Thursday, August 28, 2014

New DNA study unravels the settlement history of the New World Arctic


Prehistoric migrations
We know people have lived in the New World Arctic for about 5,000 years. Archaeological evidence clearly shows that a variety of cultures survived the harsh climate in Alaska, Canada and Greenland for thousands of years. Despite this, there are several unanswered questions about these people: Where did they come from? Did they come in several waves? When did they arrive? Who are their descendants? And who can call themselves the indigenous peoples of the Arctic? We can now answer some of these questions, thanks to a comprehensive DNA study of current and former inhabitants of Greenland, Arctic Canada, Alaska, the Aleutian Islands and Siberia, conducted by an international team headed by the Centre for GeoGenetics at the Natural History Museum of Denmark, University of Copenhagen. The results have just been published in the leading scientific journal Science.
Looking for ancient human remains in northern Greenland.
The North American Arctic was one of the last major regions to be settled by modern humans. This happened when people crossed the Bering Strait from Siberia and wandered into a new world. While the area has long been well researched by archaeologists, little is known of its genetic prehistory. In this study, researchers show that the Paleo-Eskimo, who lived in the Arctic from about 5,000 years ago until about 700 years ago, represented a distinct wave of migration, separate from both Native Americans – who crossed the Bering Strait much earlier – and the Inuit, who came from Siberia to the Arctic several thousand years after the Paleo-Eskimos.
- Our genetic studies show that, in reality, the Paleo-Eskimos – representing one single group – were the first people in the Arctic, and they survived without outside contact for over 4,000 years, says Lundbeck Foundation Professor Eske Willerslev from Centre for GeoGenetics at the Natural History Museum, University of Copenhagen, who headed the study.
- Our study also shows that the Paleo-Eskimos, after surviving in near-isolation in the harsh Arctic environment for more than 4,000 years, disappeared around 700 years ago – about the same time when the ancestors of modern-day Inuit spread eastward from Alaska, adds Dr. Maanasa Raghavan of Centre for GeoGenetics and lead author of the article.
Migration pulses into the Americas
Greenlandic Inuit from the 1930s pictured in their traditional boats (umiaq), used for hunting and transportation.
In the archaeological literature, distinctions are drawn between the different cultural units in the Arctic in the period up to the rise of the Thule culture, which replaced all previous Arctic cultures and is the source of today's Inuit in Alaska, Canada and Greenland. The earlier cultures included the Saqqaq or Pre-Dorset and Dorset, comprising the Paleo-Eskimo tradition, with the Dorset being further divided into three phases. All of these had distinctive cultural, lifestyle and subsistence traits as seen in the archaeological record. There were also several periods during which the Arctic was devoid of human settlement. These facts have further raised questions regarding the possibility of several waves of migration from Siberia to Alaska, or perhaps Native Americans migrating north during the first 4,000 years of the Arctic being inhabited.
- Our study shows that, genetically, all of the different Paleo-Eskimo cultures belonged to the same group of people. On the other hand, they are not closely related to the Thule culture, and we see no indication of assimilation between the two groups. We have also ascertained that the Paleo-Eskimos were not descendants of the Native Americans. The genetics reveals that there must have been at least three separate pulses of migration from Siberia into the Americas and the Arctic. First came the ancestors of today's Native Americans, then came the Paleo-Eskimos, and finally the ancestors of today's Inuit, says Eske Willerslev.
Genetics and archaeology
The genetic study underpins some archaeological findings, but not all of them.
It rejects the speculation that the Paleo-Eskimos represented several different peoples, including Native Americans, or that they are direct ancestors of today's Inuit. Also rejected are the theories that the Greenlanders on the east coast or the Canadian Sadlermiut, from Southampton Island in Hudson Bay, who died out as late as 1902��, were surviving groups of Dorset people. Genetics shows that these groups were Inuit who had developed Dorset-like cultural traits.
The study clearly shows that the diversity of tools and ways of life over time, which in archaeology is often interpreted as a result of migration, does not in fact necessarily reflect influx of new people. The Paleo-Eskimos lived in near-isolation for more than 4,000 years, and during this time their culture developed in such diverse ways that it has led some to interpret them as different peoples.
- Essentially, we have two consecutive waves of genetically distinct groups entering the New World Arctic and giving rise to three discrete cultural units. Through this study, we are able to address the question of cultural versus genetic continuity in one of the most challenging environments that modern humans have successfully settled, and present a comprehensive picture of how the Arctic was peopled, says Dr. Raghavan.
The first inhabitants
The study was unable to establish why the disappearance of the Paleo-Eskimos coincided with the ancestors of the Inuit beginning to colonise the Arctic. There is no doubt that the Inuit ancestors – who crossed the Bering Strait about 1,000 years ago and reached Greenland around 700 years ago – were technologically superior.
The Inuit's own myths tell stories of a people before them, which in all likelihood refer to the Paleo-Eskimos. In the myths, they are referred to as the 'Tunit' or 'Sivullirmiut', which means "the first inhabitants". According to these myths they were giants, who were taller and stronger than the Inuit, but easily frightened from their settlements by the newcomers.
Co-author Dr. William Fitzhugh from the Arctic Studies Centre at the Smithsonian Institution says:
- Ever since the discovery of a Paleo-Eskimo culture in the North American Arctic in 1925, archaeologists have been mystified by their relationship with the Thule culture ancestors of the modern Inuit. Paleo-Eskimo culture was replaced rapidly around AD 1300-1400, their only traces being references to 'Tunit' in Inuit mythology and adoption of some elements of Dorset technology. This new genomic research settles outstanding issues in Arctic archaeology that have been debated for nearly a century, finding that Paleo-Eskimo and Neo-Eskimo people were genetically distinct, with separate origins in Eastern Siberia, and the Paleo-Eskimo remained isolated in the Eastern Arctic for thousands of years with no significant mixing with each other or with American Indians, Norse, or other Europeans.



