Thursday, May 30, 2019
Ancient DNA illuminates first herders and farmers in east Africa
A collaborative study led by archaeologists, geneticists and museum curators is providing answers to previously unsolved questions about life in sub-Saharan Africa thousands of years ago. The results were published online in the journal Science Thursday, May 30. Researchers from North American, European and African institutions analyzed ancient DNA from 41 human skeletons curated in the National Museums of Kenya and Tanzania, and the Livingstone Museum in Zambia.
"The origins of food producers in East Africa have remained elusive because of gaps in the archaeological record," said co-first author Mary Prendergast, Ph.D., professor of anthropology and chair of humanities at Saint Louis University's campus in Madrid, Spain.
"This study uses DNA to answer previously unresolvable questions about how people were moving and interacting," added Prendergast.
The research provides a look at the origins and movements of early African food producers.
The first form of food production to spread through most of Africa was the herding of cattle, sheep and goats. This way of life continues to support millions of people living on the arid grasslands that cover much of sub-Saharan Africa.
"Today, East Africa is one of the most genetically, linguistically, and culturally diverse places in the world," explains Elizabeth Sawchuk, Ph.D., a bioarchaeologist at Stony Brook University and co-first author of the study. "Our findings trace the roots of this mosaic back several millennia. Distinct peoples have coexisted in the Rift Valley for a very long time."
Previous archaeological research shows that the Great Rift Valley of Kenya and Tanzania was a key site for the transition from foraging to herding. Herders of livestock first appeared in northern Kenya around 5000 years ago, associated with elaborate monumental cemeteries, and then spread south into the Rift Valley, where Pastoral Neolithic cultures developed.
The new genetic results reveal that this spread of herding into Kenya and Tanzania involved groups with ancestry derived from northeast Africa, who appeared in East Africa and mixed with local foragers there between about 4500-3500 years ago. Previously, the origins and timing of these population shifts were unclear, and some archaeologists hypothesized that domestic animals spread through exchange networks, rather than by movement of people.
After around 3500 years ago, herders and foragers became genetically isolated in East Africa, even though they continued to live side by side. Archaeologists have hypothesized substantial interaction among foraging and herding groups, but the new results reveal that there were strong and persistent social barriers that lasted long after the initial encounters.
Another major genetic shift occurred during the Iron Age around 1200 years ago, with movement into the region of additional peoples from both northeastern and western Africa. These groups contributed to ancient ancestry profiles similar to those of many East Africans today. This genetic shift parallels two major cultural changes: farming and iron-working.
The study provided insight into the history of East Africa as an independent center of evolution of lactase persistence, which enables people to digest milk into adulthood. This genetic adaptation is found in high proportions among Kenyan and Tanzanian herders today.
Wednesday, May 29, 2019
Declining fertility rates may explain Neanderthal extinction
The lack of empirical data allowing testing of hypotheses is one of the biggest challenges for researchers studying Neanderthal extinction. Many hypotheses involve catastrophic events such as disease or climate change. In order to test alternative hypothetical extinction scenarios, Degioanni and colleagues created a Neanderthal population model allowing them to explore demographic factors which might have resulted in declining populations and population extinction over a period of 4,000-10,000 years (a time frame compatible with known Neanderthal history). The researchers created baseline demographic parameters for their Neanderthal extinction model (e.g. survival, migration, and fertility rates) based on observational data on modern hunter-gatherer groups and extant large apes, as well as available Neanderthal paleo-genetic and empirical data from earlier studies. The authors defined populations as extinct when they fell below 5,000 individuals.
The authors saw that in their model, extinction would have been possible within 10,000 years with a decrease in fertility rates of young (<20 0.4="" 10="" 2.7="" 4="" 8="" a="" amplified="" by="" children="" could="" decrease="" decreased="" extinction="" fertility="" have="" if="" in="" infants="" just="" led="" less="" neanderthal="" occurred="" of="" old="" one="" p="" percent="" rate="" reduction="" survival="" than="" the="" this="" to="" was="" within="" women="" year-old="" year="" years.=""> The authors intended to explore possible Neanderthal extinction scenarios rather than to posit any definitive explanation. However, the researchers note that this study is the first to use empirical data to suggest that relatively minor demographic changes, such as a reduction in fertility or an increase in infant mortality, might have led to Neanderthal extinction. The authors note that modelling can be a useful tool in studying Neanderthals.
