Interbreeding of Neanderthals & Modern humans

Vince Smith vsmithuk at YAHOO.CO.UK
Thu Oct 21 09:49:43 CDT 2004


Dear all,

As a coauthor on the human louse paper that Dennis Brothers and others
have referred to I've read with interest the recent comments on
TAXACOM. Here are a few responses:

In essence our study reports a high level of genetic differentiation
between two variants of human head louse. One is distributed worldwide
and appears to have gone through a population bottleneck about 100,000
years ago, like modern humans. The other lineage shows no sign of a
bottleneck and has an essentially New World distribution. Using
multiple calibration points we put the split between these louse
lineage's at about 1.18ma. Using standard population genetics (which is
admittedly quite assumption laden) we suggest that the level of genetic
differentiation between these lineage's is such that it could only be
accounted for if they survived in isolation on separate host lineage's
for a prolonged period. Comparison between the louse and hominid
evolutionary history suggests the most likely host for the New World
lineage would be Homo erectus. If our calibrations were dramatically
out then this might change, although it is worth pointing out that we
used multiple calibration points that cross validate each other.

Regarding the host specificity of lice, vs fleas or other parasites,
lice are exceptional in that they are highly host specific permeant
obligate parasites. Unlike fleas they can't survive off their hosts for
more than a few hours and require direct physical contact (although not
necessarily sexual) for transmission. They also exhibit a recent
history of cospeciation with their other primate hosts. To the best of
my knowledge, fleas or other ecto's infecting humans don't show this.

Regarding other human parasites, there are in fact four additional
parasite taxa that have closely related taxonomic pairs infecting
humans. These are tapeworms, follicle mites, a protozoan and bedbugs.
See the paper for more details. As suggested by Ken Kinman, the real
test of our paper will be whether the split that we report for these
louse lineage can be found between sister taxa for these other parasite
groups.

Regarding Pediculus mjobergi, we are well aware of the strange
distribution for this louse. All I can say ifs that we are on the case
with this!

Best regards and thanks for your interest in our paper.

Vince

PS The full paper is available on the open access website for Public
Library of Science (PLoS) - Biology:
http://www.plosbiology.org/plosonline/?request=get-
document&doi=10.1371/journal.pbio.0020340
You can also access the datasets from my website.

____________________________________________________
Dr. Vincent S. Smith
Illinois Natural History Survey
607 East Peabody Drive
Champaign, IL  61820-6970
USA
Tel: +1 (217) 265-0831
Fax: +1 (217) 333-4949
E-mail: vsmith at inhs.uiuc.edu
Web: http://darwin.zoology.gla.ac.uk/~vsmith/
iChat Video Conferencing: vsmithuk at mac.com (by invitation only)
____________________________________________________




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