Very exciting stuff, which I barely got started with over at my own site on Wednesday.
I link again to the paper in Nature by Alex Ioannidis et al about Native American-Polynesian contact before the Columbian period. One commenter alertly picked up that this is the Thor Heyerdahl Kon-Tiki hypothesis from decades ago. The paper references this in the first paragraph. The Norwegian sailed a hand-made reed boat from South America to French Polynesia in the 1940’s in order to prove it could be done. He believed that the initial settlement of Oceania came from Peru and Chile, and that these people were later in contact with and eventually displaced by people in double-hulled canoes around 1100 AD. That the Polynesians have the sweet potato, a New World food, has always provided some support for this theory, though plants can also wash ashore from distant places as well.
The new paper identifies 2-3% genetic similarity in the Polynesians, especially around the Marquesas Islands, with Native American tribes in Ecuador and Colombia (Zenu) from a single* contact event around 1200 AD, before the settling of Easter Island (Rapa Nui). Because the distances are ridiculous, all theories about how this occurred seem unlikely, but there it is. It happened somehow. Did these two groups have contact in the Marquesas, or did the Polynesians keep on sailing until they reached Ecuador? If you pull up your map of the Pacific Ocean, both look extremely unlikely. The later Polynesians were extreme sailors and covered vast distances. Such peoples must not only be able to navigate using subtle signs of sky, water, and birds, they must be adapted to living on the water for long periods. To us getting in a boat is a temporary act, but for them this was much less true. Whole groups took to the open sea together, bringing with them what they needed to found colonies whenever they did reach land. There are fishing peoples who spend most of their lives on the water in SE Asia, but these stay close to land. Still, it can be done. The Austronesians were great sailors, getting all the way to settling Madagascar off the east coast of Africa to Hawaii and Easter Island in the Pacific. Plus, if you keep sailing east, South America is hard to miss. They had a culture where people struck out onto the sea looking for new places to live, likely for cultural reasons that are now lost to us. Notice that these are in similar latitudes, so that the taro and banana and coconut plants would be likely to grow in a new location. North-south movement and settlement is much more precarious on both land and sea. One of the things that Jared Diamond did get right.
However, the western coastal tribes of the New World had seaborne trade over great distances as well, focused on metals as well as food. Because sailing close to shore is not as difficult and risky, we might think they were incapable of longer voyages. We used to think that of the Phoenician traders as well but now understand they crossed long distances over water as well. When one adds in the fact that the prevailing currents off Ecuador and Columbia run to the Marquesas once one can get out into the open sea a bit, the deed looks even more possible (see Fig 1 at the link). Also, being blown off course happens regularly at sea, so reaching land and surviving wouldn’t have to happen regularly. It only had to happen once, and a sailing people might manage the shorter distances of mid-Pacific islands. They may even have attempted regular trade back to South America. But. But. The Mrquesas are about halfway to Australia.
In all the discussion of this paper I have read and listened to, there has been no mention of disease. The overwhelming fact we do know about Old World and New World contact from the other direction is that the natives of North and especially South America were devastated by the diseases of the arriving colonisers, having been separated from them for thousands of years and having no immunity. It is true that the Austranesians would not be carrying as many or the same diseases that Eurasians would, and that they would not be bringing them in intense repeated contact. But 1200AD and 1500 AD are not that far apart in the context of 20,000 year separation. The possibility that the Polynesians traveling as small villages in double-hulled boats, especially if they engaged in even minor trade with those back where they started from, could wreak similar havoc is quite possible.
That one population overwhelms the other at a rate of 30-40:1 has a few possible explanations, of which outcompeting them via disease is only one. The Polynesians could have reached South America and brought a few people back, especially wives, whether voluntarily or not. We have found no comparable Polynesian admixture in any New World group (yet), but the contacts might have been brief, with one or a very few tribes which have now gone extinct. An unplanned colony near the Marquesas might have already been marginal and were outcompeted by the newcomers in some other way, quickly or slowly.
*”Single contact event ” does not mean one mating, but single group event, even though over years.