Wednesday, February 15, 2017

Looking at Sardinian DNA for genetic clues to an island's -- and Europe's -- past


Sardinia sits at a crossroads in the Mediterranean Sea, the second largest island next to Sicily. Surrounded by sparkling turquoise waters, this Mediterranean jewel lies northwest of the toe of the Italian peninsula boot, about 350 kilometers due west of Rome. 
For evolutionary biologists, islands are often intriguing, geographically isolated pockets with unique populations that can be ripe for exploration. 
Now, in a new study appearing in the advanced online edition of Molecular Biology and Evolution an international team led by geneticist Anna Olivieri from the University of Pavia tackles a highly interesting question: what were the origins of the Sardinian population in the context of European prehistory and ancient human migrations? 
The authors analyzed 3,491 modern, whole mitochondrial DNA genomes from Sardinia (which are only passed down maternally). These were compared with 21 samples of ancient mitogenomes from the island, a large panel of non-Sardinian mitogenomes ---and even Ötzi (the nickname of Europe's oldest natural mummy, the 3,300 BCE-year old "Tyrolean Iceman") ---to better understand their origins. 
Their findings show Sardinia as an outlier in the general European genetic landscape. Almost 80 percent of modern Sardinian mitogenomes belong to branches that cannot be found anywhere else outside the island. Thus, they were defined as Sardinian-Specific Haplogroups (SSHs) that most likely arose in the island after its initial occupation. Almost all SSHs coalesce in the post-Nuragic, Nuragic and Neolithic-Copper Age periods. However, some rare SSHs display age estimates older than 7,800 years ago, the postulated archeologically-based starting time of the Neolithic in Sardinia. 
"Our analyses raise the possibility that several SSHs may have already been present on the island prior to the Neolithic," said prof. Francesco Cucca, from the Institute of Genetic and Biomedical Research (IRGB), at the CNR in Cagliari (Sardinia). 
The most plausible candidates would include haplogroups K1a2d and U5b1i1, which together comprise almost 3 percent of modern Sardinians, and possibly others. Such a scenario would not only support archaeological evidence of a Mesolithic occupation of Sardinia, but could also suggest a dual ancestral origin of its first inhabitants. K1a2d is of Late Paleolithic Near Eastern ancestry, whereas U5b1i1 harbours deep ancestral roots in Paleolithic Western Europe.
This work provides evidence that contemporary Sardinians harbour a unique genetic heritage, as a result of their distinct history and relative isolation from the demographic upheavals of continental Europe. Anna Olivieri stresses: "It now seems plausible that human mobility, inter-communication and gene flow around the Mediterranean from Late Glacial times onwards may well have left signatures that survive to this day. Some of these signals are still retained in modern Sardinians." 
"Although in the past the stress has often been on the spread of the Neolithic, genetic studies too are beginning to emphasize the complexity and mosaic nature of human ancestry in the Mediterranean, and indeed in Europe more widely," concludes prof. Antonio Torroni, from the University of Pavia. "Future work on ancient DNA should be able to test directly to what extent this more complex model is supported by genetic evidence, and whether our predictions of Mesolithic ancestry in contemporary Sardinians can be sustained."

Tuesday, February 14, 2017

Corn cultivation and nderstanding how and why Cahokia arose


A new study contradicts decades of thought, research and teaching on the history of corn cultivation in the American Bottom, a floodplain of the Mississippi River in Illinois. The study refutes the notion that Indian corn, or maize, was cultivated in this region hundreds of years before its widespread adoption at about 1000 A.D.

The findings, reported in the journal American Antiquity, are important in understanding how and why Cahokia, the first major metropolitan center in North America, arose, said Thomas Emerson, the director of the Illinois State Archaeological Survey at the University of Illinois, where the new study was conducted.

Cahokia was a vast, highly organized settlement with tens of thousands of inhabitants in its heyday, Emerson said. Its dramatic rise near present-day St. Louis and East St. Louis, Illinois, at about A.D. 950 and its sudden demise by 1350 have long been a source of fascination.

There is broad agreement that corn was cultivated in this region at about 1000 and widely consumed by the people of this time period, Emerson said. Corn fragments, including cobs and kernels, show up in sites dating to 1000 or later. Skeletal analyses from bodies buried at Cahokia also reveal the devastating impact of corn on people's teeth. These signs, as well as chemical signatures of corn consumption in the teeth and bone, also date to 1000 and after, he said.

