Friday, April 30, 2021

Widespread Amazonian depopulation and reforestation before Europeans' arrival


Research News

Fossil pollen records from across the Amazon basin suggest that depopulation and resulting forest regrowth in Amazonia began centuries before European arrival and did not contribute to the observed decline in atmospheric carbon dioxide during the 17th century, according to a new study. The results offer new insights into the human influence on Amazonian landscapes throughout history. When Europeans first arrived on the shores of South America, brutal waves of disease, warfare, slavery and genocide followed and culminated in a catastrophic loss of life that has come to be known as the "Great Dying of the Indigenous Peoples of the Americas." It's estimated that 90 to 95% of the Indigenous population in Amazonia died after 1492. As a result, many occupied sites were abandoned, including untold acres of previously cultivated land, which resulted in a surge of forest regrowth throughout the Amazon basin. It's thought that this rapid regrowth may have resulted in the marked decline in atmospheric carbon dioxide (CO2) concentration that began in the early 1600s - an anomaly also known as the Orbis spike. Mark Bush and colleagues evaluated fossil pollen records from 39 sites throughout Amazonia that record changes to forest cover over the last 2,000 years. Bush et al.found that during the Great Dying period, the number of sites where forest pollen was increasing was approximately equal to those where it was falling in abundance, "effectively rejecting the hypothesis of widespread and synchronous reforestation sufficient to cause decreases in atmospheric CO2 levels," they write. At many sites, land abandonment and forest regrowth began 300 - 600 years before the arrival of Europeans, the data suggest. While the authors note that the mechanisms driving land abandonment between 950 and 1500 years ago have yet to be identified, they suggest that the cascading effects of environmental change, pre-European pandemics, and/or social strife could have contributed. Nevertheless, Indigenous populations in some areas of Amazonia may have already been declining when Europeans arrived, a decline that was accelerated by the deadly impacts of European contact, write Bush et al.

First Australian populations followed footpath 'superhighways' across the continent


Research News




The best path across the desert is rarely the straightest. For the first human inhabitants of Sahul -- the super-continent that underlies modern Australia and New Guinea -- camping at the next spring, stream, or rock shelter allowed them to thrive for hundreds of generations. Those who successfully traversed the landmarks made their way across the continent, spreading from their landfall in the Northwest across the continent, making their way to all corners of Australia and New Guinea.

By simulating the physiology and decisions of early way-finders, an international team* of archaeologists, geographers, ecologists, and computer scientists has mapped the probable "superhighways" that led to the first peopling of the Australian continent some 50,000-70,000 years ago. Their study, published in Nature Human Behaviour, is the largest reconstruction of a network of human migration paths into a new landscape. It is also the first to apply rigorous computational analysis at the continental scale, testing 125 billion possible pathways.

"We decided it would be really interesting to look at this question of human migration because the ways that we conceptualize a landscape should be relatively steady for a hiker in the 21st century and a person who was way-finding into a new region 70,000 years ago," says archaeologist and computational social scientist Stefani Crabtree, who led the study. Crabtree is a Complexity Fellow at the Santa Fe Institute and Assistant Professor at Utah State University. "If it's a new landscape and we don't have a map, we're going to want to know how to efficiently move throughout a space, where to find water, and where to camp -- and we'll orient ourselves based on high points around the lands."

"One of the really big unanswered questions of prehistory is how Australia was populated in the distant past. Scholars have debated it for at least a hundred and fifty years," says co-author Devin White, an archaeologist and remote sensing scientist at Sandia National Laboratories. "It is the largest and most complex project of its kind that I'd ever been asked to take on."

To re-create the migrations across Sahul, the researchers first needed to simulate the topography of the supercontinent. They "drained" the oceans that now separate mainland Australia from New Guinea and Tasmania. Then, using hydrological and paleo-geographical data, they reconstructed inland lakes, major rivers, promontory rocks, and mountain ranges that would have attracted the gaze of a wandering human.

