Linguistic continuity despite genetic replacement in Remote Oceania

oceania-ancient-migration

Review of recent papers on East Asia, quite relevant these days: Human Genetics: Busy Subway Networks in Remote Oceania? by Anders Bergström & Chris Tyler-Smith, Current Biology (2018) 28.

Interesting excerpts (emphasis mine):

Ancient DNA is transforming our understanding of the human past by forcing geneticists to confront its real complexity [1]. Historians and archaeologists have long known that the development of human societies was complex and often haphazard, but geneticists have persistently tried to explain present-day patterns of genetic variation using simple models.

Early genetic analyses of present-day populations revealed a mix of Asian (Taiwanese) and Papuan (New Guinea or nearby) ancestries throughout Remote Oceania, with maternally-inherited mitochondrial DNA being predominantly Asian, paternally-inherited Y chromosomes mainly Papuan, and autosomes intermediate [7]. This led to the simple model mentioned above of an Austronesian-speaking population starting out from Taiwan, developing the Lapita culture in the islands near New Guinea while mixing with local Papuans, and then boldly launching out into the unknown Pacific.

The surprise came with the first studies of ancient DNA, when early Lapita people from Vanuatu and Tonga (ca. 2,500-3,000 yBP) showed completely Asian genetic ancestry, so the Papuan genetic component must have entered later.

This is what the most recent ancient DNA papers found:

remote-oceania-vanuatu

There thus seems to have been a migration of Papuan-ancestry people from the Bismarck archipelago off the coast of New Guinea, into the islands of Remote Oceania, shortly after those very islands were first settled by people from Asia. Few traces of such a migration and its cultural or technological underpinnings have been found in the archaeological record or in linguistic relationships, which is why it comes as such a surprise. The fact that these Near Oceanian people made the long journey to Vanuatu so soon after the Asian seafarers arrived in their neighbourhood, having had tens of thousands of years to do so previously, strongly suggest that the migration was somehow triggered by interactions with the new Austronesian-speaking arrivals and adoption of their sophisticated seafaring technology. The excess of Y chromosomes of Papuan origin in Remote Oceania, somewhat difficult to explain under the traditional model, might also make sense in the light of an active expansion of people from Near Oceania, as such expansions have often found to be male-biased [10]. Both studies speculate that the arrival of these Papuan-ancestry people might have contributed to the end of the Lapita period and its cultural unity.

The very first settlers of Vanuatu would have spoken Austronesian languages, and the Papuan-ancestry people who arrived shortly after would very likely have spoken Papuan languages. Yet today, all languages of Vanuatu are Austronesian. The arrivals from Near Oceania thus seem to have largely replaced the first settlers but adopted their languages. Posth and colleagues [5] argue that the languages of Vanuatu actually contain some elements of Papuan origin, and that the ancient DNA results are compatible with a more gradual process of cultural interaction and genetic mixing, rather than sudden replacement. Nonetheless, linguistic continuity in the face of this almost complete genetic replacement is extremely unusual in human history, perhaps even unprecedented as Posth and colleagues [5] suggest.

We are seeing now from the Anatolian expansion and in the formation of the Indo-Iranian community that such processes were actually not as unusual as some had previously thought…

Related:

Two sources of archaic Denisovan ancestry in East Asia, one possibly after the isolation of Native Americans

east-asian-ancestry

Open access paper Analysis of Human Sequence Data Reveals Two Pulses of Archaic Denisovan Admixture, by Sharon L. Browning, Brian L. Browning, Zhou, Tucci, & Akey, Cell (2018).

Summary:

Anatomically modern humans interbred with Neanderthals and with a related archaic population known as Denisovans. Genomes of several Neanderthals and one Denisovan have been sequenced, and these reference genomes have been used to detect introgressed genetic material in present-day human genomes. Segments of introgression also can be detected without use of reference genomes, and doing so can be advantageous for finding introgressed segments that are less closely related to the sequenced archaic genomes. We apply a new reference-free method for detecting archaic introgression to 5,639 whole-genome sequences from Eurasia and Oceania. We find Denisovan ancestry in populations from East and South Asia and Papuans. Denisovan ancestry comprises two components with differing similarity to the sequenced Altai Denisovan individual. This indicates that at least two distinct instances of Denisovan admixture into modern humans occurred, involving Denisovan populations that had different levels of relatedness to the sequenced Altai Denisovan.

neanderthal-denisovan-admixture
Mean detected archaic sequence per individual (Mb)

The discussion on the potential implication of the paper:

Featured image, from the article: Contour Density Plots of Match Proportion of Introgressed Segments to the Altai Neanderthal and Altai Denisovan Genomes.

