A report in the Dec. 7, 2000 issue of Nature provides significant new
evidence for the Out of Africa hypothesis. This hypothesis,
referred to by some as the "Mitochondrial Eve hypothesis', suggests that
anatomically modern humans first migrated from the African
continent about 50,000 years ago. News reports addressing the Nature
study can be found below.
http://abcnews.go.com/sections/science/DailyNews/human_evolution001206.ht
ml
http://news.bbc.co.uk/hi/english/sci/tech/newsid_1058000/1058484.stm
http://www.foxnews.com/scitech/120700/outofafrica.sml
http://www.msnbc.com/news/499641.asp?cp1=1
Note that these reports mention that mitochondrial DNA is inherited only
from the mother. It has been reported on this list that studies have
shown that this is not true, that there is paternal contribution to
mtDNA.
I would like to mention that one of the original reports alleging
paternal contribution to mtDNA on the island of Vanuatu (Hagelberg, et
al.1999 Proc Royal Soc Lon - B, vol. 266, pp. 485-492, ) has since been
retracted in full by the authors. ( Proc Royal Soc Lon - B vol. 267, pp.
1595-1596) Their original claim for evidence of recombination turned out
to be sequence alignment errors.
The second paper alleging paternal contribution was by Awadalla &
Eyre-Walker (1999 Proc Royal Soc Lon - B vol. 266, pp.477-483.) Macaulay
et al. (1999 Proc Royal Soc Lon - B vol. 266, pp. 2037-2039) commented on
their analysis and pointed out errors in the data which, when corrected,
no longer gave a significant effect. In a reply to this comment,
Eyre_Walker et al. (1999 Proc Royal Soc Lon - B vol. 266, pp.2041-2042)
admitted that removing erroneous sequences does remove the significant
effect, but they went on to argue that there was still evidence of
recombination in human mtDNA, citing a similar analysis of mtDNA, that
is, the retracted paper by Hagelberg mentioned above.
In addition, a recent technical comments in the online version of Science
was titled "Questioning Evidence for Recombination in Human
Mitochondrial DNA" ( www.sciencemag.org vol 288 16 June 2000 p. 1931a.)
Four different research teams pointed out various flaws in the
Awadalla/Eyre-Walker report. In spite of the above, and this report,
Awadalla & Eyre-Walker remain, so to speak,"unrepentant."
Mark Stoneking has just published an paper titled "Hypervariable Sites in
the mtDNA Control Region are Mutational Hotspots" (2000 Am. J. Hum.
Genet., 67:1029_1032) He writes: "both germline and somatic mtDNA
mutations occur preferentially at hypervariable sites, which supports the
view that hypervariable sites are indeed mutational hotspots" and are not
to be interpreted as recombination."
In sum,
the Hagelberg paper has been withdrawn; the Awadalla / Eyre-Walker has
been effectively impeached; Research has been presented that
hypervariable sites should not be interpreted as recombination. This,
combined with the fact that mtDNA is severely degraded by time it reaches
the egg, and that there is a powerful biochemical mechanism ("targeted
protein degradation") utilizing Ubiquitin, which is effectively a "sperm
killer" which functions to prevent and eliminate male mtDNA in the egg.
Paternal contribution of mtDNA is effectively a dead issue, and can not
be used to criticize phylogenetic studies based on the use of mtDNA.
Blaine
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