The expectation, when researchers began applying modern genomic tools to ancient human remains from the Americas, was that the science would finally settle an argument that had gone on for decades.<\/p>\n
The bones of some of the earliest known Americans looked different from later Native American populations \u2014 different enough that some researchers had proposed two separate waves of migration, two distinct founding populations, maybe even two entirely separate origins.<\/p>\n
Ancient DNA was supposed to answer the question cleanly.<\/p>\n
What the DNA found was not clean.<\/p>\n
Some of the earliest South Americans, and some present-day Indigenous populations in South America, carry a faint but statistically persistent genetic signal that resembles \u2014 in specific, technically defined ways \u2014 the genetic profiles of populations in Australia, New Guinea, and the Andaman Islands.<\/p>\n
Not European populations.<\/p>\n
Not Asian populations in the same way that other Native Americans resemble East Asians.<\/p>\n
Something older, something stranger, something that pointed across the Pacific in the wrong direction.<\/p>\n
The signal was small.<\/p>\n
It was contested.<\/p>\n
Different research teams with different datasets and different analytical methods found it at different intensities, or sometimes appeared not to find it at all.<\/p>\n
But it kept returning \u2014 in South American genomic data, in ancient samples from Brazilian caves, in statistical analyses that compared allele frequencies across thousands of genetic markers.<\/p>\n
Too persistent to be noise.<\/p>\n
Too complex for a simple headline.<\/p>\n
This signal \u2014 sometimes called “Population Y” after the designation used in a landmark 2015 study \u2014 does not mean that ancient Australians sailed to Brazil.<\/p>\n
It does not mean that the first South Americans were not Native Americans.<\/p>\n
What it points to is something more complicated and, in the end, more interesting: a question about the deep ancestral structure of the populations that populated the Americas, about how many founding groups moved through Beringia and when, and about what happened in the ancient world that left a ghost signal in the DNA of people living on the opposite side of the Pacific from each other.<\/p>\n
This is the story of that signal \u2014 where it was found, what it means, what it does not mean, why scientists disagree about it, and what it tells us about the genuine complexity of how the Americas came to be peopled.<\/p>\n
<\/p>\n
It begins in Brazil, in a landscape of caves and ancient bones, where the question started long before anyone had a genome to analyze.<\/p>\n
The Caves of Lagoa Santa and What They Held<\/p>\n
The Lagoa Santa region of the state of Minas Gerais in central Brazil is a landscape of limestone karst \u2014 a terrain shaped by the slow dissolution of rock by slightly acidic groundwater over millions of years.<\/p>\n
The result is a landscape pocked with sinkholes, threaded with underground rivers, and riddled with caves.<\/p>\n
Some of those caves have entrances large enough for human habitation.<\/p>\n
Some have passages small enough that a person must crawl to enter.<\/p>\n
And some of them have been accumulating the remains of the animals and people and plants that lived in and around them for the better part of twelve thousand years.<\/p>\n
The archaeological potential of this landscape was recognized by European researchers in the nineteenth century, when the Danish naturalist Peter Wilhelm Lund \u2014 who had come to Brazil in 1833 to study its natural history and who spent years exploring the region’s caves \u2014 began finding the bones of extinct Pleistocene megafauna mixed with the remains of apparently ancient humans.<\/p>\n
Lund’s finds were significant enough to generate international scientific discussion.<\/p>\n
Here were human bones associated with the bones of creatures that had died out at the end of the last Ice Age \u2014 giant ground sloths, horses, mastodons, and other megafauna that had vanished from the Americas roughly ten to twelve thousand years ago.<\/p>\n
The implication was that these ancient people had lived alongside those creatures, placing them at a remarkable depth of time.<\/p>\n
The Lagoa Santa skeletal material that Lund and subsequent researchers excavated was distinctive in ways that would generate controversy for the next century and a half.<\/p>\n
The skulls of these early people were, in measurable morphological terms, different from the skulls of later Native American populations.<\/p>\n
They were characterized by longer, narrower brain cases, more prominent brow ridges, and facial proportions that led researchers to describe them with terms like “gracile,” “long-headed,” or by the technical measurement term “dolichocephalic.” Later Native American populations, by contrast, tended toward skulls that were broader and more rounded \u2014 a different set of measurable proportions.<\/p>\n
<\/p>\n
The difference was real and measurable.<\/p>\n
The interpretation of what the difference meant would turn out to be far more complicated than anyone initially assumed.<\/p>\n
Lagoa Santa is not simply a collection of bones.<\/p>\n
It is one of the richest early Holocene archaeological records in the Western Hemisphere.<\/p>\n
The caves and rock shelters of the region contain not just skeletal material but evidence of the daily lives of the people who lived there: tools made from stone and bone, evidence of fire use, plant remains that reveal what people ate, and a body of rock art painted on the walls and ceilings of the shelters that offers a visual record of how these ancient people represented their world and themselves.<\/p>\n
The rock art alone would make Lagoa Santa archaeologically significant.<\/p>\n
<\/p>\n
The paintings at sites like Lapa do Santo \u2014 a rock shelter that has become one of the most intensively studied early archaeological sites in South America \u2014 include red pigment images of human figures, animals, geometric forms, and scenes whose meaning is not always clear but whose existence is unambiguous evidence of a symbolic and expressive culture.<\/p>\n
These were not simple opportunistic inhabitants of convenient caves.<\/p>\n
They were people with a rich cultural life, with representational art, with the full range of human cognitive and social capacity.<\/p>\n
The human remains themselves have been dated using a variety of methods, and the most reliably dated specimens are genuinely ancient by any standard.<\/p>\n
Radiocarbon dates on skeletal material from Lagoa Santa have produced ages ranging from approximately 10,000 to 12,000 years before present \u2014 placing the people of Lagoa Santa among the earliest known human populations in South America.<\/p>\n
Some dates are older; some are more recent.<\/p>\n
<\/p>\n
The overall picture is of a population that occupied this region during and shortly after the end of the Pleistocene, as the world’s climate was warming and the Ice Age megafauna were disappearing.<\/p>\n
The ancient people of Lagoa Santa were genuine early Americans.<\/p>\n
They were among the first human beings to leave a clear archaeological record in South America.<\/p>\n
What they were not was simple or easy to categorize.<\/p>\n
The Skull Debate and Why It Lasted So Long<\/p>\n
The distinctive morphological characteristics of the Lagoa Santa skulls \u2014 and of similar early American skeletal material from other sites across the Western Hemisphere \u2014 attracted sustained scientific attention from the mid-nineteenth century onward, and the resulting debate was sometimes scientifically rigorous, sometimes shaped by the racial assumptions of its era, and always more complicated than the simple question it appeared to be asking.<\/p>\n
The question was: if the earliest known Americans looked different from later Native American populations, what did that mean?<\/p>\n
<\/p>\n
One set of answers was deeply entangled with the racial science of the nineteenth and early twentieth centuries \u2014 with frameworks that treated skull shape as a direct marker of ancestry, race, and biological hierarchy.<\/p>\n
Early analyses of the Lagoa Santa material were conducted in intellectual environments where cranial measurement was a respectable scientific activity and where the differences between skulls were frequently interpreted in terms of the racial typologies of the era.<\/p>\n
Some of this work was straightforwardly wrong in ways that later science would establish clearly.<\/p>\n
Some of it was useful in establishing that the morphological differences between early and later American skulls were real and measurable.<\/p>\n
The modern scientific debate, which developed through the latter decades of the twentieth century, was more careful and more explicitly methodologically informed.<\/p>\n
<\/p>\n
Researchers like Walter Neves and Hector Pucciarelli contributed detailed quantitative analyses of the Lagoa Santa cranial morphology, comparing the measurable characteristics of these ancient skulls not just to later Native American populations but to skeletal reference populations from around the world.<\/p>\n
Their analyses found that the morphological characteristics of the Lagoa Santa skulls resembled, in statistical terms, the cranial profiles of populations from sub-Saharan Africa, Australia, and Melanesia \u2014 populations that had dispersed from Africa early in human prehistory and that retained certain ancestral morphological characteristics.<\/p>\n
This finding led some researchers \u2014 including Neves and his collaborators \u2014 to propose what became known as the “two-population model” of American peopling: the idea that the Americas had been colonized by two distinct groups, with an earlier group carrying the morphological characteristics seen in Lagoa Santa and related material, and a later group with the different morphological profile seen in most later Native American populations.<\/p>\n
The two-population model was not simply invented from nothing.<\/p>\n
<\/p>\n
It was an attempt to explain a real observation \u2014 the genuine morphological difference between early and later American skeletal material \u2014 using the tools and frameworks available.<\/p>\n
And it made specific predictions that could in principle be tested: if there had been two distinct founding populations, those populations should show genetic differences, and ancient DNA from early American individuals should reveal the expected genetic signals.<\/p>\n
What the ancient DNA eventually showed was more complicated than either a simple confirmation or a simple refutation of the two-population model.<\/p>\n
Before the genomic evidence arrived, however, the morphological debate generated significant heat and some light.<\/p>\n
<\/p>\n
The central methodological challenge was that cranial morphology \u2014 the shape of the skull \u2014 is determined by a complex combination of genetic and developmental factors, and that similar skull shapes can arise independently in populations that are not closely related, while closely related populations can sometimes show significant morphological differences due to developmental plasticity and environmental influences.<\/p>\n
The observation that Lagoa Santa skulls resemble those of Australian and African populations does not, by itself, tell us that Lagoa Santa people were closely related to Australians or Africans.<\/p>\n
It tells us that they shared certain morphological characteristics.<\/p>\n
The cause of that sharing \u2014 common ancestry, independent parallel development, environmental influences on skull development, or some combination of these \u2014 cannot be determined from skull shape alone.<\/p>\n
This is not a criticism of the researchers who used morphological analysis; it is a description of the inherent limitations of that type of evidence.<\/p>\n
<\/p>\n
Skull shape is genuinely informative about some aspects of human prehistory.<\/p>\n
It is not a reliable guide to genetic ancestry in the way that DNA analysis can be.<\/p>\n
The history of paleoanthropology includes multiple examples of morphological similarities that later turned out not to reflect close genetic relationships, and multiple examples of close genetic relationships between populations with strikingly different morphological profiles.<\/p>\n
The lesson is not that morphological analysis is useless.<\/p>\n
It is that morphological analysis requires careful interpretation, with explicit acknowledgment of its limitations and without the overconfident conclusions that earlier researchers sometimes drew from it.<\/p>\n
<\/p>\n
The Genomic Revolution and What Changed<\/p>\n
The development of techniques for extracting, sequencing, and analyzing ancient DNA from archaeological specimens was one of the most consequential methodological advances in the history of human prehistory research, and its application to the earliest Americans has fundamentally transformed the field in ways that are still unfolding.<\/p>\n
The basic challenge of ancient DNA analysis is preservation.<\/p>\n
DNA degrades over time, damaged by chemical reactions with the surrounding environment, by microbial activity, and by the physical breakdown of the cellular structures that originally contained it.<\/p>\n
The rate of degradation depends heavily on temperature, humidity, and the chemical composition of the burial environment: cold, dry, stable conditions preserve DNA much longer than warm, humid, chemically active environments.<\/p>\n
<\/p>\n
The tropical and subtropical conditions of much of South America are, from the perspective of DNA preservation, among the most challenging possible.<\/p>\n
The early South American skeletal material from sites like Lagoa Santa is therefore among the most difficult ancient DNA material to work with.<\/p>\n
The warm, humid conditions of the Brazilian cerrado and the cave environments where much of the skeletal material was found are not conducive to long-term DNA preservation.<\/p>\n
Researchers working with this material have had to develop and apply particularly sensitive methods for extracting and sequencing the small, degraded quantities of DNA that survive.<\/p>\n
Despite these challenges, the past decade has produced a series of ancient genome studies that have fundamentally changed what can be said about the genetic history of early South Americans.<\/p>\n
<\/p>\n
The results have confirmed some expectations, overturned others, and generated entirely new questions that nobody was asking before the genomic evidence arrived.<\/p>\n
The most fundamental finding \u2014 the one that established the basic framework within which all subsequent debates have taken place \u2014 is this: the ancient people of South America, including the ancient people of Lagoa Santa, were genetically Native American.<\/p>\n
They were not Australians.<\/p>\n
They were not Africans.<\/p>\n
They were not a separate founding population that arrived by a different route from a different part of the world.<\/p>\n
