March 11, 2003
Mitochondrial DNA affinities at the Atlantic fringe of Europe
American Journal of Physical Anthropology
Volume 120, Issue 4, 2003. Pages: 391-404
Mitochondrial DNA affinities at the Atlantic fringe of Europe
Ana M. González et al.
Abstract
Mitochondrial DNA analysis of Atlantic European samples has detected significant latitudinal clines for several clusters with Paleolithic (H) and Neolithic (J, U4, U5a1, and U5a1a) coalescence ages in Europe. These gradients may be explained as the result of Neolithic influence on a rather homogeneous Paleolithic background. There is also evidence that some Neolithic clusters reached this border by a continental route (J, J1, J1a, U5a1, and U5a1a), whereas others (J2) did so through the Mediterranean coast. An important gene flow from Africa was detected in the Atlantic Iberia. Specific sub-Saharan lineages appeared mainly restricted to southern Portugal, and could be attributed to historic Black slave trade in the area and to a probable Saharan Neolithic influence. In fact, U6 haplotypes of specific North African origin have only been detected in the Iberian peninsula northwards from central Portugal. Based on this peculiar distribution and the high diversity value (0.014 ± 0.001) in this area compared to North Africa (0.006 ± 0.001), we reject the proposal that only historic events such as the Moslem occupation are the main cause of this gene flow, and instead propose a pre-Neolithic origin for it.
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This might explain why Portugal and northwest Africa do not follow the H* gradient, since a strong Neolithic influence on Portugal, in contrast with northern Iberia, is well-documented (Martí-Oliver, [1998]). For the same reason, the negative gradients for J2 and the exclusive southern presence of J1b may be explained as signatures of the Mediterranean Neolithic wave into the Atlantic border. On the other hand, the significant positive correlations found for the rest of the Js, and the younger clusters of U5a1 and U5a1a, are better explained as the result of the continental penetration of the Neolithic.
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These results suggest that, although both prehistoric and historical influences likely contributed to the sub-Saharan African haplotype pool present in the Iberian Peninsula, the former seems to be more important. Our results are in agreement with the gene flow (19.5%) from northwest Africa to the Iberian Peninsula estimated in a recent study of variation in the autosomic CD4 locus (Flores et al., [2000b]), and with the evidence of northwest African male input in Iberia calculated at around 20%, using the relative frequency of northwest African Y-chromosome-specific markers in Iberian samples (Flores et al., [2000a]).
Posted by Dienekes at March 11, 2003 08:07 PM | PermaLink