Next, the researchers programmed in-silico stand-ins for the human travelers. The team adapted an algorithm called "From Everywhere to Everywhere," created by White*, to program the way-finders based on the caloric needs of a 25-year-old female carrying 10 kg of water and tools.

The researchers imbued these individuals with the realistic goal of staying alive, which could be achieved by finding water sources. Like backcountry hikers, the digital travelers were drawn to prominent landmarks like rocks and foothills, and the program exacted a caloric toll for activities such as hiking uphill within the artificial landscape.

When the researchers "landed" the way-finders at two points on the coast of the re-created continent, they began to traverse it, using landmarks to navigate in search of freshwater. The algorithms simulated a staggering 125 billion possible pathways, run on a Sandia supercomputer, and a pattern emerged: the most-frequently traveled routes carved distinct "superhighways" across the continent, forming a notable ring-shaped road around the right portion of Australia; a western road; and roads that transect the continent. A subset of these superhighways map to archaeological sites where early rock art, charcoal, shell, and quartz tools have been found.

"Australia's not only the driest, but it's also the flattest populated continent on Earth," says co-author Sean Ulm, an archaeologist and Distinguished Professor at James Cook University. Ulm is also Deputy Director of the Australian Research Council Centre of Excellence for Australian Biodiversity and Heritage (CABAH), whose researchers contributed to the project. "Our research shows that prominent landscape features and water sources were critical for people to navigate and survive on the continent. In many Aboriginal societies, landscape features are known to have been created by ancestral beings during the Dreaming. Every ridgeline, hill, river, beach and water source is named, storied and inscribed into the very fabric of societies, emphasising the intimate relationship between people and place. The landscape is literally woven into peoples' lives and their histories. It seems that these relationships between people and Country probably date back to the earliest peopling of the continent."

The results suggest that there are fundamental rules humans follow as they move into new landscapes and that the researchers' approach could shed light on other major migrations in human history, such as the first waves of migration out of Africa at least 120,000 years ago.

Future work, Crabtree says, could inform the search for undiscovered archaeological sites, or even apply the techniques to forecast the movements of human migration in the near future, as populations flee drowning coastlines and climate disruptions.

*Co-authors of the study are Stefani Crabtree (Santa Fe Institute, Utah State University, CABAH) who led the project and convened its first working group at the Santa Fe Institute in 2019; Devin White (Sandia National Laboratories) who wrote the primary algorithm used; and members of the Australian Research Council Centre of Excellence for Australian Biodiversity and Heritage (CABAH), who contributed expertise on the Australian landscape and the Aboriginal communities. CABAH members are Crabtree, Sean Ulm (James Cook University), Corey Bradshaw (Flinders University), Frédérick Saltré (Flinders University), Alan Williams (University of New South Wales); Robin Beaman (James Cook University); and Michael Bird (James Cook University), who also co-organized the 2019 working group in Santa Fe.

The Santa Fe Institute is a nonprofit research center located in Santa Fe, New Mexico. Its scientists collaborate across disciplines to understand the complex systems that underlie critical questions for science and humanity. The Institute is supported by philanthropic individuals and foundations, forward-thinking partner companies, and government science agencies.

Sandia National Laboratories is a multimission laboratory operated by National Technology and Engineering Solutions of Sandia LLC, a wholly-owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy's National Nuclear Security Administration. Sandia Labs has major research and development responsibilities in nuclear deterrence, global security, defense, energy technologies and economic competitiveness, with main facilities in Albuquerque, New Mexico, and Livermore, California.

CABAH is an ARC Centre of Excellence that brings together expertise from diverse academic disciplines to answer fundamental questions about the natural and human history of our region, including how and when people first came to Australia.  

Cancer rates in medieval Britain around ten times higher than previously thought, study suggests


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The first study to use x-rays and CT scans to detect evidence of cancer among the skeletal remains of a pre-industrial population suggests that between 9-14% of adults in medieval Britain had the disease at the time of their death.

