星空体育频道: 2013-06-30

2013年7月6日星期六

Jump for your life: Bipedal rodents survive in the desert with a hop, a skip and a jump

Research headed by Talia Moore at Harvard University analysed, for the first time, jerboas' bipedal locomotion. She said: "Bipedal jerboas and quadrupedal jirds share the same habitat, predators, food source, and active hours. It appears that their different forms of locomotion create differing predator evasion abilities, allowing jerboas to forage further from their burrows, thus limiting interspecific competition. In this way these Old World desert rodents can occupy different niches."

The researchers found that bipedal desert rodents move with highly unpredictable trajectories, while sympatric quadrupedal desert rodents move in much more predictable trajectories.

This study involved using inverse dynamics to calculate the forces exerted by bipedal jerboas when jumping vertically, as well as the relative contributions of individual muscles and tendons to the jump.

The researchers collected trajectories of bipedal jerboas and sympatric quadrupedal jirds in the field to quantify the maximum performance and predictability of the escape behaviour of these species in natural conditions.

The Concord Field Station at the Department of Organismic and Evolutionary Biology at Harvard University is the only breeding colony of jerboas in the US, and has the only jerboa colony specifically for scientific research in the world.

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Biomedical uses for hydrogels explored

No, it's not "flubber" -- it's a hydrogel, and now scientists at The University of Akron are exploring new biomedical uses for this polymer-based product.

Dr. Jie Zheng, associate professor of chemical and biomolecular engineering, and Dr. Robert Weiss, Hezzleton E. Simmons professor and chair of polymer engineering, are among the most recent to contribute to the growing research of hydrogels, the gelatinous substance that, because of its toughness and plasticity, has several biomedical applications, including cartilage repair, implants for minimally invasive surgery and drug delivery.

Simplifying production process

Since, as Zheng says, "all existing methods to prepare double-network hydrogels involve multiple-step processes, which are tedious and time-consuming," Zheng and his team developed a simple, efficient and one-pot method (in which reactions occur in one as opposed to several pots) to synthesize double-network hydrogels -- that is, hydrogels composed of two networks of polymer chains, one rigid, the other ductile.

Zheng not only made the synthesis of these hydrogels more efficient -- he also made the hydrogels tougher.

Most hydrogels are weak and brittle, "suffering from low mechanical strength, poor toughness, and/or limited extensibility and recoverability," Zheng says.

His hydrogels, however, "exhibit high mechanical properties, excellent recoverable properties, and a unique, free-shapeable property," he says, making them promising replacements for load-bearing soft tissues like cartilage, tendon, muscle and blood vessels.

Weiss also has synthesized a tougher brand of hydrogel, a "shape memory hydrogel," which can be bent and stretched and fixed into temporary shapes. When exposed to an external stimulus, such as temperature, light, moisture, or an electric field, shape memory polymers recover their original, permanent shape.

Useful shape-shifters

Weiss's shape memory hydrogels are thermally actuated, meaning they stretch and change shape when heated, and they retain this temporary shape when cooled.

Biocompatible, shape memory hydrogels have the potential to be used for minimally invasive surgery and drug delivery, Weiss says.

"Shape memory may be useful for deployment of hydrogels in biomedical applications using less invasive methods ... for example, one can implant a compact form of the device that would deploy into the usable shape after it is implanted," he says.

For example, a small form of the shape memory hydrogel may be inserted into the body, where, upon absorbing bodily fluids, it expands into the desired shape of the implant, thus filling a wound or replacing tissue.

The permeable hydrogels can also be loaded with drugs and placed into the body, where the sponge-like gel biodegrades and releases the drugs from its pores.

Weiss and co-author Jinkun Hao published their findings, "Mechanically Tough, Thermally Activated Shape Memory Hydrogels," on Jan. 7, 2013, in ACS Macro Letters.

