Wednesday, July 11, 2018
Humans evolved in partially isolated populations scattered across Africa
The textbook narrative of human evolution casts Homo sapiens as evolving from a single ancestral population in one region of Africa around 300,000 years ago. However, in a commentary published July 11 in the journal Trends in Ecology & Evolution, an interdisciplinary group of researchers concludes that early humans comprised a subdivided, shifting, pan-African meta-population with physical and cultural diversity. This framework better explains existing genetic, fossil, and cultural patterns and clarifies our shared ancestry.
"In the fossil record, we see a mosaic-like, continental-wide trend toward the modern human form, and the fact that these features appear at different places at different times tells us that these populations were not well connected," says Eleanor Scerri, a British Academy postdoctoral fellow in archaeology at the University of Oxford and the Max Planck Institute for the Science of Human History. "This fits with a subdivided population model in which genetic exchanges are neither random nor frequent. This allows us to start detailing the processes that shaped our evolutionary history."
Explaining this poor connectivity was a series of shifting rivers, deserts, forests, and other physical barriers separating these subpopulations, as highlighted in the ecological record. "These barriers created migration and contact opportunities for groups that may previously have been separated, and later fluctuation might have meant populations that mixed for a short while became isolated again," says Scerri.
The theory that there was mingling and isolation of subpopulations from the southern tip to the northern coasts of Africa is a much better fit with the fossil and genetic data than is a single population model. Examination of H. sapiens fossils paired with inferences made from contemporary DNA samples suggested levels of early human diversity that supported the researchers' shifting subdivided population model.
"For the first time, we've examined all the relevant archaeological, fossil, genetic, and environmental data together to eliminate field-specific biases and assumptions and confirm that a mosaic, pan-African origin view is a much better fit with the data that we have," says Scerri. "To understand our genetic and cultural diversity or where being human comes from - our behavioral flexibility and biological plasticity - we have to look at an ancient history of population subdivision and diverse ecologies across Africa."
Moving forward, this research will allow our models of human evolutionary history to reject the simple linear progression from what might be termed "archaic morphology" toward a recognizably human form in favor of a more accurate account of the complexity and irregularity involved in our evolution and an acknowledgment of a pan-African origin of our species.
"In bringing together people from such diverse fields, we've arrived at a place where we can begin to address some key questions about our shared ancestry and even emerge with new questions we haven't known to ask before," Scerri says. "We are an evolving lineage with deep African roots, so to understand this history, we must re-examine evidence from diverse sources without a priori conceptions."
Distinctive projectile point technology sheds light on peopling of the Americas
In 2002, Area 15 of the Gault Site in Central Texas was identified as an ideal area to search for remnants of early cultures. The site features five distinct layers in the stratigraphic profile that showcase different cultural components, each with stratigraphic separation between the cultural depositions. Here, Thomas J. Williams and colleagues focused on the Gault Assemblage, the oldest deposit, which they compared to materials found in the Clovis layer (stratified above the Gault Assemblage).
Based on optically stimulated luminescence (OSL) dating, the Gault Assemblage sediment samples are approximately 16- to 20-thousand-years-old, the authors say. Additionally, Williams et al. discovered ancient materials in the lowest Gault deposit, including small projectile point technology, biface stone tools, blade-and-core tools, and flake tools.
The authors compared these Gault Assemblage artifacts to Clovis tools and found that the blade-and-core traditions, in particular, are similar to Clovis blade-and-cores (meaning they continued into the time of Clovis), but biface traditions underwent significant changes in the Clovis level. Meanwhile, the early projectile point technology is "unrelated" to Clovis at all, they say.
Discovery of ancient tools in China suggests humans left Africa earlier than previously thought
Credit: Prof. Zhaoyu Zhu
The artefacts show that our earliest human ancestors colonised East Asia over two million years ago. They were found by a Chinese team that was led by Professor Zhaoyu Zhu of the Chinese Academy of Sciences, and included Professor Robin Dennell of Exeter University. The tools were discovered at a locality called Shangchen in the southern Chinese Loess Plateau. The oldest are ca. 2.12 million years old, and are c. 270,000 years older than the 1.85 million year old skeletal remains and stone tools from Dmanisi, Georgia, which were previously the earliest evidence of humanity outside Africa.