This puts cancer prevalence in a time before exposure to tumour-inducing chemicals from industry and tobacco at around ten times higher than previously thought, according to researchers.

Prior research into historic cancer rates using the archaeological record has been limited to examining the bone exterior for lesions. It suggested that cancer was rare, affecting less than 1% of the population.

A team led by the University of Cambridge have now coupled visual inspection with radiological imaging to analyse 143 skeletons from six medieval cemeteries in and around the city of Cambridge, UK, dating from the 6th to the 16th century.

The findings of the study are published today in the journal Cancer.

"The majority of cancers form in soft tissue organs long since degraded in medieval remains. Only some cancer spreads to bone, and of these only a few are visible on its surface, so we searched within the bone for signs of malignancy," said lead author Dr Piers Mitchell, who conducted the research as part of the 'After the Plague' project.

"Modern research shows a third to a half of people with soft tissue cancers will find the tumour spreads to their bones. We combined this data with evidence of bone metastasis from our study to estimate cancer rates for medieval Britain."

"We think the total proportion of the medieval population that probably suffered with a cancer somewhere in their body was between nine and fourteen per cent," said Mitchell, from Cambridge University's Department of Archaeology.

"Using CT scans we were able to see cancer lesions hidden inside a bone that looked completely normal on the outside," said study co-author and After the Plague researcher Dr Jenna Dittmar.

"Until now it was thought that the most significant causes of ill health in medieval people were infectious diseases such as dysentery and bubonic plague, along with malnutrition and injuries due to accidents or warfare."

"We now have to add cancer as one of the major classes of disease that afflicted medieval people," Dittmar said.

However, the researchers point out that in modern Britain some 40-50% of people have cancer by the time they die, making the disease 3-4 times more common today than the latest study suggests it was during medieval times.

They say that a variety of factors likely contribute to contemporary rates of the disease, such as the effects of tobacco, which began to be imported into Britain in the 16th century with the colonising of the Americas.

The researchers also point to the cancerous effects of pollutants that have become ubiquitous since the industrial revolution of the 18th century, as well as the possibility that DNA-damaging viruses are now more widespread with long-distance travel. Moreover, our longer lifespans give cancer much more time to develop.

The skeletal remains investigated for the latest study came from sites near three villages in the vicinity of Cambridge, as well as three cemeteries uncovered within the medieval centre of the university city, including the site of a former Augustinian friary, and the site of a former charitable hospital that cared for the sick and destitute (now part of St. John's College).

Very few of the excavated remains were complete, so the team limited themselves to individuals with intact spinal column, pelvis and femora (thigh bones). Modern research shows these to be the bones most likely to contain secondary malignancies - or metastases - in people with cancer.

The remains of 96 men, 46 women, and an individual of unknown sex, had their vertebrae, femurs and pelvis inspected and then imaged using x-rays and CT scans. The team found signs of malignancy in the bones of five individuals - a minimum prevalence of 3.5%. These were mostly in the pelvis, although one middle-aged man had small lesions throughout his skeleton suggesting a form of blood cancer.

Research shows that CT scans detect bone metastases around 75% of the time, and only a third to half of cancer deaths involve spread to the bone, so the team projected that 9-14% of medieval Britons developed cancer.

However, they caution that the sample size is inevitably limited and diagnosing cancer in those lain dead for many centuries is somewhat challenging.

"We need further studies using CT scanning of apparently normal skeletons in different regions and time periods to see how common cancer was in key civilizations of the past," added Mitchell.

Was North America populated by 'stepping stone' migration across Bering Sea?

Research News

LAWRENCE -- For thousands of years during the last ice age, generations of maritime migrants paddled skin boats eastward across shallow ocean waters from Asia to present-day Alaska. They voyaged from island to island and ultimately to shore, surviving on bountiful seaweeds, fish, shellfish, birds and game harvested from coastal and nearshore biomes. Their island-rich route was possible due to a shifting archipelago that stretched almost 900 miles from one continent to the other.