Related:

Genomics reveals four prehistoric migration waves into South-East Asia

Open access preprint article at bioRxiv Ancient Genomics Reveals Four Prehistoric Migration Waves into Southeast Asia, by McColl, Racimo, Vinner, et al. (2018).

Abstract (emphasis mine):

Two distinct population models have been put forward to explain present-day human diversity in Southeast Asia. The first model proposes long-term continuity (Regional Continuity model) while the other suggests two waves of dispersal (Two Layer model). Here, we use whole-genome capture in combination with shotgun sequencing to generate 25 ancient human genome sequences from mainland and island Southeast Asia, and directly test the two competing hypotheses. We find that early genomes from Hoabinhian hunter-gatherer contexts in Laos and Malaysia have genetic affinities with the Onge hunter-gatherers from the Andaman Islands, while Southeast Asian Neolithic farmers have a distinct East Asian genomic ancestry related to present-day Austroasiatic-speaking populations. We also identify two further migratory events, consistent with the expansion of speakers of Austronesian languages into Island Southeast Asia ca. 4 kya, and the expansion by East Asians into northern Vietnam ca. 2 kya. These findings support the Two Layer model for the early peopling of Southeast Asia and highlight the complexities of dispersal patterns from East Asia.

A model for plausible migration routes into Southeast Asia, based on the ancestry patterns observed in the ancient genomes.

Related:

Population turnover in Remote Oceania shortly after initial settlement

oceania-ancient-migration

Open Access article Population Turnover in Remote Oceania Shortly after Initial Settlement, by Lipson, Skoglund, Spriggs, et al. (2018), based on the recent preprint at bioRxiv.

Summary:

Ancient DNA from Vanuatu and Tonga dating to about 2,900–2,600 years ago (before present, BP) has revealed that the “First Remote Oceanians” associated with the Lapita archaeological culture were directly descended from the population that, beginning around 5000 BP, spread Austronesian languages from Taiwan to the Philippines, western Melanesia, and eventually Remote Oceania. Thus, ancestors of the First Remote Oceanians must have passed by the Papuan-ancestry populations they encountered in New Guinea, the Bismarck Archipelago, and the Solomon Islands with minimal admixture [ 1 ]. However, all present-day populations in Near and Remote Oceania harbor >25% Papuan ancestry, implying that additional eastward migration must have occurred. We generated genome-wide data for 14 ancient individuals from Efate and Epi Islands in Vanuatu from 2900–150 BP, as well as 185 present-day individuals from 18 islands. We find that people of almost entirely Papuan ancestry arrived in Vanuatu by around 2300 BP, most likely reflecting migrations a few hundred years earlier at the end of the Lapita period, when there is also evidence of changes in skeletal morphology and cessation of long-distance trade between Near and Remote Oceania [ 2, 3 ]. Papuan ancestry was subsequently diluted through admixture but remains at least 80%–90% in most islands. Through a fine-grained analysis of ancestry profiles, we show that the Papuan ancestry in Vanuatu derives from the Bismarck Archipelago rather than the geographically closer Solomon Islands. However, the Papuan ancestry in Polynesia—the most remote Pacific islands—derives from different sources, documenting a third stream of migration from Near to Remote Oceania

oceania-vanuatu
The population of Vanuatu in the Pacific was largely replaced2,900–2,300 years ago
This second wave of migrants came from New Britain, east of New Guinea
A third wave spread different ancestry to the far-flung islands of Polynesia

See also:

Population turnover in remote Oceania shortly after initial settlement

papuan-oceanian

Interesting preprint at BioRxiv by the team of the Reich lab, Population Turnover in Remote Oceania Shortly After Initial Settlement, by Mark Lipson, Pontus Skoglund, Matthew Spriggs, et al. (2018).

