millets Mongolia

How millets sustained Mongolia's empires

How millets sustained Mongolia's empires

Stable isotope analyses reveals dramatic diet diversification at the onset of the steppe's earliest empires

 

The historic economies of Mongolia are among the least understood of any region in the world. The region's persistent, extreme winds whisk away signs of human activity and prevent the buildup of sediment which archaeologists rely on to preserve the past. Today crop cultivation comprises only a small percent of Mongolia's food production, and many scholars have argued that Mongolia presents a unique example of dense human populations and hierarchical political systems forming without intensive farming or stockpiling grains.

The current study, led by Dr. Shevan Wilkin of the Max Planck Institute for the Science of Human History provides, for the first time, a detailed glimpse into the diets and lives of ancient Mongolians, underscoring the importance of millets during the formation of the earliest empires on the steppe.

Isotopic analysis and the imperial importance of millets

millets Mongolia
Mongolian landscape with pastoral herd of sheep and goats. Credits: Alicia Ventresca Miller

Collaborating with archaeologists from the National University of Mongolia and the Institute of Archaeology in Ulaanbaatar, Dr. Wilkin and her colleagues from the MPI SHH sampled portions of teeth and rib bones from 137 previously excavated individuals. The skeletal fragments were brought back to the ancient isotope lab in Jena, Germany, where researchers extracted bone collagen and dental enamel to examine the ratios of stable nitrogen and carbon isotopes within. With these ratios in hand, scientists were able to reconstruct the diets of people who lived, ate, and died hundreds to thousands of years ago.

Researchers tracked the trends in diet through the millennia, creating a "dietscape" which clearly showed significant differences between the diets of Bronze Age peoples and those who lived during the Xiongnu and Mongol Empires. A typical Bronze Age Mongolian diet was based on milk and meat, and was likely supplemented with small amounts of naturally available plants. Later, during the Xiongnu Empire, human populations displayed a larger range of carbon values, showing that some people remained on the diet common in the Bronze Age, but that many others consumed a high amount of millet-based foods. Interestingly, those living near the imperial heartlands appear to have been consuming more millet-based foods than those further afield, which suggests imperial support for agricultural efforts in the more central political regions. The study also shows an increase in grain consumption and increasing dietary diversity through time, leading up to the well-known Mongolian Empire of the Khans.

Rethinking Mongolian prehistory

Horses are still used by many for transport across Mongolia. Credits: Shevan Wilkin

The new discoveries presented in this paper show that the development of the earliest empires in Mongolia, like in other parts of the world, was tied to a diverse economy that included the local or regional production of grain. Dr. Bryan K. Miller, a co-author who studies the historical and archaeological records of Inner Asian empires, remarks that "these regimes were like most empires, in that they directed intricate political networks and sought to amass a stable surplus - in this case a primarily pastoral one that was augmented by other resources like millet."

"In this regard," Dr. Miller adds, "this study brings us one step closer to understanding the cultural processes that led humanity into the modern world."

The view that everyone in Mongolian history was a nomadic herder has skewed discussions concerning social development in this part of the world. Dr. Wilkin notes that "setting aside our preconceived ideas of what prehistory looked like and examining the archaeological record with modern scientific approaches is forcing us to rewrite entire sections of humanity's past." Dr. Spengler, the director of the archaeobotany labs at the MPI SHH, emphasizes the importance of this discovery, noting that "this study pulls the veil of myth and lore off of the real people who lived in Mongolia millennia ago and lets us peak into their lives."

millets Mongolia
Cultivated land in northern Mongolia. Credits: Alicia Ventresca Miller

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Publication information:

Title: Economic Diversification Supported the Growth of Mongolia's Nomadic Empires

Authors: Shevan Wilkin, Alicia Ventresca Miller, Bryan K. Miller, Robert N. Spengler, William T. T. Taylor, Ricardo Fernandes, Madeleine Bleasdale, Jana Zech, S. Ulziibayar, Erdene Myagmar, Nicole Boivin, Patrick Roberts

Publication: Scientific Reports

DOI: 10.1038/s41598-020-60194-0

 

Press release from the Max Planck Institute for the Science of Human History / DE


5,000-year-old milk proteins point to the importance of dairying in eastern Eurasia

5,000-year-old milk proteins point to the importance of dairying in eastern Eurasia

Recent findings push back estimates of dairying in the eastern Steppe by more than 1,700 years, pointing to migration as a potential means of introduction

 

Today dairy foods sustain and support millions around the world, including in Mongolia, where dairy foods make up to 50% of calories consumed during the summer. Although dairy-based pastoralism has been an essential part of life and culture in the eastern Eurasian Steppe for millennia, the eastward spread of dairying from its origin in southwest Asia and the development of these practices is little understood. The current study, led by Shevan Wilkin and Jessica Hendy of the Max Planck Institute for the Science of Human History, presents the earliest evidence for dairy consumption in East Asia, circa 3000 BCE, and offers insights into the arrival and evolution of dairy pastoralism in prehistoric Mongolia.

dairying Eurasia
These are horses on the steppe. Credits: Björn Reichhardt

Earliest dairy consumption & a possible path of entry

The highly mobile nature of pastoralist societies and the severe winds of the Eastern Steppe make detecting occupied sites with direct evidence into the lives and culture of ancient Mongolians exceedingly rare. Instead, the researchers looked for clues in ritual human burial mounds, often marked by stone monuments and occasionally featuring satellite animal graves.

In collaboration with the National University of Mongolia, researchers analyzed dental calculus from individuals ranging from the Early Bronze Age to the Mongol Period. Three-quarters of all individuals contained evidence that they had consumed dairy foods, which demonstrates the widespread importance of this food source in both prehistoric and historic Mongolia. The study's results include the earliest direct evidence for dairy consumption in East Asia, identified in an individual from the Afanasievo site of Shatar Chuluu, which dates to roughly 3000 BCE. Previous DNA analysis on this individual revealed non-local genetic markers consistent with Western Steppe Herder populations, presenting Early Bronze Age Afanasievo migrations westward via the Russian Altai as a viable candidate for the introduction of dairy and domestic livestock into eastern Eurasia.

Multiple different animal species were used for their milk

dairying Eurasia
These are sheep and goat herds in Mongolia. Credits: Björn Reichhardt

By sequencing the milk proteins extracted from the dental calculus, the scientists were able to determine which animal species were being used for dairy production, and thereby help to trace the progression of domestication, dairying, and pastoralism in the region. "Modern Mongolians use cow, sheep, goat, yak, camel, horse and reindeer for milk today, yet when each of these species were first utilized for dairy in Mongolia remains unclear," says Shevan Wilkin, lead author of the study. "What is clear is that the crucial renewable calories and hydration made available through the incorporation of dairying would have become essential across the arid and agriculturally challenging ancient Eastern Steppe."

