Freethought & Rationalism Archive

Sauron · 12-13-2002, 06:22 PM

I'm sure this has been discussed here before; but I can't find the right thread.

Here's the creationist trophy quotation:

Some have calculated that the "mitochondrial Eve" probably lived 100,000 to 200,000 years ago in Africa. However it has been found that mtDNA can experience a much faster mutation rate. Using this much faster mutation rate as a new clock speed, Eve can be calculated as living a mere 6000 years ago.

For a very interesting introduction to this topic read the news article "Calibrating the Mitochondrial Clock" by Ann Gibbons in the journal: Science Volume 279, Number 5347, January 2, 1998, pp. 28-29.

I'd like to read the original article, but you have to be an AAAS member to access the full text. Does anyone have more info about this?

THanks.

RufusAtticus · 12-13-2002, 09:36 PM

There is not much to tell. The article by Gibbons is not a scientific paper. It's in the section of the magazine called "Research News." It deals with the situation of "heteroplasmy" which is when one individual has multiple, different mtDNA sequences. It discusses how there appears to be more incidience of heterplasmy in humans then previously thought. Gibbons attributes this to a higher than expected mutation rate, which is not accurate. More heteroplasmy could be caused by higher mutation rate or larger (i.e. weaker) bottlenecks for mitochondria in female germ line tissue. If you're dating recent events heteroplasmy is a problem; however, the effects of heteroplasmy disappear as you look farther back in the past. The error noise generated by it dissapears so to say. The article refers to this situation as "mtDNA time zones." Because of heteroplasmy, recent events have a higher apparent mutation rate than events farther back in time.

Here is an explaination of the discrepency, mentioned in the article.

Quote:

Also, the time span of observation plays a role. For example, because hot spots mutate so frequently, over tens of thousands of years they can revert back to their original sequences, overwriting previous mutations at that site. As a result, the long-term mutation rate would underestimate how often hot spots mutate--and the average long-term mutation rate for the entire control region would be slower than that from near-term studies of families. "The easiest explanation is that these two rates are caused by hot spots," says P��bo.

If so, these short-term rates need not perturb long-term studies. "It may be that the faster rate works on the short time scale and that you use the phylogenetic rate for long-term events," says Shoubridge.
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Nevertheless, The article is prime quote-mining material.

Quote:

Regardless of the cause, evolutionists are most concerned about the effect of a faster mutation rate. For example, researchers have calculated that "mitochondrial Eve"--the woman whose mtDNA was ancestral to that in all living people--lived 100,000 to 200,000 years ago in Africa. Using the new clock, she would be a mere 6000 years old.

However, it says immediatly after this.

Quote:

No one thinks that's the case (emphasis mine), but at what point should models switch from one mtDNA time zone to the other? "I'm worried that people who are looking at very recent events, such as the peopling of Europe, are ignoring this problem," says Laurent Excoffier, a population geneticist at the University of Geneva. Indeed, the mysterious and sudden expansion of modern humans into Europe and other parts of the globe, which other genetic evidence puts at about 40,000 years ago, may actually have happened 10,000 to 20,000 years ago--around the time of agriculture, says Excoffier. And mtDNA studies now date the peopling of the Americas at 34,000 years ago, even though the oldest noncontroversial archaeological sites are 12,500 years old. Recalibrating the mtDNA clock would narrow the difference (Science, 28 February 1997, p. 1256).

RufusAtticus · 12-13-2002, 09:39 PM

Oh yeah, you should also mention that mitochondrial "eve" does not mean that there was only one woman alive at the time, or even that there was a population bottleneck. Most numbers that I have heard seem to indicate that there were about 10,000 human females contemporanous with mtEve.

12-13-2002, 06:22 PM	#1
Sauron Veteran Member Join Date: Jan 2001 Location: In the dark places of the world Posts: 8,093	rapid mutation rates in mitochondrial DNA ? I'm sure this has been discussed here before; but I can't find the right thread. Here's the creationist trophy quotation: Some have calculated that the "mitochondrial Eve" probably lived 100,000 to 200,000 years ago in Africa. However it has been found that mtDNA can experience a much faster mutation rate. Using this much faster mutation rate as a new clock speed, Eve can be calculated as living a mere 6000 years ago. For a very interesting introduction to this topic read the news article "Calibrating the Mitochondrial Clock" by Ann Gibbons in the journal: Science Volume 279, Number 5347, January 2, 1998, pp. 28-29. I'd like to read the original article, but you have to be an AAAS member to access the full text. Does anyone have more info about this? THanks.

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12-13-2002, 09:39 PM	#3
RufusAtticus Veteran Member Join Date: Nov 2001 Location: NCSU Posts: 5,853	Oh yeah, you should also mention that mitochondrial "eve" does not mean that there was only one woman alive at the time, or even that there was a population bottleneck. Most numbers that I have heard seem to indicate that there were about 10,000 human females contemporanous with mtEve.

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