A new study from the University of Kansas in partnership with universities in Bologna and Urbino, Italy, documents the newly named Bering Transitory Archipelago and then points to how, when and where the first Americans may have crossed. The authors' stepping-stones hypothesis depends on scores of islands that emerged during the last ice age as sea level fell when ocean waters were locked in glaciers and later rose when ice sheets melted. The two-part study, just published in the open-access journal Comptes Rendus Geoscience, may answer what writer Fen Montaigne calls "one of the greatest mysteries of our time . . . when humans made the first bold journey to the Americas."

The "stepping-stones" idea hinges on retrospective mapping of sea levels while accounting for isostacy -- deformation of the Earth's crust due to the changing depth and weight of ice and water, reaching its greatest extreme during the Last Glacial Maximum about 20,500 years ago.

"We digitally discovered a geographic feature of considerable size that had never been properly documented in scientific literature," said principal author Jerome Dobson, professor emeritus of geography at KU. "We named it the Bering Transitory Archipelago; it existed from about 30,000 years ago through 8,000 years ago. When we saw it, we immediately thought, 'Wow, maybe that's how the first Americans came across.' And, in fact, everything we've tested seems to bear that out -- it does seem to be true."

For more than a decade, researchers have pondered a mystery within a mystery. Mitochondrial DNA indicates that migrants were isolated somewhere for up to 15,000 years on their way over from Asia to North America. The Beringian Standstill Hypothesis arises from the fact that today Native American DNA is quite different from Asian DNA, a clear indication of genetic drift of such magnitude that it can only have happened over long periods of time in nearly complete isolation from the Asian source population. The Bering Transitory Archipelago provides a suitable refugium with internal connectivity and outward isolation.

Dobson said people crossing the Bering Sea probably didn't have sails but could have been experienced in paddling skin boats like the kayaks and umiaks that Inuits use today.

"They probably traveled in small groups," he said, "either from Asia or islands off the coast of Asia. Some maritime people are known to have existed 27,000 years ago on northern Japanese islands. They probably were maritime people -- not just living on islands, but actually practicing maritime culture, economy and travel."

Dobson recently received the American Geographical Society's Cullum Geographical Medal (the same gold medal that Neil Armstrong won for flying to the moon and Rachel Carson won for writing "Silent Spring"). He named and continuously champions "aquaterra" -- all lands that were exposed and inundated repeatedly during the Late Pleistocene ice ages -- thus creating a zone of archeological promise scattered offshore from all coastal regions around the globe.

Recently, Dobson and co-authors Giorgio Spada of the University of Bologna and Gaia Galassi of Urbino University "Carlo Bo" applied an improved Glacial Isostatic Adjustment model to nine global choke points, meaning isthmuses and straits that have funneled transport and trade throughout history. Significant human migrations are known to have occurred across some of them, including "Beringia"-- all portions of the Bering Sea that were exposed before, during and after the Last Glacial Maximum.

"These Italian ocean scientists read my 'Aquaterra' paper and took it upon themselves to refine the boundaries of aquaterra for the whole world at coarse resolution and for Beringia itself at fine resolution," Dobson said. "Later we agreed to join forces and tackle those nine global choke points. At the end of that study, we suddenly spotted these islands in the Bering Sea, and that became our focus. This had an immediate potential because it could be a real game-changer in terms of all sciences understanding how migration worked in the past. We found startling results in certain other choke points and have begun analyzing them as well."

In Beringia, the three investigators contend, this action produced a "conveyor belt" of islands that rose from the sea and fell back again, pushing bands of people eastward. "The first islands to appear were just off the coast of Siberia," the KU researcher said. "Then islands appeared ever eastward. Most likely migrants kept expanding eastward, too, generally to islands within view and an easy paddle away."

By 10,500 years ago, when the Bering Strait itself first appeared, almost all islands in the west had submerged. Only three islands remained, and paddling distances had increased accordingly. Thus, occupants were forced to evacuate, and they faced a clear choice: return to Asia, which they knew to be populated and may even have left due to population pressures and resource constraints, or paddle east to less known territory, perhaps less populated islands with ample resources.

