Thursday, March 23, 2017

Farmers in Roman Empire converted to Hun lifestyle -- and vice versa


Marauding hordes of barbarian Huns, under their ferocious leader Attila, are often credited with triggering the fall of one of history's greatest empires: Rome.

Historians believe Hunnic incursions into Roman provinces bordering the Danube during the 5th century AD opened the floodgates for nomadic tribes to encroach on the empire. This caused a destabilisation that contributed to collapse of Roman power in the West.

According to Roman accounts, the Huns brought only terror and destruction. However, research from the University of Cambridge on gravesite remains in the Roman frontier region of Pannonia (now Hungary) has revealed for the first time how ordinary people may have dealt with the arrival of the Huns.

Biochemical analyses of teeth and bone to test for diet and mobility suggest that, over the course of a lifetime, some farmers on the edge of empire left their homesteads to become Hun-like roaming herdsmen, and consequently, perhaps, took up arms with the tribes.

Other remains from the same gravesites show a dietary shift indicating some Hun discovered a settled way of life and the joys of agriculture -- leaving their wanderlust, and possibly their bloodlust, behind.

Lead researcher Dr Susanne Hakenbeck, from Cambridge's Department of Archaeology, says the Huns may have brought ways of life that appealed to some farmers in the area, as well learning from and settling among the locals. She says this could be evidence of the steady infiltration that shook an empire.

"We know from contemporary accounts that this was a time when treaties between tribes and Romans were forged and fractured, loyalties sworn and broken. The lifestyle shifts we see in the skeletons may reflect that turmoil," says Hakenbeck.

"However, while written accounts of the last century of the Roman Empire focus on convulsions of violence, our new data appear to show some degree of cooperation and coexistence of people living in the frontier zone. Far from being a clash of cultures, alternating between lifestyles may have been an insurance policy in unstable political times."

For the study, published today in the journal PLOS ONE, Hakenbeck and colleagues tested skeletal remains at five 5th-century sites around Pannonia, including one in a former civic centre as well as rural homesteads.

The team analysed the isotope ratios of carbon, nitrogen, strontium and oxygen in bones and teeth. They compared this data to sites in central Germany, where typical farmers of the time lived, and locations in Siberia and Mongolia, home to nomadic herders up to the Mongol period and beyond.

The results allowed researchers to distinguish between settled agricultural populations and nomadic animal herders in the former Roman border area through isotopic traces of diet and mobility in the skeletons.

All the Pannonian gravesites not only held examples of both lifestyles, but also many individuals that shifted between lifestyles in both directions over the course of a lifetime. "The exchange of subsistence strategies is evidence for a way of life we don't see anywhere else in Europe at this time," says Hakenbeck.

She says there are no clear lifestyle patterns based on sex or accompanying grave goods, or even 'skull modification' - the binding of the head as a baby to create a pointed skull - commonly associated with the Hun.

"Nomadic animal herding and skull modification may be practices imported by Hun tribes into the bounds of empire and adopted by some of the agriculturalist inhabitants."

The diet of farmers was relatively boring, says Hakenbeck, consisting primarily of plants such as wheat, vegetables and pulses, with a modicum of meat and almost no fish.

The herders' diet on the other hand was high in animal protein and augmented with fish. They also ate large quantities of millet, which has a distinctive carbon isotope ratio that can be identified in human bones. Millet is a hardy plant that was hugely popular with nomadic populations of central Asia because it grows in a few short weeks.

Roman sources of the time were dismissive of this lifestyle. Ammianus Marcellinus, a Roman official, wrote of the Hun that they "care nothing for using the ploughshare, but they live upon flesh and an abundance of milk."

"While Roman authors considered them incomprehensibly uncivilised and barely human, it seems many of citizens at the edge of Rome's empire were drawn to the Hun lifestyle, just as some nomads took to a more settled way of life," says Hakenbeck.

