--- In cybalist@..., "matt6219" <matt62@...> wrote:
>
> http://news.bbc.co.uk/1/hi/sci/tech/2174437.stm
The paper is 'Y genetic data support the Neolithic demic diffusion
model', Lounès Chikhi, Richard A. Nichols , Guido Barbujani , and
Mark A. Beaumont (
http://www.pnas.org - Proceedings of the National
Academy of Sciences of the USA, August 2002). Accessible to
*subscribers* after searching on the first author's surname. One-off
subscriptions are possible.
Has anyone looked at it critically? The abstract says, 'We analyze a
large dataset of 22 binary markers from the non-recombining region of
the Y chromosome (NRY), by using a genealogical likelihood-based
approach. The results reveal a significantly larger genetic
contribution from Neolithic farmers than did previous indirect
approaches based on the distribution of haplotypes selected by using
post hoc criteria.' This immediately makes me wonder how sound their
hypotheses are. There is evidence, acknowledged in some papers, that
the intense selectional pressure on the Y-chromosome can bias
statistical dating techniques. Also, mutation rates appear to be a
lot more variable in the non-recombinant part of the Y-chromosome
than in mitochondrial DNA, where there are known hot sites (with
rates dependent on certain bases) that have had to be disregarded in
some analyses.
> Contributions ranged from 15-30% in France and Germany, to 85-100%
> in southeastern European countries such as Albania, Macedonia, and
> Greece.
This is strikingly different to (Richards 2000,
http://www.stats.ox.ac.uk/~macaulay/papers/richards_2000.pdf ) where
Table 5 shows a relatively _low_ Neolithic contribution (11% ±5%)
to
the Eastern Mediterranean part of Europe, but also records a _high_
(20%) proportion of recent arrivals there, which he attributes
to 'the heavy historical gene flow between Greece and other
populations of the Eastern Mediterranean'. While greater female
mobility may blur out some gradients in proportions, I don't see how
it converts an area with a relatively high Neolithic proportion (as
evidenced by stay-at-home men) to one with a relatively low Neolithic
proportion (as evidenced by mobile women).
Regards,
Richard.