Thursday, May 29, 2008

Rewriting Greenland's immigration history

Thirty-six-year-old Professor Eske Willerslev, University of Copenhagen, and his team of fossil DNA researchers have done it a couple of times before: rewritten world history. Most recently two months ago when he and his team discovered that the ancestors of the North American Indians were the first people to populate America, and that they came to the country more than 1,000 years earlier than originally assumed. And the evidence is, so to speak, quite tangible: DNA samples of fossilised human faeces found in deep caves in southern Oregon.

This time, focus is on Greenland, and the scientific evidence is DNA analyses of hair from the Disco Bay ice fjord area in north-west Greenland, which are well-preserved after 4,000 years in permafrost soil. The team’s discovery makes it necessary to review Greenland’s immigration history. Until now, science regarded it as a possibility that the earliest people in Greenland were direct ancestors of the present-day Greenlandic population.

It now turns out that the original immigrants on the maternal side, which is reflected in the mitochondrial DNA, instead came from a Siberian population whose closest present-day descendants come from the Aleutian Islands on the boundary between the Northern Pacific Ocean and the Bering Sea and the Seriniki Yuit in north-east Siberia. Discovered in more recent times by the Dane Vitus Bering in 1741, the Aleutian Islands today include some 300 islands spanning 1,900 km from Alaska in the USA to the Kamchatka peninsula in Russia.

“They must have crossed the ice from the Aleutian Islands via Alaska and Canada and then on to Greenland. We have always known that the first immigrants came to Greenland approx. 4,500 years ago, because tools from that time have been found. But what we did not know was that they probably came via the Aleutian Islands, which our DNA research now shows. The project was actually close to being shelved. Originally, I was in the most northern part of Greenland with Claus Andreasen from the National Museum of Greenland, Nuuk, looking for DNA traces. It was a total failure. But in another context, I found out that archaeologist Bjarne Grønnow from the National Museum of Denmark, Copenhagen, had made some excavations at the Qeqertasussuk settlement in the northern part of West Greenland in the 1980s. And then, among all the samples taken from the frozen culture layers on the site, I suddenly found a tuft of hair which I analysed together with my colleague Tom Gilbert,” says Eske Willerslev.

‘The forgotten Greenlandic hair’ from the samples was subsequently analysed for so-called mitochondria. They are the genes on the maternal side, a kind of cellular power plant, and they are well-suited for comparative DNA studies of mammals, including humans. The Willerslev team then checked the results of the analysis of the Greenlandic hair against an international DNA database and the database came up with the eastern part of Siberia and the Aleutian Islands, which is populated by a group that has peopled other places in the Arctic area.

Another interesting finding is that there is no connection between this DNA mass and the most recent immigration to Greenland, the Thule culture, the ancestors of modern Greenlandic Inuit.

“Our findings prove that humans moved to other places far earlier than what is normally assumed today. We may only have studied the mitochondria – the female part, but it is the first time ever that someone has succeeded in sequencing the entire mitochondrial genome from an extinct human. Our next project will be to raise funds for recreating what is technically known as the core genome from the tuft of hair, in other words the first full picture of the genetic material of an extinct human. Today, this is technically possible, and it may tell us where the paternal line came from in the earliest immigration to Greenland, and, for example, the eye colour of these early people. The paternal line may very well come from a totally different place,” says Eske Willerslev, who will shortly publish his autobiographical book ‘Fra pelsjæger til professor – en personlig rejse gennem fortidens dna-mysterier’ (From fur hunter to professor – a personal journey through the DNA mysteries of the past).

Thursday, May 8, 2008

Genetics Confirm Oral Traditions of Druze in Israel

DNA analysis of residents of Druze villages in Israel suggests these ancient religious communities offer a genetic snapshot of the Near East as it was several thousands of years ago.

The Druze harbor a remarkable diversity of mitochondrial DNA types or lineages that appear to have separated from each other many thousands of years ago, according to a new study by multinational team, led by researchers at the Technion-Israel Institute of Technology Rappaport School of Medicine.

But instead of dispersing throughout the world after their separation, the full range of lineages can still be found within the small, tightly knit Druze population.

Technion researcher Karl Skorecki noted that the findings are consistent with Druze oral tradition suggesting the adherents came from diverse ancestral lineages "stretching back tens of thousands of years." The Druze represent a "genetic sanctuary" or "living relic" that provides a glimpse of the genetic diversity of the Near East in antiquity, the researchers write in the May 7th issue of the journal PLoS ONE.

But there is a modern twist to their story: the diversity of Druze mitochondrial DNA, which is the part of the genome that is passed on strictly through the maternal line, offers a unique opportunity for researchers to study whether people in different mitochondrial DNA lineages are predisposed to different kinds of diseases.

Skorecki points to metabolic syndrome, the combination of insulin resistance, high cholesterol, abdominal obesity and other factors, as one such disease. Mitochondria are the energy factories within cells, so one might expect that differences in mitochondrial DNA might be linked to different predispositions to energy-related diseases such as metabolic syndrome, he explained.

With the Druze, "you can look at 150 kinds of mitochondrial DNA within one group with a similar environment, and be able to see the specific contribution of these variations" to disease, Skorecki said.

Dan Mishmar, a genetics researcher at Ben-Gurion University who was not involved with the study, said there is another "great advantage" to studying the link between disease and mitochondrial DNA variation in a group like the Druze. Although the Druze have great variety in their mitochondrial genome, the rest of their genome inherited from both paternal and maternal lines has grown less diverse as a result of thousands of years of intermarriage.

That means that researchers searching for genetic mutations linked to disease would have an easier time discerning whether these mutations are limited to the mitochondrial genome, which could help researchers design specific, targeted therapies, Mishmar explained.