To fully confirm the idea set forth in the new paper, Dobson said researchers from many fields will need to collaborate as one geographer and two ocean scientists have done here.

"We ourselves are at a stage where we definitely need underwater confirmation," he said. "No doubt underwater archaeologists by title will prevail in that quest, but other disciplines, specialties and fields are essential. Working together plus scouring diverse literature, we presented a fundamentally new physical geography for scientists to contemplate. That should entice every relevant discipline to question conventional theory and explore new ideas regarding how, when and where people came to North America. More broadly, aquaterra can serve as a unifying theme for understanding human migrations, demic expansions, evolutionary biology, culture, settlement and endless other topics."

Discarded ostrich shells provide timeline for our early African ancestors

Uranium-series dating shows South African midden is world's oldest


Research News




Archeologists have learned a lot about our ancestors by rummaging through their garbage piles, which contain evidence of their diet and population levels as the local flora and fauna changed over time.

One common kitchen scrap in Africa -- shells of ostrich eggs -- is now helping unscramble the mystery of when these changes took place, providing a timeline for some of the earliest Homo sapiens who settled down to utilize marine food resources along the South African coast more than 100,000 years ago.

Geochronologists at the University of California, Berkeley, and the Berkeley Geochronology Center (BGC) have developed a technique that uses these ubiquitous discards to precisely date garbage dumps -- politely called middens -- that are too old to be dated by radiocarbon or carbon-14 techniques, the standard for materials like bone and wood that are younger than about 50,000 years.

In a paper published this month in the journal Proceedings of the National Academy of Sciences,former UC Berkeley doctoral student Elizabeth Niespolo and geochronologist and BGC and associate director Warren Sharp reported using uranium-thorium dating of ostrich eggshells to establish that a midden outside Cape Town, South Africa, was deposited between 119,900 and 113,100 years ago.

That makes the site, called Ysterfontein 1, the oldest known seashell midden in the world, and implies that early humans were fully adapted to coastal living by about 120,000 years ago. This also establishes that three hominid teeth found at the site are among the oldest Homo sapiens fossils recovered in southern Africa.

The technique is precise enough for the researchers to state convincingly that the 12.5-foot-deep pile of mostly marine shells -- mussels, mollusks and limpets -- intermixed with animal bones and eggshells may have been deposited over a period of as little as 2,300 years.

The new ages are already revising some of the assumptions archeologists had made about the early Homo sapiens who deposited their garbage at the site, including how their population and foraging strategies changed with changing climate and sea level.

"The reason why this is exciting is that this site wouldn't have been datable by radiocarbon because it is too old," Niespolo said, noting that there are a lot more such sites around Africa, in particular the coastal areas of South Africa.

"Almost all of this sort of site have ostrich eggshells, so now that we have this technique, there is this potential to go and revisit these sites and use this approach to date them more precisely and more accurately, and more importantly, find out if they are the same age as Ysterfontein or older or younger, and what that tells us about foraging and human behavior in the past," she added.

Because ostrich eggshells are ubiquitous in African middens -- the eggs are a rich source of protein, equivalent to about 20 chicken eggs -- they have been an attractive target for geochronologists. But applying uranium-thorium dating -- also called uranium series -- to ostrich shells has been beset by many uncertainties.

"The previous work to date eggshells with uranium series has been really hit and miss, and mostly miss," Niespolo said.

Precision dating pushed back to 500,000 years ago

Other methods applicable to sites older than 50,000 years, such as luminescence dating, are less precise -- often by a factor of 3 or more -- and cannot be performed on archival materials available in museums, Sharp said.

The researchers believe that uranium-thorium dating can provide ages for ostrich eggshells as old as 500,000 years, extending precise dating of middens and other archeological sites approximately 10 times further into the past.

