星空女人频道: 2013-09-08

2013年9月14日星期六

Model organism gone wild

Sep. 13, 2013 — Model organisms, brought into labs because they are easy to work with, adapt to the lab, often shedding characteristics that allowed them to survive in the wild. Scientists who work with model organisms rarely look at the wild strains, but when they do, they can be surprised by what they find.

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This is what happened with the soil-living social amoeba, Dictyostelium discoideum, or Dicty. The single-celled amoebas crawl through the soil eating bacteria until food becomes scarce. Then the amoebas gather by the tens of thousands to form a multicellular slug, which transforms itself into a fruiting body: a sterile stalk that holds aloft a sorus, a tiny sphere that releases spores that become single amoebae again.

Isolated from decaying leaves collected in a hardwood forest in North Carolina in the summer of 1933, Dicty have been used for years to study development and, more recently, conflict and cooperation.

Over the years, the model organism had adapted to growing in shaking flasks of liquid, a far cry from the soil, which Washington University in St. Louis biologist Joan Strassmann characterizes as "a noxious and terrifying environment for the little things that live there."

In 1998, David Queller and Strassmann, both then on the faculty of Rice University in Houston, began isolating and working with wild clones of Dicty from soil collected at a field station in Virginia and various other locations around the U.S. When these clones were examined closely, they revealed a whole new world.

All Dicty eat bacteria, but some clones (genetically identical amoebas) also farm them -- or at any rate, they gather up the bacteria, carry them to new sites and harvest them prudently.

The farmer clones also carry bacteria that secrete chemicals to fend off amoebae that don't bother to do their own farming. Not only do these defensive companions inhibit the growth of nonfarmers, they somehow stimulate the growth of the farmers.

The scientists, who have since moved to Washington University in St. Louis, describe this miniature ecosystem and its players in the Sept. 13, 2013, online edition of Nature Communications.

"Our results suggest that successful farming is a complex evolutionary adaptation because it requires additional strategies, such as recruiting third parties, to effectively defend and privatize the crops," the scientists wrote.

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Amoebas carrying seed corn

"A lot of work has been done on this organism," said Debra Brock, a research scientist in the Queller/Strassmann lab. "But the model organism is descended from a wild clone that was probably a nonfarmer.

"I had worked for years with the axenic clone (the model organism adapted to grow in liquid) when I joined the Queller/Strassmann lab as a graduate student. They had a large collection of wild discoideum clones, which I had never studied.

"When I looked at these clones under the microscope, I saw that some of them carried bacteria in their sorae, which were supposed to be sterile. A simple assay confirmed that the sorae from these clones seeded new patches of bacterial growth while those from clones that did not have bacteria did not."

It looked like the amoebas were carrying the bacteria around to make sure they would always have food. But other scientists weren't convinced.

After all, the amoebas are grown on bacteria in the lab; perhaps they had just picked up these bacteria by accident.

"At first it was an uphill battle," Brock said. But by isolating new clones from the wild that also carried edible bacteria in their sorae and running the clones through assays that showed, for example, that farmers cleansed of bacteria would pick them up again, the scientists eventually made their case.

As the researchers said in a Nature paper published in 2011, about a third of the wild clones carry, seed and prudently harvest edible bacteria, qualifying as farmers, albeit primitive ones.

Amoebas carrying chemical weapons

But the situation was actually more complex than this. Brock quickly realized that some of the bacteria found in association with the Dicty weren't edible. "I was sending the bacterial DNA out to be sequenced and looking up the sequence when it came back. Sometimes the bacteria were similar to human pathogens.

"Again it wasn't clear what was going on," Brock said. "Were these bacteria parasites on the amoebas? Were they free riders the amoebas picked up accidentally when they picked up the food bacteria? Were they pathogens that were making the amoebas sick? "

But the amoebas carrying these bacteria seemed to be thriving rather than sick. And she also knew that in other systems, farmers carry defensive symbionts. Leafcutter ants, for example, carry bacteria that help prevent other fungi from contaminating their fungal gardens. Could the inedible bacteria on the Dicty be defensive symbionts?

