aDNA

Ancient genome 

from Africa 

sequenced 

for the first time 

Africa, Anthropology, ArchaeoHeritage, Archaeology, Breakingnews, Ethiopia, Genetics 


 The first ancient human genome from Africa to be sequenced has revealed that a wave of migration back into Africa from Western Eurasia around 3,000 years ago was up to twice as significant as previously thought, and affected the genetic make-up of populations across the entire African continent. The Mota cave is located in a mountainous region, and its entrance is about 6,000 feet  above sea level. 

Weather and the changing conditions of the only road that runs near  the cave -- a gravel surface -- made access complicated for the research team 

[Credit: Kathryn and John Arthur] 

The genome was taken from the skull of a man buried face-down 4,500 years ago in a cave called Mota in the highlands of Ethiopia -- a cave cool and dry enough to preserve his DNA for thousands of years. Previously, ancient genome analysis has been limited to samples from northern and arctic regions. The latest study is the first time an ancient human genome has been recovered and sequenced from Africa, the source of all human genetic diversity. The findings are published in the journal Science. The ancient genome predates a mysterious migratory event which occurred roughly 3,000 years ago, known as the 'Eurasian backflow', when people from regions of Western Eurasia such as the Near East and Anatolia suddenly flooded back into the Horn of Africa. 

Entrance to the Mota Cave in the Ethiopian highlands  

[Credit: Kathryn and John Arthur] 

The genome enabled researchers to run a millennia-spanning genetic comparison and determine that these Western Eurasians were closely related to the Early Neolithic farmers who had brought agriculture to Europe 4,000 years earlier. By comparing the ancient genome to DNA from modern Africans, the team have been able to show that not only do East African populations today have as much as 25% Eurasian ancestry from this event, but that African populations in all corners of the continent -- from the far West to the South -- have at least 5% of their genome traceable to the Eurasian migration. Researchers describe the findings as evidence that the 'backflow' event was of far greater size and influence than previously thought. The massive wave of migration was perhaps equivalent to over a quarter of the then population of the Horn of Africa, which hit the area and then dispersed genetically across the whole continent. 

The view looking out from the Mota cave in the Ethiopian highlands, where the remains containing the ancient genome were found  

[Credit: Kathryn and John Arthur] 

"Roughly speaking, the wave of West Eurasian migration back into the Horn of Africa could have been as much as 30% of the population that already lived there -- and that, to me, is mind-blowing. The question is: what got them moving all of a sudden?" said Dr Andrea Manica, senior author of the study from the University of Cambridge's Department of Zoology. Previous work on ancient genetics in Africa had involved trying to work back through the genomes of current populations, attempting to eliminate modern influences. "With an ancient genome, we have a direct window into the distant past. One genome from one individual can provide a picture of an entire population," said Manica. The cause of the West Eurasian migration back into Africa is currently a mystery, with no obvious climatic reasons. Archaeological evidence does, however, show the migration coincided with the arrival of Near Eastern crops into East Africa such as wheat and barley, suggesting the migrants helped develop new forms of agriculture in the region. 

In Mota cave, located in the Gamo highlands of Ethiopia, a group of NSF-supported  researchers excavation a rock cairn. They discovered under it a burial site  containing the remains of a 4,500-year skeleton  

[Credit: Kathryn and John Arthur] 

The researchers say it's clear that the Eurasian migrants were direct descendants of, or a very close population to, the Neolithic farmers that had had brought agriculture from the Near East into West Eurasia around 7,000 years ago, and then migrated into the Horn of Africa some 4,000 years later. "It's quite remarkable that genetically-speaking this is the same population that left the Near East several millennia previously," said Eppie Jones, a geneticist at Trinity College Dublin who led the laboratory work to sequence the genome. While the genetic make-up of the Near East has changed completely over the last few thousand years, the closest modern equivalents to these Neolithic migrants are Sardinians, probably because Sardinia is an isolated island, says Jones. "The famers found their way to Sardinia and created a bit of a time capsule. Sardinian ancestry is closest to the ancient Near East." "Genomes from this migration seeped right across the continent, way beyond East Africa, from the Yoruba on the western coast to the Mbuti in the heart of the Congo -- who show as much as 7% and 6% of their genomes respectively to be West Eurasian," said Marcos Gallego Llorente, first author of the study, also from Cambridge's Zoology Department. 