However, there is one account that hints at the appeal of the Hun, that of Roman politician Priscus. While on a diplomatic mission to the court of Attila, he describes encountering a former merchant who had abandoned life in the Empire for that of the Hun enemy as, after war, they "live in inactivity, enjoying what they have got, and not at all, or very little, harassed.


Egyptian ritual images from the Neolithic period






The around 6000-year-old rock engravings can hardly be seen today. They were pecked into the rock with a hard point.
CREDIT
© Photo: David SabelL

Egyptologists at the University of Bonn discovered rock art from the 4th millennium BC during an excavation at a necropolis near Aswan in Egypt. The paintings were engraved into the rock in the form of small dots and depict hunting scenes like those found in shamanic depictions. They may represent a link between the Neolithic period and Ancient Egyptian culture. The discovery earned the scientists the award for one of the current ten most important archeological discoveries in Egypt from the Minister of Antiquities in Cairo.

For more than 100 years, Qubbet el-Hawa (English: hill of wind) has been a magnet for archeology. Over 80 burial mounds have been uncovered on the hill near Aswan in Egypt during countless excavations. The history of this necropolis for the provincial capital Elephantine extends from around 2200 to the 4th century BC. It was an important trading base for Egyptians in Nubia, and their nobles were buried in the burial mounds. Prof. Elmar Edel from the University of Bonn investigated and documented the necropolis from 1959 to 1984. "The majority of the objects in the Egyptian Museum in Bonn come from these field campaigns," reports Prof. Ludwig Morenz, who heads Egyptology at the Bonn alma mater.

A completely new aspect at Qubbet el-Hawa has now been uncovered during an excavation begun at the necropolis in 2015. The team led by Prof. Morenz with Amr El Hawary, Andreas Dorn, Tobias Gutmann, Sarah Konert and David Sabel discovered much older Neolithic rock art from the 4th millennium BC. "Style and iconography provide solid clues when dating these," says the scientist. "It opens up a new archeological dimension". Some of these engravings on the rock wall are clearly Egyptian in terms of iconography and stylistics, while others are clearly pre-Egyptian as regards the presentation method and motif.

The images were pecked into the rock with a hard point and are now barely perceivable due to their considerable age. Only the archeologically precise recording of the traces and the drawing of the outlines revealed the images with noteworthy iconography. The initially confusing-looking arrangement of dots allows three figures to be seen upon closer inspection: a hunter with bow, a dancing man with raised arms and, between them, an African ostrich.

"The archer clearly shows hunting for the large flightless bird, while the man with raised arms can be identified as a hunt dancer," reports Prof. Morenz. The dancer apparently wears a bird mask. The scene is reminiscent of the conceptual world of hunting, masks and shamanism, as known from many parts of the Earth - including of ostrich hunting by what are known as San (bushmen).

Such hunting and dancing scenes are new in Egyptology

"This social practice and the associated complex of ideas have barely been looked at in Egyptology," says Prof. Morenz. Small painted female figures with dancing, raised arms and a bird mask also come from the 4th millennium BC, and some clay masks were discovered a few years ago in the Upper Egyptian Hierakonpolis. These finds show astounding consistency with the rock paintings of Qubbet el-Hawa.

They may represent a link between the ancient Near Eastern and even southern European Neolithic period and Ancient Egyptian culture. "This opens up new horizons for research," says Prof. Morenz. However, the finds need to be investigated more closely. The much older rock art clearly has nothing to do with the necropolis directly and is probably linked to a prehistoric network of trails that also needs to be researched more intensively.

Under the Dead Sea, warnings of dire drought


Nearly 1,000 feet below the bed of the Dead Sea, scientists have found evidence that during past warm periods, the Mideast has suffered drought on scales never recorded by humans -- a possible warning for current times. Thick layers of crystalline salt show that rainfall plummeted to as little as a fifth of modern levels some 120,000 years ago, and again about 10,000 years ago. Today, the region is drying again as climate warms, and scientists say it will get worse. The new findings may cause them to rethink how much worse, in this already thirsty and volatile part of the world.

