Forests burnt in Ice Age Europe

Quickies

Jed O. Kaplan et al., Large Scale Anthropogenic Reduction of Forest Cover in Last Glacial Maximum Europe. PLoS ONE 2016. Open access → LINK [doi:10.1371/journal.pone.0166726]

Abstract

Reconstructions of the vegetation of Europe during the Last Glacial Maximum (LGM) are an enigma. Pollen-based analyses have suggested that Europe was largely covered by steppe and tundra, and forests persisted only in small refugia. Climate-vegetation model simulations on the other hand have consistently suggested that broad areas of Europe would have been suitable for forest, even in the depths of the last glaciation. Here we reconcile models with data by demonstrating that the highly mobile groups of hunter-gatherers that inhabited Europe at the LGM could have substantially reduced forest cover through the ignition of wildfires. Similar to hunter-gatherers of the more recent past, Upper Paleolithic humans were masters of the use of fire, and preferred inhabiting semi-open landscapes to facilitate foraging, hunting and travel. Incorporating human agency into a dynamic vegetation-fire model and simulating forest cover shows that even small increases in wildfire frequency over natural background levels resulted in large changes in the forested area of Europe, in part because trees were already stressed by low atmospheric CO2 concentrations and the cold, dry, and highly variable climate. Our results suggest that the impact of humans on the glacial landscape of Europe may be one of the earliest large-scale anthropogenic modifications of the earth system.

Not sure what to think, really. In any case the data they manage and share with us is very much worth taking a look at.

The destiny of a cave lion: to serve as decoration

Quickies

Spanish researchers have concluded that a carpet or other comparable fur ornament (a tapestry?, a cape?) is why a late cave lion remains, the latest ones known in Iberia, were found in an otherwise human (Magdalenian) context in the cave of La Garma (Asturias, Spain): it was a fur, claws included, used as decoration of some sort.

Marian Cueto et al., Under the Skin of a Lion: Unique Evidence of Upper Paleolithic Exploitation and Use of Cave Lion (Panthera spelaea) from the Lower Gallery of La Garma (Spain). PLoS ONE, 2016. Open access → LINK [doi:10.1371/journal.pone.0163591]

Abstract

Pleistocene skinning and exploitation of carnivore furs have been previously inferred from archaeological evidence. Nevertheless, the evidence of skinning and fur processing tends to be weak and the interpretations are not strongly sustained by the archaeological record. In the present paper, we analyze unique evidence of patterned anthropic modification and skeletal representation of fossil remains of cave lion (Panthera spelaea) from the Lower Gallery of La Garma (Cantabria, Spain). This site is one of the few that provides Pleistocene examples of lion exploitation by humans. Our archaeozoological study suggests that lion-specialized pelt exploitation and use might have been related to ritual activities during the Middle Magdalenian period (ca. 14800 cal BC). Moreover, the specimens also represent the southernmost European and the latest evidence of cave lion exploitation in Iberia. Therefore, the study seeks to provide alternative explanations for lion extinction in Eurasia and argues for a role of hunting as a factor to take into account.

Fig 4. Cave lion distal phalanxes from the Lower Gallery of La Garma.

Note that only eight of nine specimens are depicted in the figure.

Above: the claws that are the only remnants found of said lion, whose cut marks are fully coincident with skinning techniques used in more recent times with similar decorative purpose. They are believed to be all anterior claws and that one is missing therefore. That is why they imagine the fur to have been cut with an aesthetic interest, because the hind claws would not be visible if the fur was, for example, hang on the wall, so they were probably cut off.

Whether hunting of lions by humans was a decisive, contributing or negligible factor in cave lion extinction remains unclear.

Wisent co-existed with true bison already in the Paleolithic

A fascinating story this one indeed: the European bison or wisent has some ancestry related to the cow, evident in its mitochondrial DNA. This was already known but what wasn't known is that this distinct "hybrid" species of bison dated to the Upper Paleolithic. Thanks to the excellent records of anonymous prehistorical biologists who recorded them in Southwestern European rock art with great detail and naturalism, modern researchers have realized that the wisent, with its bovid heritage, existed already in the Upper Paleolithic. Ancient DNA recovery has now confirmed the artist's impression.

Julien Soubrier et al. Early cave art and ancient DNA record the origin of European bison. Nature communications, 2016. Open access → LINK [doi:10.1038/ncomms13158]

Abstract

The two living species of bison (European and American) are among the few terrestrial megafauna to have survived the late Pleistocene extinctions. Despite the extensive bovid fossil record in Eurasia, the evolutionary history of the European bison (or wisent, Bison bonasus) before the Holocene (< 11.7 thousand years ago (kya)) remains a mystery. We use complete ancient mitochondrial genomes and genome-wide nuclear DNA surveys to reveal that the wisent is the product of hybridization between the extinct steppe bison (Bison priscus) and ancestors of modern cattle (aurochs, Bos primigenius) before 120 kya, and contains up to 10% aurochs genomic ancestry. Although undetected within the fossil record, ancestors of the wisent have alternated ecological dominance with steppe bison in association with major environmental shifts since at least 55 kya. Early cave artists recorded distinct morphological forms consistent with these replacement events, around the Last Glacial Maximum (LGM, ∼21–18 kya).

The depictions of both types of bison are rather distinct but it seems nobody had noticed the difference until now, as the researchers explain in this article.

Fig. 1 - (a) Reproduction from Lascaux cave (France), from the Solutrean or early Magdalenian period (∼20,000 kya—picture adapted from ref. 53). (b) Reproduction from the Pergouset cave (France), from the Magdalenian period (<17,000 kya—picture adapted from ref. 54).

The ancient wisents sequenced now carry a distinct mtDNA haplogroup, called "clade X", which is sister to that of modern wisents (all descending from just 12 survivors). This wisent macro-haplogroup forms a clade with that of bovine cattle (cows of all sorts, both taurine and indicine) but they are joined only at the root, suggesting that the hybridization event that created the wisents as distinct species is very old, just a bit more recent than the divergence of cow and bison.

Fig. 2 - (a) Phylogenetic tree inferred from bovine mitochondrial control region sequences, showing the new clade of bison individuals. The positions of the newly sequenced individuals are marked in red for CladeX. (b) Bovine phylogeny estimated from whole-mitochondrial genome sequences, showing strong support for the grouping of wisent and CladeX with cattle (cow) and zebu. For both trees (a,b) numbers above branches represent the posterior probabilities from Bayesian inference, numbers below branches represent approximate likelihood ratio test support values from maximum-likelihood analysis and scale bars represent nucleotide substitutions per site from the Bayesian analysis. (c) Maximum-clade-credibility tree of CladeX and wisent estimated using Bayesian analysis and calibrated with radiocarbon dates associated with the sequenced bones. Dates of samples older than 50 kyr were estimated in the phylogenetic reconstruction. (d) Map showing all sampling locations, using the same colour code (red for CladeX, orange for wisent and blue for steppe bison).