"This is the first published body of data that shows that we can get really coherent results for things well out of radiocarbon range, around 120,000 years ago in this case," said Sharp, who specializes in using uranium-thorium dating to solve problems in paleoclimate and tectonics as well as archeology. "It is showing that these eggshells maintain their intact uranium-series systems and give reliable ages farther back in time than had been demonstrated before."

"The new dates on ostrich eggshell and excellent faunal preservation make Ysterfontein 1 the as-yet best dated multi-stratified Middle Stone Age shell midden on the South African west coast," said co-author Graham Avery, an archeozoologist and retired researcher with the Iziko South African Museum. "Further application of the novel dating method, where ostrich eggshell fragments are available, will strengthen chronological control in nearby Middle Stone Age sites, such as Hoedjiespunt and Sea Harvest, which have similar faunal and lithic assemblages, and others on the southern Cape coast."

The first human settlements?

Ysterfontein 1 is one of about a dozen shell middens scattered along the western and eastern coasts of Western Cape Province, near Cape Town. Excavated in the early 2000s, it is considered a Middle Stone Age site established around the time that Homo sapiens were developing complex behaviors such as territoriality and intergroup competition, as well as cooperation among non-kin groups. These changes may be due to the fact that these groups were transitioning from hunter-gatherers to settled populations, thanks to stable sources of high-quality protein -- shellfish and marine mammals -- from the sea.

Until now, the ages of Middle Stone Age sites like Ysterfontein 1 have been uncertain by about 10%, making comparison among Middle Stone Age sites and with Later Stone Age sites difficult. The new dates, with a precision of about 2% to 3%, place the site in the context of well-documented changes in global climate: it was occupied immediately after the last interglacial period, when sea level was at a high, perhaps 8 meters (26 feet) higher than today. Sea level dropped rapidly during the occupation of the site -- the shoreline retreated up to 2 miles during this period -- but the accumulation of shells continued steadily, implying that the inhabitants found ways to accommodate the changing distribution of marine food resources to maintain their preferred diet.

The study also shows that the Ysterfontein 1 shell midden accumulated rapidly -- perhaps about 1 meter (3 feet) every 1,000 years --- implying that Middle Stone Age people along the southern African coast made extensive use of marine resources, much like people did during the Later Stone Age, and suggesting that effective marine foraging strategies developed early.

For dating, eggshells are better

Ages can be attached to some archeological sites older than 50,000 years through argon-argon (40Ar/39Ar) dating of volcanic ash. But ash isn't always present. In Africa, however -- and before the Holocene, throughout the Middle East and Asia -- ostrich eggshells are common. Some sites even contain ostrich eggshell ornaments made by early Homo sapiens.

Over the last four years, Sharp and Niespolo conducted a thorough study of ostrich eggshells, including analysis of modern eggshells obtained from an ostrich farm in Solvang, California, and developed a systematic way to avoid the uncertainties of earlier analyses. One key observation was that animals, including ostriches, do not take up and store uranium, even though it is common at parts-per-billion levels in most water. They demonstrated that newly laid ostrich shells contain no uranium, but that it is absorbed after burial in the ground.

The same is true of seashells, but their calcium carbonate structure -- a mineral called aragonite -- is not as stable when buried in soil as the calcite form of calcium carbonate found in eggshell. Because of this, eggshells retain better the uranium taken up during the first hundred years or so that that they are buried. Bone, consisting mostly of calcium phosphate, has a mineral structure that also does not remain stable in most soil environments nor reliably retains absorbed uranium.

Uranium is ideal for dating because it decays at a constant rate over time to an isotope of thorium that can be measured in minute amounts by mass spectrometry. The ratio of this thorium isotope to the uranium still present tells geochronologists how long the uranium has been sitting in the eggshell.

Uranium-series dating relies on uranium-238, the dominant uranium isotope in nature, which decays to thorium-230. In the protocol developed by Sharp and Niespolo, they used a laser to aerosolize small patches along a cross-section of the shell, and ran the aerosol through a mass spectrometer to determine its composition. They looked for spots high in uranium and not contaminated by a second isotope of thorium, thorium-232, which also invades eggshells after burial, though not as deeply. They collected more material from those areas, dissolved it in acid, and then analyzed it more precisely for uranium-238 and thorium-230 with "solution" mass spectrometry.