The earliest individuals to show evidence of dairy consumption lived around 5000 years ago and consumed milk from ruminant species, such as cattle, sheep, and goats. A few thousand years later, at Bronze Age sites dated to after 1200 BCE, the researchers find the first evidence of horse milk consumption, occurring at the same time as early evidence for horse bridling and riding, as well as the use of horses at ritual burial sites. In addition, the study shows that during the Mongol Empire circa 1200-1400 CE, people also consumed the milk of camels. "We are excited that through the analysis of proteins we are able to see the consumption of multiple different animal species, even sometimes in the same individual. This gives us a whole new insight into ancient dairying practices" says Jessica Hendy, senior author of the study.

Millenia after the first evidence of horse milk consumption, horses remain vital to the daily lives of many in modern Mongolia, where mounted pastoralists rely on them to manage large herds of livestock, transport people and supplies, and provide a primary source of meat and milk. "Our findings suggest that the incorporation of horses into dairy pastoralism in Eastern Eurasia was closely linked to a broader economic transformation in the use of horses for riding, movement, and diet," says William Taylor of the University of Colorado-Boulder, one of the study's coauthors.

Although the earliest individual sampled in this study showed evidence of dairy consumption, the researchers hope future studies will examine individuals from previous time periods. "In order to form a clearer picture of the origins of dairying in this region, we need to understand the impact of western steppe herder migrations and confirm whether dairying was occurring in Mongolia prior to their arrival," Shevan Wilkin concludes.

dairying Eurasia
This is a horse burial at Morin Mort, Mongolia. Credits: William Taylor

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Publication information:

Title: Dairy pastoralism sustained Eastern Eurasian steppe populations for 5000 years

Authors: Shevan Wilkin, Alicia Ventresca Miller, William T.T. Taylor, Bryan K. Miller, Richard W. Hagan, Madeleine Bleasdale, Ashley Scott, Sumiya Gankhuyg, Abigail Ramsoe, S. Uliziibayar, Christian Trachsel, Paolo Nanni, Jonas Grossmann, Ludovic Orlando, Mark Horton, Philipp W. Stockhammer, Erdene Myagmar, Nicole Boivin, Christina Warinner, Jessica Hendy

Publication: Nature Ecology & Evolution

DOI: 10.1038/s41559-020-1120-y

 

Press release from the Max Planck Institute for the Science of Human History / DE


5,200-year-old grains in the eastern Altai Mountains redate trans-Eurasian crop exchange

5,200-year-old grains in the eastern Altai Mountains redate trans-Eurasian crop exchange

Agricultural crops dispersed across Eurasia more than five millennia ago, causing significant cultural change in human populations across the ancient world. New discoveries in the Altai Mountains illustrate that this process occurred earlier than believed

trans-Eurasian crop exchange
Dr. Xinying Zhou and his team from the IVPP in Beijing excavated the Tangtian Cave site during the summer of 2016. Credits: Xinying Zhou

Most people are familiar with the historical Silk Road, but fewer people realize that the exchange of items, ideas, technology, and human genes through the mountain valleys of Central Asia started almost three millennia before organized trade networks formed. These pre-Silk Road exchange routes played an important role in shaping human cultural developments across Europe and Asia, and facilitated the dispersal of technologies such as horse breeding and metal smelting into East Asia. One of the most impactful effects of this process of ancient cultural dispersal was the westward spread of northeast Asian crops and the eastward spread of southwest Asian crops. However, until the past few years, a lack of archaeobotanical studies in Central Asia left a dearth of data relating to when and how this process occurred.

This new study, led by scientists from the Chinese Academy of Sciences and the Max Planck Institute for the Science of Human History, provides details of recently recovered ancient grains from the far northern regions of Inner Asia. Radiocarbon dating shows that the grains include the oldest examples of wheat and barley ever recovered this far north in Asia, pushing back the dates for early farming in the region by at least a millenium. These are also the earliest domesticated plants reported from the northern half of Central Asia, the core of the ancient exchange corridor. This study pulls together sedimentary pollen and ancient wood charcoal data with archaeobotanical remains from the Tiangtian archaeological site in the Chinese Altai Mountains to reveal how humans cultivated crops at such northern latitudes. This study illustrates how adaptable ancient crop plants were to new ecological constraints and how human cultural practices allowed people to survive in unpredictable environments.

The Northern Dispersal of Cereal Grains

The ancient relatives of wheat and barley plants evolved to grow in the warm and dry climate of the eastern Mediterranean and southwest Asia. However, this study illustrates that ancient peoples were cultivating these grasses over five and a half thousand kilometers to the northeast of where they originally evolved to grow. In this study, Dr. Xinying Zhou and his colleagues integrate paleoenvironmental proxies to determine how extreme the ecology was around the archaeological cave site of Tangtian more than five millennia ago, at the time of its occupation. The site is located high in the Altai Mountains on a cold, dry landscape today; however, the study shows that the ecological setting around the site was slightly warmer and more humid at the time when people lived in and around this cave.

The slightly warmer regional conditions were likely the result of shifting air masses bringing warmer, wetter air from the south. In addition to early farmers using a specific regional climate pocket to grow crops in North Asia, analysis showed that the crops they grew evolved to survive in such northern regions. The results of this study provide scholars with evidence for when certain evolutionary changes in these grasses occurred, including changes in the programed reliance of day length, which signals to the plant when to flower, and a greater resistance to cold climates.

trans-Eurasian crop exchange
Charred seeds from Tontian Cave site. Credits: Xinying Zhou

The Trans-Eurasian Exchange and Crop Dispersal

The ancient dispersal of crops across Inner Asia has received a lot of attention from biologists and archaeologists in recent years; as Dr. Spengler, one of the study's lead authors, discusses in his recent book Fruit from the Sands, these ancient exchange routes shaped the course of human history. The mingling of crops originating from opposite ends of Asia resulted in the crop-rotation cycles that fueled demographic growth and led to imperial formation. East Asian millets would become one of the most important crops in ancient Europe and wheat would become one of the most important crops in East Asia by the Han Dynasty. While the long tradition of rice cultivation in East Asia made rice a staple of the Asian kitchen, Chinese cuisine would be unrecognizable without wheat-based food items like steamed buns, dumplings, and noodles. The discovery that these plants dispersed across Eurasia earlier than previously understood will have lasting impacts on the study of cultivation and labor practices in ancient Eurasia, as well as the history cultural contact and shifts in culinary systems throughout time.

