Genetic evidence for prehistoric demographic changes in Europe

Objectives: Two main models have been proposed to explain the origins of the patterns of genetic variation in Europe, one emphasizing Paleolithic and the other Neolithic immigration from the Southeast. In this paper, I summarize how the models developed and how they can help address some open questions. Methods: The rationale of the methods traditionally supporting the Neolithic and the Paleolithic models is discussed, and the evidence supporting either of them is reviewed. Results: Ancient DNA evidence proves for good that the studies traditionally supporting the Paleolithic model had serious methodological flaws. This does not imply that the alternative model is right, but rather calls for further analyses explicitly testing the two models against the genomic information now available. Conclusions: Questions that need to be addressed include whether the two main models differ enough to be discriminated by analyses of modern DNA diversity, and to what extent inferences from ancient mitochondrial DNA can be trusted in the absence of sufficient datasets of ancient nuclear DNA. The time seems ripe for the construction of a more complex (and hence more realistic) model, incorporating the possibility of different processes affecting different geographic locations at different times

Neolithic demic diffusion

In 1978, Paolo Menozzi, Alberto Piazza, and Luca Cavalli-Sforza paved the ground for a new multidisciplinary approach to the study of human prehistory, interpreting genetic evidence in the light of archaeological information. By producing synthetic maps of allele frequencies and summarizing them by principal component analysis (PCA), they identified an association between patterns in genetic diversity across Europe and in the Neolithic archaeological record showing the earliest documented dates of farming societies. Based on this observation, they proposed a model of demic diffusion from the Near East. They argued that the observed patterns were the result of population growth due to increased food availability in early farming communities, westward dispersal of early farmers, and relative isolation between dispersing farmers and local hunter-gatherers. These results played a major role in our understanding of the Neolithic transition, but were also criticized on methodological grounds. For instance, it has become increasingly clear that the interpretation of PCA plots is less straightforward than originally thought, and correlations should be corroborated by explicit comparison of alternative demographic models. Despite these valid criticisms, genetic and genomic studies, including those involving ancient DNA, have largely confirmed the crucial role of the Neolithic transition as a process of demographic change in European prehistory, with some qualifications. Today, there is still much to be learned about the details of that complex history, but many researchers regard the European population structure as largely reflecting the genetic consequences of three major migrations: from Africa in Upper Paleolithic times, from the Near East at the beginning of the Neolithic, and from the eastern steppes in the Bronze Age. This deep structure has not been erased, despite many additional processes involving historical migrations, isolation (i.e., drift) and local gene flow, and has been recognized thanks to the pioneering work of Menozzi, Piazza and Cavalli-Sforza

Author Correction: An earlier revolution: genetic and genomic analyses reveal pre-existing cultural differences leading to Neolithization.

A correction to this article has been published and is linked from the HTML version of this paper. The error has not been fixed in the paper

Diversidad genética, entre y dentro de los mayores grupos humanos

Varios estudios están de acuerdo cuando reportan que cerca del 85% de la diversidad del ADN autosomal y de los loci de las proteínas se debe a diferencias entre individuos dentro de la misma población, mientras que las diferencias entre los grupos de diferentes continentes son responsables de solamente 10% de la variación genética total. Estos resultados están en conflicto con nociones populares de razas humanas claramente distintas y relativamente homogéneas, y nos hacen cuestionar la utilidad de clasificaciones étnicas en diagnósticos médicos, en el campo forense y en genética farmacológica. Nuevos datos obtenidos de inserciones polimórficas de Alu y del cromosoma Y confirman los resultados previos, aunque indican una diversidad mayor en algunos (pero no todos) los loci del cromosoma Y. Estos datos nos permiten investigar dos preguntas: (1) si las diferencias continentales, aunque pequeñas, son suficientemente grandes como para asignar a individuos a sus continentes basados en sus genotipos; (2) si los genotipos observados se agrupan en grupos de población o continentales cuando el origen de la muestra se ignora. Usando varios métodos estadísticos, veremos que los errores de clasificación son por lo menos de un 30% para los polimorfismos autosomales bi-alélicos, y de un 27% para el cromosoma Y. Cuatro series de datos genéticos de todo el mundo sugieren la existencia de grupos de genotipos diferentes, pero que éstos cuatro grupos no coinciden el uno con el otro. Adicionalmente, estudios de bloques de ADN del genoma humano indican que la mayor parte de dichos bloques es compartida entre los continentes, con solamente un pequeño porcentaje siendo específico a ciertos continentes. Estos resultados no indican que haya una base clara para subdividir a los humanos en grupos biológicamente definidos. Este puede no ser un problema en áreas aplicadas de genéticas, dado que los métodos rápidos para obtener genotipos individuales posiblemente permita el obtener métodos diagnósticos individuales, y no basados en la raza.Asociación de Antropología Biológica de la República Argentin

