Native Hawaiians and Easter Islanders genetically descend from the same "ultravoyager" Polynesian group that crossed vast distances of ocean to reach these remote islands, a new study finds.

Easter Island (also known as Rapa Nui) and Hawaii are part of Polynesia, a group of more than 1,000 islands spread over an area of the Pacific Ocean roughly equal to the areas of North and South America combined. Hawaii and Easter Island are the farthest of these isles from each other, at about 4,500 miles (7,200 kilometers) apart — around the distance from San Francisco to Lima, Peru.

The researchers discovered the connection by analyzing the genomes of 1,050 modern individuals across Polynesia, including 317 Native Hawaiians and 12 Easter Islanders. "Each person's genome contains genetic code from both parents, and from all four grandparents, and their parents, and so on," study co-author Alexander Ioannidis, a computational geneticist at Stanford University, told Live Science. "Each genome encodes an enormous number of ancestors. So with even a few individuals, we can get information about an enormous number of people from each island."

Specifically, the scientists compared the length of chromosomal segments shared among people from different islands. The longer these shared segments are between two people, the more recently they shared a common ancestor.

Even though Hawaii and Easter Island are far-flung, the researchers discovered that the Indigenous people of Hawaii and Rapa Nui are the most genetically related to one another. The team reported its findings Oct. 8 in the journal Science.

"This was really shocking at first — these islands are so distant from one another," Ioannidis said.

The scientists found that Hawaii and Easter Island were likely both settled by members of a single "ultravoyager" culture from the Mangareva islands, about 3,440 miles (5,530 km) southeast of Hawaii and 1,600 miles (2,600 km) west of Easter Island. (In 2020, the researchers found that members of this ultravoyaging group had mixed with Indigenous people in what is now Colombia, although it's unclear if this partnering occurred on an island or on the continent.)

"Once you know there was this extremely capable long-distance ultravoyaging culture capable of reaching one of these islands, having it reach the other makes more sense," Ioannidis said.

The area near Mangareva, including the Austral Islands, the Society Islands, the Marquesas Islands, and the Tuamotu Archipelago, "spans an area the size of Europe," Ioannidis said. "Sailing in-between these islands would have required skilled navigation. So it makes sense that developing such long-distance navigation skills would have ultimately helped people settle far-off Easter Island and Hawaii."

All in all, these genetic findings suggest the ancestors of Native Hawaiians and Easter Islanders shared some time together as a common group after splitting away from the population of ancient Mangareva. Some members of this group then went on to settle Hawaii, and others from this Mangareva group voyaged to Easter Island.

This new genetic data linking Hawaii, Easter Island and Mangareva "agrees very well with what we see archaeologically," Patrick Kirch, an archaeologist at the University of Hawai'i at Manoa who did not take part in this research, told Live Science. "It gives scientists a lot of confidence when independent lines of evidence from different disciplines give similar results."

Founder effect

The researchers also investigated the effects of genetic bottlenecks that resulted when these islands were settled by small numbers of people — phenomena known as "founder effects."

"If you have a rare genetic trait that happens to occur in this small number of individuals, if this small population grows rapidly, this trait can go on to show up in a high percentage of the resulting population," Ioannidis said. "So if a rare genetic variant once only affected a few people, it can start affecting a decent number of individuals."

The scientists found that Native Polynesian populations examined in the study often experienced a compounding set of founder effects over time. This is because islands settled by a few people then went on to send out small groups to settle other islands, and so on.

Previous research has looked at the founder effects in groups of European descent, such as the Amish, Finns and Ashkenazi Jews, resulting in standard screenings for certain genetic conditions in these groups.

The new study revealed that an even stronger founder effect has been overlooked among Native Hawaiians, with founder effects more than 10 times larger than in those European groups.

"The founder effect doesn't just reflect genetic diversity, but also cultural and linguistic diversity," Kirch said. "It probably helps explain why the cultures of eastern Polynesia all share a lot in common — they all trace to one central group."

These findings not only shed light on Polynesians' past, but also their current health. The researchers found that three genetic variants that are exceedingly rare among the global population — linked with dislocated lenses in the eyes, progressive vision loss, and kidney failure — are carried by 2 to 3% of the eastern Polynesians they studied.

"There should be a lot more resources going into learning more about gene variants of potential clinical significance among this population of Native Hawaiians, which is twice as large as the U.S. Amish population," Ioannidis said. "There are really opportunities for precision health here."