Abstract (emphasis mine):

Ancient DNA analysis of three individuals dated to ~3000 years before present (BP) from Vanuatu and one ~2600 BP individual from Tonga has revealed that the first inhabitants of Remote Oceania (“First Remote Oceanians”) were almost entirely of East Asian ancestry, and thus their ancestors passed New Guinea, the Bismarck Archipelago, and the Solomon Islands with minimal admixture with the Papuan groups they encountered. However, all present-day populations in Near and Remote Oceania harbor 25-100% Papuan ancestry, implying that there must have been at least one later stream of migration eastward from Near Oceani>. We generated genome-wide data for 14 ancient individuals from Efate and Epi Islands in Vanuatu ranging from 3,000-150 BP, along with 185 present-day Vanuatu individuals from 18 islands. We show that people of almost entirely Papuan ancestry had arrived in Vanuatu by 2400 BP, an event that coincided with the end of the Lapita cultural period, changes in skeletal morphology, and the cessation of long-distance trade between Near and Remote Oceania. First Remote Oceanian ancestry subsequently increased via admixture but remains at 10-20% in most islands. Through a fine-grained comparison of ancestry profiles in Vanuatu and Polynesia with diverse groups in Near Oceania, we find that Papuan ancestry in Vanuatu is consistent with deriving from the Bismarck Archipelago instead of the geographically closer Solomon Islands. Papuan ancestry in Polynesia also shows connections to the ancestry profiles present in the Bismarck Archipelago but is more similar to Tolai from New Britain and Tutuba from Vanuatu than to the ancient Vanuatu individuals and the great majority of present-day Vanuatu populations. This suggests a third eastward stream of migration from Near to Remote Oceania bringing a different type of Papuan ancestry.

qpgraph-oceanian-papuan
Admixture graph model with inferred parameters, alternative visualization. Branch lengths are given in units of f2 genetic drift distance times 1000, and admixture proportions are indicated along corresponding dotted lines. Red, Solomon Islands majority source; blue, Bismarck Archipelago majority source; purple, New Guinea-related source; green, First Remote Oceanian; brown, mixed ancestry. The order of admixture events specified is arbitrary.

See also:

Islands across the Indonesian archipelago show complex patterns of admixture

austronesian-dna

An open access article Complex patterns of admixture across the Indonesian archipelago, by Hudjashov et al. (2017), has appeared in Molecular Biology and Evolution, and clarifies further the Austronesian (AN) expansion.

Abstract:

Indonesia, an island nation as large as continental Europe, hosts a sizeable proportion of global human diversity, yet remains surprisingly under-characterized genetically. Here, we substantially expand on existing studies by reporting genome-scale data for nearly 500 individuals from 25 populations in Island Southeast Asia, New Guinea and Oceania, notably including previously unsampled islands across the Indonesian archipelago. We use high-resolution analyses of haplotype diversity to reveal fine detail of regional admixture patterns, with a particular focus on the Holocene. We find that recent population history within Indonesia is complex, and that populations from the Philippines made important genetic contributions in the early phases of the Austronesian expansion. Different, but interrelated processes, acted in the east and west. The Austronesian migration took several centuries to spread across the eastern part of the archipelago, where genetic admixture postdates the archeological signal. As with the Neolithic expansion further east in Oceania and in Europe, genetic mixing with local inhabitants in eastern Indonesia lagged behind the arrival of farming populations. In contrast, western Indonesia has a more complicated admixture history shaped by interactions with mainland Asian and Austronesian newcomers, which for some populations occurred more than once. Another layer of complexity in the west was introduced by genetic contact with maritime travelers from South Asia and strong demographic events in isolated local groups.

Among its results (emphasis is mine):

Most eastern Indonesian populations show traces of admixture that appear to reflect an expansion of AN speakers (Figure 4B, S3). There is a striking similarity between inferred events – each admixed population includes both a Philippine non-Kankanaey and western Indonesian-like source likely representing Holocene movements of Asian farming groups, as well as a Papuan-like source representing local indigenous ancestry. One reason for the lack of clear Taiwanese sources may be because the aboriginal populations of Taiwan were heavily affected by post-AN movements from mainland East Asia, most recently sinicization by Han Chinese, and thus no longer depict the ancestral AN gene pool (Mörseburg, et al. 2016). However, this notable pattern could equally be explained by the dominance of language and culture transfers during early phases of the Neolithic expansion from Taiwan into the Philippines, followed by people with predominantly Philippine ancestry driving later demic diffusion into the Indonesian archipelago. Interestingly, Mörseburg, et al. (2016), by using a different sample set and genotype-based analytical toolkit, indicated that the Kankanaey ethnic group from the Philippines is likely the closest living proxy of the source population that gave rise to the AN expansion. We did not detect this population among sources of admixture in eastern Indonesia, and therefore suggest that the place of individual Philippine groups in the AN expansion needs to be further addressed by better sampling in the Philippine archipelago.

