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Nature 404, 453 - 454 (2000) © Macmillan Publishers Ltd.
Ancient DNA: Neanderthal population genetics
MATTHIAS HÖSS
Authenticity is all in research on ancient DNA. Experience has taught us
that even the most exciting claims of the retrieval of ancient DNA are not
worth much if they cannot be independently reproduced. Hence the importance
of a paper on page 490 of this
issue, in which Ovchinnikov et al.1 describe the extraction,
amplification and sequencing of DNA from 29,000-year-old archaeological bone
material of a Neanderthal recovered from the Mezmaiskaya Cave in the northern
Caucasus.
This is the second time that such a claim has been made, the first being in
1997 (ref. 2). The paper by Ovchinnikov et
al. is probably the more important of the two, for it provides invaluable
corroboration for the authenticity of Neanderthal DNA sequences. Moreover,
sequences of the DNA from a second Neanderthal offer more detailed insight
into the contentious evolutionary relationship between Neanderthals and modern
humans. Research into ancient DNA enjoys high publicity. It is perhaps the combination
of modern molecular techniques and 'old-fashioned' archaeology
that catches the interest of the scientific community and general public alike.
This fascination sometimes clouds critical judgement. But this area of research,
like all others, must meet with standards that ensure the authenticity and
reproducibility of any given result. This has not always been so. Several
of the most spectacular claims such as the retrieval of DNA sequences
from 15-million-year-old plant compression fossils3, from 80-million-year-old
bones of putative dinosaur origin4 and from insects of up to
130 million years in age trapped in amber5-7 could
not be reproduced in any other than the original laboratories, and so are
of limited value8-11. The relationship between Neanderthals and humans remains enigmatic, so
the retrieval of Neanderthal DNA has been one of the major goals of researchers
in the field of ancient DNA. The age of later Neanderthal populations is well
within the range compatible with reliable retrieval of ancient DNA (such retrieval
is possible from samples up to 100,000 years old). However, it appeared from
several studies (for example, ref. 12) that the
work done with ancient human remains was close to the technological limit
of what is possible. This is mainly because of the difficulty of distinguishing
target sequences from contaminating modern, in this case human, DNA. So it came as no surprise that the publication of the first successful
retrieval of DNA from a Neanderthal, from the Feldhofer Cave in Germany2, was greeted with caution. Although the paper was widely regarded
as being of technically high quality, the remote possibility remained that
the published sequence was an artefact or the result of contamination. The
need for DNA sequences from a second, unrelated Neanderthal specimen was clear,
as echoed in most reviews of that paper. And this is where the importance
of the work of Ovchinnikov et al.1 lies. Ovchinnikov and colleagues sequenced Neanderthal mitochondrial DNA and
found that it is closely related, but not identical, to that described previously.
Like the first paper2, the study of Ovchinnikov et al.
is convincing in itself. The authors used all the state-of-the-art controls
to monitor artefacts and contamination, including having the sequences verified
by another laboratory. However, only the combination of the papers allows
us to appreciate fully their individual worth. The identification of two Neanderthal
DNA sequences, from different specimens found in locations far apart, that
are closely related but not identical, rules out the possibility that either
sequence is an artefact or the product of contamination. By verifying each
other, the two papers provide the most reliable proof so far of the authenticity
of ancient DNA sequences. Can we learn anything from this new Neanderthal DNA sequence about the
relationship between modern humans and Neanderthals? The new sequence shares
with the Feldhofer one the same surprising feature: it is no more closely
related to DNA from modern European populations than to sequences from any
other modern human population. This argues against the idea that modern Europeans
are at least partly of Neanderthal origin. Although the two sequences were
taken from specimens at geographically distant locations, the number of differences
between the sequences indicates that these two individuals were from a single
gene pool. Furthermore, the variation between the two Neanderthal sequences
is similar to that among modern humans. Details of the Mezmaiskaya sequence also support the suggestion2
that there was no contribution of the Neanderthals to the pool of mitochondrial
genes in modern human populations. However, this does not exclude the possibility
of a contribution of nuclear Neanderthal genes. Approximate quantification
of the number of mitochondrial DNA molecules found in the Feldhofer Neanderthal
ruled out any hope of recovering nuclear DNA from this specimen2,
but the apparently excellently preserved Mezmaiskaya specimen might yield
values compatible with retrieval of nuclear DNA. Having achieved DNA sequencing from members of geographically distant Neanderthal
populations, it would be interesting to do the same for populations that are
far apart on the timescale. A specimen dated closer to the upper time limit
of Neanderthal distribution (about 230,000 years ago) would be a tempting
choice for DNA retrieval. The quality of the molecular data retrieved so far from Neanderthal specimens
is compelling. If this is how research on ancient DNA is going to proceed,
then we are truly on our way to Neanderthal population genetics.
1. | Ovchinnikov, I. V. et al. Nature 404, 490-493 (2000). |
2. | Krings, M. et al. Cell 90, 19-30 (1997). |
3. | Golenberg, E. M. et al. Nature 344, 656-658 (1990). |
4. | Woodward, S. R., Weyand, N. J. & Bunnell, M. Science 266, 1229-1232 (1994). |
5. | DeSalle, R., Gatesy, J., Wheeler, W. & Grimaldi, D. Science 257, 1933-1936 (1992). |
6. | Cano, R. J., Poinar, H. N., Roubik, D. W. & Poinar, G. O. J. Med. Sci. Res. 20, 619-622 (1992). |
7. | Cano, R. J., Poinar, H. N., Pieniazek, N. J., Acra, A. & Poinar, G. O. Jr Nature 363, 536-538 (1993). |
8. | Sidow, A., Wilson, A. C. & Pbo, S. Phil. Trans. R. Soc. Lond. B 333, 429-432 (1991). |
9. | Zischler, H. et al. Science 268, 1192-1193 (1995). |
10. | Austin, J. J., Ross, A. J., Smith, A. B., Fortey, R. A. & Thomas, R. H. Proc. R. Soc. Lond. B 264, 467-474 (1997). |
11. | Walden, K. K. & Robertson, H. M. Mol. Biol. Evol. 14, 1075-1077 (1997). |
12. | Handt, O. et al. Science 264, 1775-1778 (1994). |
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