Health

Men on the move, part n

Gene ExpressionBy Razib KhanNov 1, 2011 7:28 AM

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Ancient DNA suggests the leading role played by men in the Neolithic dissemination:

The impact of the Neolithic dispersal on the western European populations is subject to continuing debate. To trace and date genetic lineages potentially brought during this transition and so understand the origin of the gene pool of current populations, we studied DNA extracted from human remains excavated in a Spanish funeral cave dating from the beginning of the fifth millennium B.C. Thanks to a “multimarkers” approach based on the analysis of mitochondrial and nuclear DNA (autosomes and Y-chromosome), we obtained information on the early Neolithic funeral practices and on the biogeographical origin of the inhumed individuals. No close kinship was detected. Maternal haplogroups found are consistent with pre-Neolithic settlement, whereas the Y-chromosomal analyses permitted confirmation of the existence in Spain approximately 7,000 y ago of two haplogroups previously associated with the Neolithic transition: G2a and E1b1b1a1b. These results are highly consistent with those previously found in Neolithic individuals from French Late Neolithic individuals, indicating a surprising temporal genetic homogeneity in these groups. The high frequency of G2a in Neolithic samples in western Europe could suggest, furthermore, that the role of men during Neolithic dispersal could be greater than currently estimated.

Some notes: - Otzi the Iceman is G2a. - A continuity of local maternal lineages would not be so surprising. Recall that ~50% of Argentine mtDNA seems to be indigenous, even though they're ~80% European in total ancestry, and ~95% European in the paternal line. - This is not limited to Latin America. In South Asia the majority of the maternal lineages are non-West Eurasian, while the majority of paternal lineages are West Eurasian. Autosomal ancestry seems to be about half West Eurasian. - There are now several instances of Neolithic settlements yielding relatively rare paternal lineages, which are almost certainly intrusive, but left little impact. The authors step forward with the most plausible, and frankly suprising, rationale:

The high frequency of G2a haplogroup in Neolithic specimens, whereas this haplogroup is very rare in current populations, also suggests that men could have played a particularly important role in the Neolithic dissemination that is no longer visible today. This would imply that intra-European migrations related to the metal ages may have strongly affected the modern gene pool.

In other words, the European paternal lineage landscape may not be determined primarily by the hunter-gatherers or first farmers, but subsequent groups. The relative lack of the two dominant European haplogroups, R1a and R1b, is particularly notable. What's going on? Perhaps male lineages were "winner-take-all," and have a tendency to rise to near fixation and then shift toward extinction, more than female lineages? The Genghis Khan haplotype story may be less exceptional than we think. If this is right then we need to be very careful about the historical lessons we draw from mtDNA and Y chromosomes, because they may give us a skewed and unrepresentative picture of the demographics of the past.

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