Radiocarbon dating reveals mass grave did date to the Viking age

IMAGE: This is one of the female skulls from the Repton charnel. view more 

Credit: Cat Jarman

A team of archaeologists, led by Cat Jarman from the University of Bristol's Department of Anthropology and Archaeology, has discovered that a mass grave uncovered in the 1980s dates to the Viking Age and may have been a burial site of the Viking Great Army war dead.

The Great Viking Army or Great Danish^[a] Army, known by the Anglo-Saxons as the Great Heathen Army (OE: mycel hæþen here), was a coalition of Norse warriors, primarily originating from Denmark but with elements from Sweden and Norway, who came together under a unified command to invade the four Anglo-Saxon kingdoms that constituted England in 865 AD.

Although the remains were initially thought to be associated with the Vikings, radiocarbon dates seemed to suggest the grave consisted of bones collected over several centuries. New scientific research now shows that this was not the case and that the bones are all consistent with a date in the late 9th century. Historical records state that the Viking Great Army wintered in Repton, Derbyshire, in 873 A.D. and drove the Mercian king into exile.

Excavations led by archaeologists Martin Biddle and Birthe Kjølbye-Biddle at St Wystan's Church in Repton in the 1970s and 1980s discovered several Viking graves and a charnel deposit of nearly 300 people underneath a shallow mound in the vicarage garden.

The mound appears to have been a burial monument linked to the Great Army.

An Anglo-Saxon building, possibly a royal mausoleum, was cut down and partially ruined, before being turned into a burial chamber.

One room was packed with the commingled remains of at least 264 people, around 20 percent of whom were women. Among the bones were Viking weapons and artefacts, including an axe, several knives, and five silver pennies dating to the period 872-875 A.D. 80 percent of the remains were men, mostly aged 18 to 45, with several showing signs of violent injury.

During the excavations, everything pointed to the burial's association with the Viking Great Army, but confusingly, initial radiocarbon dates suggested otherwise. It seemed to contain a mix of bones of different ages, meaning that they could not all have been from the Viking Age.

Now, new dating proves that they are all consistent with a single date in the 9th century and therefore with the Viking Great Army.

Cat Jarman said: "The previous radiocarbon dates from this site were all affected by something called marine reservoir effects, which is what made them seem too old.

"When we eat fish or other marine foods, we incorporate carbon into our bones that is much older than in terrestrial foods. This confuses radiocarbon dates from archaeological bone material and we need to correct for it by estimating how much seafood each individual ate."

A double grave from the site - one of the only Viking weapon graves found in the country - was also dated, yielding a date range of 873-886 A.D.

The grave contained two men, the older of whom was buried with a Thor's hammer pendant, a Viking sword, and several other artefacts.

He had received numerous fatal injuries around the time of death, including a large cut to his left femur. Intriguingly, a boar's tusk had been placed between his legs, and it has been suggested that the injury may have severed his penis or testicles, and that the tusk was there to replace what he had lost in preparation for the after-world.

The new dates now show that these burials could be consistent with members of the Viking Great Army.

Outside the charnel mound another extraordinary grave can now be shown to be likely to relate to the Vikings in Repton as well.

Four juveniles, aged between eight and 18, were buried together in a single grave with a sheep jaw at their feet.

Next to them large stones may have held a marker, and the grave was placed near the entrance to the mass grave. At least two of the juveniles have signs of traumatic injury. The excavators suggested this may have been a ritual grave, paralleling accounts of sacrificial killings to accompany Viking dead from historical accounts elsewhere in the Viking world. The new radiocarbon dates can now place this burial into the time period of 872-885 A.D.

Cat Jarman added: "The date of the Repton charnel bones is important because we know very little about the first Viking raiders that went on to become part of considerable Scandinavian settlement of England.

"Although these new radiocarbon dates don't prove that these were Viking army members it now seems very likely. It also shows how new techniques can be used to reassess and finally solve centuries old mysteries."

Scandinavians shaped by several waves of immigration

Directly following the last ice age, people from the western parts of what is now Norway were a population that had substantially different genetics from the people living in the area corresponding to present-day Sweden.

"We were surprised that the results showed such marked dissimilarities," says associate professor and archaeologist Birgitte Skar at the Norwegian University of Science and Technology's (NTNU) University Museum. Skar is responsible for the museum's Stone Age and Bronze Age collections.
Scandinavia was one of the last parts of Europe to become habitable when the glaciers released their icy grip more than 10,000 years ago. The ocean's resources and the coastal archipelago attracted marine hunter-gatherers of yore to the region.

