Ploughable sensors help farmers get more crop per drop

AT THE end of March several small bundles of electronics will be ploughed into a field in Cheshire, UK. The sensors will measure soil temperature and moisture content, then transmit those measurements wirelessly to the surface. It is the kind of information farmers around the world need to conserve water while still growing enough crops to feed an expanding population.

Currently being tested in lab soil at the University of Manchester, UK, the sensors are cheap to produce, low-power and can be left to gather information in the soil for years without maintenance. They use radio frequency identification to communicate and harvest a small amount of power from an RFID reader mounted on a tractor that collects the data as it moves over each node, says Chuan Wang, who works on the project at the university.

Another team at the University of Nebraska-Lincoln (UNL) – based in the Midwest's Corn Belt – is already well on the way to making a large-scale version of Wang's system a reality. Nebraska is the home of the iconic center pivot irrigation system responsible for the perfect circles that decorate the fields in that part of the US. They are using wireless sensors, embedded in the soil, that transmit information about current soil conditions to a base station.

By understanding exactly how much moisture is in the soil, UNL team leader Mehmet Can Vuran says entire rotations of a pivot can be saved, along with thousands of litres of water. They are already working with one of the four major center pivot irrigation companies, TL Irrigation, to bring the system to market.

"Thirty or forty per cent water savings are possible without affecting yields," Can Vuran says. "In fact, yields can be improved by optimising water – if you provide too much water to a crop it reduces the yields."

The driving force for this kind of technology is rising population, he says. It is expected to increase by 40 per cent by 2050. Demand for food will double in developing countries. "If you look at the way we're using water, we're using 70 per cent of our freshwater resources for agriculture – most of our resources, and yet the future demands that will double. As farmers say, we basically need 'more crop for drop',"

This article appeared in print under the headline "Plough in sensors to get more crop per water drop"

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UK government to ban e-cigarettes for under 18s

"Vaping" will soon be out for kids in the UK: plans to ban sales of electronic cigarettes to under-18s were announced last week by the government and could come into force within a year. The nation joins the 26 US states that have banned sales to minors on the basis that smoking e-cigarettes, or vaping, might tempt them to try smoking, which globally kills 6 million people each year.

"We do not yet know the harm that e-cigarettes can cause to adults, let alone to children, but they are not risk-free," said Sally Davies, the UK government's Chief Medical Officer for England. E-cigarettes dispense nicotine as a vapour, but are safer than cigarettes because they do not contain the other harmful substances found in tobacco.

But fears remain that children could become addicted to the nicotine in e-cigarettes, and that vaping could de-stigmatise smoking. "It does make sense to restrict the availability of a potentially addictive product," says Martin Dockrell, director of research and policy at anti-smoking lobby group ASH.

The UK banned sales of real cigarettes to under-18s in 2007. 12-year-olds can legally buy nicotine replacement products such as gums and patches.

Research last year showed that e-cigarettes were as effective as gums and patches at helping smokers quit or cut down. European Union regulators were last week accused by a prominent group of scientists of drafting a scientifically unjustifiable law to limit too strictly the nicotine content of e-cigarettes. In a letter, the scientists expressed their concern that smokers using e-cigarettes to quit might return to real cigarettes if they find the nicotine content of e-cigarettes to be unsatisfying.

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Peanut allergy cured in children using immunotherapy

A potentially life-threatening peanut allergy has been essentially cured in nine out of 10 recipients of a new treatment which gradually escalates the amount of peanut protein the body can tolerate.

Other treatments such as vaccines and antibodies are also under development, but the new oral immunotherapy is claimed to be the first to successfully allow people to tolerate such a food allergy.

"We've shown fantastic results, with 80 to 90 per cent of children being able to tolerate eating peanuts regularly after treatment," says Andrew Clark of Addenbrooke's Hospital in Cambridge, UK, who co-led the team that developed the treatment.

"Before the treatment, children and their parents had to check every food label, but now they can go out anywhere without fear of accidentally swallowing and reacting to traces of peanuts," he says.