The authors add: "This study of the disappearance of the Neanderthals published today in PLOS ONE does not attempt to explain "why" the Neanderthals disappeared, but to identify "how" their demise may have taken place. This original approach is made on the basis of demographic modeling. The results suggest that a very small reduction in fertility may account for the disappearance of the Neanderthal population. According to this research, this decrease did not concern all female Neanderthals, but only the youngest (less than 20 years old)."
Homo sapiens may have had several routes of dispersal across Asia in the Late Pleistocene
Credit: Li et al, 2019
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".
Humans used northern migration routes to reach eastern Asia
y
Credit: Nils Vanwezer
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"? 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? "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."
Early humans deliberately recycled flint to create tiny, sharp tools
A new Tel Aviv University study finds that prehistoric humans "recycled" discarded or broken flint tools 400,000 years ago to create small, sharp utensils with specific functions. These recycled tools were then used with great precision and accuracy to perform specific tasks involved in the processing of animal products and vegetal materials.
Caption
Experimental activity of cutting tubers with a small recycled flake and a close-up of its prehension (inset).Credit
Flavia Venditti/AFTAU.In collaboration with Prof. Cristina Lemorini of Sapienza University of Rome, the research was led jointly by postdoctoral fellow Dr. Flavia Venditti in collaboration with Profs. Ran Barkai and Avi Gopher. All three are members of TAU's Department of Archaeology and Ancient Near Eastern Cultures. It was published on April 11 in the Journal of Human Evolution.
In recent years, archaeologists working in caves in Spain and North Africa and digs in Italy and Israel have unearthed evidence that prehistoric people recycled objects they used in daily life. Just as we recycle materials such as paper and plastic to manufacture new items today, early hominids collected discarded or broken tools made of flint to create new utensils for specific purposes hundreds of thousands of years ago.
"Recycling was a way of life for these people," Prof. Barkai says. "It has long been a part of human evolution and culture. Now, for the first time, we are discovering the specific uses of the recycled 'tool kit' at Qesem Cave."
Exceptional conditions in the cave allowed for the immaculate preservation of the materials, including micro residue on the surface of the flint tools.
"We used microscopic and chemical analyses to discover that these small and sharp recycled tools were specifically produced to process animal resources like meat, hide, fat and bones," Venditti explains. "We also found evidence of plant and tuber processing, which demonstrated that they were also part of the hominids' diet and subsistence strategies."
According to the study, signs of use were found on the outer edges of the tiny objects, indicating targeted cutting activities related to the consumption of food: butchery activities and tuber, hide and bone processing. The researchers used two different and independent spectroscopic chemical techniques: Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX).
"The meticulous analysis we conducted allowed us to demonstrate that the small recycled flakes were used in tandem with other types of utensils. They therefore constituted a larger, more diversified tool kit in which each tool was designed for specific objectives," Venditti says.
She adds, "The research also demonstrates that the Qesem inhabitants practiced various activities in different parts of the cave: The fireplace and the area surrounding it were eventually a central area of activity devoted to the consumption of the hunted animal and collected vegetal resources, while the so-called 'shelf area' was used to process animal and vegetal materials to obtain different by-products."
"This research highlights two debated topics in the field of Paleolithic archaeology: the meaning of recycling and the functional role of small tools," Prof. Barkai observes. "The data from the unique, well-preserved and investigated Qesem Cave serve to enrich the discussion of these phenomena in the scientific community."
"Our data shows that lithic recycling at Qesem Cave was not occasional and not provoked by the scarcity of flint," Venditti concludes. "On the contrary, it was a conscious behavior which allowed early humans to quickly obtain tiny sharp tools to be used in tasks where precision and accuracy were essential."
The researchers are continuing to investigate prehistoric recycling by applying their analysis to other sites in Africa, Europe and Asia.
Thursday, May 23, 2019
Unique Iron Age shield gives insight into prehistoric technology
The only one of its kind ever found in Europe, the shield was found south of Leicester on the Everards Meadows site, in what is believed to have been a livestock watering hole.
Following analysis of the construction of the shield by Michael Bamforth at the University of York, it became apparent that the shield had been carefully constructed with wooden laths to stiffen the structure, a wooden edging rim, and a woven boss to protect the wooden handle.
Although prior evidence has shown that prehistoric people used bark to make bowls and boxes, this is the first time researchers have seen the material used for a weapon of war.
The outside of the shield has been painted and scored in red chequerboard decoration. Radiocarbon dating has revealed that the shield was made between 395 and 255 BC.
The shield was severely damaged before being deposited in the ground, with some of the damage likely to have been caused by the pointed tips of spears. Further analysis is planned to help understand if this occurred in battle or as an act of ritual destruction.
