Unveiling 1,200 years of human occupation in Canada’s Arctic

 

New evidence suggests earlier presence of Thule-Inuit settlements in Nunavut than previously thought

 

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PHOTO: SAMPLING CREW COLLECTING A SEDIMENT CORE AT PAJS-13, A THULE-INUIT SITE ON SOMERSET ISLAND, NUNAVUT, WITH THE REMNANTS OF WHALEBONE HOUSES VISIBLE IN THE BACKGROUND. PHOTO CREDIT: JULES BLAIS, UNIVERSITY OF OTTAWA

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CREDIT: PHOTO CREDIT: JULES BLAIS, UNIVERSITY OF OTTAWA

A recent study provides new insights into ancient cultures in Canada’s Arctic, focusing on Paleo-Inuit and Thule-Inuit peoples over thousands of years. Jules Blais, professor of biology at the University of Ottawa, and a team of researchers detected human presence and settlements on Somerset Island, Nunavut, by analyzing sediment samples.

The Arctic has been home to various cultures, such as the Paleo-Inuit (2500 BCE to 1250 CE) and the Thule-Inuit (1200 to 1500 CE). Although historical evidence is scarce, this recent study provides valuable insight into their presence.

The study discovered evidence of Paleo-Inuit presence on Somerset Island in Nunavut, Canada, where it was lacking. The innovative research methodologies revealed detailed information about past human history without traditional artifacts.

Professor Jules Blais says, “By analyzing pond sediment samples, we were able to construct detailed histories of site occupation. This includes clear evidence of Paleo-Inuit presence and indications that the Thule-Inuit arrived earlier than previously estimated.”

The research used archeological evidence and sedimentary biomarkers to study prehistoric settlement on Somerset Island. Sediment cores from island ponds were analyzed for trace elements and organic compounds. Results showed that the Thule-Inuit population increased from the 13th to 15th centuries. The researchers also showed high levels of metals like lead, copper, zinc and nickel in twentieth-century sediment, suggesting air pollution during that time.

Blais says, “We used generalized additive models (GAMs) and radiocarbon dating techniques to identify key time points in the sediment record corresponding to the expected dates of Thule-Inuit arrival and site abandonment. This approach allowed us to detect periods of significant change in sediment proxies, providing a chronological framework for understanding the history of human occupation on the island.”

This research underscores the importance of interdisciplinary approaches in archeology and highlights the significance of sedimentary archives in reconstructing past human activities and environmental conditions.

Blais explains the broader implications of the study. “The use of sedimentary biomarkers and bone samples to uncover prehistoric habits demonstrates the strength of interdisciplinary studies. Our discoveries not only enhance our knowledge of the Thule-Inuit and Paleo-Inuit communities in the Arctic but also demonstrate the potential of new archeological techniques.”

The study “Sedimentary biomarkers and bone specimens reveal a history of prehistoric occupation on Somerset Island (Arctic Canada)” was published July 9 in the Proceedings of the Royal Society B journal.  

 

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JOURNAL

Proceedings of the Royal Society B Biological Sciences

DOI

10.1098/rspb.2023.2915 

Geneticists are rewriting the narrative of Neanderthals and other ancient humans

 

Modern humans and Neanderthals interacted over a 200,000 year period, says geneticist Joshua Akey

Ever since the first Neanderthal bones were discovered in 1856, people have wondered about these ancient hominins. How are they different from us? How much are they like us? Did our ancestors get along with them? Fight them? Love them? The recent discovery of a group called Denisovans, a Neanderthal-like group who populated Asia and South Asia, added its own set of questions.

Now, an international team of geneticists and AI experts are adding whole new chapters to our shared hominin history. Under the leadership of Joshua Akey, a professor in Princeton’s Lewis-Sigler Institute for Integrative Genomics, the researchers have found a history of genetic intermingling and exchange that suggests a much more intimate connection between these early human groups than previously believed.

“This is the first time that geneticists have identified multiple waves of modern human-Neanderthal admixture,” said Liming Li, a professor in the Department of Medical Genetics and Developmental Biology at Southeast University in Nanjing, China, who performed this work as an associate research scholar in Akey’s lab.

“We now know that for the vast majority of human history, we've had a history of contact between modern humans and Neanderthals,” said Akey. The hominins who are our most direct ancestors split from the Neanderthal family tree about 600,000 years ago, then evolved our modern physical characteristics about 250,000 years ago.

