Wednesday, September 17, 2014

Modern Europeans descended from three groups of ancestors

New studies of ancient DNA are shifting scientists' ideas of how groups of people migrated across the globe and interacted with one another thousands of years ago. By comparing nine ancient genomes to those of modern humans, Howard Hughes Medical Institute (HHMI) scientists have shown that previously unrecognized groups contributed to the genetic mix now present in most modern-day Europeans.
"There are at least three major, highly differentiated populations that have contributed substantial amounts of ancestry to almost everybody that has European ancestry today," says David Reich, an HHMI investigator at Harvard Medical School. Those include hunter-gatherers from western Europe, the early farmers who brought agriculture to Europe from the Near East, and a newly identified group of ancient north Eurasians who arrived in Europe sometime after the introduction of agriculture. That means there were major movements of people into Europe later than previously thought. The team, led by Reich and Johannes Krause at the University of Tübingen in Germany, reported their findings in the September 18, 2014, issue of the journal Nature.
In the last five years, genetic evidence has demonstrated that migrants from the Near East brought agriculture with them to Europe when they arrived about 8,500 years ago. But the genomes of present-day Europeans show signs that they come from more than just the indigenous hunter-gatherers and these early farmers.
Two years ago, Reich's group uncovered genetic evidence that most present-day Europeans are a mixture of groups related to southern Europeans, Near Easterners, and a third group most closely related to Native Americans. "That was a crazy observation, but it's very strong statistically," Reich says. "We argued that this is because of the contribution of an ancient north Eurasian population some of whose members contributed to the peopling of the Americas more than 15,000 years ago, and others of which later migrated to Europe."
To clarify that early history, Reich's team, including more than 100 collaborators worldwide, collected genetic data from nine ancient skeletons and 203 present-day populations living all over the world. Collaborators isolated human DNA and sequenced the complete genomes from the bones of a 7,000-year old skeleton found in Germany and eight skeletons of hunter-gatherers who lived in Luxembourg and Sweden about 8,000 years ago. They compared those genomes to those of the 2,345 people in their contemporary populations.
That required developing new computational methods for genetic analysis. "Figuring out how these populations are related is extremely hard," Reich says. "There's a lot that happened in Europe in the last 8,000 years, and this history acts like a veil, making it difficult to discern what happened at the beginning of this period. We had to find statistics that were able to tell us what happened deep in the past without getting confused by 8,000 years of intervening history, when massive and important events occurred."
"What we find is unambiguous evidence that people in Europe today have all three of these ancestries: early European farmers who brought agriculture to Europe, the indigenous hunter-gatherers who were in Europe prior to 8,000 years ago, and these ancient north Eurasians," Reich says. Further analyses showed that describing present-day Europeans as a mixture of the three populations is a good fit for most, although not all, populations.
When the study began, the ancient north Eurasian population was a "ghost population" – identified based on genetic patterns without any ancient DNA. But in 2013, another group analyzed DNA from two skeletons found in Siberia, one from 24,000 years ago and one from 17,000 years ago, and found that it shared genetic similarities with Europeans and North Americans. The ghost, Reich says, had been found.
Although DNA from ancient north Eurasians is present in nearly all modern Europeans, Reich's team did not find it in their ancient hunter-gatherers or the ancient farmers. That means the north Eurasian line of ancestry was introduced into Europe after agriculture had been established, a scenario most archaeologists had thought unlikely.
"We have this amazing observation that only two ancestries are represented among the first farmers, from about 7,000 to 5,000 years ago. And then suddenly everybody today has ancient north Eurasian ancestry," Reich says. "So there must have been a later movement of this ancestry into Europe."
Anthropologists have long thought that densely settled populations would be resistant to the arrival of new groups. "But this is hard evidence that exactly such a major migration occurred," Reich says. "It's very important because it's a major contributor to Europeans today." The time of the ancient north Eurasians' arrival remains to be determined, but Reich says their later-than-expected movement into Europe might help explain the complex mix of languages that exists there today.
The team's data also reveals that the first farmers to reach Europe from the Near East had ancestors from a previously unidentified lineage, which Reich's group named the Basal Eurasians. Basal Eurasians were the first people to separate from the larger group of non-Africans, before other non-African groups diversified. Reich says that attempts to identify the first group to split from the non-Africans had always been puzzling: genetic evidence indicates that this is likely to be Europeans or Near Easterners, even though some archaeological evidence has indicated that people were in New Guinea and Australia before they were Europe.

