Re: Question about mitocondrial Eve

Glenn Morton (
Tue, 07 Apr 1998 15:38:40 -0500

At 12:41 PM 4/7/98 -0700, Adrian Teo wrote:
>Hello friends,
>Someone sent me a note saying that a scientific study has shown that the
>molecular clock "ticks" much faster than they expected. (Science
>supposed to be 200,000 years old may have lived just 6,000 years ago
>this study and more importantly, what implications we can draw from
>that? Thanks!

here is what I view as the guts of the article:
"The researchers sequenced 610 base pairs of the mtDNA control region in
357 individuals from 134 different families, representing 327 generational
events, or times that mothers passed on mtDNA to their offspring.
Evoltuionary studies led them to expect about one mutation in 600 generations
(one every 12,000 years). So they were 'stunned' to find 10 base-pair
changes, which gave them a rate of one mutation every 40 generations, or one
every 800 years. The data were published last year in Nature Genetics, and
the rate has held up as the number of families had doubled, Parsons told
scientists who gathered at a recent international workshop ont he problem of
mtDNA mutation rates."~Ann Gibbons, "Calibrating the Mitochondrial Clock,"
Science 279(1998), p. 28-29

"For example, researchers have calculated that 'mitochondrial Eve'--the woman
years old.
"No one thinks that's the case, 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."~Ann Gibbons,
"Calibrating the Mitochondrial Clock," Science 279(1998), p. 29

There is also an original report on this issue in Nature Genetics. It says,

"The mtDNA sequence of Georgij Romanov matched that of the
putative Tsar, and was heteroplasmic at the same position. This
confirms heteroplasmy in the Tsar's lineage, and is powerful
evidence supporting the identification of Tsar Nicholas
II."~Pavel L. Ivanov et al, "Mitochondrial DNA Sequence
Heteroplasmy in the Grand Duke of Russia Georgij Romanov
establishes the Authenticity of the Remains of Tsar Nicholas II,"
Nature Genetics, 12, April 1996, p. 417-420, p. 417

His body has mtDNA with both C and T at location 16169

What all this means I don't know. One can't do what Ann Gibbons suggests
and make Eve be an early farmer who spread their genes by overpopulation for
the simply reason that there was no or very little communication between the
Old and New Worlds. Both the Near East and the America's started farming at
about the same time and if the faster rates of mtDNA were the case, then the
Native American should show much more divergence from Europe. This is
especially true if Native americans entered the new world as long ago as
33,000 years, for which there is some limited evidence.

When it comes to Australia, all agree it was occupied by 60,000 years ago.
Given the fact that the aborigines never farmed, and had no contact with the
outside world, they should be among the most divergent of all mtDNAs if the
faster rates are true. They aren't. The most divergent mtDNAs come from
Africa which always was in some contact with the rest of the old world.




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