Zheng's method has received provisional approval for a patent, and his paper, "A Robust, One-Pot Synthesis of Highly Mechanical and Recoverable Double-Network Hydrogels Using Thermo-Reversible Sol-Gel Polysaccharide," co-authored by Zheng and his UA research colleagues, Qiang Chen, Lin Zhu, Chao Zhao and Qiuming Wang, was published June 14, 2013, online in Advanced Materials.

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The evolution of fins to limbs in the land invasion race

July 5, 2013 — Why did animals with limbs win the race to invade land over those with fins? A new study comparing the forces acting on fins of mudskipper fish and on the forelimbs of tiger salamanders can now be used to analyze early fossils that spanned the water-to-land transition in tetrapod evolution, and further understand their capability to move on land.

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Research conducted by Sandy Kawano and Richard Blob at Clemson University compared terrestrial locomotion in tiger salamanders and mudskipper fish, which have similar characteristics to early tetrapod ancestors.

The researchers filmed these organisms as they walked over a force platform which measures forces like a bathroom scale but separates them into 3 directions (upward, fore-aft, and side-to-side). They compared the forces experienced by the pectoral fins of the mudskipper fishes to the forelimbs and hind limbs of walking tiger salamanders. The results showed that that mudskippers' pectoral fins experience more medial forces than the limbs of salamanders, and that the forelimbs could have a played a similar weight-bearing role as the hind limbs.

Sandy Kawano said: "The transition from fins to limbs marks the most dramatic change in orientation of the locomotor forces from contact with the ground. Using these data we can now evaluate the locomotor capabilities of numerous important fossil taxa that spanned the water-to-land transition in tetrapod evolution. We hypothesise that the medial orientation of the forces on pectoral fins would result in unreasonably high bone stresses in early amphibious fish with fins, which would explain why the evolutionary invasion of land by vertebrates was accomplished instead by tetrapods with limbs with digits."

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Researcher sheds light on M.O. of unusual RNA molecules

Now a team of researchers led by newly arrived biologist Mitchell Guttman of the California Institute of Technology (Caltech) and Kathrin Plath of UCLA, has figured out how some RNA molecules take advantage of their position within the three-dimensional mishmash of genomic material to home in on targets. The research appears in the current issue of Science Express.

The findings suggests a unique role for a class of RNAs, called lncRNAs, which Guttman and his colleagues at the Broad Institute of MIT and Harvard first characterized in 2009. Until then, these lncRNAs -- short for long, noncoding RNAs and pronounced "link RNAs" -- had been largely overlooked because they lie in between the genes that code for proteins. Guttman and others have since shown that lncRNAs scaffold, or bring together and organize, key proteins involved in the packaging of genetic information to regulate gene expression -- controlling cell fate in some stem cells, for example.

In the new work, the researchers found that lncRNAs can easily locate and bind to nearby genes. Then, with the help of proteins that reorganize genetic material, the molecules can pull in additional related genes and move to new sites, building up a "compartment" where many genes can be regulated all at once.

"You can now think about these lncRNAs as a way to bring together genes that are needed for common function into a single physical region and then regulate them as a set, rather than individually," Guttman says. "They are not just scaffolds of proteins but actual organizers of genes."

The new work focused on Xist, a lncRNA molecule that has long been known to be involved in turning off one of the two X chromosomes in female mammals (something that must happen in order for the genome to function properly). Quite a bit has been uncovered about how Xist achieves this silencing act. We know, for example, that it binds to the X chromosome; that it recruits a chromatin regulator to help it organize and modify the structure of the chromatin; and that certain distinct regions of the RNA are necessary to do all of this work. Despite this knowledge, it had been unknown at the molecular level how Xist actually finds its targets and spreads across the X chromosome.

To gain insight into that process, Guttman and his colleagues at the Broad Institute developed a method called RNA Antisense Purification (RAP) that, by sequencing DNA at high resolution, gave them a way to map out exactly where different lncRNAs go. Then, working with Plath's group at UCLA, they used their method to watch in high resolution as Xist was activated in undifferentiated mouse stem cells, and the process of X-chromosome silencing proceeded.