Genomic Evidence for an African Expansion of Anatomically Modern Humans by a Southern Route

There is general agreement among scientists about a recent (less than 200,000 yrs ago) African origin of anatomically modern humans, whereas there is still uncertainty about whether, and to what extent, they admixed with archaic populations, which thus may have contributed to the modern populations’ gene pools. Data on cranial morphology have been interpreted as suggesting that, before the main expansion from Africa through the Near East, anatomically modern humans may also have taken a Southern route from the Horn of Africa through the Arabian peninsula to India, Melanesia and Australia, about 100,000 yrs ago. This view was recently supported by archaeological findings demonstrating human presence in Eastern Arabia 90,000 yrs ago. In this study we analyzed genetic variation at 111,197 nuclear SNPs in nine populations (Kurumba, Chenchu, Kamsali, Madiga, Mala, Irula, Dalit, Chinese, Japanese), chosen because their genealogical relationships are expected to differ under the alternative models of expansion (single vs. multiple dispersals). We calculated correlations between genomic distances, and geographic distances estimated under the alternative assumptions of a single dispersal, or multiple dispersals, and found a significantly stronger association for the multiple dispersal model. If confirmed, this result would cast doubts on the possibility that some non-African populations (i.e., those whose ancestors expanded through the Southern route) may have had any contacts with Neandertals

Diversidad genética, entre y dentro de los mayores grupos humanos

Varios estudios están de acuerdo cuando reportan que cerca del 85% de la diversidad del ADN autosomal y de los loci de las proteínas se debe a diferencias entre individuos dentro de la misma población, mientras que las diferencias entre los grupos de diferentes continentes son responsables de solamente 10% de la variación genética total. Estos resultados están en conflicto con nociones populares de razas humanas claramente distintas y relativamente homogéneas, y nos hacen cuestionar la utilidad de clasificaciones étnicas en diagnósticos médicos, en el campo forense y en genética farmacológica. Nuevos datos obtenidos de inserciones polimórficas de Alu y del cromosoma Y confirman los resultados previos, aunque indican una diversidad mayor en algunos (pero no todos) los loci del cromosoma Y. Estos datos nos permiten investigar dos preguntas: (1) si las diferencias continentales, aunque pequeñas, son suficientemente grandes como para asignar a individuos a sus continentes basados en sus genotipos; (2) si los genotipos observados se agrupan en grupos de población o continentales cuando el origen de la muestra se ignora. Usando varios métodos estadísticos, veremos que los errores de clasificación son por lo menos de un 30% para los polimorfismos autosomales bi-alélicos, y de un 27% para el cromosoma Y. Cuatro series de datos genéticos de todo el mundo sugieren la existencia de grupos de genotipos diferentes, pero que éstos cuatro grupos no coinciden el uno con el otro. Adicionalmente, estudios de bloques de ADN del genoma humano indican que la mayor parte de dichos bloques es compartida entre los continentes, con solamente un pequeño porcentaje siendo específico a ciertos continentes. Estos resultados no indican que haya una base clara para subdividir a los humanos en grupos biológicamente definidos. Este puede no ser un problema en áreas aplicadas de genéticas, dado que los métodos rápidos para obtener genotipos individuales posiblemente permita el obtener métodos diagnósticos individuales, y no basados en la raza.Asociación de Antropología Biológica de la República Argentin

Reasoning has become a luxury

It is being talked about all over the world; an editorial in the Economist of 19 October 2013 entitled “How Science Goes Wrong” reports a dramatic decline in the quality of scientific publications. Research has changed the world, now it needs to change itself, the subheading reads. The detailed report is based on facts which are difficult to disprove; an example being a Harvard biologist, John Bohannon, who sent an invented article full of nonsense on how to combat cancer using lichens to 304 scientific journals. Of this number, 157 accepted it for publication. While these publications were second tier, the problem affects them all, even those of greater importance

Genealogical Relationships between Early Medieval and Modern Inhabitants of Piedmont

