Prehistoric Human Migrations

[lpetrich]

Genomic perspectives on human dispersals during the Holocene | PNAS

Nearly 20 y ago, Jared Diamond and Peter Bellwood reviewed the evidence for the associated spread of farming and large language families by the demographic expansions of farmers. Since then, advances in obtaining and analyzing genomic data from modern and ancient populations have transformed our knowledge of human dispersals during the Holocene. Here, we provide an overview of Holocene dispersals in the light of genomic evidence and conclude that they have a complex history. Even when there is a demonstrated connection between a demographic expansion of people, the spread of agriculture, and the spread of a particular language family, the outcome in the results of contact between expanding and resident groups is highly variable. Further research is needed to identify the factors and social circumstances that have influenced this variation and complex history.

There are lots of complications with such research.

As discussed in more detail by Diamond and Bellwood (2), these include clinal admixture between expanding farmers and hunter-gatherers, resulting in decreasing genetic contributions by farmers toward the periphery of expansions; some hunter-gatherer groups adopting farming by cultural diffusion; farmers reverting to hunting and gathering (if, for example, they enter areas that are unsuitable for the domesticates they are bringing); language shift by resident groups with little or no incorporation of genes from the expanding population; replacement of the original language spoken by farmers in their homeland after the expansion (leading to discrepancies between genes and languages); and expansions of hunter-gatherers. An additional complicating factor is colonialism and the associated genetic, demographic, and territorial impact on indigenous groups. Failure to take such complications into consideration can lead to incorrect conclusions concerning the role of demic vs. cultural diffusion processes in the spread of farming and/or languages.

In summary, pots != people, and words != people.

 

[lpetrich]

There are some places where spread of farming closely correlates with language families, like with the Bantu and Austronesian ones, and some places, like mainland Southeast Asia, where no less than 5 language families coexist: Austroasiatic, Tai-Kadai, Sino-Tibetan, Hmong-Mien, and Austronesian.

These farmers may mix with the people already present, very little for eastern Africans, and more for southern Africans. Mixtures are sometimes sex-biased, like Bantu-speaking men and Khoisan-speaking women in southern Africa, whether their descendants speak Bantu or Khoisan languages.

Descendants of invaders speaking the conquered ones' languages? That's what happened in most of the Western Roman Empire after it was overrun by Germanic tribes in the early Middle Ages. In what's now England, western Germany, most of Switzerland, and Austria, the people ended up speaking the invaders' languages, but in what's now France, Spain, Portugal, and Italy, the invaders became assimilated and the people continued speaking descendants of Latin, the language of the Roman Empire.

 

[lpetrich]

Massive migration from the steppe was a source for Indo-European languages in Europe - PMC

What made it succeed? I've mentioned elsewhere a novel hypothesis: lactose tolerance, enabling milk drinking, thus providing an additional source of high-quality food.

Language Dispersal Beyond Farming - 9789027264640.pdf
Chapter 13, "Milk and the Indo-Europeans"

Recent evidence from archaeology and ancient DNA converge to indicate that the Yamnaya culture, often regarded as the bearer of the Proto-Indo-European language, underwent a strong population expansion in the late 4th and early 3rd millennia BCE. It suggests that the underlying reason for that expansion might be the then unique capacity to digest animal milk in adulthood. We examine the early Indo-European milk-related vocabulary to confirm the special role of animal milk in Indo-European expansions. We show that Proto-Indo-European did not have a specialized root for ‘to milk’ and argue that the IE root *h2melg̑- ‘to milk’ is secondary and post-Anatolian. We take this innovation as an indication of the novelty of animal milking in early Indo-European society. Together with a detailed study of language-specific innovations in this semantic field, we con clude that the ability to digest milk played an important role in boosting Proto-Indo-European demography.

 

[lpetrich]

Ancient X chromosomes reveal contrasting sex bias in Neolithic and Bronze Age Eurasian migrations - PubMed

Dramatic events in human prehistory, such as the spread of agriculture to Europe from Anatolia and the late Neolithic/Bronze Age migration from the Pontic-Caspian Steppe, can be investigated using patterns of genetic variation among the people who lived in those times. In particular, studies of differing female and male demographic histories on the basis of ancient genomes can provide information about complexities of social structures and cultural interactions in prehistoric populations. We use a mechanistic admixture model to compare the sex-specifically-inherited X chromosome with the autosomes in 20 early Neolithic and 16 late Neolithic/Bronze Age human remains. Contrary to previous hypotheses suggested by the patrilocality of many agricultural populations, we find no evidence of sex-biased admixture during the migration that spread farming across Europe during the early Neolithic. For later migrations from the Pontic Steppe during the late Neolithic/Bronze Age, however, we estimate a dramatic male bias, with approximately five to 14 migrating males for every migrating female. We find evidence of ongoing, primarily male, migration from the steppe to central Europe over a period of multiple generations, with a level of sex bias that excludes a pulse migration during a single generation. The contrasting patterns of sex-specific migration during these two migrations suggest a view of differing cultural histories in which the Neolithic transition was driven by mass migration of both males and females in roughly equal numbers, perhaps whole families, whereas the later Bronze Age migration and cultural shift were instead driven by male migration, potentially connected to new technology and conquest.

So the European Neolithic expansion was both sexes together, while the steppe-pastoralist Indo-European expansion was mostly invading men marrying local women.

