April 13, 2018

R1ans still at large (or, the story of India)

Ten ago, in the pre-ancient DNA "Dark Ages" a big debate raged on about the origin of R1a  men in India. The stage had been set even earlier, by the pioneering Eurasian heartland paper which was the first (to my memory) to link M17 with steppe migrations and Indo-Iranians. Yet, there was pushback as the distribution of M17 was better described, and people started using Y-STRs to try to date and place phylogeographically its migrations.

The two poles of the debate were the "Out-of-India", which relied primarily on Y-STR based time estimates that seemed very old (even Paleolithic, if one used the wrong mutation rate) in India, and the "Into-India" which thought that the R1a distribution pointed to its being brought into India by the Indo-Aryans in the conventional ~3,500BC time frame of the "Aryan Invasion Theory" (AIT).

AIT has been much maligned because it has been received as a Western colonialist imposition on Indian history: a way to claim that Indian civilization was not native but European in origin. Europeans were certainly guilty of misusing AIT: for British colonials it represented a precedent for their colonization of India; for German National Socialists it was evidence for the greatness of the Aryan race and its past expansions eastward. It also played into internal Indian politics, espoused by some as a means of furthering their superiority as either descendants of "Aryan conquerors" or as oppressed victims of the same.

Of course, a misuse of a theory does not mean it is wrong, and if a new preprint based on ancient and modern DNA is correct, it means that AIT was basically correct: Indo-Aryans did come to India in the Late Bronze Age, via the steppe, and ultimately from central Europe.

The opposing Out-of-India theory is all but dead, although failed theories often have a long half-life, especially if they are espoused for psycho-political reasons. I would argue that Out-of-India was dead for thousands of years before it was conceived, since even in Homer's time it was known that "India" was not "one thing" but was peopled by Indians in the north and "Eastern Ethiopians" in the south (which differed from their western "actual" Ethiopians of Africa by their possession of straight rather than curly hair). These were the "Ancestral North Indians" and "Ancestral South Indians" that modern science has revealed. Out-of-India is little more than a nationalistic myth functioning as an antidote to this basic dichotomy, a way to imbue India's diverse citizens with a myth of common origins.

Yet, proponents of AIT (who have a non-trivial overlap with R1an enthusiasts) are also scratching their heads because of the 27 ancient South Asian males from South Asia studied in the preprint there is exactly one R1a, who also happened to live after the time of the Buddha and not during the Bronze Age.

Both OIT enthusiasts (who expected copious and abundant R1a in India and its environs since the Paleolithic) and AIT/R1an enthusiasts (who expected to see it come in c. 3,500BC) are bound to be disappointed.

Perhaps the R1a Indo-Aryans did come to South Asia in a conventional AIT time frame and they haven't been sampled. Or, maybe they were, indeed, there, but were not R1ans. Or, maybe both sides missed the bigger story which is that the Indo-Aryans (so closely associated with India today) were simply not there as early as people have thought. 

bioRxiv: doi: https://doi.org/10.1101/292581

The Genomic Formation of South and Central Asia

Vagheesh M Narasimhan, Nick J Patterson et al.

The genetic formation of Central and South Asian populations has been unclear because of an absence of ancient DNA. To address this gap, we generated genome-wide data from 362 ancient individuals, including the first from eastern Iran, Turan (Uzbekistan, Turkmenistan, and Tajikistan), Bronze Age Kazakhstan, and South Asia. Our data reveal a complex set of genetic sources that ultimately combined to form the ancestry of South Asians today. We document a southward spread of genetic ancestry from the Eurasian Steppe, correlating with the archaeologically known expansion of pastoralist sites from the Steppe to Turan in the Middle Bronze Age (2300-1500 BCE). These Steppe communities mixed genetically with peoples of the Bactria Margiana Archaeological Complex (BMAC) whom they encountered in Turan (primarily descendants of earlier agriculturalists of Iran), but there is no evidence that the main BMAC population contributed genetically to later South Asians. Instead, Steppe communities integrated farther south throughout the 2nd millennium BCE, and we show that they mixed with a more southern population that we document at multiple sites as outlier individuals exhibiting a distinctive mixture of ancestry related to Iranian agriculturalists and South Asian hunter-gathers. We call this group Indus Periphery because they were found at sites in cultural contact with the Indus Valley Civilization (IVC) and along its northern fringe, and also because they were genetically similar to post-IVC groups in the Swat Valley of Pakistan. By co-analyzing ancient DNA and genomic data from diverse present-day South Asians, we show that Indus Periphery-related people are the single most important source of ancestry in South Asia — consistent with the idea that the Indus Periphery individuals are providing us with the first direct look at the ancestry of peoples of the IVC — and we develop a model for the formation of present-day South Asians in terms of the temporally and geographically proximate sources of Indus Periphery-related, Steppe, and local South Asian hunter-gatherer-related ancestry. Our results show how ancestry from the Steppe genetically linked Europe and South Asia in the Bronze Age, and identifies the populations that almost certainly were responsible for spreading Indo-European languages across much of Eurasia.


