Out of Africa

Mary K. Kuhner mkkuhner at phylo.u.washington.edu
Thu Nov 21 14:22:22 EST 1991


ethan at ut-emx.uucp (Ethan Tecumseh Vishniac) writes:

>I had always been told that the competing hypothesis these days
>is not a Eurasian origin, but that local populations evolved
>through a series of contacts with more advanced populations, so that
>(for example) modern Europeans still have a substantial Neanderthal
>ancestry.  Certainly the mitochondrial evidence suggests that this
>was not the case, but proponents of the idea have argued that the
>`clock' of the mitochrondrial work is off by a factor of a few.

It is not at all clear to me (and I would welcome clarifications!) how
the mitochondrial evidence supports this view.  The fact that the
mitochondrial lineages converge doesn't say much one way or another
about whether the population existing at the time of the convergence was
modern, neanderthal, or a mixture of both.  It just says that there is
no surviving mitochondrial line dating from before that time, and thus
no people who have been isolated from all interbreeding with other
humans since before that time.

Several papers examining the 'phylogeny' of the major histocompatibility
genes (nuclear DNA) have suggested that humans share several different
alleles with chimps and gorillas, and that, therefore, human evolution
never included a really radical bottleneck (it's almost impossible to
carry 4-5 different alleles through a generation with only a few
individuals, due to drift).  If humans have always been middling to
common, their mitochondrial lineages could converge due to drift even
though there was no single origin event for the species, couldn't they?
Or am I confused?  I've talked to people in the Wilson lab about this,
but we always seem to be on different wavelengths.

I read an anthropology paper which used the mtDNA findings to argue that
H. sapiens sapiens wiped out its predecessors without any interbreeding;
this seems to me to be completely unsupported by the data.

Mary Kuhner mkkuhner at genetics.washington.edu
department of genetics. UW



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