Ancient Metal Workers Were Not Slaves But Highly Regarded Craftsmen


Iron Age copper smelters were respected leaders with sophisticated skills, say Tel Aviv University archaeologists
Excavation at Slaves' Hill. Photo: CTV project at Tel Aviv University
In 1934, American archaeologist Nelson Glueck named one of the largest known copper production sites of the Levant "Slaves' Hill." This hilltop station, located deep in Israel's Arava Valley, seemed to bear all the marks of an Iron Age slave camp — fiery furnaces, harsh desert conditions, and a massive barrier preventing escape. New evidence uncovered by Tel Aviv University archaeologists, however, overturns this entire narrative.
In the course of ongoing excavations at Timna Valley,Dr. Erez Ben-Yosef and Dr. Lidar Sapir-Hen of TAU's Department of Archaeology and Near Eastern Cultures analyzed remnants of food eaten by copper smelters 3,000 years ago. The result of this analysis, published in the journal Antiquity, indicates that the laborers operating the furnaces were in fact skilled craftsmen who enjoyed high social status and adulation. They believe their discovery may have ramifications for similar sites across the region.
"What we found represents a general trend or reality related to metal workers in antiquity," said Dr. Ben-Yosef. "They had a very unique role in society, and we can demonstrate this by looking at Timna."
Examining ancient leftovers
The rare arid conditions of Timna have resulted in unparalleled preservation of organic materials usually destroyed by the march of time: bones, seeds, fruits, and even fabric dating back to the 10th century B.C. Using a technique called "wet sieving," the archaeologists found miniscule animal and fish bones, evidence of a rich and diverse diet.
"The copper smelters were given the better cuts of meat — the meatiest parts of the animals," said Dr. Sapir-Hen. "Someone took great care to give the people working in the furnaces the best of everything. They also enjoyed fish, which must have been brought from the Mediterranean hundreds of kilometers away. This was not the diet of slaves but of highly-regarded, maybe even worshipped, craftsmen."
Copper, used at the time to produce tools and weapons, was the most valuable resource in ancient societies. According to Dr. Ben-Yosef, the smelters needed to be well-versed in the sophisticated technology required to turn stone into usable copper. This knowledge was so advanced for the time it may have been considered magical or supernatural.
"Like oil today, copper was a source of great power," said Dr. Ben-Yosef. "If a person had the exceptional knowledge to 'create copper,' it is not surprising he would have been treated well. In comparing our findings to current ethnographic accounts from Africa, we see smelters worshipped and even honored with animal sacrifices."
Copper production is a complex operation requiring many levels of expertise. Ancient mine workers at Timna may have indeed been slaves or prisoners, because theirs was a simple task performed under severe conditions. However, the act of smelting, turning stone into metal, required an enormous amount of skill and leadership. The smelter had to build a furnace out of clay in precise dimensions, provide the right amount of oxygen and charcoal, maintain a 1,200 degree (Celsius) heat, connect bellow pipes, blow a fixed amount of air, and add an exact mixture of minerals. All told, the smelter had to manage some 30-40 variables in order to produce the coveted copper ingots.
Reconstructing social diversity
According to Dr. Sapir-Hen, an expert on early complex societies, the food remains reflect the social stratification of different laborers at the site. "By studying the remains of domesticated food animals, we reveal differential access to meat that may indicate different levels of specialization among workers at the same site. This allowed us to reconstruct social diversity at the site," said Dr. Sapir-Hen.
The remains of the wall found at the Timna site, once considered a barrier used to contain slave laborers, apparently played a different role as well. "We now know it was a wall used to defend the sophisticated technology and its most precious product — the ingot, the result of the complex copper smelting process," said Dr. Ben-Yosef.
The research on the ancient societies of Timna continues as part of the Central Timna Valley (CTV) Project of Tel Aviv University.

