No evidence of Neandertal admixture in Europeans

[djoser-xyyman]

"No evidence of Neandertal admixture in the mitochondrial genomes of early European modern humans and contemporary Europeans" by

Silvia Ghirotto,
Francesca Tassi,
Andrea Benazzo,
Guido Barbujani

Article first published online: 24 AUG 2011
American Journal of Physical Anthropology

DOI: 10.1002/ajpa.21569

onlinelibrary.wiley.com/doi/10.1002/ajpa.21569/abstract


Keywords:

ancient DNA;
population genetics;
Approximate Bayesian Computations;
coalescent simulations;
admixture

Abstract

Neandertals, the archaic human form documented in Eurasia until 29,000 years ago, share no mitochondrial haplotype with modern Europeans. Whether this means that the two groups were reproductively isolated is controversial, and indeed nuclear data have been interpreted as suggesting that they admixed. We explored the range of demographic parameters that may have generated the observed mitochondrial diversity, simulating 3.0 million genealogies under six models differing as for the relationships among contemporary Europeans, Neandertals, and Upper Palaeolithic European early modern humans (EEMH), who coexisted with Neandertals for millennia. We compared by Approximate Bayesian Computations the simulation results with mitochondrial diversity in 7 Neandertals, 3 EEMH, and 150 opportunely chosen modern Europeans. A model of genealogical continuity between EEMH and contemporary Europeans, with no Neandertal contribution, received overwhelming support from the analyses. The maximum degree of Neandertal admixture, under the model of gene flow supported by nuclear data, was estimated at 1.5%, but this model proved 20–32 times less likely than a model without any gene flow. Nuclear and mitochondrial evidence might be reconciled if smaller population sizes led to faster lineage sorting for mitochondrial DNA, and Neandertals shared a longer period of common ancestry with the non-African's than with the African's ancestors. Am J Phys Anthropol, 2011. © 2011 Wiley-Liss, Inc.

[djoser-xyyman]

DISCUSSION
Nordborg (1998) first remarked that the nonoverlap
between Neandertal and modern mtDNA variation does
not imply that there was no admixture, because, at the
low Palaeolithic population sizes, drift could have eliminated
rare, and even not-so-rare, haplotypes. The question,

then, became how rare a haplotype should be, and
how small the population, to produce the observed
absence of Neandertal haplotypes in modern subjects,
despite admixture having actually occurred.
Currat and Excoffier (2004) demonstrated by simulation
that the absence of Neandertal mtDNAs in the
modern gene pool is compatible with a maximum interbreeding
rate 5 0.1%, which translates into 1 admixture
event every 100 years, during the coexistence of the two
human forms in Europe. Belle et al. (2009) incorporated
EEMH sequences in their analyses, but still failed to
find evidence for any appreciable degree of Neandertal
admixture in the European mtDNA pool. For methodological
reasons, in both studies mutation rates and population
sizes had to be fixed at the start of the simulation.
Conversely, the ABC methods we employed in this study
allowed us to explore for each model a broad and continuous
range of population sizes, mutation rates and,
when applicable, separation times and gene flow rates.
In this way, the models were compared in a statistically
rigorous way, and their final performance is independent
of any specific value of the simulation parameters. We
found that the best estimate by far of mitochondrial
admixture between Neandertals and the ancestors of
modern Europeans is zero. Even at very low population
sizes and with high mutation rates, the patterns of
diversity observed in ancient and modern samples appear
incompatible with a Neandertal contribution to the mitochondrial
genealogy of EEMH and modern Europeans.
There is reason to believe that the estimates we
obtained can be trusted. The shapes of the posterior
probability distributions, the posterior predictive tests,
and several statistics estimated from the simulated data
strongly suggest that the information available was sufficient
to discriminate among models, and that most parameters
are well estimated. The main area of uncertainty
concerns the modern population sizes, which
appear extremely large and distributed across the whole
range of the prior distribution. This finding is not unusual
in studies of this kind (Fagundes et al., 2007; Belle
et al., 2009; Wegmann et al., 2009; Laval et al., 2010),
and does not seem to reflect the choice of priors. Rather,
it is probably a consequence of a simplistic, yet unavoidable,
assumption, namely that populations evolved in
isolation. In reality, people with different mitochondrial
features must have migrated for millennia from other
regions. This process resulted in an increase of genetic
diversity, which the model accommodated by inflating
the population size estimates. However, it is hard to
imagine that the Neandertal contribution to the modern
gene pool would be more likely in a (much more complicated)
model also considering successive gene flow from
multiple modern sources. On the other hand, such a
complicated model would require the estimation of a
very large number of parameters (i.e., migration rates
between all possible pairs of populations), resulting in a

