The ancient cline of haplogroup K implies that the Neolithic transition in Europe was mainly demic

Interbreeding between farmers and hunter-gatherers along the inland and Mediterranean routes of Neolithic spread in Europe

The Neolithic (i.e., farming and stockbreeding) spread from the Near East across Europe since about 9000 years before the common era (BCE) until about 4000 yr BCE. It followed two main routes, namely a sea route along the northern Mediterranean coast and an inland one across the Balkans and central Europe. It is known that the dispersive behavior of farmers depended on geography, with longer movements along the Mediterranean coast than along the inland route. In sharp contrast, here we show that for both routes the percentage of farmers who interbred with hunter-gatherers and/or acculturated one of them was strikingly the same (about 3.6%). Therefore, whereas the dispersive behavior depended on the proximity to the Mediterranean sea, the interaction behavior (incorporation of hunter-gatherers) did not depend on geographical constraints but only on the transition in the subsistence economy (from hunting and gathering to farming) and its associated way of life. These conclusions are reached by analyzing the clines of haplogroup K, which was virtually absent in hunter-gatherers and the most frequent mitochondrial haplogroup in early farmers. Similarly, the most frequent Y-chromosome Neolithic haplogroup (G2a) displays an inland cline that agrees with the percentage of interbreeding reported above.

Mitochondrial DNA Haplogroup K Is Protective Against Autism Spectrum Disorder Risk in Populations of European Ancestry

OBJECTIVE

Accumulative evidence indicates a critical role of mitochondrial function in autism spectrum disorders (ASD), implying that ASD risk may be linked to mitochondrial dysfunction due to DNA (mtDNA) variations. Although a few studies have explored the association between mtDNA variations and ASD, the role of mtDNA in ASD is still unclear. Here, we aimed to investigate whether mitochondrial DNA haplogroups are associated with the risk of ASD.

METHOD

Two European cohorts and an Ashkenazi Jewish (AJ) cohort were analyzed, including 2,062 ASD patients in comparison with 4,632 healthy controls. DNA samples were genotyped using Illumina HumanHap550/610 and Illumina 1M arrays, inclusive of mitochondrial markers. Mitochondrial DNA (mtDNA) haplogroups were identified from genotyping data using HaploGrep2. A mitochondrial genome imputation pipeline was established to detect mtDNA variants. We conducted a case-control study to investigate potential associations of mtDNA haplogroups and variants with the susceptibility to ASD.

RESULTS

We observed that the ancient adaptive mtDNA haplogroup K was significantly associated with decreased risk of ASD by the investigation of 2 European cohorts including a total of 2,006 cases and 4,435 controls (odds ratio = 0.64, P=1.79 × 10-5), and we replicated this association in an Ashkenazi Jewish (AJ) cohort including 56 cases and 197 controls (odds ratio = 0.35, P = 9.46 × 10-3). Moreover, we demonstrate that the mtDNA variants rs28358571, rs28358584, and rs28358280 are significantly associated with ASD risk. Further expression quantitative trait loci (eQTLs) analysis indicated that the rs28358584 and rs28358280 genotypes are associated with expression levels of nearby genes in brain tissues, suggesting those mtDNA variants may confer risk for ASD via regulation of expression levels of genes encoded by the mitochondrial genome.

CONCLUSION

This study helps to shed light on the contribution of mitochondria in ASD and provides new insights into the genetic mechanism underlying ASD, suggesting the potential involvement of mtDNA-encoded proteins in the development of ASD.

PLAIN LANGUAGE SUMMARY

Increasing evidence indicates that mitochondrial dysfunction may be linked to autism spectrum disorder (ASD). This study investigated potential associations of mitochondrial DNA (mtDNA) variants in 2 European and Ashkenazi Jewish cohorts including 2,062 individuals with ASD and 4,632 healthy controls. Researchers found that the ancient mtDNA haplogroup K was linked to a reduced risk of ASD in both European and Ashkenazi Jewish populations. Additionally, specific mtDNA variants were associated with ASD risk and were shown to influence the expression of nearby genes in the brain. These findings highlight the potential involvement of mtDNA in ASD development, offering new insights into the genetic mechanisms underlying the disorder.