Wednesday, August 27, 2014

Bronze Age wine cellar found


Wine residue, herbal additives found in palace cellar jars

A Bronze Age palace excavation reveals an ancient wine cellar, according to a study published August 27, 2014 (http://dx.plos.org/10.1371/journal.pone.0106406)
 in the open-access journal PLOS ONE by Andrew Koh from Brandeis University and colleagues.

Wine production, distribution, and consumption are thought to have played a role in the lives of those living in the Mediterranean and Near East during the Middle Bronze Age (1900-1600 BC), but little archaeological evidence about Bronze Age wine is available to support art and documentation about the role wine played during this period. During a 2013 excavation of the Middle Bronze Age Canaanite palace in modern-day Israel, the researchers in this study found 40 large storage vessels in an enclosed room located to the west of the central courtyard.

An organic residue analysis using mass spectrometry revealed that all of the relatively uniform jars contained chemical compounds indicative of wine. The authors also detected subtle differences in the ingredients or additives within similarly shaped wine jars, including honey, storax resin, terebinth resin, cedar oil, cyperus, juniper, and possibly mint, myrtle, and cinnamon. The researchers suggest the detection of these additives indicates that humans at the time had a sophisticated understanding of plants and skills necessary to produce a complex beverage that balanced preservation, palatability, and psychoactivity. According to the authors, these results may contribute to a greater understanding of ancient viticulture and the Canaanite palatial economy.

Andrew Koh added, "Based on the nature of the room, it was anticipated from the beginning that residue samples extracted and studied under virtually identical circumstances with minimal variability would have the potential to reveal new and significant insights from both a scientific and archaeological perspective. We believe this study will not only change our understanding of ancient viticulture and palatial social practices, but also the manner in which we approach organic residue analysis (ORA) as an integrated, qualitative, and interdisciplinary exercise that is as field dependent as it is laboratory intensive."
 