"All the observations show this region is one of those most affected by modern climate change, and it's predicted to get dryer. What we showed is that even under natural conditions, it can become much drier than predicted by any of our models," said lead author Yael Kiro, a geochemist at Columbia University's Lamont-Doherty Earth Observatory. The findings were just published in an early online edition of the journal Earth and Planetary Science Letters.

The landlocked Dead Sea, straddling Israel, Jordan and Palestinian lands, is earth's lowest spot on land. Its current shoreline lies about 1,300 feet below sea level, and its floor extends down another 900 feet. Fed mainly by the Jordan River drainage, which extends also into Syria and Lebanon, it is a dead end for water, and so is extremely salty; its Biblical name in Hebrew is Yām ha-Melah, the sea of salt. In recent years, its level has dropped about four feet a year. But hot, dry weather is not the main cause yet; rather, booming populations in the region need more water than ever, and people are sucking so much from the watershed, very little reaches the Dead Sea, where evaporation is outweighing input.

The U.N. Food and Agriculture Organization estimates that much of the region already has per capita water availability only a tenth of the world average. Rainfall has declined about 10 percent since 1950, and existing climate models say it could sink another 20 percent this century, even as population continues to grow. Israel is meeting demand by desalinating Mediterranean seawater, but poorer, landlocked Jordan and the Palestinian territories are desperate for more. In adjoining Syria, a record 1998-2012 drought likely stoked by climate change is believed to have helped spark the ongoing civil war, which has now claimed more than 500,000 lives and infected neighboring nations.

In 2010, scientists from a half-dozen nations drilled 1,500 feet into the deepest part of the seabed, bringing up a cross section of deposits recording 200,000 years of regional climate history--the longest such archive in the Mideast. (Around-the-clock drilling went for 40 days and 40 nights -- perhaps a respectful bow to the rainfall of the Biblical Flood.) The cores revealed alternating layers of mud washed in with runoff during wet times, and crystallized salt, precipitated out during dry times when the water receded. This instantly made it clear that the region has suffered epic dry periods, but the core was not analyzed in great detail until now.

The new study shows that the salt accumulated rapidly?an estimated half-inch per year in many cases. The researchers spotted two striking periods. About halfway down they found salty layers some 300 feet thick, indicating a long-term drop below the sea's current level. This came in a period between ice ages, 115,000 to 130,000 years ago, when variations in Earth's orbit brought temperatures about 4 degrees hotter those of the 20th century?equivalent to what is projected for the end of the 21st century. The lake refilled when glaciers readvanced in sub-polar regions and the Mideast climate cooled and became moister. The cores show a similar drop in lake level just 6,000 to 10,000 years ago, following the most recent ice age, when temperatures were probably a bit cooler than now.

The chemistry of tiny fluid bubbles within the salt allowed the researchers to extrapolate rainfall and runoff patterns of these periods. They calculated that runoff to the Dead Sea generally declined 50 to 70 percent compared to today, dwarfing current projections for this century. In the most extreme periods, it went down 80 percent, and this lasted for decades to centuries at a time. The declines are probably linked to broader shifts in atmospheric flow patterns. Storms coming in from the Mediterranean could have slackened, as they appear to be doing today; and then as now, higher temperatures increase evaporation of moisture from the land.

To alleviate growing water shortages, Jordan plans to break ground next year on a canal to bring in water from the Red Sea for desalination; leftover brine would be dumped into the Dead Sea, possibly stabilizing its level. But the project is controversial, because it could cause drastic environmental changes in both seas, and could still leave much of the rest of the region with inadequate water.

"The Dead Sea is wasting away today because humans are using up all its fresh water sources," said Steven Goldstein, a geochemist at Lamont-Doherty and coauthor of the paper who helped oversee the 2010 drilling. "Our study shows that in the past, without any human intervention, the fresh water nearly stopped flowing. This means that if it keeps getting hotter now, it could stop running again. This time, it would affect millions of people."



