Posted on 09/01/2002 4:20:09 PM PDT by Ahban
Mitochondrial DNA Mutation Rates
David A. Plaisted
Recently an attempt was made to estimate the age of the human race using mitochondrial DNA. This material is inherited always from mother to children only. By measuring the difference in mitochondrial DNA among many individuals, the age of the common maternal ancestor of humanity was estimated at about 200,000 years. A problem is that rates of mutation are not known by direct measurement, and are often computed based on assumed evolutionary time scales. Thus all of these age estimates could be greatly in error. In fact, many different rates of mutation are quoted by different biologists.
It shouldn't be very hard explicitly to measure the rate of mutation of mitochondrial DNA to get a better estimate on this age. From royal lineages, for example, one could find two individuals whose most recent common maternal ancestor was, say, 1000 years ago. One could then measure the differences in the mitochondrial DNA of these individuals to bound its mutation rate. This scheme is attractive because it does not depend on radiometric dating or other assumptions about evolution or mutation rates. It is possible that in 1000 years there would be too little difference to measure. At least this would still give us some useful information.
(A project for creation scientists!)
Along this line, some work has recently been done to measure explictly the rate of substitution in mitochondrial DNA. The reference is Parsons, Thomas J., et al., A high observed substitution rate in the human mitochondrial DNA control region, Nature Genetics vol. 15, April 1997, pp. 363-367. The summary follows:
"The rate and pattern of sequence substitutions in the mitochondrial DNA (mtDNA) control region (CR) is of central importance to studies of human evolution and to forensic identity testing. Here, we report a direct measurement of the intergenerational substitution rate in the human CR. We compared DNA sequences of two CR hypervariable segments from close maternal relatives, from 134 independent mtDNA lineages spanning 327 generational events. Ten subsitutions were observed, resulting in an empirical rate of 1/33 generations, or 2.5/site/Myr. This is roughly twenty-fold higher than estimates derived from phylogenetic analyses. This disparity cannot be accounted for simply by substitutions at mutational hot spots, suggesting additional factors that produce the discrepancy between very near-term and long-term apparent rates of sequence divergence. The data also indicate that extremely rapid segregation of CR sequence variants between generations is common in humans, with a very small mtDNA bottleneck. These results have implications for forensic applications and studies of human evolution." (op. cit. p. 363).
The article also contains this section: "The observed substitution rate reported here is very high compared to rates inferred from evolutionary studies. A wide range of CR substitution rates have been derived from phylogenetic studies, spanning roughly 0.025-0.26/site/Myr, including confidence intervals. A study yielding one of the faster estimates gave the substitution rate of the CR hypervariable regions as 0.118 +- 0.031/site/Myr. Assuming a generation time of 20 years, this corresponds to ~1/600 generations and an age for the mtDNA MRCA of 133,000 y.a. Thus, our observation of the substitution rate, 2.5/site/Myr, is roughly 20-fold higher than would be predicted from phylogenetic analyses. Using our empirical rate to calibrate the mtDNA molecular clock would result in an age of the mtDNA MRCA of only ~6,500 y.a., clearly incompatible with the known age of modern humans. Even acknowledging that the MRCA of mtDNA may be younger than the MRCA of modern humans, it remains implausible to explain the known geographic distribution of mtDNA sequence variation by human migration that occurred only in the last ~6,500 years.
One biologist explained the young age estimate by assuming essentially that 19/20 of the mutations in this control region are slightly harmful and eventually will be eliminated from the population. This seems unlikely, because this region tends to vary a lot and therefore probably has little function. In addition, the selective disadvantage of these 19/20 of the mutations would have to be about 1/300 or higher in order to avoid producing more of a divergence in sequences than observed in longer than 6000 years. This means that one in 300 individuals would have to die from having mutations in this region. This seems like a high figure for a region that appears to be largely without function. It is interesting that this same biologist feels that 9/10 of the mutations to coding regions of DNA are neutral. This makes the coding regions of DNA less constrained than the apparently functionless control region of the mitochondrial DNA!
If you're having trouble finding it, so was I for a while. It's "Liujiang." I misspelled it.
This site calls the date in question, revising it into territory you like better. It has links to a good look at the skull. This site gives no date, but also has a good picture.
This discussion from sci.anthropology.paleo seems to confirm that Liujiang's dating is bad, so I guess you can forget that one.
You'll claim any gap, anywhere. But you're wishing away a whole community of skulls at Qafzeh, 100,000-92,000 years old on your own diagnosis versus the experts and Mungo Man (68,000) on a mumble.
Here's what I'm telling you. Neanderthals may or may not contribute to human ancestry. It's not that important because archaic Homo sapiens clearly didn't go extinct after giving rise to Neanderthals. The only question is whether modern humans (also arising from the archaic form) wiped out the Neanderthals or interbred to an extent. Numerous sites, especially in the Near East, show neanderthals that aren't quite neandertal (too "modern") and moderns that aren't quite modern (too neandertal). There's more detail on the web page I've linked at least twice.