“From then until the Neanderthals disappeared — that is, for about 200,000 years — modern humans have been interacting with Neanderthal populations,” he said.

The results of their work appear in the current issue of the journal Science.

Neanderthals, once stereotyped as slow-moving and dim-witted, are now seen as skilled hunters and tool makers who treated each other’s injuries with sophisticated techniques and were well adapted to thrive in the cold European weather.

(Note: All of these hominin groups are humans, but to avoid saying “Neanderthal humans,” “Denisovan humans,” and “ancient-versions-of-our-own-kind-of-humans,” most archaeologists and anthropologists use the shorthand Neanderthals, Denisovans, and modern humans.)

Using genomes from 2,000 living humans as well as three Neanderthals and one Denisovan, Akey and his team mapped the gene flow between the hominin groups over the past quarter-million years.

The researchers used a genetic tool they designed a few years ago called IBDmix, which uses machine learning techniques to decode the genome. Previous researchers depended on comparing human genomes against a “reference population” of modern humans believed to have little or no Neanderthal or Denisovan DNA.

Akey’s team has established that even those referenced groups, who live thousands of miles south of the Neanderthal caves, have trace amounts of Neanderthal DNA, probably carried south by voyagers (or their descendants).

With IBDmix, Akey’s team identified a first wave of contact about 200-250,000 years ago, another wave 100-120,000 years ago, and the largest one about 50-60,000 years ago.

That contrasts sharply with previous genetic data. “To date, most genetic data suggests that modern humans evolved in Africa 250,000 years ago, stayed put for the next 200,000 years, and then decided to disperse out of Africa 50,000 years ago and go on to people the rest of the world,” said Akey.

“Our models show that there wasn’t a long period of stasis, but that shortly after modern humans arose, we've been migrating out of Africa and coming back to Africa, too,” he said. “To me, this story is about dispersal, that modern humans have been moving around and encountering Neanderthals and Denisovans much more than we previously recognized.”

That vision of humanity on the move coincides with the archaeological and paleoanthropological research suggesting cultural and tool exchange between the hominin groups.

Li and Akey’s key insight was to look for modern-human DNA in the genomes of the Neanderthals, instead of the other way around. “The vast majority of genetic work over the last decade has really focused on how mating with Neanderthals impacted modern human phenotypes and our evolutionary history — but these questions are relevant and interesting in the reverse case, too,” said Akey.

They realized that the offspring of those first waves of Neanderthal-modern matings must have stayed with the Neanderthals, therefore leaving no record in living humans. “Because we can now incorporate the Neanderthal component into our genetic studies, we are seeing these earlier dispersals in ways that we weren't able to before,” Akey said.

The final piece of the puzzle was discovering that the Neanderthal population was even smaller than previously believed.

Genetic modeling has traditionally used variation — diversity — as a proxy for population size. The more diverse the genes, the larger the population. But using IBDmix, Akey’s team showed that a significant amount of that apparent diversity came from DNA sequences that had been lifted from modern humans, with their much larger population.

As a result, the effective population of Neanderthals was revised down from about 3,400 breeding individuals down to about 2,400.

Put together, the new findings paint a picture of how the Neanderthals vanished from the record, some 30,000 years ago.

“I don’t like to say ‘extinction,’ because I think Neanderthals were largely absorbed,” said Akey. His idea is that Neanderthal populations slowly shrank until the last survivors were folded into modern human communities.

This “assimilation model” was first articulated by Fred Smith, an anthropology professor at Illinois State University, in 1989. “Our results provide strong genetic data consistent with Fred’s hypothesis, and I think that's really interesting,” said Akey.

“Neanderthals were teetering on the edge of extinction, probably for a very long time,” he said. “If you reduce their numbers by 10 or 20%, which our estimates do, that's a substantial reduction to an already at-risk population.

“Modern humans were essentially like waves crashing on a beach, slowly but steadily eroding the beach away. Eventually we just demographically overwhelmed Neanderthals and incorporated them into modern human populations.”

“Recurrent gene flow between Neanderthals and modern humans over the past 200,000 years,” by Liming Li, Troy J. Comi, Rob F. Bierma, and Joshua M. Akey, appears in the July 13 issue of the journal Science (DOI: 10.1126/science.adi1768). This research was supported by the National Institutes of Health (grant R01GM110068 to JMA).