So it is not random auroch hybridization but a very specific and very ancient episode of admixture between the ancestors of bisons and cows.

The two species appear to have distinct ecological niches:

The detailed records of the southern Ural sites allow the timing of the population replacements between steppe bison and wisent to be correlated with major palaeoenvironmental shifts, revealing that the wisent was associated with colder, more tundra-like landscapes and absence of a warm summer.

This pattern seems to correspond with the periods in which the two species are portrayed in rock art, as two of the researchers explain in this video (third part):

Post-statement: I must say that, on second thought, I'm not really convinced by the claim of wisent corresponding to colder periods. In fig. 1 above it is apparent that it is the steppe bison which corresponds to the last glacial maximum (LGM) in Southwestern Europe and not the wisent, which only shows up after the end of this coldest period. 

I wonder if the researchers are explaining themselves well enough on this aspect or if it is a case of wishful thinking, maybe caused by different conditions in SW Europe (where the rock art is) and the Southern Urals (where most of the archaeogenetic and paleontological data comes from). 

At the very least, judging on fig. 1, it would be the steppe bison the one corresponding with the coldest spell and the wisent the one corresponding to more temperate conditions. Can someone explain me what is going on here?

Armintxe: new rock art site discovered in the Basque Country

A week ago a new rock art site was revealed to exist right in the town of Lekeitio (Biscay). The art, estimated to be from some 14,000 years ago (Magdalenian culture), is made up of several groups of engraved animals: bisons, horses, goats and deers. The cave is not far from other known sites like Lumentxa, Atxurra and Santa Catalina.

Video of the cave and art[es]:

More information:
→ Arkeobasque
→ Pileta de Prehistoria[es] (has several videos and news from several sources, quite extensive)

A 14.000 year old human settlement in Argentina

Quickies

Although the paper claims this site as the signature of arrival of our species to the South Cone (southern region of South America), there is another site with quite apparently older dates: Monte Verde (Chile), that cannot be ignored. In any case, it is a quite interesting data point for the peopling of America and the oldest one known East of the Andes.

Gustavo G. Politis et al., The Arrival of Homo sapiens into the Southern Cone at 14,000 Years Ago. PLoS ONE, 2016. Open access → LINK [doi:10.1371/journal.pone.0162870]

Abstract

The Arroyo Seco 2 site contains a rich archaeological record, exceptional for South America, to explain the expansion of Homo sapiens into the Americas and their interaction with extinct Pleistocene mammals. The following paper provides a detailed overview of material remains found in the earliest cultural episodes at this multi-component site, dated between ca. 12,170 14C yrs B.P. (ca. 14,064 cal yrs B.P.) and 11,180 14C yrs B.P. (ca. 13,068 cal yrs B.P.). Evidence of early occupations includes the presence of lithic tools, a concentration of Pleistocene species remains, human-induced fractured animal bones, and a selection of skeletal parts of extinct fauna. The occurrence of hunter-gatherers in the Southern Cone at ca. 14,000 cal yrs B.P. is added to the growing list of American sites that indicate a human occupation earlier than the Clovis dispersal episode, but posterior to the onset of the deglaciation of the Last Glacial Maximum (LGM) in the North America.

MtDNA U6 in Aurignacian Europe

The U6 haplogroup of Pestera Muierii is officially confirmed. 

Extra-officially, it also seems confirmed mtDNA H in Magdalenian El Mirón, another of the haplogroup challenged (without any reasoning) by Fu et al. In this last case, my sources suggest that Fu surely tested a bone belonging to a different individual, because the heap of bones could well include several people and the bones tested by Hervella (a tooth) and Fu (a femur) were different.

Anyhow, to the matter at hand:

Montserrat Hervella et al. The mitogenome of a 35,000-year-old Homo sapiens from Europe supports a Palaeolithic back-migration to Africa. Nature 2016. Open access → LINK [doi:10.1038/srep25501]

Abstract

After the dispersal of modern humans (Homo sapiens) Out of Africa, hominins with a similar morphology to that of present-day humans initiated the gradual demographic expansion into Eurasia. The mitogenome (33-fold coverage) of the Peştera Muierii 1 individual (PM1) from Romania (35 ky cal BP) we present in this article corresponds fully to Homo sapiens, whilst exhibiting a mosaic of morphological features related to both modern humans and Neandertals. We have identified the PM1 mitogenome as a basal haplogroup U6*, not previously found in any ancient or present-day humans. The derived U6 haplotypes are predominantly found in present-day North-Western African populations. Concomitantly, those found in Europe have been attributed to recent gene-flow from North Africa. The presence of the basal haplogroup U6* in South East Europe (Romania) at 35 ky BP confirms a Eurasian origin of the U6 mitochondrial lineage. Consequently, we propose that the PM1 lineage is an offshoot to South East Europe that can be traced to the Early Upper Paleolithic back migration from Western Asia to North Africa, during which the U6 lineage diversified, until the emergence of the present-day U6 African lineages.

The interesting part is that today U6 is pretty much constrained to Northwest Africa and parts of Iberia and it has usually been considered until now as a North African haplogroup, even if of Eurasian derivation. 

Fig. 2 - (A) Phylogenetic analysis and temporal estimates for lineages including the Peştera Muierii-1 (PM1) from the mitochondrial tree. (B) Location of the Peştera Muierii cave and surface map based on current frequencies of U6 lineages³⁰; the European borders map was generated in ArcMap 10.1 (ESRI, http://www.esri.com) by modifying the World Borders Dataset (http://www.thematicmapping.org/downloads/world_borders.php), which is licensed under the Attribution-ShareAlike 3.0 Unported license. The license terms can be found on the following link: http://creativecommons.org/licenses/by-sa/3.0/ (This map was created by A.A.).

Another interesting bit is that U6(xU6a'b'd,U6c), U6* for short, is not known to exist today anymore. So it is reasonable to speculate about the "ancestral" position of Muierii in the lineage, regardless of whether Muierii-2 was a true ancestor or just a more or less distant relative of the real ancestor of modern day U6 carriers. 

Complementary information is to be found Secher et al. (2014), which refined the knowledge of the U6 mitochondrial haplogroup, unveiling that the key basal (and rare) U6c sublineage is not only found in Morocco (as known earlier) but also in Europe. Specifically U6c, which hangs directly from the U6 root node, is found in: Hispanic America (5.7% of all U6 carriers), Spain (2.2%), Canada (12.5%), NW Europe (16.7%), Morocco (4.5%), Algeria (10%) and Tunisia (5.9%). It is missing in Brazil, Western, Central and East Africa, Romani ("Gypsies"), Jews, Azores, Madeira, Canary and Cape Verde Islands, Portugal, Central and Eastern Mediterranean, West Sahara, Mauritania and USA (African-Americans,  European-Americans and Hispanics).