The new analysis shows that the Near Easterners who came into Europe 8,000 years ago brought with them a strand of ancestry that had separated before the ancestors of Australian aborigines separated from the indigenous people of Europe. "That population must have been hanging out somewhere in the Near East for a very long time," Reich says. Now he would like to know how that population fits into the archaeological history of the region. Ancient DNA from Basal Europeans, if found, might lead to new revelations about early human history.

Tuesday, September 16, 2014

Meteorite that doomed the dinosaurs helped the forests bloom

66 million years ago, a 10-km diameter chunk of rock hit the Yukatan peninsula near the site of the small town of Chicxulub with the force of 100 teratons of TNT.

 It left a crater more than 150 km across, and the resulting megatsunami, wildfires, global earthquakes and volcanism are widely accepted to have wiped out the dinosaurs and made way for the rise of the mammals. But what happened to the plants on which the dinosaurs fed?

A new study led by researchers from the University of Arizona reveals that the meteorite impact that spelled doom for the dinosaurs also decimated the evergreen flowering plants to a much greater extent than their deciduous peers. They hypothesize that the properties of deciduous plants made them better able to respond rapidly to chaotically varying post-apocalyptic climate conditions. The results are publishing on September 16 in the open access journal PLOS Biology.

Applying biomechanical formulae to a treasure trove of thousands of fossilized leaves of angiosperms — flowering plants excluding conifers — the team was able to reconstruct the ecology of a diverse plant community thriving during a 2.2 million-year period spanning the cataclysmic impact event, believed to have wiped out more than half of plant species living at the time. The fossilized leaf samples span the last 1,400,000 years of the Cretaceous and the first 800,000 of the Paleogene.

The researchers found evidence that after the impact, fast-growing, deciduous angiosperms had replaced their slow-growing, evergreen peers to a large extent. Living examples of evergreen angiosperms, such as holly and ivy, tend to prefer shade, don't grow very fast and sport dark-colored leaves.

"When you look at forests around the world today, you don't see many forests dominated by evergreen flowering plants," said the study's lead author, Benjamin Blonder. "Instead, they are dominated by deciduous species, plants that lose their leaves at some point during the year."

Blonder and his colleagues studied a total of about 1,000 fossilized plant leaves collected from a location in southern North Dakota, embedded in rock layers known as the Hell Creek Formation, which at the end of the Cretaceous was a lowland floodplain crisscrossed by river channels. The collection consists of more than 10,000 identified plant fossils and is housed primarily at the Denver Museum of Nature and Science. "When you hold one of those leaves that is so exquisitely preserved in your hand knowing it's 66 million years old, it's a humbling feeling," said Blonder.

"If you think about a mass extinction caused by catastrophic event such as a meteorite impacting Earth, you might imagine all species are equally likely to die," Blonder said. "Survival of the fittest doesn't apply — the impact is like a reset button. The alternative hypothesis, however, is that some species had properties that enabled them to survive.

"Our study provides evidence of a dramatic shift from slow-growing plants to fast-growing species," he said. "This tells us that the extinction was not random, and the way in which a plant acquires resources predicts how it can respond to a major disturbance. And potentially this also tells us why we find that modern forests are generally deciduous and not evergreen."

Previously, other scientists found evidence of a dramatic drop in temperature caused by dust from the impact. "The hypothesis is that the impact winter introduced a very variable climate," Blonder said. "That would have favored plants that grew quickly and could take advantage of changing conditions, such as deciduous plants."

"We measured the mass of a given leaf in relation to its area, which tells us whether the leaf was a chunky, expensive one to make for the plant, or whether it was a more flimsy, cheap one," Blonder explained. "In other words, how much carbon the plant had invested in the leaf." In addition the researchers measured the density of the leaves' vein networks, a measure of the amount of water a plant can transpire and the rate at which it can acquire carbon.