Killer nut

Affecting two in every 100 children, peanut allergy kills around 50 people in the US each year – mainly through suffocating throat swellings – and results in 15,000 emergency hospital visits. "The only current 'treatments' are avoidance of peanut-containing food and shots of adrenaline to treat reactions," says co-leader of the team, Pamela Ewan, also at Addenbrooke's.

The trial, involving 99 children with peanut allergy aged between 7 and 16, is the largest ever to test an oral immunotherapy.

In the first part of the trial, 49 children received the oral immunotherapy. At their first visit to the hospital, with medical facilities standing by in case of bad reactions, the children received a tiny dose of peanut flour – around 2 milligrams – in their meal. The same amount was then added to their meals at home for two weeks. Then, every two weeks for a six-month period, the peanut flour dose was gradually boosted until it reached 800 milligrams. This is the equivalent of five whole peanuts, and 25 times the average amount of peanut that the children could tolerate beforehand.

Peanut challenge

A control group of 50 children received no therapy, and continued to avoid exposure to peanuts throughout the six-month period.

At the end of the trial period, the researchers tested all of the children's ability to safely consume gradually increasing amounts of peanut, under strict medical supervision. The researchers found that 41 of the 49 therapy recipients – 84 per cent – could handle the equivalent of five peanuts. None of the children in the control group could handle any more peanut than they could to begin with.

Next, 39 of those who could already handle five peanuts daily then faced an even sterner challenge: to try eating the equivalent of 10 peanuts, or 1400 milligrams, in one go. Twenty-four of the children, or 62 per cent, succeeded.

Finally, the 50 children in the control group underwent six months of the therapy. Of those, 91 per cent were able at the end to eat the equivalent of five peanuts a day, validating the original result in the process. "It's almost like we got two trial results for the price of one," says Ewan.

Absolutely huge

The researchers found that treatment led to a reduction in the activation of basophils, the white blood cells that trigger acute inflammation and swelling on exposure to peanut protein.

Other allergy specialists welcomed news of the therapy. "It's huge, absolutely huge," says Maureen Jenkins, director of clinical services at Allergy UK. "There hasn't been any way of treating this before."

Jenkins says that the effects of all previous attempts at treatment quickly wear off, but some children receiving the Addenbrooke's regimen have remained tolerant for five years, provided they regularly take small doses of peanut protein.

"We still need studies to see what happens if treatment stops totally, but this therapy will make a huge difference," she told New Scientist.

Don't try this at home

The research matters most for the children involved in the study. "After the trial, I felt as though a huge burden had been lifted off my shoulders," says one recipient of the treatment, 14-year-old Chris Poll of Perth, Australia. "I don't have to worry about going to parties any more, don't have to stress about going to school camps, and don't have to worry about eating in restaurants."

"A year after the trial I could eat five whole peanuts with no reaction at all," says Lena Barden, 11, from Histon in Cambridgeshire, UK. "But I still hate peanuts."

Ewan stresses that the Addenbrooke's regime should not be attempted beyond the controlled environment of a hospital until it has been developed further, such are the acute risks of peanut exposure in those with the allergy. "We must be absolutely clear to say: 'Don't try this at home'," she says.

"We're in the process of working towards being able to offer it as a specialised unit, and hope ultimately that a network of specialised units elsewhere in the UK can be set up to offer it safely," says Ewan. The team is also hoping to obtain a product license for the regime, possibly in collaboration with the pharmaceutical industry.

Journal reference: The Lancet, DOI: 10.1016/S0140-6736(13)62301-6

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Zoologger: Flying snake gets lift from UFO cross section

Video: Flying snake gets lift from UFO cross section

Zoologger is our weekly column highlighting extraordinary animals – and occasionally other organisms – from around the world

Species: Chrysopelea paradisi

Habitat: tropical rainforests of South Asia, gliding up to 100 metres from the tops of trees

Why crawl when you can fly? While their relatives slither on the ground, a few snakes take to the air, gliding from tree to tree. The most skilled of them all is the paradise tree snake, and we may finally have worked out why. It gets an aerodynamic lift by shifting its body into an unconventional, yet strangely familiar, form.

There are five species of flying snake, all native to south-east Asia. The five are reasonably average in the looks department – at least, until they begin to move. These snakes slither up trees before launching themselves from branches high in the canopy, undulating their bodies from side to side as they glide elegantly – at speeds of about 10 metres per second – to their destination.