"That's where this got really surprising," Guttman says. "It wasn't that somehow this RNA just went everywhere, searching for its target. There was some method to its madness. It was clear that this RNA actually used its positional information to find things that were very far away from it in genome space, but all of those genes that it went to were really close to it in three-dimensional space."

Before Xist is activated, X-chromosome genes are all spread out. But, the researchers found, once Xist is turned on, it quickly pulls in genes, forming a cloud. "And it's not just that the expression levels of Xist get higher and higher," Guttman says. "It's that Xist brings in all of these related genes into a physical nuclear structure. All of these genes then occupy a single territory."

The researchers found that a specific region of Xist, known as the A-repeat domain, that is known to be vital for the lncRNA's ability to silence X-chromosome genes is also needed to pull in all the genes that it needs to silence. When the researchers deleted the domain, the X chromosome did not become inactivated, because the silencing compartment did not form.

One of the most exciting aspects of the new research, Guttman says, is that it has implications beyond just explaining how Xist works. "In our paper, we talk a lot about Xist, but these results are likely to be general to other lncRNAs," he says. He adds that the work provides one of the first direct pieces of evidence to explain what makes lncRNAs special. "LncRNAs, unlike proteins, really can use their genomic information -- their context, their location -- to act, to bring together targets," he says. "That makes them quite unique."

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Search for Extraterrestrial Intelligence research network launched

The network's Patron is the Astronomer Royal, Professor Martin Rees. UKSRN will present current activity and consider future strategy in a session and panel discussion at the National Astronomy Meeting in St Andrews on Friday 5 July.

UKSRN covers a broad spectrum of research topics, including potential methods for detecting signals, the linguistic challenge of deciphering messages, the probability of an extraterrestrial civilization interacting with Earth and the longevity of civilizations.

Dr Alan Penny, the coordinator of UKSRN said, "We hope that the existence of the network will excite interest from people in the UK astronomical community that have been thinking about SETI and encourage them to contribute their work. In this session at NAM, we are presenting the whole range of UK SETI activities to the community and hope that it will promote a wider understanding of, and activity in, this subject."

Dr Tim O'Brien from The University of Manchester's Jodrell Bank Observatory will describe the capability of the UK's recently commissioned e-MERLIN array of seven radio telescopes for SETI projects and report on progress in initial test observations.

"The first proposal to search for radio signals from extraterrestrial civilisations was actually inspired by the construction of the Lovell Telescope at Jodrell Bank," said O'Brien. "We went on to take part in the SETI Institute's Project Phoenix from 1998 to 2003, searching for signals from about a thousand nearby stars. At that time the equipment required to sift through the data was expensive and unusual, but our modern telescopes are potentially capable of conducting these type of observations as a matter of course."

The e-MERLIN array, which includes the Lovell Telescope, is connected by optical fibres and spread over 217 km from Jodrell Bank to Cambridge. This multi-telescope approach offers potential for distinguishing true extraterrestrial signals from interference generated here on Earth, a key problem for all radio SETI projects.

O'Brien is excited about future prospects, "It's early days for this new SETI work at Jodrell but we think that using e-MERLIN, and future facilities such as the Square Kilometre Array, we could make an important contribution to the search for intelligent life elsewhere in the Universe."

Dr John Elliott of Leeds Metropolitan University is a researcher on the nature of communication: how language structure can be identified, and methods for subsequent decipherment and dissemination. He has analysed over 60 human languages, which cover all the different types of systems, as well as non-human communication, such as robots and dolphins. Elliott believes that by understanding our analytical capabilities for communication, we can develop strategies for extra-terrestrial message discovery and understanding.

"Suppose SETI succeeds and we detect a technological beacon. Any message is unlikely to be written in Martian English, so standard decipherment/decryption techniques used by the military and security agencies are not going to help much. To put the challenge into context, we still have scripts from antiquity that have remained undeciphered over hundreds of years, despite many serious attempts," said Elliott.

