Native Americans and Polynesians Met Around 1200 A.D.

Native Americans and Polynesians Met Around 1200 A.D.

The Pacific Ocean covers almost one-third of the Earth’s surface, yet centuries ago, Polynesian navigators were skilled enough to find and populate most of the habitable islands scattered between Oceana and the Americas. Now a new genetic analysis is revealing more about their incredible journeys—and the people they met along the way.

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A provocative new study argues Polynesians and Native Americans made contact some 800 years ago. That date would place their first meeting before the arrival of Europeans in the Americas and before the settlement of Easter Island (Rapa Nui), which has been suggested as the site of such an initial encounter.

Researchers, published in Nature, sampled genes of modern peoples living across the Pacific and along the South American coast and the results suggest that voyages between eastern Polynesia and the Americas happened around the year 1200, resulting in a mixture of those populations in the remote South Marquesas archipelago. It remains a mystery whether Polynesians, Native Americans, or both peoples undertook the long journeys that would have led them together. The findings could mean that South Americans, hailing from what’s now coastal Ecuador or Columbia, ventured to East Polynesia. Alternatively, Polynesians could have arrived in the Marquesas alone having already mixed with those South American people—but only if they’d first sailed to the American continent to meet them.

Alexander Ioannidis , who studies genomics and population genetics at Stanford University, co-authored the new study in Nature. “The genes show that the Native Americans who contributed came from the coastal regions of Ecuador and Columbia,” he says. “What they can’t show, and we don’t know, is where exactly it first took place—on a Polynesian island or the coast of the Americas.”

Legendary voyagers

Launching one of history’s great eras of exploration, Polynesians journeyed by canoe across the vast Pacific Ocean. During several centuries of voyaging to the east they found and settled the tiny islands scattered across 16 million square miles from New Zealand to Hawaii, reaching the most distant, like Easter Island (Rapa Nui) and the Marquesas, by perhaps 1200 A.D., They left no written history to chronicle these voyages, but scientists have retraced the trips using various lines of evidence. Striking similarities in languages exist across widely separated island groups, for example, and the remains of structures and stones offer clues to who erected them. Even the spread of foodstuffs like the sweet potato—of American origin but found across the Pacific and nowhere else—could offer evidence of the skills and nerve by which people eventually populated the Pacific (though some scientists suggest that the sweet potato was dispersed naturally.)

Most recently, scientists have tried to chart the paths of these ancient voyagers through the genes of their descendants. “We recapitulate, with genetic evidence, a prehistoric event that left no conclusive trace, except for the one recorded in the DNA of those who had contact 800 years ago in one of the most remote places on Earth,” explains co-author Andres Moreno Estrada, with the National Laboratory of Genomics for Biodiversity (Mexico). For this study Estrada and colleagues did a genome-wide analysis for more than 800 present-day individuals, who hail from 17 islands across the Pacific and also from peoples up and down the Pacific coast of South America, looking for evidence of mixing between the two populations. They added a handful of pre-Columbian, South American DNA samples to help confirm that any indigenous signals identified hadn’t been created by later mixing after European contact.

Their findings revealed a Native American genetic signature among people on some of Polynesia’s easternmost islands. Not only did this signature indicate a common source among Colombia’s indigenous peoples, but it also showed that the people who carry it on different islands shared the same Native American ancestors.

“It is fascinating new evidence,” says Pontus Skoglund, who leads the ancient genomics lab at the Francis Crick Institute and wasn’t involved in the research. Skoglund was particularly intrigued by the evidence that Native Americans would’ve encountered Polynesians before they encountered Europeans, contrary to what some previous studies have shown. “This suggests that the Native American ancestry is not due to events in more recent colonial history where trans-Pacific travel was documented.”

Who met whom

If Native Americans had reached these remote islands by around 1200 they likely did so by following the prevailing currents and winds. In 1947, explorer Thor Heyerdahl famously demonstrated that it was possible to travel the Pacific by drifting on winds and currents on a raft when his famed Kon-Tiki journeyed more than 4,300 miles from South America to Raroia Atoll. Those islands lie in the same region that the genetic study suggests as the likely point of contact between Polynesian and Native American peoples.

“That’s where the winds and currents will take you if you’re drifting,” Ioannidis says. “If people in boats plying coastal trade routes were blown off course or drifting to sea, those same currents and winds might have taken them to these Pacific Islands.”

Paul Wallin, an archaeologist at Uppsala University, Sweden who wasn’t involved in the research, thinks this study may confirm a Native South American contact into the Pacific. “[That’s] the same area DNA studies of sweet potato have indicated, [so] this early mix may explain the existence of sweet potato in East Polynesia,” Wallin says. The date is so early that the Native South Americans may have come to the South Marquesas just before the Polynesians did, he adds.