Tuesday, March 21, 2017

Agriculture, dietary changes, and adaptations in fat metabolism from ancient to modern Europeans


Good vs bad cholesterol. Margarine vs butter. Red meat vs. vegan. The causal links between fats and health have been a hotly debated topic for scientists, physicians and the public.

Now, evolutionary biologists are weighing in based on the increasing power of DNA analyses to explore how changes in diet over eons have caused human adaptations to genes regulating fat metabolism.

Nestled on the long arm of chromosome 11, two essential genes serve as key traffic police in the synthesis of vital fatty acids. These genes, called fatty acid desaturase 1 and 2 (FADS1 and 2), change dietary fat into components necessary for the heart, brain and muscle. They assist in the conversion of short-chain omega-3 and omega-6 poly-unsaturated fatty acids (PUFAs) to long-chain PUFAs.

Scientists have recently shown that FADS genes are frequent targets of natural selection in humans. Before modern humans moved out of Africa, roughly 85,000 years ago, natural selection targeted variants in these genes presumably associated with changes in diet. After people moved out of Africa and encountered new environments, selection again targeted the FADS genes for humans to better adapt to local conditions. Previous studies have argued that the Inuit in Greenland have adapted to a diet rich in fatty acid from animal sources, and that some groups in India have adapted to a more vegetarian diet, through changes in the DNA in the FADS genes.

"The FADS genes seem to have been frequent targets of natural selection throughout human history as our diet has been changing as a consequence of new hunting or agricultural practices," says Rasmus Nielsen, a professor of Integrative Biology at UC Berkeley, and co-author of a new study on selection on FADS genes in Europe.

In the new study, Nielsen and his colleagues examine data from 101 Bronze Age individuals and present-day human data from the 1000 Genomes Project. Nielsen's research team analyzed adaptive mutations in the FADS region in Europeans, to determine which mutations might have been targeted by recent natural selection in Europeans and to investigate the physiological effects of the mutations.
They found that certain single DNA mutations (SNPs) have been targeted by selection in Europeans since the Bronze Age, and likely before that as well, to increase the production of the long-chain PUFAs: arachidonic and eicosapentaenoic acid.

This pattern mirrors the one observed in some Indian populations but is exactly opposite of that observed in the Greenlandic Inuit. Individuals on a more vegetarian diet ingest more short-chain PUFAs, while individuals having a high intake of animal fat ingest more long-chain PUFAs. The need for additional production of these PUFAs, therefore, depends on the dietary intake. As Inuit switched to a diet based on marine mammals, they would need to produce fewer long-chain PUFAs, but when people in India switched to a more vegetarian diet they would need to increase the production.

"We hypothesize that Europeans may be in the process of adapting to a diet rich in fatty acids derived from plant sources, but relatively poor in fatty acids derived from fish or mammals," said Nielsen. "The introduction and spread of agriculture in Europe likely produced a radical dietary shift in populations that embraced this practice. Agricultural diets would have led to a higher consumption of grains and other plant-derived foods, relative to hunter-gatherer populations. Alleles that increase the production long-chain PUFAs would, therefore, have been favored."

They also compared their mutational data to data from previous studies aimed at finding connections between genetic variants and factors influencing human health, including the Global Lipids Genetics Consortium of almost 200,000 Europeans. The mutations favored in Europeans are strongly associated with several health-related traits, such as cholesterol levels. Furthermore, they found an interaction between dietary intake of PUFAs and the advantageous genetic variants on cholesterol levels, suggesting that the advantageous variant may have a protective effect.

"Clearly, these genetic variants are very important for our understanding of the effects of a high intake of omega-3 and other of PUFAs," said Matthew Buckley, the lead author of the study and an undergraduate student at UC Berkeley at the time the study was done. "It is possible that variants in the FADS region may underlie individual differences in optimal dietary fatty acid profiles. If so, the FADS region variants might help guide the development of individualized diets informed by genomics. However, more epidemiological studies are needed to identify possible interactions between genetic variants in the FADS region and diet, before specific dietary recommendations can be made," warns Buckley.

