Morphological and mtDNA analysis of Mezzena mandible

 

I've written about late Neandertals becoming more AMH-like, and a new study on an Italian specimen that postdates the arrival of AMH in Europe lends some further support to that idea.
The Mezzena jaw has Neandertal mtDNA and shares a number of morphological traits with other Neandertals, but its overall shape places it within the cluster of modern humans  (triangles; figure on the left). Notice also that Qafzeh 9 (Q9) and Shkul V (SV) are also within the cluster of modern humans, and Spy 1 (a Neandertal) is actually closer to modern humans than to other Neandertals.
From the paper:

The position on the scatter plot of our specimen of interest, Mezzena, has been calculated a posteriori. Unsurprisingly, the Mezzena mandible does not present any particular affinities with mid-Pleistocene specimens. It is most similar to AMHs being positioned within the H. sapiens cloud of points and the DFA classifies the specimen with modern humans (Table S7). Especially its shape is similar to that of Ohalo II and to a lesser extent to the recent modern human specimen China5. However, it should be noted that its position also indicates affinities with some Neanderthal specimens: the late Neanderthal Spy 1 and Saint-Césaire, the Near-East specimens Tabūn II and Amud 1, and to a lesser extent the classic Neanderthals La Ferrassie 1 and Guattari III (Figure 2).

According to the authors:

In this light, we can interpret the position of the Mezzena mandible which stands within the modern human shape space, while presenting strong shape similarities with some Neanderthal specimens. Such a conflicting taxonomical position is not surprising, considering the geological age of the mandible [30]. Indeed, numerous late Neanderthals such as Spy 1, Saint Césaire and the Near-East mandibles Amud 1 and Tabun II possess hints of a chin (i.e. tuber symphyseo) though not a true modern human morphology [37], [51]. Late Neanderthals lived in area where AMHs might have been already present [2], [23], [52], while the Levantine fossils are displaying a less derived Neanderthal morphology [35], [36]. 

Therefore, in our view, this change in morphology of the mandibular chin among the fossils of Mezzena and other late Neanderthals could have been the result of a small degree of interbreeding with AMHs.

It would be interesting to sequence Mezzena to confirm the existence of AMH admixture.
PLoS ONE 8(3): e59781. doi:10.1371/journal.pone.0059781
Possible Interbreeding in Late Italian Neanderthals? New Data from the Mezzena Jaw (Monti Lessini, Verona, Italy)
Silvana Condemi et al.
In this article we examine the mandible of Riparo Mezzena a Middle Paleolithic rockshelter in the Monti Lessini (NE Italy, Verona) found in 1957 in association with Charentian Mousterian lithic assemblages. Mitochondrial DNA analysis performed on this jaw and on other cranial fragments found at the same stratigraphic level has led to the identification of the only genetically typed Neanderthal of the Italian peninsula and has confirmed through direct dating that it belongs to a late Neanderthal. Our aim here is to re-evaluate the taxonomic affinities of the Mezzena mandible in a wide comparative framework using both comparative morphology and geometric morphometrics. The comparative sample includes mid-Pleistocene fossils, Neanderthals and anatomically modern humans. This study of the Mezzena jaw shows that the chin region is similar to that of other late Neanderthals which display a much more modern morphology with an incipient mental trigone (e.g. Spy 1, La Ferrassie, Saint-Césaire). In our view, this change in morphology among late Neanderthals supports the hypothesis of anatomical change of late Neanderthals and the hypothesis of a certain degree of interbreeding with AMHs that, as the dating shows, was already present in the European territory. Our observations on the chin of the Mezzena mandible lead us to support a non abrupt phylogenetic transition for this period in Europe.
Link

High-quality Neandertal genome online

The Max Planck institute has posted their high-coverage Neandertal genome on their site. The data can be downloaded from here. They had done the same with the high-quality Denisova genome, and it's great that they're making data available ahead of the official scientific publication, as this allows others to start using it much earlier.
From their site:

The genome sequence was generated from a toe bone discovered in Denisova Cave in southern Siberia in 2010.  The bone is described in Mednikova (Ethnology & Anthropology of Eurasia 2011. 39: 129-138).
DNA sequences were generated on the Illumina HiSeq platform and constitute an average 50-fold coverage of the genome. 99.9% of the 1.7GB of uniquely mappable DNA sequences in the human genome are covered at least ten times.
Contamination with modern human DNA, estimated from mitochondrial and nuclear DNA sequences, is around 1%.

It then appears that Neandertals occupied the same cave as the elusive Denisovans. When? I guess we'll have to wait to find out, but the preliminary genetic analysis shown on the figure (top-left) makes it clear that the "Altai" specimen marked in red which is the source of the high-coverage Neandertal genome does indeed group with other Neandertals, while Denisova is more related to Neandertals than to modern humans.
I've highlighted this before, but it bears repeating: divergence between Neandertals and Denisovans --who were in the same place (Denisova cave), perhaps some thousands of years apart-- seems to exceed that found between any two modern human groups which span the entire Earth.

New Neandertal remains from Mani

The age and cave origin of these remains may conceivably make them useful for ancient DNA studies.
Journal of Human Evolution doi:10.1016/j.jhevol.2013.02.002
New Neanderthal remains from Mani peninsula, Southern Greece: The Kalamakia Middle Paleolithic cave site
Katerina Harvati et al.
The Kalamakia cave, a Middle Paleolithic site on the western coast of the Mani peninsula, Greece, was excavated in 1993–2006 by an interdisciplinary team from the Ephoreia of Paleoanthropology and Speleology (Greek Ministry of Culture) and the Muséum national d'Histoire naturelle (Paris). The site is dated to between ca. 100,000 and >39,000 years BP (Before Present) and has yielded Mousterian lithics, a rich fauna, and human remains from several layers. The latter include 10 isolated teeth, a cranial fragment and three postcranial elements. The remains represent at least eight individuals, two of them subadults, and show both carnivore and anthropogenic modifications. They can be identified as Neanderthal on the basis of diagnostic morphology on most specimens. A diet similar to that of Neanderthals from mixed habitat is suggested by our analysis of dental wear (occlusal fingerprint analysis) and microwear (occlusal texture microwear analysis), in agreement with the faunal and palynological analyses of the site. These new fossils significantly expand the Neanderthal sample known from Greece. Together with the human specimens from Lakonis and Apidima, the Kalamakia human remains add to the growing evidence of a strong Neanderthal presence in the Mani region during the Late Pleistocene.
Link

Extreme mobility in the late Pleistocene (Shaw and Stock 2013)