These new discoveries provide reason to question these views, and seem to suggest that mixed small-scale human populations made major contributions to world history through migration and cultural and technological exchange. "This study not only presents the earliest dates for domesticated grains in far North Asia," says Professor Xiaoqiang Li, director of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, "it represents the earliest beginning of a trans-Eurasian exchange that would eventually develop into the great Silk Road".

Dr. Xinying Zhou, who headed the study and directs a research team at the IVPP in Beijing, emphasizes that "this discovery is a testament to human ingenuity and the amazing coevolutionary bond between people and the plants that they maintain in their cultivated fields."

photo of the stone men (????? Chimulchek Culture) in the steppe area of Altai Mountains. These figures are characteristic of the peoples who live in the area around the time of occupation at Tongtian. These specific examples are located at the Chimulchek site (ca. 4000 years old) and not far from Tongtian Cave. Ceramic sherds from the cave suggest that the occupants in the cave shared similar cultural traits to other people in the region. Credits: Jianjun Yu

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Title: 5200-year-old cereal grains from the eastern Altai Mountains predate the trans-Eurasian crop exchange
Authors: Xinying Zhou, Jianjun Yu, Robert Nicolas Spengler, Hui Shen, Keliang Zhao, Junyi Ge, Yige Bao, Junchi Liu, Qingjiang Yang, Guanhan Chen, Peter Weiming Jia, and Xiaoqiang Li
Publication: Nature Plants
DOI: https://doi.org/10.1038/s41477-019-0581-y

 

The press release about the trans-Eurasian crop exchange is from Max Planck Institute for the Science of Human History / DE


Neanderthals glue stone tools

Neanderthals used resin 'glue' to craft their stone tools

Neanderthals used resin 'glue' to craft their stone tools

Neanderthals glue stone tools
Artist's rendition of Earth approximately 60,000 years ago. Picture from nasa.gov

Archaeologists working in two Italian caves have discovered some of the earliest known examples of ancient humans using an adhesive on their stone tools--an important technological advance called "hafting."

The new study, which included CU Boulder's Paola Villa, shows that Neanderthals living in Europe from about 55 to 40 thousand years ago traveled away from their caves to collect resin from pine trees. They then used that sticky substance to glue stone tools to handles made out of wood or bone.

The findings add to a growing body of evidence that suggests that these cousins of Homo sapiens were more clever than some have made them out to be.

"We continue to find evidence that the Neanderthals were not inferior primitives but were quite capable of doing things that have traditionally only been attributed to modern humans," said Villa, corresponding author of the new study and an adjoint curator at the CU Museum of Natural History.

Neanderthals glue stone tools
Flints bearing traces of pine resin. The letter "R" indicates the presence of visible resin, and the arrows point to spots where researchers sampled material for chemical analysis. (Credit: Degano et al. 2019, PLOS ONE)

That insight, she added, came from a chance discovery from Grotta del Fossellone and Grotta di Sant'Agostino, a pair of caves near the beaches of what is now Italy's west coast.

Those caves were home to Neanderthals who lived in Europe during the Middle Paleolithic period, thousands of years before Homo sapiens set foot on the continent. Archaeologists have uncovered more than 1,000 stone tools from the two sites, including pieces of flint that measured not much more than an inch or two from end to end.

In a recent study of the tools, Villa and her colleagues noticed a strange residue on just a handful of the flints--bits of what appeared to be organic material.

"Sometimes that material is just inorganic sediment, and sometimes it's the traces of the adhesive used to keep the tool in its socket" Villa said.

Warm fires

To find out, study lead author Ilaria Degano at the University of Pisa conducted a chemical analysis of 10 flints using a technique called gas chromatography/mass spectrometry. The tests showed that the stone tools had been coated with resin from local pine trees. In one case, that resin had also been mixed with beeswax.

Villa explained that the Italian Neanderthals didn't just resort to their bare hands to use stone tools. In at least some cases, they also attached those tools to handles to give them better purchase as they sharpened wooden spears or performed other tasks like butchering or scraping leather.

"You need stone tools to cut branches off of trees and make them into a point," Villa said.

The find isn't the oldest known example of hafting by Neanderthals in Europe--two flakes discovered in the Campitello Quarry in central Italy predate it. But it does suggest that this technique was more common than previously believed.

The existence of hafting also provides more evidence that Neanderthals, like their smaller human relatives, were able to build a fire whenever they wanted one, Villa said--something that scientists have long debated. She said that pine resin dries when exposed to air. As a result, Neanderthals needed to warm it over a small fired to make an effective glue.

"This is one of several proofs that strongly indicate that Neanderthals were capable of making fire whenever they needed it," Villa said.

In other words, enjoying the glow of a warm campfire isn't just for Homo sapiens.

Other coauthors on the study included researchers at Paris Nanterre University in France, University of the Witwatersrand in South Africa, University of Wollongong in Australia, Max Planck Institute for the Science of Human History in Germany, Istituto Italiano di Paleontologia Umana and the University of Pisa.

The research was funded by a National Science Foundation grant to Paola Villa and Sylvain Soriano.

 

Press release from the University of Colorado at Boulder.


Dramatic change in ancient nomad diets coincides with expansion of networks across Eurasia

Dramatic change in ancient nomad diets coincides with expansion of networks across Eurasia

nomad pastoralists diets
Map of millet and wheat/barley consumption over time: a) 1000-500 cal BC, b) 500-200 cal BC, and c) 200 BC-AD 400. Credit: Map of millet and wheat/barley consumption over time: a) 1000-500 cal BC, b) 500-200 cal BC, and c) 200 BC-AD 400

A meta-analysis of dietary information recorded in the bones of ancient animals and humans recovered from sites scattered across the Eurasian steppe, from the Caucasus region to Mongolia, demonstrates that pastoralists spread domesticated crops across the steppe through their trade and social networks. Researchers from Kiel University sifted through previously published stable isotopic data and applied new quantitative analyses that calibrate human dietary intake against environmental inputs. The results have allowed them to better isolate the timing of the incorporation of agricultural products into the diets of pastoral nomads and, crucially, link burgeoning socio-political networks to this dietary transformation.

Through a big data project that explored over a thousand stable isotope data points, researchers were able to find evidence for an early transition to agriculture - based on dietary intake across Eurasia. "Our understanding of the pace of crop transmission across the Eurasian steppe has been surprisingly unclear due in part to a focus on the excavation of cemeteries, rather than settlements where people threw out their food," says Alicia Ventresca Miller, lead author, formerly of Kiel University and currently at the Max Planck Institute for the Science of Human History. "Even when settlement sites are excavated, the preservation of carbonized seed remains is often poor. This is what makes stable isotope analyses of human remains from this region so valuable - it provides direct insights into the dietary dynamics of ancient pastoralists who inhabited diverse environments."