John Arthur, an NSF-supported archaeologist at the University  of South Florida St. Petersburg, excavates the Mota cave site  

[Credit: Kathryn and John Arthur]

 "Africa is a total melting pot. We know that the last 3,000 years saw a complete scrambling of population genetics in Africa. So being able to get a snapshot from before these migration events occurred is a big step," Gallego Llorente said. The ancient Mota genome allows researchers to jump to before another major African migration: the Bantu expansion, when speakers of an early Bantu language flowed out of West Africa and into central and southern areas around 3,000 years ago. Manica says the Bantu expansion may well have helped carry the Eurasian genomes to the continent's furthest corners. The researchers also identified genetic adaptations for living at altitude, and a lack of genes for lactose tolerance -- all genetic traits shared by the current populations of the Ethiopian highlands. In fact, the researchers found that modern inhabitants of the area highlands are direct descendants of the Mota man. Finding high-quality ancient DNA involves a lot of luck, says Dr Ron Pinhasi, co-senior author from University College Dublin. "It's hard to get your hands on remains that have been suitably preserved. The denser the bone, the more likely you are to find DNA that's been protected from degradation, so teeth are often used, but we found an even better bone -- the petrous." The petrous bone is a thick part of the temporal bone at the base of the skull, just behind the ear. "The sequencing of ancient genomes is still so new, and it's changing the way we reconstruct human origins," added Manica. "These new techniques will keep evolving, enabling us to gain an ever-clearer understanding of who our earliest ancestors were." The study was conducted by an international team of researchers, with permission from the Ethiopia's Ministry of Culture and Authority for Research and Conservation of Cultural Heritage. 

Source: University of Cambridge [October 08, 2015]

Perfidi Archeologi Colpiscono ancora

Baboon bone found in famous Lucy skeleton 




 Lucy, arguably the world's most famous early human fossil, is not quite all she seems. 

A careful look at the ancient hominin's skeleton suggests one bone may actually belong to a baboon. 

Lucy 

[Credit: Dave Einsel/Getty] 

In November 1974, palaeoanthropologists Donald Johanson and Tom Gray made the discovery of a lifetime near the village of Hadar in Ethiopia: dozens of fossil fragments belonging to a single hominin skeleton dating back 3.2 million years. 

Once the fragments had been pieced together, the skeleton was declared to be of the species Australopithecus afarensis. But the skeleton became known as Lucy, inspired by a Beatles song that blasted out of a cassette player as the researchers celebrated their discovery that evening. 
Forty years later, thanks to its age and completeness, Lucy remains an important specimen. It shows, for instance, that our distant ancestors began to walk upright on two legs long before they developed big brains. It's no surprise, then, that replicas of the skeleton are on display at museums across the world. 

But when Gary Sawyer and Mike Smith at the American Museum of Natural History in New York recently began work on a new reconstruction of Lucy's skeleton, with help from Scott Williams at New York University, they noticed something odd. 
"Mike pointed out that one of the [vertebra] fragments, which no one, including me, had really paid close attention to, looked fairly small to fit with the rest of Lucy's vertebral column," says Williams. 
Williams had been working with Marc Meyer at Chaffey College in Rancho Cucamonga, California, on the spinal column of another early hominin, Australopithecus sediba, and so the two researchers decided to study the fragment. They soon concluded that it didn't belong to Lucy. "It was just too small," says Williams. 
One possible explanation was that the vertebra fragment came from a second, juvenile member of Lucy's species. So Williams and Meyer did a comparative study that included vertebrae from other Australopithecus fossils. 
To satisfy a personal hunch, Williams also added vertebrae from other animals known to have lived in the Hadar region 3.2 million years ago, such as porcupines and pigs. 
The results showed, surprisingly, that the fragment may not have belonged to Australopithecus at all. 
"Baboons were a close match, both in shape and size," says Williams. "So we think we've solved this mystery. 
It seems that a fossil gelada baboon thoracic vertebra washed or was otherwise transported in the mix of Lucy's remains." He stresses, though, that the analysis, which he will present at a meeting of the Paleoanthropology Society in San Francisco next week, also confirms that the other 88 fossil fragments belonging to Lucy's skeleton are correctly identified. 
And the mislabelled baboon bone fragment doesn't undermine Lucy's important position in the evolution of our lineage. 
There may be a simple reason why no one noticed that Lucy's remains included a baboon bone fragment. Although many scientists have examined Lucy's skeleton, most experts have not worked as extensively on bones of the back relative to the limbs, says Dan Gebo at the Northern Illinois University in DeKalb. "Given that broken bones are always a problem and most of us are not vertebral specialists, it would not be unusual to make a small mistake." Also, there was no sign of a baboon skeleton at the site where Lucy was discovered in 1974, says William Sanders at the University of Michigan in Ann Arbor. 
"So there was no reason to assume intermingling of elements between two different animals," he says. Even so, Sanders wants to see the analysis in detail before he accepts that the vertebra fragment really does belong to a baboon. "Offhand, I don't see any morphological features in this element that cry out for recognition as a baboon," he says. If the fragment really does prove to belong to a baboon, he says, "we can cut Don Johanson and his colleagues some slack".

Author: Colin Barras | Source: New Scientist [April 13, 2015]