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JOURNAL

Science

DOI

10.1126/science.adi1768 

The plague may have caused the downfall of the Stone Age farmers

 

Peer-Reviewed Publication

Ancient DNA from bones and teeth hints at a role of the plague in Stone Age population collapse. Contrary to previous beliefs, the plague may have diminished Europe's populations long before the major plague outbreaks of the Middle Ages, new research shows.

In the 14th century Europe, the plague ravaged the population during the so-called 'Black Death,' claiming the lives of nearly a third of the population.

But the plague arrived in Scandinavia several thousand years earlier, and despite several theories suggesting otherwise, the plague might have caused an epidemic, according to new research from the University of Copenhagen.

In collaboration with researchers from the University of Gothenburg in Sweden, researchers from the Globe Institute, have analyzed DNA from ancient teeth and bones of 108 individuals who died 5,000 years ago.

"The analyses show that 18 of these individuals, 17 percent, were infected with the plague when they died. Furthermore, our results suggests that the youngest plague strain we identify might have had epidemic potential," says postdoc Frederik Seersholm, who led the DNA analysis.

This means that the plague at that time may have been a contributing factor to the population collapse in the end of the Neolithic, known as the Neolithic decline. This population bust caused large parts of the farming population in Scandinavia and Northwestern Europe to disappear within just a few centuries, 5000 years ago.

"We cannot – yet – prove that this was exactly how it happened. But the fact that we can now show that it could have happened this way is significant. The cause of this population decline, which we have known about for a long time, has always been subject of debate," says Frederik Seersholm.

The archaeological material analysed comes mainly from passage graves in Sweden, but one of the individuals is from a stone cist in Stevns, Denmark.

Ancient DNA provides answers

The analyses were conducted using a method called "deep shotgun sequencing," which allows researchers to extract highly detailed information from archaeological material, even though ancient DNA is often heavily damaged or degraded. The researchers examined DNA from tooth and bone material from the Neolithic time period, studying both familial relations and diseases in the individuals.

“We have been able to carry out a comprehensive mapping of plague lineages, and a detailed  description of other microbes in the DNA data. At the same time, through these analyses, we have been able to look at the human DNA from a broad perspective to a local one – and right down to the individual level, getting a picture of the social organization that existed back then,” says Associate Professor Martin Sikora at the Globe Institute, who is also behind the study.

 

The finding that 17 percent of the individuals whose DNA was analyzed had plague, indicates that the plague was common in Scandinavia during the late Stone Age.

In one of the analyzed families, at least three plague outbreaks was observed over the six generations in the family that researchers have been able to map.

“The question of possible kinship relations between individuals whose bones and teeth have been found in megalithic tombs has been debated for at least 200 years. There have been many theories and speculations, but now, thanks to DNA, we have data,” says Karl-Göran Sjögren, Associate Professor of Archaeology at the University of Gothenburg, who was also involved in the new study.

Frederik Seersholm believes that the new results rules out previous theories suggesting that the population decline could not have been caused by plague.

“In connection with the population decline in the end of the Neolithic, both war and outbreaks of infectious diseases, including plague, have been suggested. There have been several theories involving the plague, and one of them suggested that the plague could not have caused an epidemic – but that assumption no longer holds,” says Frederik Seersholm.

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JOURNAL

Nature

DOI

10.1038/s41586-024-07651-2 

Archaeologists report earliest evidence for plant farming in east Africa

 

Peer-Reviewed Publication

 

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LOCATED IN THE FOOTHILLS OF MOUNT ELGON NEAR THE KENYA-UGANDA BORDER, KAKAPEL ROCKSHELTER IS THE SITE WHERE WASHU ARCHAEOLOGIST NATALIE MUELLER AND HER COLLABORATORS HAVE UNCOVERED THE EARLIEST EVIDENCE FOR PLANT FARMING IN EAST AFRICA. 

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CREDIT: STEVEN GOLDSTEIN

A trove of ancient plant remains excavated in Kenya helps explain the history of plant farming in equatorial eastern Africa, a region long thought to be important for early farming but where scant evidence from actual physical crops has been previously uncovered.

In a new study published July 10 in the Proceedings of the Royal Society B, archaeologists from Washington University in St. Louis, the University of Pittsburgh and their colleagues report the largest and most extensively dated archaeobotanical record from interior east Africa.