Despite Heyerdahl’s success, most scientists have pushed back against his ideas that Native Americans settled Polynesian islands in this manner. However, this new DNA research could also support an alternate explanation that some of those dissenting scientists favor: that Polynesians might have sailed to the Americas.

“We can speculate that possibly the Polynesians found the Americas, and there was some interaction with Native Americans,” Ioannidis says. “Then as they go and settle the last of these most remote islands, including Easter Island, they take that genetic ancestry with them because they themselves now carry part of that Native American ancestry.”

There’s little doubt that the Polynesians—gifted mariners who used the night sky, the sun, birds, clouds, and the reading of ocean swells—had the oceanic skills necessary to reach the Americas. As Ioannidis notes, we know they reached Easter Island. “They made it well to the east of where North America begins, although they were in the Southern Hemisphere,” he says. “If they could have made it there, they could have made it all the way. And why would they have stopped?”

David Burley, an archaeologist at Simon Fraser University not involved in the study, finds the explanation of Polynesians visiting America far more likely. “A North American group from Colombia making it to the southern Marquesas and interbreeding with Polynesians seems a stretch,” he says. “Polynesian seafarers had well developed maritime technologies and were quite capable of reaching the Americas. Not sure that is at all the case for Colombia.”

Mysteries of Easter Island

The new study’s genetic results also offer clues to possibly unraveling the history behind Easter Island (Rapa Nui), whose inhabitants erected the famed Moai monoliths before their civilization collapsed. Some researchers have pointed to the island as a possible landing point for any South American peoples venturing into the Pacific, as it is the closest inhabited island to South America’s Pacific Coast, though it lies 2,200 miles away.

Previous studies that sought to untangle the history of Polynesian settlement haven’t been conclusive. A 2017 Current Biology study (co-authored by Pontus Skogland) sampled human remains dating from before Europeans reached the island in 1722 and found only Polynesian DNA. However, the study included only five individuals, meaning other ancestries might have been present on the island but not represented in the group. A 2014 paper sampled 27 modern inhabitants and found that they had a significant amount of Native American DNA (about 8 percent). It concluded that Native Americans may have journeyed, alone or with Polynesians, to Easter Island before 1500—before Europeans ventured there.

As part of their new study, Ioannidis and colleagues sampled DNA from 166 inhabitants of Easter Island. They determined that admixture between Native American and Polynesian peoples didn’t occur here until around 1380 though the island was settled by at least 1200, perhaps by a Polynesian group that hadn’t had any contact with Native Americans.

“The surprising thing is that the Rapa Nui admixture happened later, although the cultural impact might have been stronger there than in other parts of East Polynesia,” Paul Wallin says. He stresses that it’s too early to make too many sweeping conclusions about this phase of the island’s history. We know South Americans and Polynesians have a shared history on the Pacific Ocean. The exact wheres and whens are mysteries still to be solved.

Why Scientists Are Studying the Genetic Tricks of the Longest-Lived Animals

Life, for most of us, ends far too soon — hence the effort by biomedical researchers to find ways to delay the aging process and extend our stay on Earth. But there’s a paradox at the heart of the science of aging: The vast majority of research focuses on fruit flies, nematode worms and laboratory mice, because they’re easy to work with and lots of genetic tools are available. And yet, a major reason that geneticists chose these species in the first place is because they have short lifespans. In effect, we’ve been learning about longevity from organisms that are the least successful at the game.

Today, a small number of researchers are taking a different approach and studying unusually long-lived creatures — ones that, for whatever evolutionary reasons, have been imbued with lifespans far longer than other creatures they’re closely related to. The hope is that by exploring and understanding the genes and biochemical pathways that impart long life, researchers may ultimately uncover tricks that can extend our own lifespans, too. Everyone has a rough idea of what aging is, just from experiencing it as it happens to themselves and others. Our skin sags, our hair goes gray, joints stiffen and creak — all signs that our components — that is, proteins and other biomolecules — aren’t what they used to be. As a result, we’re more prone to chronic diseases such as cancer, Alzheimer’s and diabetes — and the older we get, the more likely we are to die each year. “You live, and by living you produce negative consequences like molecular damage. This damage accumulates over time,” says Vadim Gladyshev, who researches aging at Harvard Medical School. “In essence, this is aging.” This happens faster for some species than others, though — the clearest pattern is that bigger animals tend to live longer lives than smaller ones. But even after accounting for size, huge differences in longevity remain. A house mouse lives just two or three years, while the naked mole rat, a similar-sized rodent, lives more than 35. Bowhead whales are enormous — the second-largest living mammal — but their 200-year lifespan is at least double what you’d expect given their size. Humans, too, are outliers: We live twice as long as our closest relatives, the chimpanzees.

