Solving the mystery of migration into Micronesia

Penn anthropologist Theodore Schurr explains how the use of both ancient DNA and modern genetic materials revealed five paths into this western Pacific region of Oceania, and uncovered subtleties about the society’s marital customs.

A map of the Pacific Ocean. Australia is in the bottom-left corner, with Indonesia and New Guinea to the north. Also pinpointed are Polynesia, Melanesia, and Micronesia, with arrows signifying five migration paths designated M1, M2, M3, M4, and M5. M1, M2, and M4 originate in East Asia. M3 originates around New Guinea, and M5 originates between Polynesia and Melanesia.
Map of five inferred streams of migration into Micronesia. (Image: Liu et al., 2022, “Ancient DNA reveals five streams of migration into Micronesia and matrilocality in early Pacific seafarers,” Science, Vol 377, Issue 6601, pp. 72-79, DOI: 10.1126/science.abm6536)

To the northeast of Papua New Guinea and to the east of the Philippines sits an archipelago of islands known as Micronesia, part of the western Pacific region of Oceania. Precisely how people first arrived there has remained largely a mystery. Now, a team that includes Penn anthropologist Theodore Schurr has discerned the likely trajectory.

Theodore Schurr
Theodore Schurr is a professor in the Department of Anthropology in the School of Arts & Sciences. He runs the Laboratory of Molecular Anthropology. (Image: Matthew Hamilton/MHamilton Visuals)

Using ancient DNA and modern genetic material from a combined 276 individuals, the researchers discovered five migration paths into Micronesia. Three derived from East Asia, one from Polynesia, and the final from Papua New Guinea. The team also determined that the early populations were matrilocal, meaning male partners joined the community where their female partners lived.

The researchers published their findings in the journal Science.

Penn Today spoke with Schurr, a professor in the Department of Anthropology, about his role in this research. Schurr founded and has run the Laboratory of Molecular Anthropology for more than two decades.

What would you describe as the work’s main finding?

This study reveals the complex sequence of human expansion into this area as a whole and traces the origins of those expansions into Micronesia. We find that the earliest colonization was done in several pulses.

Beyond that, based on the patterns of genetic diversity that we see in those communities both past and present, we now understand that the population that settled the islands was likely matrilocal in its marriage arrangements and social organizations. This finding tends to cohere with other ethnographic data that suggest that’s how Polynesians and Micronesians may have organized themselves prior to European contact. So, we’re getting a much more nuanced and complex picture of the history of Micronesia.

How did you get involved?

Miguel Vilar, another paper co-author who is now at the University of Maryland, came into my lab as a postdoc in 2010, and we’ve collaborated on many projects since that time, including investigating the history of the populations of Guam and the Mariana Islands. Last year, Miguel and I were asked to become collaborators on this project with Harvard researchers by contributing data samples from our populations, which offer a picture of modern genetic diversity. The idea was that they could be compared with ancient DNA samples from the same area in Micronesia.

Ultimately, the aim was to reconstruct the peopling of this area from the first humans landing there to the more modern influences on population diversity that happened in the context of colonization and European entry into the region.

How did you and your colleagues conduct the science?

With contemporary populations, you recruit people into the project and, with their permission, obtain their DNA for analysis. In most cases, their genome is sequenced so that you can see how genetically similar or different they are to each other and to comparative populations. In addition, 164 samples of ancient DNA were obtained at archaeological sites in Micronesia and then sequenced. Those genomes become reference points to look for connections between past and contemporary populations.

You compared ancient DNA to ancient DNA, modern DNA to modern DNA, and then these groups to each other?

Yes, that’s right. With the earliest samples, you’re trying to determine whether there’s a genetic signature that represents a founder population—the first people to arrive—or whether there might be distinct genetic signals representing different founder groups. You are trying to make connections between ancient and modern DNA data.

In essence, it boils down to how much of your genome that you share with other individuals. Is there a specific signature that indicates that you share a common ancestry because that chunk of your genome looks the same as someone else’s? The more DNA you share with people, the more likely it is that you have some kind of biological relationship. You can still see that connection over thousands of years because some part of the founder population remains in the genomes of its descendants.

What are the implications of these findings?

Micronesia is a place that people know mostly because it was part of the Pacific theater in World War II. These places were always, at least in the past several thousand years, places of dynamic settlement. They’ve been part of a complex series of human expansions into Oceania that have been incompletely understood. At one time, it was thought they were settled the same way and around the same time as Polynesia, but that’s not true.

This research offers us a new view of the population history of Micronesia. From an archaeological standpoint, there’s also the reconstruction of the population dynamics of Micronesia; to be able to get at subtleties like the demographics of founder populations is a bonus. We’re beginning to piece together this story in a more complex and intellectually satisfying way.

Theodore Schurr is a professor in the Department of Anthropology in the School of Arts & Sciences at the University of Pennsylvania. He is also a consulting curator in the Physical Anthropology and American sections of the University of Pennsylvania Museum of Archaeology and Anthropology, director of the North American Regional Center of the Genographic Project, and head of the Laboratory of Molecular Anthropology at Penn.