Up until now, scientists have had virtually no success in gathering ancient plant remains from east Africa and, as a result, have had little idea where and how early plant farming got its start in the large and diverse area comprising Kenya, Tanzania and Uganda.

“There are many narratives about how agriculture began in east Africa, but there’s not a lot of direct evidence of the plants themselves,” said WashU’s Natalie Mueller, an assistant professor of archaeology in Arts & Sciences and co-first author of the new study. The work was conducted at the Kakapel Rockshelter in the Lake Victoria region of Kenya.

“We found a huge assemblage of plants, including a lot of crop remains,” Mueller said. “The past shows a rich history of diverse and flexible farming systems in the region, in opposition to modern stereotypes about Africa.”

The new research reveals a pattern of gradual introductions of different crops that originated from different parts of Africa.

In particular, the remnants of cowpea discovered at Kakapel rock shelter and directly dated to 2,300 years ago constitute the earliest documented arrival of a domesticated crop — and presumably of farming lifeways — to eastern Africa. Cowpea is assumed to have originated in west Africa and to have arrived in the Lake Victoria basin concurrent with the spread of Bantu-speaking peoples migrating from central Africa, the study authors said.

“Our findings at Kakapel reveal the earliest evidence of domesticated crops in east Africa, reflecting the dynamic interactions between local herders and incoming Bantu-speaking farmers,” said Emmanuel Ndiema from the National Museums of Kenya, a project partner. “This study exemplifies National Museums of Kenya’s commitment to uncovering the deep historical roots of Kenya’s agricultural heritage and fostering an appreciation of how past human adaptations can inform future food security and environmental sustainability.”

Constantly changing landscape

Situated north of Lake Victoria, in the foothills of Mount Elgon near the Kenya-Uganda border, Kakapel is a recognized rock art site that contains archaeological artifacts that reflect more than 9,000 years of human occupation in the region. The site has been recognized as a Kenyan national monument since 2004.

“Kakapel Rockshelter is one of the only sites in the region where we can see such a long sequence of occupation by so many diverse communities,” said Steven T. Goldstein, an anthropological archaeologist at the University of Pittsburgh (WashU PhD ’17), the other first author of this study. “Using our innovative approaches to excavation, we have been uniquely able to detect the arrival of domesticated plants and animals into Kenya and study the impacts of these introductions on local environments, human technology and sociocultural systems.”

Mueller first joined Goldstein and National Museums of Kenya to conduct excavations at the Kakapel Rockshelter site in 2018. Their work is ongoing. Mueller is the lead scientist for plant investigations at Kakapel; the Max Planck Institute of Geoanthropology (in Jena, Germany) is another partner on the project.

Mueller used a flotation technique to separate remnants of wild and domesticated plant species from ashes and other debris in a hearth excavated at Kakapel. Although she has used this technique in her research in many other parts of the world, it is sometimes difficult to use this approach in water-scarce locations — so it has not been widely used in east Africa.

The scientists used direct radiocarbon dating on carbonized seeds to document the arrival of cowpea (also known as the black-eyed pea, today an important legume around the world) about 2,300 years ago, at about the same time that people in this area began to use domesticated cattle. Researchers also found evidence that sorghum arrived from the northeast at least 1,000 years ago. They also recovered hundreds of finger millet seeds, dating back to at least 1,000 years ago. This crop is indigenous to eastern Africa and is an important heritage crop for the communities that live near Kakapel today.

One unusual crop that Mueller uncovered was field pea (Pisum), burnt but perfectly intact. Peas were not previously considered to be part of early agriculture in this region. “To our knowledge, this is the only evidence of peas in Iron Age eastern Africa,” Mueller said.

The exceptional pea is pictured in the paper, and it represents its own little mystery. “The standard peas that we eat in North America were domesticated in the near east,” Mueller said. “They were grown in Egypt and probably ended up in east Africa by traveling down the Nile through Sudan, which is also likely how sorghum ended up in east Africa. But there is another kind of pea that was domesticated independently in Ethiopia called the Abyssinian pea, and our sample could be either one!”

Many of the plant remnants that Mueller and her team found at Kakapel could not be positively identified, Mueller said, because even modern scientists working in Kenya, Tanzania and Uganda today don’t have access to a good reference collection of samples of plants from east Africa. (As a separate project, Mueller is currently working on building such a comparative collection of Tanzania’s plants.)