Elliott's research focuses on whether there is something unique to communication phenomena, irrespective of the source, that makes them distinguishable from other signals in the universe. "By looking beneath the surface veneer of the arbitrary sounds and symbols used, we can 'see' the language machine itself: its mechanisms, constraints, and evolutionary forces of efficiency and compromise that shape it. By understanding these structures, it should be possible to glean information on the intelligence of the message author," said Elliott.

Back in 1950 during a conversation on SETI, the physicist, Enrico Fermi, posed the question 'Where is everybody?' The paradox between the high estimates for the probability of the existence of extraterrestrial civilizations and the lack of contact or evidence remains a key area of SETI research. Dr Anders Sandberg, of the Future of Humanity Institute at Oxford University, is investigating the question of how far away in space and time a civilization could start and still have a chance of interacting with Earth today.

"If this were a very limited range, the Fermi question, "Where are they?" would be easy to answer: they couldn't have got here yet. However, we show in our paper that, beyond a certain technological level, civilizations can spread not just across their own galaxy but across enormous intergalactic distances. This is mostly limited by how fast their devices are and the expansion of the universe. There are millions or billions of galaxies from which a civilization could have reached us, if it were established early," said Sandberg.

Sandberg and his colleagues have concluded that the answer to the Fermi question is more extreme than normally thought. "If life or intelligence is rare, it must be millions or billions of times rarer; if advanced societies wipe themselves out, or decide to not go exploring, they need to converge to this outcome with extremely high probability, since it only takes one that escapes this fate to fill the universe," said Sandberg.

The work of Dr Austin Gerig, senior research fellow in Complex Networks at the University of Oxford, estimates the fraction of civilizations in the universe that are long-lived and analyses the human race's prospects for survival.

Dr Gerig said, "We know that (1) we exist and that (2) our birth number within our civilization is approximately 70 billion (i.e., approximately 70 billion people were born before us). From such little information, we can reasonably, and perhaps surprisingly, conclude that (1) many other civilizations exist and that (2) most of these civilizations are small, i.e., most will die out before producing trillions of people."

Gerig and his colleagues have focused on a specific consequence of this reasoning, called the "universal doomsday argument": long-lived civilizations must be rare because if they were not, we would find ourselves living in one.

"If most civilizations are small, then our own civilization is likely to be small, i.e., it is likely to die out within the next few centuries. Our research indicates this is the case, but that our estimates of survival are greater than previously thought using a more traditional form of the doomsday argument," said Gerig.

Duncan Forgan, from the Royal Observatory Edinburgh, is looking at the possibility of detecting large structures built by civilizations orbiting other stars. The transit method of detecting extrasolar planets involves measuring the dip in starlight as a planet passes in front of its star. The Kepler Space Telescope has detected a whole host of new exoplanets using the transit technique, and there are many future telescopes and missions lined up to succeed it. Forgan has investigated whether the obstruction of the stellar disc by a large orbiting structure would make a detectable difference in the shape of the lightcurve of an exoplanet transit.

"I looked at one type of megastructure, which is essentially a very large mirror. The mirror reflects the star's own radiation and produces thrust, much like a sail produces thrust from wind. This thrust could be used to move a civilization's host star from its "natural" orbit if it posed some harm to the civilization, for example a dangerous close approach to another star or dust cloud," said Forgan.

Forgan's study showed that a giant mirror of this type would leave a characteristic trace in exoplanet transit data, which could be detectable with the next generation of telescopes.

"While the odds of seeing megastructures are probably very low, we will soon have a huge archive of exoplanet data to search for these objects -- at no extra cost to SETI scientists. We may detect the presence, or remains, of an alien civilization that felt the need to move their star!" said Forgan.

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2013年7月5日星期五

Ancient jigsaw puzzle of past supercontinent revealed

Researchers from Royal Holloway University, The Australian National University and Geoscience Australia, have helped clear up previous uncertainties on how the plates evolved and where they should be positioned when drawing up a picture of the past.