Sure enough, assays showed that when farmers carried certain nonedible strains, nonfarmer spore production was reduced, in some cases by more than half. Supernatants (washings) from bacterial cultures had similar effects, suggesting that the bacteria were secreting biomolecules that poisoned nonfarmers, preventing them from eating the farmers' crops.

But that wasn't the end of the surprises. The defensive symbionts don't just squash nonfarmers, they seem also to help the farmers thrive. Brock suspects the amoebas and the bacteria are cross feeding. "They're probably providing something for those bacteria and the bacteria are providing something for them. I'm currently trying to figure that out," she said.

Does it pay to farm?

The big question for the team, all evolutionary biologists, was why is farming evolutionarily stable among Dicty? Why does this adaptation persist and, conversely why doesn't it take over the entire population? The answer is that the value of farming as a strategy depends on the circumstances.

Farming, by itself, does not confer a selection advantage on the Dicty clones. If food is abundant, nonfarmers alone produce more spores than farmers alone. The reason is that farming is costly. Farmers save roughly half the bacteria available to them, forgoing considerable food to save some for dispersal at a new site. Like human farmers, they try never to touch their "seed corn."

The tables are turned, however, if food is scarce -- if the amoebas are dispersed to a site without a good source -- farmers produce more spores than nonfarmers because they are able to make their new site productive.

What happens when farmers and nonfarmers are in direct competition? The farmers produce a valuable crop that could be eaten by nonfarmer clones that do not pay the costs of farming, making farming a losing strategy again.

That's where the defensive symbionts come in. In the Nature Communications' article, the scientists describe assays where they mixed farmers and nonfarmers in different proportions to see how they would do in direct competition with one another.

As the percentage of farmers in the mix increased, nonfarmers produced far fewer spores, and the spore production of farmers was unchanged.

These results suggest that social amoebas make farming pay much as human farmers all over the world have done, by privatizing their crops. Without the benefit of human institutions that guarantee property rights or a just division of goods, they enforce their rights through chemical warfare.

"This is a neat example that shows that when you start looking at the natural history of things, even microbes, which people don't study very much, you discover that amazing things are going on," Queller said.

"It's also about being open-minded," Strassmann said. "When you see things that don't quite fit the standard story, a good scientist will not try to jam them into the story, but instead recognize something different is going on and try to figure it out."

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Tiny plankton could have big impact on climate: CO<sub>2</sub>-hungry microbes might short-circuit the marine foodweb

Tiny plankton could have big impact on climate: CO₂-hungry microbes might short-circuit the marine foodweb

Sep. 13, 2013 — As the climate changes and oceans' acidity increases, tiny plankton seem set to succeed. An international team of marine scientists has found that the smallest plankton groups thrive under elevated carbon dioxide (CO₂) levels. This could cause an imbalance in the food web as well as decrease ocean CO₂ uptake, an important regulator of global climate. The results of the study, conducted off the coast of Svalbard, Norway, in 2010, are now compiled in a special issue published in Biogeosciences, a journal of the European Geosciences Union.

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"If the tiny plankton blooms, it consumes the nutrients that are normally also available to larger plankton species," explains Ulf Riebesell, a professor of biological oceanography at the GEOMAR Helmholtz Centre for Ocean Research Kiel in Germany and head of the experimental team. This could mean the larger plankton run short of food.

Large plankton play an important role in carbon export to the deep ocean, but in a system dominated by the so-called pico- and nanoplankton, less carbon is transported out of surface waters. "This may cause the oceans to absorb less CO₂ in the future," says Riebesell.

The potential imbalance in the plankton food web may have an even bigger climate impact. Large plankton are also important producers of a climate-cooling gas called dimethyl sulphide, which stimulates cloud-formation over the oceans. Less dimethyl sulphide means more sunlight reaches Earth's surface, adding to the greenhouse effect. "These important services of the ocean may thus be significantly affected by acidification."