The new findings challenge earlier reports that maize was cultivated and consumed in the American Bottom as early as 60 years B.C.

The early conclusions - in studies conducted before 2000 - were based on flawed approaches to analyzing ancient materials, said Mary Simon, an archaeobotanist with ISAS who conducted the new study. Rather than dating charred plant fragments directly, researchers analyzed charcoal or other "associated materials" to determine the age of the plants, she said.

"We have since learned that a piece of charcoal or other material found adjacent to a corn kernel in an archaeological site could date to a later or earlier time period than the corn," Simon said. Also, visual identifications can be wrong, she said.

Scientists now date plant fragments directly using accelerated mass spectrometry, a technology that was just "coming into vogue in the 1990s" and used at that time to determine the age of materials, Simon said.

Today, stable isotope mass spectrometry can be used in conjunction with AMS to detect differences between plant types, information that aids in plant identification, she said. Corn and other grasses absorb atmospheric carbon differently than other plants. This is reflected in the ratio of carbon isotopes - carbon atoms with differing masses - in plant tissues, Simon said.

"The beauty of this procedure is not only do you get an absolute date, you also get that carbon isotope ratio, so you know, first, how old it is, and, second, whether or not it's corn," she said.

In the new study, Simon revisited botanical samples from Holding, an archaeological site in western Illinois that was occupied from about 150 B.C. to A.D. 300. Simon was among those who mistakenly identified plant fragments from this site as very early corn, and later AMS data confirmed its age. Those findings were published by a group of archaeologists in 1994, and were widely recognized as being the oldest directly dated corn in the eastern United States.

The new analysis, of remaining botanical samples from the Holding site, used both AMS and SIMS and found that the samples that looked like corn either were not corn or dated to A.D. 900 or later, Simon said. Researchers at Arizona State University found samples from the original study and also tested those for carbon isotope ratios. Their results confirmed that although it was old, the material dated in 1994 was not, in fact, corn.

"Basically, what we found is that myths of early corn in the central Mississippi River Valley are simply inaccurate. They've been disproved. We no longer believe that corn was at all important, that people were growing corn, that anybody was using corn to any extent at A.D. zero," Simon said. The two new studies suggest that corn was not in widespread use until 900 or later, she said.

"You can never say it wasn't present here before then," she said. "For example, there was Wyoming obsidian here at A.D. 60, so it's totally possible that a cob of corn made it here from the southwestern U.S. at an earlier date. But, until it was cultivated here, it doesn't really count."


Ancient jars found in Judea reveal earth's magnetic field is fluctuating, not diminishing



Albert Einstein considered the origin of the Earth's magnetic field one of the five most important unsolved problems in physics. The weakening of the geomagnetic field, which extends from the planet's core into outer space and was first recorded 180 years ago, has raised concern by some for the welfare of the biosphere.

But a new study published in PNAS from Tel Aviv University, Hebrew University of Jerusalem, and University of California San Diego researchers finds there is no reason for alarm: The Earth's geomagnetic field has been undulating for thousands of years. Data obtained from the analysis of well-dated Judean jar handles provide information on changes in the strength of the geomagnetic field between the 8th and 2nd centuries BCE, indicating a fluctuating field that peaked during the 8th century BCE.

"The field strength of the 8th century BCE corroborates previous observations of our group, first published in 2009, of an unusually strong field in the early Iron Age. We call it the 'Iron Age Spike,' and it is the strongest field recorded in the last 100,000 years," says Dr. Erez Ben-Yosef of TAU's Institute of Archaeology, the study's lead investigator. "This new finding puts the recent decline in the field's strength into context. Apparently, this is not a unique phenomenon -- the field has often weakened and recovered over the last millennia."

Delving into the inner structure of the planet

"We can gain a clearer picture of the planet and its inner structure by better understanding proxies like the magnetic field, which reaches more than 1,800 miles deep into the liquid part of the Earth's outer core," Dr. Ben-Yosef observes.

The new research is based on a set of 67 ancient, heat-impacted Judean ceramic storage jar handles, which bear royal stamp impressions from the 8th to 2nd century BCE, providing accurate age estimates.

"The period spanned by the jars allowed us to procure data on the Earth's magnetic field during that time -- the Iron Age through the Hellenistic Period in Judea," says Dr. Ben-Yosef. "The typology of the stamp impressions, which correspond to changes in the political entities ruling this area, provides excellent age estimates for the firing of these artifacts."