Dr Lloyd White from the Department of Earth Sciences at Royal Holloway University said: "The Earth's tectonic plates move around through time. As these movements occur over many millions of years, it has previously been difficult to produce accurate maps of where the continents were in the past.

"We used a computer program to move geological maps of Australia, India and Antarctica back through time and built a 'jigsaw puzzle' of the supercontinent Gondwana. During the process, we found that many existing studies had positioned the plates in the wrong place because the geological units did not align on each plate."

The researchers adopted an old technique used by people who discovered the theories of continental drift and plate tectonics, but which had largely been ignored by many modern scientists.

"It was a simple technique, matching the geological boundaries on each plate. The geological units formed before the continents broke apart, so we used their position to put this ancient jigsaw puzzle back together again," Dr White added.

"It is important that we know where the plates existed many millions of years ago, and how they broke apart, as the regions where plates break are often where we find major oil and gas deposits, such as those that are found along Australia's southern margin."

A video demonstrating the ancient jigsaw puzzle can be viewed here: http://vimeo.com/68311221

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Unique epigenomic code identified during human brain development

July 5, 2013 — Changes in the epigenome, including chemical modifications of DNA, can act as an extra layer of information in the genome, and are thought to play a role in learning and memory, as well as in age-related cognitive decline. The results of a new study by scientists at the Salk Institute for Biological Studies show that the landscape of DNA methylation, a particular type of epigenomic modification, is highly dynamic in brain cells during the transition from birth to adulthood, helping to understand how information in the genomes of cells in the brain is controlled from fetal development to adulthood. The brain is much more complex than all other organs in the body and this discovery opens the door to a deeper understanding of how the intricate patterns of connectivity in the brain are formed.

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"These results extend our knowledge of the unique role of DNA methylation in brain development and function," says senior author Joseph R. Ecker, professor and director of Salk's Genomic Analysis Laboratory and holder of the Salk International Council Chair in Genetics. "They offer a new framework for testing the role of the epigenome in healthy function and in pathological disruptions of neural circuits."

A healthy brain is the product of a long process of development. The front-most part of our brain, called the frontal cortex, plays a key role in our ability to think, decide and act. The brain accomplishes all of this through the interaction of special cells such as neurons and glia. We know that these cells have distinct functions, but what gives these cells their individual identities? The answer lies in how each cell expresses the information contained in its DNA. Epigenomic modifications, such as DNA methylation, can control which genes are turned on or off without changing letters of the DNA alphabet (A-T-C-G), and thus help distinguish different cell types.

In this new study, published July 4 in Science, the scientists found that the patterns of DNA methylation undergo widespread reconfiguration in the frontal cortex of mouse and human brains during a time of development when synapses, or connections between nerve cells, are growing rapidly. The researchers identified the exact sites of DNA methylation throughout the genome in brains from infants through adults. They found that one form of DNA methylation is present in neurons and glia from birth. Strikingly, a second form of "non-CG" DNA methylation that is almost exclusive to neurons accumulates as the brain matures, becoming the dominant form of methylation in the genome of human neurons. These results help us to understand how the intricate DNA landscape of brain cells develops during the key stages of childhood.

The genetic code in DNA is made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). DNA methylation typically occurs at so-called CpG sites, where C (cytosine) sits next to G (guanine) in the DNA alphabet. About 80 to 90 percent of CpG sites are methylated in human DNA. Salk researchers previously discovered that in human embryonic stem cells and induced pluripotent stem cells, a type of artificially derived stem cell, DNA methylation can also occur when G does not follow C, hence "non-CG methylation." Originally, they thought that this type of methylation disappeared when stem cells differentiate into specific tissue-types such as lung or fat cells. The current study finds this is not the case in the brain, where non-CG methylation appears after cells differentiate, usually during childhood and adolescence when the brain is maturing.