Ecosystems in the Arctic are some of the most vulnerable to acidification because the cold temperatures here mean that the ocean absorbs more carbon dioxide. "Acidification is faster there than in temperate or tropical regions," explains the coordinator of the European Project on Ocean Acidification (EPOCA), Jean-Pierre Gattuso of the Laboratory of Oceanography of Villefranche-sur-Mer of the French National Centre for Scientific Research (CNRS).

The increasing acidity is known to affect some calcifying organisms in the Arctic, including certain sea snails, mussels and other molluscs. But scientists did not know until now how ocean acidification alters both the base of the marine food web and carbon transport in the ocean.

The five-week long field study conducted in the Kongsfjord off the Arctic archipelago of Svalbard, under the EPOCAframework, intended to close this knowledge gap. For the experiment, the scientists deployed nine large 'mesocosms', eight-metre long floatation frames carrying plastic bags with a capacity of 50 cubic metres. These water enclosures, developed at GEOMAR, allow researchers to study plankton communities in their natural environment under controlled conditions, rather than in a beaker in the lab. Few studies have looked at whole communities before.

The scientists gradually added CO₂ to the mesocom water so that it reached acidity levels expected in 20, 40, 60, 80 and 100 years, with two bags left as controls. They also added nutrients to simulate a natural plankton bloom, as reported in the Biogeosciences special issue.

The team found that, where CO₂ was elevated, pico- and, to a lesser extent, nanoplankton grew, drawing down nutrients so there were less available to larger plankton. "The different responses we observed made it clear that the communities' sensitivity to acidification depends strongly on whether or not nutrients are available," Riebesell summarises.

"Time and [time] again the tiniest plankton benefits from the surplus CO₂, they produce more biomass and more organic carbon, and dimethyl sulphide production and carbon export are decreasing," he concludes.

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'Terminator' polymer: Self-healing polymer that spontaneously and independently repairs itself

Self-healing polymers mend themselves by reforming broken cross-linking bonds. However, the cross-linking healing mechanism usually requires an external stimulus.

Triggers to promote bond repair include energy inputs, such as heat or light, or specific environmental conditions, such as pH. Self-healing polymers that can spontaneously achieve quantitative healing in the absence of a catalyst have never been reported before, until now.

Ibon Odriozola previously came close when his group at the CIDETEC Centre for Electrochemical Technologies in Spain developed self-healing silicone elastomers using silver nanoparticles as cross-linkers. Unfortunately, an applied external pressure was required and the expensive sliver component disfavoured commercialisation. But now they have achieved their goal to prepare self-healing elastomers from common polymeric starting materials using a simple and inexpensive approach.

An industrially familiar, permanently cross-linked poly(urea-urethane) elastomeric network was demonstrated to completely mend itself after being cut in two by a razor blade. It is the metathesis reaction of aromatic disulphides, which naturally exchange at room temperature, that causes regeneration.

Ibon stresses the use of commercially available materials is important for industrial applications. He says the polymer behaves as if it was alive, always healing itself and has dubbed it a "terminator" polymer -- a tribute to the shape-shifting, molten T-1000 terminator robot from the Terminator 2 film. It acts as a velcro-like sealant or adhesive, displaying an impressive 97% healing efficiency in just two hours and does not break when stretched manually.

David Mecerreyes, a polymer chemistry specialist at the University of the Basque Country in Spain, sees opportunities to use this elastomer to improve the security and duration of many plastic parts, for example in cars, houses, electrical components and biomaterials.

'The introduction of a room temperature exchangeable covalent bond in classic thermoset elastomers provides unique autonomous self-healing abilities without comprising the pristine material properties,' says Richard Hoogenboom, head of the Supramolecular Chemistry group at Ghent University in Belgium. 'Close resemblance of this novel self-healing thermoset elastomer with current commercial materials makes it highly interesting for extending the lifetime of such materials.'