The artefacts include a notch, scrapers, cobble, hammer stones and pointed pieces. All show signs of use - the stone had been intentionally flaked. Most were made of quartzite and quartz that probably came from the foothills of the Qinling Mountains 5 to 10 km to the south of the site, and the streams flowing from them. Fragments of animal bones 2.12 million years old were also found.
The Chinese Loess Plateau covers about 270,000 square kilometres, and during the past 2.6m years between 100 and 300m of wind-blown dust - known as loess - has been deposited in the area.
The 80 stone artefacts were found predominantly in 11 different layers of fossil soils which developed in a warm and wet climate. A further 16 items were found in six layers of loess that developed under colder and drier conditions. These 17 different layers of loess and fossil soils were formed during a period spanning almost a million years. This shows that early types of humans occupied the Chinese Loess Plateau under different climatic conditions between 1.2 and 2.12 million years ago.
The layers containing these stone tools were dated by linking the magnetic properties of the layers to known and dated changes in the earth's magnetic field.
Professor Dennell said: "Our discovery means it is necessary now to reconsider the timing of when early humans left Africa".
Eating bone marrow played a key role in the evolution of the human hand
The strength required to access the high calorie content of bone marrow may have played a key role in the evolution of the human hand and explain why primates hands are not like ours, research at the University of Kent has found.
In an article in The Journal of Human Evolution, a team lead by Professor Tracy Kivell of Kent's School of Anthropology and Conservation concludes that although stone tool making has always been considered a key influence on the evolution of the human hand, accessing bone marrow generally has not.
It is widely accepted that the unique dexterity of the human hand evolved, at least in part, in response to stone tool use during our evolutionary history.
Archaeological evidence suggests that early hominins participated in a variety of tool-related activities, such as nut-cracking, cutting flesh, smashing bone to access marrow, as well as making stone tools. However, it is unlikely that all these behaviours equally influenced modern human hand anatomy.
To understand the impact these different actions may have had on the evolution of human hands, researchers measured the force experienced by the hand of 39 individuals during different stone tool behaviours - nut-cracking, marrow acquisition with a hammerstone, flake production with a hammerstone, and handaxe and stone tool (i.e. a flake) - to see which digits were most important for manipulating the tool.
They found that the pressures varied across the different behaviours, with nut-cracking generally requiring the lowest pressure while making the flake and accessing marrow required the greatest pressures. Across all of the different behaviours, the thumb, index finger and middle finger were always most important.
Professor Kivell says this suggests that nut-cracking force may not be high enough to elicit changes in the formation of the human hand, which may be why other primates are adept nut-crackers without having a human-like hand.
In contrast, making stone flakes and accessing marrow may have been key influences on our hand anatomy due to the high stress they cause on our hands. The researchers concluded that eating marrow, given its additional benefit of high calorific value, may have also played a key role in evolution of human dexterity.
The manual pressures of stone tool behaviors and their implications for the evolution of the human hand by Erin Marie Williams-Hatala, Kevin G. Hatala, McKenzie Gordon and Margaret Kasper, all Chatham University, Pittsburgh, USA and Alastair Key and Tracy Kivell, University of Kent is published in the Journal of Human Evolution.
Monday, July 9, 2018
Discoveries by archaeology team give new clues on life in ancient Jewish village
Credit: Jim Haberman
"The mosaics decorating the floor of the Huqoq synagogue revolutionize our understanding of Judaism in this period," said Magness. "Ancient Jewish art is often thought to be aniconic, or lacking images. But these mosaics, colorful and filled with figured scenes, attest to a rich visual culture as well as to the dynamism and diversity of Judaism in the Late Roman and Byzantine periods."