Sumba and Flores, the two westernmost islands to the east of Wallace’s line, display a high proportion of Java and Bali surrogates in their AN admixing source. This suggests that the AN movement into eastern Indonesia, especially for Sumba and Flores, had earlier experienced some degree of genetic contact with western Indonesian groups. In contrast, the sources of AN admixture in Lembata, Alor, Pantar and Timor are dominated by Sulawesi (Figure 4B, S3, Table S3, S5). This generally agrees with expectations from the geography of the region, whereby AN groups exiting the southern Philippines were likely funneled into at least two streams, including a western path through Borneo and a central path through Sulawesi (Blust 2014).

Point estimates of genetic admixture times in eastern Indonesia lie within a narrow timeframe ranging between ca 185 BCE to 360 CE or 75 to 56 generations ago (95% CI 510 BCE – 475 CE or 87–52 generations) (Figure 4B, Table S3). These inferred dates are younger than some previous estimates (120–200 generations ago) (Xu, et al. 2012; Sanderson, et al. 2015; Sedghifar, et al. 2015). A major analysis of admixture in Indonesia estimated the date of AN contact in the eastern part of archipelago to be around 500 to 600 CE (ca 50 generations, CI estimates between 58–42 generations ago) (Lipson, et al. 2014), surprisingly young given the archaeological evidence. However, the study pooled a very small sample of genetically heterogeneous eastern Indonesian islands including, for example, Flores and Alor. As we show here (Figure 2, 4, 5, S3, Table S3, S5, S6), while the wave of AN speakers left a common genetic trace across the whole of eastern Indonesia, the details and dates of this contact vary considerably not only between islands (e.g., Flores and Alor), but also within individual islands (e.g., Flores Rampasasa vs. Flores Bama). The genetic dates, which were obtained here by denser geographical sampling of 8 eastern islands, a much larger number of individuals (28 per island on average) and a greater number of SNPs, are up to 30 generations older, predating the Common Era in many cases.

It therefore took migrants at least half a millennium to proceed from islands around Wallace’s line to the easternmost sampled part of eastern Indonesia. Nevertheless, observed dates for AN contact in eastern Indonesia are still approximately a millennium younger than the earliest Neolithic archaeological evidence in the region, and two explanations seem most likely here. First, the AN migration may have involved several waves of people leaving Taiwan, spanning multiple generations, which would bias date estimates later than the first arrival of the Neolithic archeological assemblage (Sedghifar, et al. 2015). Second, there may have been a substantial time gap between the spread of culture and technological traditions, and the beginning of extensive genetic contact between incoming farming groups and native inhabitants in Indonesia (Lansing, et al. 2011). The lack of considerable admixture with Papuan groups was recently noted in ancient Lapita individuals from Remote Oceania, whose genomes are mostly Asian and carry little to no Papuan ancestry, suggesting limited contact as they moved through Melanesia to previously uninhabited islands in the Pacific (Skoglund, et al. 2016). A lag in admixture between local and incoming Neolithic groups has also been observed in Europe, where hunter-gatherer and farming populations initially co-existed for nearly a thousand years without substantial genetic interaction (Malmström, et al. 2015).

austronesian-admixture Ancestral genomic components in regional populations. For every K, the modal solution with the highest number of ADMIXTURE runs is shown; individual ancestry proportions were averaged across all runs from the same mode and the number of runs (out of 50) assigned to the presented solution is shown in parentheses. Average cross validation statistics were calculated across all runs from the same mode (insert). The minimum cross-validation score is observed at K=9. Note major ancestry components in Indonesia and ISEA – Papuan (light purple), mainland Asian (light yellow) and AN (light blue) – as well as major differences in the distribution of these three ancestries between eastern and western Indonesia. Populations from the Philippines and Flores are abbreviated as ‘Ph.’ and ‘Fl.’, respectively.

Featured images are taken from the article.

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