

Of course, there were doubtless plenty of other people alive then as well. It just so happens that -- by the luck of the genetic draw -- she appears to have been an ancestor of all currently-living people. [Of course, so was her mother, and her mother's mother, and so on and so on.]

Cheers,

Michael

[ Edited to add <a href="http://www.talkorigins.org/faqs/homs/mitoeve.html" target="_blank">this</a> link from talk.origins. ]

[ September 30, 2002: Message edited by: The Lone Ranger ]</p>

Liquidrage · 09-30-2002, 07:29 PM

I don't doubt the 200K YA.

I have only seen the long Discovery channel documentary on it and they stated 80K which coincided with a super volcano erruption the likes of which would even today would threaten humanity. Well, at least they made it sound menacing

Godless Dave · 10-01-2002, 07:54 AM

200,000 years is what I heard too. And while it could be interpreted as being the equivalent of the Genesis Eve, it could also fit the female progenitor of plenty of other myths.

Jesse · 10-01-2002, 09:20 AM

Here's what Dawkins has to say about this in the foreward to <a href="http://www.amazon.com/exec/obidos/ASIN/0521467861/internetinfidelsA/" target="_blank">The Cambridge Encyclopedia of Human Evolution</a>:

Quote:

Mitochondrial DNA is inherited only down the female line, and it evolves at a high and measurable rate. Evidence has been presented that all mitochondrial DNA in non-African women originates from a single common ancestor living in Africa between 50,000 and half a million years ago. This would suggest that our ancestry went through a 'bottleneck', a single, individual woman who lived in Africa within the last few hundred thousand years. This hypothetical woman has been given the all-too-catchy name of Eve.

I have been surprised at the number of people that have asked me whether the alleged evidence of 'bottlenecking' supported the Biblical account of the origin of humanity! It is hard to blame these questioners when one reads some accounts of the 'Eve' story by people who should know better.

As it happens, very recent evidence now calls into question the story of African Eve, and this Encyclopedia is right up to date. But I want to concentrate on a more important point, one that is also clearly made in the Encyclopedia and one that remains true regardless of the new evidence. This is that 'any Eve can never be more than a statistical artefact' (p. 321). To put it another way, it is statistically certain that there is not just one 'Eve' but many, scattered back through our history , and many 'Adams' too. Although it takes me beyond the usual brief of a Foreward, I'd like to explain this further.

Each of us has two parents, four grandparents, sixteen great great grandparents, and so on. Except that, if you think about it, it can't really go on being 'and so on'. If it were, the number of my ancestors alive half a million years ago would be a ridiculously large number with more than 1000 noughts! What have we done wrong in our calculation? We've forgotten that an individual can be an ancestor in more than one way. One's mate is always one's (usually distant) cousin, many times over. Go back sufficiently far in history, and the following statement must be true. If an individual from remote antiquity has any descendants alive today, we are all her descendants. If I am not descended from a particularly remote ancient individual, then neither are you, and neither is anyone.

You can prove this to yourself by the following piece of simple reasoning. Go back a ridiculously long way, say to a fish-like ancestor 400 million years ago. It must be true of an individual fish that either you are descended from her or you are not. If you are, it is obvious that I am too. If you are not, I am not. Survey this population of Devonian fishes, and the individuals would divide up into those from whom all modern humans are descended, and those from whom no modern humans are descended. There are no intermediates.

Let's invent the term 'focal ancestor' for any individual that is ancestral to all living humans. It is clear that there is no focal ancestor alive today. From the argument of the previous paragraph it is also clear that, if you go sufficiently far back into the past, you are bound to find a focal ancestor. Somewhere between these two extremes must be the most recent focal ancestor. There is room for us to wonder when and where the most recent focal ancestor lived.

So, as far as the existence of an 'Eve' is concerned (as opposed to where she lived and how long ago), the mitochondrial evidence tells us nothing that we couldn't have worked out from an armchair. There must have been lots of individuals that were focal ancestors of any given group of humans. There is no reason to suspect a true bottleneck in the sense of a very small population: 'Eve', wherever and whenever she lived, was very likely surrounded by multitudes of friends and relations.