The findings also guide the approach to screen for genetic disease among the Druze. Instead of scanning for disease-linked genes associated with an entire population--as is the case with Ashkenazi Jews, for example-it may make sense to screen within smaller groups. "Since they are comprised of so many distinct lineages, genetic disease may vary from clan to clan and village to village," Skorecki explained.

The researchers, including Druze co-authors Fuad Basis of the Rambam Medical Center and former Technion student Yarin Hadid, took genetic samples from 311 Druze households in 20 villages in Israel. They soon discovered an unusually high frequency of a mitochondrial DNA haplogroup-a distinct collection of genetic markers - called haplogroup X - among the Druze. Haplogroup X is found at low frequencies throughout the world, and is not confined to a specific geographical region as are most other mitochondrial DNA haplogroups.

Even more unusual, the Druze villages contained a striking range of variations on the X haplogroup. Together, the high frequency and high diversity of the X haplogroup "suggest that this population provides a glimpse into the past genetic landscape of the Near East, at a time when the X haplogroup was more prevalent," the researchers note.

How did the Druze become a genetic sanctuary in the Near East? The religious minority has lived for centuries in remote, mountainous regions, and unlike other monotheistic religions, the group has not sought converts since shortly after the "Dawa" or "revelation" of the religion in 1017 C.E. These factors, along with other cultural and political practices, may have kept the Druze a people apart for thousands of years, according to Skorecki and colleagues.

Skorecki is best-known for his 1997 discovery of genetic evidence indicating that the majority of modern-day Jewish priests (Kohanim) are descendants of a single common male ancestor, consistent with the Biblical high priest, Aaron. He also led an international team of researchers who, in 2006, found that some 3.5 million or 40 percent of Ashkenazi Jews are descended from just four "founding mothers," who lived in Europe 1,000 years ago.

Earliest known human settlement in the Americas

New evidence from earliest known human settlement in the Americas

Provides support for coastal migration theories

New evidence from the Monte Verde archaeological site in southern Chile confirms its status as the earliest known human settlement in the Americas and provides additional support for the theory that one early migration route followed the Pacific Coast more than 14,000 years ago.

The study was conducted by a team of anthropologists, geologists and botanists headed by Vanderbilt University’s Distinguished Professor of Anthropology Tom Dillehay and was reported in the May 9 issue of the journal Science.

The paper, which includes the first new data reported from the site in 10 years, includes the identification of nine species of seaweed and marine algae recovered from hearths and other areas in the ancient settlement. The seaweed samples were directly dated between 14,220 to 13,980 years ago, confirming that the upper layer of the site, labeled Monte Verde II, was occupied more than 1,000 years earlier than any other reliably dated human settlements in the Americas.

The Monte Verde site was discovered in 1976. It is located in a peat bog about 500 miles south of Santiago and has revealed well-preserved ruins of a small settlement of 20 to 30 people living in a dozen huts along a small creek. A wide variety of food has been found at the site, including extinct species of llama and an elephant-like animal called a gomphothere, shellfish, vegetables and nuts.

In 1979, when Dillehay and his colleagues first reported that the radiocarbon dating of the bones and charcoal found at Monte Verde returned dates of more than 14,000 years before the present, it stirred up a major controversy because the early dates appeared to conflict with other archaeological evidence of the settlement of North America.

Since at least 1900, the prevailing theory had been that human colonization began at the end of the last Ice Age about 13,000 years ago, when groups of big game hunters, called the Clovis culture, followed herds from Siberia to Alaska over a land bridge across the Bering Strait and then gradually spread southward. None of the Clovis artifacts were dated earlier than 13,000 years ago. So having a substantially older human settlement in southern Chile was difficult to reconcile with this view.

It wasn’t until 1997 that the controversy was resolved by a prominent group of archaeologists who reviewed the evidence, visited the Monte Verde site and unanimously approved the dating.

Most scholars now believe that people first entered the new world through the Bering land bridge more than 16,000 years ago. After entering Alaska, it is not known whether they colonized the hemisphere by moving down the Pacific coast, by inland routes or both. The general view is that the early immigrants would have spread down the coast much faster than they could move inland because they could exploit familiar coastal resources more readily and get much of their food from the sea. However, evidence to support the coastal migration theory has been particularly hard to find because sea levels at the time were about 200 feet lower than today: As the sea level rose, it would have covered most of the early coastal settlements.

According to Dillehay, the new Monte Verde findings provide additional support for the coastal migration theory but, at the same time, raise the possibility that the process may have been considerably slower than currently envisioned.

At the time it was inhabited, Monte Verde was situated on a small tributary of a large river. It was about 400 feet above sea level and located more than 50 miles from the coast and about 10 miles from a large marine bay. Despite its inland location, the researchers identified a total of nine different species of seaweed and algae in the material collected at the site — material that the Monte Verdeans must have brought from the coast and the bay. The researchers have also found a variety of other beach or coastal resources, including flat beach pebbles, water plants from brackish estuaries and bitumen.

“Finding seaweed wasn’t a surprise, but finding five new species in the abundance that we found them was a surprise,” said Dillehay. “There are other coastal resources at the site. The Monte Verdeans were really like beachcombers: The number and frequency of these items suggests very frequent contact with the coast, as if they had a tradition of exploiting coastal resources.”

In addition, the scientists have found a number of inland resources, such as the gomphothere meat, in the ancient village. This suggests that the group was moving back and forth between different ecological zones, a process called transhumance.

“It takes time to adapt to these inland resources and then come back out to the coast. The other coastal sites that we have found also show inland contacts. If all the early American groups were following a similar pattern of moving back and forth between inland and coastal areas, then the peopling of the Americas may not have been the blitzkrieg movement to the south that people have presumed, but a much slower and more deliberate process,” Dillehay observed.