New genetic research from remote islands in the Pacific offers fresh insights into the ancestry and culture of the world’s earliest transoceanic seafarers, including family structure, social customs, and the ancestral populations of the people living there today.
The study, published in the journal Science, reveals five previously undocumented migrations into this subregion and suggests that between 2,500 and 3,500 years ago, early inhabitants of these Pacific islands — including Guam in the north and Vanuatu in the south — had matrilocal population structures, in which women almost always remained in their communities after marriage while men moved out to join them.
The practice is opposed to patrilocal societies in which women often relocate. These data support the idea that these early mariners came from communities organized around female lineages.
The findings are based on a genome-wide analysis of 164 people dating from 2,800 to 300 years ago, as well as 112 modern people. A team of researchers led by Harvard geneticists David Reich and Yue-Chen Liu, Ron Pinhasi of the University of Vienna, and Rosalind Hunter-Anderson, an independent researcher based in Albuquerque, New Mexico, published the study.
“Learning about cultural trends from genetic data is an unexpected gift,” said Reich, a professor in the Department of Human Evolutionary Biology and a genetics professor at Harvard Medical School. “Today, traditional communities in the Pacific have both patrilocal and matrilocal population structures, and there was a debate about what the common practice was in the ancestral populations. These results suggest that in the earliest seafarers, matrilocality was the rule.”
The genetic analysis compared the mitochondrial DNA sequences of the first seafarers from Guam to those of the first seafarers from the southwest islands of Vanuatu and Tonga who lived 2,500-3,000 years ago. It revealed that the two lineages of the first Remote Oceanians derived from two distinctly different maternal lineages but that kind of stark differentiation didn’t exist in terms of the rest of their DNA.
Researchers ran these findings through mathematical simulations, which revealed that this kind of genetic drift in the two groups could not have happened at random, leading them to the conclusion that the cause was most likely the result to women not moving around to different islands as men.“
Females certainly moved to new islands, but when they did so they were part of joint movements of both females and males” Reich explained. “This pattern of leaving the community must have been nearly unique to males in order to explain why genetic differentiation is so much higher in mitochondrial DNA than in the rest of the genome.”
The new study from an interdisciplinary team of geneticists and archaeologists quintuples the body of ancient DNA data from the vast Pacific region called Remote Oceania, the last habitable place on earth to be peopled. It also provides surprising insights into the extraordinarily complex peopling of one of Remote Oceania’s major subregions.
Humans arrived and spread through Australia, New Guinea, the Bismarck Archipelago, and the Solomon Islands beginning 50,000 years ago, but it wasn’t until after 3,500 years ago that they began living in Remote Oceania for the first time after developing the technology to cross open water in long-distance canoes.
This expansion included the region called Micronesia — about 2,000 small islands north of the equator, including Guam, the Marshall Islands, the Caroline Islands, Palau, and the Northern Mariana Islands.
It’s long been a mystery what routes people took to arrive in the region. The discovery that there were five streams of migration into Micronesia helps bring clarity to this mystery and the origins of the people there today.
“These migrations we document with ancient DNA are the key events shaping this region’s unique history,” said Liu, a postdoctoral fellow in Reich’s lab and the study’s lead author. “Some of the findings were very surprising.”
Of the five migrations, three were from East Asia, one from Polynesia, and one involved Papuans from the northern fringes of mainland New Guinea. This represented a new wrinkle for researchers because a prior stream of migration to the southwest Pacific and Central Micronesia came not from the mainland but New Britain, an island chain to the east of it.
The researchers also found that present-day Indigenous people of the Mariana Islands in Micronesia, including Guam and Saipan, derive nearly all their pre-European-contact ancestry from two of the East Asian-associated migrations the researchers detected. It makes them the “only people of the open Pacific who lack ancestry from the New Guinea region,” Liu said.
The researchers consulted with several Indigenous communities in Micronesia for the study. This is the Reich group’s fourth publication of original ancient DNA data from remote Pacific islands.
“It’s important that when we do ancient DNA work, we don’t just write a paper about the population history of a region and then move on,” Reich said. “Each paper raises as many new questions as it answers, and this requires long-term commitment to follow up the initial findings. In the Pacific islands there are so many open questions, so many surprises still to be discovered.” — by Harvard University