The first mosaics in the Huqoq synagogue were discovered by Magness' team in 2012. Since then, Magness, director of the Huqoq excavations and Kenan Distinguished Professor of Early Judaism in the department of religious studies in Carolina's College of Arts & Sciences, assisted by Shua Kisilevitz of the Israel Antiquities Authority and Tel Aviv University have uncovered additional mosaics every summer. This year, the team's specialists and students focused their efforts on a series of mosaic panels in the north aisle. Magness said this series is part of the richest, most diverse collection of mosaics ever found in an ancient synagogue.
Along the north aisle, mosaics are divided into two rows of panels containing figures and objects with Hebrew inscriptions. One panel labeled "a pole between two" depicts a biblical scene from Numbers 13:23. The images show two spies sent by Moses to explore Canaan carrying a pole with a cluster of grapes. Another panel referencing Isaiah 11:6 includes the inscription "a small child shall lead them."
The panel shows a youth leading an animal on a rope. A fragmentary Hebrew inscription concluding with the phrase "Amen selah," meaning "Amen forever," was uncovered at the north end of the east aisle.
During this eighth dig, the team also continued to expose a rare discovery in ancient synagogues: columns covered in colorful, painted plaster still intact after nearly 1,600 years.
The mosaics have been removed from the site for conservation and the excavated areas have been backfilled. Excavations are scheduled to continue in the summer of 2019. Additional information and updates can be found at the project's website: http://www.
Mosaics uncovered by this project include:
- 2012: Samson and the foxes
- 2013: Samson carrying the gate of Gaza on his shoulders
- 2013, 2014 and 2015: a Hebrew inscription surrounded by human figures, animals and mythological creatures including cupids; and the first non-biblical story ever found decorating an ancient synagogue -- perhaps the legendary meeting between Alexander the Great and the Jewish high priest
- 2016: Noah's Ark; the parting of the Red Sea showing Pharaoh's soldiers being swallowed by giant fish
- 2017: a Helios-zodiac cycle; Jonah being swallowed by three successive fish; the building of the Tower of Babel
Friday, July 6, 2018
Ancient DNA testing solves 100-year-old controversy in Southeast Asian prehistory
Credit: Fabio Lahr
Southeast Asia is one of the most genetically diverse regions in the world, but for more than 100 years scientists have disagreed about which theory of the origins of the population of the area was correct.
One theory believed the indigenous Hòabìnhian hunter-gatherers who populated Southeast Asia from 44,000 years ago adopted agricultural practices independently, without the input from early farmers from East Asia. Another theory, referred to as the 'two-layer model' favours the view that migrating rice farmers from what is now China replaced the indigenous Hòabìnhian hunter-gatherers.
Academics from around the world collaborated on new research just published in Science which found that neither theory is completely accurate. Their study discovered that present-day Southeast Asian populations derive ancestry from at least four ancient populations.
DNA from human skeletal remains from Malaysia, Thailand, the Philippines, Vietnam, Indonesia, Laos and Japan dating back as far as 8,000 years ago was extracted for the study - scientists had previously only been successful in sequencing 4,000-year-old samples from the region. The samples also included DNA from Hòabìnhian hunter-gatherers and a Jomon from Japan - a scientific first, revealing a long suspected genetic link between the two populations.
In total, 26 ancient human genome sequences were studied by the group and they were compared with modern DNA samples from people living in Southeast Asia today.
The pioneering research is particularly impressive because the heat and humidity of Southeast Asia means it is one of the most difficult environments for DNA preservation, posing huge challenges for scientists.
Professor Eske Willerslev, who holds positions both at St John's College, University of Cambridge, and the University of Copenhagen, led the international study.
He explained: "We put a huge amount of effort into retrieving ancient DNA from tropical Southeast Asia that could shed new light on this area of rich human genetics. The fact that we were able to obtain 26 human genomes and shed light on the incredible genetic richness of the groups in the region today is astonishing."
Hugh McColl, PhD student at the Centre for GeoGenetics in the Natural History Museum of Denmark of the University of Copenhagen, and one of the lead authors on the paper, said: "By sequencing 26 ancient human genomes - 25 from South East Asia, one Japanese J?mon - we have shown that neither interpretation fits the complexity of Southeast Asian history. Both Hòabìnhian hunter-gatherers and East Asian farmers contributed to current Southeast Asian diversity, with further migrations affecting islands in South East Asia and Vietnam. Our results help resolve one of the long-standing controversies in Southeast Asian prehistory."
