February 8, 2013

Only two dates lead adventurous prehistorians to happily question late Neanderthal survival in Iberia

A recent paper has made the headlines all around questioning the, so far widely accepted, late Neanderthal survival in the Iberian Peninsula. I was so puzzled by the conclusions that I decided to hold back and await if I could muster some more information. Soon I was made to realize that the limelight-seeking authors only provided two new datings and could not even question at all some of the most relevant "late survival" dates like those from Gibraltar or the more recent one of very late Mousterian (22,000 BP) in a remote district of Cantabria (apparently not even known to the authors).

Rachel E. Wood et al., Radiocarbon dating casts doubt on the late chronology of the Middle to Upper Palaeolithic transition in southern Iberia. PNAS 2013. Pay per view (6 months embargo) → LINK [doi: 10.1073/pnas.1207656110]

Abstract

It is commonly accepted that some of the latest dates for Neanderthal fossils and Mousterian industries are found south of the Ebro valley in Iberia at ca. 36 ka calBP (calibrated radiocarbon date ranges). In contrast, to the north of the valley the Mousterian disappears shortly before the Proto-Aurignacian appears at ca. 42 ka calBP. The latter is most likely produced by anatomically modern humans. However, two-thirds of dates from the south are radiocarbon dates, a technique that is particularly sensitive to carbon contaminants of a younger age that can be difficult to remove using routine pretreatment protocols. We have attempted to test the reliability of chronologies of 11 southern Iberian Middle and early Upper Paleolithic sites. Only two, Jarama VI and Zafarraya, were found to contain material that could be reliably dated. In both sites, Middle Paleolithic contexts were previously dated by radiocarbon to less than 42 ka calBP. Using ultrafiltration to purify faunal bone collagen before radiocarbon dating, we obtain ages at least 10 ka 14C years older, close to or beyond the limit of the radiocarbon method for the Mousterian at Jarama VI and Neanderthal fossils at Zafarraya. Unless rigorous pretreatment protocols have been used, radiocarbon dates should be assumed to be inaccurate until proven otherwise in this region. Evidence for the late survival of Neanderthals in southern Iberia is limited to one possible site, Cueva Antón, and alternative models of human occupation of the region should be considered. 

From confidential personal communication with qualified prehistorians, I gather the following criticisms:
  • Achieving two new dates (out of eleven trials) is no major hit, even if useful.
  • The results have been oversimplified when presented to the media (and/or by the journalists themselves).
  • The new dates do not disprove that Neanderthals may have been there in later periods.
  • Any conclusions would need to wait for a more extended revision of dates.
  • Collagen preservation is much worse in Southern than Northern Iberia, what may actually imply some need for revision of dates towards more ancient ones (not just the Middle Paleolithic ones but also those from the initial Upper Paleolithic). This part is rather supportive but with due caution.
  • Dates should not be considered alone but in their stratigraphic and archaeological context.
  • The two sites have a very complex stratigraphy, what affects the interpretation of the new dates.
  • There may be pre-conceptions behind this exaggerated claim, such as attachment to the Finlayson model of Neanderthal collapse in Europe before the arrival of modern humans, which is surely wrong.
Also I will add on my own account that, unlike what has been published in some media, this result would not cast absolutely any doubt on the Neanderthal admixture episode, which must have happened not in Europe but, surely, in West Asia long before our ancestors set foot in Europe at all, just at the beginnings of the migration out of Africa (to Asia first of all, not to Europe) c. 125-90 Ka ago.


Update (Feb 12): Basque prehistorian Joseba Ríos Garaizar inaugurates his new blog with an article[es] on this issue. He argues that the two new dates do not seem enough to revolutionize the whole understanding of Neanderthal periodization in SW Europe, especially with the recent re-dating of Saint-Césaire (which confirmed Neanderthal authorship of Chatelperronian and gives a date as late as c. 36 Ka BP, uncalibrated) and the various and also recent datings for Mousterian in the North of the Iberian Peninsula (Arrillor, Fuentes de San Cristobal, Esquilleu, Sopeña) all with dates more recent than 40 Ka BP (uncalibrated). In addition to these Axlor (Basque Country) has a Mousterian layer above another dated to c. 42 Ka BP (uncal.) and Lezetxiki is probably in the same situation. On top of those Mousterian layers many sites have their own Chatelperronian layer, of clear Neanderthal manufacture.

And then there are the already mentioned cases of the anomalous late Mousterian from Cantabria recently dated to 22 Ka BP and several Southern Iberian caves, including Gorham (Gibraltar), which appear also to be more recent than the dates managed by Wood et al.

6 comments:

  1. "Neanderthal admixture episode.... in West Asia... at the beginnings of the migration out of Africa... 125-90 Ka ago."

    Pygmy(?) arm bone at Narmada R India 80ka, no indication of Neanderthal/Denisovan mix...

    Toba ~74ka perhaps a series of Hs/Hn admixture events due to massive environmental change and movements.

    I'd speculate that OOA2 (ex-Congo) pygmy x West Asian neanderthal produced larger-framed humans, first Negritos, then larger still.

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    1. First: you are banned for abusing this space and my patience repeatedly. Second: no idea what bone you mean. Third: that bone surely has not been genetically sequenced (otherwise, provide a link because it'd be quite the news). Fourth: the archaeological evidence (Petraglia 2007) tells us that some people at least survived Toba in India, using the same Africa-related technology before and after the thick Toba ash layer. Fifth: early H. sapiens from Africa (Idaltu for example) was probably already large, judging from their heads, H. erectus was also quite large, Neanderthal instead was rather short (robust but short). Sixth: size adaption seems to have evolved several times independently, being a trait for which our species is relatively flexible.

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  2. Maju, you absolutely must read this http://arkeobasque.wordpress.com/2013/02/11/neandertales_ultrafiltracion/

    It is the new blog from Joseba Rios. His first post is about this very issue.

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    1. Well, it is interesting and I'll see if I can get from that something to add to the post above in form of an update. Of what I did not say, maybe the most relevant is the recent re-dating of Saint-Césaire, which actually supports both the Neanderthal authorship of Chatelperronian and the Neanderthal survival until much later than Wood et al. claim. Also the four recent re-datings of Mousterian after 40 Ka BP (uncal) in the North of the peninsula are important. And let's not forget Gorham (only mentioned in the comments but anyhow). But the central issue is that two re-datings alone are not enough to jump to the adventurous conclusions reached by Wood.

      I look forward to see more of Ríos Garaizar's blogging.

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    2. Now the paper is accesible on author's Academia.edu profile

      http://www.academia.edu/2589608/Radiocarbon_dating_casts_doubt_on_the_late_chronology_of_the_Middle_to_Upper_Palaeolithic_transition_in_southern_Iberia

      Delete

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