They were members of the same broad ancestral group that populated all of the Americas \u2014 a group that originated in Asia, crossed into the Americas through Beringia (the land bridge between Siberia and Alaska that existed when sea levels were lower), and then spread rapidly across both continents.<\/p>\n
<\/p>\n
This finding was, in a sense, expected.<\/p>\n
The hypothesis that the Americas were populated by people who moved from Asia through Beringia is the best-supported model of American settlement, supported by genetic evidence from living Native American populations, by linguistic evidence, by the archaeological record, and by the basic geographic logic of how the Americas could have been reached from the Old World during the period when sea levels were low enough to expose a land connection.<\/p>\n
What was not expected \u2014 or at least not clearly anticipated \u2014 was what happened when the ancient South American genomes were compared in detail to the genomes of populations from different parts of the world, and specifically when certain statistical analyses were applied to detect patterns of shared ancestry.<\/p>\n
What “Allele Sharing” Actually Means<\/p>\n
<\/p>\n
Before going further into the specific findings, it is worth pausing to explain, in plain terms, what the genetic analyses are actually measuring when they report “affinity” or “allele sharing” between ancient South Americans and Australasian populations.<\/p>\n
This is one of the most commonly misunderstood aspects of the Population Y story, and the misunderstanding tends to produce dramatically oversimplified headlines.<\/p>\n
Alleles are the different versions of a gene \u2014 or more broadly, the different variants of a specific position in the genome \u2014 that exist in a population.<\/p>\n
Every human being inherits two copies of each chromosome (one from each parent), and at any given position in the genome, those two copies may carry the same variant (if both parents passed on the same version) or different variants.<\/p>\n
Across the three billion or so positions in the human genome, the specific combination of variants that an individual carries is their genotype.<\/p>\n
<\/p>\n
When geneticists compare the genomes of different populations, they look at which variants \u2014 which alleles \u2014 are present at different frequencies in different groups.<\/p>\n
If two populations share a particular variant at a higher frequency than would be expected by chance, that “excess allele sharing” or “affinity” is evidence of a closer genetic relationship between those populations than between each of them and a third population used as a reference.<\/p>\n
The statistical tool most commonly used to detect these patterns is called the D-statistic or ABBA-BABA test (the names refer to the specific pattern of allele frequencies being counted).<\/p>\n
This test was developed specifically to detect patterns of excess allele sharing that indicate genetic mixing \u2014 admixture \u2014 between populations.<\/p>\n
<\/p>\n
It compares the observed frequencies of specific allele patterns to what would be expected under a simple tree-like model of population separation, and if the observed frequencies differ significantly from the expected frequencies, it indicates that something more complex than simple population branching has happened.<\/p>\n
When this test was applied to datasets that included ancient South American genomes alongside modern genomes from populations around the world, it found something unexpected: some ancient South Americans, and some present-day Indigenous populations in South America, showed statistically significant excess allele sharing with populations from Australia, New Guinea, and the Andaman Islands.<\/p>\n
The excess was small \u2014 not large enough to suggest that Australasians made up a major portion of the ancestry of these populations.<\/p>\n
But it was statistically significant, meaning it was larger than could be explained by random variation.<\/p>\n
<\/p>\n
And it was found in multiple analyses by different research teams using different datasets, which made it difficult to dismiss as an artifact of any single study.<\/p>\n
This is the Population Y signal.<\/p>\n
It is not a finding that Australians reached South America.<\/p>\n
It is a finding that certain South American populations share more alleles with Australasian populations than would be expected if both groups had simply descended independently from a common ancestral pool without any additional contact or shared ancestry.<\/p>\n
The question \u2014 and it is a genuinely hard question \u2014 is what caused that excess sharing.<\/p>\n
The 2015 Study That Named the Problem<\/p>\n
<\/p>\n
The paper that most clearly articulated the Population Y signal and brought it to broad scientific attention was published in Nature in 2015, by Pontus Skoglund and a large team of co-authors including David Reich, Eske Willerslev, and others.<\/p>\n
The paper analyzed genome-wide data from a large number of Native American populations, both ancient and modern, and applied a range of statistical tests to characterize the genetic relationships among them.<\/p>\n
The paper’s central finding regarding American settlement was that all Native American populations shared a common founding ancestry \u2014 consistent with the Beringian dispersal model \u2014 but that the data from certain South American populations and certain ancient samples showed an additional signal that could not be explained by that founding ancestry alone.<\/p>\n
This additional signal was named Population Y \u2014 using Y not to indicate the male Y chromosome but as a variable name in the statistical model, the unknown element whose characteristics needed to be determined.<\/p>\n
<\/p>\n
Population Y was proposed as a distinct ancestral component that contributed to some South American populations and that was most genetically similar, among modern and ancient populations, to Australasians \u2014 specifically to populations from Australia, New Guinea, and the Andaman Islands.<\/p>\n
The paper was careful about what it was and was not claiming.<\/p>\n
It was not claiming that modern Australians had sailed to South America.<\/p>\n
It was claiming that the statistical signal in certain South American genomes was most similar to the signal expected from a contribution of Australasian-like ancestry \u2014 the kind of ancestry that, in the deep human past, characterized the populations that spread out of Africa early and populated the southern route through Asia toward Australia and Melanesia.<\/p>\n
The paper proposed several models that could explain the signal.<\/p>\n
<\/p>\n
One was that there had been a separate migration to the Americas by a population related to Australasians \u2014 a second wave of dispersal from Asia that arrived in the Americas after the main Beringian founding population but before significant mixing between the two groups.<\/p>\n
Another was that the signal reflected deep ancestral structure within the Asian populations that gave rise to Native Americans \u2014 that the ancestral Beringian population itself contained distinct subgroups, one of which was more closely related to Australasian populations than the other, and that this internal diversity was preserved in different proportions in different descendant populations.<\/p>\n
The 2015 paper’s authors acknowledged that distinguishing between these models would require additional data \u2014 specifically, ancient genomes from the relevant time periods and geographic regions \u2014 and that the current data were consistent with multiple explanations.<\/p>\n
They were, in other words, appropriately cautious about what the finding meant while being clear that the finding itself was robust.<\/p>\n
<\/p>\n
The paper generated significant scientific attention and media coverage.<\/p>\n
The media coverage was, in many cases, less careful than the paper itself.<\/p>\n
Headlines that declared “Australians may have been among the first Americans” or “Ancient Australians reached South America” appeared in multiple outlets, despite the paper’s explicit statement that these interpretations went beyond what the data supported.<\/p>\n
This is a recurring challenge in the communication of complex genomic findings to a general audience.<\/p>\n
The statistical finding \u2014 excess allele sharing between certain South American populations and Australasian populations \u2014 is real and significant.<\/p>\n
<\/p>\n
The popular translation \u2014 Australians reached South America \u2014 is both wrong and potentially harmful, because it misrepresents both the genetic science and the history of the Indigenous peoples involved.<\/p>\n
What the Ancient Lagoa Santa Genomes Showed<\/p>\n
The application of ancient DNA analysis to skeletal material from Lagoa Santa itself produced one of the most important contributions to the Population Y debate.<\/p>\n
If the Population Y signal was real and if it reflected a distinct ancestral component in early South Americans, then the ancient people of Lagoa Santa \u2014 among the earliest known South Americans \u2014 should show that signal in their own genomes.<\/p>\n
The results were, as is so often the case with complex scientific questions, more nuanced than a simple confirmation or refutation would have been.<\/p>\n
<\/p>\n
In 2018, a major study by Jo\u00e3o Arroyo-Kalin and colleagues, and separately a study by Cosimo Posth, Johannes Krause, and a large international team, published ancient genomes from Lagoa Santa individuals.<\/p>\n
The Lagoa Santa genomes showed the expected Native American ancestry \u2014 these were unambiguously genetically Native American individuals, consistent with descent from the Beringian founding population.<\/p>\n
They were not genetically Australian or Melanesian.<\/p>\n
They did not show evidence of direct ancestry from populations outside of the broader Native American founding group.<\/p>\n
But when the statistical tests for excess allele sharing were applied to the Lagoa Santa ancient genomes, the results were complex.<\/p>\n
Some analyses found signals consistent with Population Y in the Lagoa Santa material.<\/p>\n
<\/p>\n
Others found weaker or less statistically clear signals.<\/p>\n
The results depended on which reference populations were used in the comparison, which statistical methods were applied, and which specific ancient individuals were included in the analysis.<\/p>\n
This variability in the results was itself informative \u2014 it suggested that the Population Y signal, whatever its ultimate cause, was not a uniform feature of all early South Americans, was sensitive to the specific analytical choices made by researchers, and required more data and more careful analysis than the 2015 study had been able to bring to bear.<\/p>\n
The 2018 studies also contributed a new layer of evidence relevant to a specific question: had the people of Lagoa Santa contributed ancestry to later South American populations?<\/p>\n
<\/p>\n
The answer, broadly, was yes \u2014 the Lagoa Santa ancient genomes showed patterns of genetic similarity to later South American populations that were consistent with population continuity rather than replacement.<\/p>\n
This was not a trivial finding.<\/p>\n
One plausible explanation for the difference between early and later American skeletal morphology had been that there was an actual population replacement \u2014 that a population with one morphological profile was replaced by a population with a different morphological profile, with minimal genetic mixing.<\/p>\n
The ancient genome data did not support this strong version of the replacement model.<\/p>\n
Instead, the evidence supported a picture of population continuity \u2014 with genetic contributions from the early inhabitants of Lagoa Santa persisting into later populations \u2014 combined with the changes in morphological characteristics that can occur over time within a genetically continuous population through developmental plasticity, dietary changes, and other non-genetic factors.<\/p>\n
<\/p>\n
This was an important finding for the interpretation of the skull morphology debate.<\/p>\n
The morphological differences between early and later South American populations did not require a population replacement to explain.<\/p>\n
They could be explained within a framework of overall genetic continuity, with morphological change occurring over time within an ancestral population.<\/p>\n
Deep Ancestral Structure and the Asian Connection<\/p>\n
The most scientifically interesting explanations for the Population Y signal involve not a separate migration from Australia but something that happened much earlier, in Asia, before anyone reached the Americas at all.<\/p>\n
To understand this, it helps to understand the deep structure of human populations in Asia during the period when the Americas were first being settled.<\/p>\n
<\/p>\n
Modern humans spread out of Africa beginning around 60,000 to 70,000 years ago (though the precise timing is still a matter of active research).<\/p>\n
One major dispersal route went along the southern coast of Asia \u2014 through what is now India, Southeast Asia, and eventually to Australia and New Guinea, which were connected by lower sea levels and could be reached by short water crossings even then.<\/p>\n
The populations that took this southern route, and that eventually settled Australia and New Guinea, are the ancestral populations whose genetic legacy is most relevant to the Population Y discussion.<\/p>\n
A separate dispersal, somewhat later, went through northeastern Asia and eventually into Beringia and the Americas.<\/p>\n
<\/p>\n
The ancestral population that gave rise to all Native Americans \u2014 sometimes called the “First Peoples” or the “Ancestral Native American” population \u2014 spent an extended period in the Beringia region before the genetic and archaeological evidence suggests they dispersed into the Americas, probably around 16,000 to 20,000 years ago, though the exact timing and the question of one versus multiple dispersal events continues to be debated.<\/p>\n
Here is the key question: what was the deep structure of the ancestral Beringian population before it entered the Americas?<\/p>\n
If the population that eventually crossed into the Americas was itself genetically diverse \u2014 if it contained subgroups or lineages that had different amounts of ancestry from different ancient Asian populations, including populations related to the southern-route dispersal toward Australia \u2014 then those differences in ancestry would have been preserved in different proportions in different descendant populations as they spread across the Americas.<\/p>\n
This model \u2014 deep ancestral structure within the founding population \u2014 can produce the Population Y signal without requiring any migration from Australia to the Americas.<\/p>\n
<\/p>\n
If the ancestral Native American population contained some individuals or lineages with more “Australasian-like” ancestry because they had more ancestry from the ancient southern-route populations of Asia, and if those individuals contributed differentially to some South American populations compared to North American populations, then the excess allele sharing between South American populations and Australasians could reflect this ancient, pre-American internal diversity.<\/p>\n