Millet spreads across the Eurasian steppe

Millet, originally domesticated in China, appears to have been occasionally consumed at low levels by pastoralists inhabiting the far-flung regions of Siberia and southeastern Kazakhstan, possibly as early as the late third millennium. This initial uptake of millet coincided with the expansion of trans-regional networks across the steppe, when objects and ideas were first regularly exchanged over long-distances.

However, it was not until a thousand years later that millet became a regular feature of pastoralist diets. This timing coincides with the intensification of complex political structures at the transition to the Iron Age. Burgeoning socio-political confederations drove a marked increase in the exchange of costly prestige goods, which strengthened political networks - and facilitated the transfer of cultigens.

Wheat and Barley in the Trans-Urals

Despite taking part in these political networks, groups in the Trans-Urals invested in wheat and barley farming rather than millet. A dietary focus on wheat and barley may have been due to different farming techniques, greater water availability, or a higher value on these cultigens. "Our research suggests that cultigens were converted from a rare luxury during the Bronze Age to a medium demarcating elite participation in political networks during the Iron Age," states Cheryl Makarewicz of Kiel University.

Regional variation in millet consumption

While herding of livestock was widespread, not all regions adopted millet. In southwest Siberia, dietary intake was focused on pastoral animal products and locally available wild plants and fish. In contrast, the delayed adoption of millet by populations in Mongolia during the Late Iron Age coincides with the rise of the Xiongnu nomadic empire. "This is particularly interesting because it suggests that communities in Mongolia and Siberia opted out of the transition to millet agriculture, while continuing to engage with neighboring groups," explains Ventresca Miller.

This study shows the great potential of using the available isotope record to provide evidence for human dietary intake in areas where paleobotany is understudied. Further research should clarify the exact type of grains, for example broomcorn or foxtail millet, were fundamental to the shift in dietary intake and how networks of exchange linked different regions.

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Original publication:

Ventresca Miller and Makarewicz, Intensification in pastoralist cereal use coincides with the expansion of trans-regional networks in the Eurasian Steppe, Scientific Reports (2019). DOI: https://doi.org/10.1038/s41598-018-35758-w

 

Press release from Kiel University / Christian-Albrechts-Universität zu Kiel


Details of first historically recorded plague pandemic revealed by ancient genomes

Details of first historically recorded plague pandemic revealed by ancient genomes

Analysis of 8 new plague genomes from the first plague pandemic reveals previously unknown levels of plague diversity, and provides the first genetic evidence of the Justinianic Plague in the British Isles

Justinianic Plague Yersinia pestis
Map and phylogenetic tree showing the newly published (yellow) and previously published (turquoise) genomes. Shaded areas and dots represent historically recorded outbreaks of the First Pandemic. Credit: Marcel Keller

An international team of researchers has analyzed human remains from 21 archaeological sites to learn more about the impact and evolution of the plague-causing bacterium Yersinia pestis during the first plague pandemic (541-750 AD). In a study published in PNAS, the researchers reconstructed 8 plague genomes from Britain, Germany, France and Spain and uncovered a previously unknown level of diversity in Y. pestis strains. Additionally, they found the first direct genetic evidence of the Justinianic Plague in the British Isles.

The Justinianic Plague began in 541 in the Eastern Roman Empire, ruled at the time by the Emperor Justinian I, and recurrent outbreaks ravaged Europe and the Mediterranean basin for approximately 200 years. Contemporaneous records describe the extent of the pandemic, estimated to have wiped out up to 25% of the population of the Roman world at the time. Recent genetic studies revealed that the bacterium Yersinia pestis was the cause of the disease, but how it had spread and how the strains that appeared over the course of the pandemic were related to each other was previously unknown.

In the current study, an international team of researchers led by the Max Planck Institute for the Science of Human History analyzed human remains from 21 sites with multiple burials in Austria, Britain, Germany, France and Spain. They were able to reconstruct 8 new Y. pestis genomes, allowing them to compare these strains to previously published ancient and modern genomes. Additionally, the team found the earliest genetic evidence of plague in Britain, from the Anglo-Saxon site of Edix Hill. By using a combination of archaeological dating and the position of this strain of Y. pestis in its evolutionary tree, the researchers concluded that the genome is likely related to an ambiguously described pestilence in the British Isles in 544 AD.

High diversity of Y. pestis strains during the First Pandemic

The researchers found that there was a previously unknown diversity of strains of Y. pestis circulating in Europe between the 6th and 8th centuries AD. The 8 new genomes came from Britain, France, Germany and Spain. "The retrieval of genomes that span a wide geographic and temporal scope gives us the opportunity to assess Y. pestis' microdiversity present in Europe during the First Pandemic," explains co-first author Marcel Keller, PhD student at the Max Planck Institute for the Science of Human History, now working at the University of Tartu. The newly discovered genomes revealed that there were multiple, closely related strains of Y. pestis circulating during the 200 years of the First Pandemic, some possibly at the same times and in the same regions.

Despite the greatly increased number of genomes now available, the researchers were not able to clarify the onset of the Justinianic Plague. "The lineage likely emerged in Central Asia several hundred years before the First Pandemic, but we interpret the current data as insufficient to resolve the origin of the Justinianic Plague as a human epidemic, before it was first reported in Egypt in 541 AD. However, the fact that all genomes belong to the same lineage is indicative of a persistence of plague in Europe or the Mediterranean basin over this time period, instead of multiple reintroductions."

Sampling of a tooth from a suspected plague burial. Credit: Evelyn Guevara

Possible evidence of convergent evolution in strains from two independent historical pandemics

Another interesting finding of the study was that plague genomes appearing towards the end of the First Pandemic showed a big deletion in their genetic code that included two virulence factors. Plague genomes from the late stages of the Second Pandemic some 800-1000 years later show a similar deletion covering the same region of the genomes. "This is a possible example of convergent evolution, meaning that these Y. pestis strains independently evolved similar characteristics. Such changes may reflect an adaptation to a distinct ecological niche in Western Eurasia where the plague was circulating during both pandemics," explains co-first author Maria Spyrou of the Max Planck Institute for the Science of Human History.

The current study offers new insights into the first historically documented plague pandemic, and provides additional clues alongside historical, archaeological, and palaeoepidemiological evidence, helping to answer outstanding questions. "This study shows the potential of palaeogenomic research for understanding historical and modern pandemics by comparing genomes across millennia," explains senior author Johannes Krause of the Max Planck Institute for the Science of Human History. "With more extensive sampling of possible plague burials, we hope to contribute to the understanding of Y. pestis' microevolution and its impact on humans during the course of past and present pandemics."

