Unravelling the climate behind the collapse of Bronze Age civilizations

 

Peer-Reviewed Publication

Stockholm University

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The Eastern Mediterranean dried as part of a broader climate transition; weakening monsoons and shifting atmospheric circulation reduced moisture from Africa and rainfall across the region. Image: Katherine Power/Stockholm University

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Credit: Katherine Power/Stockholm University

The most severe droughts in the ancient Eastern Mediterranean arose when multiple natural climate cycles coincided, according to a new study from Stockholm University published in Science Advances. The findings shed new light on the climate conditions surrounding the Late Bronze Age collapse and may help improve understanding of future drought risks in a warming world.

“Rather than being caused by a single climatic event, we found that the most extreme droughts emerged when natural climate cycles operating over different timescales coincided. This helps explain why the drought associated with the Late Bronze Age collapse were so severe”, says Katherine Power, PhD student, Department of Physical Geography, Stockholm University, and first author of the study.

Around 3,200 years ago, many of the great civilizations of the Eastern Mediterranean, including the Mycenaeans, Minoans and Hittite Empire, experienced widespread societal collapse. Although severe droughts have long been linked to this period, the climatic processes behind these events remain uncertain. To investigate this, Katherine Power and Qiong Zhang, professor in paleoclimate modelling, Department of Physical Geography, Stockholm University and co-author of the study, used a state-of-the-art climate model to reconstruct the evolution of the Mediterranean climate over the past 8,000 years.

“Our results show that the region underwent a gradual drying trend over thousands of years, driven by slow changes in Earth’s orbit. Superimposed on this long-term trend we also found shorter-term fluctuations in the Atlantic Ocean and atmosphere”, says Katherine Power.

The researchers found that most severe droughts occurred when several natural climate cycles aligned, temporarily reinforcing one another and producing droughts far more intense than the long-term drying trend alone.

“The convergence of these processes pushed the Eastern Mediterranean beyond a critical hydroclimatic threshold, reducing water availability and increasing pressure on agriculture and food security within already vulnerable societies”, Katherine Power says.

These findings change how we think about past droughts, the researcher say, and understanding these processes is highly relevant today:

“The Mediterranean is one of the world’s climate change hotspots and the area is projected to become warmer and drier during the coming century. Our findings suggest that future drought risk may depend not only on long-term human-driven warming, but also on how natural variability in the Atlantic Ocean interacts with that background trend”, Katherine Power explains.

By revealing how different climate processes combine to amplify drought, this research can provide new insights into the risks of future hydroclimatic extremes in a warming world, the researchers say. 

The study “Holocene ocean-atmosphere coupling and Mediterranean sensitivity to Atlantic circulation: Lessons from the Late Bronze Age collapse” was published in Science Advances. DOI: 10.1126/sciadv.aed5439.
For this research the model EC-Earth was used.
 

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Journal

Science Advances

DOI

10.1126/sciadv.aed5439 

Subject of Research

Not applicable

Article Title

Holocene ocean-atmosphere coupling and Mediterranean sensitivity to Atlantic circulation: Lessons from the Late Bronze Age collapse

Ceramic vessels reveal how social inequalities were also cooked into 19th-century Brazil

 

Peer-Reviewed Publication

Universitat Autonoma de Barcelona

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The study analysed the lipids preserved in more than 180 ceramic fragments and the proteins present in a selection of these pieces.

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Credit: ICTA-UAB

Fish, shellfish, maize, manioc, rice and even chicken eggs. Molecular residues preserved in more than 180 ceramic vessels from southern Brazil have made it possible to reconstruct what different communities were cooking more than a century ago, showing that access to food varied according to the origin and social status of their inhabitants.

An international study led by researchers from the Institute of Environmental Science and Technology at the Universitat Autònoma de Barcelona (ICTA-UAB) reveals that Indigenous, African and Afro-descendant communities relied more heavily on marine resources, while communities of immigrants from Germany consumed mainly plant species and terrestrial products.

Brazil is a multicultural and ethnically diverse country whose history has been shaped by the interaction between Indigenous peoples, African populations, Luso-Brazilian communities and, later, European immigrant communities. However, little is known about how this cultural diversity was reflected in people's everyday diet. The research has reconstructed part of this history by analysing food residues preserved in ceramics used between the late nineteenth and early twentieth centuries in Babitonga Bay, southern Brazil.

The study, recently published in Royal Society Open Science, analysed the lipids preserved in more than 180 ceramic fragments and the proteins present in a selection of these pieces. Thanks to molecular archaeology techniques, the researchers were able to identify the types of food that were cooked or stored in the vessels used by Indigenous, Luso-Brazilian, Afro-descendant communities, and the first German immigrants established in the region.