Future work by the group will concentrate on stronger polymeric materials as the current poly(urea-urethane) composite is relatively soft.

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Business Rohde Schwarz chosen by BAE Systems for Royal Navys Type 26 ship

2013/09/13

T26 hi res 2 Rohde & Schwarz UK has been selected by BAE Systems to be the preferred partner for the design phase of the Integrated Communications System for the future Royal Navy’s Type 26 Global Combat Ship

Rohde & Schwarz said its proposal for the Type 26 emphasised system reliability to reduce the though life cost with respect to support.

This down selection after a 12 month competition process follows on from previous Rohde & Schwarz Naval successes in the UK which include providing communication solutions to the Royal Navy’s Queen Elizabeth Class Aircraft Carriers, River Class Offshore Patrol vessels and the Royal Fleet Auxiliary’s Bay Class, Vessels.

The company has already supplied communications systems to the Australian Hobert Class Air Warfare Destroyer’s, the Royal Dutch Navy LCF Frigates and Landing Platform Docking LPD’s, and the Spanish Navy with the F100 Class Frigate’s and LPD.

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Machine learning used to boil down the stories that wearable cameras are telling

Sep. 13, 2013 — Computers will someday soon automatically provide short video digests of a day in your life, your family vacation or an eight-hour police patrol, say computer scientists at The University of Texas at Austin.

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The researchers are working to develop tools to help make sense of the vast quantities of video that are going to be produced by wearable camera technology such as Google Glass and Looxcie.

"The amount of what we call 'egocentric' video, which is video that is shot from the perspective of a person who is moving around, is about to explode," said Kristen Grauman, associate professor of computer science in the College of Natural Sciences. "We're going to need better methods for summarizing and sifting through this data."

Grauman and her colleagues developed a superior technique that uses machine learning to automatically analyze recorded videos and assemble a better short "story" of the footage than what is available from existing methods.

Better video summarization should prove important in helping military commanders managing data coming in from soldiers' cameras, investigators trying to sift through cellphone video data in the wake of disasters like the Boston Marathon bombing, and senior citizens using video summaries of their days to compensate for memory loss, said Grauman.

"There's research showing that if people suffering from memory loss wear a camera that takes a snapshot once a minute, and then they review those images at the end of the day, it can help their recall," said Grauman. "That's pretty inspiring. What if instead of images that were selected just because they were a minute apart, they had a video or photographic summary that was selected because it told a good story? Maybe that would help even more. That's the kind of thing we're hoping to achieve."

Grauman, her postdoc Lu Zheng and doctoral student Yong Jae Lee presented their method, which they call "story-driven" video summarization, at the IEEE Conference on Computer Vision and Pattern Recognition this summer.

Their findings are based on video amassed by volunteers wearing commercially available Looxcie cameras, which cost about $200, record five hours of video at a stretch, connect to smartphones and fit in an ear as a large Bluetooth device does.

"The task is to take a very long video and automatically condense it into very short video clips, or a series of stills, that convey the essence of the story," said Grauman. "To do that, though, we first have to ask: What makes a good visual story? Our answer is that beyond displaying important persons, objects and scenes, it must also convey how one thing leads to the next."

To tackle the challenge, Grauman and her colleagues took a two-step approach. The first step involved using machine learning techniques to teach their system to "score" the significance of objects in view based on egocentric factors such as how often the objects appeared in the center of the frame, which is a good proxy for where the camera wearer's gaze is, or whether they are touched by the wearer's hands.

"If you give us a region in the video, then we will give back an importance level, based on all those properties that we have extracted and learned how to combine," said Grauman. "So at that point you can select frames that will maximize the importance."

The next step was to use those important frames, through the video, and look for early ones that influence later ones. To do that they adapted a method developed by researchers at Carnegie Mellon University that could predict how one news article leads to another, assembling a series of articles to transition from a starting point to a known end point.