"There is a spectrum between fast- and slow-growing species," said Blonder. "There is the 'live fast, die young' strategy and there is the 'slow but steady' strategy. You could compare it to financial strategies investing in stocks versus bonds." The analyses revealed that while slow-growing evergreens dominated the plant assemblages before the extinction event, fast-growing flowering species had taken their places afterward.

Wednesday, September 10, 2014

New digital map reveals stunning hidden archaeology of Stonehenge

A host of previously unknown archaeological monuments have been discovered around Stonehenge as part of an unprecedented digital mapping project that will transform our knowledge of this iconic landscape – including remarkable new findings on the world's largest 'super henge', Durrington Walls.

The Stonehenge Hidden Landscapes Project, led by the University of Birmingham in conjunction with the Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology, is the largest project of its kind.

Remote sensing techniques and geophysical surveys have discovered hundreds of new features which now form part of the most detailed archaeological digital map of the Stonehenge landscape ever produced. The startling results of the survey, unveiled in full at the British Science Festival, include 17 previously unknown ritual monuments dating to the period when Stonehenge achieved its iconic shape. Dozens of burial mounds have been mapped in minute detail, including a long barrow (a burial mound dating to before Stonehenge) which revealed a massive timber building, probably used for the ritual inhumation of the dead following a complicated sequence of exposure and excarnation (defleshing), and which was finally covered by an earthen mound.

The project has also revealed exciting new – and completely unexpected – information on previously known monuments. Among the most significant relate to the Durrington Walls 'super henge', situated a short distance from Stonehenge. This immense ritual monument, probably the largest of its type in the world, has a circumference of more than 1.5 kilometers (0.93 miles).

A new survey reveals that this had an early phase when the monument was flanked with a row of massive posts or stones, perhaps up to three metres high and up to 60 in number – some of which may still survive beneath the massive banks surrounding the monument. Only revealed by the cutting-edge technology used in the project, the survey has added yet another dimension to this vast and enigmatic structure.

Work also revealed novel types of monument including massive prehistoric pits, some of which appear to form astronomic alignments, plus new information on hundreds of burial mounds, Bronze Age, Iron Age and Roman settlements and fields at a level of detail never previously seen. Taken together, these results – which will be featured in a major new BBC Two series titled Operation Stonehenge: What Lies Beneath – show that new technology is reshaping how archaeologists understand the landscape of Stonehenge and its development over a period of more than 11,000 years.

In the year marking the centenary of the First World War, the new Stonehenge map even impacts on our knowledge of that momentous event. Surveys have produced detailed maps of the practice trenches dug around Stonehenge to prepare troops for battle on the western front, as well as maps of RAF/RFC Stonehenge – one of Britain's first military airbases used by the Royal Flying Corps between 1917 and 1920.

British project leader Professor Vincent Gaffney, Chair in Landscape Archaeology and Geomatics at the University of Birmingham, said: 'The Stonehenge Hidden Landscapes Project is unique at a global level. Not only has it revolutionised how archaeologists use new technologies to interpret the past, it has transformed how we understand Stonehenge and its landscape.

'Despite Stonehenge being the most iconic of all prehistoric monuments and occupying one of the richest archaeological landscapes in the world, much of this landscape in effect remains terra incognita.

'This project has revealed that the area around Stonehenge is teeming with previously unseen archaeology and that the application of new technology can transform how archaeologists and the wider public understand one of the best-studied landscapes on Earth.

'New monuments have been revealed, as well as new types of monument that have previously never been seen by archaeologists. All of this information has been placed within a single digital map, which will guide how Stonehenge and its landscape are studied in the future.

'Stonehenge may never be the same again.'

Professor Wolfgang Neubauer, Director of the Ludwig Boltzmann Institute, said: 'Developing non-invasive methods to document our cultural heritage is one of the greatest challenges of our time and can only be accomplished by adapting the latest technology such as ground-penetrating radar arrays and high-resolution magnetometers. The developments of the Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology (LBI ArchPro) offer Europe the opportunity to carry out fundamental archaeological research at a scale and precision never previously attempted.