Neolithic expansion and the 17q21.31 inversion in Iberia: an evolutionary approach to H2 haplotype distribution in the Near East and Europe

The chromosomal region 17q21.31 harbors a 900 kb inversion polymorphism named after the microtubule-associated protein tau (MAPT) gene. Since no recombination occurs, two haplotypes are recognized: a directly oriented variant (H1) and an inverted variant (H2). The H2 haplotype features a distribution pattern with high frequencies in the Near East and Europe, medium levels in South Asia and North Africa, and low levels elsewhere. Studies of this genomic region are relevant owing to its likely association with numerous neurodegenerative diseases. However, the causes underlying the geographic distribution of the haplotype frequencies remain a bone of contention among researchers. With this work, we have intended to outline a plausible hypothesis on the origin of the high European H2 frequencies. To that end, we have analyzed an extensive population database (including three new Iberian populations) to explore potential clinal variations of H2 frequencies. We found a sigmoidal frequency cline with an upward trend from South Asia to Europe. The maximum value was detected in the Basques from Gipuzkoa province (0.494) with the curve's inflection point in the Near East. From our results, we suggest that the most likely scenario for high H2 frequencies in Europe would be a founding event in the Near East during the late Paleolithic or early Neolithic. Subsequently, such H2 overrepresentation would have reached Europe with the arrival of the first Neolithic farmers. The current frequencies and geographic distribution of the 17q21.31 inversion suggest that the founding events mainly affected the H2D subhaplotype.

Ancient mitochondrial diversity reveals population homogeneity in Neolithic Greece and identifies population dynamics along the Danubian expansion axis

The aim of the study is to investigate mitochondrial diversity in Neolithic Greece and its relation to hunter-gatherers and farmers who populated the Danubian Neolithic expansion axis. We sequenced 42 mitochondrial palaeogenomes from Greece and analysed them together with European set of 328 mtDNA sequences dating from the Early to the Final Neolithic and 319 modern sequences. To test for population continuity through time in Greece, we use an original structured population continuity test that simulates DNA from different periods by explicitly considering the spatial and temporal dynamics of populations. We explore specific scenarios of the mode and tempo of the European Neolithic expansion along the Danubian axis applying spatially explicit simulations coupled with Approximate Bayesian Computation. We observe a striking genetic homogeneity for the maternal line throughout the Neolithic in Greece whereas population continuity is rejected between the Neolithic and present-day Greeks. Along the Danubian expansion axis, our best-fitting scenario supports a substantial decrease in mobility and an increasing local hunter-gatherer contribution to the gene-pool of farmers following the initial rapid Neolithic expansion. Οur original simulation approach models key demographic parameters rather than inferring them from fragmentary data leading to a better understanding of this important process in European prehistory.

Genomic and dietary discontinuities during the Mesolithic and Neolithic in Sicily

Sicily is a key region for understanding the agricultural transition in the Mediterranean because of its central position. Here, we present genomic and stable isotopic data for 19 prehistoric Sicilians covering the Mesolithic to Bronze Age periods (10,700–4,100 yBP). We find that Early Mesolithic hunter-gatherers (HGs) from Sicily are a highly drifted lineage of the Early Holocene western European HGs, whereas Late Mesolithic HGs carry ∼20% ancestry related to northern and (south) eastern European HGs, indicating substantial gene flow. Early Neolithic farmers are genetically most similar to farmers from the Balkans and Greece, with only ∼7% of ancestry from local Mesolithic HGs. The genetic discontinuities during the Mesolithic and Early Neolithic match the changes in material culture and diet. Three outlying individuals dated to ∼8,000 yBP; however, suggest that hunter-gatherers interacted with incoming farmers at Grotta dell’Uzzo, resulting in a mixed economy and diet for a brief interlude at the Mesolithic-Neolithic transition.

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Genetic transition between Early Mesolithic and Late Mesolithic hunter-gatherers

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A near-complete genetic turnover during the Mesolithic-Neolithic transition

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Exchange of subsistence practices between hunter-gatherers and early farmers

A 5700 year-old human genome and oral microbiome from chewed birch pitch

The rise of ancient genomics has revolutionised our understanding of human prehistory but this work depends on the availability of suitable samples. Here we present a complete ancient human genome and oral microbiome sequenced from a 5700 year-old piece of chewed birch pitch from Denmark. We sequence the human genome to an average depth of 2.3× and find that the individual who chewed the pitch was female and that she was genetically more closely related to western hunter-gatherers from mainland Europe than hunter-gatherers from central Scandinavia. We also find that she likely had dark skin, dark brown hair and blue eyes. In addition, we identify DNA fragments from several bacterial and viral taxa, including Epstein-Barr virus, as well as animal and plant DNA, which may have derived from a recent meal. The results highlight the potential of chewed birch pitch as a source of ancient DNA.

