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From The Trenches

Turning Back the Human Clock

By KATHERINE SHARPE

Monday, December 17, 2012

DNA-clock.jpgFor years, archaeologists and geneticists have been troubled by the fact that their time lines for key events in human evolution don’t always match up. While archaeologists rely on the dating of physical remains to determine when and how human beings spread across the globe, geneticists use a DNA “clock” based on the assumption that the human genome mutates at a constant rate. By comparing differences between modern and ancient DNA, geneticists then calculate when early humans diverged from other species and when human populations formed different genetic groups.

 

The DNA clock is a powerful tool, but its conclusions—for example, that modern humans first emerged from Africa about 60,000 years ago—can disagree with archaeological evidence that shows signs of modern human activity well before that date at sites in regions as far-flung as Arabia, India, and China.

 

Now, new work, based on observation of the genetic differences between present-day parents and children, suggests that the genetic clock may actually run about twice as slowly as previously believed, at least for the last million years or so of primate history. In their review paper in the journal Nature Reviews Genetics, Aylwyn Scally and Richard Durbin of the Wellcome Trust Sanger Institute in Hinxton, England, propose much earlier dates for watershed events in human evolution, which could help bring the genetic and archaeological records in line. For instance, a slower clock places the migration of modern humans out of Africa at around 120,000 years ago, which is more consistent with archaeological evidence.

 

The revised clock also supports archaeological signs of modern human activity from more than 60,000 years ago at sites such as Jwalapuram, India (“Stone Age India,” January/February 2010), and Liujiang, China—evidence that has often been dismissed by geneticists as impossible. While more work is needed to confirm the findings, Scally says that archaeologists who work on such sites should be excited: “It can no longer be said that the genetic evidence is unequivocally against them.”

Denisovan DNA

By ZACH ZORICH

Monday, December 17, 2012

denisovan-DNA.jpgA new technique for sequencing ancient DNA has allowed a multinational research team to reconstruct the genome of a person who lived in Siberia’s Denisova Cave between 30,000 and 82,000 years ago—with the same level of accuracy as genomes from modern people. This new DNA sequence gives researchers a clearer picture of how early hominins such as the Denisovans and Neanderthals were related to modern humans and to each other. 

 

The analysis showed that Denisovans were much more closely related to Neanderthals than to Homo sapiens, and that in spite of coming from a small population, they managed to contribute genes to modern populations in Island Southeast Asia and Australia. According to David Reich, a geneticist at Harvard Medical School and a member of the research team, the new DNA sequence also shows that Native Americans and people from East Asia have more Neanderthal DNA, on average, than Europeans. Archaeologists have long thought that the largest population of Neanderthals lived in Europe, so the finding complicates the picture of the way modern people and Neanderthals are related. Either there was a separate event in which Neanderthals interbred with people in Asia, or the genetic contribution of Neanderthals in Europe was diluted by later migrations of Homo sapiens

Neutron Beams and Lead Shot

By NIKHIL SWAMINATHAN

Monday, December 17, 2012

neutron-mary-rose.jpgBritish researchers are going beyond standard X-rays to study nearly 500-year-old lead cannonballs found on the wreck of Mary Rose, a Tudor warship brought to the surface of the English Channel in 1982. The ship sank when the British fleet squared off with the French during the Battle of the Solent in 1545.

 

Using neutron-based imaging, which employs beams of the neutral subatomic particles that can pass through lead, the team has developed 2-D and 3-D renderings that reveal the Mary Rose’s cannonballs had lumps of iron in them. Why was the iron used? Possibly to save on expensive lead or because it altered the flight or impact of the projectiles. 

 

According to battlefield archaeologist Glenn Foard of the University of Huddersfield, Mary Rose’s 1,600 rounds of unfired shot can help researchers understand state-of-the-art weaponry in the fifteenth and sixteenth centuries. Says Foard, “We can compare it to the much rarer battlefield finds of projectiles which have firing and impact evidence telling us something of the guns that fired them.”

Site of a Forgotten War

By JUDE ISABELLA

Monday, December 17, 2012


hungry-hillIn the remote mountains of southwestern Oregon, researchers have uncovered a pre–Civil War battlefield that was lost for more than a century and a half. The Battle of Hungry Hill was a pivotal fight during the Rogue River Wars of 1855 to 1856, a conflict between Oregon settlers and Native Americans. The battle, a defeat for the U.S. Army and a local militia, prompted the government to evict the native population from Oregon’s Rogue and Umpqua Valleys. 

 

For years, pioneer family stories led researchers searching for evidence of the battle in the wrong direction. However, archaeological surveys, according to Mark Tveskov, an archaeologist with Southern Oregon University, eventually identified the location where it had been fought. During the research, which began in 2009, Tveskov found previously unknown primary documentation, including a front-page article in the New York Herald, published 12 days after the battle concluded on October 31, 1855, and eyewitness accounts. This led the team to 24 square miles of the Grave Creek Hills, several miles northwest of the spot where the battle was previously thought to have taken place. 

 

In September, the team turned up three artifacts that match weaponry used by the U.S. Army during the mid-nineteenth century—two .69 caliber lead musketballs and a lead stopper from a gunpowder container. Tveskov hopes to uncover more details, which might, among other things, corroborate two historical accounts of a Native American sniper picking off the majority of the Army’s 39 casualties.

Maya Mural Miracle

By ZACH ZORICH

Monday, December 17, 2012

chajul-maya-mural.jpg

 

Lucas Asicona Ramírez probably had no idea that he was embarking on an archaeological excavation five years ago when he began scraping down the plaster on the walls of his 300-year-old home in Chajul, Guatemala. But his renovation uncovered a series of murals that had been painted by his Ixil Maya ancestors in the years after the Spanish conquest. Some of the paintings depict what archaeologists Lars Frühsorge, Jarosław Źrałka, and William Saturno believe to be a ritual called the Dance of Conquest. The people in this painting seem to be Maya, yet wear some pieces of European clothing. The seated figures are playing instruments while the figure on the right, wearing a jaguar skin and cape, dances.

 

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