To accurately measure the geomagnetic intensity, the researchers conducted experiments at the Paleomagnetic Laboratory of Scripps Institution of Oceanography (SIO), University of California San Diego, using laboratory-built paleomagnetic ovens and a superconducting magnetometer.

"Ceramics, baked clay, burned mud bricks, copper slag -- almost anything that was heated and then cooled can become a recorder of the components of the magnetic field at the time of the event," said Dr. Ben-Yosef. "Ceramics have tiny minerals -- magnetic 'recorders' -- that save information about the magnetic field of the time the clay was in the kiln. The behavior of the magnetic field in the past can be studied by examining archaeological artifacts or geological material that were heated then cooled, such as lava."

Advanced dating method

Observed changes in the geomagnetic field can, in turn, be used as an advanced dating method complementary to the radiocarbon dating, according to Dr. Ben-Yosef. "The improved Levantine archaeomagnetic record can be used to date pottery and other heat-impacted archaeological materials whose date is unknown.

"Both archaeologists and Earth scientists benefit from this. The new data can improve geophysical models -- core-mantle interactions, cosmogenic processes and more -- as well as provide an excellent, accurate dating reference for archaeological artefacts," says Dr. Ben-Yosef.

The researchers are currently working on enhancing the archaeomagnetic database for the Levant, one of the most archaeologically-rich regions on the planet, to better understand the geomagnetic field and establish a robust dating reference.


Wednesday, February 8, 2017

Archaeologists find 12th Dead Sea Scrolls cave



Excavations in a cave on the cliffs west of Qumran, near the northwestern shore of the Dead Sea, prove that Dead Sea scrolls from the Second Temple period were hidden in the cave, and were looted by Bedouins in the middle of the last century. With the discovery of this cave, scholars now suggest that it should be numbered as Cave 12.


A piece of parchment to be processed for writing, found rolled up in a jug, in a cave on the cliffs west of Qumran excavated by Hebrew University archaeologists.
CREDIT
(Photo: Casey L. Olson and Oren Gutfeld)

The surprising discovery, representing a milestone in Dead Sea Scroll research, was made by Dr. Oren Gutfeld and Ahiad Ovadia from the Hebrew University of Jerusalem's Institute of Archaeology, with the collaboration of Dr. Randall Price and students from Liberty University in Virginia, USA.

The excavators are the first in over 60 years to discover a new scroll cave and to properly excavate it.

The excavation was supported by the Civil Administration of Judea and Samaria, by the Israel Nature and Parks Authority, and the Israel Antiquities Authority (IAA), and is a part of the new "Operation Scroll" launched at the IAA by its Director-General, Mr. Israel Hasson, to undertake systematic surveys and to excavate the caves in the Judean Desert.

Excavation of the cave revealed that at one time it contained Dead Sea scrolls. Numerous storage jars and lids from the Second Temple period were found hidden in niches along the walls of the cave and deep inside a long tunnel at its rear. The jars were all broken and their contents removed, and the discovery towards the end of the excavation of a pair of iron pickaxe heads from the 1950s (stored within the tunnel for later use) proves the cave was looted.

Until now, it was believed that only 11 caves had contained scrolls. With the discovery of this cave, scholars have now suggested that it would be numbered as Cave 12. Like Cave 8, in which scroll jars but no scrolls were found, this cave will receive the designation Q12 (the Q=Qumran standing in front of the number to indicate no scrolls were found).

"This exciting excavation is the closest we've come to discovering new Dead Sea scrolls in 60 years. Until now, it was accepted that Dead Sea scrolls were found only in 11 caves at Qumran, but now there is no doubt that this is the 12th cave," said Dr. Oren Gutfeld, an archaeologist at the Hebrew University's Institute of Archaeology and director of the excavation. "Finding this additional scroll cave means we can no longer be certain that the original locations (Caves 1 through 11) assigned to the Dead Sea scrolls that reached the market via the Bedouins are accurate."

Dr. Gutfeld added: "Although at the end of the day no scroll was found, and instead we 'only' found a piece of parchment rolled up in a jug that was being processed for writing, the findings indicate beyond any doubt that the cave contained scrolls that were stolen. The findings include the jars in which the scrolls and their covering were hidden, a leather strap for binding the scroll, a cloth that wrapped the scrolls, tendons and pieces of skin connecting fragments, and more."