The results show clear differences between the communities. Hand-modelled vessels, associated with Indigenous, Afro-descendant and Luso-Brazilian communities, show a greater presence of marine resources, such as fish and shellfish, as well as maize. In contrast, wheel-thrown ceramics, used mainly by German immigrants, show a greater presence of crops and terrestrial products, including meat and, in some cases, dairy products.

The molecular analysis made it possible to go one step further and identify specific foods cooked more than a century ago. These include fish from the Sciaenidae family, chicken egg and biomarkers compatible with the processing of maize, rice, manioc, beans, fruits and vegetables, and animal fats. According to the researchers, this combination of lipid and protein analyses provides a more accurate picture of the everyday diet of the different communities that lived around Babitonga Bay.

"The residues preserved in these ceramics show that everyday diet reflected the profound social and cultural differences that characterised Brazil at the end of the nineteenth century. Molecular archaeology allows us to recover part of this history that is unlikely to appear in written documents," explains André Colonese, ICTA-UAB researcher and co-author of the study, which was carried out as part of the ERC Tradition project.

According to the researchers, the differences observed are not explained solely by culinary preferences, but also by unequal access to food. While livestock and certain crops were more closely linked to private property and an expanding market economy, fishing and the exploitation of coastal resources provided a more accessible source of food for communities with fewer resources. The results suggest that these foods played a fundamental role in ensuring the subsistence of many households in a context marked by significant social inequalities.

In addition to reconstructing the diet of these populations, the study demonstrates the potential of biomolecular archaeology to understand how economic, social and cultural changes transformed everyday diet. The authors believe that many of the differences dating back more than a century help explain the culinary diversity that characterises Brazil today.

 

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Journal

Royal Society Open Science

DOI

10.1098/rsos.260385 

Silkworm cultivation predated the Silk Road in southern Central Asia

 

Silk production skills reached Central Asia as early as 4,000 years ago, long before start of Silk Road trading route, WashU research finds

Peer-Reviewed Publication

Washington University in St. Louis

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By Talia Ogliore

The silkworm moth, whose caterpillars have been used in silk production since antiquity, may have been brought to southern Central Asia 4,000 years ago — nearly 2,000 years earlier than previously assumed — according to new research from Washington University in St. Louis.

The discovery of three well-preserved cocoons at an archaeological site in Uzbekistan pushes back the earliest verified date for silkworms cultivated outside of China.

Up until now, it was generally accepted that silk products and their accompanying knowledge spread from ancient China to Central Asia and beyond within the context of the Silk Road, the famed route used by traders during the Roman and Han period. While many goods including spices, teas, porcelain and glassware were traded along this route, silk was the most coveted luxury item exported from China to the Roman Empire, giving the expansive route its iconic name.

The new archaeological evidence opens up the possibility of an earlier dispersal of silk and sericulture, according to Xinyi Liu, a professor of archaeology in WashU Arts & Sciences, corresponding author of a study in the journal Science Advances.

“This is the oldest reliable archaeological record of preserved silkworm cocoons with direct radiocarbon dates,” Liu said. “Even in China, where the silkworm moth was domesticated, we don’t have preserved cocoons as old as this, in part because of challenges with archaeological preservation.”

The cocoons were discovered by a Chinese and Uzbek research team conducting excavations at three Bronze Age archaeological sites situated along the Surkhan-Darya River in Uzbekistan, including a site known as Sapalli Tepe. Locally arid conditions at Sepalli Tepe allowed for these cocoons to remain intact and identifiable among fragments of wood charcoal and plant seed remains. Silk proteins extracted from the cocoons were subsequently dated and confirmed to belong to the Bombyx mori silkworm moth species. 

“The identification of these cocoons as Bombyx mori is particularly significant because it links them to the mulberry-based silk tradition that originated in ancient China,” Liu said. “This differs from the non-Bombyx silk traditions historically prevalent in South Asia, including Tussar, Eri and Muga silks, which relied on other moth species and host plants.

“Our study reveals the presence of domesticated Bombyx silkworms, mulberry trees and other fruits and crops at nearly 2,000 BCE,” Liu said. “Taken together, the evidence shows that East Asian Bombyx-mulberry sericulture had reached southern Central Asia by about 4,000 years ago, long before the establishment of the historical Silk Road.”

Very hungry caterpillars

The practice of rearing silkworms by feeding them leaves from specially grown mulberry trees is historically important to cultures across Asia. 

A story about the origin of silk is often retold. According to Chinese legend, silk was discovered by Empress Leizu, wife of the Yellow Emperor, when a silkworm cocoon fell into her hot cup of tea. As the tight knot of the cocoon loosened in the hot water, its fibers partly unspooled. The empress had a vision for how this filament could be used.

A single silkworm can spin a continuous filament of silk up to 900 meters in length. But to harvest silk in useful amounts, people needed a way to purposefully raise many silkworm caterpillars at once. And that meant feeding those very hungry caterpillars what they wanted to eat: mulberry leaves.