Swedish and Norwegian researchers have collaborated on analysing the DNA in 9500-year-old bone samples from the southern and western Norwegian coast and from the Swedish islands of Gotland and Stora Karlsö. This period corresponds to the Mesolithic Stone Age.

Researchers examined seven excavated individuals and compared their genetic material with samples from other parts of Europe.

"People from the Norwegian south and west coast were genetically similar to populations east of the Baltic Sea that came from today's Russia. People from eastern Scandinavia - present-day Sweden - were more genetically similar to populations from central and western Europe," says population geneticist Torsten Günther from Uppsala University. He is one of the main authors of the new study.

Norwegian results are key
 
This finding may seem strange if you just look at the geography, but it may due to multiple waves of migration to Scandinavia. About 11,500 years ago, people migrated from the south, through Germany and Denmark and then by sea to Norway. About 1000 years later, people traveled from the northeast and followed the Norwegian Atlantic coast southward.

"To understand the migration routes, it was essential to obtain data from the Norwegian individuals," explains Skar, co-author of the study. The Norwegian skeletal remains from southern Norway are also the oldest of the individuals studied.

Over time, the various migration waves led to extensive contact between the diverse populations, and this is also reflected in the genetic data.

The researchers analysed the genetic data in conjunction with other archaeological findings and new insights from climate models to increase their understand of the migration routes, settlement patterns and the first people to settle in Scandinavia as the ice retreated.

Archaeological artefacts and isotopic analysis - which can tell us something about what people ate - help to fill out the picture. The new immigrants that came from the northeast learned new boating and fishing skills to access marine resources, which offered their main source of food.

The researchers discovered that these immigrants also introduced new tools and innovative ways to produce them. This shift in material culture can now be linked to a particular migration wave.

"We expect that a migrating population comes with an entire cultural package - a knowledge of nature, ways of life, craft traditions, beliefs and other customs," says Skar. "Now we can explore more closely how the relationship between the original and new populations evolved. The original inhabitants were highly skilled and adventurous seafaring hunters, whereas the new population was originally an inland people. Archaeologists can track the processes of change in their material culture," she adds.

Light pigmentation variants may have been advantageous
 
People at that time were largely dependent on the ocean for food. They braved challenging climate conditions that required behavioral adaptations in the short term, and that in the longer term could lead to changes in the population's genetic composition.

"The two groups that migrated to Scandinavia at that time were genetically distinct. People from the south probably had blue eyes and dark skin, while those from the northeast had various eye colours and light skin," says population geneticist Mattias Jakobsson from Uppsala University, another of the main authors.

The genetic variation between the Mesolithic individuals from Scandinavia is surprisingly high, and greater than in the populations who lived in western and central Europe. This contrasts with the Europe of today, where the largest genetic variation is found in the south.

The lighter variations of skin and eye color that are more common in Scandinavia than in other parts of Europe also appear to have been the case at the time of the migrations. Pigmentation, now as then, tends to decrease the farther away a population group lives from the equator. We can assume this to be an indicator of climate adaptation.

Good results
 
The results are presented in a research article recently published in PLoS Biology. The sample quality is very high.

The remains of one of the individuals studied yielded aDNA results with the best coverage, or depth, achieved for any human being from prehistoric times. The abbreviation aDNA stands for ancient DNA and refers to the study of genetic data obtained from fossil subjects.

Reconstructing an ancient lethal weapon

IMAGE: University of Washington researchers re-created ancient projectile points to test their effectiveness. From left to right: stone, microblade and bone tips. view more 

Credit: Janice Wood

Archaeologists are a little like forensic investigators: They scour the remains of past societies, looking for clues in pottery, tools and bones about how people lived, and how they died.

And just as detectives might re-create the scene of a crime, University of Washington archaeologists have re-created the weapons used by hunter-gatherers in the post-Ice Age Arctic some 14,000 years ago. Looking for clues as to how those early people advanced their own technology, researchers also considered what that might tell us about human migration, ancient climates and the fate of some animal species.