“Our work shows that African farming was constantly changing as people migrated, adopted new crops and abandoned others at a local level,” Mueller said. “Prior to European colonialism, community-scale flexibility and decision-making was critical for food security — and it still is in many places.”

Findings from this study may have implications for many other fields, Mueller said, including historical linguistics, plant science and genetics, African history and domestication studies.

Mueller is continuing to work on identifying the wild plants in the assemblage, especially those from the oldest parts of the site, before the beginning of agriculture. “This is where human evolution occurred,” Mueller said. “This is where hunting and gathering was invented by people at the dawn of time. But there has been no archaeological evidence about which plants hunter-gatherers were eating from this region. If we can get that kind of information from this assemblage, then that is a great contribution.”

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JOURNAL

Proceedings of the Royal Society B Biological Sciences

DOI

10.1098/rspb.2023.2747 

Extinct humans survived on the Tibetan plateau for 160,000 years

Bone remains found in a Tibetan cave 3,280 m above sea level indicate an ancient group of humans survived here for many millennia, according to a new study published in Nature.  

The Denisovans are an extinct species of ancient human that lived at the same time and in the same places as Neanderthals and Homo sapiens. Only a handful Denisovan remains have ever been discovered by archaeologists. Little is known about the group, including when they became extinct, but evidence exists to suggest they interbred with both Neanderthals and Homo sapiens. 

A research team led by Lanzhou University, China, the University of Copenhagen, Denmark, the Institute of Tibetan Plateau Research, CAS, China, and involving the University of Reading studied more than 2,500 bones from the Baishiya Karst Cave on the high-altitude Tibetan Plateau, one of the only two places where Denisovans are known to have lived.  

Their new analysis, published today (Wednesday, 3 July) in Nature, has identified a new Denisovan fossil and shed light on the species’ ability to survive in fluctuating climatic conditions — including the ice age — on the Tibetan plateau from around 200,000 to 40,000 years ago. 

Dr Geoff Smith, a zooarchaeologist at the University of Reading, is a co-author of the study. He said: “We were able to identify that Denisovans hunted, butchered and ate a range of animal species. Our study reveals new information about the behaviour and adaptation of Denisovans both to high altitude conditions and shifting climates. We are only just beginning to understand the behaviour of this extraordinary human species.” 

Dietary diversity 

Bone remains from Baishya Karst Cave were broken into numerous fragments preventing identification. The team used a novel scientific method that exploits differences in bone collagen between animals to determine which species the bone remains came from.  

Dr Huan Xia, of Lanzhou University, said: “Zooarchaeology by Mass Spectrometry (ZooMS) allows us to extract valuable information from often overlooked bone fragments, providing deeper insight into human activities.”  

The research team determined that most of the bones were from blue sheep, known as the bharal, as well as wild yaks, equids, the extinct woolly rhino, and the spotted hyena. The researchers also identified bone fragments from small mammals, such as marmots, and birds.  

Dr Jian Wang, of Lanzhou University, said: “Current evidence suggests that it was Denisovans, not any other human groups, who occupied the cave and made efficient use of all the animal resources available to them throughout their occupation.”  

Detailed analysis of the fragmented bone surfaces shows the Denisovans removed meat and bone marrow from the bones, but also indicate the humans used them as raw material to produce tools.  

A new Denisovan fossil 

The scientists also identified one rib bone as belonging to a new Denisovan individual. The layer where the rib was found was dated to between 48,000 and 32,000 years ago, implying that this Denisovan individual lived at a time when modern humans were dispersing across the Eurasian continent. The results indicate that Denisovans lived through two cold periods, but also during a warmer interglacial period between the Middle and Late Pleistocene eras.   

Dr Frido Welker, of the University of Copenhagen, said: “Together, the fossil and molecular evidence indicates that Ganjia Basin, where Baishiya Karst Cave is located, provided a relatively stable environment for Denisovans, despite its high-altitude. 

"The question now arises when and why these Denisovans on the Tibetan Plateau went extinct.” 

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JOURNAL

Nature

DOI

10.1038/s41586-024-07612-9 

New study adds to mystery of Cahokia exodus

 

Peer-Reviewed Publication

 

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THE REMAINS OF THE MOST SOPHISTICATED PREHISTORIC NATIVE CIVILIZATION NORTH OF MEXICO ARE PRESERVED AT CAHOKIA MOUNDS STATE HISTORIC SITE IN ILLINOIS. ARCHAEOLOGIST NATALIE MUELLER'S NEW STUDY CASTS DOUBT ON A POPULAR THEORY ABOUT WHY THE ANCIENT CITY WAS ABANDONED.