Nielsen and his colleagues also compared the DNA in the FADS region to that found in the archaic genomes of Neanderthals and Denisovans, and found that the genetic variability in humans dates to a time from before humans split up from Denisovans and Neanderthals, "However, we don't see the pattern expected if the genetic variants were transferred by interbreeding from either of the groups, as has been observed in some other cases. It is possible that natural selection has been acting a very long time, in ways we don't quite understand, to maintain these old genetic variants in the population," said Fernando Racimo, a former Ph.D. student at UC Berkeley, now a researcher at the New York Genome Center.


Thursday, March 9, 2017

Discovery of widespread platinum may help solve Clovis people mystery


No one knows for certain why the Clovis people and iconic beasts -- mastodon, mammoth and saber-toothed tiger - living some 12,800 years ago suddenly disappeared. However, a discovery of widespread platinum at archaeological sites across the United States by three University of South Carolina archaeologists has provided an important clue in solving this enduring mystery.

The research findings are outlined in a new study released Thursday (March 9) in Scientific Reports, a publication of Nature. The study, authored by 10 researchers, builds on similar findings of platinum - an element associated with cosmic objects like asteroids or comets - found by Harvard University researchers in an ice-core from Greenland in 2013.

The South Carolina researchers found an abundance of platinum in soil layers that coincided with the "Younger-Dryas," a climatic period of extreme cooling that began around 12,800 ago and lasted about 1,400 years. While the brief return to ice-age conditions during the Younger-Dryas has been well-documented by scientists, the reasons for it and the demise of the Clovis people and animals have remained unclear.

"Platinum is very rare in the Earth's crust, but it is common in asteroids and comets," says Christopher Moore, the study's lead author. He calls the presence of platinum found in the soil layers at 11 archaeological sites in California, Arizona, New Mexico, Ohio, Virginia, North Carolina and South Carolina an anomaly.

"The presence of elevated platinum in archaeological sites is a confirmation of data previously reported for the Younger-Dryas onset several years ago in a Greenland ice-core. The authors for that study concluded that the most likely source of such platinum enrichment was from the impact of an extraterrestrial object," Moore says.

"Our data show that this anomaly is present in sediments from U.S. archaeological sites that date to the start of the Younger-Dryas event. It is continental in scale -- possibly global -- and it's consistent with the hypothesis that an extraterrestrial impact took place."

He says the Younger-Dryas coincides with the end of Clovis culture and the extinction of more than 35 species of ice-age animals. Moore says while evidence has shown that some of the animals were on the decline before Younger-Dryas, virtually none are found after it. 

Moore says that would indicate an extinction event for North America.

He also says the platinum anomaly is similar to the well-documented finding of iridium, another element associated with cosmic objects, that scientists have found in the rock layers dated 65 million years ago from an impact that caused dinosaur extinction. That event is commonly known as Cretaceous-Tertiary or K-Pg by scientists.

"In both cases, the anomalies represent the atmospheric fallout of rare elements resulting from an extraterrestrial impact," Moore says.

He says the K-Pg dinosaur extinction was the result of a very large asteroid impact while the Younger-Dryas onset impact is likely the result of being hit by fragments of a much smaller sized comet or asteroid, possibly measuring up to two-thirds a mile in diameter. 

"Another difference is that the Younger-Dryas impact event is not yet associated with any known impact crater," Moore says. "This may be because the fragments of the large object struck the glacial ice-sheet or exploded in the atmosphere. Several candidate craters are under investigation but have not been confirmed."

Moore says while his team's data does not contradict the Young-Dryas impact hypothesis, it also does not explain the likely effects that such an impact could have had on the environment, Paleoindians or ice-age animals.

Contributing to the study is Moore's university colleagues Mark Brooks, a geo-archaeologist who conducts research and excavations at the Savannah River Site, and archaeologist Albert Goodyear, who has spent decades documenting Clovis culture at the famed Topper site. Topper, located in Allendale County, South Carolina, along the banks of the Savannah River, is considered one of the most pristine U.S. sites for research on Clovis, one of the earliest ancient people.