In an article published Jan. 31 in the Journal of Archaeological Science, Janice Wood, recent UW anthropology graduate, and Ben Fitzhugh, a UW professor of anthropology, show how they reconstructed prehistoric projectiles and points from ancient sites in what is now Alaska and studied the qualities that would make for a lethal hunting weapon.

The UW team chose to study hunting weapons from the time of the earliest archaeological record in Alaska (around 10,000 to 14,000 years ago), a time that is less understood archaeologically, and when different kinds of projectile points were in use. Team members designed a pair of experiments to test the effectiveness of the different point types. By examining and testing different points in this way, the team has come to a new understanding about the technological choices people made in ancient times.

"The hunter-gatherers of 12,000 years ago were more sophisticated than we give them credit for," Fitzhugh said. "We haven't thought of hunter-gatherers in the Pleistocene as having that kind of sophistication, but they clearly did for the things that they had to manage in their daily lives, such as hunting game. They had a very comprehensive understanding of different tools, and the best tools for different prey and shot conditions."

Prior research has focused on the flight ballistics of the hunting weapons in general, and no prior study has looked specifically at the ballistics of tools used in Siberia and the Arctic regions of North America just after the Ice Age. In addition to foraging for plants and berries (when available), nomadic groups hunted caribou, reindeer and other animals for food, typically with spears or darts (thrown from atlatl boards). Without preservation of the wood shafts, these tools are mainly differentiated in the archaeological record by their stone and bone points. But it was not known how effective different kinds of points were in causing lethal injury to prey.

Nor is it known, definitively, whether different types of points were associated with only certain groups of people, or whether with the same groups used certain point types to specialize on particular kinds of game or hunting practices. It is generally accepted that different point types were developed in Africa and Eurasia and brought to Alaska before the end of the Ice Age. These included rudimentary points made of sharpened bone, antler or ivory; more intricate, flaked stone tips popularly familiar as "arrowheads"; and a composite point made of bone or antler with razor blade-like stone microblades embedded around the edges.

The three likely were invented at separate times but remained in use during the same period because each presumably had its own advantages, Wood said. Learning how they functioned informs what we know about prehistoric hunters and the repercussions of their practices.

So Wood traveled to the area around Fairbanks, Alaska, and crafted 30 projectile points, 10 of each kind. She tried to stay as true to the original materials and manufacturing processes as possible, using poplar projectiles, and birch tar as an adhesive to affix the points to the tips of the projectiles. While ancient Alaskans used atlatls (a kind of throwing board), Wood used a maple recurve bow to shoot the arrows for greater control and precision.

• For the bone tip, modeled on a 12,000-year-old ivory point from an Alaskan archaeological site, Wood used a multipurpose tool to grind a commercially purchased cow bone;
• For the stone tip, she used a hammerstone to strike obsidian into flakes, then shaped them into points modeled on those found at another site in Alaska from 13,000 years ago;
• And for the composite microblade tip -- modeled microblade technologies seen in Alaska since at least 13,000 years ago and a rare, preserved grooved antler point from a more recent Alaskan site used more than 8,000 years ago -- Wood used a saw and sandpaper to grind a caribou antler to a point. She then used the multipurpose tool to gouge out a groove around its perimeter, into which she inserted obsidian microblades.

Wood then tested how well each point could penetrate and damage two different targets: blocks of ballistic gelatin (a clear synthetic gelatin meant to mimic animal muscle tissue) and a fresh reindeer carcass, purchased from a local farm. Wood conducted her trials over seven hours on a December day, with an average outdoor temperature of minus 17 degrees Fahrenheit.

In Wood's field trial, the composite microblade points were more effective than simple stone or bone on smaller prey, showing the greatest versatility and ability to cause incapacitating damage no matter where they struck the animal's body. But the stone and bone points had their own strengths: Bone points penetrated deeply but created narrower wounds, suggesting their potential for puncturing and stunning larger prey (such as bison or mammoth); the stone points could have cut wider wounds, especially on large prey (moose or bison), resulting in a quicker kill.

Wood said the findings show that hunters during this period were sophisticated enough to recognize the best point to use, and when. Hunters worked in groups; they needed to complete successful hunts, in the least amount of time, and avoid risk to themselves.

"We have shown how each point has its own performance strengths," she said. Bone points punctured effectively, flaked stone created a greater incision, and the microblade was best for lacerated wounds. "It has to do with the animal itself; animals react differently to different wounds. And it would have been important to these nomadic hunters to bring the animal down efficiently. They were hunting for food."