Lunel-Viel (Languedoc-Southern France). Victim of the plague thrown into a demolition trench of a Gallo-Roman house; end of the 6th-early 7th century. Credit: 1990; CNRS - Claude Raynaud

Press release from the Max Planck Institute for the Science of Human History / Max-Planck-Instituts für Menschheitsgeschichte


Unexpected potential paths for the spread of Homo Sapiens across Asia in Late Pleistocene

Humans used northern migration routes to reach eastern Asia

New article suggests wetter climates may have allowed Homo sapiens to expand across the deserts of Central Asia by 50-30,000 years ago

 

Northern and Central Asia have been neglected in studies of early human migration, with deserts and mountains being considered uncompromising barriers. However, a new study by an international team argues that humans may have moved through these extreme settings in the past under wetter conditions. We must now reconsider where we look for the earliest traces of our species in northern Asia, as well as the zones of potential interaction with other hominins such as Neanderthals and Denisovans.

Archaeologists and palaeoanthropologists are increasingly interested in discovering the environments facing the earliest members of our species, Homo sapiens, as it moved into new parts of Eurasia in the Late Pleistocene (125,000-12,000 years ago). Much attention has focused on a 'southern' route around the Indian Ocean, with Northern and Central Asia being somewhat neglected. However, in a paper published in PLOS ONE, scientists of the Max Planck Institute for the History of Human Science in Jena, Germany, and colleagues at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China, argue that climate change may have made this a particularly dynamic region of hominin dispersal, interaction, and adaptation, and a crucial corridor for movement.

'Heading North' Out of Africa and into Asia

"Archaeological discussions of the migration routes of Pleistocene Homo sapiens have often focused on a 'coastal' route from Africa to Australia, skirting around India and Southeast Asia," says Professor Michael Petraglia of the Max Planck Institute for the Science of Human History, a co-author of the new study. "In the context of northern Asia, a route into Siberia has been preferred, avoiding deserts such as the Gobi." Yet over the past ten years, a variety of evidence has emerged that has suggested that areas considered inhospitable today might not have always been so in the past.

"Our previous work in Saudi Arabia, and work in the Thar Desert of India, has been key in highlighting that survey work in previously neglected regions can yield new insights into human routes and adaptations," says Petraglia. Indeed, if Homo sapiens could cross what is now the Arabian Deserts then what would have stopped it crossing other currently arid regions such as the Gobi Desert, the Junggar Basin, and the Taklamakan Desert at different points in the past? Similarly, the Altai Mountains, the Tien Shan and the Tibetan Plateau represent a potentially new high altitude window into human evolution, especially given the recent Denisovan findings from Denisova Cave in Russia and at the Baishiya Karst Cave in China.

Nevertheless, traditional research areas, a density of archaeological sites, and assumptions about the persistence of environmental 'extremes' in the past has led to a focus on Siberia, rather than the potential for interior routes of human movement across northern Asia.

A "Green Gobi"?

The sand dunes of Mongol Els jutting out of the steppe in Mongolia. Many of these desert barriers only appeared after the Last Glacial Maximum (~20,000 years ago). Credit: Nils Vanwezer

Indeed, palaeoclimatic research in Central Asia has increasingly accumulated evidence of past lake extents, past records of changing precipitation amounts, and changing glacial extents in mountain regions, which suggest that environments could have varied dramatically in this part of the world over the course of the Pleistocene. However, the dating of many of these environmental transitions has remained broad in scale, and these records have not yet been incorporated into archaeological discussions of human arrival in northern and Central Asia.

"We factored in climate records and geographical features into GIS models for glacials (periods during which the polar ice caps were at their greatest extent) and interstadials (periods during the retreat of these ice caps) to test whether the direction of past human movement would vary, based on the presence of these environmental barriers," says Nils Vanwezer, PhD student at the Max Planck Institute for the Science of Human History and a joint lead-author of the study.

"We found that while during 'glacial' conditions humans would indeed likely have been forced to travel via a northern arc through southern Siberia, during wetter conditions a number of alternative pathways would have been possible, including across a 'green' Gobi Desert," he continues. Comparisons with the available palaeoenvironmental records confirm that local and regional conditions would have been very different in these parts of Asia in the past, making these 'route' models a definite possibility for human movement.

Where did you come from, where did you go?

Ancient lake landforms around Biger Nuur, Mongolia, which is evidence of larger lake sizes in the past. Credit: Nils Vanwezer

"We should emphasize that these routes are not 'real', definite pathways of Pleistocene human movement. However, they do suggest that we should look for human presence, migration, and interaction with other hominins in new parts of Asia that have been neglected as static voids of archaeology," says Dr. Patrick Roberts also of the Max Planck Institute for the Science of Human History, co-author of the study. "Given what we are increasingly discovering about the flexibility of our species, it would be of no surprise if we were to find early Homo sapiens in the middle of modern deserts or mountainous glacial sheets."

"These models will stimulate new survey and fieldwork in previously forgotten regions of northern and Central Asia," says Professor Nicole Boivin, Director of the Department of Archaeology at the Max Planck Institute for the Science of Human History, and co-author of the study. "Our next task is to undertake this work, which we will be doing in the next few years with an aim to test these new potential models of human arrival in these parts of Asia."

 

Press release from the Max Planck Institute for the Science of Human History / Max-Planck-Instituts für Menschheitsgeschichte

 

Homo sapiens may have had several routes of dispersal across Asia in the Late Pleistocene

A new model identifies unexpected potential paths for the spread of human culture and technology

Eastern Asia Central Homo Sapiens migrations
Illustrated dispersal routes from the results of the Least Cost Path analysis: The three routes from the "wet" simulations and the single route from the "dry" simulation are presented together in conjunction with palaeoclimatic extents (glaciers and palaeolakes). Sites: 4. Obi-Rakhmat, 5. Shugnou, 8. Denisova, 9. Ust-Karakol, 10. Kara-Tenesh, 11. Kara-Bom, 12. Luotuoshi, 14. Gouxi, 15. Lenghu 1, 17. Chikhen Agui, 18. Tsagaan Agui, 19. Tolbor 4, 20. Kharganyn Gol 5, 21. Orkhon 1 & 7, 22. Makarovo 4, 23. Kandabaevo, 24. Varvarina Gora, 25. Tolbaga, 27. Shuidonggou 1, 28. Shuidonggou 9, 42. Yushuwan, 70. Shibazhan (75075). I. 'Altai' Route, II. 'Tian Shan' Route, III. 'Tarim' Route, IV. "Revised Overland' Route. Base map raster is from naturalearthdata.com. Credit: Li et al, 2019

Homo sapiens may have had a variety of routes to choose from while dispersing across Asia during the Late Pleistocene Epoch, according to a study released May 29, 2019 in the open-access journal PLOS ONE by Feng Li of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing and colleagues.