These procedures avoid some of the previous limitations of the technique, giving about the same precision as carbon-14, but over a time range that is 10 times larger.

"The key to this dating technique that we have developed that differs from previous attempts to date ostrich egg shells is the fact that we are explicitly accounting for the fact that ostrich eggshells have no primary uranium in them, so the uranium that we are using to date the eggshells actually comes from the soil pore water and the uranium is being taken up by the eggshells upon deposition," Niespolo said.

Wednesday, April 28, 2021

Climate crises in Mesopotamia prompted the first stable forms of State

Research News

During the Bronze Age, Mesopotamia was witness to several climate crises. In the long run, these crises prompted the development of stable forms of State and therefore elicited cooperation between political elites and non-elites. This is the main finding of a study published in the journal PNAS and authored by two scholars from the University of Bologna (Italy) and Eberhard Karls Universität Tübingen (Germany).

This study investigated the impact of climate shocks in Mesopotamia between 3100 and 1750 bC. The two scholars looked at these issues through the lenses of economics and adopted a game-theory approach. They applied this approach to the first detailed database on climate and institutional evolution of the 44 most important states of Mesopotamia.

"Severe and prolonged droughts pushed elites of landowners to grant political and property rights to the non-elites, who had the skills and tools to stem the damages brought by climate change. Elites did so to persuade non-elites that a sufficient part of the crops would be shared through the production of public goods", explains Carmine Guerriero, a professor at the Department of Economics at the University of Bologna and one of the authors of this study. "On their end, non-elites promoted institutional changes, embracing a culture of cooperation to persuade elites of their commitment to future cooperations".

Three severe droughts seem to confirm these intuitions. In the last stages of the Urban Revolution (3800-3300 b.C.), religious groups stepped in and eventually coordinated the effort of building the first human-made canals. Then, during the Protodynastic Period (3100-2550 b.C.), the Palatine military promoted the cooperation between farmers, granting them protection and the resources of the military enlistment. During the Imperial Period (2350-1750 b.C.), a valuable and climate shock-independent alternative to agricultural activities was put forward by corporations of merchants that had increasingly taken hold. Conversely, periods of milder climate promoted the cooperation between non-elites and elites while elites were not forced to give up their power and non-elites were not obliged to adopt a culture of intense cooperation.

"Because of their primarily agricultural economic systems, some developing countries are experiencing climate change in a way that resembles that of Mesopotamian States, and they will also experience politically relevant consequences", adds Guerriero. "On the one hand, unfavourable climate shocks can promote cooperation between normally contrasting parties by granting more rights to non-elites. On the other hand, favourable climate conditions allow for the cooperation between elites and non-elites through less inclusive social orders and with some degree of cultural accumulation. Therefore, two major objectives in this sense are spreading a strong culture of cooperation and avoiding the random transfer of more inclusive social orders in developing countries".

All in all, analyzing events concerning lost civilizations can offer useful insights to understand and solve issues of present times. "The past offers a more encouraging perspective against which we can measure the gravity of today's crises including the pandemic", suggests Guerriero. "Moreover, the past shows the importance of an interdisciplinary approach involving social and natural sciences to obtain a more precise evaluation of short-, medium- and long-term effects of climate change".

This paper appeared in the journal PNAS with the title "Climate Change and State Evolution". It reports about a research project funded by the Alma Idea Programme of the University of Bologna and the Programme for Young Researchers "Rita Levi Montalcini". The authors are Giacomo Benati, Eberhard Karls Universität Tübingen, and Carmine Guerriero, University of Bologna. Federico Zaina (Research Fellow at the Department of Architecture, Construction and Constructed Environment Engineering of the Polytechnic University of Milan) and Laura Righi (Research Fellow at John XXIII Foundation of Religious Sciences) also took part in the study.