Monday, August 25, 2014

One of oldest metal objects found to date in Middle East


Copper awl.
Credit: Image courtesy of University of Haifa
A copper awl, one of the oldest metal objects found to date in the Middle East, was discovered during the excavations at Tel Tsaf, according to a recent study published by researchers from the Zinman Institute of Archaeology and the Department of archaeology at the University of Haifa , in conjunction with researchers from the Hebrew University of Jerusalem and the German Archaeological Institute of Berlin. According to the study, which appeared in the journal PLoS ONE, the awl dates back to the late 6th millennium or the early 5th millennium BCE, moving back by several hundred years the date it was previously thought that the peoples of the region began to use metals.
Tel Tsaf, a Middle Chalcolithic village dated to about 5200-4600 BCE, is located near the Jordan River and the international border with Jordan. The site was first documented in the 1950s and excavations there began at the end of the 1970s. From the earliest digs nearly 40 years ago, this area, the most important archeological site in the region dated to this period, has been supplying researchers with a great deal of valuable data, and continues to do so during this latest research project led by Dr. Danny Rosenberg of the University of Haifa in conjunction with Dr. Florian Klimscha of the Eurasia Department of the German Archaeological Institute in Berlin. For example, the researchers learned of the community's great wealth and the long-distance commercial ties it maintained from the large buildings made of mud-bricks and the large number of silos in which wheat and barley were stored on an unprecedented scale. There were many roasting ovens in the courtyards, all filled with burnt animal bones testifying to the holding of large events and many other findings, among them items made of obsidian (a volcanic glass with origins in Anatolia or Armenia), shells from the Nile River in Egypt and other areas around the Mediterranean, figurines of people and animals, and pottery unlike that found in almost any other location in the region.
But the most important finding to date is only 4 centimeters long. This unique item, a copper awl, which is 1 millimeter thick at the tip that was set in a wooden handle, was actually found during a previous excavation at the site by Prof. Yosef Garfinkel of the Hebrew University. The cone-shaped awl was found in a sealed grave of a woman about 40 years old that was dug inside a silo, and around her waist was a belt made of 1,668 ostrich-egg shell beads. The grave was covered with several large stones, and according to Dr. Rosenberg, its location within a silo testifies to both the importance of the deceased and the importance the community ascribed to the facility in which she was buried.
But while the grave, the woman's skeleton, and the beaded belt were all previously reported in scientific journals, the little awl was only reported on recently, after its chemical components were analyzed by Prof. Sariel Shalev of the Department of Archaeology at the University of Haifa's. As noted, the awl was found to made of copper, and according to Dr. Rosenberg, the fact that it was found just above the skeleton ad in a sealed grave, meant that it was buried with the woman, apparently as a burial offering, and may have belonged to her.
This artifact is important because until now, researchers believed that area residents began to use metals only in the Late Chalcolithic period (during the second half of the 5th millennium BCE), so that this finding moves back the appearance of metal in our region by several hundred years. This has significant impact on our understanding of the developing use of complex technologies and the related social contexts.
But this is not the only reason the awl is significant. The chemical examination of the metal shows it may have come from the Caucasus, some 1,000 kilometers from Tel Tsaf. According to Dr. Rosenberg, while the long-distance commercial ties maintained by village communities in our region were already known from even earlier periods, the import of a new technology combined with the processing of a new raw material coming from such a distant location is unique to Tel Tsaf and provides additional evidence of the importance of this site in the ancient world.
The researchers are still not sure what the awl was used for, but the early use of a metal object, as well as its distant source, also testify to the high social status of the woman and the importance of the building she was buried in.
"The appearance of the item in a woman's grave, which represents one of the most elaborate burials we've seen in our region from that era, testifies to both the importance of the awl and the importance of the woman, and it's possible that we are seeing here the first indications of social hierarchy and complexity," said Dr. Rosenberg. "However, in this area far more is unknown than is known, and although the discovery of the awl at Tel Tsaf constitutes evidence of a peak of technological development among the peoples of the region and is a discovery of global importance, there's a lot of progress still to be made and many parts of the wider picture are still unknown to us."
"It seems that at least some of the questions raised by this unique item will be answered by an interdisciplinary research project we have been conducting at the site since last year," Dr. Rosenberg continued. "This project integrates multinational archeologists and researchers from a variety of other scientific disciplines, who will address the even more complex questions that will undoubtedly arise."


Yosef Garfinkel, Florian Klimscha, Sariel Shalev, Danny Rosenberg. The Beginning of Metallurgy in the Southern Levant: A Late 6th Millennium CalBC Copper Awl from Tel Tsaf, IsraelPLoS ONE, 2014; 9 (3): e92591 

Friday, July 18, 2014

New mosaics discovered in synagogue excavations in Galilee

 This photo shows the head of the possible Alexander figure in the mosaic.

Excavations led by a University of North Carolina at Chapel Hill faculty member revealed stunning new mosaics decorating the floor of the Late Roman (fifth century) synagogue at Huqoq, an ancient Jewish village in Israel’s Lower Galilee.

Since 2012, three well-preserved mosaics have been discovered in the same location in excavations directed by Jodi Magness, Kenan Distinguished Professor for Teaching Excellence in Early Judaism in the College of Arts and Sciences, and co-directed by Shua Kisilevitz of the Israel Antiquities Authority.

In 2012, a mosaic showing Samson and the foxes (as related in the Bible’s Judges 15:4) was discovered in the synagogue’s east aisle. Last summer (2013), a second mosaic was found which shows Samson carrying the gate of Gaza on his shoulders (Judges 16:3).

A third mosaic discovered in the synagogue’s east aisle is divided into three horizontal registers (strips), and differs in style, quality and content from the Samson scenes. It is the first time a non-biblical story has been found decorating any ancient synagogue. Portions of this mosaic were uncovered in 2013, and the rest was revealed this summer.