After leaving Africa, Homo sapiens dispersed across the Asian continent during the Late Pleistocene, but it isn't known exactly what routes our species followed. Most models assume that the Gobi Desert and Altai Mountain chains of North and Central Asia formed impassable barriers on the way to the east, so archaeological exploration has tended to neglect those regions in favor of seemingly more likely paths farther north and south.

In this study, Li and colleagues use Geographic Information Systems (GIS) software alongside archaeological and paleoclimate data to reconstruct the conditions of North and Central Asia over the Late Pleistocene and to identify possible routes of travel. Their data suggest that the desert and mountain regions were likely impassable during cold and dry glacial periods, but that during warmer and wetter interglacial times it would have been possible for human populations to traverse these regions via at least three routes following ancient lake and river systems.

The authors caution that these data do not demonstrate definite routes of dispersal and that more detailed models should be constructed to test these results. However, these models do identify specific routes that may be good candidates for future archaeological exploration. Understanding the timing and tempo of Homo sapiens dispersal across Asia will be crucial for determining how culture and technology spread and developed, as well as how our species interacted with our extinct cousins, the Neanderthals and Denisovans.

Roberts adds: "Our modelling of the available geographic and past climate data suggest that archaeologists and anthropologists should look for early human presence, migration, and interaction with other hominins in new parts of Asia that have been neglected as static voids. Given what we are increasingly discovering about the flexibility of our species, it would be of no surprise if we were to find early Homo sapiens in the middle of modern deserts or mountainous glacial sheets all across Asia. Indeed, it may be here that the key to our species' uniqueness lies".

###

Citation: Li F, Vanwezer N, Boivin N, Gao X, Ott F, Petraglia M, et al. (2019) Heading north: Late Pleistocene environments and human dispersals in central and eastern Asia. PLoS ONE 14(5): e0216433. https://doi.org/10.1371/journal.pone.0216433

Funding: This study was funded by Max-Planck-Gesellschaft (DE) to Nicole Boivin, Strategic Priority Research Program of Chinese Academy of Sciences grant XDB26000000 to Feng Li, and Youth Innovation Promotion Association of the Chinese Academy of Sciences grant 2017102 to Feng Li. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: The authors have declared that no competing interests exist.

 

Press release from the Public Library of Sciences


apple

Exploring the origins of the apple

Exploring the origins of the apple

Apples originally evolved in the wild to entice ancient megafauna to disperse their seeds; more recently, humans began spreading the trees along the Silk Road with other familiar crops; dispersing the apple trees led to their domestication

wild horses apple
Horses eating wild apples in the Tien Shan Mountains. These domesticated horses demonstrate the process of seed dispersal that wild apple trees evolved to support millions of years ago, when large monogastric mammals such as these were prominent across Eurasia. Credit: Artur Stroscherer

Recent archaeological finds of ancient preserved apple seeds across Europe and West Asia combined with historical, paleontological, and recently published genetic data are presenting a fascinating new narrative for one of our most familiar fruits. In this study, Robert Spengler of the Max Planck Institute for the Science of Human History traces the history of the apple from its wild origins, noting that it was originally spread by ancient megafauna and later as a process of trade along the Silk Road. These processes allowed for the development of the varieties that we know today.

The apple is, arguably, the most familiar fruit in the world. It is grown in temperate environments around the globe and its history is deeply intertwined with humanity. Depictions of large red fruits in Classical art demonstrate that domesticated apples were present in southern Europe over two millennia ago, and ancient seeds from archaeological sites attest to the fact that people have been collecting wild apples across Europe and West Asia for more than ten thousand years. While it is clear that people have closely maintained wild apple populations for millennia, the process of domestication, or evolutionary change under human cultivation, in these trees is not clear.

Several recent genetic studies have demonstrated that the modern apple is a hybrid of at least four wild apple populations, and researchers have hypothesized that the Silk Road trade routes were responsible for bringing these fruits together and causing their hybridization. Archaeological remains of apples in the form of preserved seeds have been recovered from sites across Eurasia, and these discoveries support the idea that fruit and nut trees were among the commodities that moved on these early trade routes. Spengler recently summarized the archaeobotanical and historical evidence for cultivated crops on the Silk Road in a book titled Fruit from the Sands, published with the University of California Press. The apple holds a deep connection with the Silk Road - much of the genetic material for the modern apple originated at the heart of the ancient trade routes in the Tien Shan Mountains of Kazakhstan. Furthermore, the process of exchange caused the hybridization events that gave rise to the large red sweet fruits in our produce markets.

Understanding how and when apple trees evolved to produce larger fruits is an important question for researchers, because fruit trees do not appear to have followed the same path towards domestication as other, better-understood crops, such as cereals or legumes. Many different wild and anthropogenic forces apply selective pressure on the crops in our fields, it is not always easy to reconstruct what pressures caused which evolutionary changes. Therefore, looking at evolutionary processing in modern and fossil plants can help scholars interpret the process of domestication. Fleshy sweet fruits evolve to attract animals to eat then and spread their seeds; large fruits specifically evolve to attract large animals to disperse them.

apple
The wild apples in the Tien Shan Mountains represent the main ancestral population for our modern apple. These trees produce large fruits, which are often red when ripe and have a varying array of flavors. These were the ancestors of the trees that people first started to cultivate and spread along the Silk Road. Credit: Prof. Dr. Martin R. Stuchtey

Large fruits evolved to attract ancient megafauna

While most scholars studying domestication focus on the period when humans first start cultivating a plant, in this study Spengler explores the processes in the wild that set the stage for domestication. Spengler suggests that understanding the process of evolution of large fruits in the wild will help us understand the process of their domestication. "Seeing that fruits are evolutionary adaptations for seed dispersal, the key to understanding fruit evolution rests in understanding what animals were eating the fruits in the past," he explains.

Many fruiting plants in the apple family (Rosaceae) have small fruits, such as cherries, raspberries, and roses. These small fruits are easily swallowed by birds, which then disperse their seeds. However, certain trees in the family, such as apples, pears, quince, and peaches, evolved in the wild to be too large for a bird to disperse their seeds. Fossil and genetic evidence demonstrate that these large fruits evolved several million years before humans started cultivating them. So who did these large fruits evolve to attract?