This model is sometimes called the “Australasian ghost population” model or the “deep ancestral structure” model, and it is one of the most seriously discussed explanations in the current scientific literature.<\/p>\n
It does not require Australasians to have reached South America.<\/p>\n
It requires only that the population from which all Native Americans descend was itself structured in specific ways that left different genetic traces in different descendant groups.<\/p>\n
The challenge with this model \u2014 and with all of the models proposed to explain Population Y \u2014 is that it requires ancient genetic data from the right times and places to test it directly.<\/p>\n
<\/p>\n
What is needed, specifically, is ancient DNA from northeastern Asian and Beringian populations from the relevant periods \u2014 roughly 20,000 to 30,000 years ago \u2014 that would allow researchers to directly characterize the genetic diversity of the populations that eventually gave rise to Native Americans.<\/p>\n
Collecting such data is extremely challenging: the relevant sites are largely under water (because sea level rise flooded much of the Beringian landscape after the end of the last Ice Age) or in remote and archaeologically difficult locations, and DNA preservation in the cold but wet conditions of much of the relevant region is variable.<\/p>\n
Some ancient DNA data from northeastern Asia is available, and it has contributed important evidence to the debate.<\/p>\n
Ancient genomes from Siberian populations dating to the relevant period show complex genetic histories that include components related to both East Asian and more western Eurasian populations, with different ancient Siberian individuals showing different proportions.<\/p>\n
<\/p>\n
This diversity is consistent with the idea that the ancestral Native American population was itself genetically diverse in ways that could produce descendant populations with different affinities to different parts of the Old World.<\/p>\n
But the specific ancient data needed to definitively test the deep ancestral structure model \u2014 Beringian genomes from the period just before the American dispersal \u2014 are not yet available.<\/p>\n
This means that the Population Y debate cannot currently be resolved by direct evidence from the relevant ancestral populations, and that the competing models must be evaluated on the basis of their consistency with the available evidence rather than by direct test.<\/p>\n
The Geography of the Signal<\/p>\n
<\/p>\n
One of the most informative aspects of the Population Y signal is its geographic distribution within the Americas \u2014 the fact that it is found at significantly different intensities, or not at all, in different Native American populations.<\/p>\n
The signal is strongest in certain populations from the Amazon basin, in some populations from Brazil more broadly, and in some populations from the Pacific coast of South America.<\/p>\n
It is weaker or undetectable in many North American populations, in populations from the Caribbean, and in many populations from the southern cone of South America.<\/p>\n
This geographic pattern is itself evidence that can help distinguish between different models of the signal’s origin.<\/p>\n
A model in which a separate Australasian-related population migrated to South America and mixed with the founding Native American population would predict that the signal should be strongest in the geographic area where that mixing occurred and should decrease with distance from that area.<\/p>\n
<\/p>\n
The geographic distribution of the signal is broadly consistent with this prediction, in the sense that it is concentrated in the parts of South America closest to the Pacific \u2014 the ocean that would have to be crossed if there were a direct connection to Australasian populations.<\/p>\n
But the geographic distribution also poses challenges for simple migration models.<\/p>\n
If a population related to Australasians reached South America by crossing the Pacific, that crossing would have been extraordinarily difficult with the technology available to human populations in the early Holocene.<\/p>\n
The Pacific Ocean is vast.<\/p>\n
No human population is known to have made sustained trans-Pacific crossings before the Polynesian expansion, which occurred within the past two to three thousand years \u2014 far too recently to account for a signal in populations that were already present in South America ten to twelve thousand years ago.<\/p>\n
Some researchers have proposed a coastal route model \u2014 the idea that a population related to Australasians could have reached the Americas by following a coastal route along the edge of Asia, through Beringia, and then down the Pacific coast of North and South America, rather than by crossing the open Pacific directly.<\/p>\n
<\/p>\n
This model avoids the need for an open-ocean crossing but requires that the Australasian-related population made it to Beringia and then to the Americas without leaving the genetic traces that would be expected if it had mixed substantially with North American populations along the way.<\/p>\n
The coastal route model is logistically possible in a way that a direct trans-Pacific crossing is not, but it requires a specific set of population dynamics \u2014 essentially, a population that moved quickly along the coast without significant admixture with interior populations \u2014 that would need to be verified rather than assumed.<\/p>\n
The geographic distribution of the signal is also complicated by the fact that it is not simply “present in South America and absent in North America.” It shows up in some North American populations as well, and its intensity varies in ways that do not perfectly match any simple geographic pattern.<\/p>\n
This variability is consistent with the deep ancestral structure model, in which the signal reflects ancient diversity within the founding population that was distributed differently across different descendant groups as a result of the specific population dynamics of the American dispersal and subsequent differentiation.<\/p>\n
<\/p>\n
When Populations Diverged: The Rapid Expansion Problem<\/p>\n
One of the most challenging aspects of the Population Y puzzle is that it must be explained against the backdrop of what the genomic evidence tells us about the pace of the initial American settlement.<\/p>\n
The genetic evidence from living and ancient Native American populations is consistent with a rapid, sweeping dispersal across the Americas \u2014 a founding population that entered the Americas from Beringia and then spread southward with remarkable speed, reaching the tip of South America within a relatively short period after the initial entry.<\/p>\n
The archaeological evidence supports this rapid dispersal model: well-dated sites from the southern cone of South America appear within a few thousand years of the earliest sites from the north, and the genetic diversity of Native American populations is consistent with a rapid expansion from a small founding group rather than a slow, gradual spread.<\/p>\n
<\/p>\n
This rapid dispersal creates a specific problem for models that propose a second migration, or a significant admixture event, as the explanation for Population Y.<\/p>\n
If the Americas were peopled rapidly and if the founding population quickly differentiated into geographically distinct groups, then there was a limited window of time during which a second, distinct population could have entered South America and mixed with the existing population without leaving detectable traces in North American populations.<\/p>\n
The rapid expansion model is not itself in question \u2014 the genetic and archaeological evidence for it is strong.<\/p>\n
The puzzle is how to fit the Population Y signal into the framework that the rapid expansion model creates.<\/p>\n
<\/p>\n
One approach is to allow for the possibility that the rapid expansion was not quite as geographically uniform as the simplest model suggests \u2014 that there were populations in different geographic areas at slightly different times, creating opportunities for localized admixture events that would show up in some regions and not others.<\/p>\n
The complexity of the early archaeological record in South America \u2014 with sites from different time periods and different geographic locations showing different material culture assemblages \u2014 is consistent with a more complex early settlement history than a single undifferentiated wave would suggest.<\/p>\n
Another approach is to focus on the deep ancestral structure model, in which the Population Y signal is not the product of a post-entry admixture event at all but rather reflects diversity that was present in the founding population itself.<\/p>\n
Under this model, the geographic concentration of the signal in South America reflects not where mixing occurred after entry into the Americas but rather which specific lineages within the founding population settled in which geographic areas and then expanded locally.<\/p>\n
<\/p>\n
Both of these approaches are scientifically defensible on the current evidence.<\/p>\n
The challenge is that they make somewhat different predictions about what future ancient DNA data should show, and testing those predictions requires data that is not yet available.<\/p>\n
The Ancient DNA from Brazil, Uruguay, and Panama<\/p>\n
The broader dataset of ancient South American genomes \u2014 not just Lagoa Santa but other early sites across the continent \u2014 has contributed important additional evidence to the Population Y debate, with results that are revealing in their pattern of consistency and inconsistency.<\/p>\n
Ancient genomes from the Atacama Desert of Chile, where the extreme dryness of the environment has allowed remarkable preservation of organic material, have been analyzed and show the expected Native American ancestry without clear evidence of the Population Y signal at the intensity seen in some Amazonian populations.<\/p>\n
<\/p>\n
This geographic pattern is consistent with some models but not others.<\/p>\n
Ancient genomes from Uruguay have been analyzed and also show Native American ancestry.<\/p>\n
The relationships between these ancient individuals and the populations of the Lagoa Santa region have been characterized, contributing to an emerging picture of the genetic landscape of early South America.<\/p>\n
Some of these individuals show evidence of the same kind of ancestry as the Lagoa Santa people; others show different patterns.<\/p>\n
Ancient material from Panama \u2014 geographically positioned at the narrowest point of the land connection between North and South America and therefore at a critical juncture in any model of South American settlement \u2014 has also been analyzed.<\/p>\n
<\/p>\n
The Panamanian ancient genomes contribute to understanding the genetic relationship between North and South American populations at an early period and help constrain the timing of population divergence events.<\/p>\n
The overall pattern from the growing dataset of ancient South American genomes is one of genuine complexity.<\/p>\n
There is not a simple uniform signal that appears in all early South Americans.<\/p>\n
There are variations between individuals and between populations that reflect the specific local histories of different communities \u2014 local population dynamics, genetic drift, admixture events that may have been localized rather than continental in scale.<\/p>\n
This complexity is, arguably, exactly what should be expected.<\/p>\n
<\/p>\n
The early settlement of South America was not a single uniform event.<\/p>\n
It was a process that played out over thousands of years, in diverse geographic environments, by populations that were themselves diverse and that experienced different subsequent histories.<\/p>\n
The genomic record of that process is correspondingly complex, and attempts to fit it into a simple two-population or three-population model are likely to be inadequate to the actual historical reality.<\/p>\n
The Second Opening: A Question of Interpretation<\/p>\n
Around the point where the basic Population Y evidence has been laid out, and the competing scientific models have been described, a deeper question emerges that is worth addressing directly: what are researchers actually arguing about, and why does the argument matter?<\/p>\n
<\/p>\n
On one level, the debate is about which specific model best explains the observed genetic signals.<\/p>\n
That is a technical question with technical answers, amenable in principle to resolution as more data becomes available.<\/p>\n
But at a deeper level, the debate touches on questions about how we tell the story of the first Americans \u2014 about which frameworks we use to organize that story, whose interests those frameworks serve, and what is at stake in getting the story right or wrong.<\/p>\n
The question “who were the first Americans?” has been asked for a very long time, and the answers to it have sometimes served purposes that had nothing to do with historical truth.<\/p>\n
<\/p>\n
In the nineteenth century, the Mound Builder Myth \u2014 the idea that the earthen mounds of North America had been built by a now-vanished race rather than by the ancestors of contemporary Native Americans \u2014 served to sever the connection between Native people and the archaeological evidence of sophisticated pre-contact civilization, making it easier to justify the dispossession of Native lands.<\/p>\n
More recent versions of similar arguments \u2014 the Solutrean hypothesis, which proposed that Ice Age Europeans rather than Asians were the first Americans, or various claims about pre-Columbian contact \u2014 have sometimes been deployed in ways that serve similar ends, undermining the specific historical connections between Native Americans and their ancestral lands and cultures.<\/p>\n
Population Y is not in this category \u2014 it is a genuine scientific finding that has been reported carefully by researchers who are aware of its potential for misinterpretation.<\/p>\n
But the misinterpretations have occurred anyway, as evidenced by the headlines claiming that Australians were among the first Americans.<\/p>\n
<\/p>\n
And the misinterpretations matter, because they can be used to argue that the ancestry and historical claims of Indigenous South American peoples are more uncertain or more contested than the actual evidence supports.<\/p>\n
The scientific evidence does not support any such conclusion.<\/p>\n
The ancient people of Lagoa Santa were Native Americans.<\/p>\n
The Indigenous people of South America today are the descendants of the people who have lived in the Americas since the first settlement.<\/p>\n
The Population Y signal, whatever its ultimate explanation, does not change either of these facts.<\/p>\n
What it does is indicate that the population history of the Americas was more complex than the simplest models suggested \u2014 which is itself a finding of genuine scientific and historical interest, independent of any implications for the specific cultural or legal claims of Indigenous peoples.<\/p>\n