Michael Bamforth, from the University of York's Department of Archaeology, said: "This truly astonishing and unparalleled artefact has given us an insight into prehistoric technology that we could never have guessed at.
"Although we know that bark has many uses, including making boxes and containers it doesn't survive well in the archaeological record. Initially we didn't think bark could be strong enough to use as a shield to defend against spears and swords and we wondered if it could be for ceremonial use.
"It was only through experimentation that we realised it could be tough enough to protect against blows from metal weapons. Although a bark shield is not as strong as one made from wood or metal, it would be much lighter allowing the user much more freedom of movement."
The shield was first discovered by archaeologists at the University of Leicester's Archaeological Services in 2015 at an Iron Age site within a farming landscape known to have been used and managed by Iron Age communities, with the Fosse Way Roman road running close by.
Many cutting-edge analytical techniques have been used to understand the construction of the object, including CT scanning and 3D printing.
Dr Rachel Crellin, Lecturer in later Prehistory at the University of Leicester, who assessed the evidence for impact damage, said: "The first time I saw the shield I was absolutely awed by it: the complex structure, the careful decorations, and the beautiful boss.
"I must admit I was initially sceptical about whether the shield would have functioned effectively, however the experimental work showed that the shield would have worked very effectively, and analysis of the surface of the object has identified evidence of use."
Tuesday, May 21, 2019
Eastern forests shaped more by Native Americans' burning than climate change
Credit: Marc Abrams, Penn State
"I believe Native Americans were excellent vegetation managers and we can learn a lot from them about how to best manage forests of the U.S.," said Marc Abrams, professor of forest ecology and physiology in the College of Agricultural Sciences. "Native Americans knew that to regenerate plant species that they wanted for food, and to feed game animals they relied on, they needed to burn the forest understory regularly."
Over the last 2,000 years at least, according to Abrams -- who for three decades has been studying past and present qualities of eastern U.S. forests -- frequent and widespread human-caused fire resulted in the predominance of fire-adapted tree species. And in the time since burning has been curtailed, forests are changing, with species such as oak, hickory and pine losing ground.
"The debate about whether forest composition has been largely determined by land use or climate continues, but a new study strongly suggests anthropogenic fire has been the major driver of forest change in the East," said Abrams. "That is important to know because climate change is taking on an ever larger proportion of scientific endeavor."
But this phenomenon does not apply to other regions, Abrams noted. In the western U.S., for example, climate change has been much more pronounced than in the East. That region has received much more warming and much more drought, he explained.
"Here in the East, we have had a slight increase in precipitation that has ameliorated the warming," said Abrams.
To learn the drivers of forest change, researchers used a novel approach, analyzing both pollen and charcoal fossil records along with tree-census studies to compare historic and modern tree composition in the forests of eastern North America. They looked at seven forest types in the north and central regions of the eastern United States. Those forest types encompass two distinct floristic zones -- conifer-northern hardwood and sub-boreal to the north, and oak-pine to the south.
The researchers found that in the northernmost forests, present-day pollen and tree-survey data revealed significant declines in beech, pine, hemlock and larches, and increases in maple, poplar, ash, oak and fir. In forests to the south, both witness tree and pollen records pointed to historic oak and pine domination, with declines in oak and chestnut and increases in maple and birch, based on present-day data.
"Modern forests are dominated by tree species that are increasingly cool-adapted, shade-tolerant, drought-intolerant pyrophobes -- trees that are reduced when exposed to repeated forest burning," Abrams said. "Species such as oak are largely promoted by low-to moderate-level forest fires. Furthermore, this change in forest composition is making eastern forests more vulnerable to future fire and drought."
Researchers also included human population data for the region, going back 2,000 years, to bolster their findings, which recently were published in the Annals of Forest Science. After hundreds of years of fairly stable levels of fire caused by relatively low numbers of Native Americans in the region, they report, the most significant escalation in burning followed the dramatic increase in human population associated with European settlement prior to the early 20th century. Moreover, it appears that low numbers of Native Americans were capable of burning large areas of the eastern U.S. and did so repeatedly.
After 1940, they found, fire suppression was an ecologically transformative event in all forests.
"Our analysis identifies multiple instances in which fire and vegetation changes were likely driven by shifts in human population and land use beyond those expected from climate alone," Abrams said. "After Smokey Bear came on the scene, fire was mostly shut down throughout the U.S. and we have been paying a big price for that in terms of forest change. We went from a moderate amount of fire to too much fire to near zero fire -- and we need to get back to that middle ground in terms of our vegetation management."
Subscribe to:
Posts (Atom)