There is a recent article analyzing the mtDNA extraction and phylogenies of
Neanderthals. Claims have been made by some that the mtDNA of Neanderthals
is so different from modern humans that they must be a different species.
The authors point out that many of the comparisons between the Neanderthal
and modern mtDNA were performed with a biased dataset-a dataset which is
over represented by some populations and underrepresented by some
populations. When this is fixed, the Neanderthals are not so far from us.
They say:
ìRecent reports analyzing mitochondrial DNA sequences from Neandertal bones
have claimed that Neandertals and modern humans are different species. The
phylogenetic analyses carried out in these articles did not take into
account the high substitution rate variation among sites observed in the
human mitochondrial D-loop region and also lack an estimation of the
parameters of the nucleotide substitution model. The separate phylogenetic
position of Neandertals is not supported when these factors are considered.
Our analysis shows that Neandertal-Human and Human-Human pairwise distance
distributions overlap more than what previous studies suggested. We also
show that the most ancient Neandertal HVI region is the most divergent when
compared with modern human sequences. However, the opposite would be
expected if the sequence had not been modified since the death of the
specimen. Such incongruence is discussed in the light of diagenetic
modifications in ancient Neandertal DNA sequences.î Gabriel Gutierrez, Diego
Sanchez and Antonio Marin, ìA Reanalysis of the Ancient Mitochondrial DNA
Sequences Recovered from Neandertal Bones,î Molecular Biology and Evolution,
19(8):1359-1366, p. 1359
**
NSG = Neanderthal Sequencing Groups
ìThe NSG reported that the pairwise comparisons between the Neandertal and
human sequences demonstrate that Neandertals are outside of modern human
D-loop variability. In particular, Krings et al. (1997) stated that ëa total
of 0.002% of the pairwise comparisons between human mtDNA sequences were
larger than the smallest difference between the Neandertal and the humans.í
We think that this point merits further analysis. The current database is
biased because of the overrepresentation of some populations and the
underrepresentation of others. For instance, the MOUSE database contains
6,012 entries for the HVI region, but 31% of the entries belong to only 20
populations out of 206 populations represented (10% of the total of
populations). The extreme cases are 306 Koreans, 126 Yaps, 120 Cayapa
Amerindians, 119 Mandeka, 115 Palau, and 100 white British. There are also
1,417 entries of undetermined population (40% of them are from North America
and 23% European, but only 9% are from Africa). Thus, African populations
containing the most ancient lineages and the highest variation are
underrepresented in the database. ì
ìBecause of the database overrepresentation of some human populations, the
distribution of pairwise distances is biased. A large part of pairwise
comparisons are made between individuals belonging to the same population.
Likewise, it is expected that most individuals from a single population will
show similar distances to a given outgroup (Neandertal, in this case). To
overcome this problem, we considered another sample of the human variation.
We first sorted the HVI sequences in our data set according to its
uncorrected distance to the reference sequence (Anderson et al. 1981 ). Then
we grouped them into 171 classes, containing equidistant sequences
(considering four decimals), and chose one sequence at random from each
class. The computation of pairwise distances between the 171 randomly
selected sequences and the Neandertals rendered 1.6% of human-human
comparisons larger than the smallest difference between Neandertals and
humans. Likewise, 27% of the comparisons are lower than the largest
human-human difference. This result suggests that Neandertals sequences are
not so different from those of extant humans, in contrast to the NSG
claims.î
Gabriel Gutierrez, Diego Sanchez and Antonio Marin, ìA Reanalysis of the
Ancient Mitochondrial DNA Sequences Recovered from Neandertal Bones,î
Molecular Biology and Evolution, 19(8):1359-1366, p. 1362-1363
glenn
see http://www.glenn.morton.btinternet.co.uk/dmd.htm
for lots of creation/evolution information
anthropology/geology/paleontology/theology\
personal stories of struggle
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