Keys to Successful Aging

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Bats above average

Perhaps the most remarkable animal Methuselahs are among bats. One individual of Myotis brandtii, a small bat about a third the size of a mouse, was recaptured, still hale and hearty, 41 years after it was initially banded. That is especially amazing for an animal living in the wild, says Emma Teeling, a bat evolutionary biologist at University College Dublin who coauthored a review exploring the value of bats in studying aging in the 2018 Annual Review of Animal Biosciences. “It’s equivalent to about 240 to 280 human years, with little to no sign of aging,” she says. “So bats are extraordinary. The question is, Why?”

There are actually two ways to think about Teeling’s question. First: What are the evolutionary reasons that some species have become long-lived, while others haven’t? And, second: What are the genetic and metabolic tricks that allow them to do that?

Answers to the first question, at least in broad brushstrokes, are becoming fairly clear. The amount of energy that a species should put toward preventing or repairing the damage of living depends on how likely an individual is to survive long enough to benefit from all that cellular maintenance. “You want to invest enough that the body doesn’t fall apart too quickly, but you don’t want to over-invest,” says Tom Kirkwood, a biogerontologist at Newcastle University in the UK. “You want a body that has a good chance of remaining in sound condition for as long as you have a decent statistical probability to survive.”

This implies that a little scurrying rodent like a mouse has little to gain by investing much in maintenance, since it will probably end up as a predator’s lunch within a few months anyway. That low investment means it should age more quickly. In contrast, species such as whales and elephants are less vulnerable to predation or other random strokes of fate and are likely to survive long enough to reap the benefits of better-maintained cellular machinery. It’s also no surprise that groups such as birds and bats — which can escape enemies by flying — tend to live longer than you’d expect given their size, Kirkwood says. The same would apply for naked mole rats, which live their lives in subterranean burrows where they are largely safe from predators.

But the question that researchers most urgently want to answer is the second one: How do long-lived species manage to delay aging? Here, too, the outline of an answer is beginning to emerge as researchers compare species that differ in longevity. Long-lived species, they’ve found, accumulate molecular damage more slowly than shorter-lived ones do. Naked mole rats, for example, have an unusually accurate ribosome, the cellular structure responsible for assembling proteins. It makes only a tenth as many errors as normal ribosomes, according to a study led by Vera Gorbunova, a biologist at the University of Rochester. And it’s not just mole rats: In a follow-up study comparing 17 rodent species of varying longevity, Gorbunova’s team found that the longer-lived species, in general, tended to have more accurate ribosomes.

The proteins of naked mole rats are also more stable than those of other mammals, according to research led by Rochelle Buffenstein, a comparative gerontologist at Calico, a Google spinoff focused on aging research. Cells of this species have greater numbers of a class of molecules called chaperones that help proteins fold properly. They also have more vigorous proteasomes, structures that dispose of defective proteins. Those proteasomes become even more active when faced with oxidative stress, reactive chemicals that can damage proteins and other biomolecules; in contrast, the proteasomes of mice become less efficient, thus allowing damaged proteins to accumulate and impair the cell’s workings.

DNA, too, seems to be maintained better in longer-lived mammals. When Gorbunova’s team compared the efficiency with which 18 rodent species repaired a particular kind of damage (called a double-strand break) in their DNA molecules, they found that species with longer lifespans, such as naked mole rats and beavers, outperformed shorter-lived species such as mice and hamsters. The difference was largely due to a more powerful version of a gene known as Sirt6, which was already known to affect lifespan in mice.

Watching the “epigenetic clock”

But it’s not just the genes themselves that suffer as animals age — so does their pattern of activation. An important way that cells turn genes on and off at the right time and place is by attaching chemical tags called methyl groups to sites that control gene activity. But these tags — also known as epigenetic marks — tend to get more random over time, leading gene activity to become less precise. In fact, geneticist Steve Horvath of UCLA and his colleagues have found that by assessing the status of a set of almost 800 methylation sites scattered around the genome, they can reliably estimate an individual’s age relative to the maximum lifespan of its species. This “epigenetic clock” holds for all the 192 species of mammals that Horvath’s team has looked at so far.

Notably, the epigenetic marks of longer-lived mammals take longer to degrade, which presumably means that their genes maintain youthful activity longer. In bats, for example, the longest-lived bats often have the slowest rate of change in methylations, while shorter-lived species change more quickly (see diagram).