Figure 1

Surface maps, based on HVI frequencies (in o/oo), for total U6 (U6), total U6a (Tot U6a), U6a without 16189 (U6a), U6a with 16189 (U6a-189), U6b'd, U6c, U6b and U6d.

While the exact pattern of U6 expansion is not clear except for Africa (with a Moroccan origin surely), Sacher et al. believe that at least this part is related to the Iberomaurusian (aka Oranian) culture, which seems primarily an offshoot of Iberian Solutrean, also with origin in North Morocco (Taforalt) and European-like human looks (Cromagnoid).

Another complementary reference is Carmela L. Hernández et al. (2015):

An inspection of the U6 phylogenetic tree (S1 Dataset) showed that it is not easy to infer whether Iberia or North Africa bear more basal lineages. (...) The U6c (9.9 ky [5.0–15.0]) and U6d (12.0 ky [6.9–17.3]) are present in Iberia, Europe and North Africa at low frequencies.

While she seems to support a North African origin, the data is in fact somewhat contradictory:

Fig 5. Founder analysis for mtDNA U6 haplogroup. The plots show probabilistic distributions of U6 founder clusters for HVS-I sequences (A) and complete genomes (B) across migration times scanned at 200-year intervals from 0 to 60 ky.

Fig 7. Bayesian Skyline Plot (BSP) analysis of entire mtDNA U6 sequences.

Temporal changes of the effective population size, Ne in sub-Saharan Africa (brown color), North Africa (green color), and Iberian Peninsula (red color) are depicted. Solid lines represent the median values for the log10 of Ne on the Y-axis within each analyzed geographic region. The 95% HPD (highest posterior density) interval is shown for the three distributions (dashed lines).
Notice that the "LGM" label is very wrong: it should be around 21.000 years ago!

Usually U6 genetic history is envisioned as a migration from southwest Asia through North Africa [50]. This hypothesis is based on the general origin of haplogroup U sub-clades in Southwest Asia, which is also the center of the geographical distribution of U sub-clades: Europe, India, Central Asia, East Africa and North Africa. Two possible scenarios for the first U6 haplotype (bearing mutations 3348 and 16172) can be advanced: i) these mutations aroused in the founder region but did not leave any genetic legacy in current human populations there; ii) they originated probably somewhere in North Africa, after the arrival of the U6 founder haplotype. Within North Africa U6 is only significantly frequent at its western edge (as well as in South-western Europe). More importantly, all the most basal branches are virtually restricted to that region (U6b, U6c and U6d), what could indicate its western origin. Nevertheless, it cannot be excluded the major sub-clade U6a, which shows a richness of sub-clades in Northwest Africa [29] although a few of derivative branches also include sequences from East African and the Middle Eastern populations (e.g. U6a2).

Her conclusions (insisting on an African origin and first arrival via Egypt) are not something I can share at this stage of the research but her data is clearly very interesting and, combined with the rest, useful in discerning the possible route of primeval U6 to the Gibraltar Strait area, where it found no doubt its niche for consolidated expansion. 

After the Muierii finding the question is open: did primeval U6 arrive to North Africa via Iberia, being pruned in Europe afterwards just because of genetic drift and the sizable impact of Paleolithic migrations in low density areas? I cannot be 100% sure but I would say it is a very likely conclusion based not just on Muierii but also on the rather high basal diversity of U6 in Iberia (and surprisingly NW Europe!) and also on the archaeological data that makes almost necessary to root the first Upper Paleolithic of NW Africa (the Iberomaurusian) in the Iberian Solutrean.


(Special thanks to Jean Lohizun again).


Update (Jun 17):

The Hernández 2015 paper also mentions that  U6a1 appears to be of European and specifically Portuguese origin:

Our U6 tree built from mitogenomes shows that U6a1 is predominantly European because it contains a significant number of sequences of Mediterranean individuals mainly from the northwestern shore with a leading Iberian contribution (21 of the 29 European samples) and has an ancestral node in Portugal (accession number HQ651694).

Thanks to Geog M. for highlighting this important detail.

A Magdalenian campsite map from Catalonia

Quickies

A neat curiosity from the Ice Age:

Marcos García Díez & Manuel Vaquero, Looking at the Camp: Paleolithic Depiction of a Hunter-Gatherer Campsite. PLoS ONE 2015. Open access → LINK [doi:10.1371/journal.pone.0143002]

Abstract

Landscapes and features of the everyday world were scarcely represented in Paleolithic art, especially those features associated with the human landscape (huts and campsites). On the contrary, other figurative motifs (especially animals) and signs, traditionally linked to the magic or religious conceptions of these hunter-gatherer societies, are the predominant themes of Upper Paleolithic art. This paper seeks to present an engraved schist slab recently found in the Molí del Salt site (North-eastern Iberia) and dated at the end of the Upper Paleolithic, ca. 13,800 years ago. This slab displays seven semicircular motifs that may be interpreted as the representation of dome-shaped huts. The analysis of individual motifs and the composition, as well as the ethnographic and archeological contextualization, suggests that this engraving is a naturalistic depiction of a hunter-gatherer campsite. Campsites can be considered the first human landscape, the first area of land whose visible features were entirely constructed by humans. Given the social meaning of campsites in hunter-gatherer life-styles, this engraving may be considered one of the first representations of the domestic and social space of a human group.

Archaeologists studying Monte Verde claim an age of 18 Ka BP and add some detail

Quickies

I'm going in this and upcoming short entries through my backlog. You are warned.

New archaeology from Monte Verde (Chile) suggests a date of 18 Ka BP (slightly older than the oldest known North American site) and also that it was a transiting site for highly mobile peoples and not a main base, as they were not using superior local lithics but bringing their own.

Tom D. Dillehay et al. New Archaeological Evidence for an Early Human Presence at Monte Verde, Chile. PLoS ONE 2015. Open access → LINK [doi:10.1371/journal.pone.0141923]

Abstract

Questions surrounding the chronology, place, and character of the initial human colonization of the Americas are a long-standing focus of debate. Interdisciplinary debate continues over the timing of entry, the rapidity and direction of dispersion, the variety of human responses to diverse habitats, the criteria for evaluating the validity of early sites, and the differences and similarities between colonization in North and South America. Despite recent advances in our understanding of these issues, archaeology still faces challenges in defining interdisciplinary research problems, assessing the reliability of the data, and applying new interpretative models. As the debates and challenges continue, new studies take place and previous research reexamined. Here we discuss recent exploratory excavation at and interdisciplinary data from the Monte Verde area in Chile to further our understanding of the first peopling of the Americas. New evidence of stone artifacts, faunal remains, and burned areas suggests discrete horizons of ephemeral human activity in a sandur plain setting radiocarbon and luminescence dated between at least ~18,500 and 14,500 cal BP. Based on multiple lines of evidence, including sedimentary proxies and artifact analysis, we present the probable anthropogenic origins and wider implications of this evidence. In a non-glacial cold climate environment of the south-central Andes, which is challenging for human occupation and for the preservation of hunter-gatherer sites, these horizons provide insight into an earlier context of late Pleistocene human behavior in northern Patagonia.

