Using ancient DNA to examine genetic continuity at the Mesolithic-Neolithic transition in Portugal

Using ancient DNA to examine genetic continuity at the Mesolithic-Neolithic transition in Portugal

Two main mechanisms for the introduction of agriculture at the transition from the Mesolithic to the Neolithic in Portugal have been proposed: indigenous adoption and colonisation. Distinguishing between these mechanisms can be regarded as a question of genetic continuity or discontinuity at the transition. A genetic comparison of late Mesolithic and early Neolithic populations at the transition using ancient DNA is described here. Mitochondrial DNA (mtDNA) was extracted from human remains collected in several Mesolithic sites of the Sado estuary and from Neolithic cave sites. Phylogenetic analysis, based on the mitochondrial hypervariable region 1 (HVSI), and comparison with DNA from modern European populations was performed. The absence of mtDNA haplogroup J in the ancient Portuguese Neolithic sample suggests that this population was not derived directly from Near Eastern farmers. The Mesolithic and Neolithic groups show genetic discontinuity implying colonisation at the Neolithic transition in Portugal.

A study of Mesolithic and Neolithic Mt DNA from sites inPortugal.

mesoneoportugal1

J shows iself to be absent from the Mesolithic and Neolithic samples, and there was some loss of diversity in less common Hg’s. There’s a fair difference between the Mesolithic and Neolithic samples, suggestin population discontinuity-probably a large amount of immgration at the start of the neolithic, although the lack of J suggests this wasn’t from the near East

mesodna

old-dna-port

It also mentions isotope studies on the bones show a very abrupt change from the Meolithic Maritime diet to the land based Neolithic diet, the same as in Britain.

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3 responses to “Using ancient DNA to examine genetic continuity at the Mesolithic-Neolithic transition in Portugal

  1. Nice finding, thanks. :-)

    I can’t but help noticing a total contradiction between what I see in the data (continuity) and what the authors conclude (discontuity, albeit by arrival of Western, and not Eastern, Mediterranean peoples). This inconsistent conclusion can only be due to the influence of co-author Zilhao who has argued for an ousider origin of Portuguese Neolithic on archaeological grounds.

    If you look at the info in figure 4 (and ignore the simplistic bidimensionalization of fig. 5), you can perfectly see how most of the mtDNA is the same and there are only two rather minor differences:

    1. N* vanishes
    2. V appears

    Both accidents affect a minor apportion of the sample and it is only N* what makes the Mesolithic dot appear so abnormal in the PC graph, obviously.

    V could be a Neolithic arrival admittedly but not from far away in any case (V is believed to be of SW European origin and is strongest, excluding the Sami, among Catalans). N* is intriguing but its disappearence could perfectly be the product of normal drift (or alternatively be an artifact of aDNA analysis: downstream mutations being corrupted). Wonder if it was part of N1, most common in West Asia (to which I belongs) or what?

    In any case the bulk of the structure (hegemony of H with some U) remains.

    Notice please the U* node, that is with all likehood U6 (only U5 and U6 are notable in Iberia nowadays, apart of K and Basque-only U8).

    Noticeable also that neither T nor K are present, suggesting that they are “recent” arrivals, the same as J and X-W. I wonder when exactly did these “oriental” clades arrive, as they cannot be said to be “Neolithic” after this study. They must be at least Chalcolithic.

  2. The study is not very conclusive. Using such small samples of Mesolithic and Neolithic samples compared with larger samples from living peoples. Use 9 Basque samples and you may not get any J, T or even V in the results just mainly H. Basques are known to have high mtDNA H rates. Similarly V may have existed in the Mesolithic peoples but the sample was so small that it was not picked up.
    It is a foolish thing to make comparisons of modern people with old remains. It has been shown that we are not like our ancestors. Take Otzi as am example.

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