The idea of Pleistocene remains having "extremely active and mobile lives" is consistent with the hypothesis that people moved around during prehistory, and did not simply grow roots after their initial colonization of the planet, as some models of "Paleolithic continuity" have affirmed.
Journal of Human Evolutiondoi:10.1016/j.jhevol.2013.01.004
Extreme mobility in the Late Pleistocene? Comparing limb biomechanics among fossil Homo, varsity athletes and Holocene foragers
Colin N. Shaw, Jay T. Stock
Descriptions of Pleistocene activity patterns often derive from comparisons of long bone diaphyseal robusticity across contemporaneous fossilized hominins. The purpose of this study is to augment existing understanding of Pleistocene hominin mobility patterns by interpreting fossil variation through comparisons with a) living human athletes with known activity patterns, and b) Holocene foragers where descriptions of group-level activity patterns are available. Relative tibial rigidity (midshaft tibial rigidity (J)/midshaft humeral rigidity (J)) was compared amongst Levantine and European Neandertals, Levantine and Upper Palaeolithic Homo sapiens, Holocene foragers and living human athletes and controls. Cross-country runners exhibit significantly (p < 0.05) greater relative tibial rigidity compared with swimmers, and higher values compared with controls. In contrast, swimmers displayed significantly (p < 0.05) lower relative tibial rigidity than both runners and controls. While variation exists among all Holocene H. sapiens, highly terrestrially mobile Later Stone Age (LSA) southern Africans and cross-country runners display the highest relative tibial rigidity, while maritime Andaman Islanders and swimmers display the lowest, with controls falling between. All fossil hominins displayed relative tibial rigidity that exceeded, or was similar to, the highly terrestrially mobile Later Stone Age southern Africans and modern human cross-country runners. The more extreme skeletal structure of most Neandertals and Levantine H. sapiens, as well as the odd Upper Palaeolithic individual, appears to reflect adaptation to intense and/or highly repetitive lower limb (relative to upper limb) loading. This loading may have been associated with bipedal travel, and appears to have been more strenuous than that encountered by even university varsity runners, and Holocene foragers with hunting grounds 2000–3000 square miles in size. Skeletal variation among the athletes and foraging groups is consistent with known or inferred activity profiles, which support the position that the Pleistocene remains reflect adaptation to extremely active and mobile lives.
Link

Late Middle Pleistocene teeth from South China (Liu et al. 2013)

From the paper:

The Panxian Dadong P3 falls in the upper left quadrant, an area that, with the exception of two out of the nine Atapuerca-SH specimens and S7-34, is exclusively occupied by recent humans. Thus this geometric morphometric analysis indicates that the general crown conformation of the Panxian Dadong P3 resembles some European Middle Pleistocene hominins, Chinese Upper Pleistocene hominins, and particularly the recent human specimens. 

According to the above comparisons, the Panxian Dadong P3 preserves some primitive and highly polymorphic traits, but in general its conformation is derived. Its occlusal morphology is simple, and the contour is symmetrical with a lingual cusp that is narrower than the buccal one. All these features make the Panxian Dadong P3 most similar to Upper Pleistocene hominins and recent humans in our comparative samples.

I suspect that the age of these teeth will render them useless for ancient DNA work.
Journal of Human Evolution doi:10.1016/j.jhevol.2012.10.012
Late Middle Pleistocene hominin teeth from Panxian Dadong, South China
Wu Liu et al.
The hominin teeth and evidence of hominin activities recovered from 1991 to 2005 at the Panxian Dadong site in South China are dated to the late Middle Pleistocene (MIS 8–6 or ca. 130–300 ka), a period for which very little is known about the morphology of Asian populations. The present study provides the first detailed morphometric description and comparisons of four hominin teeth (I1, C1, P3 and P3) from this site. Our study shows that the Panxian Dadong teeth combine archaic and derived features that align them with Middle and Upper Pleistocene fossils from East and West Asia and Europe. These teeth do not display any typical Neanderthal features and they are generally more derived than other contemporaneous populations from Asia and Africa. However, the derived traits are not diagnostic enough to specifically link the Panxian Dadong teeth to Homo sapiens, a common problem when analyzing the Middle Pleistocene dental record from Africa and Asia. These findings are contextualized in the discussion of the evolutionary course of Asian Middle Pleistocene hominins, and they highlight the necessity of incorporating the Asian fossil record in the still open debate about the origin of H. sapiens.
Link

Our rabbit-hunting ancestors (Fa et al. 2013)

From the paper:

Relative to other mammal groups, rabbit bone abundance was always significantly higher during the Upper Palaeolithic (76%) and Mesolithic (59%) than during the Middle Palaeolithic (Fig. 4). The difference between the average rabbit remains and that of cervids, the second most abundant prey item, were less than 10% during the Mousterian. In contrast, during the Upper Palaeolithic and Mesolithic, the difference between the rabbit and the second-most important prey items was over 60% and 20%, respectively. After the rabbit, large ungulates (caprids, cervids and equids) were relatively important during the Middle and Upper Palaeolithic, while caprids, cervids and suids took that place during the Mesolithic (Fig. 4).

and:

Our evidence indicates that hominin diets may have changed from one dependent on large mammals during the Middle Palaeolithic to diets dominated by smaller species in the Upper Palaeolithic, in particular by the wild rabbit. The explanation for this transition is either that climate change negatively impacted large mammal populations, forcing prehistoric people to incorporate smaller vertebrate species into their diets, or that people themselves negatively impacted large mammal populations, which in turn forced foragers to add smaller species to their diets.

I am not sure how modern hunter-gatherers hunt rabbits, but I would think that trapping, or some type of slingshot or blowdart would be ideal for this small and fast-moving animal. Did Neandertals simply lack efficient technology to capture rabbit, or is there some other reason why they underutilized the species?
Journal of Human Evolution DOI: 10.1016/j.jhevol.2013.01.002
Rabbits and hominin survival in Iberia
John E. Fa et al.
High dependence on the hunting and consumption of large mammals by some hominins may have limited their survival once their preferred quarry became scarce or disappeared. Adaptation to smaller residual prey would have been essential after the many large-bodied species decreased in numbers. We focus on the use of a superabundant species, the rabbit, to demonstrate the importance of this taxon in Iberia as fundamental to predators. We show that the use of the rabbit over time has increased, and that there could have been differential consumption by Neanderthals and Anatomically Modern Humans (AMH). Analysis of bone remains from excavations throughout Iberia show that this lagomorph was a crucial part of the diet of AMH but was relatively unutilised during the Mousterian, when Neanderthals were present. We first present changes in mammalian biomass and mean body mass of mammals over 50,000 years, to illustrate the dramatic loss of large mammalian fauna and to show how the rabbit may have contributed a consistently high proportion of the available game biomass throughout that period. Unlike the Italian Peninsula and other parts of Europe, in Iberia the rabbit has provided a food resource of great importance for predators including hominins. We suggest that hunters that could shift focus to rabbits and other smaller residual fauna, once larger-bodied species decreased in numbers, would have been able to persist. From the evidence presented here, we postulate that Neanderthals may have been less capable of prey-shifting and hence use the high-biomass prey resource provided by the rabbit, to the extent AMH did.
Link