Weapon use can shed light on the movement of people and animals as humans spread across the globe and how ecosystems changed before, during and after the ice ages.

"The findings of our paper have relevance to the understanding of ballistic properties affecting hunting success anywhere in the world people lived during the 99 percent of human history that falls between the invention of stone tools more than 3 million years ago in Africa and the origins of agriculture," Fitzhugh said.

It could also inform debates on whether human hunting practices directly led to the extinction of some species. The team's findings and other research show that our ancestors were thinking about effectiveness and efficiency, Wood said, which may have influenced which animals they targeted. An animal that was easier to kill may have been targeted more often, which could, along with changing climates, explain why animals such as the horse disappeared from the Arctic. A shot to the lung was lethal for early equines, Wood said, but a caribou could keep going.

"I see this line of research as looking at the capacity of the human brain to come up with innovations that ultimately changed the course of human history," she said. "This reveals the human capacity to invent in extreme circumstances, to figure out a need and a way to meet that need that made it easier to eat and minimized the risk."

Upon completion of the experiment, the bones were sterilized for future study of projectile impact marks.

Archaeologists may have discovered one of the earliest examples of a 'crayon'

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The crayon revealed a sharpened end.

Credit: Paul Shields/University of York

Archaeologists say they may have discovered one of the earliest examples of a 'crayon' -- possibly used by our ancestors 10,000 years ago for applying colour to their animal skins or for artwork.

The ochre crayon was discovered near an ancient lake, now blanketed in peat, near Scarborough, North Yorkshire. An ochre pebble was found at another site on the opposite side of the lake.

The pebble had a heavily striated surface that is likely to have been scraped to produce a red pigment powder. The crayon measures 22mm long and 7mm wide.

Ochre is an important mineral pigment used by prehistoric hunter-gatherers across the globe. The latest finds suggest people collected ochre and processed it in different ways during the Mesolithic period.

The ochre objects were studied as part of an interdisciplinary collaboration between the Departments of Archaeology and Physics at the University of York, using state-of-the-art techniques to establish their composition.

The artefacts were found at Seamer Carr and Flixton School House. Both sites are situated in a landscape rich in prehistory, including one of the most famous Mesolithic sites in Europe, Star Carr.
A pendant was discovered at Star Carr in 2015 and is the earliest known Mesolithic art in Britain. Here, more than 30 red deer antler headdresses were found which may have been used as a disguise in hunting, or during ritual performances by shamans when communicating with animal spirits.

Lead author, Dr Andy Needham from the University of York's Department of Archaeology, said the latest discoveries helped further our understanding of Mesolithic life.

He commented: "Colour was a very significant part of hunter-gatherer life and ochre gives you a very vibrant red colour. It is very important in the Mesolithic period and seems to be used in a number of ways.

"One of the latest objects we have found looks exactly like a crayon; the tip is faceted and has gone from a rounded end to a really sharpened end, suggesting it has been used.

"For me it is a very significant object and helps us build a bigger picture of what life was like in the area; it suggests it would have been a very colourful place."

The research team say Flixton was a key location in the Mesolithic period and the two objects help paint a vibrant picture of how the people interacted with the local environment.

"The pebble and crayon were located in an area already rich in art. It is possible there could have been an artistic use for these objects, perhaps for colouring animal skins or for use in decorative artwork," Dr Needham added.

Northern European population history revealed by ancient human genomes

An international team of scientists, led by researchers from the Max Planck Institute for the Science of Human History, analyzed ancient human genomes from 38 northern Europeans dating from approximately 7,500 to 500 BCE. The study, published today in Nature Communications, found that Scandinavia was initially settled via a southern and a northern route and that the arrival of agriculture in northern Europe was facilitated by movements of farmers and pastoralists into the region.
Northern Europe could be considered a late bloomer in some aspects of human history: initial settlement by hunter-gatherers occurred only about 11,000 years ago, after the retreat of the lingering ice sheets from the Pleistocene, and while agriculture was already widespread in Central Europe 7,000 years ago, this development reached Southern Scandinavia and the Eastern Baltic only millennia later.

Several recent studies of ancient human genomes have dealt with the prehistoric population movements that brought new technology and subsistence strategies into Europe, but how they impacted the very north of the continent has still been poorly understood.