As the food source for Bombyx silkworms, mulberry trees — notably the white mulberry tree — were globally dispersed, but when and how this dispersal unfolded remains obscure, Liu said. At the Sapalli Tepe archaeological site, researchers also found chunks of charcoal that they identified as remnants of mulberry trees.

“The evidence of the mulberry tree is quite important. Ecologically, these trees are not native to Central Asia and could adapt to the southern Himalayan environment much better than the northern arid environment,” Liu said. “So that’s hinting at a trans-Himalayan connection, rather than an inner-Asian mountain connection. The recovery of citrus wood charcoal at the site further strengthens this interpretation, as cultivated citrus likely originated in South Asia.

“Why this early dispersal of Bombyx-mulberry sericulture, possibly along a Himalayan route, did not lead to a clearly documented and enduring Bombyx silk tradition in the region remains unclear,” Liu said. “Historically, South Asian sericulture was characterized with use of non-Bombyx silkworms. Future research investigating archaeological evidence along both the northern and southern fringes of the Tibetan Plateau will therefore be timely.”

The study also describes additional evidence for local silk production in the form of a fabric fragment recovered from Sapalli Tepe during an older excavation, completed by Soviet archaeologists in the 1970s. Although a new, direct analysis of this fragment wasn’t possible due to conservation restrictions, Liu said existing documentation confirms that this fabric was produced using a traditional plain-weave technique of spun yarn, consistent with the Chinese style of silk manufacture. 

“The co-occurrence of Bombyx mori cocoons, mulberry charcoal and silk-like fabrics at Sapalli Tepe indicates an unambiguous connection with East Asia sericultural traditions,” Liu said. 

Another form of early globalization

The findings from this new study are the latest to challenge the conventional timeline of the Silk Road and of Eurasian interconnectivity. Liu is one of a handful of scholars who have recently uncovered evidence documenting the spread of cereals, fruits, metallurgy and livestock connecting ancient China with the Central and South Asian environments during the third and second millennia BCE — much earlier than the Han dynasty and the Silk Road. 

“We know this was a period of time when communities across the Eurasian continent were exchanging goods and learning from one another, in some cases underlined by population movement and in some cases by cultural inspiration,” Liu said.

“Before this evidence, we saw the appearance of a globalization focused on domesticated grains — such as wheat, barley and millets — and livestock, including sheep, goat and cattle,” he said. “Now it looks like making silk fibers is part of that early globalization.”

This alternate path and timeline adds to the momentum for rethinking the Silk Road, Liu said. 

“It is likely that dispersals of silk and sericulture were much older than the Silk Road, starting from the Bronze Age,” he said.

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This study was completed in collaboration with researchers at the Chinese Academy of Sciences in Beijing and the Academy of Sciences of the Republic of Uzbekistan.

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Journal

Science Advances

DOI

10.1126/sciadv.aec8738 

The lost golden age of language diversity

New modelling suggests that tens of thousands of languages were spoken between 1,000 and 3,000 years ago - and that their decline began well before European colonial expansion

Peer-Reviewed Publication

Max Planck Institute for Evolutionary Anthropology

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Contemporary languages and endangerment status. Made with a Natural Earth base map using data from Glottolog 5.3 and information adapted from GlottoScope.

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Credit: © Claire Bowern

To the Point

• Fewer languages before agriculture: The researchers estimate that between approximately 4,500 and 6,200 languages were spoken at the beginning of the Holocene, around 12,000 years ago - probably fewer than the roughly 7,500 languages spoken and signed today.

• A linguistic “golden age”: As the global human population grew, language diversity also increased. The models suggest that tens of thousands of languages may have existed between 1,000 and 3,000 years ago.

• A deep history of language loss: The decline in linguistic diversity appears to have begun with the expansion of large states and empires, long before modern European colonialism.

• Today’s languages are survivors: The languages spoken today represent a small and historically biased sample of past linguistic diversity, with important implications for how researchers explain global patterns in language and culture.

Today, people speak or sign around 7,500 languages. Yet this figure provides only a snapshot of a constantly changing history. How many languages existed before written records? Did agriculture reduce linguistic diversity by allowing expanding farming populations to replace smaller hunter-gatherer groups? Or did population growth initially create more opportunities for new languages to emerge?

An international research team involving researchers from Spain, the USA and Germany have reconstructed plausible trajectories of global language diversity across the last 12,000 years. Their study, published in Science, suggests that language diversity increased for most of the Holocene, reached a remarkable peak between approximately 1,000 and 3,000 years ago, and then declined rapidly thereafter.

Reconstructing a history without written records

“This paper presents an innovative approach to understanding the dynamics of human cultural diversity in the past, addressing one of the central yet least accessible questions in the human sciences. Progress has been limited not by a lack of theoretical interest but by the exceptional difficulty of observing the relevant dynamics empirically”, says Marcus Hamilton of the University of Texas at San Antonio.