The lowest register shows a bull pierced by spears, with blood gushing from his wounds, and a dying or dead soldier holding a shield. The middle register depicts an arcade, with the arches framing young men arranged around a seated elderly man holding a scroll, and lighted oil lamps above each arch. The uppermost register depicts a meeting between two large male figures. A bearded, diademed soldier wearing elaborate battle dress and a purple cloak is leading a large bull by the horns, accompanied by a phalanx of soldiers and elephants with shields tied to their sides. He is meeting with a grey-haired, bearded elderly man wearing a ceremonial white tunic and mantle, accompanied by young men with sheathed swords, also wearing ceremonial white tunics and mantles.

The identification of the figures in this mosaic is unclear because there are no stories in the Hebrew Bible involving elephants, Magness said.

”Battle elephants were associated with Greek armies beginning with Alexander the Great, so this might be a depiction of a Jewish legend about the meeting between Alexander and the Jewish high priest,” Magness suggested. “Different versions of this story appear in the writings of Flavius Josephus and in rabbinic literature.”

The mosaics have been removed from the site for conservation, and the excavated areas have been backfilled. Excavations are scheduled to continue in summer 2015.

More on the excavations



Monday, July 14, 2014

Prehistoric 'bookkeeping' continued long after invention of writing






An archaeological dig in southeast Turkey has uncovered a large number of clay tokens that were used as records of trade until the advent of writing, or so it had been believed.

But the new find of tokens dates from a time when writing was commonplace – thousands of years after it was previously assumed this technology had become obsolete. Researchers compare it to the continued use of pens in the age of the word processor.

The tokens – small clay pieces in a range of simple shapes – are thought to have been used as a rudimentary bookkeeping system in prehistoric times.

One theory is that different types of tokens represented units of various commodities such as livestock and grain. These would be exchanged and later sealed in more clay as a permanent record of the trade – essentially, the world's first contract.

The system was used in the period leading up to around 3000 BC, at which point clay tablets filled with pictorial symbols drawn using triangular-tipped reeds begin to emerge: the birth of writing, and consequently history.

From this point on in the archaeological record, the tokens dwindle and then disappear, leading to the assumption that writing quickly supplanted the token system.

However, recent excavations at Ziyaret Tepe – the site of the ancient city Tušhan, a provincial capital of the Neo-Assyrian Empire – have unearthed a large quantity of tokens dating to the first millennium BC: two thousand years after 'cuneiform' – the earliest form of writing – emerged on clay tablets.

"Complex writing didn't stop the use of the abacus, just as the digital age hasn't wiped out pencils and pens," said Dr John MacGinnis from Cambridge's MacDonald Institute for Archaeological Research, who led the research.

"In fact, in a literate society there are multiple channels of recording information that can be complementary to each other. In this case both prehistoric clay tokens and cuneiform writing used together."

The tokens were discovered in the main administrative building in Tušhan's lower town, along with many cuneiform clay tablets as well as weights and clay sealings. Over 300 tokens were found in two rooms near the back of the building that MacGinnis describes as having the character of a 'delivery area', perhaps an ancient loading bay.

"We think one of two things happened here. You either have information about livestock coming through here, or flocks of animals themselves. Each farmer or herder would have a bag with tokens to represent their flock," said MacGinnis.

"The information is travelling through these rooms in token form, and ending up inscribed onto cuneiform tablets further down the line."

Archaeologists say that, while cuneiform writing was a more advanced accounting technology, by combining it with the flexibility of the tokens the ancient Assyrians created a record-keeping system of greater sophistication.

"The tokens provided a system of moveable numbers that allowed for stock to be moved and accounts to be modified and updated without committing to writing; a system that doesn't require everyone involved to be literate."

MacGinnis believes that the new evidence points to prehistoric tokens used in conjunction with cuneiform as an empire-wide 'admin' system stretching right across what is now Turkey, Syria and Iraq. In its day, roughly 900 to 600 BC, the Assyrian empire was the largest the world had ever seen.

Types of tokens ranged from basic spheres, discs and triangles to tokens that resemble oxhide and bull heads.

While the majority of the cuneiform tablets found with the tokens deal with grain trades, it's not yet known what the various tokens represent. The team say that some tokens likely stand for grain, as well as different types of livestock (such as goats and cattle), but – as they were in use at the height of the empire – tokens could have been used to represent commodities such as oil, wool and wine.