For this study, the research team, which included scientists from Lithuania, Latvia, Estonia, Russia and Sweden, assembled genomic data from 38 ancient northern Europeans, from mobile hunter-gatherers of the Mesolithic (approximately 12,000 to 7,000 years ago) and the first Neolithic farmers in southern Sweden (approximately 6,000 to 5,300 years ago) to the metallurgists of the Late Bronze Age in the Eastern Baltic (approximately 1300 to 500 BCE). This allowed the researchers to uncover surprising aspects of the population dynamics of prehistoric northern Europe.

Two routes of settlement for Scandinavia
Previous analysis of ancient human genomes has revealed that two genetically differentiated groups of hunter-gatherers lived in Europe during the Mesolithic: the so-called Western Hunter-Gatherers excavated in locations from Iberia to Hungary, and the so-called Eastern Hunter-Gatherers excavated in Karelia in north-western Russia. Surprisingly, the results of the current study show that Mesolithic hunter-gatherers from Lithuania appear very similar to their Western neighbors, despite their geographic proximity to Russia. The ancestry of contemporary Scandinavian hunter-gatherers, on the other hand, was comprised from both Western and Eastern Hunter-Gatherers.

"Eastern Hunter-Gatherers were not present on the eastern Baltic coast, but a genetic component from them is present in Scandinavia. This suggests that the people carrying this genetic component took a northern route through Fennoscandia into the southern part of the Scandinavian peninsula. There they genetically mixed with Western Hunter-Gatherers who came from the South, and together they formed the Scandinavian Hunter-Gatherers," explains Johannes Krause, Director of the Department of Archaeogenetics at the Max Planck Institute for the Science of Human History, and senior author of the study.

Agriculture and animal herding - cultural imports by incoming people
Large-scale farming first started in southern Scandinavia around 6,000 years ago, about one millennium after it was already common in Central Europe. In the Eastern Baltic, the inhabitants relied solely on hunting, gathering and fishing for another 1000 years. Although some have argued that the use of the new subsistence strategy was a local development by foragers, possibly adopting the practices of their farming neighbors, the genetic evidence uncovered in the present study tells a different story.

The earliest farmers in Sweden are not descended from Mesolithic Scandinavians, but show a genetic profile similar to that of Central European agriculturalists. Thus it appears that Central Europeans migrated to Scandinavia and brought farming technology with them. These early Scandinavian farmers, like the Central European agriculturalists, inherited a substantial portion of their genes from Anatolian farmers, who first spread into Europe around 8,200 years ago and set in motion the cultural transition to agriculture known as the Neolithic Revolution.

Similarly, a near-total genetic turnover is seen in the Eastern Baltic with the advent of large-scale agro-pastoralism. While they did not mix genetically with Central European or Scandinavian farmers, beginning around 2,900 BCE the individuals in the Eastern Baltic derive large parts of their ancestry from nomadic pastoralists of the Pontic-Caspian steppe.

"Interestingly, we find an increase of local Eastern Baltic hunter-gatherer ancestry in this population at the onset of the Bronze Age," states Alissa Mittnik of the Max Planck Institute for the Science of Human History, lead author of the study. "The local population was not completely replaced but coexisted and eventually mixed with the newcomers."

This study emphasizes the regional differences of cultural transitions and sets the stage for more in-depth studies of later periods in northern European prehistory, such as the Iron Age and Viking Age.

Ancient Eurasian DNA sequencing is revealing links with modern humans

IMAGE: This is a schematic of populations in Eurasia and the Americas from 45,000 to 7,500 years ago. A summary of major events in each of the time periods is on the left.

Credit: Melinda A.Yang and Qiaomei Fu

Until recently, very little was known about the genetic relationship between modern humans of the Upper Paleolithic age (the period of time between 50,000 and 10,000 years ago, also called the Late Stone age) and today's populations. But with direct DNA sequencing, researchers are discovering unexpected genetic connections between individuals on opposing sides of Eurasia. These suggest a complex history that may represent early gene flow across Eurasia or an early population structure that eventually led to Europeans and Asians.

In a review published in the journal Trends in Genetics on January 25, scientists at the Chinese Academy of Sciences in Beijing discuss what we know about the genetics of ancient individuals from Eurasia (Europe and Western Asia) between 45,000-7,500 years ago. The authors summarized work that investigated the genomes of more than 20 ancients in the Eurasian family tree, including the 45,000-year-old Ust'-Ishim individual from Central Siberia, for their paper.