 

[lpetrich]

Climatic windows for human migration out of Africa in the past 300,000 years | Nature Communications

Our present species originated in Africa, and non-Africans are descended from a population that left Africa around 65,000 years ago. The authors considered two routes, a northern route, down the Nile River and eastward across the Sinai Peninsula, and a southern one, across the Bab el Mandeb strait at the southern end of the Red Sea.

They also estimated the average rainfall for both routes, and the width of BeM. That strait is now 20 km wide, and during glacial periods, it dropped to 5 km.

For hunter-gatherers, none are known below 90 mm/yr, except a few that live near freshwater sources. That amount of rain is at the desert - dry shrubland boundary, and it is thus the minimum for supporting grazing animals.

It is possible to exit Africa at both routes during interglacials, but during glacials, only the southern route was feasible, and only feasible some of the time. Looking at 65 kyr, it was feasible in the south but not in the north, so all of us non-Africans are descended from people who crossed the BeM some 65 kyr ago. We are living in an interglacial one, and the previous one, the Eemian, was about 130 - 100 kyr ago, and at its peak near its beginning.

Then discussing "Failure of early waves to settle in Eurasia", like one that exited Africa in the Eemian or before then and got into the Levant, but not much further.

 

[lpetrich]

100 ancient genomes show repeated population turnovers in Neolithic Denmark - PMC

Major migration events in Holocene Eurasia have been characterized genetically at broad regional scales(1–4). However, insights into the population dynamics in the contact zones are hampered by a lack of ancient genomic data sampled at high spatiotemporal resolution(5–7). Here, to address this, we analysed shotgun-sequenced genomes from 100 skeletons spanning 7,300 years of the Mesolithic period, Neolithic period and Early Bronze Age in Denmark and integrated these with proxies for diet (13C and 15N content), mobility (87Sr/86Sr ratio) and vegetation cover (pollen). We observe that Danish Mesolithic individuals of the Maglemose, Kongemose and Ertebølle cultures form a distinct genetic cluster related to other Western European hunter-gatherers. Despite shifts in material culture they displayed genetic homogeneity from around 10,500 to 5,900 calibrated years before present, when Neolithic farmers with Anatolian-derived ancestry arrived. Although the Neolithic transition was delayed by more than a millennium relative to Central Europe, it was very abrupt and resulted in a population turnover with limited genetic contribution from local hunter-gatherers. The succeeding Neolithic population, associated with the Funnel Beaker culture, persisted for only about 1,000 years before immigrants with eastern Steppe-derived ancestry arrived. This second and equally rapid population replacement gave rise to the Single Grave culture with an ancestry profile more similar to present-day Danes. In our multiproxy dataset, these major demographic events are manifested as parallel shifts in genotype, phenotype, diet and land use.

The first Holocene population, the Mesolithic population, gradually transitioned from largely land foods to largely marine foods.

Our results demonstrate a population turnover in Denmark at the onset of the neolithisation by incomers who displayed a mix of Anatolian Neolithic farmer ancestry and non-local hunter-gatherer ancestry. Ancestry related to the local Danish hunter-gatherers could be detected only late in the Danish Neolithic gene pool, suggesting gene flow with groups of late surviving hunter-gatherers, as also documented in other European regions (Iron Gates(45), Central Europe(13) and Spain(46)). We do not know how the Mesolithic Ertebølle population disappeared. Some may have been isolated in small ‘pockets’ of brief existence and/or adapted to a Neolithic lifestyle.

If the incoming farmers' agriculture could support a greater population density, then the existing population could simply have been swamped by the incomers. However, some of the indigenous HG's joined the early farmers as they spread over Europe, with Danish Neolithic people having some of the largest admixture of HG's: 10–35%.

In any case, agriculture was their main source of food since around 5,900 BP.

Europe was transformed by large-scale migrations from the Pontic–Caspian Steppe around 5,000–4,800 cal. bp. This introduced steppe-related ancestry to most parts of the continent within a 1,000-year span and gave rise to the Corded Ware culture (CWC) complex(1,2). In Denmark, this coincided with the transition from the FBC to the SGC, the regional manifestation of the CWC complex.

FBC = Funnel Beaker culture
SGC = Single Grave culture

 

[lpetrich]

During the Mesolithic, the landscape was dominated by primary forest trees (Tilia, Ulmus, Quercus, Fraxinus, Alnus and so on). At the onset of the Neolithic, the primary forest diminished, cleared by FBC farmers. A new type of forest with more secondary and early successional trees (Betula and then Corylus) appeared, whereas the proportion between forest and open land remained almost unaltered. From about 5,650 cal. bp deforestation intensified, resulting in an open grassland-dominated landscape. This open phase was short-lived, and the secondary forest expanded again from around 5,500 to 5,000 cal. bp, until another episode of forest clearance occurred during the last part of the FBC epoch. We conclude that the agricultural practice during the FBC was characterized by repeated clearing of the forest followed by regrowth. After about 4,600 cal bp, this strategy changed with the emergence of the SGC and the arrival of Steppe-related ancestry in Denmark. In Western Denmark (Jutland), the arrival of the SGC was characterized by permanent large-scale opening of the landscape to create pastureland(63,64) and we observe here a similar increase in grassland and cropland at Højby Sø in Eastern Denmark around 4,600 cal. bp (Fig. (Fig.3).3). Notably, this was accompanied by an increase in primary forest cover, especially Tilia and Ulmus, probably reflecting a development of a more permanent division of the landscape into open grazing areas and primary forests.

Land use:

• Mesolithic: forests intact
• Neolithic: forests chopped down now and then
• Steppe pastoralists: forests permanently chopped down

The steppe pastoralists likely spoke an ancestor of Proto-Germanic.