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Researchers find that first Samoan settlers were a small, isolated community

Samoa’s original population of no more than 3,500 people may hold answers to the non-communicable disease crisis in Polynesia, according to landmark genetic research published this month by Brown University School of Public Health.

In a new study using genetic material from over a thousand Samoans, researchers have proven that the first inhabitants of the Samoan islands would have numbered between 700 and 3,500 people, and remained a small population for around 1,500 years. 

Lead researcher Dr. Stephen McGarvey, Professor of Epidemiology and Anthropology at Brown University School of Public Health said knowing how small the founding population of the islands were could begin to explain why Samoan genetics look the way they do. 

“The chance for rare genetic frequencies or variants increases when you have a small population,” he said. 

“It means there were genetic events and evolutionary events that would have concentrated certain genes. We don’t know yet whether the genes that were concentrated are the genes that are related to the contemporary public health problems but it gives us insight into that.”

The research was published last week in Proceedings of the National Academy of Sciences (PNAS) of the United States of America.

It was built using genetic data collected from 1,197 Samoans back in 2010 (253 from Savaii, 263 from the Apia Urban Area, 358 from North Western Upolu and 323 Samoans from the rest of Upolu).

Participants, having had the research and its purpose explained to them and having given their consent to share their genetic material, were also interviewed about their ancestry (where each of their grandparents was from). 

The research may eventually lead to more discoveries about what causes Samoa’s exceptionally high rates of diabetes, obesity and over non-communicable diseases often associated with Western diet and static lifestyles.

In time, this could lead to the development of treatments or medicines to better treat these diseases in a Samoan or Pacific population.

“What we think we know about the genetic contribution to these conditions (obesity, diabetes) is mainly based on people with European ancestry, white people like me,” Dr. McGarvey said.

“If we want to know with more precision then we need to understand more about Samoan or Polynesian genetics and if there are susceptibilities, […and] knowing something about how the population was small and for a while gives us greater chance to find those genes.

This kind of research had already borne fruit. In 2016, Dr. McGarvey and colleagues published their findings on what they called the ‘thrifty gene,’ that until today has shown to be only found in Polynesian genetics. 

“One of the men or women chosen for those initial voyages 3000 years ago could have had this gene in their D.N.A. and that then replicated when they had children,” he said. 

“That would have an overrepresentation in the continuing population. We call that the Founder Effect.”

Dr. McGarvey said when it comes to non-communicable diseases, they are caused by not only a combination of genetics and lifestyle but also an interaction between the two. 

“So this [research] increases our chance to find genes, with greater effectively, that are contributing, that are part of the picture to why Samoans have so much obesity and overweight right now.”

As well as learning how small the founding population was, the research also found Samoan ancestry reveals less connection to the Papuan people than in other parts of the Pacific, and more in common with the Austronesians which came from Taiwan, among other scattered places. 

Neighbouring Polynesians on average have about 35 per cent Papuan ancestry, while Samoans appear to have only around 24 per cent. 

“For the first 1,500 years Samoa was somewhat isolated and didn’t have any other waves of people coming to Samoa, and that fits with archaeology data,” Dr. McGarvey said.

“Settlements [archaeologists] can find are limited, the sea level was higher and so farming land near the shore was limited, so it meant there was a small and somewhat scattered population that remained like the original inhabitants until only 1,500 years ago.

“We don’t know exactly why or what happened about that time but it was well before Europeans came to Samoa.”

The research also reveals slight but significant genetic differences in the Savaii and Upolu population, which reflects the country’s history, Dr. McGarvey continued. 

“There are differences on this very fine-grain level. We don’t know what it means but it means genetics follow what we know about social patterns in history.

Dr. McGarvey said the researchers were able to identify how significant the population reduction was when Europeans first came to Samoa, even before the 1918 influenza that claimed 20 per cent of the population, using the genetic data.

“This probably happened 150 years ago, not 100 years ago, which is when there began to be more regular contact from traders, folks coming in trying to find a new life, make a buck, convert people, anything. 

“Samoans had been by themselves for almost 2500, [they] did not necessarily have immunity to the infectious diseases that those outsiders brought in and so there was a population decline around that time that is reflected in the genetic data too.” 

Dr. McGarvey said the genetic data, while revealing a small and not particularly diverse population, does not reveal any of the traits of an inbred population nor the genetic malfunctions associated with it.

Unlike much smaller population that practice inbreeding more intentionally, the Samoan genetic data does not show “deleterious mutations” or mutations that lead to disease.

While the population, having been isolated for so long, does have less genetic variation than other populations, still does not have such a limited variety as studied in smaller, more isolated populations, the professor said. 

University of Auckland Associate Professor Dr. Ethan Cochrane was among the research group. He said the study on the Samoan population may hold clues to how Tahiti, Hawaii and the Cook Islands were populated.

“The jump in Samoan population size might also be related to archaeologically documented changes in agriculture, as well as an increasing number of monumental mound structures, both of which might signify hierarchical society. We could be seeing the origins of the Samoan chiefly system 1000 years ago,” he said. 

The researchers worked alongside Muagututi‘a Sefuiva Reupena, former head of the Samoa Bureau of Statistics and one of Samoa’s longest serving public servants, and the Ministry of Health.

The study was supported by the TransOmics for Precision Medicine (T.O.P.Med) program of the National Heart, Lung and Blood Institute (N.H.L.B.I.) of the U.S. National Institutes of Health (N.I.H.).

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