You're inventing the difficulties here. The fossil record shows a perfectly lovely transition from chimpanzee to man, and you find Reasons Not To Believe. You apparently have no idea how your scratching and clawing away from simple hard evidence must be playing to anyone with a brain.
In psychiatry, that's called "projection."
It appears that everything you've said or intend to say is is in this article. Thus, the Glenn Morton Rebuttal would apply.
One thing you're probably not counting on:
Uranium-series dating relies on the observation that a fresh bone buried in soil takes up uranium from ground-water very readily, but the important daughter elements are mostly insoluble in water and therefore are not incorporated into the bone as it fossilizes. The conditions under which uranium uptake occurs, length of time taken, and whether uranium uptake or leaching continues to occur long after burial are not completely known and subject to considerable uncertainty.They aren't measuring the decay of uranium already present when the fossil animal died. They're measuring uranium absorption by buried bone. Your whole model of the process is wrong.
Carbon 14 is maxed out trying to age a fossil 68,000 years old. The difference in C14 between a 45,000 yo fossil and 68,000 yo one is probably negligible. The half-life is less than 6,000 years.
Ludicrous. It doesn't matter what papers I direct you to. They'll all be written by evolutionists. That's all you're going to get because there are no creationists who know how to make a statistical/mathematical model.
One feature of uranium-series dating which can be exploited to learn something about uranium mobilization is that the method can provide two estimates of the age. This is because uranium has two naturally-occurring isotopes, 235 U and 238 U, each with a long-lived daughter of considerably different half-life, 231 Pa (T½ = 32.8 ka) and 230 Th (T½ = 75.4 ka>). In summarizing a large body of data where both of these uranium isotopes have been used to determine the ages of the samples, this paper attempts . . .Emphasis mine.
While the uranium-lead system can measure intervals in the millions of years generally without problems from the intermediate isotopes, those intermediate isotopes with the longest half-lives span long enough time intervals for dating events less than several hundred thousand years ago. (Note that these intervals are well under a tenth of a percent of the half-lives of the long-lived parent uranium and thorium isotopes discussed earlier.) Two of the most frequently-used of these "uranium-series" systems are uranium-234 and thorium-230.Which is just what was done for Mungo Man, as already noted. Three different methods.. . .
The uranium-234 / thorium-230 method is now being used to date animal and human bones and teeth. Previously, dating of anthropology sites had to rely on dating of geologic layers above and below the artifacts. But with improvements in this method, it is becoming possible to date the human and animal remains themselves. Work to date shows that dating of tooth enamel can be quite reliable. However, dating of bones can be more problematic, as bones are more susceptible to contamination by the surrounding soils. As with all dating, the agreement of two or more methods is highly recommended for confirmation of a measurement. If the samples are beyond the range of radiocarbon (e.g., > 40,000 years), a second method for confirmation of thorium-230 ages may need to be a non-radiometric method such as ESR or TL, mentioned below.
(The stuff you find out you don't know when you try to be your own expert on everything since the authorities aren't objective!)
Succintly put.
When Dr. Hugh Ross writes about it, Ahban will read about it.
When a paleontologist calls a find 'archaic' this or that, it means only one thing - it cannot be properly classified because there is insufficient evidence to do so. This lack may be questions about date, or questions as to similarity with other specimens. If they are classifiable, if they are known to be something, they are classified into either a known species or into a new species. In other words archaic means BIG QUESTION MARK.
We are down to insults I see. It is not ludicrous at all. It is only a model based on evolutionary assumptions, therefore it is proof of nothing at all. Let's remember how for a dozen years evolutionists had this model for mtDNA and never bothered to test it against real life. Let's remember how they assumed withoug conducting any experiments. Let's remember how once somebody did the hard work of looking at just how fast mtDNA changed all the assumptions were thrown down. Now you wish us to believe in more totally baseless assumptions??????
We are down to insults I see. It is not ludicrous at all. It is only a model based on evolutionary assumptions, therefore it is proof of nothing at all. Let's remember how for a dozen years evolutionists had this model for mtDNA and never bothered to test it against real life. Let's remember how they assumed withoug conducting any experiments. Let's remember how once somebody did the hard work of looking at just how fast mtDNA changed all the assumptions were thrown down. Now you wish us to believe in more totally baseless assumptions??????
Sir, I am archiving your replies on this thread. Are you willing to base your future credibility upon this report on how fast mtDNA changes?
As new information is learned, one of use will end up looking like a fool.
Personally, I find the original thread article totally bogus, but if future data verifies it, then you have my respect and appologies.
They mean to ask for evidence that they want to believe. I'll hunt up some models written on stone tablets.
See if you can piece together the one an overburdened Mel Brooks/Moses dropped in History of the World, Part I.
"I bring you these fifteen commandments . . ."(Crash!)
" . . . ten commandments . . ."
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.