>I meant to add the following to my previous note.
>
>Vince Sarich (a long time practitioner of molecular evolution
> methodology) apparently argues for a much younger origin of man and
>claims that the mtDNA data have been misinterpreted incorrectly in the
>other direction! He argues for an origin 15,000 to 20,000 years ago.
>This article seems to be at least 3 years old, but he does mention the
>*The Runaway Brain* by Christopher Willis so he is aware of the
>criticisms of the mt DNA data thatGlenn mentions.
>
>This article is on the web at
>
>http://wilmot.unh.edu/~jel/sarich.html
And you accused me of citing a minority positions. :-) This is a
fascinating article but he is the first person I have ever heard argue for
a 15,000 year Eve. Seriously, I appreciate your pointing this article
out. I think Sarich's paper supports my position more easily than yours.
For the moment, lets assume that Sarich is correct. What are the
implications?
Sarich argues that due to population movement during the last glaciation,
the world's gene pool, including the mtDNA was thoroughly mixed. This
means that all differences have arisen within the past 20,000 years.
He says:
"I suggest that as recently as perhaps 15,000 years ago the human
population was something very close to "panmictic" at all levels, and that
most of the interpopulational differences we observe today, and in the
recent past, have accumulated since then. The proposed "panmixis" is seen
as driven by the last of the glacial pulsations which would have
necessitated recurrent large-scale movements of populations, not only in
areas "directly" affected by the glaciers themselves, but also in those
that suffered the secondary effects of shifting climatic zones and major
sea level changes. It thus must have been essentially world-wide, and
only after populations began to settle down in more-or-less their current
areas could regional differentiation leading have begun again. Thus we
would have had episodic, glacial cycle driven, regional racial)
differentiation subsequent to the expansion of Homo out of Africa, and
concomitant episodic obliteration ("panmixis") of most or all of the
regionality. We then simply appear to be living in one of those episodes
of regional differentiation, with ours beginning with the last glacial
retreat."
If this is true, then mtDNA data has absolutely nothing to say about the
origins of modern humans! Morphologically modern humans first appear
120,000 years ago at Klasies River Mouth in South Africa. Since the
population was mixed after that point (20,000 years ago), the mtDNA clock
was "reset" at that time and now we don't know anything from molecular
data about human origins.
Sarich writes:
"The reasons for my rejection of the "regional continuity" model are
two-fold. First, it seems to me that the mitochondrial DNA data make it
untenable. If regional continuity were a fact, then we should expect to
see ancient, and region-specific, mitochondrial lineages (clades) in
several areas of the world. But, in fact, this situation characterizes
only sub-Saharan Africa (and even that is currently in doubt), and not
Europe, nor the Far East, nor Australia/New Guinea (Cann, Stoneking, and
Wilson, 1987)."
If the mtDNA clock was reset to 15-20,000 years ago, how can he possibly
use this as evidence against the regional continuity model? We would not
expect ancient and region-specific continuity IF Sarich's suggested
panmictic population existed 20,000 years ago. All evidence of regional
continuity would be destroyed at that time. Under Sarich's view one could
believe in a recent Eve at 20,000 years ago and regional continuity!
Within Sarich's new position one could say that the only region showing
deep roots is Africa and it is the only region free of large scale
population movements during the last glaciation. A panmictic Europe and
Asia with an unmixed Africa. This scenario would fit what Sarich suggests
also.
However, even Sarich agrees that Rebecca Cann's work (about Eve living
200,000 years ago) is "fundamentally flawed".[his words].
He also says:
"All we can be reasonably certain of is that the actual base of the human
mtDNA tree is much older than the 200,000 or so years given by Cann,
Stoneking, and Wilson in their landmark 1987 Nature article. The only
published suggestion as to just how much older is by Wills (1993: 53-4):"
Wills suggested that Eve lived between 600,000 to 1,000,000 years ago.
This is the age of Homo erectus! (Wills, The Runaway Brain, 1993, p. 55.
Terry, this supports my position, not yours.
glenn
Foundation,Fall and Flood
http://members.gnn.com/GRMorton/dmd.htm