Why Studies Have Produced Different Results<\/p>\n
<\/p>\n
The fact that different research teams using different datasets and different methods have found the Population Y signal at different intensities \u2014 or have sometimes appeared not to find it at all \u2014 is one of the most important aspects of the scientific debate and deserves careful explanation.<\/p>\n
Several factors can produce variation in the results of ancient genome analyses when applied to questions like Population Y.<\/p>\n
The composition of the reference panel \u2014 the set of modern and ancient genomes used as comparison populations in the statistical tests \u2014 can significantly affect the results.<\/p>\n
If the reference panel includes populations that carry the signal themselves, or if it omits populations that would help calibrate the baseline expectations, the results of the statistical tests will be affected.<\/p>\n
Different research teams have used different reference panels, and this methodological difference is one source of variation in reported results.<\/p>\n
<\/p>\n
The specific ancient individuals included in the analysis also matter.<\/p>\n
The Population Y signal is not uniformly present in all ancient South Americans, and the specific individuals for whom ancient genomes are available are not a random sample of the ancient population.<\/p>\n
If a study includes individuals who happen to carry more or less of the Population Y-related ancestry, the overall result will be affected by that specific sample composition.<\/p>\n
The statistical methods used to detect and quantify the signal also vary between studies.<\/p>\n
<\/p>\n
Different tests have different statistical properties \u2014 different sensitivities, different abilities to distinguish between closely related models \u2014 and the results they produce are not always directly comparable.<\/p>\n
A study that uses a test with lower sensitivity to weak signals may not detect a Population Y signal that a more sensitive test in a different study would find.<\/p>\n
The quality and quantity of ancient DNA from individual specimens is another source of variation.<\/p>\n
Ancient genomes sequenced at low coverage \u2014 where the genome has been read only a small number of times on average, leaving many positions without reliable data \u2014 are less informative for the statistical tests that detect population structure than high-coverage genomes.<\/p>\n
If the key ancient specimens from Lagoa Santa were sequenced at low coverage, the results will be less definitive than if they were sequenced at high coverage.<\/p>\n
<\/p>\n
None of these factors makes the Population Y signal simply an artifact.<\/p>\n
Multiple studies using different methods and different datasets have found signals consistent with Population Y, and the consistency across different approaches is one reason the finding is taken seriously.<\/p>\n
But the variability in results means that the signal is not as robust or as clearly quantified as it would be if all studies found it at the same intensity using the same methods.<\/p>\n
This variability is itself scientifically informative: it suggests that the Population Y signal, if real, is a subtle one \u2014 a small contribution to the ancestry of some populations rather than a dominant component \u2014 and that resolving its nature will require larger datasets, better-preserved ancient specimens, and more carefully calibrated analytical methods than have been available to date.<\/p>\n
<\/p>\n
The 2020s Genomic Work and What It Has Added<\/p>\n
The years since the 2015 Population Y paper and the 2018 ancient South American genome studies have seen significant additional work on Native American population history, and the resulting picture has become both richer and more complex.<\/p>\n
Studies published in the early 2020s have dramatically expanded the number of ancient Native American genomes available for analysis, including new material from North America, Central America, and South America.<\/p>\n
The expanded dataset has allowed researchers to characterize the genetic history of the Americas at a level of detail that was previously impossible.<\/p>\n
<\/p>\n
One of the most important contributions of the 2020s work is a better characterization of the internal genetic diversity of the ancient Native American founding population.<\/p>\n
Early work had treated the founding population as relatively uniform, differing from later populations primarily in having experienced less genetic drift over time.<\/p>\n
More recent work has found evidence of finer internal structure within the early Native American population \u2014 distinct genetic lineages that diverged early in the history of the founding population and that contributed differentially to different parts of the Americas.<\/p>\n
This finding is directly relevant to the Population Y debate.<\/p>\n
<\/p>\n
If the founding population contained distinct genetic lineages that diverged before the dispersal into the Americas, then the differential distribution of those lineages across the Americas could produce patterns of allele sharing that might be interpreted as reflecting post-entry admixture events but actually reflect the structure of the founding population itself.<\/p>\n
The more complex picture of founding population structure that is emerging from 2020s genomic work is broadly consistent with the deep ancestral structure explanation of Population Y, though it does not definitively resolve the question.<\/p>\n
The 2020s work has also contributed important evidence on the population history of South America after the initial settlement.<\/p>\n
The genetic record shows significant complexity in South American population history \u2014 patterns of local differentiation, evidence of contact and gene flow between different geographic groups, and in some areas evidence of more dramatic population replacement events in which earlier populations were replaced by later ones with substantially different ancestry.<\/p>\n
This internal complexity of South American population history complicates the interpretation of any signal found in contemporary or ancient South American genomes, because it means that the ancestry of any given ancient or modern individual reflects not just the original settlement history but the subsequent population dynamics of the region.<\/p>\n
<\/p>\n
A signal that looks like a contribution from Population Y might, in some cases, reflect later population mixing events within South America that brought together individuals with different proportions of the original founding lineages.<\/p>\n
South American Population Turnover and What It Reveals<\/p>\n
One of the most striking findings of ancient South American DNA research is evidence for significant population turnover in various regions \u2014 episodes in which the people living in a particular area in one period are genetically quite different from the people living in the same area in a later period.<\/p>\n
The evidence for such turnover comes from comparing the ancient genomes of individuals from the same geographic area but different time periods.<\/p>\n
In some cases, the comparison shows clear continuity \u2014 the later population descends primarily from the earlier population, with gradual change over time.<\/p>\n
<\/p>\n
In other cases, the comparison shows significant discontinuity \u2014 the later population is genetically different from the earlier population in ways that are not easily explained by gradual drift or selection, suggesting that the later population arrived from elsewhere and partially or largely replaced the earlier one.<\/p>\n
The patterns of turnover vary significantly across South America.<\/p>\n
Some areas \u2014 particularly in Brazil, where the Lagoa Santa region is one focus of research \u2014 show evidence of continuity between early populations and later ones, with the genetics of ancient individuals from the early Holocene contributing to the ancestry of later populations from the same region.<\/p>\n
Other areas show more evidence of turnover.<\/p>\n
This spatial variability in population continuity has important implications for how Population Y should be interpreted.<\/p>\n
<\/p>\n
If the Population Y signal is concentrated in the areas that show the most continuity with the early settlement \u2014 the areas where the descendants of the earliest South Americans are most clearly represented in later populations \u2014 then the signal’s geographic distribution might reflect the distribution of the earliest settlers rather than the distribution of any later admixture event.<\/p>\n
This interpretation would be consistent with the deep ancestral structure model: the earliest South Americans carried the Population Y-related ancestry because it was part of the deep structure of the founding population, and those populations that maintained the most continuity with the earliest settlers \u2014 those that were replaced or admixed the least over the subsequent millennia \u2014 retained the signal most clearly.<\/p>\n
Testing this interpretation requires detailed mapping of both the Population Y signal and the evidence for population continuity across South America at a resolution that the current dataset does not fully provide.<\/p>\n
The expanding collection of ancient South American genomes is gradually providing that resolution, but the coverage is still uneven, with some regions much better represented than others.<\/p>\n
<\/p>\n
The Ethical Dimensions of Ancient DNA Research in Indigenous Communities<\/p>\n
Any serious discussion of the ancient DNA research related to Population Y must engage with the ethical dimensions of that research \u2014 the specific ethical challenges of studying the genetic material of Indigenous people’s ancestors, and the evolving frameworks for how such research should be conducted.<\/p>\n
The Native American Graves Protection and Repatriation Act (NAGPRA) in the United States provides a legal framework for the treatment of Native American human remains and associated cultural items in federal collections and on federal lands.<\/p>\n
Similar legal frameworks exist in other countries, though their specific provisions differ.<\/p>\n
<\/p>\n
But the legal frameworks are minimum standards, not ideal ones, and the ethical questions surrounding ancient DNA research on Indigenous ancestors go beyond what any current law requires.<\/p>\n
The fundamental ethical challenge is this: the people whose ancestors’ remains are being studied \u2014 Indigenous communities in Brazil, in other South American countries, in North America, and elsewhere \u2014 have specific interests in how those ancestors are treated, how the research is conducted, how the findings are reported and used, and what happens to the genetic data that is generated.<\/p>\n
Those interests deserve respect, and the scientific community has not always provided that respect.<\/p>\n
Early ancient DNA research in the Americas sometimes proceeded without meaningful consultation with or consent from the Indigenous communities most directly connected to the individuals being studied.<\/p>\n
<\/p>\n
The Kennewick Man case in the United States \u2014 which involved years of legal dispute between Native American nations who claimed the ancient individual as an ancestor deserving repatriation and scientists who wanted to study the remains \u2014 was the most public example of this tension, but it was far from the only one.<\/p>\n
In Brazil, the situation is complicated by the specific legal and political frameworks governing Indigenous rights and by the history of relationships between Brazilian scientific institutions and Indigenous communities.<\/p>\n
The Lagoa Santa skeletal material was collected largely in the nineteenth and early twentieth centuries, before any of the current ethical frameworks existed, and much of it has been housed in Brazilian museum collections for decades.<\/p>\n
The question of how contemporary Indigenous communities relate to this ancient material \u2014 whether they regard the Lagoa Santa people as their ancestors, whether they have standing to make claims about how the material is treated \u2014 is not straightforward and has been handled differently by different researchers.<\/p>\n
<\/p>\n
The evolution of ethical standards in ancient DNA research has accelerated in recent years, driven in part by advocacy from Indigenous communities and in part by the development of explicit ethical guidelines by professional associations and research institutions.<\/p>\n
The CARE Principles for Indigenous Data Governance \u2014 which stand for Collective Benefit, Authority to Control, Responsibility, and Ethics \u2014 provide a framework for thinking about how research involving Indigenous data, including ancient DNA, should center Indigenous community interests rather than treating research access as a default entitlement.<\/p>\n
Researchers working with the Lagoa Santa material have engaged with these ethical questions to varying degrees.<\/p>\n
Some studies have been conducted with explicit attention to community relationships and with efforts to engage relevant Brazilian Indigenous communities in the research.<\/p>\n
<\/p>\n
Others have proceeded with less engagement.<\/p>\n
The field is still developing the norms for what constitutes ethically adequate research in this context, and those norms are likely to continue to evolve as Indigenous communities become more effectively organized to advocate for their interests in how their ancestral heritage is studied.<\/p>\n
The specific question of how the Population Y findings should be communicated to Indigenous communities \u2014 particularly to communities in South America whose ancestors may be the subject of the research \u2014 is one that researchers have addressed imperfectly.<\/p>\n
Findings that are potentially misrepresented in headlines as suggesting that South American Indigenous people’s ancestors were Australians or that the Native American identity of early South Americans is in question can cause real harm to communities that are already navigating complex relationships with both the scientific establishment and with political systems that have historically used uncertainty about Indigenous ancestry to undermine land rights and cultural claims.<\/p>\n
<\/p>\n
Responsible communication of the Population Y findings \u2014 clearly distinguishing what the signal means from what it does not mean, explicitly affirming the Native American identity of the ancient and modern peoples involved, and engaging with Indigenous communities in the process of conducting and communicating the research \u2014 is not merely a courtesy.<\/p>\n
It is an ethical obligation that comes with the privilege of studying ancient human genetic material.<\/p>\n
What the Signal Might Tell Us About Deep Asian Prehistory<\/p>\n