Most studies into the snakes' gliding skills have focused on these wave-like body undulations, but Jake Socha of Virginia Tech in Blacksburg and his colleagues decided to focus on another factor.

Shape-shifter

It is clear that, once airborne, the snakes flatten their cylindrical bodies by splaying out their ribs. Slice a snake open, and the cross-sectional shape the body makes is reminiscent of a UFO from the classic Space Invaders arcade game. It's not a shape conventionally regarded as aerodynamic – but the biologists decided to investigate its properties anyway.

Socha's team recreated a 2D model of a mid-body snake slice, and then placed it in a tank filled with flowing water – a technique that allowed them to model how air would flow around it. It was much more aerodynamic than Socha expected, producing forces that, in air, would allow it to maintain near-maximum lift. "The forces are what allow it to move forward in the air and not fall down," he says.

In fact, the UFO shape outperformed more conventional aerofoil designs, like those used to construct the aircraft wings.

Scale is everything

Does that imply the aircraft industry could improve its designs? Probably not, says Socha. The trouble is, the UFO design works better than our conventional designs only for small objects gliding relatively slowly. An object about the size of a snake, in fact. Scale the design up to the size and speed of a jumbo jet, and the airflow no longer provides good lift. "If you tried to scale it up to make the wing of a passenger plane, it would be a terrible idea," says Socha.

The snakes' unusual cross-section will be a factor in their gliding ability that works with the body undulations, says Socha. His team's model suggests that the amount of lift the UFO shape provides varies depending on its orientation in the air, so the body movements may help the snake to carefully control the amount of lift while airborne.

The tip of the snake's tail, meanwhile, does not flatten out during flight and might be acting as a rudder. "One of the snakes I worked with had a naturally paralysed tail, it could glide well but it could never turn," Socha notes.

Together, these factors come together to produce a surprisingly effective little glider. Based on glide performance, Socha says their aerodynamics are pretty similar to flying squirrels.

Not bad for an animal with no limbs.

Journal reference: Journal of Experimental Biology DOI: 10.1242/jeb.090902

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Did newborn sun have weirdly weak solar wind?

OUR young sun may have been a late bloomer. The first reading of charged particles streaming from a younger solar twin shows that this constant particle flow, or wind, is rather wimpy. If our baby sun behaved like this, its timidity perhaps bought time for early Mars to play host to water.

Other young, sun-like stars are much more active than our middle-aged sun, blasting out more flares and high-energy radiation. For our sun, an increase in activity is often linked to a stronger wind, so astronomers suspected that these highly active stars would have very strong winds, and that our sun had a stormier youth too. That's why the latest find was a shock.

"Winds are hard to detect directly," says Brian Wood at the US Naval Research Laboratory in Washington DC. Instead, his team looked for the effect of stellar winds colliding with surrounding gas. That creates an ultraviolet glow which intensifies as winds get stronger (Astrophysical Journal Letters, doi.org/q33).

Using the Hubble Space Telescope, the team checked out a star that is almost exactly like our 5-billion-year-old sun but is just 500 million years old. The star shows lots of flares and other activity – but its wind is about half as strong as the sun's is today.

Other look-a-likes, about a billion years old, have much stronger winds, with around 10 times the oomph of the modern sun's output. This suggests a scenario where the stars start sleepy, ramp up and then settle back down by middle age.

If the young sun was sluggish, it might have given early Mars the time it needed for water, and perhaps life, to take hold. Evidence from NASA's rovers strongly supports the notion that the cold, dry Red Planet was once warm enough for rivers and oceans.

If so, it probably had a thicker atmosphere that vanished, perhaps stripped away by a strengthening solar wind, says Wood. NASA's MAVEN spacecraft is en route to Mars to study when and how the atmosphere was lost, including the possible influence of the sun.

This article appeared in print under the headline "Newborn sun's weak winds a boon to Mars?"

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More harm than good? Antioxidants defend cancer in body

They may be marketed as a way to protect yourself against disease, but antioxidant supplements are increasingly thought of as more foe than friend. We now have an idea why: antioxidants may protect healthy cells from DNA damage but they also protect cancer cells from our bodies' defences.