Fig. 5. Schematic view of the gene genealogies for markers transmitted by one (left) and two (right) parents, in Neandertals
and modern humans. a: time since the mitochondrial most recent common ancestors; b: time since the autosomal most recent common
ancestor; d: excess evolutionary time shared with Neandertals only by the lineage leading to non-African modern people; AF,
NON-AF: African and Non-African modern populations.


loss of accuracy in the estimation of the parameters that
really matter, i.e., admixture rates between Neandertals
and anatomically modern people.
In the recent genome survey, Neandertals appeared
genetically closer to non-Africans than to Africans. This
observation was interpreted as evidence of admixture
between Neandertals and the common ancestors of
Asians and Europeans, in the Levant, resulting in a
Neandertal contribution to the modern genomes estimated
between 1% and 4%. Alternative explanations are
possible, but were considered less likely (Green et al.,
2010). However, the poor performance of Model 6 in this
study shows that the hypothesis of early admixture in
the Levant has some problems too. Unless we have made
serious errors in the interpretation of mitochondrial
data, the model favored by the analysis of nuclear diversity
seems to account very poorly, if at all, for the
observed patterns of mitochondrial diversity in archaic
and contemporary populations of Europe.
Only one complete Neandertal genome has been studied
so far, and, given the rigid standards established to guarantee
the quality of the data, sample size is not going to
increase any time soon. A second problem is that the
admixture model between Neandertal and anatomically
modern populations proposed by Green et al. (2010) implies
that the ancestors of all modern humans who left Africa
had contacts with Neandertals, including those from Papua
New Guinea. On the contrary, it is possible that ancestral
modern humans also dispersed from Africa via a Southern
route, through the Arab peninsula, the Indian subcontinent
and Melanesia. This hypothesis was proposed to
account for temporal and spatial patterns of cranial diversity
(Lahr and Foley, 1994), has been supported by analyses
of mtDNA variation (Quintana-Murci et al., 1999; Maca-
Meyer et al., 2001; Macaulay et al., 2005) and, recently, by
the analysis of [100,000 nuclear single-nucleotide polymorphisms
(Ghirotto et al., 2011). If some modern populations
of Southern Asia and Papua New Guinea are
descended frompeople who left Africa without crossing Palestine,
we see no way that their ancestors could have met,
and hybridized with, Neandertals. Therefore, their genetic
affinities with Neandertals must have a different origin.

It is thus necessary to find another explanation for the
discrepancy between the apparent implications of the mitochondrial
and nuclear analyses. In principle, two possibilities,
neither simple to support empirically, would be sex-biased
gene flow and hybrid selection. The former means
that maybe Neandertal males, but not females, admixed
with early anatomically modern Europeans. This is in contrast
with studies of sex-biased admixture in modern communities,
suggesting that the invading population tends to
incorporate females more than males (Abe-Sandes et al.,
2004; Goncalves et al., 2008; Gonzalez-Andrade et al.,
2007; Stefflova et al., 2009; Quintana-Murci et al., 2010); to
what extent this might also apply to prehistoric populations,
nobody knows. Hybrid selection could account for the
observed differences between admixture estimates if Neandertal
mtDNAs had lower fitness in combination with a
hybrid nuclear genome. Once again, we see no way to test
empirically whether that was actually the case.
Moving on to testable hypotheses, a simple process of
genetic drift after admixture is not the explanation we
seek (see Fig. 3). In addition, in a simple admixture model,
alleles passed from a resident to an invading population
are expected to often surf to high frequencies if the invading
populations also undergoes demographic growth
(Currat et al., 2008). Because the incoming EEMH
doubtless increased in numbers, even small Neandertal
contributions should be detectable in the gene pool of their
descendants, which is not the case for the European
mtDNAs (Currat and Excoffier, 2004; this study).
To reconcile findings based on nuclear and mitochondrial
variation we thus need a more articulate model, of
which genetic drift is only a component. Many studies of
modern DNA data have suggested that the common
ancestors of Neandertals and modern humans might
have been geographically structured (Falush et al., 2003;
Harding and McVean, 2004; Lahr and Foley, 1994). A
few simple calculations show that this possibility, also
mentioned by Green et al. (2010), should be taken seriously
(see Fig. 5). The expected time since the MRCA is
2N generations for mtDNA, where N is the female population
size; if the sex ratio among Neandertals was 1
female : 1 male, the age of the nuclear DNA MRCA

