DNA Evidence Of Polynesian Admixture With Native Americans Ca. 1200 CE

This has long been suspected, but the new evidence that it predated settlement of Easter Island is an interesting and novel twist to the hypothesis that the DNA evidence otherwise confirms.

The possibility of voyaging contact between prehistoric Polynesian and Native American populations has long intrigued researchers. Proponents have pointed to the existence of New World crops, such as the sweet potato and bottle gourd, in the Polynesian archaeological record, but nowhere else outside the pre-Columbian Americas, while critics have argued that these botanical dispersals need not have been human mediated. The Norwegian explorer Thor Heyerdahl controversially suggested that prehistoric South American populations had an important role in the settlement of east Polynesia and particularly of Easter Island (Rapa Nui). Several limited molecular genetic studies have reached opposing conclusions, and the possibility continues to be as hotly contested today as it was when first suggested. 

Here we analyse genome-wide variation in individuals from islands across Polynesia for signs of Native American admixture, analysing 807 individuals from 17 island populations and 15 Pacific coast Native American groups. We find conclusive evidence for prehistoric contact of Polynesian individuals with Native American individuals (around AD 1200) contemporaneous with the settlement of remote Oceania. Our analyses suggest strongly that a single contact event occurred in eastern Polynesia, before the settlement of Rapa Nui, between Polynesian individuals and a Native American group most closely related to the indigenous inhabitants of present-day Colombia.

Ioannidis, A.G., Blanco-Portillo, J., Sandoval, K. et al. "Native American gene flow into Polynesia predating Easter Island settlement." Nature (July 8, 2020). https://doi.org/10.1038/s41586-020-2487-2 Some of the literature cited in the paper is below the fold. (Open access for a limited time).

Razib Khan, who has interviewed one of the authors regarding this paper, notes:

The major finding using high density SNP chips and local ancestry deconvolution seems to be that a group of people from mainland South America, probably coastal Columbia, was admixed into the population of the Marquesas. It is from the Marquesas that this genetic ancestry propagated across the eastern fringe of Oceania, including Easter Island.

A comment at the linked post notes that:

Wilmshurst et al. 2011 established that the remoter parts of Polynesia were discovered in a single pulse 1190-1290 so it lines up nicely.  

The abstract of the referenced PNAS paper is as follows: 

The 15 archipelagos of East Polynesia, including New Zealand, Hawaii, and Rapa Nui, were the last habitable places on earth colonized by prehistoric humans. The timing and pattern of this colonization event has been poorly resolved, with chronologies varying by >1000 y, precluding understanding of cultural change and ecological impacts on these pristine ecosystems. In a meta-analysis of 1,434 radiocarbon dates from the region, reliable short-lived samples reveal that the colonization of East Polynesia occurred in two distinct phases: earliest in the Society Islands A.D. ∼1025–1120, four centuries later than previously assumed; then after 70–265 y, dispersal continued in one major pulse to all remaining islands A.D. ∼1190–1290. We show that previously supported longer chronologies have relied upon radiocarbon-dated materials with large sources of error, making them unsuitable for precise dating of recent events. Our empirically based and dramatically shortened chronology for the colonization of East Polynesia resolves longstanding paradoxes and offers a robust explanation for the remarkable uniformity of East Polynesian culture, human biology, and language. Models of human colonization, ecological change and historical linguistics for the region now require substantial revision.

The exchange may not have been entirely one directional. There is evidence of chickens with Asian origins arriving in South America. 

Two issues long debated among Pacific and American prehistorians are (i) whether there was a pre-Columbian introduction of chicken (Gallus gallus) to the Americas and (ii) whether Polynesian contact with South America might be identified archaeologically, through the recovery of remains of unquestionable Polynesian origin. We present a radiocarbon date and an ancient DNA sequence from a single chicken bone recovered from the archaeological site of El Arenal-1, on the Arauco Peninsula, Chile. These results not only provide firm evidence for the pre-Columbian introduction of chickens to the Americas, but strongly suggest that it was a Polynesian introduction.

Alice A. Storey, et al., "Radiocarbon and DNA evidence for a pre-Columbian introduction of Polynesian chickens to Chile", 104(25) PNAS 10335-10339 (June 19, 2007).

doi: 10.1073/pnas.0703993104

* Montenegro, A., Avis, C. & Weaver, A. "Modeling the prehistoric arrival of the sweet potato in Polynesia." 35 J. Archaeol. Sci. 355–367 (2008).

* Roullier, C., Benoit, L., McKey, D. B. & Lebot, V. "Historical collections reveal patterns of diffusion of sweet potato in Oceania obscured by modern plant movements and recombination." 110 PNAS 2205–2210 (2013).

* Clarke, A. C., Burtenshaw, M. K., McLenachan, P. A., Erickson, D. L. & Penny, D. "Reconstructing the origins and dispersal of the Polynesian bottle gourd (Lagenaria siceraria)." 23 Mol. Biol. Evol. 893–900 (2006).

* Muñoz-Rodríguez, P. et al. "Reconciling conflicting phylogenies in the origin of sweet potato and dispersal to Polynesia." 28 Curr. Biol. 1246–1256 (2018).

* Lie, B. A. et al. "Molecular genetic studies of natives on Easter Island: evidence of an early European and Amerindian contribution to the Polynesian gene pool." 69 Tissue Antigens 10–18 (2007).

* Thorsby, E. "The Polynesian gene pool: an early contribution by Amerindians to Easter Island." 367 Phil. Trans. R. Soc. Lond. B 812–819 (2012).

* Moreno-Mayar, J. V. et al. "Genome-wide ancestry patterns in Rapanui suggest pre-European admixture with Native Americans." 24 Curr. Biol. 2518–2525 (2014).

* Fehren-Schmitz, L. et al. "Genetic ancestry of Rapanui before and after European contact." 27 Curr. Biol. 3209–3215 (2017).

* Hagelberg, E., Quevedo, S., Turbon, D. & Clegg, J. B. "DNA from ancient Easter Islanders." 369 Nature 25–26 (1994).

* Wilmshurst, J. M., Hunt, T. L., Lipo, C. P. & Anderson, A. J. "High-precision radiocarbon dating shows recent and rapid initial human colonization of East Polynesia." 108 PNAS 1815–1820 (2011).

* Hunt, T. L. & Lipo, C. P. "Late colonization of Easter Island."  311 Science 1603–1606 (2006).

* Mulrooney, M. A. "An island-wide assessment of the chronology of settlement and land use on Rapa Nui (Easter Island) based on radiocarbon data." 40 J. Archaeol. Sci. 4377–4399 (2013).