Dr Fernando Racimo, Assistant Professor at the Centre for GeoGenetics in the Natural History Museum of the University of Copenhagen, the other lead author, said: "The human occupation history of Southeast Asia remains heavily debated. Our research spanned from the Hòabìnhian to the Iron Age and found that present-day Southeast Asian populations derive ancestry from at least four ancient populations. This is a far more complex model than previously thought."
Some of the samples used in the two and a half year study were from The Duckworth Collection, University of Cambridge, which is one of the world's largest repositories of human remains. Professor Marta Mirazón Lahr, Director of the Duckworth Laboratory and one of the authors on the paper, said: "This study tackles a major question in the origins of the diversity of Southeast Asian people, as well as on the ancient relationships between distant populations, such as Jomon and Hòabìnhian foragers, before farming. The fact that we are learning so much from ancient genomes, such as the one from Gua Cha, highlights the importance of amazing collections such as the Duckworth."
Ancestral people of Chaco Canyon likely grew their own food
Credit: Samantha Fladd/UC
A multidisciplinary team of experts from the University of Cincinnati determined that the sandy soils of Chaco Canyon were not too salty to grow crops such as maize, beans and squash for the more than 1,200 people who occupied this beautiful but harsh landscape during its most prolific years.
Researchers have long debated whether the people who lived here between 800 and 1300 AD were self-sufficient or relied partially or entirely on imported food to survive. These ancestral Puebloans built elaborate adobe structures, some of them four stories tall and recessed among cliff faces under the hot New Mexico sun.
Some previous research suggested that the desert soils simply were too saline for agriculture. The implication was that Chaco Canyon could not support a large resident population without lots of outside help. Alternately, researchers speculated that Chaco Canyon, a place of religious importance, maintained a small resident population that served and benefited from a larger population of visitors making pilgrimages.
But UC's soil analysis suggests that the most significant challenge for growing crops was irrigation. That's where ancestral Puebloans demonstrated particularly adroit farming skills and perceptive land management, said Jon-Paul McCool, a UC graduate and lead author of the study.
"The major limitation is water. You couldn't rely on rain for field agriculture," McCool said. "You'd have to gather and control water, which we know people in the region did."
McCool earned PhD and master's degrees in geography and museum studies at UC and now teaches at Valparaiso University.
Chaco Canyon has evidence of constructed canals -- water-diversion channels designed to direct rainfall to farm fields.
"If you have a population of 1,200 people, how did they survive?" McCool asked. "The part I'm interested in is the interrelationships between people and their environment and how each of them influences the other."
The study was published in June in the journal PLOS ONE.
One prevailing theory is that residents of Chaco Canyon depended heavily on outside assistance for sustenance. But the most likely resource for imported agriculture was in the Chuska Mountains on the Arizona border, more than 50 miles from Chaco Canyon.
Traveling great distances in a dry environment is commonplace in other parts of the world. But what makes travel in the ancient Southwest especially taxing is that every step was taken on foot -- human foot.
Ancient North Americans had no camels, horses, mules, llamas, alpacas, oxen or sled dogs to carry supplies. There were precious few navigable waterways. So if you wanted to bring something on such a trip, you were carrying it every step, said Nicholas Dunning, a professor of geography in UC's McMicken College of Arts and Science.
"You have to go to the Andes before you find a native beast of burden in the New World," Dunning said. "So if you're using human porters, you quickly reach a point of diminishing returns."
Dunning said the study was able to determine that the soils could support agriculture in Chaco Canyon and that irrigation canals found at the site were built at least as early as the eighth century.
"The evidence is compelling that they produced most of the food that they consumed in Chaco Canyon and devised sophisticated irrigation strategies to do it," Dunning said.