should be 4 times as large. Briggs et al. (2009) quantified
the size of the Neandertal female population around
3,500 or less. This means that the mitochondrial and nuclear
MRCAs of Neandertals can be placed respectively
7,000 generations (or 175,000 years) and 28,000 generations
(or 700,000 years) ago. These figures come with a
large standard error, but imply that if the lineages leading
to Neandertals and modern humans separated
between 175,000 and 700,000 years ago, one would
expect exactly what has been observed, namely independent
mtDNA genealogies, and a certain degree of
allele sharing at the autosomal level (see Fig. 5). On the
basis of cranial measurements, anatomically archaic and
modern humans separated between 311,000 and 435,000
years ago, with an upper limit of 592,000 (Weaver et al.
2008, and references therein). In this paper, we estimated
that the same event occurred about 295,000 years
ago (median value), with an upper 95% limit of 646,200
years. Therefore, the Replacement model with structured
ancestral population is in reasonable agreement with
fossil, nuclear DNA and mtDNA evidence, whereas the
model of admixture fails to account for the observed relationships
between ancient and modern mtDNAs.
Under a model in which the ancestral population was
structured, the greater nuclear similarity between Neandertals
and non-Africans would not necessarily require
admixture between them. Indeed, if the non-Africans
shared with Neandertals a longer section of their genealogy
(represented by the interval labeled as d in Fig. 5),
they would also share more alleles than Africans and
Neandertals, including the derived alleles upon which
Green et al. (2010) based their estimates. This view is
also supported by data on the DNA of the human gastric
parasite Helicobacter pilori, in which ancestral genetic
clusters seem to have given rise to two distinct populations,
one exclusively African and the other cosmopolitan
(Falush et al., 2003), and by the extreme levels of DNA
variation still present in Africa (Schuster et al., 2010;
Henn et al., 2011). The only additional assumption one
has to make to account for the observed results is that
the latter population was also ancestral to the European
Neandertals typed by Green et al. (2010). Therefore, the
hypothesis of genetic drift in a structured ancestral population,
in which Neandertals shared a longer period of
common ancestry with the non-African’s than with the
African’s ancestors, seems to reconcile most findings
about DNA diversity in Neandertal and modern people.
This hypothesis predicts that the nuclear alleles preferentially
shared by Neandertals and non-African will
have MRCAs falling in the upper part of the genealogy
(d interval in Fig. 5), and we are preparing to test this
hypothesis.

[zarahan]

How do you see the claim of EUropeans having traces of Neanderthal DNA, namely the article
"Draft Sequence of the Neanderthal Genome" by Green et al, 2010?

Abstract

Neandertals, the closest evolutionary relatives of present-day humans, lived in large parts of Europe and western Asia before disappearing 30,000 years ago. We present a draft sequence of the Neandertal genome composed of more than 4 billion nucleotides from three individuals. Comparisons of the Neandertal genome to the genomes of five present-day humans from different parts of the world identify a number of genomic regions that may have been affected by positive selection in ancestral modern humans, including genes involved in metabolism and in cognitive and skeletal development. We show that Neandertals shared more genetic variants with present-day humans in Eurasia than with present-day humans in sub-Saharan Africa, suggesting that gene flow from Neandertals into the ancestors of non-Africans occurred before the divergence of Eurasian groups from each other.


WHat's your take, or critique of the claim?

[Tukuler al~Takruri]

This thread's title is misleading in omitting the mtDNA qualifier.

Neanderthal mtDNA may be absent but the Homo saiens sapiens
genome has both Neanderthal and Denisovan, i.e., extinct human
genetic markers.

Sexual bias may be the reason for no Neanderthal mtDNA in Hss
or inability of Neanderthal females to birth fertile offspring from
male Hss seed. Eg. jack + mare = mule; mule = end of the line.