Extremely old (237–581 kya) root of human Y-chromosome phylogeny

I had mentioned this research before, and now it has officially been published. There are three things to be excited about this new paper:
First, it forces us to consider the possibility of either (i) archaic admixture in Africa, or (ii) a much more ancient time depth of modern humans than the first fossils from Ethiopia dated to about ~200 thousand years ago.
Second, it underscores the importance of collaboration between academia and regular folk, since it was the combined contributions of academics, genetic genealogists, and the owners of the new A00 basal Y-chromosomes that made this new discovery possible.
And, third, it shows that the extraordinary can be discovered without contacting isolated tribes or seeking human bones in remote regions, but rather through careful scrutiny of large volumes of data for the proverbial needle in the haystack.
The paper developed a model of Y-chromosome mutation based on the estimate of Kong et al. Significantly, though:

If we were to use the higher mutation rate (1.0x10^-9 per base per year6) rather than a realistic range derived from whole-genome sequencing (4.39x10^-9  -   7.07x10^- 9), the estimated TMRCA for the tree incorporating A00 as the basal lineage would be 209 kya, which is only slightly older than current estimates of the TMRCA of mtDNA and the age of the oldest AMH fossil remains. We note, however, that the higher mutation rate produces an estimate for the common ancestor of all non-African Y chromosome haplogroups (C through T) of ~39 kya6 (i.e., versus ~63 kya for the mutation rate used here).

A 39kya common ancestor for Eurasian Y-chromosomes makes no sense, since we now know for sure that by that time, the differentiation of Eurasians was already well on its way and modern humans in remote parts of the Old World have been documented much earlier than that time.
A ~63kya common ancestor, on the other hand, fits nicely with my "two deserts" theory of modern human origins, according to which the ancestors of Eurasians faced an ecological crisis in Arabia when it became much drier post-70kya; that seems like a most opportune time for the major Eurasian bottleneck and the corresponding coalescence of Eurasian Y-chromosomes to a single man. And, while there is no a priori reason for Y chromosomes and mtDNA to behave similarly, the age of the "older" Eurasian ur-mother, haplogroup N at 59 thousand years, with presumably an older ancestor within mtDNA haplogroup L3 founding the Eurasian population.
Also, if modern human-Neandertal admixture had occurred  "most likely 47,000–65,000 years ago", then the expansion of modern Proto-Eurasians within a 70-60kya timeframe north Out-of-Arabia would have brought them in contact with their northern Neandertal neighbors. On the other hand, it would be incredible if modern humans experienced admixture with Neandertals but were still much later a very small population (to allow for the coalescence of their Y-chromosomes to one man ~39kya).
So, in summary, the mutation rate used by the authors seems consistent with what we know about an important calibration point of the human story.
But, who were the people in Africa responsible for the introgression of A00 chromosomes? Mendez et al. used the haplotype of the African American A00 individual and discovered his patrilineal kin among theMbo of Cameroon, who are Bantu farmers.
I have observed before that Pygmies and Bushmen represent only a tiny fraction of pre-existing African genetic diversity, the part that had not yet been absorbed into the farmers' expanding population by the time that Africa came to the attention of of modern science. We see traces of Pygmy and Bushman ancestry in some African farmers, and there were probably other groups, no longer extant as distinct ethno-cultural entities, but, nonetheless, surviving as genetic fragments in the genomes of the farmers.
Thus, while it still makes sense to study the surviving hunter-gatherers of Africa who make up perhaps a percent or less of the population of Africa, it may be equally important to study different groups of African farmers who may possess a much richer treasure trove (albeit diluted) of such "Palaeoafrican" ancestry.
Finally:

Although the stochastic nature of the evolutionary process can explain the aforementioned incongruences, the extreme age and rarity of the A00 lineage point to the possibility of a highly structured ancestral population, consistent with recent work on the autosomes.40,41,43,44 This could take the form of long-standing population structure among AMH populations45 or archaic introgression from an archaic form into the ancestors of AMHs.46 Interestingly, the Mbo live less than 800 km away from a Nigerian site known as Iwo Eleru, where human skeletal remains with both archaic and modern features were found and dated to ~13 kya.47 Further surveys in sub- Saharan Africa and in the African Diaspora might uncover more diverged basal lineages, which will help to disentangle some of the complex evolutionary processes that shape patterns of Y chromosome diversity.

AJHG 10.1016/j.ajhg.2013.02.002
An African American Paternal Lineage Adds an Extremely Ancient Root to the Human Y Chromosome Phylogenetic Tree
Fernando L. Mendez et al.
We report the discovery of an African American Y chromosome that carries the ancestral state of all SNPs that defined the basal portion of the Y chromosome phylogenetic tree. We sequenced ∼240 kb of this chromosome to identify private, derived mutations on this lineage, which we named A00. We then estimated the time to the most recent common ancestor (TMRCA) for the Y tree as 338 thousand years ago (kya) (95% confidence interval = 237–581 kya). Remarkably, this exceeds current estimates of the mtDNA TMRCA, as well as those of the age of the oldest anatomically modern human fossils. The extremely ancient age combined with the rarity of the A00 lineage, which we also find at very low frequency in central Africa, point to the importance of considering more complex models for the origin of Y chromosome diversity. These models include ancient population structure and the possibility of archaic introgression of Y chromosomes into anatomically modern humans. The A00 lineage was discovered in a large database of consumer samples of African Americans and has not been identified in traditional hunter-gatherer populations from sub-Saharan Africa. This underscores how the stochastic nature of the genealogical process can affect inference from a single locus and warrants caution during the interpretation of the geographic location of divergent branches of the Y chromosome phylogenetic tree for the elucidation of human origins.
Link

AAPA 2013 abstracts

AAPA 2013 abstracts

The program of the 2013 meeting of the American Association of Physical Anthropologists is now online (pdf). As always, there is plenty of interest here, so I'll just highlight a few titles that caught my eye; feel free to add more in the comments.


Neolithic human mitochondrial haplogroup H genomes and the genetic origins of Europeans.