For the text work, researchers used word frequencies and correlations across articles to quantify influence. For the video work, Grauman and Lu used their significant objects and frames to do the same. Then they were able to identify a chain of video clips that efficiently filled in the story from beginning to end.

"We ran human 'taste tests' comparing our method to previous methods," said Grauman, "and between 75 and 90 percent of people evaluating the summaries, depending on the datasets and method being compared, found that our system is superior."

Grauman said that as video summarization techniques continue to improve, they will become invaluable aids not just to people with very specialized needs, like police investigators and those suffering from memory loss, but to everyday Web surfers as well.

"My hope is that we'll be able to get video browsing much closer to what we experience with image browsing," she said. "Consider browsing 50 images on a webpage. It's manageable, since you can scroll down and see them all in one pass. Now imagine trying to browse 50 videos online. It's simply not efficient. We need summarization algorithms in order to improve video search considerably."

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Scientists achieve highest open-circuit voltage for quantum dot solar cells

"These results clearly demonstrate that there is a tremendous opportunity for improvement of open-circuit voltages greater than one volt by using smaller QDs in QD solar cells," said Woojun Yoon, Ph.D., NRC postdoctoral researcher, NRL Solid State Devices Branch. "Solution processability coupled with the potential for multiple exciton generation processes make nanocrystal quantum dots promising candidates for third generation low-cost and high-efficiency photovoltaics."

Despite this remarkable potential for high photocurrent generation, the achievable open-circuit voltage is fundamentally limited due to non-radiative recombination processes in QD solar cells. To overcome this boundary, NRL researchers have reengineered molecular passivation in metal-QD Schottky junction (unidirectional metal to semiconductor junction) solar cells capable of achieving the highest open-circuit voltages ever reported for colloidal QD based solar cells.

Experimental results demonstrate that by improving the passivation of the PbS QD surface through tailored annealing of QD and metal-QD interface using lithium fluoride (LiF) passivation with an optimized LiF thickness. This proves critical for reducing dark current densities by passivating localized traps in the PbS QD surface and metal-QD interface close to the junction, therefore minimizing non-radiative recombination processes in the cells.

Over the last decade, Department of Defense (DoD) analyses and the department's recent FY12 Strategic Sustainability Performance Plan, has cited the military's fossil fuel dependence as a strategic risk and identified renewable energy and energy efficiency investments as key mitigation measures. Research at NRL is committed to supporting the goals and mission of the DoD by providing basic and applied research toward mission-ready renewable and sustainable energy technologies that include hybrid fuels and fuel cells, photovoltaics, and carbon-neutral biological microorganisms.

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Tuna closely related to some of the strangest fish in the sea

Sep. 13, 2013 — Some of the strangest fish in the sea are closely related to dinner table favourites the tunas and mackerels, an international team including Oxford University scientists has found.

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Deep sea fish such as the black swallower, with an extendable stomach that enables it to eat fish larger than itself, and manefishes, some sporting spiky fins like a Mohican haircut, are close cousins to mackerels and tuna despite having completely different body shapes and lifestyles.

The team, led by Dr Masaki Miya at Chiba Natural History Museum in Japan, suggests that this extended family of fishes might owe its success today to the devastating extinction that marked the demise of dinosaurs and many other creatures 66 million years ago.

The researchers report in the journal PLOS ONE this week how they combined DNA analysis of over 5,000 modern fish species with fossil evidence to solve the mystery of which species were closest to tunas and mackerels in the fish family tree.

'What was immediately clear from our result is that the extended family of tunas and mackerels is made up of fishes that all look very different from one another, with different ways of life, but which share one key trait: they all dwell in the open ocean,' said Dr Miya of Chiba Natural History Museum. 'This had been suggested before, but we were able to show that many additional groups of fishes inhabiting the open ocean -- called the pelagic realm -- were closely related to one another and to tunas.'