One of the most intellectually productive consequences of the Population Y finding is the way it has directed scientific attention to the deep population history of Asia \u2014 to the period, tens of thousands of years before anyone reached the Americas, when the ancestral populations of both Native Americans and Australasians were living in the same broad geographic area of northeastern and southeastern Asia.<\/p>\n
The genomic evidence from ancient Asian populations is considerably less complete than the evidence from ancient European populations \u2014 a reflection of the differential effort that has been devoted to ancient DNA research in different geographic regions, and of the variable preservation conditions across different parts of Asia.<\/p>\n
<\/p>\n
But what is available provides important context for the Population Y debate.<\/p>\n
Ancient genomes from Siberia dating to the period relevant to American settlement \u2014 roughly 20,000 to 40,000 years before present \u2014 show a complex genetic landscape.<\/p>\n
Different ancient Siberian individuals show different combinations of ancestral components, including components related to East Asian populations, components related to western Eurasian populations (sometimes called “Ancient North Eurasian” ancestry), and in some cases components that are more distantly related to the populations that eventually moved south toward Australia and Melanesia.<\/p>\n
This ancient Siberian diversity is relevant to Population Y because the ancestral Native American population is thought to have formed in the Beringian region from a mixture of different Asian source populations \u2014 and if those source populations included groups with more “Australasian-related” ancestry from the deep past, then the founding Native American population would have contained some proportion of that ancestry.<\/p>\n
<\/p>\n
If that ancestry was not uniformly distributed within the founding population \u2014 if some lineages had more and some had less \u2014 then the differential distribution of those lineages across descendant populations could produce the population Y signal.<\/p>\n
This model does not require Australasians to have traveled to Asia and mixed with the founding Native American population at the time of American settlement.<\/p>\n
It requires only that the ancient Asian populations that contributed to the founding Native American population included groups that had retained more “Australasian-related” ancestry from the deep human past \u2014 ancestry that was part of the shared human heritage of the populations that spread out of Africa along the southern route tens of thousands of years before the Americas were settled.<\/p>\n
This deep ancestry model is perhaps the most parsimonious explanation of the Population Y signal available \u2014 it requires fewer specific historical events than models that involve separate migrations, and it is consistent with the overall picture of human population history that the genomic evidence from Asia, the Americas, and Australasia has produced.<\/p>\n
<\/p>\n
But it is also the model that is most difficult to test directly, because it requires characterizing the genetic diversity of ancient Beringian and northeastern Asian populations at a time period and geographic scale for which the ancient DNA evidence is sparse.<\/p>\n
The Turnover Question Revisited at Continental Scale<\/p>\n
The genomic picture of the Americas is, at continental scale, one of remarkable complexity.<\/p>\n
The earliest Native Americans \u2014 the descendants of the founding Beringian population \u2014 spread across two continents in a geologically brief period.<\/p>\n
As they spread, they differentiated genetically, adapting to different environments, experiencing different local population histories, and establishing the diverse genetic profiles that characterize Native American populations today.<\/p>\n
Overlaid on this initial differentiation is a complex history of subsequent contact, admixture, and in some cases dramatic population change.<\/p>\n
<\/p>\n
The late Holocene \u2014 the last several thousand years \u2014 saw significant population movements across the Americas, driven by climate change, agricultural expansion, political and military competition, and other factors.<\/p>\n
Some of these movements resulted in substantial genetic exchange between previously distinct populations; others resulted in the partial or complete replacement of one population by another.<\/p>\n
Understanding the Population Y signal in this context requires distinguishing between ancestry components that reflect the original settlement history of the Americas \u2014 including whatever deep ancestral structure the founding population may have contained \u2014 and ancestry components that reflect subsequent population dynamics.<\/p>\n
This is not always easy to do with the available data.<\/p>\n
<\/p>\n
The increasing density of ancient genome data from across the Americas is helping to clarify this picture.<\/p>\n
By comparing ancient genomes from different time periods in the same geographic area, researchers can track the specific timing of population changes and can distinguish between changes that occurred before and after the periods when the Population Y signal first appears in the record.<\/p>\n
One of the most important findings of this kind of temporal analysis is that the Population Y signal, where it is found in ancient specimens, appears to be present in the earliest individuals from certain regions rather than appearing later in the record as a new introduction would be expected to do.<\/p>\n
This is consistent with the deep ancestral structure model \u2014 the signal was there from the beginning because it was part of the ancestry of the founding population \u2014 and less consistent with models that require a separate, later migration to introduce the Australasian-related ancestry.<\/p>\n
<\/p>\n
But this finding is based on a limited number of ancient specimens from the relevant regions, and the temporal resolution of the data is still insufficient to be definitive.<\/p>\n
The question of when the Population Y signal first appears in the ancient South American record, and whether that timing is consistent with the founding settlement or with a later introduction, remains open.<\/p>\n
The Question “Who Got Here First?” and Why It Is Often Wrong<\/p>\n
The Population Y debate has sometimes been framed as a question of “who got here first” \u2014 as if the finding of Australasian-related ancestry in some South American populations implies that there was a race to the Americas, with one founding group arriving before the main Native American founding population.<\/p>\n
This framing is wrong in multiple ways, and understanding why it is wrong reveals something important about how population history actually works.<\/p>\n
<\/p>\n
First, the “who got here first” framing presupposes that the Americas were populated by two distinct, competing groups \u2014 Group A and Group B \u2014 and that determining which group arrived first determines something important about the historical priority or legitimacy of the resulting populations.<\/p>\n
This is not how human population history works.<\/p>\n
Populations are not discrete entities that move through space as coherent units; they are dynamic collections of individuals who reproduce, interact, mix, and disperse in complex ways.<\/p>\n
The question of whether “Population Y” arrived before or after the “main” Native American founding population is, in an important sense, a category error \u2014 it treats populations as if they were ships in a race rather than as what they actually were: people.<\/p>\n
Second, the “who got here first” framing implies that arriving first confers some kind of historical priority or special status on the resulting population.<\/p>\n
<\/p>\n
This implication has sometimes been used in politically motivated arguments about Indigenous land rights \u2014 the suggestion that if the “first Americans” were replaced by a different group before European contact, then the land rights of contemporary Native Americans are somehow less firmly grounded.<\/p>\n
This implication is both historically wrong and ethically incoherent.<\/p>\n
The historical relationships between contemporary Indigenous peoples and the specific ancient peoples whose DNA is being studied are complex and cannot be simply read off from genetic signals, and the rights of contemporary Indigenous peoples do not depend on proving that no group preceded them.<\/p>\n
Third, the “who got here first” framing misses what is scientifically most interesting about the Population Y signal.<\/p>\n
The most interesting question is not which of two competing groups arrived first but rather what the deep structure of the ancestral population was \u2014 what the internal diversity of the founding Native American population looked like before and during the American settlement, and how that internal diversity was distributed across the continent as the settlement proceeded.<\/p>\n
<\/p>\n
This is a question about human population genetics and human prehistory that has implications well beyond the Americas, because it touches on the deep history of how different human populations diverged from each other in Asia and how those divergence patterns were subsequently shuffled as populations moved and mixed.<\/p>\n
What Is Not Known and Why It Matters<\/p>\n
The honest summary of where the Population Y debate stands is that the signal is real, its explanation is not definitively known, and the resolution of the debate will require data and methods that are not yet available.<\/p>\n
What is known: Some ancient and modern South American populations show statistically significant excess allele sharing with Australasian populations.<\/p>\n
The signal is strongest in certain parts of South America and weaker or undetectable in others.<\/p>\n
<\/p>\n
The ancient people of Lagoa Santa were genetically Native American, not Australasian.<\/p>\n
The signal does not represent a dominant component of the ancestry of the populations in which it is found.<\/p>\n
Multiple plausible models have been proposed to explain the signal, none of which has been definitively confirmed or refuted.<\/p>\n
What is not known: Whether the signal reflects a separate migration event or deep ancestral structure in the founding Native American population.<\/p>\n
The specific timing of when the Australasian-related ancestry diverged from other Asian populations.<\/p>\n
<\/p>\n
The specific route \u2014 if any separate migration occurred \u2014 by which Australasian-related ancestry reached South America.<\/p>\n
Why the signal is found in some South American populations and not others.<\/p>\n
How much of the geographic variability in the signal reflects the original settlement history versus subsequent population dynamics.<\/p>\n
Why it matters: The Population Y story is not merely an academic puzzle about ancient DNA statistics.<\/p>\n
It touches on fundamental questions about the deep history of human populations \u2014 about how humanity spread across the planet, about the ancestral structure of the populations that gave rise to the diverse array of human groups alive today, and about the specific history of how the Americas came to be inhabited.<\/p>\n
Getting the story right \u2014 including being honest about what is and is not known \u2014 is important both for the scientific record and for the communities whose ancestors’ DNA is being studied.<\/p>\n
<\/p>\n
The People Beneath the Signal<\/p>\n
At the end of the statistical analyses and the competing models and the methodological debates, it is important to return to what the Lagoa Santa material actually represents: the remains of human beings who lived, loved, worked, and died in the cerrado landscape of central Brazil more than ten thousand years ago.<\/p>\n
These ancient people painted on the walls of rock shelters.<\/p>\n
They processed plant foods and hunted game.<\/p>\n
<\/p>\n
They buried their dead with care.<\/p>\n
They built the kinds of social relationships and cultural practices that make human communities possible.<\/p>\n
They were, in every meaningful sense, fully human \u2014 not primitive precursors to “real” civilization but people whose cognitive and social capacities were identical to those of any human alive today.<\/p>\n
The scientific debates about Population Y and ancient migration routes are conducted using the biological traces those people left behind \u2014 their DNA, their bones, their teeth.<\/p>\n
The debates can sometimes make it easy to lose sight of the people themselves, to treat the ancient individuals as data points rather than as human beings with their own histories and their own descendants.<\/p>\n
<\/p>\n
The descendants of the ancient people of Lagoa Santa are alive today.<\/p>\n
They are the Indigenous communities of Brazil \u2014 Tup\u00ed, Macro-J\u00ea, and others \u2014 whose historical and cultural connections to the region go back across the millennia that the ancient DNA research is attempting to characterize.<\/p>\n
Those communities have interests in how their ancestors are studied, how the findings are communicated, and how the science is used \u2014 or misused \u2014 in public discourse about Indigenous identity and rights.<\/p>\n
The scientific community’s obligation to those communities goes beyond merely avoiding the most egregious misrepresentations.<\/p>\n
<\/p>\n
It includes actively working to ensure that the research is conducted with genuine engagement with Indigenous perspectives, that the findings are communicated in ways that are accurate and respectful, and that the genomic data generated from ancient Indigenous individuals is governed in ways that serve Indigenous community interests rather than being treated as a resource for scientific extraction.<\/p>\n
The Population Y debate is, among other things, a test of whether the scientific community has learned from the ethical failures of the past \u2014 from the Kennewick Man dispute, from the long history of museum collections built without Indigenous consent, from the racial science that misused cranial morphology data in the service of colonial ideology.<\/p>\n
The evidence for such learning is mixed.<\/p>\n
There are researchers working in this area who take the ethical dimensions seriously and who engage with Indigenous communities genuinely.<\/p>\n
<\/p>\n
There are others for whom the ethical obligations seem secondary to the scientific questions.<\/p>\n
Getting this right requires sustained effort and genuine humility \u2014 the recognition that scientific knowledge, however valuable, is not the only form of knowledge that matters, and that the communities most directly connected to the people being studied have standing that no scientific finding can override.<\/p>\n
The Signal’s Deeper Meaning<\/p>\n
What the Population Y signal ultimately tells us \u2014 whatever its specific explanation turns out to be \u2014 is that the human past was more complex than simple narratives allow.<\/p>\n
The first Americans did not emerge from a single, undifferentiated founding population that swept across the continents without internal structure or subsequent diversification.<\/p>\n
<\/p>\n