"Aside from these individuals, it is a fact that sampling for the Eurasian region is sparse for all time periods except the present-day," says co-author Qiaomei Fu, a paleogeneticist at the Chinese Academy of Sciences. "But with the information from the several individuals available for ancient DNA sequencing we do have hints at interesting population structure, migration and interaction in East Asia."

The researchers learned that in Eurasia between 35,000 and 45,000 years ago, at least four distinct populations were present. These were early Asian and Europeans, as well as populations with ancestry hardly found or not at all in modern populations.

By 15,000-34,000 years ago, however, DNA sequencing showed that modern humans in Eurasia are similar to either Europeans or to Asians, suggesting that a genetic Asian-European separation likely occurred prior to 40,000 years ago. By 7,500-14,000 years ago, the populations across Eurasia shared genetic similarities, suggesting greater interactions between geographically distant populations.

These analyses also revealed at least two Neanderthal population mixing events, one approximately 50,000-60,000 years ago and a second more than 37,000 years ago. This Neanderthal ancestry gradually declined in archaic ancestry in Europeans dating from ~14,000-37,000 years ago.

"Genetic studies of ancient individuals have become more frequent in recent years because of technology," says Fu. "As a result, we can now see the presence of multiple distinct subpopulations in Europe and in Asia, and these in turn contribute different amounts of ancestry to more recent subpopulations."

"Right now is a great time to study human evolutionary genetics because the development of sequencing technology and computing resources minimizes destruction of samples and maximizes data generation and storage," Fu says. "With large present-day genomic datasets and increased international collaboration to handle the many newly sequenced ancient datasets, there is huge potential to understand the biology of human prehistory in a way that has never been accessible before."

Looking ahead, Fu and colleagues hope to extend this type of sequencing and analysis to learn more about the genetic prehistory of East Asia and other regions, including Oceania, Africa, and the Americas. "All of those areas have a rich human prehistory, particularly in Africa, so any ancient DNA from those continents will likely resolve some major questions on human migration," she says.

Historical migrations left genetic footprints on the Irish genome

A genome-wide study of the people of Ireland reveals a previously hidden genetic landscape, shaped through geography and historical migrations. Ross Byrne and Russell McLaughlin of Trinity College Dublin in Ireland report their findings January 25th, 2018 in PLOS Genetics.

In the 10,000 years that people have continuously inhabited the Emerald Isle, they have established distinct cultural and geographic regions. Previous studies, however, had found no clear genetic groups within the Irish population. In the current study, researchers took a more detailed look at genetic diversity across the islands. They analyzed genetic variation across almost 1,000 Irish genomes and over 6,000 genomes from Britain and mainland Europe.

 The study revealed 23 distinct Irish genetic clusters, separated by geography. The clusters are most distinct in western Ireland, but less pronounced in the east, where historical migrations have erased the genetic divisions. When the researchers took into account genetic contributions from people with British ancestry, a clear trend arose, showing input from Britain dropping off in populations to the west. The researchers also detected genetic input from Europe and estimated the timing of the historical migrations of the Norse-Vikings and the Anglo-Normans to Ireland, yielding dates that were consistent with historical records.

The study paints a new and more complex picture of the genetic landscape of Ireland, and demonstrates the signatures that historical migrations have left on the modern Irish genome. The findings also show that a distinct genetic structure can exist, even within small, isolated populations. The researchers suggest that this newly revealed structure should be taken into account in future studies that use the Irish population to identify the genetics underlying various traits and diseases.

On the impact of the study, Ross P. Byrne says:

"This subtle genetic structure within such a small country has implications for medical genetic association studies. As it stands current corrections for population structure in study designs may not adequately account for this within country variation, which may potentially lead to false positive results emerging. We feel this will be particularly important in the analysis of rare variants as these are expected to be less uniformly distributed throughout a country. We intend to explore this further and identify if this structure should be accounted for in corrections. 

Russell McLaughlin adds:

"The long and complex history of population dynamics in Ireland has left an indelible mark on the genomes of modern inhabitants of the island. We have shown that, using only genetic data, we can accurately reconstruct elements of this past and demonstrate a striking correlation between geographical provenance and genetic affinity. Understanding this fine-grained population structure is crucially important for ongoing and future studies of rare genetic variation in health and disease."