April 10, 2018

The slow death of Out of Africa

The significance of the discovery of modern humans in Arabia >85kya is that it provides a second spot (other than Israel) were modern humans existed outside Africa long before the alleged 60kya blitz out of the continent. We now have modern humans outside Africa in roughly two locations (Israel and Arabia), and three time slices (~175-85kya) in Misliya, Shkul/Qafzeh, and Al Wusta-1. It is no longer tenable to claim that these modern humans "died out" to make way for the alleged 60kya OoA event.

An important implication of pre-60kya Eurasians not dying out is that in all likelihood mtDNA haplogroup L3 and Y-chromosome haplogroup E originated in Eurasia, not Africa, and represent major Eurasian admixture into Africa.

Out of Africa theory is not dead (yet), but it resembles Rocky Balboa taking punch after punch round after round over the last 10 years or so. Will it make a cinematic last round comeback and prove itself, or will it be dealt a knockout punch in the near future? 

Nature Ecology and Evolution (2018) doi:10.1038/s41559-018-0518-2

Homo sapiens in Arabia by 85,000 years ago

Understanding the timing and character of the expansion of Homo sapiens out of Africa is critical for inferring the colonization and admixture processes that underpin global population history. It has been argued that dispersal out of Africa had an early phase, particularly ~130–90 thousand years ago (ka), that reached only the East Mediterranean Levant, and a later phase, ~60–50 ka, that extended across the diverse environments of Eurasia to Sahul. However, recent findings from East Asia and Sahul challenge this model. Here we show that H. sapiens was in the Arabian Peninsula before 85 ka. We describe the Al Wusta-1 (AW-1) intermediate phalanx from the site of Al Wusta in the Nefud desert, Saudi Arabia. AW-1 is the oldest directly dated fossil of our species outside Africa and the Levant. The palaeoenvironmental context of Al Wusta demonstrates that H. sapiens using Middle Palaeolithic stone tools dispersed into Arabia during a phase of increased precipitation driven by orbital forcing, in association with a primarily African fauna. A Bayesian model incorporating independent chronometric age estimates indicates a chronology for Al Wusta of ~95–86 ka, which we correlate with a humid episode in the later part of Marine Isotope Stage 5 known from various regional records. Al Wusta shows that early dispersals were more spatially and temporally extensive than previously thought. Early H. sapiens dispersals out of Africa were not limited to winter rainfall-fed Levantine Mediterranean woodlands immediately adjacent to Africa, but extended deep into the semi-arid grasslands of Arabia, facilitated by periods of enhanced monsoonal rainfall.


March 25, 2018

Statistical Palaeoafricans

According to a new preprint by Durvasula and Sankararaman (D+S):
Using this method, we find that ~7.97±0.6% of the genetic ancestry from the West African Yoruba population traces its origin to an unidentified, archaic population
This ~8% matches well the ~9% of "West Africa A" in Yoruba of the model of Skoglund et al. Figure 3D. If "West Africa A" corresponds to the Archaic Ghost of D+S, then the Mende have the most of it at ~13%.

I have long maintained that the higher genetic diversity of extant Sub-Saharan Africans is the result of admixture between "Afrasians" (a population that spawned Eurasians and much of the ancestry of Sub-Saharans and which had "low" (Eurasian-level) of genetic diversity) and multiple layers of "Palaeoafricans". It would seem that one such layer has now been discovered.

Where did the Afrasians live? Recent developments pushed back the presence of modern humans in both North Africa and the Middle East, making both regions highly competitive as the cradle of the Afrasians. The odds for Sub-Saharan Africa have greatly diminished also by the discovery of late non-sapiens H. naledi in South Africa (which was naively postulated as a cradle based on the presence there today of genetically diverse San Bushmen, but who are not descendants of even Late Pleistocene South Africans), as well as of the archaic component in the genomes of West Africans. These discoveries pile up on top of known archaic skulls of late provenance in both Central and West Africa.

Remember though, that the archaic admixture in West Africans is "less archaic" (more closely related to H. sapiens) than the Neandertal/Denisovan ancestry which contributed to extant Eurasians. All Africans (modern or archaic) are a branch within the phylogeny of Eurasians, with Australoids (and now apparently East Asians too) having the deepest known strain of human ancestry inherited from the elusive Denisovans.

Long Live the 25th March, 1821

January 26, 2018

Out of Africa: a theory in crisis

The sensational discovery of modern humans in the Levant 177-194 thousand years ago should cause a rethink of the currently held Out-of-Africa orthodoxy.

By Out-of-Africa, I mean here the origin of anatomically modern humans, as opposed to the earlier origin of the genus Homo or the later origin of behaviorally fully modern humans.