'No landscape deserves to benefit from a study at this level of detail more than Stonehenge. The terabytes of digital survey data collected, processed and visualised by LBI ArchPro provide the base for the precise mapping of the monuments and archaeological features buried in the subsurface or still visible in the landscape surrounding Stonehenge. After centuries of research, the analysis of all mapped features makes it possible, for the first time, to reconstruct the development of Stonehenge and its landscape through time.'

The Stonehenge Hidden Landscapes Project is a collaboration between the University of Birmingham; Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology, Vienna and its international partners; University of Bradford; University of St Andrews; University of Nottingham; and the 'ORBit' Research Group of the Department of Soil Management at the University of Ghent, Belgium.

The project operates under the auspices of the National Trust and English Heritage.

Dr Nick Snashall, National Trust Archaeologist for the Avebury and Stonehenge World Heritage Site, said: 'Using 21st-century techniques, the Stonehenge Hidden Landscapes team have transformed our knowledge of this ancient, precious and very special landscape. Their work has revealed a clutch of previously unsuspected sites and monuments showing how much of the story of this world-famous archaeological treasure house remains to be told.'

Dr Heather Sebire of English Heritage, Curator of Stonehenge, said: 'This is such an exciting project. The surveys will help us form an understanding of possible new sites which have not been recorded before but which will need further investigation.'

A rock engraving made by Neanderthals in Gibraltar

The production of purposely made painted or engraved designs on cave walls—a means of recording and transmitting symbolic codes in a durable manner—is recognized as a major cognitive step in human evolution. Considered exclusive to modern humans, this behavior has been used to argue in favor of significant cognitive differences between our direct ancestors and contemporary archaic hominins, including the Neanderthals.

A new article in PNAS, ( ) presents the first known example of an abstract pattern engraved by Neanderthals, from Gorham’s Cave in Gibraltar. It consists of a deeply impressed cross-hatching carved into the bedrock of the cave that has remained covered by an undisturbed archaeological level containing Mousterian artifacts made by Neanderthals and is older than 39 cal kyr BP (39,000 calibrated years before the present).

Geochemical analysis of the epigenetic coating over the engravings and experimental replication show that the engraving was made before accumulation of the archaeological layers, and that most of the lines composing the design were made by repeatedly and carefully passing a pointed lithic tool into the grooves, excluding the possibility of an unintentional or utilitarian origin (e.g., food or fur processing).

This discovery demonstrates the capacity of the Neanderthals for abstract thought and expression through the use of geometric forms.

