Interesting and insightful take on Iberomaurusians and their relationship with BE.

[real expert]

Note:The interpretation of the data from the original genetic study on the Iberomaurusians is not verified and anonymous. Nevertheless, the assessment provides some alternative modeling of the Taforalt individuals that also includes UP Europeans which would correlate with the findings of anthropologists about the Taforalts. There is also an analysis of the possible relationship between Iberomaurusians and Basal Eurasians, etc.

In "Pleistocene North African genomes link Near Eastern and sub-Saharan African human populations", van de Loosdrecht et al. have concluded that the Iberomaurusian population was formed with no European source, and with a significant sub-Saharan African component.
On the first of these questions this critique will ask whether the researchers may not have fully taken into account one of their own test results, and on the second it will investigate some uncertainties of demographic modeling.

The potential evidence for European ancestry is found in Supplementary Materials Fig. S19(B), where the qpGraph diagram shows the Natufians as 37% WHG-like and 63% Basal Eurasian-like. Taforalt is then 70%Natufian-like and 30% sub-Saharan-like, which calculates to 26%WHG-like. These data are supported by Lazaridis et al. (2016) [1],who report an even larger WHG-like component of 47% for the Natufians in their Fig. S4.11.
It should be noted that Fig. S19(B) does not give information on whether the Iberomaurusians descend from the Natufians or vice versa. The branching node above the "Natufian" oval can be either"Pre-Natufian" or "Early Iberomaurusian".

To the contrary the ADMIXTURE results in Figs. 2B and S11 show no WHG component in Natufian or Taforalt. But ADMIXTURE can be idiosyncratic depending on the particulars of population histories and weighting of samples [2]. The researchers also conduct tests of possible"three-way" ancestry for Taforalt (Supplementary Materials S8). By this they mean a unitary Natufian source, a sub-Saharan source, and a separate and additional ancient European source. The qpAdm results slightly favor models with an additional European source, however they are rejected as being less parsimonious and having higher error estimates. The qpGraph tests consistently find a 0% additional European source. But this entire approach seems unreliable, and the ambiguous qpAdm results make sense, if Natufianis itself actually 37% WHG-like — as is still illustrated in the Fig. S19(C-E) qpGraph diagrams, presented to show the 0% "additional"WHG-like input to Taforalt.



If the WHG-like ancestry as shown in Fig. S19 is tentatively accepted,there are several basic models that can be formulated for how it reaches the Iberomaurusians. It could be native to the Levant, o rarrive there from the Bohunician, and expand to Libya with the Dabban. It could be an Epigravettian migration to North Africa via Gibraltar/Sicily establishing the Iberomaurusians, and expand by 15kya to the Levant (without the sub-Saharan-like admixture). It could be an Epigravettian migration to the Levant via Anatolia, and expand to North Africa for the Iberomaurusian. It could be separate migrations to North Africa via Gibraltar/Sicily by 25 kya, and to the Levant via Anatolia by 15kya, with similar admixture ratios (noting that Iran Neolithic has a similar 40% EHG). Each model has its problems, and more complex scenarios are possible.

The researchers seem not to dismiss the qpGraph result as an artifact, as in Supplementary Materials S7 they discuss the Natufians being only about half Basal Eurasian. Presumably they have a conception similar to the first model above, regarding the WHG-like ancestry as very ancient and out of scope for the specific formation of the Iberomaurusian culture. While this would fit the statement in the paper's abstract that they "do not find evidence for gene flowf rom Paleolithic Europeans into Late Pleistocene North Africans", the study would have benefited from overt development of the issue.
A point to be mentioned in passing on this subject is Kefi et al.(2016), cited by the authors in Supplementary Materials S10 [3]. This work finds individuals at Taforalt with mtDNA H1, generally proposed to come from the Franco-Cantabrian refuge [4]. Its samples were not individually dated, and could be up to 2ky later than those of the present study [5]. But hypothetically this population could be the source of some of the WHG-like autosomal component in the present study's Fig. S19. It is certainly very interesting to have any Iberian presence at all at Taforalt, in considering the plausibility of a trans-Mediterranean Epigravettian.
As to the sub-Saharan-like DNA in Taforalt, the study seems to assume that it must come from geographical sub-Saharan Africans. An alternative which might be available is the indigenous Aterians of North Africa.

One possible model for the Aterians is that they are Basal Eurasian-like.They would be the proto-Natufian-like population, with local development from the North African MSA into the Iberomaurusian. The study's demographic modeling is somewhat indirect, but this principle can be found in Supplementary Materials S7, and as one of the options in the main paper, penultimate paragraph. In this case, as the authors posit, the origin of the sub-Saharan-like DNA would probably be located south of the Sahara. However, with the Aterians in situ for perhaps 300ky of "African multiregionalism" [6][7], and no clear population replacement in North Africa in the ROA time frame[8], this scenario may require a major deconstruction of ROA and its bottleneck.
If instead the Basal Eurasian-like DNA is native to Southwest Asia orthe Nile (other options in the main paper, loc. cit.), the sub-Saharan-like DNA can plausibly be either Aterian or sub-Saharan.The Aterians are the more obvious first choice, available as a substratum in the Iberomaurusian core territory. The hyper arid Sahara of the LGM, impeding contact with the sub-Saharan region, may add to this argument depending on other chronology. The study's description of the East African-like signal could be a good fit for a some what isolated northwestern regional population: "These results can only be explained by Taforalt harboring an ancestry that contains additional affinity with South, East and Central African out groups. None of the present-day or ancient Holocene African groups serve as a good proxy for this unknown ancestry". Given the geography, the West African-like signal could reasonably be a further element of the inherent Aterian DNA. Turning to archeological evidence, a dental study by Irish (2000) finds Taforalt specimens to have no sub-Saharan traits [9].

The Aterians could also in theory have both the Basal Eurasian-like andsub-Saharan-like signals as their inherent DNA. They would be a western variant of the pre-ROA population, which does not go through the ROA bottleneck. In practice this is currently excluded by the qpGraph analysis, which shows Basal Eurasian-like and WHG-like populations intermixing prior to admixture from a Yoruba-like population. Even with a different mixing order, separate WHG-like migrations would be required, with the (as analyzed) exact proportionality of the ratios problematic.

Some or all of the sub-Saharan-like signals in Taforalt could certainly come from sub-Saharans. There is the Y-chromosome E issue. The late Iberomaurusians at Gobero are 2m tall [10], which might show gene flow from ancestors of today's ultra-tall populations of the Sahel belt. The distinction of the East African-like and West African-like signals might require them to be from separate populations, perhaps one Aterian and one sub-Saharan. Sub-Saharans can migrate to North Africa before the LGM (as postulated in Supplementary Materials S9),and Nile and perhaps Atlantic coastal routes can remain open during that desert period.
A complicating factor is that the signals detected in Taforalt could be skewed by any unmodeled migrations into sub-Saharan Africa. In particular, Iberomaurusian descendants as the Cushitics are now a tempting source of some of the "Levantine" DNA that appears in the Horn of Africa c. 1000 BC and filters to the Khoisan. Skoglund et al. (2017) report a revolutionary two-source formation of West Africans, with an archaic Homo sapiens component, and one "most closely related to eastern Africans and non-Africans" [11].

The present study has characterized its Taforalt specimens as non-European and a third sub-Saharan. There is some evidence that they could instead be a quarter European and a third North African. It is proposed here that these questions should remain open for further investigation.

https://science.sciencemag.org/content/questions-origins-iberomaurusians