The finds from the excavation include not only the storage jars, which held the scrolls, but also fragments of scroll wrappings, a string that tied the scrolls, and a piece of worked leather that was a part of a scroll. The finding of pottery and of numerous flint blades, arrowheads, and a decorated stamp seal made of carnelian, a semi-precious stone, also revealed that this cave was used in the Chalcolithic and the Neolithic periods.

This first excavation to take place in the northern part of the Judean Desert as part of "Operation Scroll" will open the door to further understanding the function of the caves with respect to the scrolls, with the potential of finding new scroll material. The material, when published, will provide important new evidence for scholars of the archaeology of Qumran and the Dead Sea caves.

"The important discovery of another scroll cave attests to the fact that a lot of work remains to be done in the Judean Desert and finds of huge importance are still waiting to be discovered," said Israel Hasson, Director-General of the Israel Antiquities Authority. "We are in a race against time as antiquities thieves steal heritage assets worldwide for financial gain. The State of Israel needs to mobilize and allocate the necessary resources in order to launch a historic operation, together with the public, to carry out a systematic excavation of all the caves of the Judean Desert."


Thursday, February 2, 2017

Baltic hunter-gatherers began farming without influence of migration, ancient DNA suggests


New research indicates that Baltic hunter-gatherers were not swamped by migrations of early agriculturalists from the Middle East, as was the case for the rest of central and western Europe. Instead, these people probably acquired knowledge of farming and ceramics by sharing cultures and ideas -- rather than genes -- with outside communities.

Scientists extracted ancient DNA from a number of archaeological remains discovered in Latvia and the Ukraine, which were between 5,000 and 8,000 years old. These samples spanned the Neolithic period, which was the dawn of agriculture in Europe, when people moved from a mobile hunter-gatherer lifestyle to a settled way of life based on food production.

We know through previous research that large numbers of early farmers from the Levant (the Near East) - driven by the success of their technological innovations such as crops and pottery - had expanded to the peripheral parts of Europe by the end of the Neolithic and largely replaced hunter-gatherer populations.

However, the new study, published today in the journal Current Biology, shows that the Levantine farmers did not contribute to hunter-gatherers in the Baltic as they did in Central and Western Europe.

The research team, which includes scientists from Trinity College Dublin, the University of Cambridge, and University College Dublin, says their findings instead suggest that the Baltic hunter-gatherers learned these skills through communication and cultural exchange with outsiders.

The findings feed into debates around the 'Neolithic package,' -- the cluster of technologies such as domesticated livestock, cultivated cereals and ceramics, which revolutionised human existence across Europe during the late Stone Age.

Advances in ancient DNA work have revealed that this 'package' was spread through Central and Western Europe by migration and interbreeding: the Levant and later Anatolian farmers mixing with and essentially replacing the hunter-gatherers.

But the new work suggests migration was not a 'universal driver' across Europe for this way of life. In the Baltic region, archaeology shows that the technologies of the 'package' did develop -- albeit less rapidly - even though the analyses show that the genetics of these populations remained the same as those of the hunter-gatherers throughout the Neolithic.

Andrea Manica, one of the study's senior authors from the University of Cambridge, said: "Almost all ancient DNA research up to now has suggested that technologies such as agriculture spread through people migrating and settling in new areas."

"However, in the Baltic, we find a very different picture, as there are no genetic traces of the farmers from the Levant and Anatolia who transmitted agriculture across the rest of Europe."

"The findings suggest that indigenous hunter-gatherers adopted Neolithic ways of life through trade and contact, rather than being settled by external communities. Migrations are not the only model for technology acquisition in European prehistory."

While the sequenced genomes showed no trace of the Levant farmer influence, one of the Latvian samples did reveal genetic influence from a different external source -- one that the scientists say could be a migration from the Pontic Steppe in the east. The timing (5-7,000 years ago) fits with previous research estimating the earliest Slavic languages.

Researcher Eppie Jones, from Trinity College Dublin and the University of Cambridge, was the lead author of the study. She said: "There are two major theories on the spread of Indo-European languages, the most widely spoken language family in the world. One is that they came from the Anatolia with the agriculturalists; another that they developed in the Steppes and spread at the start of the Bronze Age."

"That we see no farmer-related genetic input, yet we do find this Steppe-related component, suggests that at least the Balto-Slavic branch of the Indo-European language family originated in the Steppe grasslands of the East, which would bring later migrations of Bronze Age horse riders."

The researchers point out that the time scales seen in Baltic archaeology are also very distinct to the rest of Europe, with a much more drawn-out and piecemeal uptake of Neolithic technologies, rather than the complete 'package' that arrives with migrations to take most of Europe by storm.