Notice that Monte Verde is quite towards the south and, in Ice Age contexts, it was a rather extreme environment, barely outside of the glaciers. I wonder what they looked for in such a remote place, even if they probably only went there in summer.

Ancient mitochondrial DNA from Alaska babies

Quickies

Two new ancient Native American mtDNA sequences from what is now Alaska and back in the day, some 11,500 years ago, was linked to Asia forming the Beringia isthmus.

Justin C. Tackney et al., Two contemporaneous mitogenomes from terminal Pleistocene burials in eastern Beringia. PNAS 2015. Pay per view (free in 6 months) → LINK [doi: 10.1073/pnas.1511903112]

Abstract

Pleistocene residential sites with multiple contemporaneous human burials are extremely rare in the Americas. We report mitochondrial genomic variation in the first multiple mitochondrial genomes from a single prehistoric population: two infant burials (USR1 and USR2) from a common interment at the Upward Sun River Site in central Alaska dating to ∼11,500 cal B.P. Using a targeted capture method and next-generation sequencing, we determined that the USR1 infant possessed variants that define mitochondrial lineage C1b, whereas the USR2 genome falls at the root of lineage B2, allowing us to refine younger coalescence age estimates for these two clades. C1b and B2 are rare to absent in modern populations of northern North America. Documentation of these lineages at this location in the Late Pleistocene provides evidence for the extent of mitochondrial diversity in early Beringian populations, which supports the expectations of the Beringian Standstill Model.

A very good article in Spanish is available at Paleoantropología Hoy, which mentions that the only modern population to have both matrilineages are the Hualapai, who live in the state of Arizona (USA). 

Other populations carrying the C1b lineage are the Pima (Arizona), Delta Yuman (California), Ignacianos (Bolivia), extinct Tainos from Puerto Rico and the Norris Farm remains from pre-contact Illinois, as well as a few unspecificied "other tribes". 

B2 is more common, being found in some 37 populations, including Yakama, Wishram, Northern Paiute-Shoshone, Navajo, Zuni, Jemez (all these from North America), Quechua and Aymara (Peru, Bolivia). It was also common among the old Fremont and Anasazi populations of SW USA. 

He also mentions that the archaeological data for the remains was described by Potter et al. 2014. The two babies are post-natal and pre-natal deaths respectively and were carefully buried with ochre paint on their bodies, arrow points (bow and arrows originally, I presume) and organic remains (food). Then a hearth was built over the tomb, which had absolutely normal use, including disposing of food remains (although it can be speculated that they were additional food offerings), except for another baby that was apparently cremated at it in later times. The deaths of the two babies took place in summer, judging from the animal remains of the burial context.

Twitter in the Aurignacian?

Heh, why not?

The curious fact is that a flint stone engraving recently found in the Aurignacian layers of Cantalouette II (Dordogne, SW France) bears a striking resemblance to the logo of the social network, what is quite funny at the very least.

Otherwise it is a very impressive early artistic expression of a rare type (avians are not common in Upper Paleolithic rock art). The Cantalouette II site was a flint stone quarry used by groups of the area and Arkeobasque (which is my source) speculates that it could be an expression of "art for the sake of art", an artist's caprice with no further meaning but excellent and very unusual technique, that was probably abandoned after its execution.

Detailed analysis of South Iberian Solutrean

A new study has been published that reviews all the data on the Southern Iberian Solutrean, which (excepted probably Asturias) is a distinct autonomous facies relative to Franco-Cantabrian Solutrean.

João Cascalheira & Nuno Bicho, On the Chronological Structure of the Solutrean in Southern Iberia. PLoS ONE 2015. Open access → LINK [doi:10.1371/journal.pone.0137308]

Abstract

The Solutrean techno-complex has gained particular significance over time for representing a clear demographic and techno-typological deviation from the developments occurred during the course of the Upper Paleolithic in Western Europe. Some of Solutrean’s most relevant features are the diversity and techno-typological characteristics of the lithic armatures. These have been recurrently used as pivotal elements in numerous Solutrean-related debates, including the chronological organization of the techno-complex across Iberia and Southwestern France. In Southern Iberia, patterns of presence and/or absence of specific point types in stratified sequences tend to validate the classical ordering of the techno-complex into Lower, Middle and Upper phases, although some evidence, namely radiocarbon determinations, have not always been corroborative. Here we present the first comprehensive analysis of the currently available radiocarbon data for the Solutrean in Southern Iberia. We use a Bayesian statistical approach from 13 stratified sequences to compare the duration, and the start and end moments of each classic Solutrean phase across sites. We conclude that, based on the current data, the traditional organization of the Solutrean cannot be unquestionably confirmed for Southern Iberia, calling into doubt the status of the classically-defined type-fossils as precise temporal markers.

Mallaetes, but not nearby Parpalló, is confirmed as one of the oldest sites of the Southern Iberian Solutrean, but has to share the honor with Nerja and La Boja. In general this would support the old idea of rapid expansion from Southern France (Dordogne is slightly older for this culture than the oldest Iberian sites) along the Eastern Mediterranean coast, mimicking what happened before with Aurignacian and Gravettian and what would happen later with Magdalenian and Epipaleolithic cultures of Magdalenian derivation. 

The ulterior evolution is rather fast and does not fit too well the French chronology: Middle Solutrean is short-lasting (mostly affecting Central Portugal) and almost overlaps with Upper Solutrean (oldest in Southern Portugal) and Gravetto-Solutrean (oldest in El Bajoncillo, an inland site not involved in the previous phases). 

All the new phases do impact the core site of Mallaetes, which seems to be well connected.

Fig 5. Time slices for Southern Iberia between 26 and 20 ka cal BP showing the distribution of modelled ages of the classical Solutrean phases.

The size of the dots represents increasing and decreasing levels of the 95.4% probability ranges determined from the duration (date range) of each phase, as calculated by individual Bayesian site models (see Appendix A in S1 File). Dots with two colors indicate overlapping date range probabilities for two or more phases found at the same site.

The authors underline that:

Two clear tendencies can be outlined related to the distribution patterns of the Lower Solutrean and Solutreo-Gravettian type assemblages. In fact, these two components seem to be restricted to the Mediterranean region and totally absent from the Atlantic facade.

They conclude that:

... the main impacts of our analysis on the current knowledge of the LGM adaptations in Southern Iberia can be summarized as follow:

1. The call into doubt of the status of the traditionally-defined type-fossils as precise temporal markers for each Solutrean phase in Southern Iberia;
2. The confirmation of the presence of tanged “Parpalló-type” points at a much earlier time (c. 25 ka cal BP) than previously thought;
3. The potential contemporaneity at a very early moment (c. 25 ka cal BP) of the so-called Middle and Upper Solutrean/Solutreo-Gravettian phases (and thus should preferably be called facies)
4. The likely organization, from a broad chrono-cultural point of view, of the adaptive systems surrounding the LGM event in just two discrete contiguous entities, known as the Proto-Solutrean and the Solutrean.