Haplogroup (hg) H dominates present-day Western European mitochondrial (mt) DNA variability (>40%), yet was less prevalent amongst early Neolithic farmers (~19%) and virtually absent in Mesolithic hunter-gatherers. To investigate this haplogroup’s significance in the maternal population history of Europeans we employed novel techniques such as DNA immortalization and hybridization-enrichment to sequence 39 hg H mt genomes from ancient human remains across a transect through time in Neolithic Central Europe. The results of our population genetic analyses reveal that the current patterns of diversity and distribution of hg H were largely established during the Mid-Neolithic, but with substantial genetic contributions from subsequent pan-European cultures such as the Bell Beakers, which expanded out of Iberia in the Late Neolithic (~2800 BC). Using a strict diachronic approach allowed us to reconcile ‘real-time’ genetic data from the most common European mtDNA hg with cultural changes that took place between the Early Neolithic (~5450 BC) and Bronze Age (~2200 BC) in Central Europe. This revealed the Late Neolithic (2800-2200 BC) as a dynamic period that profoundly shaped the genetic landscape of modern-day Europeans. Furthermore, linking ancient hg H genome sequences to specific points in time by using radiocarbon dates as tip calibrations allowed us to reconstruct a precise lineage history of hg H and to calculate a mutation rate 45% higher than traditional estimates based on the human/chimp split.

Preliminary research on hereditary features of Yinxu Population.

... The 37 individuals sampled in this study have been discovered in middle to small size burials, and therefore constitute a representative sample to study Yinxu commoners’ society. Mitochondrial DNA analysis showed that the Yinxu population included the haplogroups D, G, A, C, Z, M10, M*, B, F and N9a. According to the analysis of molecular variance, the distribution frequency and the rare published data, the Yinxu population shows a closest genetic affinity with the populations of Dadianzi and Zhukaigou early Bronze Age sites (Inner Mongolia), but a more distant relation to the historical period populations. The Yinxu population is also very similar to the modern northern Han Chinese. ... 

Investigating lactase persistence in a Medieval German cemetery: A step towards understanding the rise of the European lactase persistence polymorphism (-3910C/T).

Previous ancient DNA-based studies on the Neolithic found that the incidence of LP falls below detection levels in most regions. Our research shows that between the Neolithic and Medieval periods, the frequency of LP rose from near 0% to over 50%. Also, given that the frequency of LP genotypes in modern-day Germany is estimated at 78.5%, our results indicate that rather than being stable by the Medieval period, the lactase persistent genotype has continued to increase in frequency over the last 1000 years. This new evidence sheds light on the dynamic evolutionary history of the European lactase persistent trait and its global cultural implications.

 New Neanderthal remains from Kalamakia cave, Mani peninsula, Southern Greece.

Peeling back the layers: additional evidence for the date of the Petralona skull (Homo heidelbergensis), Greece.

,.. We conclude that there is no white sinter deposited directly on the skull and therefore the initial date of the skull given by Henning et al. and Grun’s revised date of ca. 200 ka are correct.

Analysis of archaic introgression in Ötzi the Tyrolean Iceman, a 5300 year-old prehistoric modern human.

... We carried out a series of comparisons to address these questions. By examining the Neandertal similarity of individuals from the 1000 Genomes Project, we have substantially expanded the sample of Neandertal-human comparisons. We also examined the genome of the Tyrolean Iceman, a European from approximately 5300 years ago. This is the first comparison of Neandertal genomes to the genome of a prehistoric modern human individual.

A quantitative approach for late Pleistocene hominin brain size.

... The results of our study show that Neanderthals have smaller brains than the Pleistocene AMH despite the fact that the latter are smaller in body mass. However, the Holocene AMH (7 populations) have smaller brain sizes than those of Neanderthals. ...

Re-evaluating the functional and adaptive significance of Neandertal nasofacial anatomy.

... Among Middle and Late Pleistocene Homo, there is evidence that nasal morphology varies with climate, albeit within an archaic architectural nasofacial framework. Neandertal internal nasal dimensions are greater in both height and length than archaic humans from sub-Saharan Africa. Furthermore, while other aspects of the nose are relatively broad, superior internal breadth dimensions in Neandertals are narrowed relative to sub-Saharan archaics. These differences parallel those seen in modern humans, indicating that Neandertals had an increased capacity for nasal heat and moisture exchange over their African counterparts and thus exhibit clear evidence for cold-climate adaptation.

Higher Levels of Neanderthal Ancestry in East Asians Than in Europeans (Wall et al. 2013)

Higher Levels of Neanderthal Ancestry in East Asians Than in Europeans (Wall et al. 2013)

The title seems to say it all; such a conclusion was also arrived at by Meyer et al. (high coverage Denisova paper). However, the extent of this ancestry appears to be differently estimated in the new paper:

By using the high coverage Denisova genome, we are able to show that the admixture rate into East Asians is 40% higher than into Europeans.

Of course, the interesting question is why East Asians have this excess of Neandertal ancestry, given that Neandertals were a west Eurasian-distributed species (for the most part). Similarly, we would not have expected Australo-Melanesians to possess higher Denisovan admixture, and yet they do. Some models of multiregional evolution assumed regional continuity with pre-existing archaic populations in different parts of the world (e.g., Europeans with Neandertals), but clearly much more interesting things were taking place in deep prehistory.

Of particular interest is this conclusion:

In particular, at least some Neanderthal-modern human admixture must postdate the separation of the ancestors of modern European and modern East Asian populations.

The publication of Tianyuan has shown that by ~40kya, differentiation of Asians from Europeans was already on its way, and this is a date close to the disappearance of the Neandertals, the date of which is contested, but one can imagine that already-differentiated Eurasians may have encountered some lingering Neandertal groups.

Genetics doi: 10.1534/genetics.112.148213

Higher Levels of Neanderthal Ancestry in East Asians Than in Europeans

Jeffrey D. Wall et al.

Neanderthals were a group of archaic hominins that occupied most of Europe and parts of Western Asia from roughly 30-300 thousand years ago (Kya). They coexisted with modern humans during part of this time. Previous genetic analyses that compared a draft sequence of the Neanderthal genome with genomes of several modern humans concluded that Neanderthals made a small (1-4%) contribution to the gene pools of all non-African populations. This observation was consistent with a single episode of admixture from Neanderthals into the ancestors of all non-Africans when the two groups coexisted in the Middle East 50-80 Kya. We examined the relationship between Neanderthals and modern humans in greater detail by applying two complementary methods to the published draft Neanderthal genome and an expanded set of high-coverage modern human genome sequences. We find that, consistent with the recent finding of Meyer et al. (2012), Neanderthals contributed more DNA to modern East Asians than to modern Europeans. Furthermore we find that the Maasai of East Africa have a small but significant fraction of Neanderthal DNA. Because our analysis is of several genomic samples from each modern human population considered, we are able to document the extent of variation in Neanderthal ancestry within and among populations. Our results combined with those previously published show that a more complex model of admixture between Neanderthals and modern humans is necessary to account for the different levels of Neanderthal ancestry among human populations. In particular, at least some Neanderthal-modern human admixture must postdate the separation of the ancestors of modern European and modern East Asian populations.