[zarahan]

Thanks

[djoser-xyyman]

Says who!! Neanderthals did NOT admix with AMH! Please keep up. **sigh**


=======
Neandertals, the archaic human form documented in Eurasia until 29,000 years ago, share no mitochondrial haplotype with modern Europeans


Whether this means that the two groups were reproductively isolated is controversial

[seekeroftruth]

How does the Neanderthal admixture hypothesis factor into this?

[djoser-xyyman]

^ not sure who you are replying to but. . . . .

the 2010 study concluded that about 4% of non-African genome are from Neanderthal.

The 2011 study conclude - - -and- - - many previous studies (notably Baubatngi's?) conclude Europeans have absolutely no Neanderthal genes. Some of the reasons being - AMH travelled across the Horn then headed south. Therefore it was impossible for them to come in contact with their cousins. . in the Levant. (in case you miss the point - that means Australians had no contact with Neanderthals).

Two, The timeline do not add up.

And three, the genes location do NOT match.

eg. Neandethal may have had red hair, yes, but they did not give AMH(Europeans) their red hair. The location of this specific red hair gene has no correlation between AMH and their cousins. and the mechanism is totally different. But that does not stop Genetic testing companies from selling snake oil. Many racist and the ignorant are lured into believing they are related to Neanderthals.

[seekeroftruth]

Mar 15, 2012 19:18:10 GMT -5 djoser-xyyman said:

^ not sure who you are replying to but. . . . .

the 2010 study concluded that about 4% of non-African genome are from Neanderthal.

The 2011 study conclude - - -and- - - many previous studies (notably Baubatngi's?) conclude Europeans have absolutely no Neanderthal genes. Some of the reasons being - AMH travelled across the Horn then headed south. Therefore it was impossible for them to come in contact with their cousins. . in the Levant. (in case you miss the point - that means Australians had no contact with Neanderthals).

Two, The timeline do not add up.

And three, the genes location do NOT match.

eg. Neandethal may have had red hair, yes, but they did not give AMH(Europeans) their red hair. The location of this specific red hair gene has no correlation between AMH and their cousins. and the mechanism is totally different. But that does not stop Genetic testing companies from selling snake oil. Many racist and the ignorant are lured into believing they are related to Neanderthals.

I wasn't replying to anyone in particular, just to anyone who cared to share.

[djoser-xyyman]

Cioclovina (Romania): affinities of an early modern European.

Harvati K, Gunz P, Grigorescu D.

Source

Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, Leipzig, Germany. [e-mail]

Abstract

The current modern human origins debate centers on the possibility and degree of admixture between indigenous archaic humans and modern human populations migrating out of Africa into Europe and Asia in the Late Pleistocene. Evidence for such admixture must be sought in the earliest fossil record of modern humans outside Africa, as it is those populations that would have encountered, and possibly interbred with, archaic hominins. In the case of Europe, the recent application of direct dating techniques has eliminated several specimens from the Upper Paleolithic fossil record, while confirming early ages for others. Among these earliest reliably dated specimens is the Cioclovina calvaria from Romania. This individual is of highest importance for the understanding of modern human origins in Europe, and has recently been proposed to represent a Neanderthal-modern human hybrid. We present a short description and a three-dimensional (3D) geometric morphometric analysis of the Cioclovina specimen using a large geographic sample of recent humans, Neanderthals and Middle and Late Pleistocene fossil hominins from Europe, Africa, and the Levant, in order to establish its phenetic affinities and to evaluate its morphology for evidence of admixture between Neanderthals and early modern Europeans. Our results show Cioclovina to be entirely modern in its cranial shape, and do not support the hypothesis that it represents a hybrid.

[djoser-xyyman]

A critical review of the German Paleolithic hominin record.

Street M, Terberger T, Orschiedt J.

Source

Forschungsbereich Altsteinzeit des Römisch-Germanischen Zentralmuseums, Schloss Monrepos, D-56567 Neuwied, Germany. [e-mail]