Some further context (my elaboration)

The Iberian Solutrean (roughly coincident with the Last Glacial Maximum) was the most populous period of the Upper Paleolithic in that province, at least according to the research of Bocquet-Appel. 

It was maybe even more important for North Africa (Iberomaurusian culture), something not discussed in this study but that I am conscious interests many readers, as well as myself. For this reason I checked for a good reference on oldest calibrated dates for Taforalt's Iberomaurusian (alias Oranian) and found this 2013 study that states that it is as old as at least 21,160 Cal BP. 

That would correspond with the fifth map (22-21 Ka cal BP), in which we see an increase of the closest site to North Africa: Gorham's Cave. It would be indeed interesting if someone compared the specifics of Upper Solutrean and that cave with Taforalt, which is by all accounts the oldest Iberomaurusian site. 

The Iberomaurusian genesis, the first known Upper Paleolithic of NW Africa, surely carried a still very apparent Iberian-like genetic signature to across the strait, notably mtDNA haplogroups H1, H3, H4 and H7, and also maybe V. The H subclades were claimed to have an unmistakable Iberian origin by Cherni 2008, while the distribution of the H subhaplogroups in the region was researched by Enafaa & Cabrera 2009. Comparison with Álvarez-Iglesias 2009 suggests that H7 should rather be French than Iberian by origin however, as it is rare in the peninsula. It could still be a Solutrean founder effect anyhow. 

Another possible founder effect of this Paleolithic trans-Mediterranean connection might be mtDNA U6. This lineage has a most likely origin in Northern Morocco but also has a lot of basal diversity across the strait in Iberia. However it could also represent a, so far archaeologically invisible, Aurignacoid migration via NE Africa with re-expansion to Iberia (and also in North Africa) in this period maybe. This could also explain its apparent connection with Y-DNA E1b-M81, which seems very old in NW Africa and is distributed in a similar way to U6 in the Iberian Peninsula and Europe in general.

Weed evolution in the context of earliest proto-farming in Palestine

Ohalo II, at (often under) the Sea of Galilee, is probably the oldest site of sedentary proto-farming, dating to before the Last Glacial Maximum, experiment that may have been interrupted afterwards. A new study finds the first signals of not just many edible plants that would eventually become crops but also the signature of evolution of weeds already towards the forms we are familiar with nowadays.

A. Snir et al., The Origin of Cultivation and Proto-Weeds, Long Before Neolithic Farming. PLoS ONE 2015. Open access → LINK [doi:10.1371/journal.pone.0131422]

Abstract

Weeds are currently present in a wide range of ecosystems worldwide. Although the beginning of their evolution is largely unknown, researchers assumed that they developed in tandem with cultivation since the appearance of agricultural habitats some 12,000 years ago. These rapidly-evolving plants invaded the human disturbed areas and thrived in the new habitat. Here we present unprecedented new findings of the presence of “proto-weeds” and small-scale trial cultivation in Ohalo II, a 23,000-year-old hunter-gatherers' sedentary camp on the shore of the Sea of Galilee, Israel. We examined the plant remains retrieved from the site (ca. 150,000 specimens), placing particular emphasis on the search for evidence of plant cultivation by Ohalo II people and the presence of weed species. The archaeobotanically-rich plant assemblage demonstrates extensive human gathering of over 140 plant species and food preparation by grinding wild wheat and barley. Among these, we identified 13 well-known current weeds mixed with numerous seeds of wild emmer, barley, and oat. This collection provides the earliest evidence of a human-disturbed environment—at least 11 millennia before the onset of agriculture—that provided the conditions for the development of "proto-weeds", a prerequisite for weed evolution. Finally, we suggest that their presence indicates the earliest, small-scale attempt to cultivate wild cereals seen in the archaeological record.

19 Ka BP old mtDNA H from Cantabria

Jean Lohizun points me to this new study by the EHU-UPV paleogeneticist team, which reviews the ancient DNA evidence from the Cantabrian strip (or "fringe" as they call it) and, most importantly announces the oldest confirmed mtDNA H to date: belonging to an individual from El Mirón cave (Ramales, Cantabria, bordering the Basque Country), which is assigned to earliest Magdalenian culture and dated to 19,000 BP.

Update (Apr 24): the genetic findings of El Mirón were first published (in Spanish) in: M. Hervella et al., El ADN mitocondrial de los cazadores-recolectores de la región cantábrica: nueva evidencia de la cueva de El Mirón, Revista Española de Antropología Física - Vol. 35 (2014). I could not find an online reference but I have a copy of the article thanks again to Jean.

Concepción de la Rúa et al., Ancient DNA in the Cantabrian fringe populations: A mtDNA study from Prehistory to Late Antiquity. Quaternary International, 2015. Pay per view → LINK [doi:10.1016/j.quaint.2015.01.035]

Abstract

The present mtDNA study on human remains of fourteen archaeological sites from Cantabria, Basque Country and Navarra provided a diachronic overview from Paleolithic–Mesolithic to Late Antiquity period of some communities settled in the Cantabrian fringe. Ancient DNA studies in European human remains indicated a genetic discontinuity between the hunter–gatherers and later populations. However, some of the mtDNA lineages found in the Cantabrian fringe in Paleolithic–Mesolithic times persist in present-day populations.

The mtDNA variability observed in hunter–gatherers and farmers in Europe denoted a complex pattern for the Neolithic transition, occurring along several different routes into and across Europe. The mtDNA lineages found in the Cantabrian fringe indicated that the dispersion of Neolithic farmers had a different genetic impact in this area with respect to Central and Mediterranean regions of Europe. The differences in mtDNA variability were also apparent after the Neolithic, as shown by the genetic distance between the Chalcolithic populations from the Cantabrian fringe and the Bell Beaker Culture (BBC) populations of Central Europe. 

It must be mentioned that they seem to have forgotten the thesis of Marie Lacan[fr], which reported mtDNA H in Linatzeta cave (Basque Country, Epipaleolithic) and Franchthi cave (Greece, Meso-Neolithic transition), among other more recent aDNA sequences. See here for my English language synthesis.