By sequencing the genomes of mouse and human brain tissue as well as neurons and glia (from the frontal cortex of the brain) during early postnatal, juvenile, adolescent and adult stages, the Salk team found that non-CG methylation accumulates in neurons through early childhood and adolescence, and becomes the dominant form of DNA methylation in mature human neurons. "This shows that the period during which the neural circuits of the brain mature is accompanied by a parallel process of large-scale reconfiguration of the neural epigenome," says Ecker, who is a Howard Hughes Medical Institute and Gordon and Betty Moore Foundation investigator.

The study provides the first comprehensive maps of how DNA methylation patterns change in the mouse and human brain during development, forming a critical foundation to now explore whether changes in methylation patterns may be linked to human diseases, including psychiatric disorders. Recent studies have demonstrated a possible role for DNA methylation in schizophrenia, depression, suicide and bipolar disorder. "Our work will let us begin to ask more detailed questions about how changes in the epigenome sculpt the complex identities of brain cells through life," says co-first author Eran Mukamel, from Salk's Computational Neurobiology Laboratory.

"The human brain has been called the most complex system that we know of in the universe," says Ryan Lister, co-corresponding author on the new paper, previously a postdoctoral fellow in Ecker's laboratory at Salk and now a group leader at The University of Western Australia. "So perhaps we shouldn't be so surprised that this complexity extends to the level of the brain epigenome. These unique features of DNA methylation that emerge during critical phases of brain development suggest the presence of previously unrecognized regulatory processes that may be critically involved in normal brain function and brain disorders."

At present, there is consensus among neuroscientists that many mental disorders have a neurodevelopmental origin and arise from an interaction between genetic predisposition and environmental influences (for example, early-life stress or drug abuse), the outcome of which is altered activity of brain networks. The building and shaping of these brain networks requires a long maturation process in which central nervous system cell types (neurons and glia) need to fine-tune the way they express their genetic code.

"DNA methylation fulfills this role," says study co-author Terrence J. Sejnowski, a Howard Hughes Medical Institute Investigator, holder of the Francis Crick Chair and head of Salk's Computational Neurobiology Laboratory. "We found that patterns of methylation are dynamic during brain development, in particular for non-CG methylation during early childhood and adolescence, which changes the way that we think about normal brain function and dysfunction."

By disrupting the transcriptional expression of neurons, adds co-corresponding author M. Margarita Behrens, a staff scientist in the Computational Neurobiology Laboratory, "the alterations of these methylation patterns will change the way in which networks are formed, which could, in turn, lead to the appearance of mental disorders later in life."

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White dwarf star throws light on possible variability of a constant of Nature

July 4, 2013 — An international team led by the University of New South Wales has studied a distant star where gravity is more than 30,000 times greater than on Earth to test its controversial theory that one of the constants of Nature is not a constant.

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Dr Julian Berengut and his colleagues used the Hubble Space Telescope to measure the strength of the electromagnetic force -- known as alpha -- on a white dwarf star.

Their results, which do not contradict the variable constant theory, are to be published in the journal Physical Review Letters. Dr Berengut, of the UNSW School of Physics, said the team's previous research on light from distant quasars suggests that alpha -- known as the fine-structure constant -- may vary across the universe.

"This idea that the laws of physics are different in different places in the cosmos is a huge claim, and needs to be backed up with solid evidence," he says.

"A white dwarf star was chosen for our study because it has been predicted that exotic, scalar energy fields could significant alter alpha in places where gravity is very strong."

"Scalar fields are forms of energy that often appear in theories of physics that seek to combine the Standard Model of particle physics with Einstein's general theory of relativity."

"By measuring the value of alpha near the white dwarf and comparing it with its value here and now in the laboratory we can indirectly probe whether these alpha-changing scalar fields actually exist."

White dwarfs are very dense stars near the ends of their lives. The researchers studied the light absorbed by nickel and iron ions in the atmosphere of a white dwarf called G191-B2B. The ions are kept above the surface by the star's strong radiation, despite the pull of its extremely strong gravitational field.

"This absorption spectrum allows us to determine the value of alpha with high accuracy. We found that any difference between the value of alpha in the strong gravitational field of the white dwarf and its value on Earth must be smaller than one part in ten thousand," Dr Berengut says.