The founding population itself contained diversity that reflected the complex history of human populations in Asia over tens of thousands of years.<\/p>\n
The dispersal across the Americas was a complex, multi-stage process that produced genetic patterns whose full implications are still being worked out.<\/p>\n
This complexity is not a puzzle to be anxious about.<\/p>\n
It is a reflection of the genuine richness of human history \u2014 of the reality that human populations have always been moving, mixing, diverging, and reconnecting in ways that resist simple categorization.<\/p>\n
The genomic revolution in human prehistory research has made it possible to see this complexity in unprecedented detail, and what it is revealing is a past that is more dynamic, more interconnected, and more interesting than any simple model would have predicted.<\/p>\n
<\/p>\n
For the ancient people of Lagoa Santa, the Population Y debate is a footnote to a much larger story.<\/p>\n
They were people who lived successfully in a challenging environment for thousands of years, who developed rich cultural traditions that are partially visible in the archaeological record, and whose descendants continue to live in the Americas today.<\/p>\n
The statistical signal in their DNA is one small piece of evidence about their origins \u2014 evidence that points to the complexity of the ancestral populations from which they descended, and that connects them, across the vast distances of the deep human past, to people on the other side of the planet who shared ancient ancestors with them.<\/p>\n
That connection is real, in the sense that the genetic signal reflects genuine shared ancestry from the deep past.<\/p>\n
<\/p>\n
It is also, in the context of the actual history of the Americas and the actual identities and rights of contemporary Indigenous peoples, a connection that needs to be understood at the appropriate level of abstraction.<\/p>\n
The ancient people of Lagoa Santa were Native Americans.<\/p>\n
Their descendants are Native Americans.<\/p>\n
The Population Y signal tells us something about the deep structure of the populations from which those Native Americans descended \u2014 it does not change who they are.<\/p>\n
Why Simple Origin Stories Fail<\/p>\n
The history of attempts to tell the story of the first Americans is, in many ways, a history of the failure of simple stories.<\/p>\n
The Mound Builder Myth was a simple story \u2014 a mysterious, superior race had built the earthen monuments of the Mississippi Valley and had then vanished, leaving no descendants among the Native Americans who followed.<\/p>\n
<\/p>\n
It was wrong.<\/p>\n
The Solutrean hypothesis was a simple story \u2014 Ice Age Europeans had crossed the Atlantic and been the first Americans.<\/p>\n
It was not supported by the evidence.<\/p>\n
The two-population model was a simple story \u2014 two distinct groups, with different morphological profiles, had settled the Americas in sequence.<\/p>\n
The ancient DNA evidence showed it was more complicated than that.<\/p>\n
Population Y is, in its way, a warning against simple stories about complex processes.<\/p>\n
The ancestral history of any human population is never a straight line from a single point of origin to the present.<\/p>\n
<\/p>\n
It is a branching, converging, diverging network of ancestral relationships that reflects millions of individual decisions about where to live, whom to reproduce with, and how to respond to the environmental, social, and historical pressures of each successive generation.<\/p>\n
The genomic tools now available to researchers can, for the first time, begin to reveal some of the structure of that network in the deep human past.<\/p>\n
What those tools are revealing is not simplicity but complexity \u2014 not a single clean origin story but a many-stranded web of ancestral connections that links the people of Lagoa Santa to people in Asia, to people in Australia and New Guinea, and ultimately to all of humanity.<\/p>\n
That is, in the end, the most important thing the Population Y signal tells us.<\/p>\n
<\/p>\n
Not that Australians were among the first Americans.<\/p>\n
Not that the Native American ancestry of South American peoples is somehow qualified or uncertain.<\/p>\n
But that human beings have always been more connected to each other, across more distances and more time, than any simple story of separate origins can capture.<\/p>\n
The ancient people who painted the rock shelters of Lagoa Santa, who buried their dead in the caves of the cerrado, who left behind a genetic signal that researchers would spend decades trying to interpret \u2014 those people were part of a human story that is bigger than any single continent’s history.<\/p>\n
The signal in their DNA is a thread that, if pulled carefully, leads not to a simple answer about where they came from but to a deeper understanding of what it means to be human \u2014 to be part of a species that has spent its entire history moving, mixing, and connecting across the surface of a planet that is smaller than any simple origin story makes it seem.<\/p>\n
<\/p>\n
The caves of Lagoa Santa are still there.<\/p>\n
The bones of the ancient people are still there, in museums and in the soil.<\/p>\n
The signal is still there, in the genomes of their descendants and in the sequencing data of the ancient specimens.<\/p>\n
And the question \u2014 what does it mean? \u2014 is still being asked, by researchers with increasingly powerful tools and increasingly careful methods, toward an answer that is not yet complete.<\/p>\n
That incompleteness is not a failure.<\/p>\n
<\/p>\n
It is where the story actually is.<\/p>\n
And the story, as with all the best stories, turns out to be bigger and more interesting than anyone expected.<\/p>\n
\u2014 END \u2014<\/p>\n
\u2014 EXTENDED SECTIONS \u2014<\/p>\n
Peter Wilhelm Lund and the Discovery That Would Not Stay Simple<\/p>\n
Peter Wilhelm Lund arrived in Brazil in 1833 as a young Danish naturalist with a broad scientific curiosity and no particular expectation of making a discovery that would occupy scientific debate for the next two centuries.<\/p>\n
He had come to study the natural history of the country \u2014 its plants, its animals, the geological record of its past.<\/p>\n
<\/p>\n
What he found in the limestone caves of the Lagoa Santa region was something that natural history alone could not adequately explain: the bones of animals that were extinct, mixed with the bones of people who appeared to have lived alongside them.<\/p>\n
Lund’s excavations in the caves of Lagoa Santa between 1835 and 1844 produced a collection of skeletal material that was, for the mid-nineteenth century, remarkable in its scope and its implications.<\/p>\n
He found hundreds of animal specimens representing dozens of species, many of them belonging to the extinct megafauna of the Pleistocene \u2014 the giant ground sloths, the glyptodonts, the horses, the mastodons that had vanished from the Americas at the end of the last Ice Age.<\/p>\n
He also found human bones.<\/p>\n
<\/p>\n
And the human bones appeared to be associated with the extinct animal bones in ways that suggested contemporaneity \u2014 that the people had lived at the same time as the animals, during or at the end of the Pleistocene.<\/p>\n
The implications were, by the scientific standards of the time, extraordinary.<\/p>\n
The prevailing understanding of human prehistory in the mid-nineteenth century was shaped by biblical chronology, which placed the creation of humanity only a few thousand years before the present.<\/p>\n
Lund’s finds \u2014 human remains associated with Ice Age animals \u2014 implied a much greater antiquity for human presence in the Americas than most scientists of the period were prepared to accept.<\/p>\n
Lund himself was cautious about the implications of his finds.<\/p>\n
<\/p>\n
He was aware that the association between human and animal bones in a cave context did not necessarily prove contemporaneity \u2014 bones from different time periods can become mixed in caves through the action of water, animals, or subsequent human disturbance.<\/p>\n
He reported his findings carefully, noting the associations and the questions they raised without overstating what he could actually prove.<\/p>\n
The subsequent history of the interpretation of Lund’s finds was considerably less cautious.<\/p>\n
The Lagoa Santa skeletal material became a focus of debate about human antiquity, about the morphological characteristics of ancient Americans, and about the relationship between the ancient people of Lagoa Santa and the living Indigenous populations of Brazil.<\/p>\n
That debate involved some of the leading physical anthropologists of the nineteenth and early twentieth centuries, and its conclusions were sometimes shaped as much by the racial assumptions of the era as by the actual evidence.<\/p>\n
<\/p>\n
What Lund could not have imagined \u2014 what no one in 1844 could have imagined \u2014 was that nearly 180 years after his excavations, researchers would be extracting DNA from the bones he had found, comparing that DNA to genomes from populations on the other side of the planet, and finding a faint but persistent signal that would require a fundamental reconsideration of the models used to explain how the Americas had been peopled.<\/p>\n
Lund’s discovery set in motion a chain of scientific inquiry that has still not reached its endpoint.<\/p>\n
The caves of Lagoa Santa are still being studied.<\/p>\n
New specimens are still being found.<\/p>\n
New techniques are still being applied to old collections.<\/p>\n
And the questions that Lund’s finds first raised \u2014 about the identity and antiquity of the first South Americans, about the relationship between ancient and modern populations, about the deep history of human migration across the Americas \u2014 are still being answered, incompletely and imperfectly, by researchers working with tools that Lund could not have conceived.<\/p>\n
The Archaeological Record Beyond the Bones<\/p>\n
<\/p>\n
The skeletal material from Lagoa Santa is the most discussed aspect of the region’s early archaeological record, but it is not the only evidence for the lives of the ancient people who lived there.<\/p>\n
Understanding the archaeological context of the skeletal material \u2014 the material culture, the environmental data, the evidence of daily life \u2014 is essential for placing the genetic findings in their proper human context.<\/p>\n
The stone tool assemblages from Lagoa Santa and related sites in the region show a distinctive technological tradition that archaeologists have characterized in various ways over the years.<\/p>\n
The tools include scrapers, burins, points, and other implements made from locally available stone, worked using techniques that reflect substantial skill and accumulated knowledge of the material’s properties.<\/p>\n
The specific types of tools and the specific techniques used to make them vary across the region and across time, reflecting the kind of gradual technological change that characterizes the archaeological record of a long-occupied region.<\/p>\n
<\/p>\n
The lithic technology of Lagoa Santa is distinctive in ways that have led some researchers to characterize it as representing a tradition different from the fluted-point technologies found in parts of North America and associated with what are sometimes called “Clovis” or related early American cultures.<\/p>\n
Whether this represents a genuinely different technological tradition, a local adaptation of a shared broader tradition, or simply variation within a single tradition is a question that continues to generate archaeological debate.<\/p>\n
What is not debated is that the people of Lagoa Santa were effective stone workers who produced the tools they needed for their way of life.<\/p>\n
The variety of tool types found at sites in the region \u2014 tools suited for cutting, scraping, drilling, and hunting \u2014 reflects a broad subsistence strategy that included both hunting and plant processing.<\/p>\n
The faunal remains at the sites are consistent with hunting of deer, armadillos, peccaries, and other animals, while botanical remains and the specific tool types associated with plant processing suggest that plant foods \u2014 roots, seeds, fruits \u2014 were also important parts of the diet.<\/p>\n
<\/p>\n
The environment that the ancient Lagoa Santa people inhabited was, in the early Holocene, broadly similar to the present-day cerrado \u2014 the Brazilian savanna \u2014 but with some significant differences related to the different climate conditions of the period.<\/p>\n
The early Holocene in central Brazil was characterized by a climate that was, in some periods, somewhat drier than today, with the consequence that the distribution of vegetation types was different from the present.<\/p>\n
The rock shelters and cave environments that the ancient people used for habitation and for burial provided protection from the elements and may have been important for the preservation of food and the conduct of ceremony.<\/p>\n
The rock art of the Lagoa Santa region is one of the most visually striking elements of the archaeological record and one of the aspects most difficult to interpret with precision.<\/p>\n
<\/p>\n
The paintings \u2014 made with red pigment, predominantly iron oxide \u2014 appear on the walls and ceilings of rock shelters and caves, representing human figures, animals, geometric forms, and complex scenes whose narrative or symbolic content is not fully understood.<\/p>\n
Some of the images appear to depict hunting scenes or other activities.<\/p>\n
Some appear to represent figures in ritual or ceremonial contexts.<\/p>\n
Some are abstract geometric forms with no obvious representational content.<\/p>\n
The chronology of the rock art is difficult to establish precisely \u2014 pigment is difficult to date directly, and the images cannot always be linked to datable archaeological contexts.<\/p>\n
Some of the paintings in the Lagoa Santa region may be as old as the skeletal material; others may be significantly more recent.<\/p>\n
<\/p>\n
The full temporal span of the art tradition is not known.<\/p>\n
What the rock art makes clear is that the ancient people of Lagoa Santa had a rich symbolic life \u2014 that they used visual representation as a way of recording and communicating aspects of their experience, their beliefs, or their social relationships.<\/p>\n
This symbolic capacity is not surprising \u2014 it is a characteristic of modern human beings everywhere \u2014 but its visible presence in the Lagoa Santa record is a reminder that the people being discussed in the context of the Population Y debate were not simply biological specimens but full human beings with cultural lives of genuine complexity.<\/p>\n
The Lapa do Santo Site and What It Tells Us<\/p>\n
<\/p>\n
Among the many archaeological sites in the Lagoa Santa region, Lapa do Santo has emerged in recent decades as one of the most scientifically significant, contributing evidence on multiple fronts that has helped clarify the picture of early human life in the region and has provided some of the key ancient genome data relevant to the Population Y debate.<\/p>\n