The evidence suggests that large fruits are an evolutionary adaptation to attract large animals that can eat the fruits and spread the seeds. Certain large mammals, such as bears and domesticated horses, eat apples and spread the seeds today. However, prior to the end of the last Ice Age, there were many more large mammals on the European landscape, such as wild horses and large deer. Evidence suggests that seed dispersal in the large-fruiting wild relatives of the apple has been weak during the past ten thousand years, since many of these animals went extinct. The fact that wild apple populations appear to map over glacial refugial zones of the Ice Age further suggests that these plants have not been moving over long distances or colonizing new areas in the absence of their original seed-spreaders.

Trade along the Silk Road likely enabled the development of the apple we know today

Silk Road apple
Venders in every Central Asian bazaar sell a diverse array of apples. This women in the Bukhara bazaar is selling a variety of small sweet yellow apples, which she locally cultivated in Uzbekistan. Some of the fruits sold in these markets today travel great distances, similar to how they would have during the peak of the Silk Road. Credit: Robert Spengler

Wild apple tree populations were isolated after the end of the last Ice Age, until humans started moving the fruits across Eurasia, in particular along the Silk Road. Once humans brought these tree lineages back into contact with each other again, bees and other pollinators did the rest of the work. The resulting hybrid offspring had larger fruits, a common result of hybridization. Humans noticed the larger fruiting trees and fixed this trait in place through grafting and by planting cuttings of the most favored trees. Thus, the apples we know today were primarily not developed through a long process of the selection and propagation of seeds from the most favored trees, but rather through hybridization and grafting. This process may have been relatively rapid and parts of it were likely unintentional. The fact that apple trees are hybrids and not "properly" domesticated is why we often end up with a crabapple tree when we plant an apple seed.

This study challenges the definition of "domestication"' and demonstrates that there is no one-shoe-fits-all model to explain plant evolution under human cultivation. For some plants, domestication took millennia of cultivation and human-induced selective pressure - for other plants, hybridization caused rapid morphological change. "The domestication process is not the same for all plants, and we still do not know much about the process in long-generation trees," notes Spengler. "It is important that we look past annual grasses, such as wheat and rice, when we study plant domestication. There are hundreds of other domesticated plants on the planet, many of which took different pathways toward domestication." Ultimately, the apple in your kitchen appears to owe its existence to extinct megafaunal browsers and Silk Road merchants.

 

 

Press release from the Max Planck Institute for the Science of Human History / Max-Planck-Institut für Menschheitsgeschichte


Inner Eurasia

Details of the history of inner Eurasia revealed by new study

Details of the history of inner Eurasia revealed by new study

Researchers combining genetics, archaeology, history and linguistics have gained new insights into the history of inner Eurasia, once a cultural and genetic crossroads connecting Europe and Asia

Inner Eurasia
Children from one of the Tajikistan communities included in the study. Credit: Elena Balanovska

An international team of researchers has combined archaeological, historical and linguistic data with genetic information from over 700 newly analyzed individuals to construct a more detailed picture of the history of inner Eurasia than ever before available. In a study published in Nature Ecology & Evolution, they found that the indigenous populations of inner Eurasia are very diverse in their genes, culture and languages, but divide into three groups that stretch across the area in east-west geographic bands.

Inner Eurasia, including areas of modern-day Armenia, Georgia, Kazakhstan, Moldova, Mongolia, Russia, Tajikistan, Ukraine and Uzbekistan, was once the cross-roads connecting Asia and Europe, and a major intersection for the exchange of culture, trade goods and genes in prehistory and historical periods, including the era of the famous Silk Road.

This vast area can also be divided into several distinct ecological regions that stretch in largely east-west bands across Inner Eurasia, consisting of the deserts at the southern edge of the region, the steppe in the central part, taiga forests further north, and tundra towards the Arctic region. The subsistence strategies used by indigenous groups in these regions largely correlate with the ecological zones, for example reindeer herding and hunting in the tundra region and nomadic pastoralism on the steppe.

Despite the long and important history of inner Eurasia, details about past migrations and interactions between groups are not always clear, especially in prehistory. "Inner Eurasia is a perfect place to investigate the relationship between environmental conditions and the pattern of human migration and mixture, as well as changes driven by cultural innovations such as the introduction of dairy pastoralism into the steppe," states Choongwon Jeong of the Max Planck Institute for the Science of Human History, co-first and senior author of the paper. In order to clarify our understanding of some of the nuances of the history of the region, an international team of researchers undertook an ambitious project to use modern and ancient DNA from a broad geographic range and time period, in concert with archaeological, linguistic and historical information, to clarify the relationships between the different populations. "A few ethnic groups were studied previously," comments Oleg Balanovsky from the Vavilov Institute of General Genetics in Moscow, also co-first author, "but we conducted more than a hundred field trips to study this vast region systematically, and reached communities speaking almost all of the Inner Eurasian languages".

Three distinct east-west groupings

For this study, the researchers analyzed DNA from 763 individuals from across the region as well as reanalyzed the genome-wide data from two ancient individuals from the Botai culture, and compared those results with previously published data from modern and ancient individuals. They found three distinct genetic groupings, which geographically are arranged in east-west bands stretching across the region and correlating generally to ecological zones, where populations within each band share a distinct combination of ancestries in varying proportions.

The northernmost grouping, which they term "forest-tundra", includes Russians, all Uralic language-speakers, which includes Hungarian, Finnish and Estonian, and Yeniseian-language speakers, of which only one remains today and is spoken in central Siberia. The middle grouping, which they term "steppe-forest", includes Turkic- and Mongolic-speaking populations from the Volga and the region around the Altai and Sayan mountains, near to where Russia, China, Mongolia and Kazakhstan meet. The southernmost grouping, "southern-steppe", includes the rest of Turkic- and Mongolic-speaking populations living further south, such as Kazakhs, Kyrgyzs and Uzbeks, as well as Indo-European-speaking Tajiks.

Previously unknown genetic connections revealed

Because the study includes data from a broad time period, it is able to show shifts in ancestry in the past that reveal previously unknown interactions. For example, the researchers found that the southern-steppe populations had a larger genetic component from West and South Asia than the other two groupings. This component is also widespread in the ancient populations of the region since the second half of the first millennium BC, but not found in Central Kazakhstan in earlier periods. This hints at a population movement from the southern-steppe region to the steppe-forest region that was previously unknown.

"Inner Eurasia has functioned as a conduit for human migration and cultural transfer since the first appearance of modern humans in this region. As a result, we observe deep sharing of genes between Western and Eastern Eurasian populations in multiple layers," explains Jeong. "The opportunity to find direct evidence for the hidden old layers of admixture, which is often difficult to appreciate from present-day populations, is very exciting."

"We found not only corridors, but also barriers for migrations," adds Balanovsky. "Some of them separate the historical groups of populations, while others, like the distinct barrier following the Great Caucasus mountain ridge, were obviously shaped by the geographic landscape."