Ancient Rome: A genetic crossroads of Europe and the Mediterranean

Ancient Rome was the capital of an empire of ~70 million inhabitants, but little is known about the genetics of ancient Romans. Here we present 127 genomes from 29 archaeological sites in and around Rome, spanning the past 12,000 years. We observe two major prehistoric ancestry transitions: one with the introduction of farming and another prior to the Iron Age. By the founding of Rome, the genetic composition of the region approximated that of modern Mediterranean populations. During the Imperial period, Rome's population received net immigration from the Near East, followed by an increase in genetic contributions from Europe. These ancestry shifts mirrored the geopolitical affiliations of Rome and were accompanied by marked interindividual diversity, reflecting gene flow from across the Mediterranean, Europe, and North Africa.

Assessing the importance of cultural diffusion in the Bantu spread into southeastern Africa

The subsistence of Neolithic populations is based on agriculture, whereas that of previous populations was based on hunting and gathering. Neolithic spreads due to dispersal of populations are called demic, and those due to the incorporation of hunter-gatherers are called cultural. It is well-known that, after agriculture appeared in West Africa, it spread across most of subequatorial Africa. It has been proposed that this spread took place alongside with that of Bantu languages. In eastern and southeastern Africa, it is also linked to the Early Iron Age. From the beginning of the last millennium BC, cereal agriculture spread rapidly from the Great Lakes area eastwards to the East African coast, and southwards to northeastern South Africa. Here we show that the southwards spread took place substantially more rapidly (1.50–2.27 km/y) than the eastwards spread (0.59–1.27 km/y). Such a faster southwards spread could be the result of a stronger cultural effect. To assess this possibility, we compare these observed ranges to those obtained from a demic-cultural wave-of-advance model. We find that both spreads were driven by demic diffusion, in agreement with most archaeological, linguistic and genetic results. Nonetheless, the southwards spread seems to have indeed a stronger cultural component, which could lead support to the hypothesis that, at the southern areas, the interaction with pastoralist people may have played a significant role.

Estimating the relative importance of demic and cultural diffusion in the spread of the Neolithic in Scandinavia

Using a database of early farming sites in Scandinavia, we estimate that the spread rate of the Neolithic was in the range 0.44-0.66 km yr-1 This is substantially slower (by about 50%) than the rate in continental Europe. We interpret this result in the framework of a new mathematical model that includes horizontal cultural transmission (acculturation), vertical cultural transmission (interbreeding) and demic diffusion (reproduction and dispersal of farmers). To parametrize the model, we estimate reproduction rates of early farmers using archaeological data (sum-calibrated probabilities for the dates of early Neolithic Scandinavian sites) and use them in a wave-of-advance model for the first time. Comparing the model with the archaeological data, we find that the percentage of the spread rate due to cultural diffusion is below 50% (except for very extreme parameter values, and even for them it is below 54%). This strongly suggests that the spread of the Neolithic in Scandinavia was driven mainly by demic diffusion. This conclusion, obtained from archaeological data, agrees qualitatively with the implications of ancient genetic data, but the latter are yet too few in Scandinavia to produce any quantitative percentage for the spread rate due to cultural diffusion. We also find that, on average, fewer than eight hunter-gatherers were incorporated in the Neolithic communities by each group of 10 pioneering farmers, via horizontal and/or vertical cultural transmission.

Mitochondrial variability in the Mediterranean area: a complex stage for human migrations

CONTEXT

The Mediterranean area has always played a significant role in human dispersal due to the large number of migratory events contributing to shape the cultural features and the genetic pool of its populations.

OBJECTIVE

This paper aims to review and diachronically describe the mitogenome variability in the Mediterranean population and the main demic diffusions that occurred in this area over time.

METHODS

Frequency distributions of the leading mitochondrial haplogroups have been geographically and chronologically evaluated. The variability of U5b and K lineages has been focussed to broaden the knowledge of their genetic histories.

RESULTS

The mitochondrial genetic makeup of Palaeolithic hunter-gatherers is poorly defined within the extant Mediterranean populations, since only a few traces of their genetic contribution are still detectable. The Neolithic lineages are more represented, suggesting that the Neolithic revolution had a marked effect on the peopling of the Mediterranean area. The largest effect, however, was provided by historical migrations.

CONCLUSION

Although the mitogenome variability has been widely used to try and clarify the evolution of the Mediterranean genetic makeup throughout almost 50 000 years, it is necessary to collect whole genome data on both extinct and extant populations from this area to fully reconstruct and interpret the impact of multiple migratory waves and their cultural and genetic consequences on the structure of the Mediterranean populations.