Goodyear's work with Moore builds on research in which he found traces of extraterrestrial elements, including iridium, at the Younger-Dryas layer at Topper that was published in the Proceedings of the National Academy of Sciences in 2012.

Moore, Goodyear and Brooks conduct research through the South Carolina Institute of Anthropology and Archaeology in the university's College of Arts and Sciences.

In addition to Topper, the remaining 10 archaeological sites that Moore, Goodyear and others on their team conducted research in 2016 included Arlington Canyon on Santa Rosa Island, California; Murray Springs, Arizona; Blackwater Draw, New Mexico; Sheriden Cave, Ohio; Squires Ridge and Barber Creek, North Carolina; and Kolb, Flamingo Bay, John Bay and Pen Point, South Carolina.

Moore says the bottom line of the study and paper in the journal Scientific Reports is the presence of an easily identifiable hemispheric marker (platinum) in sediment layers for the start of Younger-Dryas. That discovery contributes to the body of evidence that a potential cosmic impact event occurred and warrants further scientific investigation.


Wednesday, March 8, 2017

Silk Road structured by ecological strategies of nomadic herders


Nearly 5,000 years ago, long before the vast east-west trade routes of the Great Silk Road were traversed by Marco Polo, the foundations for these trans-Asian interaction networks were being carved by nomads moving herds to lush mountain pastures, suggests new research from Washington University in St. Louis.

"Our model shows that long-term strategies of mobility by highland nomadic herders structured enduring routes for seasonal migrations to summer pastures, which correspond significantly with the evolving geography of 'Silk Road' interaction across Asia's mountains," said Michael Frachetti, lead author of the study and an associate professor of anthropology in Arts & Sciences at Washington University.

The study, forthcoming in the journal Nature, combines satellite analysis, human geography, archaeology and Geographic Information Systems (GIS) to show that 75 percent of ancient Silk Road sites across highland Inner Asia fall along the paths its model simulates as optimal for moving herds to and from prime mountain meadows.

The model's innovative approach of tracing pasture-driven pathways suggests a number of alternate routes to many known Silk Road sites. It also provides a high-resolution mapping of other possibly important Silk Road routes that are previously unidentified and little researched, including an unexplored corridor into the Tibetan Plateau to the south of Dunhuang, China.

For over a century, the Silk Road -- a term coined in 1877 by German explorer Baron von Richthofen -- has intrigued modern historians and archaeologists who wish to understand the emergence of what many consider the world's most complex ancient overland trade system.

"The locations of ancient cities, towns, shrines and caravan stops have long illustrated key points of interaction along this vast network, but defining its many routes has been far more elusive," Frachetti said. "As a result, there is little known of the detailed pathways used for millennia by merchants, monks and pilgrims to navigate and interact across the highlands of Inner Asia."

Scholars have previously traced Silk Road trade corridors by modeling the shortest "least-cost" paths between major settlements and trade hubs. This connect-the-dots approach makes sense in lowland areas where direct routes across arid plains and open deserts correlate with ease of travel between trade centers. But it's not the way highland pastoralists traditionally move in rugged mountain regions, Frachetti argues.

"The routes of Silk Road interaction were never static, and certainly not in the mountains," Frachetti said. "Caravans traversing Asia were oriented by diverse factors, yet in the mountains their routes likely grew out of historically ingrained pathways of nomads, who were knowledgeable and strategic in mountain mobility."

Though Inner Asia's massive mountains separated oasis societies living in hot, arid lowlands, the region's mountain nomads were united by a shared ecological challenge: hot summers that left lowland pastures parched and barren. In response, mobile pastoralists evolved a similar strategy for success across the entire mountain corridor: escaping the grass-withering summer heat by driving flocks to higher elevations, Frachetti contends.

"Archaeology documents the development of mountain-herding economies in highland Asia as early as 3000 B.C., and we argue that centuries of ecologically strategic mobility on the part of these herders etched the foundational routes and geography of ancient trans-Asian trade networks," Frachetti said.