Reflecting this preference for the open ocean the team has called the extended tuna family tree: 'Pelagia'. Although they share a preference for open-ocean habitats, members of Pelagia show radically different ways of life ranging from deep-sea fishes that live inside sac-like invertebrates to speedy, shallow-water predators such as the tuna.

'Discovering that such radically different fish species are related is a bit like finding that a seal is more closely related to a cat than it is to a walrus!' said Dr Matt Friedman of Oxford University's Department of Earth Sciences, a co-author of the PLOS ONE paper. 'By comparing genetic data with fossil evidence we were able to show that the origins of all these disparate groups lie in a period of rapid evolution that occurred around 65 million years ago. This is significant because this is when the Cretaceous extinction event that wiped out the dinosaurs also killed off many groups of large fishes inhabiting the open ocean.

'It's likely that the common ancestor of this family lived in the deep ocean, helping it to survive this ancient extinction. It then emerged from its refuge to diversify and colonise the shallower waters to produce the profusion of related, but very different, species we see today.'

According to the team the new findings suggest a different way of thinking about past extinctions.

'We tend to think of extinction events as damaging diversity but in fact they always offer opportunities for other species -- for example, we mammals famously took advantage when the dinosaurs died out,' said Dr Friedman. 'What our study shows is that while extinctions sweep away old diversity they also see a new kind of diversity rapidly, at least on an evolutionary timescale, flooding in.'

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Pinpointing when the First Dynasty of Kings ruled Egypt

The findings are published in the journal Proceedings of the Royal Society A.

Egypt was the first territorial state to be brought under one political ruler, and the new dating evidence suggests that this period of unification happened far more quickly than previously thought.

Until now scholars had relied on archaeological evidence alone, using the evolving styles of ceramics excavated at human burial sites to try to piece together the timings of key chronological events in the Predynastic period and the First Dynasty. For example, among the most significant pieces of evidence surviving today are two mud seals, excavated at the royal tombs at Abydos, containing lists in successive order of the First Dynasty kings.

Using the fresh radiocarbon dates combined with existing archaeological evidence, the research team's mathematical model pinpointed the likeliest date for each king's accession. The date for each king is thought to be accurate to within 32 years (with 68% probability). The modelled timeline reveals lengths of reign that are approximately what you would expect in terms of lifespan, say the study authors.

The Egyptian state is often defined as starting when King Aha acceded to the throne. According to the new model, this is likely to have happened between 3111 BC and 3045 BC (with 68% probability). It also shows that the Predynastic period -- when inhabitants along the River Nile started to form permanent settlements and concentrate on crop farming -- was shorter than previously thought. It had been widely assumed that the Predynastic period started around 4000 BC. However, this model suggests it was probably closer to 3800-3700 BC, and the Neolithic period that preceded it lasted longer and finished later.

Lead author of the study Dr Michael Dee, from the Research Laboratory for Archaeology at the University of Oxford, said: 'The origins of Egypt began a millennium before the pyramids were built, which is why our understanding of how and why this powerful state developed is based solely on archaeological evidence. This new study provides new radiocarbon dating evidence that resets the chronology of the first dynastic rulers of Ancient Egypt and suggests that Egypt formed far more rapidly than was previously thought.'

The first kings and queens of Egypt in order of succession were Aha, Djer, Djet, Queen Merneith, Den, Anedjib, Semerkhet and Qa'a. They would have ruled over a territory spanning a similar area to Egypt today with formal borders at Aswan in the south, the Mediterranean Sea in the north and across to the modern-day Gaza Strip in the east.

Organic materials from key burial sites of the Badarin and Naqada periods and the First Dynasty were dated using the Oxford Radiocarbon Acceleterator Unit (ORAU) at the Research Laboratory for Archaeology, Oxford. All the remains were from museum collections in Europe and North America with freshly excavated seed samples from the Gaza Strip. The research was led by the University of Oxford in collaboration with University College London and Cranfield University. The project was funded by the Leverhulme Trust.