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CREDIT: PHOTO: JOE ANGELES / WASHINGTON UNIVERSITY

Nine hundred years ago, the Cahokia Mounds settlement just across the Mississippi River from present-day St. Louis bustled with roughly 50,000 people in the metropolitan area, making it one of the largest communities in the world. By 1400, however, the once-popular site was practically deserted, a mass departure that remains shrouded in mystery.

One popular theory is that the Cahokia residents abandoned the settlement after a massive crop failure brought on by a prolonged drought. But a new study in the journal The Holocene by Natalie Mueller, assistant professor of archaeology in Arts & Sciences at Washington University in St. Louis, and Caitlin Rankin, PhD ’20, suggests the Cahokians likely had other reasons to leave town.

Rankin dug deep into the soil at the historic Cahokia site to collect isotopes of carbon, atoms left behind by the plants growing when the human population collapsed and drought was common across the Midwest.

All plants use one of two types of carbon, Carbon 12 and Carbon 13, for photosynthesis, but not all plants do photosynthesis the same way. Plants adapted to dry climates — including prairie grasses and maize, an important new crop during the Cahokia period — incorporate carbon into their bodies at rates that leave behind a tell-tale signature when the plants die and decay.

Most of the other plants that the Cahokians would have harvested for food — including squash, goosefoot and sumpweed — will leave a different signature, one they share with plants from wetlands and native forests.

Rankin’s samples showed that ratios of Carbon 12 and Carbon 13 stayed relatively consistent during that crucial period — a sign there was no radical shift in the types of plants growing in the area. “We saw no evidence that prairie grasses were taking over, which we would expect in a scenario where widespread crop failure was occurring,” Mueller said.

The Cahokians are known for their ingenuity, and Rankin said they may have had the engineering and irrigation skills to keep crops flourishing under difficult conditions. “It’s possible that they weren’t really feeling the impacts of the drought,” said Rankin, now an archaeologist with the Bureau of Land Management in Nevada.

Mueller added that the sophisticated society that blossomed at Cahokia almost certainly included a storage system for grains and other foods. Residents also enjoyed a varied and diverse diet — including fish, birds, deer, bear and forest fruits and nuts — that would have kept them nourished even if a few food sources disappeared.

To get a better grasp of the diets and agricultural practices of Indigenous people of the Midwest, Mueller hopes to build a database that collects paleo-botanical evidence from across the region. “Gathering that information would help us see if people switched to different crops in response to climate change,” she said. She’s also planning to grow certain food crops in controlled conditions on campus to understand how they might have responded to ancient droughts and other challenges.

So, why did the Cahokians leave their land of plenty? Mueller suspects it was a gradual process. “I don’t envision a scene where thousands of people were suddenly streaming out of town,” she said. “People probably just spread out to be near kin or to find different opportunities.”

“They put a lot of effort into building these mounds, but there were probably external pressures that caused them to leave,” Rankin said. “The picture is likely complicated.”

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This story was originally published on the Ampersand website.

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JOURNAL

The Holocene

DOI

10.1177/09596836241254488 

Humans were responsible for the extinction of large mammals

 

Human hunting, not climate change, played a decisive role in the extinction of large mammals over the last 50,000 years. This conclusion comes from researchers at Aarhus University, who reviewed over 300 scientific articles

 

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PREHISTORIC HUMANS HUNT A WOOLLY MAMMOTH. MORE AND MORE RESEARCH SHOWS THAT THIS SPECIES – AND AT LEAST 46 OTHER SPECIES OF MEGAHERBIVORES – WERE DRIVEN TO EXTINCTION BY HUMANS.

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CREDIT: ENGRAVING BY ERNEST GRISE, PHOTOGRAPHED BY WILLIAM HENRY JACKSON. COURTESY GETTY'S OPEN CONTENT PROGRAM

The debate has raged for decades: Was it humans or climate change that led to the extinction of many species of large mammals, birds, and reptiles that have disappeared from Earth over the past 50,000 years?

By "large," we mean animals that weighed at least 45 kilograms – known as megafauna. At least 161 species of mammals were driven to extinction during this period. This number is based on the remains found so far.