Andrea Manica added: "Our evidence of genetic continuity in the Baltic, coupled with the archaeological record showing a prolonged adoption of Neolithic technologies, would suggest the existence of trade networks with farming communities largely independent of interbreeding."

"It seems the hunter-gatherers of the Baltic likely acquired bits of the Neolithic package slowly over time through a 'cultural diffusion' of communication and trade, as there is no sign of the migratory wave that brought farming to the rest of Europe during this time.

"The Baltic hunter-gatherer genome remains remarkably untouched until the great migrations of the Bronze Age sweep in from the East."

About the study

The researchers analysed eight ancient genomes - six from Latvia and two from Ukraine - that spanned a timeframe of three and a half thousand years (between 8,300 and 4,800 years ago). This enabled them to start plotting the genetic history of Baltic inhabitants during the Neolithic.

DNA was extracted from the petrous area of skulls that had been recovered by archaeologists from some of the region's richest Stone Age cemeteries. The petrous, at the base of the skull, is one of the densest bones in the body, and a prime location for DNA that has suffered the least contamination over millennia.


Wednesday, February 1, 2017

Ancient DNA reveals 'continuity' between Stone Age and modern populations in East Asia


Researchers working on ancient DNA extracted from human remains interred almost 8,000 years ago in a cave in the Russian Far East have found that the genetic makeup of certain modern East Asian populations closely resemble that of their hunter-gatherer ancestors.

The study, published today in the journal Science Advances, is the first to obtain nuclear genome data from ancient mainland East Asia and compare the results to modern populations.

The findings indicate that there was no major migratory interruption, or "population turnover", for well over seven millennia. Consequently, some contemporary ethnic groups share a remarkable genetic similarity to Stone Age hunters that once roamed the same region.

The high "genetic continuity" in East Asia is in stark contrast to most of Western Europe, where sustained migrations of early farmers from the Levant overwhelmed hunter-gatherer populations. This was followed by a wave of horse riders from Central Asia during the Bronze Age. These events were likely driven by the success of emerging technologies such as agriculture and metallurgy

The new research shows that, at least for part of East Asia, the story differs - with little genetic disruption in populations since the early Neolithic period.

Despite being separated by a vast expanse of history, this has allowed an exceptional genetic proximity between the Ulchi people of the Amur Basin, near where Russia borders China and North Korea, and the ancient hunter-gatherers laid to rest in a cave close to the Ulchi's native land.

The researchers suggest that the sheer scale of East Asia and dramatic variations in its climate may have prevented the sweeping influence of Neolithic agriculture and the accompanying migrations that replaced hunter-gatherers across much of Europe. They note that the Ulchi retained their hunter-fisher-gatherer lifestyle until recent times.

"Genetically speaking, the populations across northern East Asia have changed very little for around eight millennia," said senior author Andrea Manica from the University of Cambridge, who conducted the work with an international team, including colleagues from Ulsan National Institute of Science and Technology in Korea, and Trinity College Dublin and University College Dublin in Ireland.

"Once we accounted for some local intermingling, the Ulchi and the ancient hunter-gatherers appeared to be almost the same population from a genetic point of view, even though there are thousands of years between them."

The new study also provides further support for the 'dual origin' theory of modern Japanese populations: that they descend from a combination of hunter-gatherers and agriculturalists that eventually brought wet rice farming from southern China. A similar pattern is also found in neighbouring Koreans, who are genetically very close to Japanese.

However, Manica says that much more DNA data from Neolithic China is required to pinpoint the origin of the agriculturalists involved in this mixture.

The team from Trinity College Dublin were responsible for extracting DNA from the remains, which were found in a cave known as Devil's Gate. Situated in a mountainous area close to the far eastern coast of Russia that faces northern Japan, the cave was first excavated by a soviet team in 1973.

Along with hundreds of stone and bone tools, the carbonised wood of a former dwelling, and woven wild grass that is one of the earliest examples of a textile, were the incomplete bodies of five humans.

If ancient DNA can be found in sufficiently preserved remains, sequencing it involves sifting through the contamination of millennia. The best samples for analysis from Devil's Gate were obtained from the skulls of two females: one in her early twenties, the other close to fifty. The site itself dates back over 9,000 years, but the two women are estimated to have died around 7,700 years ago.