Link

Balanica BH-1: 397-525 thousand years old

Balanica BH-1: 397-525 thousand years old

The occurrence of derived Neandertal traits in Sima vs. their absence in penecontemporaneous samples from  southeastern Europe is fairly interesting. It might suggest that the Neandertal suite of traits first appeared in western Europe.

We tend to think of Old World H. heidelbergensis as a parental species which produced -at least in the western part of the Old World- two descendant species, sapiens and neanderthalensis, but clearly that is not the whole story. Unrelated to the current paper, but perhaps worthy of note is that these two descendant species make their appearance far apart in time, with Neandertaloid traits already in evidence very early in Europe, and modern human ones late in east Africa. We may wonder about what was taking place in the temporal gap between 600 and 200 thousand years ago, and the spatial gap between Europe and Africaa.

PLoS ONE 8(2): e54608. doi:10.1371/journal.pone.0054608

New Radiometric Ages for the BH-1 Hominin from Balanica (Serbia): Implications for Understanding the Role of the Balkans in Middle Pleistocene Human Evolution

William J. Rink et al.

Newly obtained ages, based on electron spin resonance combined with uranium series isotopic analysis, and infrared/post-infrared luminescence dating, provide a minimum age that lies between 397 and 525 ka for the hominin mandible BH-1 from Mala Balanica cave, Serbia. This confirms it as the easternmost hominin specimen in Europe dated to the Middle Pleistocene. Inferences drawn from the morphology of the mandible BH-1 place it outside currently observed variation of European Homo heidelbergensis. The lack of derived Neandertal traits in BH-1 and its contemporary specimens in Southeast Europe, such as Kocabaş, Vasogliano and Ceprano, coupled with Middle Pleistocene synapomorphies, suggests different evolutionary forces acting in the east of the continent where isolation did not play such an important role during glaciations.

Link

Late Neandertal survival in Iberia questioned

Late Neandertal survival in Iberia questioned

Neanderthal remains point to earlier extinction

In the latest study1, Higham and his former graduate student Rachel Wood, now at the Australian National University in Canberra, tried to date remains from 11 sites on the Iberian Peninsula using their decontamination methods. Previous efforts put the remains as young as 36,000 years old.

However, Wood and Higham found that just two of the sites — Jarama, outside Madrid, and Cueva del Boquete de Zafarraya, near the southern tip of Spain — contained bones with enough carbon to be dated. Their work suggests that these remains are more than 45,000 years old, with some older than 50,000 years, the practical limit of carbon dating. Wood says that the team’s study calls into question evidence that the last populations of Neanderthals found refuge in the Iberian Peninsula.

PNAS doi: 10.1073/pnas.1207656110

Radiocarbon dating casts doubt on the late chronology of the Middle to Upper Palaeolithic transition in southern Iberia

Rachel E. Wood et al.

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.

Link

Breeding a (part-/quasi-) Neandertal the old-fashioned way

Breeding a (part-/quasi-) Neandertal the old-fashioned way

Razib has an interesting suggestion about how one could breed a Neandertal:

The most humane and viable manner in which you might do this is simply start a religion in a Bene Gesserit fashion where the prophesied Kwisatz Haderach is a Neandertal. Over the generations by selecting individuals within the population (which could draw in converts) enriched for Neandertal ancestry to mate assortatively one could slowly increase the proportion of that ancestral component. 

The idea is simple: if you mate two persons with x% and y% Neandertal ancestry, you will get (in the expected sense) a baby with 0.5(x+y)% Neandertal ancestry. In actuality the baby's Neandertal ancestry will be a random variable z with mean 0.5(x+y) and some variation around that mean.

Now, if x and y are very different from each other (e.g., at the limit you had crossed a full Neandertal with x=100% and a full sapiens with y=0%), then z will always be in-between x and y.

But, if x and y are fairly close to each other, it's possible that thanks to the wonders of recombination it will happen that z will be greater than both x and y, because the offspring might actually happen -by chance- to inherit many Neandertal alleles from both mom and dad.

Project the above procedure over the millennia, and it's easy to see how one might incrementally increase the proportion of Neandertal ancestry in the gene pool to an arbitrary degree: individuals might start with, say, 2% Neandertal ancestry, and given enough crossings per generation (so that enough individuals with >2% Neandertal ancestry will be produced), and enough generations, the number will inch along, and converge to 100%.

But, actually, reaching a 100% Neandertal might be impossible. To see why, consider that while many Neandertal alleles introgressed into the modern human population a few tens of thousands of years ago, surviving down to the present, some of them did not introgress and some that did were culled away by either drift or natural selection. 

Moreover, we might not be able to utilize all extant Neandertal alleles because we can mostly identify Neandertal-ness with respect to ancient DNA samples.

In other words, the modern human gene pool has a lot of Neandertal alleles floating around, but some of these don't look like Neandertal alleles (because we didn't find them in any ancient specimen yet), while others are simply long gone.

Such a breeding program would therefore not produce a Neandertal in the end, for the same reason that you cannot produce a grey hue by mixing different shades of red and blue: you also need some yellow. The modern human gene pool may have lots of Neandertal alleles but it may not have enough.

In any case, it would still be possible to create a, say, 50% Neandertal, or whatever the proportion of Neandertal alleles still in existence is. But, will such an individual be a Neandertal in the physical sense?

Which were the alleles that conferred Neandertal-ness to their bearers? We don't know, but this property may very well have involved both (i) combinations of alleles that exist in modern humans, and, (ii) alleles we no longer possess.

As an analogy, imagine that in the future, polar bears are extinct, but some of their DNA introgressed into other bear populations. Future zoologists might breed specimens that have a lot of polar bear alleles, but will lack the alleles conferring white coat color. Such a hypothetical breed of bear might possess a high degree of genome-wide similarity to actual polar bears, but it won't be the same where it counts.

Thus, it may very well be possible to create individuals from extinct human populations (be they archaic hominins such as Neandertals, or even admixed modern humans such as Tainos), but one might not get a 100% replica of such populations by breeding alone. Even if one was able to reconstruct a great part of such creatures' genome, the most important portions might still be missing.

Ancient DNA from Tianyuan Cave

Ancient DNA from Tianyuan Cave

Another new PNAS paper that hasn't yet appeared in the journal website. Still, from this description at ScienceNews this appears to be Very Important, as it pertains to a 40,000-year-old modern human, which, if I'm not mistaken is the oldest modern human tested so far:

Ancient DNA from cell nuclei and maternally inherited mitochondria indicates that this individual belonged to a population that eventually gave rise to many present-day Asians and Native Americans, says a team led by Qiaomei Fu and Svante Paabo, evolutionary geneticists at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. 