Lapa do Santo is a large rock shelter in the limestone karst landscape of Lagoa Santa, excavated systematically by a team led by Andr\u00e9 Strauss and other researchers from the University of S\u00e3o Paulo and international partner institutions.<\/p>\n
The excavations have been notable for their methodological rigor \u2014 the use of detailed spatial recording, systematic sampling for biological and environmental evidence, and careful radiocarbon dating of the relevant layers \u2014 and for the extraordinary quality of the material they have recovered.<\/p>\n
The site has produced evidence of human occupation spanning thousands of years, with the earliest well-dated occupation beginning around 12,000 years ago.<\/p>\n
<\/p>\n
The archaeological sequence at the site shows gradual changes in material culture and subsistence practices over this long period of occupation, with the early Holocene layers containing the skeletal material most directly relevant to the Population Y debate.<\/p>\n
One of the most remarkable finds from Lapa do Santo is evidence of a burial practice that is unique in the early archaeological record of the Americas: what has been described as a “decapitated and amputated” burial, in which a human skull was buried separately from the body, with the hands positioned around the skull.<\/p>\n
This complex burial practice implies a specific set of mortuary rituals and beliefs about the treatment of the dead that goes well beyond simple interment of the deceased.<\/p>\n
It is evidence of a culture with sophisticated symbolic and ritual practices \u2014 practices that required specific knowledge, specific materials, and specific organizational capacity to carry out.<\/p>\n
<\/p>\n
The ancient genomes from Lapa do Santo that have been analyzed in the context of the Population Y research were drawn from this well-documented archaeological context \u2014 individuals whose burial practices are known, whose dating is established by multiple radiocarbon measurements, and whose relationship to each other and to the archaeological layers they come from is carefully documented.<\/p>\n
This contextual richness makes the Lapa do Santo ancient genomes particularly valuable data points for the Population Y debate, because the genetic findings can be related to a specific archaeological context rather than floating free of any interpretation.<\/p>\n
The results from the Lapa do Santo ancient genomes \u2014 Native American ancestry, complex signals when analyzed for Population Y, evidence of continuity with later populations in the region \u2014 are discussed in detail elsewhere in this article.<\/p>\n
The point here is that those results come from a specific, well-documented human context that gives them meaning beyond the statistics.<\/p>\n
<\/p>\n
These were real people, living in a specific place at a specific time, doing specific things that left traces in the archaeological record.<\/p>\n
The DNA is one more trace \u2014 a particularly informative one \u2014 but it is not the whole story.<\/p>\n
The Morphological Question in Detail<\/p>\n
The debate about the morphological characteristics of the Lagoa Santa skulls and what those characteristics mean for the interpretation of early American settlement requires somewhat more technical detail than has been provided so far, because the technical details matter for understanding why the debate was as contentious and as long-lived as it was.<\/p>\n
Cranial morphology \u2014 the shape of the skull \u2014 is described and quantified using a set of measurements and ratios that capture different aspects of skull form.<\/p>\n
<\/p>\n
The most commonly used approach in studies of ancient Americans is a multivariate statistical analysis that places each skull within a mathematical space defined by multiple measurements simultaneously, and then identifies which other populations’ skulls occupy the nearest position in that mathematical space.<\/p>\n
When this kind of analysis is applied to the Lagoa Santa skulls, the result is consistently that the Lagoa Santa skulls are more similar, in this multivariate morphological space, to skulls from sub-Saharan Africa, Australia, and Melanesia than to skulls from East Asia or from later Native American populations.<\/p>\n
This finding has been replicated by multiple research teams using different skull samples and different measurement protocols, which gives it reasonable robustness as a morphological finding.<\/p>\n
The controversy is not about whether the morphological finding is real \u2014 it is \u2014 but about what it means.<\/p>\n
<\/p>\n
The key issue is that cranial morphology reflects both genetic influences and non-genetic influences, including developmental plasticity (the ability of the skull to change its shape in response to different developmental environments), dietary factors (certain diets produce different amounts of mechanical stress on the jaw and face, which can influence overall skull shape), and natural selection (different environments may favor different skull shapes, leading to convergent evolution of similar skull forms in unrelated populations).<\/p>\n
The populations from sub-Saharan Africa, Australia, and Melanesia that the Lagoa Santa skulls resemble morphologically are populations that are understood, on genetic grounds, to have diverged from the ancestral human population that eventually gave rise to all modern humans and then to have experienced somewhat less subsequent genetic mixing with other populations than some other human groups.<\/p>\n
This population history has left some populations with certain cranial characteristics that are, in a statistical sense, more similar to the characteristics of early modern humans than the characteristics of populations that have experienced more subsequent mixing and selection.<\/p>\n
If the Lagoa Santa population shared this ancestry \u2014 if the founding Native American population contained lineages that were more closely related to these early-diverging populations, as the Population Y hypothesis suggests \u2014 then the morphological similarity between Lagoa Santa skulls and Australian and African skulls might reflect a genuine ancestral connection.<\/p>\n
<\/p>\n
The population Y signal in the DNA could, in this interpretation, be related to the same ancestral diversity that produces the morphological similarity.<\/p>\n
This interpretation is not established fact; it is a plausible connection between two different lines of evidence.<\/p>\n
The morphological similarity between Lagoa Santa skulls and Australian and African skulls has been documented for a long time.<\/p>\n
The Population Y signal in Lagoa Santa-related genomes has been documented more recently.<\/p>\n
Whether these two observations reflect the same underlying cause \u2014 some form of shared deep ancestry \u2014 or whether they are coincidentally related is a question that the current evidence cannot definitively answer.<\/p>\n
What the juxtaposition of the morphological and genetic evidence does suggest is that the Lagoa Santa population was, in some sense, genetically distinctive in ways that had morphological consequences \u2014 that the founding Native American population was not perfectly genetically uniform, and that different founding lineages may have had different morphological characteristics as well as different specific genetic profiles.<\/p>\n
<\/p>\n
This picture of a structured founding population is consistent with the deep ancestral structure explanation of Population Y.<\/p>\n
The Beringian Standstill and What It Created<\/p>\n
One of the most important developments in the scientific understanding of early American settlement over the past twenty years is the accumulation of evidence for what has been called the “Beringian standstill” \u2014 a period during which the ancestral Native American population was isolated in the Beringia region, neither moving back into Asia nor yet moving into the Americas, for a period of time that may have lasted several thousand years.<\/p>\n
The evidence for this standstill comes from multiple sources.<\/p>\n
<\/p>\n
Genetic analysis of Native American populations suggests that the founding population was isolated from other Asian populations for a period before the dispersal into the Americas \u2014 a period of isolation long enough to allow the founding population to accumulate genetic variants that are distinct from the source populations in Asia.<\/p>\n
Modeling of the genetic data suggests an isolation period of roughly 2,000 to 9,000 years, though the uncertainty in these estimates is large.<\/p>\n
The geographic context of this isolation was Beringia \u2014 the landmass that connected northeastern Asia to northwestern North America when sea levels were lower during the Last Glacial Maximum.<\/p>\n
Beringia was not the frozen wasteland that the name might suggest; during the Last Glacial Maximum, it was a landscape of shrub tundra and grassland, with a more temperate climate than the areas immediately to its south and east where the great ice sheets covered much of North America.<\/p>\n
The Beringian environment could have supported a human population, and the evidence suggests that it did.<\/p>\n
<\/p>\n
During the Beringian standstill, the ancestral Native American population would have been evolving in relative isolation from the other Asian populations from which it had derived.<\/p>\n
The specific genetic diversity of the founding population \u2014 including whatever ancestral structure related to Population Y it may have contained \u2014 would have been the product of this isolated period of evolution, plus the specific admixture history that preceded the formation of the Beringian population.<\/p>\n
The timing and nature of the Beringian standstill has implications for how Population Y should be interpreted.<\/p>\n
If the standstill was long enough for significant internal differentiation to occur within the isolated founding population \u2014 for distinct subgroups or lineages to form with somewhat different genetic profiles \u2014 then the differential distribution of those lineages across the Americas could produce patterns of allele sharing that look like separate migrations when analyzed with certain statistical tools.<\/p>\n
<\/p>\n
The Beringian standstill model, combined with the deep ancestral structure explanation of Population Y, suggests a specific picture of the founding of the Americas: a genetically diverse founding population, formed in Beringia from the coming together of multiple Asian source populations with different ancestry proportions, isolated long enough to develop additional internal diversity, and then dispersing into the Americas in ways that distributed different founding lineages differently across the continent.<\/p>\n
This is not a simple story.<\/p>\n
It is also not an implausible one, and the available genetic evidence is broadly consistent with it.<\/p>\n
The challenge is that it requires data from Beringian ancient genomes \u2014 data that, for geographic and preservation reasons, is very difficult to obtain \u2014 to test directly.<\/p>\n
The Role of the Amazon Basin<\/p>\n
The Amazon Basin is one of the regions where the Population Y signal has been found with some consistency in genetic studies of living Indigenous populations, and the specific demographic and ecological history of Amazonian populations is relevant to understanding why this might be.<\/p>\n
The Amazon Basin contains one of the highest densities of Indigenous linguistic and cultural diversity in the world \u2014 hundreds of distinct languages representing multiple unrelated language families, associated with communities that have maintained distinct identities and distinct subsistence practices for thousands of years.<\/p>\n
<\/p>\n
This linguistic and cultural diversity is itself evidence of a long and complex history of human occupation and differentiation in the region.<\/p>\n
The genetic diversity of Amazonian Indigenous populations is correspondingly complex.<\/p>\n
Studies of Amazonian genomes have found evidence of multiple distinct genetic lineages within the region, reflecting a population history that includes early settlement from multiple directions, subsequent isolation of different communities in different river drainage systems, and patterns of genetic exchange between communities that do not always follow the boundaries of linguistic or cultural affiliation.<\/p>\n
The Population Y signal in Amazonian populations has been found most clearly in certain linguistically and geographically specific groups rather than uniformly across all Amazonian peoples.<\/p>\n
<\/p>\n
This pattern of uneven distribution \u2014 some Amazonian populations carrying the signal and others not \u2014 is consistent with either a model in which a Population Y-related founding group settled some parts of the Amazon basin but not others, or a model in which the founding Beringian population contained structured diversity that was differentially distributed as different founding lineages settled different parts of the continent.<\/p>\n
The specific demographic history of the Amazon basin is relevant to distinguishing between these models.<\/p>\n
If the genetic analysis shows that the Amazonian populations with the strongest Population Y signal are also the populations that show the most evidence of deep genetic ancestry \u2014 the most continuity with early settlement and the least evidence of later genetic mixing from populations without the signal \u2014 then the deep ancestral structure model is supported.<\/p>\n
If the signal appears to have been introduced into some Amazonian populations at a specific time that can be dated genetically, and if that time is consistent with a demographic event in the region’s history, then an admixture model is more plausible.<\/p>\n
<\/p>\n
Researchers have used the available Amazonian genomic data to address these questions, with results that are, as yet, not definitive.<\/p>\n
The data are consistent with multiple models, and additional ancient genomes from the Amazon region \u2014 a region where preservation conditions for ancient DNA are extremely challenging \u2014 would be needed to resolve the question more clearly.<\/p>\n
The Genomic History of South American Diversity<\/p>\n
The full story of how South American Indigenous genetic diversity came to be as it is today is one that researchers are only now beginning to reconstruct with the kind of resolution that the ancient DNA revolution makes possible.<\/p>\n
The picture that is emerging is one of remarkable complexity \u2014 multiple founding lineages, subsequent differentiation, periods of expansion and contraction driven by environmental and demographic factors, and episodes of contact and gene flow between populations that were previously genetically distinct.<\/p>\n
<\/p>\n
The founding of South America appears, on current evidence, to have occurred relatively quickly after the entry into the Americas from Beringia \u2014 with ancestral South American populations diverging from ancestral North American populations at a time that genetic models place somewhere between 16,000 and 20,000 years ago, though the uncertainty in these estimates is substantial.<\/p>\n
