They are postcard idylls. Behind a bright sandy beach on the crystal clear waters of the Pacific, the dark green leaves of palm trees sway in the wind. Such islands in the Pacific Ocean often have large populations, although they are often hundreds of kilometers apart. The first settlers probably reached uninhabited islands on outrigger canoes. Until now, little was known about where they came from.
David Reich from Harvard University in the US state of Massachusetts and his team have tried to clarify this for the Micronesian islands to the east and north of Papua New Guinea using genetic material analyses. The team reports in the journal Science that thousands of years ago there were at least five waves of immigration from East Asia, Papua New Guinea and Polynesia.
For their study, the group analyzed genetic material from the remains of 164 people recovered from five sites on Micronesia’s more than 2,000 islands. Using radiocarbon dating, she determined the age of 30 of these finds. The oldest is from a human who lived 2800 years ago and the youngest from a human who lived 500 years ago. In addition, the group analyzed the genomes of 112 current residents of this island world.
From comparisons, they concluded that there were three waves of immigrants that came at least 2800, 2400, and 2100 years ago, respectively, from regions inhabited by people of Indonesian and Philippine origin. This result is consistent with archaeological finds on the islands of Micronesia. Clay shards unearthed there are at most 3,500 years old and are similar to the pottery used in the Philippines at the same time.
According to genetic analysis, the people of the fourth wave of settlements came from what is now Papua New Guinea. However, the carriers of this genetic material do not have to have come directly to Micronesia.
Cosimo Posth, who analyzed similar migrations at the University of Tübingen using genetic analyzes but was not involved in the Science study, found indications of another route. In mid-June of this year, the Tübingen researcher, together with colleagues from the Max Planck Institute for Evolutionary Anthropology in Leipzig, published a study in the journal “Nature”, in which they analyzed the genome of people who once lived on the Wallacea Islands . This archipelago between Indonesia and Papua New Guinea has been separated from both East Asia and New Guinea by wide and deep straits for millions of years.
And yet there are clear traces in the genome of human remains there, according to which people from East Asia have mixed with Papua groups several times for at least 3000 years. “Something similar could of course also have played a role in the settlement of Micronesia,” Posth suspects. It is possible that people from East Asia, who formed the third migratory wave after David Reich and his team, may have previously mixed with Papuan groups on other islands in this region.
Should these people then have come to Micronesia, the third wave from East Asia would merge with the fourth wave with Papuan heritage. “These possibilities should be explored further,” says Posth.
According to the study by Reich and his team, the fifth wave of settlements could have reached Micronesia at least a thousand years ago. But Posth is skeptical about the conclusion, “since it is based on the genome of a single individual whose location in Micronesia is not even known.” this discovery could well represent everyday mobility and not a wave of immigration. This possible fifth wave should also be investigated further.
The analysis of the genome from the mitochondria of the remains of the Micronesians, on the other hand, is amazing but clear. This DNA from the power plants of the body cells is only passed on from mothers to their children, the fathers have no influence on this genome. This mitochondrial DNA from long-dead humans varies greatly between the remote islands of Micronesia, but is very consistent within each group.
From this, David Reich and his team conclude that the women almost always raised their children in the same group in which they themselves were born. The men of these women, on the other hand, often came from other islands and then probably stayed with their partner’s group. According to these genome analyses, men in particular brought the Papua genome to a number of Micronesian islands, possibly in search of mates.
“This behavior is extremely interesting because, according to previous studies, the conditions in Stone Age Europe were exactly the opposite,” explains Posth: “There the women came into the group of men with whom they later had children.”