"This means any scalar fields present in the star's atmosphere must only weakly affect the electromagnetic force." Dr Berengut said that more precise measurements of the iron and nickel ions on earth are needed to complement the high-precision astronomical data.

"Then we should be able to measure any change in alpha down to one part per million. That would help determine whether alpha is a true constant of Nature, or not."

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Study of mitochondrial DNA ties ancient remains to living descendants

The findings are reported in the journal PLOS ONE.

The researchers compared the complete mitochondrial genomes of four ancient and three living individuals from the north coast of British Columbia, Canada. This region is home to the indigenous Tsimshian, Haida and Nisga'a people, all of whom have oral traditions and some written histories indicating that they have lived in the region for uncounted generations. Archaeological sites, some with human remains, date back several millennia. But until the current study, nothing definitively tied the current inhabitants of the area to the ancient human remains found there, some of which are 5,000 to 6,000 years old.

"Having a DNA link showing direct maternal ancestry dating back at least 5,000 years is huge as far as helping the Metlakatla prove that this territory was theirs over the millennia," said Barbara Petzelt, an author and participant in the study and liaison to the Tsimshian-speaking Metlakatla community, one of the First Nations groups that participated in the study.

Only one previous study of ancient remains found in the Americas -- the hair of an Eskimo man who lived in Greenland 3,400 to 4,500 years ago -- analyzed all of the ancient mitochondrial DNA sequences (the mitochondrial genome, or mitogenome). Most such studies look at only a small subset (less than 2 percent) of mitogenomic sequences.

The new analysis was made possible by technological advances that cut the cost and complexity of sequencing ancient DNA.

"This is the beginning of the golden era for ancient DNA research because we can do so much now that we couldn't do a few years ago because of advances in sequencing technologies," said University of Illinois anthropology and Institute for Genomic Biology professor Ripan Malhi, who led the analysis. "We're just starting to get an idea of the mitogenomic diversity in the Americas, in the living individuals as well as the ancient individuals."

Focusing on the mitogenome is a good way to study the evolutionary history of these groups, Malhi said. DNA is often degraded in ancient remains, and unlike nuclear DNA, which is present in only two copies per cell, mitochondria are abundant in cells, giving researchers many DNA duplicates to sequence and compare.

Mitochondrial DNA does not recombine with paternal DNA and is passed down from mother to offspring more or less intact. This makes it easier to track unique sequences through the generations. And since the participants in the study belong to matrilineal cultures, their oral histories can be compared to evidence from the maternal lineages reflected in the mitogenome.

Another complication associated with analyzing nuclear DNA in Native Americans involves the European influence, Malhi said.

"There's a pattern of European males mixing with Native American females after European contact and so lots of the Y chromosomes in the community trace back to Europe," he said. The mitogenome offers a clearer picture of Native American lineages before European contact, he said.

Scientists, including David Archer, an anthropology professor at Northwest Community College in Prince Rupert, and biological anthropologist and co-author Jerome Cybulski, of the Canadian Museum of Civilization in Gatineau, Quebec, have worked since the 1960s to recover and analyze human remains and ancient structures in the region around Prince Rupert.

One particularly fruitful site, the Lucy Islands, yielded human remains and evidence of a house structure that is 5,300 to 6,400 years old. Careful study revealed that one of the ancient individuals found there, a young adult female, lived roughly 5,500 years ago. Her mitogenome matched that of another female found on Dodge Island, near the city of Prince Rupert. Her remains were about 2,500 years old. A living participant in the study also carried the same mitogenomic signature, the researchers found, and so is a direct maternal descendant of those two women or their mothers.

Three other living participants host a different mitogenomic sequence that matches another individual found on Dodge Island who lived about 5,000 years ago.

The archaeological sites also point to a long period of continuous occupation and stability in terms of the types of structures people used and the ways they used them, Archer said.