Otherwise they list all the sequences considered in their paper in table 1:

Annotations by Maju: red: El Mirón (new sequence), orange: other Paleolithic or Epipaleolithic sequences

After including Linatzeta (Lacan 2011), we get the following frequencies in the Eastern Cantabrian sub-region (Basque Country + Cantabria) for pre-Neolithic times:

• H: 4/6=2/3=67%
• H-CRS (H1 surely): 33%
• H6: 16%
• H*: 16%
• U5: 2/6=1/3=33%
• U5*: 16%
• U5b1: 16%

Notice anyhow that if we choose to draw a line between Cantabria and the Basque Country, then we get a sharp contrast: 

• Cantabria: 100% H
• Basque Country: 67% U5 + 33% H* (or even an illusory 100% U5 if we use only the table above, ignoring Lacan's data)

Does this apparent sharp contrast make any sense? Well, one possible interpretation comes from carefully taking into account the data we have on Iberian Solutrean and Magdalenian, which indicates that:

1. South Iberian (from Valencia to Portugal) Solutrean is heavily influenced by the Gravettian substrate (otherwise "pure Solutrean" is restricted to two caves), configuring a unique facies sometimes called Gravetto-Solutrean.
2. South Iberian Gravetto-Solutrean, probably in its way to Portugal, strongly affected the Upper Paleolithic of Northwest Africa, being a decisive force in the Iberomaurusian or Oranian genesis. Backflows can't be discarded because of the innovation of tanged and winged arrow points, which may have been inspired by North African Aterian technology.
3. The Portuguese branch of this Gravetto-Solutrean was the actual source (via Salamanca) of Asturian Solutrean, unlike what happened in Cantabria and the Basque Country, directly influenced by Aquitaine. 
4. In the subsequent Magdalenian there might have been an expansion eastward of the Asturian population, because the facies divide moves to the east (so we have a Cantabro-Astur facies and a Basque facies).

In addition to that, it may be worth considering the issue of North African genetic influence in the Western Third of the Iberian Peninsula, which incidentally and irregularly includes Cantabria but not the Basque Country. Also Chandler et al. 2005 reported high frequencies of mtDNA H (and low of U) in Epipaleolithic Portugal.

I guess that other interpretations are possible such a more subtle cline or patchy distribution but I would not discard this hypothesis, which in essence proposes that Solutrean and Magdalenian were in general dominated by U5 but this did not affect (at least not very intensely) most of Iberia, nor surely other regions like Italy or Eastern Europe, where we see haplogroups that are not U5 (Sunghir's and Karelian H, Italian mysterious HV, etc.)

This implies that the main redistribution of mtDNA H in Europe, that part organized around H1 (which also includes H3 and various H*) actually happened mostly in the Neolithic from areas like Portugal. However we know nearly nothing about the Atlantic pre-Neolithic DNA North of the Bidasoa River (some of which could also be H, particularly R*-CRS reported in Britain) so multiple sources are possible. The huge blank of data corresponding to the Western French State and also Atlantic Islands, etc. is crying for a comprehensive sampling, and not just for mtDNA. 

Neolithic Basque mtDNA is unlike what is found in Continental Europe

The authors pay limited attention to the issues relative to Paleolithic and dedicate most of the paper to analyze the Basque ancient mtDNA in contrast to other comparable data from elsewhere in Europe. This is synthesized in fig. 2:

Fig. 2. Multidimensional Scaling analysis (MDS), based on a Fst genetic matrix calculated from the frequency distribution of the mtDNA haplogroups of different populations [Neolithics (green), Chalcolithics (purple), Late Antiquity (red), present-day Near East and northern Caucasus (orange) and Europeans (black)]. Abbreviations for present-day populations in Europe: Eastern Mediterranean (MdE), Central Mediterranean (MdC), Western Mediterranean (MdW), Northeast Europe (NE), NortheCentral Europe (NC), Northwest Europe (NW), Southeast Europe (SE) and Alps (ALP). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.).

Notice that all the ancient mtDNA from the so-called "Cantabrian Fringe" in this graph is from the Basque Country (Navarre included), often outside of the Cantabrian strip and rather from the Upper Ebro basin. Notice also that the all the Chalcolithic data belongs to military contexts from the Ebro Valley and are probably therefore not representative of the overall Basque region, although they may represent well the Upper Ebro in that period (more influenced apparently by Mediterranean inputs of Cardial affinity).

Also I already discussed all this (and more) quite in depth in my dedicated entry of 2013. 

The authors argue that Germany's Bell Beaker samples (BBC) are not quite similar to the Basque ancient and modern pools, what is true if you are nit-picky enough, but they share the same common tendency in PC1 towards modernity. In contrast all other Neolithic samples are clearly non-modern European and must have been largely suffered by replacement in the Chalcolithic or later periods.


PS- I forgot to mention that apparently Paabo and co. had already sequenced this very same specimen in 2013, yet they have not published anything for unknown reasons, some think that ideological ones. It's of course possible that they do have good reasons but two years is a long time to await publication really, we the people, who pay their salaries and budget with our extreme economic pains, expect reliability from our well-paid researchers.

Ancient inter-continental admixture in the Horn of Africa

A new and quite interesting study finds strong support for Upper Paleolithic (~ LSA) Eurasian inflows into the Horn of Africa and confirms that most of the populations of that region are in essence an ancient mix of West Eurasian and African ancestries.

Jason A. Hodgson et al., Early Back-to-Africa Migration into the Horn of Africa. PLoS Genetics 2014. Open access → LINK [doi:10.1371/journal.pgen.1004393]

Abstract

Genetic studies have identified substantial non-African admixture in the Horn of Africa (HOA). In the most recent genomic studies, this non-African ancestry has been attributed to admixture with Middle Eastern populations during the last few thousand years. However, mitochondrial and Y chromosome data are suggestive of earlier episodes of admixture. To investigate this further, we generated new genome-wide SNP data for a Yemeni population sample and merged these new data with published genome-wide genetic data from the HOA and a broad selection of surrounding populations. We used multidimensional scaling and ADMIXTURE methods in an exploratory data analysis to develop hypotheses on admixture and population structure in HOA populations. These analyses suggested that there might be distinct, differentiated African and non-African ancestries in the HOA. After partitioning the SNP data into African and non-African origin chromosome segments, we found support for a distinct African (Ethiopic) ancestry and a distinct non-African (Ethio-Somali) ancestry in HOA populations. The African Ethiopic ancestry is tightly restricted to HOA populations and likely represents an autochthonous HOA population. The non-African ancestry in the HOA, which is primarily attributed to a novel Ethio-Somali inferred ancestry component, is significantly differentiated from all neighboring non-African ancestries in North Africa, the Levant, and Arabia. The Ethio-Somali ancestry is found in all admixed HOA ethnic groups, shows little inter-individual variance within these ethnic groups, is estimated to have diverged from all other non-African ancestries by at least 23 ka, and does not carry the unique Arabian lactase persistence allele that arose about 4 ka. Taking into account published mitochondrial, Y chromosome, paleoclimate, and archaeological data, we find that the time of the Ethio-Somali back-to-Africa migration is most likely pre-agricultural.

The study makes three different formal admixture tests (f3, Adler and D-stat), as well as a Rolloff simulation, in order to confirm these findings. This part is quite technical and therefore I am not going to discuss it further. Feel free to explore the extensive supplemental materials. 

I will instead stop on what I know better, which is ADMIXTURE and FST distances, which are more visually amenable and ultimately tell the same story. 