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Low Omega-3 could explain why some children struggle with reading

Sep. 13, 2013 — An Oxford University study has shown that a representative sample of UK schoolchildren aged seven to nine years had low levels of key Omega-3 fatty acids in their blood. Furthermore, the study found that children's blood levels of the long-chain Omega-3 DHA (the form found in most abundance in the brain) 'significantly predicted' how well they were able to concentrate and learn.

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Oxford University researchers explained the findings, recently published in the journal PLOS One, at a conference in London on 4 September.

The study was presented at the conference by co-authors Dr Alex Richardson and Professor Paul Montgomery from Oxford University's Centre for Evidence-Based Intervention in the Department of Social Policy and Intervention. It is one of the first to evaluate blood Omega-3 levels in UK schoolchildren. The long-chain Omega-3 fats (EPA and DHA) found in fish, seafood and some algae, are essential for the brain's structure and function as well as for maintaining a healthy heart and immune system. Parents also reported on their child's diet, revealing to the researchers that almost nine out of ten children in the sample ate fish less than twice a week, and nearly one in ten never ate fish at all. The government's guidelines for a healthy diet recommend at least two portions of fish a week. This is because like vitamins, omega-3 fats have to come from our diets -- and although humans can in theory make some EPA and DHA from shorter-chain omega-3 (found in some vegetable oils), research has shown this conversion is not reliable, particularly for DHA, say the researchers.

Blood samples were taken from 493 schoolchildren, aged between seven and nine years, from 74 mainstream schools in Oxfordshire. All of the children were thought to have below-average reading skills, based on national assessments at the age of seven or their teachers' current judgements. Analyses of their blood samples showed that, on average, just under two per cent of the children's total blood fatty acids were Omega-3 DHA (Docosahexaenoic acid) and 0.5 per cent were Omega-3 EPA (Eicosapentaenoic acid), with a total of 2.45 per cent for these long-chain Omega-3 combined. This is below the minimum of 4 per cent recommended by leading scientists to maintain cardiovascular health in adults, with 8-12 per cent regarded as optimal for a healthy heart, the researchers reported.

Co-author Professor Paul Montgomery said: 'From a sample of nearly 500 schoolchildren, we found that levels of Omega-3 fatty acids in the blood significantly predicted a child's behaviour and ability to learn. Higher levels of Omega-3 in the blood, and DHA in particular, were associated with better reading and memory, as well as with fewer behaviour problems as rated by parents and teachers. These results are particularly noteworthy given that we had a restricted range of scores, especially with respect to blood DHA but also for reading ability, as around two-thirds of these children were still reading below their age-level when we assessed them. Although further research is needed, we think it is likely that these findings could be applied generally to schoolchildren throughout the UK.'

Co-author Dr Alex Richardson added: 'The longer term health implications of such low blood Omega-3 levels in children obviously can't be known. But this study suggests that many, if not most UK children, probably aren't getting enough of the long-chain Omega-3 we all need for a healthy brain, heart and immune system. That gives serious cause for concern because we found that lower blood DHA was linked with poorer behaviour and learning in these children. 'Most of the children we studied had blood levels of long-chain Omega-3 that in adults would indicate a high risk of heart disease. This was consistent with their parents' reports that most of them failed to meet current dietary guidelines for fish and seafood intake. Similarly, few took supplements or foods fortified with these Omega-3.'

The current findings build on earlier work by the same researchers, showing that dietary supplementation with Omega-3 DHA improved both reading progress and behaviour in children from the general school population who were behind on their reading. Their previous research has already shown benefits of supplementation with long-chain omega-3 (EPA+DHA) for children with ADHD, Dyspraxia, Dyslexia, and related conditions. The DHA Oxford Learning and Behaviour (DOLAB) Studies have now extended these findings to children from the general school population.

'Technical advances in recent years have enabled the measurement of individual Omega-3 and other fatty acids from fingerstick blood samples. 'These new techniques have been revolutionary -- because in the past, blood samples from a vein were needed for assessing fatty acids, and that has seriously restricted research into the blood Omega-3 status of healthy UK children until now,' said Dr Richardson.