Thursday, August 28, 2014

New DNA study unravels the settlement history of the New World Arctic

Prehistoric migrations
We know people have lived in the New World Arctic for about 5,000 years. Archaeological evidence clearly shows that a variety of cultures survived the harsh climate in Alaska, Canada and Greenland for thousands of years. Despite this, there are several unanswered questions about these people: Where did they come from? Did they come in several waves? When did they arrive? Who are their descendants? And who can call themselves the indigenous peoples of the Arctic? We can now answer some of these questions, thanks to a comprehensive DNA study of current and former inhabitants of Greenland, Arctic Canada, Alaska, the Aleutian Islands and Siberia, conducted by an international team headed by the Centre for GeoGenetics at the Natural History Museum of Denmark, University of Copenhagen. The results have just been published in the leading scientific journal Science.
Looking for ancient human remains in northern Greenland.
The North American Arctic was one of the last major regions to be settled by modern humans. This happened when people crossed the Bering Strait from Siberia and wandered into a new world. While the area has long been well researched by archaeologists, little is known of its genetic prehistory. In this study, researchers show that the Paleo-Eskimo, who lived in the Arctic from about 5,000 years ago until about 700 years ago, represented a distinct wave of migration, separate from both Native Americans – who crossed the Bering Strait much earlier – and the Inuit, who came from Siberia to the Arctic several thousand years after the Paleo-Eskimos.
- Our genetic studies show that, in reality, the Paleo-Eskimos – representing one single group – were the first people in the Arctic, and they survived without outside contact for over 4,000 years, says Lundbeck Foundation Professor Eske Willerslev from Centre for GeoGenetics at the Natural History Museum, University of Copenhagen, who headed the study.
- Our study also shows that the Paleo-Eskimos, after surviving in near-isolation in the harsh Arctic environment for more than 4,000 years, disappeared around 700 years ago – about the same time when the ancestors of modern-day Inuit spread eastward from Alaska, adds Dr. Maanasa Raghavan of Centre for GeoGenetics and lead author of the article.
Migration pulses into the Americas
Greenlandic Inuit from the 1930s pictured in their traditional boats (umiaq), used for hunting and transportation.
In the archaeological literature, distinctions are drawn between the different cultural units in the Arctic in the period up to the rise of the Thule culture, which replaced all previous Arctic cultures and is the source of today's Inuit in Alaska, Canada and Greenland. The earlier cultures included the Saqqaq or Pre-Dorset and Dorset, comprising the Paleo-Eskimo tradition, with the Dorset being further divided into three phases. All of these had distinctive cultural, lifestyle and subsistence traits as seen in the archaeological record. There were also several periods during which the Arctic was devoid of human settlement. These facts have further raised questions regarding the possibility of several waves of migration from Siberia to Alaska, or perhaps Native Americans migrating north during the first 4,000 years of the Arctic being inhabited.
- Our study shows that, genetically, all of the different Paleo-Eskimo cultures belonged to the same group of people. On the other hand, they are not closely related to the Thule culture, and we see no indication of assimilation between the two groups. We have also ascertained that the Paleo-Eskimos were not descendants of the Native Americans. The genetics reveals that there must have been at least three separate pulses of migration from Siberia into the Americas and the Arctic. First came the ancestors of today's Native Americans, then came the Paleo-Eskimos, and finally the ancestors of today's Inuit, says Eske Willerslev.
Genetics and archaeology
The genetic study underpins some archaeological findings, but not all of them.
It rejects the speculation that the Paleo-Eskimos represented several different peoples, including Native Americans, or that they are direct ancestors of today's Inuit. Also rejected are the theories that the Greenlanders on the east coast or the Canadian Sadlermiut, from Southampton Island in Hudson Bay, who died out as late as 1902��, were surviving groups of Dorset people. Genetics shows that these groups were Inuit who had developed Dorset-like cultural traits.
The study clearly shows that the diversity of tools and ways of life over time, which in archaeology is often interpreted as a result of migration, does not in fact necessarily reflect influx of new people. The Paleo-Eskimos lived in near-isolation for more than 4,000 years, and during this time their culture developed in such diverse ways that it has led some to interpret them as different peoples.
- Essentially, we have two consecutive waves of genetically distinct groups entering the New World Arctic and giving rise to three discrete cultural units. Through this study, we are able to address the question of cultural versus genetic continuity in one of the most challenging environments that modern humans have successfully settled, and present a comprehensive picture of how the Arctic was peopled, says Dr. Raghavan.
The first inhabitants
The study was unable to establish why the disappearance of the Paleo-Eskimos coincided with the ancestors of the Inuit beginning to colonise the Arctic. There is no doubt that the Inuit ancestors – who crossed the Bering Strait about 1,000 years ago and reached Greenland around 700 years ago – were technologically superior.
The Inuit's own myths tell stories of a people before them, which in all likelihood refer to the Paleo-Eskimos. In the myths, they are referred to as the 'Tunit' or 'Sivullirmiut', which means "the first inhabitants". According to these myths they were giants, who were taller and stronger than the Inuit, but easily frightened from their settlements by the newcomers.
Co-author Dr. William Fitzhugh from the Arctic Studies Centre at the Smithsonian Institution says:
- Ever since the discovery of a Paleo-Eskimo culture in the North American Arctic in 1925, archaeologists have been mystified by their relationship with the Thule culture ancestors of the modern Inuit. Paleo-Eskimo culture was replaced rapidly around AD 1300-1400, their only traces being references to 'Tunit' in Inuit mythology and adoption of some elements of Dorset technology. This new genomic research settles outstanding issues in Arctic archaeology that have been debated for nearly a century, finding that Paleo-Eskimo and Neo-Eskimo people were genetically distinct, with separate origins in Eastern Siberia, and the Paleo-Eskimo remained isolated in the Eastern Arctic for thousands of years with no significant mixing with each other or with American Indians, Norse, or other Europeans.