The partial skeleton, unearthed in Tianyuan Cave near Beijing in 2003, carries roughly the same small proportions of Neandertal and Denisovan genes as living Asians do (SN: 8/25/12, p. 22), the scientists report online January 21 in the Proceedings of the National Academy of Sciences.

The Max Planck press release adds some information:

The genetic profile reveals that this early modern human was related to the ancestors of many present-day Asians and Native Americans but had already diverged genetically from the ancestors of present-day Europeans.

This is an important finding because some published demographic models had Europeans and East Eurasians diverging as recently as ~20 thousand years ago. It now appears that they did so already at around the time of the Upper Paleolithic revolution, when unambiguous evidence of modern humans across Eurasia exists.

UPDATE I: While we wait for this paper to appear on the PNAS website, it might be useful to wonder whether the Tianyuan sample might fall on the East Asian/Amerindian group or the more general "Ancestral South Indian" (ASI)/East Eurasian group.

According to current dating, haplogroup M itself is ~50 thousand years old, and most of the subclades therein coalesce to younger than 40ky times. It's possible that the Tianyuan sample dates from a period where ASI/East Asian differentiation had only just begun or was just about to begin.

The press release makes clear that Tianyuan was already "Asian" rather than generalized Eurasian, proving that East/West Eurasian differentiation had begun by ~40kya. It will be interesting to see whether it can be placed on a more specific "East Eurasian" group rather than a generalized "Asian" one.

UPDATE II: The paper is now online.

UPDATE III: From the paper:

Thus, it is related to the mtDNA that was ancestral to present-day haplogroup B (Fig. 1), which has been estimated to be around 50,000 y old (18) (50. 7 ka BP; 95% CI: 38.1–68.3 ka BP). We note that the age of the Tianyuan individual is compatible with this date.

So, it appears to be within macro-haplogroup N, with haplogroup B being, I think, a fairly unambiguously East Asian/Native American clade of the phylogeny. It will certainly be interesting to see how the much more successful -and younger- M subclades ended up dominating East Eurasia.

UPDATE IV: The TreeMix analysis clearly places Tianyuan within the Asian group, but does not resolve whether Papuans are an outgroup to East Asians/Tianyuan:

I guess that is expected (see my UPDATE I), since Tianyuan dates from a period where within-Asia differentiation had only just begun or was about to begin.

UPDATE V: With respect to sharing of alleles with archaic Eurasian hominins, the Tianyuan sample is within the modern range of variation.

PNAS doi: 10.1073/pnas.1221359110

DNA analysis of an early modern human from Tianyuan Cave, China

Qiaomei Fu et al.

Hominins with morphology similar to present-day humans appear in the fossil record across Eurasia between 40,000 and 50,000 y ago. The genetic relationships between these early modern humans and present-day human populations have not been established. We have extracted DNA from a 40,000-y-old anatomically modern human from Tianyuan Cave outside Beijing, China. Using a highly scalable hybridization enrichment strategy, we determined the DNA sequences of the mitochondrial genome, the entire nonrepetitive portion of chromosome 21 (~30 Mbp), and over 3,000 polymorphic sites across the nuclear genome of this individual. The nuclear DNA sequences determined from this early modern human reveal that the Tianyuan individual derived from a population that was ancestral to many present-day Asians and Native Americans but postdated the divergence of Asians from Europeans. They also show that this individual carried proportions of DNA variants derived from archaic humans similar to present-day people in mainland Asia.

Link

Neandertal origin of Châtelperronian; likely modern human origin of Châtelperronian body ornamentation

Neandertal origin of Châtelperronian; likely modern human origin of Châtelperronian body ornamentation

Related:

• Earliest sapiens remains in Europe
• Rapid onset of Aurignacian in Southwest France
• Redating of the Early Upper Paleolithic site of Riparo Mochi (Italy)
• 43,000-year old Aurignacian in Swabian Jura

PNAS doi: 10.1073/pnas.1212924109

Radiocarbon dates from the Grotte du Renne and Saint-Césaire support a Neandertal origin for the Châtelperronian

Jean-Jacques Hublin et al.

The transition from the Middle Paleolithic (MP) to Upper Paleolithic (UP) is marked by the replacement of late Neandertals by modern humans in Europe between 50,000 and 40,000 y ago. Châtelperronian (CP) artifact assemblages found in central France and northern Spain date to this time period. So far, it is the only such assemblage type that has yielded Neandertal remains directly associated with UP style artifacts. CP assemblages also include body ornaments, otherwise virtually unknown in the Neandertal world. However, it has been argued that instead of the CP being manufactured by Neandertals, site formation processes and layer admixture resulted in the chance association of Neanderthal remains, CP assemblages, and body ornaments. Here, we report a series of accelerator mass spectrometry radiocarbon dates on ultrafiltered bone collagen extracted from 40 well-preserved bone fragments from the late Mousterian, CP, and Protoaurignacian layers at the Grotte du Renne site (at Arcy-sur-Cure, France). Our radiocarbon results are inconsistent with the admixture hypothesis. Further, we report a direct date on the Neandertal CP skeleton from Saint-Césaire (France). This date corroborates the assignment of CP assemblages to the latest Neandertals of western Europe. Importantly, our results establish that the production of body ornaments in the CP postdates the arrival of modern humans in neighboring regions of Europe. This new behavior could therefore have been the result of cultural diffusion from modern to Neandertal groups.

Link

Bulging modern human foreheads

Bulging modern human foreheads

AJPA DOI: 10.1002/ajpa.22202

Geometric variation of the frontal squama in the genus homo: Frontal bulging and the origin of modern human morphology

Emiliano Bruner et al.

The majority of studies of frontal bone morphology in paleoanthropology have analyzed the frontal squama and the browridge as a single unit, mixing information from different functional elements. Taking into account that the bulging of the frontal bone is often described as a species-specific trait of Homo sapiens, in this article we analyze variation in the midsagittal profile of the genus Homo, focusing on the frontal squama alone, using landmark-based superimpositions and principal components analysis. Our results demonstrate that anatomically modern humans are definitely separated from extinct human taxa on the basis of frontal bulging. However, there is minor overlap among these groups, indicating that it is necessary to exercise caution when using this trait alone to make taxonomic inferences on individual specimens. Early modern humans do not show differences with recent modern humans, and “transitional” individuals such as Jebel Irhoud 1, Maba, and Florisbad, show modern-like frontal squama morphology. The bulging of the frontal squama in modern humans may represent a structural consequence of more general cranial changes, or it could be a response to changes in the morphology of the underlying prefrontal brain elements. A subtle difference between Neandertals and the Afro-European Middle Pleistocene Homo sample is associated with flattening at bregma in the former group, a result that merits further investigation.