The authors believe these findings may be relevant to the general UK population, as the spread of scores in this sample was within the normal population range for both reading and behaviour. However, they caution that these findings may not apply to more ethnically diverse populations as some genetic differences can affect how Omega-3 fatty acids are metabolised. Most of the children participating in this study were white British.

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Dating of beads sets new timeline for early humans

The research team radiocarbon dated 20 marine shells from the top 15 metres of archaeological layers at Ksar Akil, north of Beirut. The shells were perforated, which indicates they were used as beads for body or clothes decoration by modern humans. Neanderthals, who were living in the same region before them, were not making such beads. The study confirms that the shell beads are only linked to the parts of the sequence assigned to modern humans and shows that through direct radiocarbon dating they are between 41,000-35,000 years old.

The Middle East has always been regarded as a key region in prehistory for scholars speculating on the routes taken by early humans out of Africa because it lies at the crossroads of three continents -- Africa, Asia and Europe. It was widely believed that at some point after 45,000 years ago early modern humans arrived in Europe, taking routes out of Africa through the Near East, and, from there, along the Mediterranean rim or along the River Danube. However, this dating evidence suggests populations of early modern humans arrived in Europe and the Near East at roughly the same time, sparking a new debate about where the first populations of early humans travelled from in their expansion towards Europe and which alternative routes they may have taken.

In Ksar Akil, the Lebanese rockshelter, several human remains were found in the original excavations made 75 years ago. Unfortunately since then, the most complete skeleton of a young girl, thought to be about 7-9 years of age buried at the back of the rock shelter, has been lost. Lost also are the fragments of a second individual, found next to the buried girl. However, the team was able to calculate the age of the lost fossil at 40,800-39,200 years ago, taking into account its location in the sequence of archaeological layers in relation to the marine shell beads.

Another fossil of a recently rediscovered fragment of the upper jaw of a woman, now located in a museum in Beirut, had insufficient collagen to be dated by radiocarbon methods. A method using statistical modelling was used to date by association the jaw fragment at 42,400-41,700 years old.

Ksar Akil is one of the most important Palaeolithic sites in Eurasia. It consists of a 23 metre deep sequence of archaeological layers that lay undisturbed for thousands of years until a team of American Jesuit priests excavated the rockshelter in 1937-38, and again after the end of the WWII, in 1947-48. The cave layers were found to contain the human fossils and hundreds of shell beads, as well as thousands of stone tools and broken bones of hunted and consumed animals.

Study lead author Dr Katerina Douka, from the School of Archaeology at the University of Oxford, said: 'This is a region where scholars have been expecting to find early evidence of anatomically and behaviourally modern humans, like us, leaving Africa and directly replacing Eurasian Neanderthal populations that lived there for more than 150,000 years. The human fossils at Ksar Akil appear to be of a similar age to fossils in other European contexts. It is possible that instead of the Near East being the single point of origin for modern humans heading for Europe, they may also have used other routes too. A maritime route across Mediterranean has been proposed although evidence is scarce. A wealth of archaeological data now pinpoints the plains of Central Asia as a particularly important but relatively unknown region which requires further investigation.'

The earliest European modern fossil, from Romania, dates to between 42,000-38,000 years before the present time, and specialists have estimated the age of Kent's Cavern maxilla from southern England, between 44,000-41,000 years, and that of two milk teeth in southern Italy, at 45,000-43,000 years old. The new dating evidence from Ksar Akil is largely comparable to these ages, if not slightly younger.

The work was led by Dr Katerina Douka of Oxford University, along with Professor Robert Hedges and Professor Tom Higham (Oxford); American Palaeolithic archaeologist Dr Christopher Bergman from URS Corporation, Cincinnati; and Frank P Wesselingh from the Naturalis Biodiversity Center, Leiden, The Netherlands.

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