Two main pieces of evidence supported the conventional OOA theory:

1. The observation that modern Eurasians possess a subset of the genetic variation of modern Africans.
2. The greater antiquity of AMH humans in the African rather than the Eurasian palaeoanthropological record.

Both these observations are in crisis.

1a. The oldest African fossil AMH is in North Africa (Morocco, Jebel Irhoud); modern genetic variation does not single out this region as a potential source of modern humans. In short, modern genetic variation has nothing to say about where AMH originated.
1b. Eurasians can no longer be seen as a subset of Africans, given that they possess genetic variation from Denisovans, a layer of ancestry earlier than all extant AMH. While it is still true that most Eurasian genetic material is a subset of that of modern Africans, it is also true that the deepest known lineage of humans is the Denisovan-Sima de los huesos, with no evidence for any deeper African lineage. Within humans as a whole, Africans possess a subset of Eurasian genetic variation.
2a. African priority received a boost by 0.1My by the redating of Jebel Irhoud last year. And, non-African AMH received a boost of 0.05My by the Hershkovitz et al. paper yesterday. A very short time ago, Ethiopia boasted the oldest AMH by 0.07My and now it's tied with the Levant and beaten by Morocco. It's a bit silly to argue for temporal priority based on the spotty and ever-shifting palaeoanthropological record.
2b. It is virtually untenable to consider the ~120,000 year old Shkul/Qafzeh hominins as a failed Out-of-Africa, since it now seems that they may have been descendants from the Mislya Cave population of >50,000 or even >100,000 years earlier.

I had previously supported a "two deserts" theory of human origins in which AMH originated in North Africa (Sahara) and then left Africa >100kya as evidenced by the Shkul/Qafzeh hominins and/or the Nubian technocomplex in Arabia. While I am still convinced that AMH originated somewhere in North Africa or the Near East, I am less certain as to where.

Science 26 Jan 2018: Vol. 359, Issue 6374, pp. 456-459 DOI: 10.1126/science.aap8369

The earliest modern humans outside Africa

Israel Hershkovitz et al.

To date, the earliest modern human fossils found outside of Africa are dated to around 90,000 to 120,000 years ago at the Levantine sites of Skhul and Qafzeh. A maxilla and associated dentition recently discovered at Misliya Cave, Israel, was dated to 177,000 to 194,000 years ago, suggesting that members of the Homo sapiens clade left Africa earlier than previously thought. This finding changes our view on modern human dispersal and is consistent with recent genetic studies, which have posited the possibility of an earlier dispersal of Homo sapiens around 220,000 years ago. The Misliya maxilla is associated with full-fledged Levallois technology in the Levant, suggesting that the emergence of this technology is linked to the appearance of Homo sapiens in the region, as has been documented in Africa.


January 05, 2018

Eurasian origin of mtDNA L3 and Y-chromosome DE

I've argued for a similar scenario for years, so it's nice to see a preprint on the topic.

bioRxiv doi: https://doi.org/10.1101/233502

Carriers of mitochondrial DNA macrohaplogroup L3 basic lineages migrated back to Africa from Asia around 70,000 years ago.

Vicente M Cabrera et al.

Background: After three decades of mtDNA studies on human evolution the only incontrovertible main result is the African origin of all extant modern humans. In addition, a southern coastal route has been relentlessly imposed to explain the Eurasian colonization of these African pioneers. Based on the age of macrohaplogroup L3, from which all maternal Eurasian and the majority of African lineages originated, that out-of-Africa event has been dated around 60-70 kya. On the opposite side, we have proposed a northern route through Central Asia across the Levant for that expansion. Consistent with the fossil record, we have dated it around 125 kya. To help bridge differences between the molecular and fossil record ages, in this article we assess the possibility that mtDNA macrohaplogroup L3 matured in Eurasia and returned to Africa as basic L3 lineages around 70 kya. Results: The coalescence ages of all Eurasian (M,N) and African L3 lineages, both around 71 kya, are not significantly different. The oldest M and N Eurasian clades are found in southeastern Asia instead near of Africa as expected by the southern route hypothesis. The split of the Y-chromosome composite DE haplogroup is very similar to the age of mtDNA L3. A Eurasian origin and back migration to Africa has been proposed for the African Y-chromosome haplogroup E. Inside Africa, frequency distributions of maternal L3 and paternal E lineages are positively correlated. This correlation is not fully explained by geographic or ethnic affinities. It seems better to be the result of a joint and global replacement of the old autochthonous male and female African lineages by the new Eurasian incomers. Conclusions: These results are congruent with a model proposing an out-of-Africa of early anatomically modern humans around 125 kya. A return to Africa of Eurasian fully modern humans around 70 kya, and a second Eurasian global expansion by 60 kya. Climatic conditions and the presence of Neanderthals played key roles in these human movements.