Link

Mating between Modern Humans, Neanderthals and other Archaics (Waddell & Tan 2012)

Mating between Modern Humans, Neanderthals and other Archaics (Waddell & Tan 2012)

arXiv:1212.6820 [q-bio.GN]

New g%AIC, g%AICc, g%BIC, and Power Divergence Fit Statistics Expose Mating between Modern Humans, Neanderthals and other Archaics

Peter J. Waddell, Xi Tan

The purpose of this article is to look at how information criteria, such as AIC and BIC, relate to the g%SD fit criterion derived in Waddell et al. (2007, 2010a). The g%SD criterion measures the fit of data to model based on a normalized weighted root mean square percentage deviation between the observed data and model estimates of the data, with g%SD = 0 being a perfectly fitting model. However, this criterion may not be adjusting for the number of parameters in the model comprehensively. Thus, its relationship to more traditional measures for maximizing useful information in a model, including AIC and BIC, are examined. This results in an extended set of fit criteria including g%AIC and g%BIC. Further, a broader range of asymptotically most powerful fit criteria of the power divergence family, which includes maximum likelihood (or minimum G^2) and minimum X^2 modeling as special cases, are used to replace the sum of squares fit criterion within the g%SD criterion. Results are illustrated with a set of genetic distances looking particularly at a range of Jewish populations, plus a genomic data set that looks at how Neanderthals and Denisovans are related to each other and modern humans. Evidence that Homo erectus may have left a significant fraction of its genome within the Denisovan is shown to persist with the new modeling criteria.

Link

Neandertal STAT2 haplotype in Eurasians

Neandertal STAT2 haplotype in Eurasians

Two recent papers have argued that African population structure or late Middle Paleolithic/Upper Paleolithic Neandertal admixture have contributed to the finding that Non-Africans appear to be a few percent more similar to Neandertals than Africans are across the genome. I would add that modern human admixture in the Vindija individual remains a distinct possibility.

What percentage of the ~3% Eurasian excess can be accounted by each of these three processes? The jury is out, and we won't find out until someone decides to tackle the problem comprehensively and/or new ancient DNA samples become available to inform the discussion. African population structure cannot be discounted, and intriguing new evidence may appear thanks to ancient DNA analysis.

But, there is a different approach to detecting Neandertal admixture that zeroes in on specific genomic locations and dissects them in great detail. This single-region approach provides evidence for admixture, without necessarily arguing about how extensive it was.

The single-region dissection was previously used in the Hammer lab to identify the first very convincing evidence for archaic admixture in Africans and Melanesians. In a new paper, Mendez et al. identify a small region in chromosome 12 that shows evidence for archaic introgression from Neandertals, or a species closely related to them.

But, it is worthwhile to begin with a list of other Neandertal introgression candidates from the literature:

Thus far, only a handful of loci have been hypothesized to have entered the human gene pool through archaic admixture and positive selection, including MAPT (MIM 157140),5 MCPH1 (MIM 607117),3 and particular alleles at the HLA locus (MIM 142800, 142830, 142840).6 However, analysis of the Neanderthal genome failed to provide evidence of introgressive alleles at the former two loci.1 Because of its role in fighting pathogens, HLA presents an instance where it is relatively easy to conceive of an a priori reason that acquisition of an archaic Eurasian HLA allele would benefit human ancestors, especially as they expanded into new habitats.7 However, the fact that HLA haplotypes are known to exhibit transspecific polymorphism and show evidence of strong balancing selection 8,9 increases the probability that similarities between modern and archaic haplotypes are due to ancestral shared polymorphism (i.e., as opposed to archaic admixture). In addition, the SNPs tagging the main HLA haplotype that was said to have introgressed were not observed in the Denisova or Neanderthal draft genomes. 

So, what lines of evidence support the notion that the new STAT2 haplotype is the "real deal"?

First, N matches the Neanderthal sequence at all 18 sites that fall within the resequenced 8.6 kb STAT2 region and have Neanderthal sequence coverage (Table 1). Second, N lineages are broadly distributed at relatively low frequencies in Eurasian populations (Figure 3) and are not observed in sub-Saharan African populations (Table S6). Third, the N haplotype extends for ~130 kb in West Eurasians and up to ~260 kb in some East Asians and Melanesians, producing much stronger LD than that observed in sub-Saharan Africans.

...

Given that the N lineage and the reference sequence diverged ~600 kya, these results suggest that population structure has influenced the recent evolution of this locus. Balancing selection alone is not expected to maintain this extent of LD and consequently is not sufficient to explain these patterns. Moreover, although a strong bottleneck could generate extended LD similar to the levels we observe near STAT2 in non-Africans, it would not explain why the N lineage went extinct in Africa (i.e., why the SNPs associated with the N lineage in non- Africans were not observed in sub-Saharan Africans that are part of our WGS or public SNP panels).

...

We point out that although a recent common ancestry between a human lineage and Neanderthal sequences might indicate gene flow between Neanderthals and modern humans, this information alone does not inform us about the direction of gene flow. With the additional evidence of the observed extent of LD in modern human sequences, it is possible to infer that the N lineage introgressed into modern humans (either from Neanderthals or another archaic source that contributed to both Neanderthals and AMH).

Actually, the N haplotype is observed in North Africa, but this might be due to relatively recent back-migration. One might also argue that a recent bottleneck in a Eurasian population generated the high degree of LD, and the N haplotype was lost in a back-to-Africa migration, or North-to-Sub-Saharan Africa migration. But, that would not seem to explain how the deeply divergent lineage persisted in the North African population of proto-modern humans for such a long time; the evidence for recent common ancestry of N with the Neandertal haplotype would argue against incomplete lineage sorting (=inheritance of related forms of the haplotype from before the modern-Neandertal divergence).

All in all, this probably represents the best evidence for Neandertal-to-modern introgression to date. As full genomes of different human groups become available, it will be possible to automate this analysis and pick off other such strong signals. This may not indicate the level of admixture, but it might provide strong evidence against the idea of reproductive isolation between modern humans and Neandertals.

It is also noteworthy that this is barely consistent with the coastal migration theory with respect to the origin of Australo-Melanesians, because humans trekking along the coast would not have the opportunity to admix with Neandertals who are completely unattested there in either their physical, or archaeological (Mousterian) form.

But, it is consistent with my Out-of-Arabia theory. Australo-Melanesian Y chromosomes belong to the CF clade of the phylogeny. I have speculated that the post-70ka climate crisis in Arabia spurred some human groups to escape north (CF), and others to remain south (DE). The latter eventually gave rise to the major African lineage, heading west (E), as well as a relic Asian lineage heading east (D) that was later inundated by the descendants of CF. If Australo-Melanesians are descended from the CF folk who went north out of Arabia, then they too would have had the opportunity to admix with Neandertals in the Near East.