"Archaeology is one important source of information about the past, and oral traditions give us a lot of verifiable information about the past cultural events and patterns," he said. "But the genetic information is something that is immediately recognizable. If somebody is told that their DNA links to somebody who was present 2,500 years ago and also to someone who was present 5,500 years ago, you can summarize that in a sentence and it's very easily understood and it's exciting."

The new findings were the result of an unusual effort by the researchers to enlist the help of the indigenous people they study.

"I believe this is really a unique collaboration," said Joycelynn Mitchell, a Metakatla co-author and participant in the study. "It's very exciting to be able to have scientific proof that corroborates what our ancestors have been telling us for generations. It's very amazing how fast technology is moving to be able to prove this kind of link with our past."

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Archaeologists unearth carved head of Roman god in ancient rubbish dump

July 4, 2013 — An 1,800-year-old carved stone head of what is believed to be a Roman god has been unearthed in an ancient rubbish dump.

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Archaeologists made the discovery at Binchester Roman Fort, near Bishop Auckland, in County Durham.

First year Durham University archaeology student Alex Kirton found the artefact, which measures about 20cm by 10cm, in buried late Roman rubbish within what was probably a bath house.

The sandstone head, which dates from the 2nd or 3rd century AD, has been likened to the Celtic deity Antenociticus, thought to have been worshipped as a source of inspiration and intercession in military affairs.

A similar sandstone head, complete with an inscription identifying it as Antenociticus, was found at Benwell, in Newcastle upon Tyne, in 1862.

Dr David Petts, Lecturer in Archaeology at Durham University, said: "We found the Binchester head close to where a small Roman altar was found two years ago. We think it may have been associated with a small shrine in the bath house and dumped after the building fell out of use, probably in the 4th century AD.

"It is probably the head of a Roman god -- we can't be sure of his name, but it does have similarities to the head of Antenociticus found at Benwell in the 19th century.

"We may never know the true identity of this new head, but we are continuing to explore the building from which it came to help us improve our understanding of late Roman life at Binchester and the Roman Empire's northern frontier in Northern England.

"Antenociticus is one of a number of gods known only from the northern frontier, a region which seems to have had a number of its own deities.

"It's also an excellent insight into the life and beliefs of the civilians living close to the Roman fort. The style is a combination of classical Roman art and more regional Romano-British traditions. It shows the population of the settlement taking classical artistic traditions and making them their own."

Alex, 19, from Bishop's Stortford, in Hertfordshire, said: "As an archaeology student this is one of the best things and most exciting things that could have happened."

He added: "It was an incredible thing to find in a lump of soil in the middle of nowhere -- I've never found anything remotely exciting as this."

Dr David Mason, Principal Archaeologist with the site's owner, Durham County Council, said: "The head is a welcome addition to the collection of sculpture and inscriptions from Binchester. Previous religious dedications from the site feature deities from the classical pantheon of gods and goddesses such as the supreme god Jupiter and those associated with healing and good health such as Aesculapius, Salus and Hygeia.

"This one however appears to represent a local Romano-Celtic god of the type frequently found in the frontier regions of the Empire and probably representing the conflation of a classical deity with its local equivalent. The similarity with the head of Antenociticus is notable, but this could be a deity local to Binchester."

The Binchester head is African in appearance, but Dr Petts, who is also Associate Director of Durham University's Institute of Medieval and Early Modern Studies, said experts were unsure whether these features were deliberate or coincidental.

He explained: "This is something we need to consider deeply. If it is an image of an African, it could be extremely important, although this identification is not certain."

Dr Mason added: "The African style comparison may be misleading as the form is typical of that produced by local craftsmen in the frontier region."

The find was made as part of a five year project at Binchester Roman Fort which is shedding new light on the twilight years of the Roman Empire.

The Binchester dig is a joint project between Durham University's Department of Archaeology, site owner Durham County Council, Stanford University's Archaeology Centre and the Architectural and Archaeological Society of Durham and Northumberland.

Each summer, undergraduate archaeology students from Durham and the United States are joined by volunteer members of the public to painstakingly reveal more fascinating details from Binchester's past.

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