Antioxidants are chemicals such as beta-carotene and vitamins C and E, which mop up destructive free radicals produced when our cells metabolise energy. The new finding could help explain why some research, particularly in smokers, has shown that antioxidants end up raising rather than reducing the risk of getting cancer.

For example, in a prostate cancer prevention trial in 2011, men who took vitamin E for 5.5 years had a 17 per cent greater risk of developing the disease than men who took a placebo.

Now, research in mice has yielded a plausible explanation, at least for lung cancer. It seems antioxidants help early tumours survive and grow by protecting them and their DNA from damage from free radicals.

They do this by deactivating a gene called p53, dubbed the guardian of the genome, whose job is to destroy cells with defective DNA, including cancer cells. "Basically, the antioxidants shut off p53," which means the cancer cells can keep growing, says team leader Martin Bergö at the University of Gothenburg in Sweden.

To work out what was going on, Bergö and his colleagues triggered small lung cancers in mice and then gave some of them antioxidants. Of those receiving treatment, half got vitamin E and the other half an antioxidant called N-acetyl cysteine (NAC), a drug given to reduce mucus levels in people with chronic obstructive pulmonary disease (COPD).

Total knock-out

The results were dramatic. "The tumour number, size and aggressiveness increased threefold in the mice receiving either antioxidant, compared with non-recipients," says Bergö. "Also, survival was cut by at least 50 per cent."

Further experiments on colonies of tumour cells from humans and mice showed that they grew faster after exposure to the antioxidants. Moreover, the activity of p53 fell dramatically, suggesting that the antioxidants switched off the gene's ability to sense and destroy defective cells. The effect of antioxidants on tumour growth was the same as knocking out p53 altogether, Bergö found.

Bergö says the results only suggest risks for people who already have small lung tumours, or are at risk of them. "Our study doesn't say anything about the use of antioxidants in healthy people, and their risk of cancer in the future," he says. "But if you have lung cancer, or increased risk of lung cancer because you smoke or you have COPD, our results suggest antioxidants would fuel the growth of any tumours, so use them with caution, or not at all."

Balanced diet

Concerns have also been raised that antioxidants may interfere with cancer treatments, says Emma Smith, a spokesperson for Cancer Research UK. "We recommend that people stick to a healthy balanced diet, which should provide all the nutrients needed without taking supplements," she says.

Shyam Biswal of Johns Hopkins Bloomberg School of Public Health in Baltimore says the next step will be to see if NAC and other antioxidants promote tumours in mice at high risk of cancer having been exposed to a carcinogen, as well as those bred to have the disease. "It also warrants more study in patients with COPD," he says.

Bergö plans to perform some of this follow-up work, as well as investigating the effects of antioxidants on other cancers, including malignant melanomas and gut cancers.

Journal reference: Science Translational Medicine, DOI: 10.1126/scitranslmed.3007653

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Why you should care about the end of net neutrality

Companies can now pay for their pages to be delivered faster in the US. Does this mean the end of the internet as we know it?

IS THIS the end of the internet as we know it? On 14 January, the guiding principle of internet freedom, known as net neutrality, was demolished in a US appeals court in Washington DC. Pro-neutrality activists say it is the harbinger of dark times for our connected world. Information will no longer be free, but governed by the whims of big business. Internet Service Providers (ISPs) like Verizon and AT&T argue that since they built the physical backbone of the net they should be able to charge people to use it.

Lost amid the rancour is any hint of what this might mean for the average user – but there are several possibilities. The court ruling found that the US Federal Communications Commission (FCC) cannot regulate ISPs to prevent them from charging for different connection speeds. That means they are now free to demand users – whether they are big companies like Google or Netflix, or individuals – pay a premium for fast delivery of web pages, video and other content. Those who opt for cheaper schemes could see their traffic capped at slower speeds, or interrupted to make way for the big spenders.

If companies and ISPs can come to an agreement, though, things aren't likely to be quite as bleak, and the new landscape might look more like existing television subscription packages. Just as you can shell out for premium channels like HBO and Sky Movies, ISPs could offer internet packages that include Netflix and Hulu. In such a set-up, users only pay for what they want – like news channels or gaming sites – but not for the rest.