Abstract

We review the hominin fossil record from western Central Europe in light of the recent major revisions of the geochronological context. The mandible from Mauer (Homo heidelbergensis), dated to circa 500,000 years ago, continues to represent the earliest German hominin and may coincide with the occupation of Europe north of the high alpine mountain chains. Only limited new evidence is available for the Middle Pleistocene, mostly in the form of skull fragments, a pattern that may relate to taphonomic processes. These finds and their ages suggest the gradual evolution of a suite of Neandertal features during this period. Despite new finds of classic Neandertals, there is no clear proof for Neandertal burial from Germany. Alternatively, cut marks on a skull fragment from the Neandertal type site suggest special treatment of that individual. New Accelerator Mass Spectrometry (AMS) radiocarbon dates of previous finds leave little reliably dated evidence for anatomically modern humans (AMH) in Europe before 30,000 BP; the remains from Hahnöfersand, Binshof-Speyer, Paderborn-Sande, and Vogelherd are now of Holocene age. Thus, a correlation of AMH with the Aurignacian remains to be proven, and the general idea of a long coexistence of Neandertals and AMH in Europe may be questioned. In western Central Europe, evidence of Gravettian human fossils is also very limited, although a new double grave from lower Austria may be relevant. The only dated burial from the German Upper Paleolithic (from Mittlere Klause) falls into a time period (circa 18,600 BP) represented by only a few occupation sites in western Central Europe. A number of human remains at Magdalenian sites appear to result from variable (secondary) burial practices. In contrast, the Final Paleolithic (circa 12,000-9600 cal. BC) yields an increase of hominin finds, including multiple burials (Bonn-Oberkassel, Neuwied-Irlich), similar to the situation in western and southern Europe

[djoser-xyyman]

Vindija cave and the modern human peopling of Europe.

Jankoviæ I, Karavaniæ I, Ahern JC, Brajkoviæ D, Lenardiæ JM, Smith FH.

Source

Institute for Anthropological Research, Zagreb, Croatia. [e-mail]

Abstract

Vindija cave in Croatia has yielded the youngest securely dated Neandertal skeletal remains in Central/Eastern Europe. In addition, these remains have been found in association with archaeological material exhibiting Upper Paleolithic elements. Due to its geographic location and date, the Vindija remains are particularly crucial for the understanding of initial modern human peopling of Europe and the nature of the Neandertal demise. The significance of archaeological and paleontological finds and hominin fossils from this site is discussed in the light of new finds at Vindija and recent developments in the fields of paleoanthropology and prehistoric archaeology. Furthermore, the impact of revised chronology for several crucial specimens and sites throughout Europe, including Vindija, is discussed.

PMID:

17058508

[PubMed - indexed for MEDLINE]

Hunters of the Ice Age: The biology of Upper Paleolithic people.

Holt BM, Formicola V.

Source

Department of Anthropology, University of Massachusetts, Amherst, MA 01003, USA. [e-mail]

Abstract

The Upper Paleolithic represents both the phase during which anatomically modern humans appeared and the climax of hunter-gatherer cultures. Demographic expansion into new areas that took place during this period and the diffusion of burial practices resulted in an unprecedented number of well-preserved human remains. This skeletal record, dovetailed with archeological, environmental, and chronological contexts, allows testing of hypotheses regarding biological processes at the population level. In this article, we review key studies about the biology of Upper Paleolithic populations based primarily on European samples, but integrating information from other areas of the Old World whenever possible. Data about cranial morphology, skeletal robusticity, stature, body proportions, health status, diet, physical activity, and genetics are evaluated in Late Pleistocene climatic and cultural contexts. Various lines of evidence delineate the Last Glacial Maximum (LGM) as a critical phase in the biological and cultural evolution of Upper Paleolithic populations. The LGM, a long phase of climatic deterioration culminating around 20,000 BP, had a profound impact on the environment, lifestyle, and behavior of human groups. Some of these effects are recorded in aspects of skeletal biology of these populations. Groups living before and after the LGM, Early Upper Paleolithic (EUP) and Late Upper Paleolithic (LUP), respectively, differ significantly in craniofacial dimensions, stature, robusticity, and body proportions. While paleopathological and stable isotope data suggest good health status throughout the Upper Paleolithic, some stress indicators point to a slight decline in quality of life in LUP populations. The intriguing and unexpected incidence of individuals affected by congenital disorders probably indicates selective burial practices for these abnormal individuals. While some of the changes observed can be explained through models of biocultural or environmental adaptation (e.g., decreased lower limb robusticity following decreased mobility; changes in body proportions along with climatic change), others are more difficult to explain. For instance, craniodental and upper limb robusticity show complex evolutionary patterns that do not always correspond to expectations. In addition, the marked decline in stature and the mosaic nature of change in body proportions still await clarifications. These issues, as well as systematic analysis of specific pathologies and possible relationships between genetic lineages, population movements and cultural complexes, should be among the goals of future research.