Direct evidence for the number of languages is almost entirely absent before the appearance of writing around 6,000 years ago, and remains fragmentary until quite recently. The researchers therefore combined ethnographic information, estimates of prehistoric population size, and statistical and social-computational modelling.

They began with ethnographic data from 171 hunter-gatherer and fisher societies whose traditional subsistence and mobility had not been profoundly transformed by contact with food-producing populations. These data allowed the researchers to estimate the likely distribution of ethnolinguistic group sizes near the beginning of the Holocene.

The team then combined these estimates with reconstructions suggesting that the global human population 12,000 years ago was between approximately 4.4 and seven million. Assuming that ethnolinguistic groups at that time generally corresponded to distinct languages, the models produced an early-Holocene estimate centred on roughly 4,500 to 6,200 languages, although broader plausible estimates ranged from around 3,300 to 7,800.

“One of the first surprises was that the world immediately before agriculture was probably not exceptionally rich in languages. There were most likely fewer languages than there are today. Linguistic diversity then grew alongside the human population for thousands of years”, says Russell Gray, Director of the Department of Linguistic and Cultural Evolution at the Max Planck Institute for Evolutionary Anthropology in Leipzig.

Tens of thousands of languages

Agriculture, technological innovation and more stable food production allowed the global population to expand dramatically. At the same time, however, societies became larger, meaning that progressively more people could share the same language.

To capture these opposing processes, the researchers modelled thousands of possible trajectories connecting estimates at the beginning of the Holocene with the present. The models allowed the number of people per language to increase over time, while incorporating independent reconstructions of global population growth.

Although the precise trajectory remains uncertain, the models consistently produced a striking general pattern. Language diversity increased over most of the Holocene and typically peaked between 1,000 and 3,000 years ago. Many trajectories imply an approximately tenfold increase from early-Holocene levels, placing the peak number of languages in the tens of thousands.

“The most unexpected result is how recent the peak appears to have been. The period of greatest linguistic diversity may have occurred not in the remote Palaeolithic, but during the era of expanding states and early empires”, says Claire Bowern of Yale University.

The authors describe this period as a linguistic “golden age”. It has largely escaped previous discussion because most surviving historical records were produced by the expanding societies whose languages eventually became dominant.

Language loss before modern colonialism

The linguistic golden age was followed by a rapid decline, particularly during the last two millennia. The results therefore challenge the view that the present language-endangerment crisis began only with European colonial expansion around 500 years ago.

European colonialism unquestionably intensified language replacement on an enormous scale. The new models suggest, however, that the process had deeper roots in the expansion of earlier multinational states and empires. Such expansions brought previously separated populations into sustained contact and spread dominant languages together with political institutions, technologies, cultural practices and pathogens.

The model does not identify which particular empires, regions or historical events caused the global decline. Rather, it shows that a very large reduction in linguistic diversity must have taken place before the present.

Today’s languages passed through a bottleneck

This loss means that the languages spoken today are not a representative sample of those that once existed. Languages associated with expanding populations were disproportionately likely to survive, while the languages of absorbed, displaced or declining populations disappeared.

This historical bottleneck may also have altered the global frequency of grammatical structures, speech sounds and other linguistic features. Researchers often explain common features by suggesting that they are especially easy to learn, efficient to communicate or well suited to human cognition. The new study suggests that demographic expansion and extinction must also be considered.

“The languages we see today are the survivors of a massive and highly selective historical bottleneck. A linguistic feature may be common not because it is inherently superior, but because it happened to be carried by populations that expanded. Extinction may have shaped linguistic diversity much more profoundly than we previously appreciated”, says Damian Blasi, lead author of the study and researcher at the Catalan Institution for Research and Advanced Studies (ICREA) and Harvard University.

Because languages are often transmitted together with religious practices, kinship systems, social institutions and other forms of cultural knowledge, the authors argue that this bottleneck extended beyond language. Many cultural traditions may also have vanished without leaving direct historical evidence.

A model, not a prehistoric census

The researchers emphasise that the study provides a coarse global reconstruction rather than a direct count of prehistoric languages. Its estimates depend on assumptions about early ethnolinguistic group sizes and the long-term relationship between population and language numbers. Regional histories undoubtedly differed, and short-term collapses caused by warfare, disease and environmental disruption cannot be individually reconstructed by the model.

Nevertheless, the central pattern persisted across a wide range of modelling conditions and alternative assumptions. The results suggest that the history of language diversity was not a simple, continuous decline from a highly diverse Palaeolithic world. Instead, linguistic diversity rose with human population growth, reached an extraordinary but short-lived peak, and then underwent a severe global contraction.

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Journal

Science

DOI

10.1126/science.adx4343