Melanesians Conquered Tonga and Vanuatu

Razib has the straight and scientific account of a recent ancient DNA study which shows that early Austronesian settlements in Oceania were by pureblooded Taiwanese who were then conquered by Melanesian/Papuan men, resulting in the 25% Melanesian admixture found in Papuans today. 

This ancient DNA result was contrary to widespread expectations that the admixture happened before Oceania was settled and in a manner less unfavorable to the Lapita people who were the first wave of Austronesians in the region and widely considered more "advanced" than the Papuans by anthropologists and historians, even if they wouldn't necessary admit to that in those terms.

But, in this case, a curmudgeonly summary tells the story more quickly and effectively:

Polynesians are mostly descended from a population on Taiwan, represented today by Taiwanese aboriginals, and from a Melanesian population similar to New Guinea or the Solomon Islands. They’re about 25% Melanesian autosomally, 6% Melanesian in mtDNA, 65% Melanesian in Y-chromosomes. . . .

Now they’ve looked at ancient DNA from Tonga and Vanuatu. The old samples don’t have any noticeable amount of Melanesian ancestry. So it was like this: the Lapita derived from Taiwan (thru the Philippines), settled Vanuatua and Tonga – then were conquered by some set of Melanesian men, who killed most of the local men and scooped up the women. Probably their sons extended the process, which resulted in a lower percentage of Melanesian ancestry while keeping the Y-chromosomes mostly Melanesian. 

After this conquest, the Polynesians expanded further east, and those later settlement (Tahiti, Marquesas, Hawaii, etc) all had that ~25% Melanesian component.

From here. 

A rough look at the numbers fits that scenario, with perhaps 44% of the men and 6% of the women in the first generation of conquest being Melanesian, leaving 21% of the Y-DNA mix to come from descendants of the original men (just about half of the original percentage of Melanesian men).

Increasingly, this is looking like an all too common scenario in both the Bronze and Iron Ages. In contrast, the Neolithic era appeared to involve mostly whole families or tribes migrating together as a colonial unit, rather than as a conquering group mostly made up of men. For example, ancient DNA from the Bronze Age conquests by Indo-Europeans of Eastern and Central Europe tells much the same story.

Given the dates of the ancient DNA samples, and the dates that subsequent Polynesian expansions occurred to particular islands, the timing of the Melanesian conquest ought to be possible to bracket to a reasonable narrow range of dates.  The ancient DNA in Vanuatu was from ca. 1100 BCE to 700 BCE.  The ancient DNA from Tonga was from about 700 BCE to 300 BCE. Razib notes: "Looking at the distribution of Melanesian ancestry they concluded this admixture occurred on the order of ~1,500 years before the present (their intervals were wide, but the ancient samples serve as a boundary)." In other words, around 500 CE, around the same time that half way around the world, the Roman Empire was falling.

In defense of those who saw the Lapita as more advanced than the Melanesians, however, it is notable that this is one of the rare instances when the language of the conquered people (the Austronesians) was adopted by the conquerors, rather than the other way around. The only other example of this kind of reverse language shift that comes easily to mind is the adoption of Greek by the Romans in the Eastern Roman Empire after the Romans conquered the Greeks.

It could also be that the Melanesian language shift to Austronesian languages took place before the men arrived in Tonga and Vanuatu at which time these men also mastered Austronesian maritime technology that made their arrival in Tonga and Vanuatu possible.