There are two points I should like to add to this Encyclopedia's own treatment. First, contrary to many articles on 'African Eve', the mitochondrial method is very unlikely to find the most recent focal ancestor. It finds ancestors only down the female-female-female line. There are millions more ways of being an ancestor than purely down the female line, and correspondingly millions more candidates for being a focal ancestor. Think of it this way. You have eight great grandparents, but only one purely maternal great grandparent. You have 32 great great great grandparents, but still only one purely maternal great great great grandparent. In this generation, there are 31 other ancestors. In any one generation, it is possible that the female-line-only ancestor is a focal ancestor. But since, in that generation, there are so many more non-female-line-only ancestors, it is far more likely that one of these is a focal ancestor. Therefore, whoever the most recent mitochondrial focal ancestor may have been, and whether she lived in Africa or not, she is highly unlikely to be the most recent of all focal ancestors. She is almost certainly far more ancient that the most recent focal ancestor.

My second point is that the most recent focal ancestor was, anyway, probably an Adam. Harems of females are more likely than harems of males. Therefore if anybody fails to reproduce, it is most likely to be a male. And if anybody has a disproportionate share of descendents, it, too, is likely to be a male. So, in any one generation, if anybody is the ancestor of a large number of descendants, that ancestor is probably a male. And this goes for our most recent focal ancestor.

tronvillain · 10-01-2002, 01:24 PM

"Mitochondrial Eve" is defined as "the most recent common human ancestor with respect to matrilineal descent." Since not every mother has a daughter, her existence is essentially a mathematical inevitability, and her existence says nothing about a genetic bottleneck (though one is indicated by other genetic evidence).

Ah, I see it's all been said, or linked too. Oh well.

[ October 01, 2002: Message edited by: tronvillain ]</p>

09-30-2002, 06:56 PM	#1
B. H. Manners Veteran Member Join Date: Jan 2002 Location: Texas Posts: 1,213	The first woman and mitochondrial DNA I have a woman over at a Christian board saying that mitochondrial DNA shows that all humankind has descended from one woman. What is the truth on this?

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09-30-2002, 07:05 PM	#2
Doubting Didymus Veteran Member Join Date: Jul 2002 Location: East Coast. Australia. Posts: 5,455	If you think about it from an evolutionary perspective it should be obvious that all humans are descended from the same couple, if you go back far enough. The 'woman' part is due to the fact that what we use to determine the phylogeny in this case is the DNA from the mitochondria, which everyone inherits only from the female. However, recent results have suggested that it is possible to inherit them from your father, as well. I am not sure what impact (if any) this discovery has on the mitochondrial eve hypothesis. What should be noted is that 'eve' was not the first woman. She was simply the human races most recent common ancestor, and she was certainly just one of a large population of humans. The only thing that makes her special is that, eventually, only her descendants made it, eventually trumping everyone else. I have gone and forgotten the date she was supposed to have lived at.

09-30-2002, 07:20 PM	#5
The Lone Ranger Veteran Member Join Date: Oct 2001 Location: Eastern U.S. Posts: 1,230	The phylogenetic evidence suggests that "Mitochondrial Eve" lived about 200,000 years ago, probably in Africa. Of course, there were doubtless plenty of other people alive then as well. It just so happens that -- by the luck of the genetic draw -- she appears to have been an ancestor of all currently-living people. [Of course, so was her mother, and her mother's mother, and so on and so on.] Cheers, Michael [ Edited to add <a href="http://www.talkorigins.org/faqs/homs/mitoeve.html" target="_blank">this</a> link from talk.origins. ] [ September 30, 2002: Message edited by: The Lone Ranger ]</p>

09-30-2002, 07:29 PM	#6
Liquidrage Veteran Member Join Date: Dec 2001 Location: Tallahassee Posts: 1,301	I don't doubt the 200K YA. I have only seen the long Discovery channel documentary on it and they stated 80K which coincided with a super volcano erruption the likes of which would even today would threaten humanity. Well, at least they made it sound menacing

10-01-2002, 07:54 AM	#7
Godless Dave Contributor Join Date: Feb 2002 Location: With 10,000 lakes who needs a coast? Posts: 10,762	200,000 years is what I heard too. And while it could be interpreted as being the equivalent of the Genesis Eve, it could also fit the female progenitor of plenty of other myths.

10-01-2002, 01:24 PM	#9
tronvillain Veteran Member Join Date: Oct 2000 Location: Alberta, Canada Posts: 5,658	"Mitochondrial Eve" is defined as "the most recent common human ancestor with respect to matrilineal descent." Since not every mother has a daughter, her existence is essentially a mathematical inevitability, and her existence says nothing about a genetic bottleneck (though one is indicated by other genetic evidence). Ah, I see it's all been said, or linked too. Oh well. [ October 01, 2002: Message edited by: tronvillain ]</p>

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