^:lol:
ok back to DNA. The 10,000 year mtDNA mutation branching that you queried - this research was done in 97:
It 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.
Now Im not pretending to undestand even half of that not having the requisite background knowledge but you might find it interesting - from what I understand myslef there are basically two ways of estimating a mutation rate- either you measure it by direct observations from one generation to the next, or you see how many mutations have accumulated in 2 different groups (tribes, populations, species) that have separated for a known length of time. The first estimate of mutation rate, the speed of the molecular clock was made by comparing the diferences between humans and chimps and combining this with the time since they last shared a common ancestor, est. at between 4 and 6 million years ago. The other route is to estimate the mutation rate changes which accumulated in native americans who first arrived in america about 12,000 years ago. Both methods agree with each othe rand come out with a mutation rate of one mutation every 20,000 years down a single maternal line.
Im going to hear Richard Dawkins speak at the LSE tomorrow night - its free - I'll ask him ! - although its not his area of expertise Im sure he has an opinion! ( I know you hate uninformed opinions - just thought Id throw the potential Dawkins one in there for ya ! )
As an aside - Dawkins writing in the Sunday Times of his own book "the SelfishGene" and the reactions it caused. The last paragraph particularly rang true to me:
""What are we to make of the following verdict, from a reader in Australia? “Fascinating, but at times I wish I could unread it . . . On one level, I can share in the sense of wonder Dawkins so evidently sees in the workings-out of such complex processes . . . But at the same time, I largely blame The Selfish Gene for a series of bouts of depression I suffered from for more than a decade . . . Never sure of my spiritual outlook on life, but trying to find something deeper — trying to believe, but not quite being able to — I found that this book just about blew away any vague ideas I had along these lines, and prevented them from coalescing any further. This created quite a strong personal crisis for me some years ago.”
I have previously described similar responses from readers. A teacher reproachfully wrote that a pupil had come to him in tears after reading the same book, because it had persuaded her that life was empty and purposeless. But if something is true, no amount of wishful thinking can undo it. As I went on to write, “Presumably there is indeed no purpose in the ultimate fate of the cosmos, but do any of us really tie our life’s hopes to the ultimate fate of the cosmos anyway? Of course we don’t; not if we are sane. Our lives are ruled by all sorts of closer, warmer, human ambitions and perceptions. To accuse science of robbing life of the warmth that makes it worth living is so preposterously mistaken, so diametrically opposite to my own feelings and those of most working scientists, I am almost driven to the despair of which I am wrongly suspected""
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