Geographic locations of the Eneolithic Botai, groups including newly sampled individuals, and nearby groups with published data. The map is overlayed with ecoregional information, divided into 14 biomes downloaded from https://ecoregions2017.appspot.com/ (credited to Ecoregions 2017 © Resolve). Credit: Jeong & Balanovsky et. al. 2019. The genetic history of admixture across inner Eurasia. Nature Ecology & Evolution, http://dx.doi.org/10.1038/s41559-019-0878-2.

Two ancient individuals resequenced in this study originated from the Botai culture in Kazakhstan where the horse was initially domesticated. Analysis of the Y-chromosome (inherited along the paternal genealogical lines) revealed a genetic lineage which is typical in the Kazakh steppe up to the present day. But analysis of the autosomes, which both parents contribute to their children, show no trace of Botai ancestry left in present-day people, likely due to repeated migrations into the region both from the west and the east since the Bronze Age.

The researchers emphasize that their model of three groupings does not perfectly explain all known populations and that there are examples of both outliers and intermediate groups. "It is important to organize a future study for further sampling of sparsely populated regions between the clines, for example, Central Kazakhstan or East Siberia," states Johannes Krause, also of the Max Planck Institute for the Science of Human History, and senior author of the paper.

Researchers from the study conducting field work along the Amur River. Credit: Yuri Bogunov

Press release from the Max Planck Institute for the Science of Human History / Max-Planck-Institut für Menschheitsgeschichte


Trees in Amazonia reveal pre-colonial human disturbance

Human history through tree rings: Trees in Amazonia reveal pre-colonial human disturbance

New study shows that tropical trees act as a living record of past human activity in the Amazon

 

The Brazil nut tree (Bertholletia excelsa) is well known around the world today and has been an important part of human subsistence strategies in the Amazon forest from at least the Early Holocene. These trees can live for hundreds of years and are managed today by humans for their valuable, energy-filled nuts. Patterns in the establishment and growth of living Brazil nut trees in Central Amazonia reflect over 400 years of changes in human occupation, politics, and socio-economic activities in the region.

Brazil nut fruit and tree in the background. Credit: Victor L. Caetano Andrade

In a new paper published in PLOS ONE, an international team of scientists reports the combined use of dendrochronology and historical survey to investigate the effects of societal and demographic changes on forest disturbances and growth dynamics in a neotropical tree species, the Brazil nut tree. The study, led by scientists from the National Institute for Amazonian Research, alongside colleagues from the Max Planck Institute for the Science of Human History, shows the influence of human populations and their management practices on the domestication of rainforest landscapes. The researchers used non-destructive sampling, in which small samples are removed from the bark to the center of the trees, and compared tree-ring data from cores of 67 trees. This is the first study of human influence on the growth of trees that extends as far back as 400 years, to pre-colonial times in that region of Brazil. This work also reinforces that pre-colonial populations left important imprints in the Amazon, contributing to changing forest structure and resources through time.

Domesticated Amazonia

Until recently, forests in the Amazon Basin have often been argued to be "pristine" or the site of only small-scale human occupation and use prior to the arrival of European explorers in the 16th century. However, recent archaeobotanical, archaeological, palaeoenvironmental, and ecological research has highlighted extensive and diverse evidence for plant domestication, plant dispersal, forest management, and landscape alteration by pre-Columbian societies.

Nevertheless, human management of tropical forests has undergone a number of drastic changes with the rise of global industrialized societies. Many economically important trees dominate modern Amazonian forests, some of which have undergone domestication processes. Therefore, understanding the changes in forest management witnessed by Amazonian forests over the course of the last centuries has significant implications for ongoing human interaction with these threatened ecosystems.

"The results of this study demonstrate that Brazil nut tree growth reflects human occupation intensity and management. This is one more step to understanding the crucial interactions that led the Amazon forest to be the dynamic, humanized landscape it is today", says Victor Caetano Andrade, lead author of the study, of the Max Planck Institute for the Science of Human History.

Brazil nut tree close to a house on the lakeshore. Credit: Victor L. Caetano Andrade

A history recorded in rings

Recently, dendroecological studies have emerged as a promising avenue for the investigation of changes in the environment in tropical forests. These studies evaluate the rings formed annually in some tree species to obtain information on their age and annual growth, as is the case with the Brazil nut tree. Patterns of establishment and abrupt changes in tree growth, which are visible in a tree's rings, provide insights into past local environmental conditions. In the current study, the researchers worked in an area of Central Amazonia near Manaus with high Brazil nut tree density, known locally as castanhais. Through non-destructive sampling, in which small samples are removed from the bark to the center of the trees, they compared tree-ring data from cores of 67 trees with the available historical information on the political, economic, and human demographic changes in the region over the last 400 years.

Amazonia tree rings dendrochronology Brazil nut tree
Measuring the diameter of a Brazil nut tree trunk. Credit: Victor L. Caetano Andrade

Indigenous and colonial: a change in the way of living with the forest

Based on their interpretation of the tree rings, the researchers were able to construct a picture of the life-histories of these nut trees and how they correlate with pre- and post-colonial human forest management. The management of trees in Amazon forest often involves practices that include the clearance of the understory, opening of the forest canopy, cutting down woody vining plants, and active protection of individuals. The researchers undertook the study hoping to find evidence of these practices in tree rings.

The researchers gathered historical information about the Mura indigenous people, who inhabited the region before the establishment of the Portuguese colonial administration and witnessed their own population decline from the 18th century onwards, followed by the emergence of a new post-colonial society. During the transition between Indigenous population decline and the expansion of a post-colonial political center (the city of Manaus), human population was low, coinciding with a period during which no new trees were established in the region.

This gap in the establishment of new trees suggests that there was an interruption of indigenous management practices likely due to population collapse, as in many other pre-Columbian societies. A later period of renewed tree establishment, also associated with changes in growth rates of existing trees, aligns with a shift to modern exploitation of the forest in the late 19th and 20th century.

Understanding how forest management has changed following the arrival of European colonists and the rise of industrial powers over the course of the past centuries has implications for the future of sustainable forestry and conservation in Amazonia. "Our findings shed light on how past histories of human-forest interactions can be revealed by the growth rings of trees in Amazonia," explains Caetano Andrade. "Future interdisciplinary analysis of these trees, including the use of genetics and isotopes, should enable more detailed investigations into how human forest management has changed in this part of the world, through pre-colonial, colonial, and industrial periods of human activity, with potential implications for conservation."

 

Press release from the Max Planck Institute for the Science of Human History/Max-Planck-Institut für Menschheitsgeschichte (MPI-SHH)