Austronesian-Papuan People Replaced The First Modern Humans In Wallacea

Wallacea is the ecological region between the Wallace Line and the Lydekker Line (image via Wikipedia at the link). The plants and animals there differ greatly from those to the west (which were connected by land to mainland Asia when sea levels were lower) because neither animals nor 46,000 years of settlers after the first modern humans to cross into it, could cross the roughly 30 miles of deep sea between the regions.

The most basal modern human populations outside Africa, which also have the greatest Denisovan admixture, are the indigenous people of Papua New Guinea and Australia. People from this wave were also present on the islands of the Wallacean Archipelago in Indonesia and lived there undisturbed for about 46,000 years. 

But, when Papuans made contact with and fused with Austronesian sea farers (who originated on the island that is now called Taiwan) around 3500 years ago, contemporaneously with the late Bronze Age in Europe, the resulting fused population replaced the descendants of the first wave of modern humans in the Wallacean Achipelago.

Significance

We present a comprehensive study of the human genetic history of the Wallacean Archipelago and West Papuan regions of Indonesia, including 254 newly sequenced genomes, mostly from previously undocumented populations. In combination with linguistic and archaeological evidence, we show that Wallacean societies were transformed by the spread of genes and languages from West Papua in the past 3,500 y—the same period that Austronesian seafarers were actively mixing with Wallacean and Papuan groups. These migrant groups have largely replaced local Wallacean ancestry sources, challenging common assumptions that Papuan-related ancestry in Wallacea descends from first human migrants enroute to Sahul >50,000 y ago, and suggesting that these ancient movements may not be readily recoverable from modern genetic data alone.

Abstract

The tropical archipelago of Wallacea was first settled by anatomically modern humans (AMH) by 50 thousand years ago (kya), with descendent populations thought to have remained genetically isolated prior to the arrival of Austronesian seafarers around 3.5 kya. 

Modern Wallaceans exhibit a longitudinal countergradient of Papuan- and Asian-related ancestries widely considered as evidence for mixing between local populations and Austronesian seafarers, though converging multidisciplinary evidence suggests that the Papuan-related component instead comes primarily from back-migrations from New Guinea. 

Here, we reconstruct Wallacean population genetic history using more than 250 newly reported genomes from 12 Wallacean and three West Papuan populations and confirm that the vast majority of Papuan-related ancestry in Wallacea (~75 to 100%) comes from prehistoric migrations originating in New Guinea and only a minor fraction is attributable to the founding AMH settlers. 

Mixing between Papuan and local Wallacean lineages appears to have been confined to the western and central parts of the archipelago and likely occurred contemporaneously with the widespread introduction of genes from Austronesian seafarers—which now comprise between ~40 and 85% of modern Wallacean ancestry—though dating historical admixture events remains challenging due to mixing continuing into the Historical Period. In conjunction with archaeological and linguistic records, our findings point to a dynamic Wallacean population history that was profoundly reshaped by the spread of Papuan genes, languages, and culture in the past 3,500 y.

Gludhug A. Purnomo , Shimona Kealy, Sue O’Connor, Raymond Tobler, et al., "The genetic origins and impacts of historical Papuan migrations into Wallacea" 121 (52) PNAS e2412355121 (December 17, 2024). Hat tip to DDeden.