Figure 2. Population structure of Horn of Africa populations in a broad context.
ADMIXTURE analysis reveals both well-established and novel ancestry components in HOA populations. We used a cross-validation procedure to estimate the best value for the parameter for the number of assigned ancestral populations (K) and found that values from 9 to 14 had the lowest and similar cross-validation errors (Figure S2). (A) The differences in inferred ancestry from K = 9–14 are most pronounced in the HOA for K = 10–12, where two ancestry components that are largely restricted to the HOA appear (the dark purple and dark green components). (B) Surface interpolation of the geographic distribution of eight inferred ancestry components that are relatively unchanging and common to the ADMIXTURE results from K = 10–12. (C) Individual ancestry estimation for HOA populations (with language groups indicated) and surface plots of the changing distributions of the Nilo-Saharan (light blue) and Arabian (brown) ancestry components for K = 10–12. At K = 11, a new HOA-specific ancestry component that we call Ethiopic appears (dark purple) and at K = 12 a second new ancestry component that we call Ethio-Somali (dark green) appears with its highest frequencies in the HOA.

Above we have the original presentation of ADMIXTURE results for K=10-12. It must be said that the cross validation score is lowest (optimal) for K=12 but that this value is only slightly smaller than those for K=9-14, which make a plateau (fig. S2). 

Therefore their use of K=10 and K=11 is justified, particularly because it is also interesting to turn off the old amalgamation reflected in the Ethiopic (Ari, Woloytta) and Ethio-Somali (Cushitic, Ethiopian Semitic) components, and that is done by using K=10 instead of the optimal K=12.

This issue is best perceived in the FST distances table (within text S1), which I include here with some convenient annotations:

The red-orange colored frames (as well as the red notes on the components) in the table above were added by me to better illustrate the meaning of these FST values:

• The red frames capture two groups of components with very low differences (<50): West Asia-Europe and West-East Africa.
• The dark orange frames indicate other two groups with quite low distances (<70): South-Central Asian and the West Eurasian core.
• The lighter orange frames indicate large clusters of middling distances (<125) of continental nature: Eurasian and African. 
• Intercontinental FST scores are systematically larger, for example European-West African is 176, while European East African ("Nilo-Saharan") is 172, only slightly smaller. 

K=12

It is quite apparent that there are three components that overflow these continental boundaries:

• The so-called Mahgrebi (North African) has some extra affinity with the Ethiopic (Omotic) component, and vice versa. These two components fall otherwise within my approximative continental boxes but they still show lower scores for all the other components of the other "box". This is consistent with their nature as Afro-Eurasian admixed components, each with its own proportions.
• The Ethio-Somali (Cushitic?) component is actually more intermediate than the previous ones: although its strongest affiliation is towards Eurasia and particularly with the North African and Arabian components, it also shows strong affinity with the core African components (East and West African, i.e. Nilo-Saharan and Niger-Congo). This is consistent with the other evidence in this study that reveals it as an ancient Afro-Asian mix.

I must mention here that some of the labels used by the authors are not at all the ones I would have chosen and this is particularly true re. the Nilo-Saharan (light blue) component, which peaks among the Sandawe (Aboriginal East Africans from Southern Tanzania, speaking a click language), the Anuak (Nilo-Saharan Ethiopians) and the Gumuz (other Ethiopians of quite dubious Nilo-Saharan linguistic affiliation). Hence I prefer to call it East African or East African 1. 

The authors conclude with the following remarks (emphasis mine):

We find that most of the non-African ancestry in the HOA can be assigned to a distinct non-African origin Ethio-Somali ancestry component, which is found at its highest frequencies in Cushitic and Semitic speaking HOA populations (Table 2, Figure 2). In addition to verifying that most HOA populations have substantial non-African ancestry, which is not controversial [11]–[14], [16], we argue that the non-African origin Ethio-Somali ancestry in the HOA is most likely pre-agricultural. In combination with the genomic evidence for a pre-agricultural back-to-Africa migration into North Africa [43], [61] and inference of pre-agricultural migrations in and out-of-Africa from mitochondrial and Y chromosome data [13], [32]–[37], [47], [99]–[102], these results contribute to a growing body of evidence for migrations of human populations in and out of Africa throughout prehistory [5]–[7] and suggests that human hunter-gatherer populations were much more dynamic than commonly assumed.

We close with a provisional linguistic hypothesis. The proto-Afro-Asiatic speakers are thought to have lived either in the area of the Levant or in east/northeast Africa [8], [107], [108]. Proponents of the Levantine origin of Afro-Asiatic tie the dispersal and differentiation of this language group to the development of agriculture in the Levant beginning around 12 ka [8], [109], [110]. In the African-origins model, the original diversification of the Afro-Asiatic languages is pre-agricultural, with the source population living in the central Nile valley, the African Red Sea hills, or the HOA [108], [111]. In this model, later diversification and expansion within particular Afro-Asiatic language groups may be associated with agricultural expansions and transmissions, but the deep diversification of the group is pre-agricultural. We hypothesize that a population with substantial Ethio-Somali ancestry could be the proto-Afro-Asiatic speakers. A later migration of a subset of this population back to the Levant before 6 ka would account for a Levantine origin of the Semitic languages [18] and the relatively even distribution of around 7% Ethio-Somali ancestry in all sampled Levantine populations (Table S6). Later migration from Arabia into the HOA beginning around 3 ka would explain the origin of the Ethiosemitic languages at this time [18], the presence of greater Arabian and Eurasian ancestry in the Semitic speaking populations of the HOA (Table 2, S6), and ROLLOFF/ALDER estimates of admixture in HOA populations between 1–5 ka (Table 1).

K=12 detail for a fraction of the Horn of Africa and distribution of the four main components

The oldest know rope and spoon

Noticias de Prehistoria-Prehistoria al Día[es] mentions this week two quite impressive archaeological findings that illustrate the richness of the lives of our remote ancestors.

Ardales petrified rope

A petrified rope (right) was found in the cave of Ardales (Andalusia). The rope now transformed into stone by the same mechanism that forms stalactites was apparently tended to allow access to a remote section of the cave rich in rock art. 

Other findings are several fixed lamps created by the breaking of stalagmites, as well as several portable lamps found earlier in the research. In these lamps marrow or wax was burned. 

The rope has been indirectly dated to c. 30 Ka BP, what in Southern Iberia would still be the Aurignacian period.

Evidences of ropes of slightly more recent age are also known from Moravia (Gravettian) thanks to patterns left on their famous terracotta figurines.

The other not less spectacular finding comes from Russia, where an ivory spoon was found in Avdeevo cave, near Kursk. It belongs to the Gravettian period and is dated c. 23-22 Ka BP. 

The same site also provided a beautiful spatula almost identical to another one previously found in Kostenki, as well as other materials including a "Venus" figurine.

These findings illustrate the wealth of creativity displayed by the Paleolithic hunter-gatherers, not so different from ours after all.