Vai, Stefania et al.In the period between 400 to 800 AD, also known as the period of the Barbarian invasions, intense migration is documented in the historical record of Europe. However, little is known about the demographic impact of these historical movements, potentially ranging from negligible to substantial. As a pilot study in a broader project on Medieval Europe, we sampled 102 specimens from 5 burial sites in Northwestern Italy, archaeologically classified as belonging to Lombards or Longobards, a Germanic people ruling over a vast section of the Italian peninsula from 568 to 774. We successfully amplified and typed the mitochondrial hypervariable region I (HVR-I) of 28 individuals. Comparisons of genetic diversity with other ancient populations and haplotype networks did not suggest that these samples are heterogeneous, and hence allowed us to jointly compare them with three isolated contemporary populations, and with a modern sample of a large city, representing a control for the effects of recent immigration. We then generated by serial coalescent simulations 16 millions of genealogies, contrasting a model of genealogical continuity with one in which the contemporary samples are genealogically independent from the medieval sample. Analyses by Approximate Bayesian Computation showed that the latter model fits the data in most cases, with one exception, Trino Vercellese, in which the evidence was compatible with persistence up to the present time of genetic features observed among this early medieval population. We conclude that it is possible, in general, to detect evidence of genealogical ties between medieval and specific modern populations. However, only seldom did mitochondrial DNA data allow us to reject with confidence either model tested, which indicates that broader analyses, based on larger assemblages of samples and genetic markers, are needed to understand in detail the effects of medieval migration.This work was supported by the Italian Ministry for Universities and Research (MIUR), PRIN 2012 funds to DC, AA, AT and GB, FIRB funds “Futuro in Ricerca” 2008 (RBFR08U07M) and 2012 (RBFR126B8I) to AA, AO and ER; Compagnia di San Paolo, Turin to DC; the Anneliese Maier Research Award of the Alexander von Humboldt Foundation and the German Federal Ministry for Education and Research to PG; FEDER and Spanish Government grant BFU2012-34157 to CLF; European Research Council (ERC Advanced Grant No. 295733 “LanGeLin”) to GB.Peer reviewe

An earlier revolution: genetic and genomic analyses reveal pre-existing cultural differences leading to Neolithization

Archaeological evidence shows that, in the long run, Neolitization (the transition from foraging to food production) was associated with demographic growth. We used two methods (patterns of linkage disequilibrium from whole-genome SNPs and MSMC estimates on genomes) to reconstruct the demographic profiles for respectively 64 and 24 modern-day populations with contrasting lifestyles across the Old World (sub-Saharan Africa, south-eastern Asia, Siberia). Surprisingly, in all regions, food producers had larger effective population sizes ($N_e$) than foragers already 20k years ago, well before the Neolithic revolution. As expected, this difference further increased ~12–10k years ago, around or just before the onset of food production. Using paleoclimate reconstructions, we show that the early difference in $N_e$ cannot be explained by food producers inhabiting more favorable regions. A number of mechanisms, including ancestral differences in census size, sedentism, exploitation of the natural resources, social stratification or connectivity between groups, might have led to the early differences in Ne detected in our analyses. Irrespective of the specific mechanisms involved, our results provide further evidence that long term cultural differences among populations of Palaeolithic hunter-gatherers are likely to have played an important role in the later Neolithization process.This work was supported by the European Research Council ERC-2011-AdG_295733 grant (LanGeLin) to GB and ERC Consolidator Grant 647787 ‘LocalAdaptation’ to AM. ML has been awarded with the SIBE (Società Italiana di Biologia Evolutiva) “Doctor Darwin prize” for this research

Formal linguistics as a cue to demographic history

Beyond its theoretical success, the development of molecular genetics has brought about the possibility of extraordinary progress in the study of classification and in the inference of the evolutionary history of many species and populations. A major step forward was represented by the availability of extremely large sets of molecular data suited to quantitative and computational treatments. In this paper, we argue that even in cognitive sciences, purely theoretical progress in a discipline such as linguistics may have analogous impact. Thus, exactly on the model of molecular biology, we propose to unify two traditionally unrelated lines of linguistic investigation: 1) the formal study of syntactic variation (parameter theory) in the biolinguistic program 2) the reconstruction of relatedness among languages (phylogenetic taxonomy) The results of our linguistic analysis have thus been plotted against data from population genetics and the correlations have turned out to be largely significant: given a non-trivial set of languages/populations, the description of their variation provided by the comparison of systematic parametric analysis and molecular anthropology informatively recapitulates their history and relationships. As a result, we can claim that the reality of some parametric model of the language faculty and language acquisition/transmission (more broadly of generative grammar) receives strong and original support from its historical heuristic power. Then, on these grounds, we can begin testing Darwin's prediction that, when properly generated, the trees of human populations and of their languages should eventually turn out to be significantly parallel