To test this theory, Frachetti and colleagues designed a model that simulates highland herding mobility as "flows" directed by seasonally available meadows. Although the model is generated without using Silk Road sites in its calculations, the pathways it projects show remarkable geographic overlap with known Silk Road locations compiled independently by Tim Williams, a leading Silk Road scholar at the Institute of Archaeology, University College London.

"The development of the Silk Roads through lowland deserts, fertile piedmonts and oases was influenced by many factors. However, the overlay of pasture-driven routes and known Silk Road sites indicate that the highland Silk Roads networks (750 m to 4,000 m) emerged in relation to long-established seasonal mobility patterns used by nomadic herders in the mountains of Inner Asia" said Williams, a co-author of this study. Williams also is author of the International Council on Monuments and Sites (ICOMOS) thematic study of the Silk Roads, which underpinned the UNESCO World Heritage serial transnational nominations.

Frachetti, who directs the Spatial Analysis, Interpretation, and Exploration (SAIE) laboratory at Washington University, has studied nomadic herding cultures and their ancient trade networks around the world. He has led excavations at sites in Uzbekistan, Kazakhstan and other Central Asian countries.

His field work documents that these societies had inter-continental connections spanning thousands of years, a phenomenon he traces to the antiquity of cross-valley pathways that, once engrained, formed the grassroots network that became the Silk Road.

Proving that theory is challenging because the Silk Road's central corridor runs through some of Inner Asia's most remote mountain ranges: the Hindu Kush in Northern Afghanistan; the Pamir in Tajikistan; the Dzhungar in Kazakhstan; the Tian Shan in Kyrgyzstan, Kazakhstan and Xinjiang (China); and the Altai Mountains in Kazakhstan, Russia and Mongolia.

His approach relies on the creative application of GIS and Remote Sensing tools normally used to simulate the flow of streams, rivers and other drainage through watersheds. In hydrological applications, "flow accumulation" relies on the known properties of water being pulled to lower elevations by gravity, generating calculations that show how runoff feeds into a network of ever-larger streams and rivers.

Frachetti swaps gravity for grass and uses the flow accumulation algorithm to calculate how the quality of lush pasture might channel flows of seasonally nomadic herders across a massive, 4,000-kilometer-wide cross-section of Asia's mountainous corridor.

The study area, which spans portions of Iran, India, Russia, Mongolia and China, was divided into a grid of one-kilometer cells, each of which received a numerical rating for grass productivity based on the reflectance of vegetation detected in multi-spectral satellite imagery. GIS software was used to calculate paths highland herders likely followed as pursuit of best-available grazing pulled them toward lowland settlements. The most likely routes were defined as those with the greatest cumulative flow over top pastures.

As Frachetti has found in earlier research, nomads do not wander aimlessly. Pastoralist movement through the mountains is rooted in local knowledge of the landscape and is guided by ecological factors, like the seasonal productivity of grassy meadows. Most confine their migrations to a small regular orbit that is closely repeated from year to year.

His flow model accommodates variation through time in the scale and distribution of prime highland grasslands, but suggests that the broad geography of mountain pasture has not changed drastically over the past several thousand years. Routes oriented for the best grazing would be well known to nomads making similar seasonal migrations over many generations.

Varying the simulated mobility model over 500 iterations (the rough equivalent of 20 generations), well-defined, grass-driven mobility patterns emerged. When the route-building process is shown dynamically, small pasture-based paths appear as rivulets and streams that converge over zones of rich pasture to form rivers of nomadic mobility.

While the study provides broad support for Frachetti's theories about the early evolution of the Silk Road, it also provides a roadmap for future research aimed at uncovering ancient structures of social participation across the mountains of Central Asia.

It also offers lessons, he suggests, about the importance of participation and connectivity in overcoming the great challenges that continue to confront civilizations.