The early indications are, however, that the net-based firms who rely on ISPs the most are far from happy. Netflix, whose streaming video service accounts for more than a quarter of all internet traffic, is likely to be a prime target for ISPs planning to capitalise on the ruling. In reaction to the court's decision, Reed Hastings, the company's CEO, promised to vigorously protest any draconian discrimination from ISPs.

If such conflicts aren't resolved, things could get ugly. "Tweets, emails and texts will be mysteriously delayed or dropped. Videos will load slowly, if at all. Websites will work fine one minute, and time out another," said media advocacy group the Free Press in a statement after the verdict. "Your ISP will claim it's not their fault, and you'll have no idea who is to blame."

But the FCC could still intervene to keep net neutrality. The agency could designate ISPs as "common carriers", a label that would enable them to treat ISPs like phone companies, which are highly regulated. If the FCC doesn't act, activists worry about what it will mean for the little guys.

"The internet was supposed to be this great equaliser. It didn't matter where you lived or how wealthy you were," says Bartees Cox at Public Knowledge, a digital rights advocacy group. Without net neutrality, the poor and underprivileged are particularly at risk of losing out. If the internet is only available in high-priced bundles, then people will be restricted to what they can afford, he says.

Cox says the scales will also be tipped against internet start-ups, which won't have the capital to compete with established companies.

"It's a shame if this really goes through," he says. "The only person that wins at the end of the day is the ISPs."

This article appeared in print under the headline "Net not free for all"

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Beams of sound immerse you in music others can't hear

From restaurant music that only certain tables can hear to flying emails, the ability to place sound exactly where you want it has all kinds of unusual uses

IF YOU'RE sick of wading through a clogged email inbox or scrolling through endless Twitter timelines, Jörg Müller has a more fun way of sifting through your messages: sound.

In his audio-enabled "BoomRoom" at the Technical University of Berlin, Germany, emails and tweets fly around you like a flock of birds, each chirping a subtly different sound that identifies the sender. More urgent messages whizz directly over your head. Touch one and a computer reads it out.

Being able to direct sound in such a focused way has only recently become possible thanks to smarter audio processing algorithms, directional loudspeakers and gesture-recognition technology, says Müller. His flying email concept might still seem a bit far-fetched, but steering sound exactly where it is wanted is already catching on elsewhere in a number of different real-world applications. One day, it might even help create smart homes that can speak to their visually impaired owners.

For example, Parametric Sound of San Diego, California, has developed a highly directional "hypersound" loudspeaker that makes audible sound ride on an inaudible ultrasound carrier wave. This allows a gamer to be immersed in stereo audio that only they can hear – and it was a gaming highlight of January's Consumer Electronics Show in Las Vegas, Nevada.

Hypersound is also being trialled in branches of McDonald's in Disneyland and North Euclid, California. "There's often a TV on in McDonald's but not everyone wants to listen to it. So you can decide whether you want the TV sound beamed to your table," says Parametric Sound spokesman David Lowey. In toy shops, the Build-A-Bear chain is beaming instructions on how to build the toy to children using hypersound. "Car makers are looking at it too – so only the driver hears the GPS navigation instructions," Lowey says.

Back in Berlin, the BoomRoom consists of a ring of 56 loudspeakers that allow sounds to be assigned stationary or mobile positions in the space around you (see diagram). An array of 16 gesture-recognising cameras allows you to control what those sounds do. A music track, for instance, could be assigned to an object in the room such as a vase. To play the track you simply pick up the vessel and "pour out" a track in mid air. Gestures such as moving your hands apart or bringing them together can alter qualities like volume, treble and bass. "The instruments exist in mid-air so you can do your own sound mixing," says Müller, whose team is working alongside Sascha Spors of the University of Rostock, Germany.

The BoomRoom relies on a technique developed at the Delft University of Technology in the Netherlands called wave field synthesis (WFS). This constructs a 3D sound field by cancelling and reinforcing sound waves in much the same way as a hologram does with light waves. The trick is to use an algorithm that controls the speakers precisely and uses constructive and destructive interference of the sound waves to place sounds where they are wanted, moment by moment. "It's actually easier to produce a 3D sound field than it is with light because audio frequencies are so much lower," says Spors.