PMID:

[djoser-xyyman]

GB, Brisighelli F, Sanchez-Diz: The peopling of Europe and the cautionary tale of Y chromosome lineage R-M269. 2012



Abstract

Recently, the debate on the origins of the major European Y chromosome haplogroup R1b1b2-M269 has reignited, and opinion has moved away from Palaeolithic origins to the notion of a younger Neolithic spread of these chromosomes from the Near East. Here, we address this debate by investigating frequency patterns and diversity in the largest collection of R1b1b2-M269 chromosomes yet assembled. Our analysis reveals no geographical trends in diversity, in contradiction to expectation under the Neolithic hypothesis, and suggests an alternative explanation for the apparent cline in diversity recently described. We further investigate the young, STR-based time to the most recent common ancestor estimates proposed so far for R-M269-related lineages and find evidence for an appreciable effect of microsatellite choice on age estimates. As a consequence, the existing data and tools are insufficient to make credible estimates for the age of this haplogroup, and conclusions about the timing of its origin and dispersal should be viewed with a large degree of caution.

[djoser-xyyman]

For those insisting on Neanderthal admixture....


A major Y-chromosome haplogroup R1b Holocene era

founder effect in Central and Western Europe



Natalie M Myres1, Siiri Rootsi2, Alice A Lin3, Mari Ja¨rve2, Roy J King3, Ildus Kutuev2,4, Vicente M Cabrera5,

Elza K Khusnutdinova4, Andrey Pshenichnov2,6, Bayazit Yunusbayev2,4, Oleg Balanovsky2,6, Elena Balanovska6,

Pavao Rudan7, Marian Baldovic2,8, Rene J Herrera9, Jacques Chiaroni10, Julie Di Cristofaro10, Richard Villems2,

Toomas Kivisild11 and Peter A Underhill*,3





The phylogenetic relationships of numerous branches within the core Y-chromosome haplogroup R-M207 support a West Asian

origin of haplogroup R1b, its initial differentiation there followed by a rapid spread of one of its sub-clades carrying the M269

mutation to Europe. Here, we present phylogeographically resolved data for 2043 M269-derived Y-chromosomes from 118 West

Asian and European populations assessed for the M412 SNP that largely separates the majority of Central and West European

R1b lineages from those observed in Eastern Europe, the Circum-Uralic region, the Near East, the Caucasus and Pakistan.

Within the M412 dichotomy, the major S116 sub-clade shows a frequency peak in the upper Danube basin and Paris area with

declining frequency toward Italy, Iberia, Southern France and British Isles. Although this frequency pattern closely approximates

the spread of the Linearbandkeramik (LBK), Neolithic culture, an advent leading to a number of pre-historic cultural

developments during the past r10 thousand years, more complex pre-Neolithic scenarios remain possible for the L23(xM412)

components in Southeast Europe and elsewhere.



European Journal of Human Genetics (2011) 19, 95–101; doi:10.1038/ejhg.2010.146; published online 25 August 2010





INTRODUCTION

The complex pattern of European Y-chromosome diversity has been

ascribed to anatomically modern human dispersals, incorporating the

combined heritage of initial upper Paleolithic colonization, secondary

post-glacial mesolithic re-expansions and the Neolithic era demic

diffusion of agriculturalists from the Near East.1 Regardless of possibly

a minor autosomal contribution, as yet, there is no Y-chromosome

evidence of hybridization between Neanderthals and modern human

beings.2,3

[djoser-xyyman]

Quote:


Figure 4.

Locating the source of the strongest linear trend of Neanderthal fraction. Evenly-spaced
locations were chosen across Africa and Eurasia (worldgraph.10k, geography package, R) and from
each all land-only distances to the Eurasian samples in the Simons Genome Diversity Panel set were
calculated and the t-value of the regression against Neanderthal fraction noted. The resulting
heatmap reveals a high-point (dark red) around Northeast Egypt and a strongly positive slope
indicating the Neanderthal fraction increases with distance from Africa.




Differential base-sharing between humans and Neanderthals: inter-breeding
or greater mutability in heterozygotes?
Author and corresponding author: William Amos
Affiliation: Department of Zoology, Downing Street, Cambridge, CB2 3EJ, UK