The American Journal of Human Genetics, Volume 91, Issue 2, 265-274, 10 August 2012

A Haplotype at STAT2 Introgressed from Neanderthals and Serves as a Candidate of Positive Selection in Papua New Guinea

Fernando L. Mendez, Joseph C. Watkins and Michael F. Hammer

Signals of archaic admixture have been identified through comparisons of the draft Neanderthal and Denisova genomes with those of living humans. Studies of individual loci contributing to these genome-wide average signals are required for characterization of the introgression process and investigation of whether archaic variants conferred an adaptive advantage to the ancestors of contemporary human populations. However, no definitive case of adaptive introgression has yet been described. Here we provide a DNA sequence analysis of the innate immune gene STAT2 and show that a haplotype carried by many Eurasians (but not sub-Saharan Africans) has a sequence that closely matches that of the Neanderthal STAT2. This haplotype, referred to as N, was discovered through a resequencing survey of the entire coding region of STAT2 in a global sample of 90 individuals. Analyses of publicly available complete genome sequence data show that haplotype N shares a recent common ancestor with the Neanderthal sequence (∼80 thousand years ago) and is found throughout Eurasia at an average frequency of ∼5%. Interestingly, N is found in Melanesian populations at ∼10-fold higher frequency (∼54%) than in Eurasian populations. A neutrality test that controls for demography rejects the hypothesis that a variant of N rose to high frequency in Melanesia by genetic drift alone. Although we are not able to pinpoint the precise target of positive selection, we identify nonsynonymous mutations in ERBB3, ESYT1, and STAT2—all of which are part of the same 250 kb introgressive haplotype—as good candidates.

Link

Introgression of archaic haplotype at OAS1 in Melanesians (Mendez et al. 2012)

Introgression of archaic haplotype at OAS1 in Melanesians (Mendez et al. 2012)

It seems that Michael Hammer was good on his promise that in 2012 "This year, we should be able to confirm what we found and go way beyond that."  In a new paper, conclusive evidence is presented about introgression of an archaic sequence into Melanesian populations. The argument is as follows:

• Melanesians are more diverse in that region than Africans.
• The common ancestor of the "archaic" and "African" haplotypes lived >3 million years ago.
• The "archaic" haplotype matches the ancient DNA from the Denisova hominin.
• Balancing selection (which can sometimes maintain extremely old polymorphism) is not reasonable in this case, because it would need to maintain both "archaic" and "African" haplotypes for a long time, but then (inexplicably) would continue to operate in Melanesia and cease to operate everywhere else.

Notice that once again, this is based on resequencing a small region of the genome. This is why I am all the more confident in my prediction that the advent of full genome sequencing will uncover more archaic admixture in humans. It may not always be able to use all the above listed criteria to confirm this admixture (since we do not and cannot have ancient DNA from all the archaic hominins that once roamed the planet), but all the remaining ones will suffice to make a very good case for introgression.

What I find particularly interesting, is that Mendez et al. re-iterate a few times that genomewide averages admit to different explanations:

Full genome comparisons of the Neandertal and Denisova draft genomes with modern human sequences have revealed different amounts of shared ancestry between each of these archaic forms and anatomically modern human (AMH) populations from different geographic regions. For example, a higher proportion of SNPs was shared between non-African and Neandertal, and between Melanesian and the Denisova genomes, than between either Neandertal or Denisova and extant African genomes (Green et al. 2010; Reich et al. 2010). An intriguing possibility is that these patterns result from introgression of archaic genes into AMH populations in Eurasia. However, this SNP sharing pattern could also be explained by ancestral population structure in Africa (i.e., without the need to posit introgression). For example, if non-Africans and the ancestors of Neandertals descend from the same deme in a subdivided African population, and this structure persisted with low levels of gene flow among African residents until the ancestors of non-Africans migrated into Eurasia, then we would expect more SNP sharing between non-Africans and Neandertals (Durand et al. 2011). 

... 

While genome-wide comparisons detect more sequence agreement between non-African and Neandertal genomes, and between Melanesian and Denisova genomes, the specific loci exhibiting these signals have not yet been identified. Furthermore, current analyses do not elucidate the relative roles of recent introgression versus long-term population structure in Africa in explaining these patterns.

The current paper does a good job at showing how in one particular region archaic introgression into Melanesians is indeed the best explanation for the evidence. But, the fact that the authors seem to re-iterate the possibility of African population structure and repeatedly caution against using patterns of genomewide sharing between modern and archaic humans is a strong hint that there are more things to come on the topic.

We should remember that the widely-circulated estimates of Neandertal->Eurasian introgression are based on genomewide averages. It is true that Reich et al. (2010) identified 13 regions of potential Neandertal introgression, which together make up a very small portion of the human genome. So, the jury is out on whether African population structure or Neandertal introgression is responsible for most of the genomewide pattern.

What you can be sure of is that many scientists are busy lining up full genomes from different human populations as we speak, and finding plenty of regions where haplotypes of extremely old divergence times co-exist in our species. We will probably learn more about such efforts during 2012.



Mol Biol Evol (2012)doi: 10.1093/molbev/msr301

Global genetic variation at OAS1 provides evidence of archaic admixture in Melanesian populations

Fernando L. Mendez, Joseph C. Watkins and Michael F. Hammer

Recent analysis of DNA extracted from two Eurasian forms of archaic human show that more genetic variants are shared with humans currently living in Eurasia than with anatomically modern humans in sub-Saharan Africa. While these genome-wide average measures of genetic similarity are consistent with the hypothesis of archaic admixture in Eurasia, analyses of individual loci exhibiting the signal of archaic introgression are needed to test alternative hypotheses and investigate the admixture process. Here, we provide a detailed sequence analysis of the innate immune gene, OAS1, a locus with a divergent Melanesian haplotype that is very similar to the Denisova sequence from the Altai region of Siberia. We re-sequenced a 7 kb region encompassing the OAS1 gene in 88 individuals from 6 Old World populations (San, Biaka, Mandenka, French Basque, Han Chinese, and Papua New Guineans) and discovered previously unknown and ancient genetic variation. The 5' region of this gene has unusual patterns of diversity, including 1) higher levels of nucleotide diversity in Papuans than in sub-Saharan Africans, 2) very deep ancestry with an estimated time to the most recent common ancestor of >3 million years, and 3) a basal branching pattern with Papuan individuals on either side of the rooted network. A global geographic survey of >1500 individuals showed that the divergent Papuan haplotype is nearly restricted to populations from eastern Indonesia and Melanesia. Polymorphic sites within this haplotype are shared with the draft Denisova genome over a span of ∼90 kb and are associated with an extended block of linkage disequilibrium, supporting the hypothesis that this haplotype introgressed from an archaic source that likely lived in Eurasia.

Link