"This model demonstrates that these rugged mountains were not huge barriers that forced regional communities into isolation, but acted as channels for economic and political forms of participation that supported long-standing connections between neighboring communities," Frachetti said. "It illustrates that civilization's greatest accomplishments -- evidenced in the amazing scale of Silk Road connectivity -- often arise organically in environments where connectivity is the norm; isolation here would be a formula for disaster."


Dental plaque DNA shows Neandertals used 'aspirin'


Ancient DNA found in the dental plaque of Neandertals - our nearest extinct relative - has provided remarkable new insights into their behaviour, diet and evolutionary history, including their use of plant-based medicine to treat pain and illness.

Published today in the journal Nature, an international team led by the University of Adelaide's Australian Centre for Ancient DNA (ACAD) and Dental School, with the University of Liverpool in the UK, revealed the complexity of Neandertal behaviour, including dietary differences between Neandertal groups and knowledge of medication.

"Dental plaque traps microorganisms that lived in the mouth and pathogens found in the respiratory and gastrointestinal tract, as well as bits of food stuck in the teeth - preserving the DNA for thousands of years," says lead author Dr Laura Weyrich, ARC Discovery Early Career Research Fellow with ACAD.

"Genetic analysis of that DNA 'locked-up' in plaque, represents a unique window into Neandertal lifestyle - revealing new details of what they ate, what their health was like and how the environment impacted their behaviour."

The international team analysed and compared dental plaque samples from four Neandertals found at the cave sites of Spy in Belgium and El Sidrón in Spain. These four samples range from 42,000 to around 50,000 years old and are the oldest dental plaque ever to be genetically analysed.

"We found that the Neandertals from Spy Cave consumed woolly rhinoceros and European wild sheep, supplemented with wild mushrooms," says Professor Alan Cooper, Director of ACAD. "Those from El Sidrón Cave on the other hand showed no evidence for meat consumption, but appeared instead to have a largely vegetarian diet, comprising pine nuts, moss, mushrooms and tree bark - showing quite different lifestyles between the two groups."

"One of the most surprising finds, however, was in a Neandertal from El Sidrón, who suffered from a dental abscess visible on the jawbone. The plaque showed that he also had an intestinal parasite that causes acute diarrhoea, so clearly he was quite sick. He was eating poplar, which contains the pain killer salicylic acid (the active ingredient of aspirin), and we could also detect a natural antibiotic mould (Penicillium) not seen in the other specimens."

"Apparently, Neandertals possessed a good knowledge of medicinal plants and their various anti-inflammatory and pain-relieving properties, and seem to be self-medicating. The use of antibiotics would be very surprising, as this is more than 40,000 years before we developed penicillin. Certainly our findings contrast markedly with the rather simplistic view of our ancient relatives in popular imagination."

Neandertals, ancient and modern humans also shared several disease-causing microbes, including the bacteria that cause dental caries and gum disease. The Neandertal plaque allowed reconstruction of the oldest microbial genome yet sequenced - Methanobrevibacter oralis, a commensal that can be associated with gum disease. Remarkably, the genome sequence suggests Neandertals and humans were swapping pathogens as recently as 180,000 years ago, long after the divergence of the two species.

The team also noted how rapidly the oral microbial community has altered in recent history. The composition of the oral bacterial population in Neandertals and both ancient and modern humans correlated closely with the amount of meat in the diet, with the Spanish Neandertals grouping with chimpanzees and our forager ancestors in Africa. In contrast, the Belgian Neandertal bacteria were similar to early hunter gatherers, and quite close to modern humans and early farmers.

"Not only can we now access direct evidence of what our ancestors were eating, but differences in diet and lifestyle also seem to be reflected in the commensal bacteria that lived in the mouths of both Neandertals and modern humans," says Professor Keith Dobney, from the University of Liverpool.

"Major changes in what we eat have, however, significantly altered the balance of these microbial communities over thousands of years, which in turn continue to have fundamental consequences for our own health and well-being. This extraordinary window on the past is providing us with new ways to explore and understand our evolutionary history through the microorganisms that lived in us and with us."