The largest of them were hit the hardest – land-dwelling herbivores weighing over a ton, the megaherbivores. Fifty thousand years ago, there were 57 species of megaherbivores. Today, only 11 remain. These remaining 11 species have also seen drastic declines in their populations, but not to the point of complete extinction.

A research group from the Danish National Research Foundation's Center for Ecological Dynamics in a Novel Biosphere (ECONOVO) at Aarhus University now concludes that many of these vanished species were hunted to extinction by humans.

Many different fields of research

They present this conclusion in a review article invited by and published in the scientific journal Cambridge Prisms: Extinction. A review article synthesizes and analyses existing research within a particular field.

In this case, the researchers from Aarhus University incorporated several research fields, including studies directly related to the extinction of large animals, such as:

- The timing of species extinctions

- The animals' dietary preferences

- Climate and habitat requirements

- Genetic estimates of past population sizes

- Evidence of human hunting

Additionally, they included a wide range of studies from other fields necessary to understand the phenomenon, such as:

- Climate history over the past 1-3 million years

- Vegetation history over the past 1-3 million years

- Evolution and dynamics of fauna over the past 66 million years

- Archaeological data on human expansion and lifestyle, including dietary preferences

Climate change played a lesser role

The dramatic climate changes during the last interglacial and glacial periods (known as the late Pleistocene, from 130,000 to 11,000 years ago) certainly affected populations and distributions of both large and small animals and plants worldwide. However, significant extinctions were observed only among the large animals, particularly the largest ones.

An important observation is that the previous, equally dramatic ice ages and interglacials over the past couple of million years did not cause a selective loss of megafauna. Especially at the beginning of the glacial periods, the new cold and dry conditions caused large-scale extinctions in some regions, such as trees in Europe. However, there were no selective extinctions of large animals.

"The large and very selective loss of megafauna over the last 50,000 years is unique over the past 66 million years. Previous periods of climate change did not lead to large, selective extinctions, which argues against a major role for climate in the megafauna extinctions," says Professor Jens-Christian Svenning. He leads ECONOVO and is the lead author of the article. He adds, "Another significant pattern that argues against a role for climate is that the recent megafauna extinctions hit just as hard in climatically stable areas as in unstable areas."

Effective hunters and vulnerable giants

Archaeologists have found traps designed for very large animals, and isotope analyses of ancient human bones and protein residues from spear points show that they hunted and ate the largest mammals.

Jens-Christian Svenning adds, "Early modern humans were effective hunters of even the largest animal species and clearly had the ability to reduce the populations of large animals. These large animals were and are particularly vulnerable to overexploitation because they have long gestation periods, produce very few offspring at a time, and take many years to reach sexual maturity."

The analysis shows that human hunting of large animals such as mammoths, mastodons, and giant sloths was widespread and consistent across the world.

It also shows that the species went extinct at very different times and at different rates around the world. In some local areas, it happened quite quickly, while in other places it took over 10,000 years. But everywhere, it occurred after modern humans arrived, or in Africa's case, after cultural advancements among humans.

…in all types of environments

Species went extinct on all continents except Antarctica and in all types of ecosystems, from tropical forests and savannas to Mediterranean and temperate forests and steppes to arctic ecosystems.

"Many of the extinct species could thrive in various types of environments. Therefore, their extinction cannot be explained by climate changes causing the disappearance of a specific ecosystem type, such as the mammoth steppe – which also housed only a few megafauna species," explains Jens-Christian Svenning. "Most of the species existed under temperate to tropical conditions and should actually have benefited from the warming at the end of the last ice age."

Consequences and recommendations

The researchers point out that the loss of megafauna has had profound ecological consequences. Large animals play a central role in ecosystems by influencing vegetation structure (e.g., the balance between dense forests and open areas), seed dispersal, and nutrient cycling. Their disappearance has resulted in significant changes in ecosystem structures and functions.

"Our results highlight the need for active conservation and restoration efforts. By reintroducing large mammals, we can help restore ecological balances and support biodiversity, which evolved in ecosystems rich in megafauna," says Jens-Christian Svenning.

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FACTS: The numbers of extinct and surviving species come from the freely accessible database PHYLACINE 1.2.1, which lists all known mammals that have lived in the past 129,000 years, including those that have gone extinct recently or are only found in captivity.

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JOURNAL

Cambridge Prisms Extinction

DOI

10.1017/ext.2024.4