Today, Chaco Canyon sees about 9 inches of rain per year, four times less than the breadbasket of the American Midwest. To make the most of this precious resource, ancestral Puebloans built elaborate canals to divert rainfall to their farm fields.
UC researchers re-examined soil samples taken from sites in and around Chaco Canyon. While some of these sites indeed did have saline levels too high to support agriculture, that was the exception, researchers found.
Instead, researchers found that the desert soils were not much different from soils in other parts of the Southwest where agriculture was practiced.
"The evidence is persuasive that they grew their own food," Dunning said.
"My experience in traditional societies is farmers and agricultural populations are very risk averse," Dunning said. "So you tend to think in ways of making sure you have enough to eat yourself each year along with seed for next year."
UC's team consisted of geologists, archaeologists and biologists. They spent weeks each summer studying different aspects of Chaco Canyon. Many of the study sites are accessible only by foot so researchers would hike in at dawn before the afternoon heat became too oppressive. A collapsible tent shelter provided some relief from the sun.
Researchers could drink as much as four liters of water each workday, packing in provisions and packing out soil samples. Dunning said New Mexico's evening sky was full of stars.
"The skies were extraordinary. We were there for the Perseid meteor shower," Dunning said. "The environment is quite amazing. We would set off for work before dawn. We wanted to be at the excavation sites before the sun came up because the morning was the only decent time to work."
UC's research is adding to what scientists already know about ancestral Puebloans in New Mexico. These former occupants of Chaco Canyon left behind evidence of having traded goods with people from distant places. Archaeologists have found seashells from California and macaw feathers and cacao from Mexico.
Co-author and UC research associate Samantha Fladd thinks it is improbable that residents would rely on regular deliveries of staple goods from places so far away, especially if they could grow food themselves.
"It seems highly unlikely that this would be a sustainable system," Fladd said.
"It makes more sense to me that there would be trade relationships where populations would help each other in bad years. To rely on one location for most of your food would not be the most sustainable system," she said. "I would be skeptical you would see that much patronage."
Fladd said a round trip between Chaco Canyon and the Chuska Mountains would take as long as a week, depending on how many supplies were carried.
The people of Chaco Canyon left behind petroglyphs carved into the rock -- drawings of animals, people and symbols. These included the famed "Sun Dagger," a notch in a slot canyon that casts a dagger-shaped beam of light onto a shaded rock face upon which is a carved petroglyph spiral that marks the sun dagger's path across the wall over the four seasons.
They also were known for their turquoise carvings, including a famous frog figure among the collection of the National Park Service.
UC professor emeritus Vernon Scarborough, one of the paper's co-authors, spent his career studying ancient land-use strategies around the world. Chaco Canyon demonstrates how people were able to engineer their landscape in a resourceful and sustainable way, he said.
"Chaco Canyon captures the ingenuity and creativity of the human spirit like few other places," Scarborough said.
"Our work and that of other colleagues is beginning to show the significance of low-tech adaptations in attempting to accommodate life on Earth," Scarborough said. "A greater understanding of just how these ancient, 'primitive' systems adapted and function merits a thoughtful assessment given the social and environmental stress we face globally today."
Scientists still aren't sure why the population of Chaco Canyon declined over the centuries. Chaco Canyon continued to be occupied intermittently after 1300.
"Every civilization comes to an end. But they went through a lot," McCool said. "What strategies allowed that civilization to continue? You're dealing with people who lived in a place for hundreds of years. What adaptations did they make to deal with changing circumstances?"
Fladd said when she goes to Chaco Canyon, she likes to hike up the Pueblo Alto trail. From the top of the mesa, she can survey all of Pueblo Bonito below her.
"I don't want to pretend I can understand their concerns 800 years ago," Fladd said. "But I am in awe of what they were able to do. It's a testament to how adaptable and creative they were."
Chaco Canyon has a long history of generating academic debates, in part because it's such a fascinating place. Chaco Canyon has been studied or referenced in thousands of research papers.
"Archaeology is a fun science because it requires a lot of imagination," Dunning said. "You're never dealing with complete data sets, so one has to fill in the holes. That's where the controversy comes in."
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