As he digs deeper, Horvath is finding that certain methylation sites may predict a species’ lifespan regardless of the age at which he samples them. “To me, this is a miracle,” he says. “Let’s say you go into the jungle and find a new species — could be a new bat or any other mammal. I can tell you pretty accurately the maximum lifespan of the species.” The methylation clues also predict maximum lifespan for dog breeds, which may emerge as an important study organism for aging (see sidebar: “What Rover knows”). These lifespan-related methylations tend to be associated with genes related to development, Horvath finds, though more detailed connections have yet to be worked out. He hopes that this work, which is not yet published, can eventually point the researchers toward genes that are key for regulating lifespan and aging.

Improvements in molecular techniques are already giving researchers more powerful tools to tease out the ways in which extraordinarily long-lived organisms may differ from the ordinary. One promising technique involves sequencing not the DNA in cells, but the messenger RNA. Individual genes are copied into mRNA as the first step in producing proteins, so mRNA sequencing reveals which genes in the genome are active at any given moment. This profile — referred to as the transcriptome — gives a more dynamic view of a cell’s activity than just listing the genes in the genome.

Gladyshev’s team, for example, sequenced the transcriptomes of cells from the liver, kidney and brain of 33 species of mammals, then looked for patterns that correlated with lifespan. They found plenty, including differences in activity levels of many genes involved in cellular maintenance functions such as DNA repair, antioxidant defense and detoxification.

Other paths to old age

More recently, Teeling’s team studied Myotis myotis bats from five roosts in France for eight years, capturing each bat every year and taking small samples of blood for transcriptome sequencing. This allowed them to track how the bats’ transcriptomes changed as they aged and compare the process to that of mice, wolves and people — the only other species for which similar long-term transcriptome data were available. “As the bats age,” Teeling wondered, “do they show the same dysregulation that we would show as we age?”

The answer, it turned out, was no. Whereas the other mammals produced fewer and fewer mRNA molecules related to maintenance functions such as DNA repair and protein stability the older they got, the bats did not. Instead, their maintenance systems seemed to get stronger as they got older, producing more repair-related mRNAs.

Skeptics note that conclusive evidence is still lacking, because the presence of more mRNA molecules does not necessarily mean more effective maintenance. “It’s an important first step, but it’s only that,” says Steven Austad, a biogerontologist at the University of Alabama, Birmingham. Still, the fact that the analysis identified processes that were already linked to longevity, such as DNA repair and protein maintenance, suggests that other genes flagged by this method could be solid leads: “We could then go look at new pathways that we haven’t yet explored,” Teeling says. In particular, the team found 23 genes that become much more active with age in bats but less active in other mammals. They are now looking at these genes with great interest, in the hopes of discovering new levers to alter the course of aging.

One of the principles beginning to emerge from comparative studies of aging is that different species may follow different paths to longevity. All long-lived mammals need to delay the onset of cancer, for example. Elephants do this by having multiple copies of key tumor-suppressing genes, so that every cell has backups if one gene breaks during the wear and tear of life. Naked mole rats, on the other hand, gain cancer resistance from an unusual molecule involved in sticking cells together, while bowhead whales have amped up their DNA repair pathways.

Geroscientists tend to view this diversity of solutions as an aid in their quest, not a problem. “That makes our job more difficult, but actually more interesting,” says Austad. “By studying the diversity of ways to achieve slow aging and long life, I think we’re more likely to stumble on things that are more easily translated to humans.”

Can we live longer, healthier lives by learning how to be more like naked mole rats, bats and bowhead whales? Not anytime soon — but the early results from research on these animal Methuselahs show definite promise.

Knowable Magazine is an independent journalistic endeavor from Annual Reviews.

Evan Birnholz’s Feb. 24 Post Magazine crossword, “Upscale”

On occasion I’ll come up with a theme but struggle to get enough theme answers to get a complete set, so I’ll put it down for a few weeks and come back to it later. For this puzzle, I didn’t have much trouble coming up with theme answers, but I put it down for eight months. That’s because filling my original grid back in June 2018 was an absolute bear. I don’t know if it was the lengths of the initial theme entries, or the positions in which I tried to place them, but last year I couldn’t generate any grid with any fewer than 152 answers (far above my normal range of 144 words for normal puzzles and 148 if the grid is especially demanding). That’s in part because I’m running a single answer through what is, essentially, three Across entries, but also because the notes had to go in a specific order and because I wasn’t allowed to put any black squares below the pair of black squares on which the notes sit. For instance, if I needed an extra black square where 54D starts, that would mean I’d need another black square where 83A starts to keep with symmetry, and that would delete the first L from CORAL ATOLL. I realize things like word count and symmetry are mostly just aesthetic preference; in fact, my colleague Francis Heaney recently advised that I free myself from the “prison of symmetry,” and doing so would have come in handy here. But in any case, those are the constraints I sought to adhere to.