"One of my dreams is that one day we'll dig up the tablet of an accountant who was making a meticulous inventory of goods and systems, and we will be able to crack the token system's codes," said MacGinnis.

"The inventions of recording systems are milestones in the human journey, and any finds which contribute to the understanding of how they came about makes a basic contribution to mapping the progress of mankind," he said. 




Thursday, July 3, 2014

Denisovan gene helped Tibetans adapt to low oxygen at high altitudes


Tibetans were able to adapt to high altitudes thanks to a gene picked up when their ancestors mated with a species of human they helped push to extinction, according to a new report by University of California, Berkeley, scientists.

An unusual variant of a gene involved in regulating the body's production of hemoglobin – the molecule that carries oxygen in the blood – became widespread in Tibetans after they moved onto the high-altitude plateau several thousand years ago. This variant allowed them to survive despite low oxygen levels at elevations of 15,000 feet or more, whereas most people develop thick blood at high altitudes, leading to cardiovascular problems.

"We have very clear evidence that this version of the gene came from Denisovans," a mysterious human relative that went extinct 40,000-50,000 years ago, around the same time as the more well-known Neanderthals, under pressure from modern humans, said principal author Rasmus Nielsen, UC Berkeley professor of integrative biology. "This shows very clearly and directly that humans evolved and adapted to new environments by getting their genes from another species."

This is the first time a gene from another species of human has been shown unequivocally to have helped modern humans adapt to their environment, he said.

Nielsen and his colleagues at BGI-Shenzhen in China will report their findings online July 2 in advance of publication in the journal Nature.

The gene, called EPAS1, is activated when oxygen levels in the blood drop, triggering production of more hemoglobin. The gene has been referred to as the superathlete gene because at low elevations, some variants of it help athletes quickly boost hemoglobin and thus the oxygen-carrying capacity of their blood, upping endurance. At high altitude, however, the common variants of the gene boost hemoglobin and its carrier, red blood cells, too much, increasing the thickness of the blood and leading to hypertension and heart attacks as well as low-birth-weight babies and increased infant mortality. The variant or allele found in Tibetans raises hemoglobin and red blood cell levels only slightly at high elevation, avoiding the side-effects seen in most people who relocate to elevations above 13,000 feet.

"We found part of the EPAS1 gene in Tibetans is almost identical to the gene in Denisovans and very different from all other humans," Nielsen said. "We can do a statistical analysis to show that this must have come from Denisovans. There is no other way of explaining the data."

Harsh conditions on Tibetan plateau

The researchers first reported the prevalence of a high-altitude version of EPAS1 in Tibetans in 2010, based on sequencing of the genomes of numerous Han Chinese and Tibetans. Nielsen and his colleagues argued that this was the result of natural selection to adapt to about 40 percent lower oxygen levels on the Tibetan plateau. That is, people without the variant died before reproducing at a much higher rate than those with it. About 87 percent of Tibetans now have the high-altitude version, compared to only 9 percent of Han Chinese, who have the same common ancestor as Tibetans.

Nielsen and his colleagues subsequently sequenced the EPAS1 gene in an additional 40 Tibetans and 40 Han Chinese. The data revealed that the high-altitude variant of EPAS1 is so unusual that it could only have come from Denisovans. Aside from its low frequency in Han Chinese, it occurs in no other known humans, not even Melanesians, whose genomes are nearly 5 percent Denisovan. A high quality sequence of the Denisovan genome was published in 2012.

Nielsen sketched out a possible scenario leading to this result: modern humans coming out of Africa interbred with Denisovan populations in Eurasia as they passed through that area into China, and their descendants still retain a small percentage – perhaps 0.1 percent – Denisovan DNA. The group that invaded China eventually split, with one population moving into Tibet and the other, now known as Han Chinese, dominating the lower elevations.

He and his colleagues are analyzing other genomes to pin down the time of Denisovan interbreeding, which probably happened over a rather short period of time.

"There might be many other species from which we also got DNA, but we don't know because we don't have the genomes," Nielsen said. "The only reason we can say that this bit of DNA is Denisovan is because of this lucky accident of sequencing DNA from a little bone found in a cave in Siberia. We found the Denisovan species at the DNA level, but how many other species are out there that we haven't sequenced?"