The rapid dispersal of people across South America after this founding event is reflected in the genetic record as a pattern of rapid differentiation of regional populations, with different groups in different geographic areas accumulating distinct genetic profiles through the combined effects of local population dynamics and limited gene flow between regions.<\/p>\n
On top of this early differentiation, the genetic record shows evidence of subsequent contact and gene flow \u2014 episodes in which populations that had previously diverged came back into contact and mixed.<\/p>\n
The timing and geographic pattern of these contact episodes is complex and varies across the continent.<\/p>\n
<\/p>\n
In some areas, the genetic record shows evidence of substantial gene flow between neighboring populations over extended periods; in other areas, populations maintained genetic distinctiveness despite geographic proximity, suggesting that geographic barriers or social practices limiting intermarriage maintained the separation.<\/p>\n
The late Holocene \u2014 the last several thousand years \u2014 saw significant changes in South American population history associated with the spread of agriculture, the growth of larger polities, and the demographic changes associated with these developments.<\/p>\n
These changes involved the expansion of some populations at the expense of others, with corresponding genetic consequences.<\/p>\n
The Tup\u00ed-Guaran\u00ed language family, which spread across a large part of lowland South America in the millennia before European contact, is associated in the genetic record with the expansion of populations carrying specific genetic signatures \u2014 an expansion that partially displaced or mixed with earlier populations in the areas it entered.<\/p>\n
Understanding the Population Y signal against this complex backdrop requires distinguishing between a signal that has been present since the initial settlement \u2014 because it was part of the ancestral diversity of the founding population \u2014 and signals introduced later through specific episodes of gene flow or population replacement.<\/p>\n
<\/p>\n
This is a technically challenging but not impossible task with the right data, and researchers are progressively developing both the datasets and the methods needed to address it.<\/p>\n
The Scientific Method as Applied to Uncertainty<\/p>\n
One of the most valuable lessons that the Population Y debate offers \u2014 for people interested not just in the specific science but in how science works \u2014 is a demonstration of how scientific knowledge develops in the face of genuine uncertainty.<\/p>\n
The 2015 paper that named Population Y was not wrong to report what it found.<\/p>\n
The statistical signal it identified was real, and the models it proposed to explain the signal were reasonable responses to the evidence available at the time.<\/p>\n
<\/p>\n
What the paper could not do \u2014 what no paper can do with limited data \u2014 was definitively resolve the question of which model was correct.<\/p>\n
The subsequent work \u2014 the 2018 ancient genome studies, the expanding datasets of the 2020s, the ongoing methodological refinements \u2014 has not dramatically changed the fundamental finding.<\/p>\n
The Population Y signal is still there, in the same general geographic distribution, at roughly the same intensity.<\/p>\n
What has changed is the understanding of what that signal might mean, as additional data has tested and refined the competing models.<\/p>\n
This pattern \u2014 a finding that generates multiple competing models, followed by progressive accumulation of evidence that constrains but does not yet definitively eliminate any of the models \u2014 is typical of how science works when confronting genuinely complex historical questions.<\/p>\n
<\/p>\n
The evidence for deep human prehistory is inherently limited: we cannot run experiments, we cannot observe the past directly, and the available evidence is always incomplete.<\/p>\n
In this context, the goal of research is not to arrive at a single certain answer quickly but to progressively narrow the range of plausible answers by accumulating evidence that eliminates some explanations while remaining consistent with others.<\/p>\n
The Population Y debate is at this progressive-narrowing stage.<\/p>\n
The most extreme interpretations \u2014 that Australians literally sailed to South America, that the first South Americans were not Native Americans \u2014 have been eliminated by the evidence.<\/p>\n
The remaining competing models are all variations on a theme of ancestral complexity within the Native American founding population, differing primarily in the specific mechanism by which that complexity arose and was distributed.<\/p>\n
<\/p>\n
That is genuine scientific progress, even if it does not feel like it from the outside.<\/p>\n
The question has been transformed from “did a completely separate, non-Native American population reach South America?” \u2014 a question the evidence has answered, with a clear no \u2014 to “what specific ancestral structure within the founding Native American population produced the observed pattern of allele sharing?” \u2014 a question that requires more data and more refined methods to answer, and that researchers are actively working to address.<\/p>\n
The Polynesian Question and Why It Is Different<\/p>\n
Because the Population Y discussion involves genetic affinities between South American populations and Pacific populations, it sometimes gets conflated with a related but distinct question: the documented pre-Columbian contact between Polynesian peoples and Native Americans that has been established by genetic evidence from sweet potato dispersal, from chicken bones in archaeological sites, and most recently from genomic analysis of living Native American populations.<\/p>\n
<\/p>\n
The Polynesian contact with Native Americans is a different phenomenon from Population Y, and it is important to keep the two distinct.<\/p>\n
The Polynesian contact \u2014 specifically, contact between Polynesian voyagers and populations on the Pacific coast of South America sometime in the period roughly 700 to 1200 CE \u2014 is documented in the genetic record of both Native American and Polynesian populations.<\/p>\n
Some Polynesian populations carry a small but detectable amount of Native American ancestry, and some South American Indigenous populations carry a small but detectable amount of Polynesian ancestry.<\/p>\n
The timing, the geographic pattern, and the specific nature of the admixture are consistent with contact in the pre-Columbian period, most likely involving Polynesian voyagers reaching the Pacific coast of South America and producing offspring with local populations.<\/p>\n
<\/p>\n
This Polynesian contact is a genuinely separate event from whatever produced the Population Y signal.<\/p>\n
The Population Y signal involves allele sharing between South American populations and Australasian populations \u2014 specifically Australia, New Guinea, and the Andaman Islands \u2014 not Polynesia.<\/p>\n
Polynesian populations are genetically distinct from Australian and Melanesian populations in ways that matter for this analysis.<\/p>\n
The ancestors of Polynesians moved through Melanesia and mixed with Austronesian populations before spreading across the Pacific; the Polynesian genetic profile is a specific combination of East Asian, Austronesian, and Melanesian-related ancestry that is different from the purely Australasian-related ancestry that the Population Y signal is most similar to.<\/p>\n
The Polynesian contact is sometimes raised in discussions of Population Y as if it might explain the signal, but the two phenomena involve different populations, different time periods, different geographic patterns, and different statistical signals.<\/p>\n
<\/p>\n
They do not explain each other.<\/p>\n
The Population Y signal, which appears in populations from the interior of South America as well as from the Pacific coast, and which involves affinities to Australian and Andamanese populations rather than to Polynesian populations, cannot be explained by the Polynesian contact event.<\/p>\n
Keeping these two distinct phenomena clear is important for the accurate communication of the science.<\/p>\n
The Polynesian contact is documented and established.<\/p>\n
The Population Y signal is documented and its explanation is debated.<\/p>\n
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Conflating the two produces confusion that does not serve either the science or the public understanding of it.<\/p>\n
The Andamanese Connection<\/p>\n
Among the Australasian populations most frequently cited in the Population Y literature as showing the highest affinity to the relevant South American and ancient Lagoa Santa populations are the Andamanese \u2014 the Indigenous people of the Andaman Islands in the Bay of Bengal, between India and Myanmar.<\/p>\n
The Andamanese are particularly interesting in this context because of their specific position in global human genetic history.<\/p>\n
The Andaman Islands were populated very early in the history of human dispersal from Africa \u2014 the ancestors of the Andamanese appear to have arrived by the same southern coastal route that eventually led to the peopling of Australia and New Guinea, and the Andamanese have remained relatively isolated on their island archipelago since that early arrival.<\/p>\n
<\/p>\n
As a result, they carry a genetic profile that is in some ways more similar to the ancient southern-route populations than many other contemporary populations.<\/p>\n
The genetic similarity between Andamanese populations and the Population Y signal in South American genomes is statistically significant and consistently found across multiple analyses.<\/p>\n
This consistency with the Andamanese \u2014 a specific population that is geographically far from South America, that has a well-characterized position in global human ancestry, and that has maintained relative genetic isolation \u2014 provides some important constraints on the models proposed to explain the signal.<\/p>\n
The Andamanese genetic profile reflects ancestry from an early dispersal out of Africa along the southern coastal route.<\/p>\n
<\/p>\n
The populations that eventually populated Australia and New Guinea were part of the same broad dispersal.<\/p>\n
The populations that later moved through northeastern Asia toward Beringia would have shared some ancestry with these early southern-route dispersers, because the early human populations of Asia were not completely separate from each other \u2014 they interacted and mixed to varying degrees.<\/p>\n
The specific affinity of the Population Y signal to Andamanese, Australian, and New Guinean populations \u2014 rather than to East Asian or South Asian populations more broadly \u2014 points to a specific ancestral component related to these early-dispersing southern-route populations, rather than a general affinity to Asian populations as a whole.<\/p>\n
This specificity is one of the aspects of the Population Y signal that makes it scientifically interesting and that constrains the range of plausible explanations.<\/p>\n
<\/p>\n
Why the Story Cannot End With Simple Answers<\/p>\n
The history of research on the first Americans \u2014 from Lund’s nineteenth-century cave excavations to the twenty-first-century genomic analyses \u2014 is a history of progressive complication.<\/p>\n
Each generation of researchers has found that the simple story inherited from the previous generation needed to be revised in response to new evidence.<\/p>\n
The simple story once was: the Americas were empty before a single wave of migrants crossed from Asia and populated both continents.<\/p>\n
Then it became: the Americas were populated by multiple migrations from Asia, perhaps with an earlier wave or two followed by the ancestors of modern Native Americans.<\/p>\n
<\/p>\n
Then the genomic revolution suggested: all Native Americans share a single founding ancestry, but that founding ancestry was itself structured in ways that left different genetic traces in different descendant populations.<\/p>\n
And now: within that founding ancestry, there appears to be a specific signal of affinity to Australasian populations that is distributed unevenly across the Americas and whose explanation involves deep ancestral structure in Asia before the American dispersal.<\/p>\n
Each revision has not overturned the previous understanding so much as deepened and complicated it.<\/p>\n
The Americas were populated from Asia \u2014 this remains true, and no evidence challenges it.<\/p>\n
The founding population crossed through Beringia \u2014 this remains the best-supported model, and no alternative migration route has credible genetic support.<\/p>\n
<\/p>\n
The ancient people of Lagoa Santa were Native Americans \u2014 this is established by the genomic evidence and is not in question.<\/p>\n
What has changed is the understanding of the internal structure of the founding population, the specific genetic diversity that that population carried, and the ways in which that diversity was distributed across the Americas as the initial settlement proceeded.<\/p>\n
This is a finer-grained picture than was available before, and it is more accurate as a result \u2014 not despite the complexity but because of it.<\/p>\n
The Population Y debate is not a crisis for the understanding of the first Americans.<\/p>\n
<\/p>\n
It is a normal, productive scientific controversy \u2014 one in which real evidence is being brought to bear on a genuinely difficult question, in which the competing models are being progressively constrained by accumulating data, and in which the eventual resolution will produce a more accurate picture of human prehistory than any of the models currently on the table.<\/p>\n
The resolution is not yet available.<\/p>\n
The data needed to definitively answer the remaining questions \u2014 specifically, ancient Beringian genomes from the period just before the American dispersal \u2014 does not yet exist.<\/p>\n
But the scientific community is working toward it, using increasingly powerful tools and increasingly thoughtful methods, and there is reasonable confidence that the question will eventually be answered.<\/p>\n
When it is, the answer will almost certainly be complicated.<\/p>\n
It will involve specific population dynamics in specific times and places, ancestral diversity that was distributed in specific ways across the founding population, and a story of the first Americans that is more detailed, more specific, and more interesting than any simple summary can capture.<\/p>\n
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That is, in the end, what the bones and the DNA of the ancient people of Lagoa Santa have been trying to tell us all along: that human history is never as simple as we want it to be, and that the complexity, when you understand it, is always more interesting than the simplicity it replaces.<\/p>\n