Researchers were able to glean the most from the middle-aged woman. Her DNA revealed she likely had brown eyes and thick, straight hair. She almost certainly lacked the ability to tolerate lactose, but was unlikely to have suffered from 'alcohol flush': the skin reaction to alcohol now common across East Asia.

While the Devil's Gate samples show high genetic affinity to the Ulchi, fishermen from the same area who speak the Tungusic language, they are also close to other Tungusic-speaking populations in present day China, such as the Oroqen and Hezhen.

"These are ethnic groups with traditional societies and deep roots across eastern Russia and China, whose culture, language and populations are rapidly dwindling," added lead author Veronika Siska, also from Cambridge.

"Our work suggests that these groups form a strong genetic lineage descending directly from the early Neolithic hunter-gatherers who inhabited the same region thousands of years previously."

Climate change drove population decline in New World before Europeans arrived


What caused the rapid disappearance of a vibrant Native American agrarian culture that lived in urban settlements from the Ohio River Valley to the Mississippi River Valley in the two centuries preceding the European settlement of North America? In a new study, researchers from Indiana University-Purdue University Indianapolis reconstructed and analyzed 2,100 years of temperature and precipitation data -- and point the finger at climate change.

Employing proxies of prehistoric temperature and precipitation preserved in finely layered lake sediments, somewhat analogous to tree-ring records used to reconstruct drought and temperature, the IUPUI scientists have reported on the dramatic environmental changes that occurred as the Native Americans -- known as Mississippians -- flourished and then vanished from the Midwestern United States. The researchers theorize that the catastrophic climate change they observed, which doomed food production, was a primary cause of the disappearance.

"Abrupt climate change can impose conditions like drought. If these conditions are severe and sustained, as we have determined that they became for the Mississippians, it is virtually impossible for societies, especially those based on agriculture, to survive," said paleoclimatologist Broxton Bird, corresponding author of the new study. "From the lake records, we saw that the abundant rainfall and consistent good weather -- which supported Mississippian society as it grew -- changed, making agriculture unsustainable." Bird is an assistant professor of earth sciences in the School of Science at IUPUI.

This failure of their principal food source likely destabilized the sociopolitical system that supported Mississippian society, according to archeologist Jeremy Wilson, a study co-author. He is an associate professor of anthropology in the School of Liberal Arts at IUPUI.

"Archeologists have recognized that from 1300 onward, Mississippian villages started disappearing -- one after the other -- almost like lightbulbs in a string, but the question has always been 'why?,'" said Wilson. "Dr. Bird and his students have shown from the lake-sediment evidence that during the period known as the Little Ice Age, from 1300 to 1800, there was a profound change in climate to colder and drier conditions, which would have negatively impacted the growing of maize in and around Mississippian villages.

"It's important for us to understand how past civilizations coped with climate change as we encounter things like changing precipitation patterns and temperatures that appear to be rising around the world today."

As the Mississippians' culture waned, the IUPUI researchers found, there were lower temperatures and significantly less summer rainfall than during its rise. They attribute these changes to more El Niño-like conditions in the Pacific Ocean and cooling during the Little Ice Age, which altered atmospheric circulation such that moisture delivered to the Midwest was derived from the northwestern U.S. (Pacific and Arctic) instead of the Gulf of Mexico, as was the case during the Mississippians' rise. The longer transport distance of Pacific air masses during the Little Ice Age left less moisture available for rainfall in the Midwest, resulting in drought conditions that undermined agricultural production.

"Climate change had been previously postulated as one of the factors responsible for the disappearance of the Mississippians," Bird said. "What our research did was develop the highest-resolution record yet produced of rainfall in the midcontinental U.S. for the last 2,100 years, including the time frame from the beginning of the Mississippian period -- about 1,000 years ago -- to 500 years ago, when much of the lower Midwest was totally abandoned by these people. Our results strongly support climate change -- drought, specifically -- as a significant cause of the disappearance of Mississippians from the midcontinent through its impact on their ability to farm and produce food surpluses.

"Mississippians did not have irrigation and relied on rainfall to grow their crops. Modern agriculture in the Midwest corn belt likewise relies on rainfall with very little irrigation infrastructure, making us similarly vulnerable to drought," Bird said.

"Midcontinental Native American Population Dynamics and Late Holocene Hydroclimate Extremes" is published in Scientific Reports, an open access, peer-reviewed Nature research journal.
The sediment studied was from Martin Lake in northeast Indiana. Bird and Wilson are continuing their research at additional lakes, especially those adjacent to archeological sites, throughout the midcontinent.