Avdeevo ivory spoon

A genetic legacy of North Africa: mtDNA U6 under the microscope

An excellent new study on mtDNA haplogroup U6 has been published this week:

Bernard Sechel et al., The history of the North African mitochondrial DNA haplogroup U6 gene flow into the African, Eurasian and American continents. BMC Evolutionary Biology 2014. Open access → LINK [doi:10.1186/1471-2148-14-109]

Abstract (provisional)

Background

Complete mitochondrial DNA (mtDNA) genome analyses have greatly improved the phylogeny and phylogeography of human mtDNA. Human mitochondrial DNA haplogroup U6 has been considered as a molecular signal of a Paleolithic return to North Africa of modern humans from southwestern Asia.

Results

Using 230 complete sequences we have refined the U6 phylogeny, and improved the phylogeographic information by the analysis of 761 partial sequences. This approach provides chronological limits for its arrival to Africa, followed by its spreads there according to climatic fluctuations, and its secondary prehistoric and historic migrations out of Africa colonizing Europe, the Canary Islands and the American Continent.

Conclusions

The U6 expansions and contractions inside Africa faithfully reflect the climatic fluctuations that occurred in this Continent affecting also the Canary Islands. Mediterranean contacts drove these lineages to Europe, at least since the Neolithic. In turn, the European colonization brought different U6 lineages throughout the American Continent leaving the specific sign of the colonizers origin.

Figure 1 Surface maps, based on HVI frequencies (in o/oo), for total U6 (U6), total U6a
(Tot U6a), U6a without 16189 (U6a), U6a with 16189 (U6a-189), U6b'd, U6c, U6b and U6d.

U6 can be considered a somewhat strange haplogroup. While it is derived from U (and hence from R and N), which has an Asian origin, it seems to have expanded from NW Africa, more specifically from the Northern mountainous areas of the Moroccan state, a country known as Rif or in the native Tamazigh language Arif (of which Rif is an Arabized version), not the usual place one tends to imagine as the origin of any human expansion wave. 

Actually there is at least one important cultural expansion from that area: the Oranian or Iberomaurusian culture of the Mid-to-Late Upper Paleolithic. To some extent at least the expansion of this lineage is probably associated to this ancient culture. 

Whatever the case, U6 is not a common haplogroup: its highest peak in frequency is in the Canary Islands (16%), followed by North-West Africa (5-9%). Then come Portugal and its insular colonies, as well as Cape Verde and Ethiopia (~3%) and then there is some scatter in Spain, West Africa, NE Africa and peninsular Arabia (~1%), as well as in some other parts of Europe, Africa and West Asia (<1%). 

On the other hand it is one of the four basal branches of the major West Eurasian haplogroup U (U5 and U2'3'4'7'8'9 are more common, while U1 is even rarer and less studied), so understanding U6 seems important to better understand its parent lineage. 

Therefore this new study with its great wealth of detail and care is much welcome.

Chronological estimates and expansion patterns of U6

It may surprise you that I am even in tentative agreement with the chronological estimates for U6 and its subclades, listed in tables 2 and 3. But it is for a good reason: they make sense (assuming a reasonable CI). And the fact that they seem to make sense is probably because the authors took great care to calibrate the ages for this lineage, using as main (but not only) reference a Canadian derived lineage that seems to be a colonial founder effect. 

Anyhow all these dates should be considered as center-points of a variably wider range of possibilities, the so-called confidence interval (CI) or error margin (em). If we do that, as we should, we get the "power" to stretch the figures forth and back as need be to some extent without losing consistency, and that alone should be enough to get the estimates fit better with the material evidence (archaeology mostly). 

The authors actually mention some of those CIs in a lengthy section dedicated to explore the possible patterns of U6 spread in Africa and elsewhere.

Interestingly they suggest that the first radiation of U6 took place from NW Africa in largely eastwards direction, belonging almost necessarily to the Iberomaurusian (Oranian) culture:

This first African expansion of U6a in the Maghreb was suggested in a previous analysis [6]. This radiation inside Africa occurred in Morocco around 26 kya (Table 2) and, ruling out the earlier Aterian, we suggested the Iberomaurusian as the most probable archaeological and anthropological correlate of this spread in the Maghreb [6]. Others have pointed to the Dabban industry in North Africa and its supposed source in the Levant, the Ahmarian, as the archaeological footprints of U6 coming back to Africa [7,9]. However, we disagree for several reasons: firstly, they most probably evolved in situ from previous cultures, not being intrusive in their respective areas [42-44]; second, their chronologies are out of phase with U6 and third, Dabban is a local industry in Cyrenaica not showing the whole coastal expansion of U6. In addition, recent archaeological evidence, based on securely dated layers, also points to the Maghreb as the place with the oldest implantation of the Iberomaurusian culture [45], which is coincidental with the U6 radiation from this region proposed in this and previous studies [6].

Some millennia later, U62 appears to expand in Ethiopia, while, as mentioned, U6a1 does the same in Europe (mostly Western Iberia) and other sister lineages do the same in NW Africa itself.

A second wave of radiation corresponds to the early Holocene:

Basic clusters like U6b, U6c and U6d also emerged within a window between 13 to 10 kya (Table 2). U6b lineages spread from the Maghreb, through the Sahel, to West Africa and the Canary Islands (U6b1a), and are also present from the Sudan to Arabia, but not detected in Ethiopia. In contrast, U6c and U6d are more localized in the Maghreb. Further spreads of secondary U6a branches are also apparent, going southwards to Sahel countries and  reaching West Africa (U6a5a). Autochthonous clusters in sub-Saharan Africa first appeared at around 7 kya (U6a5b), coinciding with a period of gradual desiccation that would have obliged pastoralists to abandon many desert areas [52]. Consequently, no more U6 lineages in the Sahel are detected, while later expansions continued in West Africa (U6a3f, U6a3c, and U6b3) and the Maghreb with an additional spread to the Mediterranean shores of Europe involving U6b2, U6a3e, U6a1b and U6a3b1.

For easier understanding of the U6 phylogeny and its sometimes hard to interpret migration patterns, I made up the following graph, based on the supplemental material of this study:

U6 phylogeny, color coded by regions:

• North Africa
• Europe
• Tropical Africa
• West Asia
• intermediate colors: equal weight between two regions, black: undecided
• italic type: unnamed lineages

I must say that, I have some doubts about the exact origins of several subhaplogroups, notably:

• U6a is so diverse in some branches that it is difficult to identify it as unmistakably of NW African origin. NW Africa still gets the greatest weight (3/7) but not a clear majority.
• In U6b Tropical African lineages weight 4.5/10, while NW African ones weight only 3/10. It is a good candidate for expansion from the "Wet Sahara" indeed.
• In U6c1 European and NW African lineages weight exactly the same, although I guess that it may be reasonable to imagine Andalusian U6c1c as derived from North Africa.

However overall U6, as well as its derived lineages U6b'd and U6c clearly originated in NW Africa, so I understand that, when unclear, NW Africa gets the benefit of doubt for the derived origins.