Timing so many loudspeakers at once is crucial and it has only just become possible because the computer power needed to run the algorithms has finally been developed, says Müller. The speakers aren't special in any way: all the WFS algorithms need to know is where each speaker is. "All the magic happens in software," says Müller. The system will be presented at the annual computer human interaction conference in Toronto, Canada, in April.

For Müller, the standout application of this technology is as a future smart room for people who are blind or sight-impaired. If a blind person entered a room, the important objects inside could announce their location. Users could also leave messages for one another in mid-air to be read out by a computer.

Another aim is to assign sounds to items in a room to reduce the number of gadgets we need. A bowl of marbles, for instance, could become an answering machine: the bowl could click when there are messages in it – and the user picks up a marble to hear a message. When they have heard it, pretending to pluck it out of the marble deletes the message.

To work in everyday life, the hope is that the flat panel actuators that act as loudspeakers by making glass and other flat surfaces vibrate will drop in price in coming years, making it cheap enough to fill houses with them. "We believe that in the future loudspeaker panels will be integrated in walls," says Müller.

The technology could also be a boon to gamers. The BoomRoom was first used for an audio-based lightsaber game in which a blindfolded person had to react to the "zummm, zummm" of a digital adversary's lightsaber, their voice or their breath on the back of their neck. It worked too well: "They found it impressively immersive and fun to use. But some hit out quite frantically and we had to calm them down to stop them hitting the speakers," says Müller.

Sound sculptor Bill Fontana of San Francisco, California – who once turned London's Millennium Bridge into a "live musical instrument" playing in the hall of the nearby Tate Modern – describes the Berlin technology as having fantastic potential to push sound in novel directions. "There is a lot of uncharted territory with using sound in our living and architectural spaces. Culturally, we are acoustically illiterate in many ways and regard most sound as noise."

This article appeared in print under the headline "Pure sound, direct to you"

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Cyclones hitting Australia plummet to 1500-year low

Off the chart: cyclone activity in Australia has been lower over the last 40 years than at any time in the past 1500 years. But the seemingly good news comes with a sting in the tail for people living on the coast.

Radar and satellite records of tropical cyclones – rotating storm systems – stretch back only about four decades. For an idea of trends on the longer term, researchers must go underground.

Compared with typical monsoonal rains, the severe rains associated with tropical cyclones are unusually low in the heavier oxygen isotope – oxygen-18. Stalagmites forming in caves record this difference, so by analysing their growth bands – which form each year in the wet season – geologists can establish whether or not a given year was characterised by cyclone activity.

The future, today

Jordahna Haig and Jonathan Nott of James Cook University in Cairns, Queensland, Australia, and their colleagues examined stalagmites from the coast of Queensland and Western Australia. Their results show that cyclone activity in Australia since 1900 has been dramatically lower than at any time since about AD 500. There was an even steeper drop from about 1960, corresponding closely with the sharp increase in global temperatures.

Climate models predict that cyclone frequency will decrease – and individual cyclones will become more intense – as the world warms. However, these effects were only expected to be significant by about 2050. "Models are saying this is going to occur later on. What we're saying is that we're seeing this now," says Nott.

Nott says anthropogenic climate change cannot be ruled out as a factor in the cyclone activity trend, although the link will be difficult to prove. But he notes that a cyclone record going back 1500 years provides an opportunity for long-term comparisons with records of other things that might affect cyclone activity, like solar minima and El Niño. It seems that these have not caused such a change in cyclone activity in the past.

Grossly underestimated risk

If cyclones are to become less frequent but more intense, that is bad news for people living on Australia's coast. It suggests they may have to deal with stronger cyclone-induced storm surges and flooding in future. "We've grossly underestimated the risks with building close to sea level," says Nott.

Scott Power from the Bureau of Meteorology in Canberra, Australia, says the issue is particularly important today because there are more people living along Australia's coast than ever before.

Whether a drop in cyclone activity around Australia means an increase in other regions of the planet is not clear, says Kevin Walsh at the University of Melbourne, Australia. For that, similar studies would need to be done elsewhere.

Nott and his colleagues are already on the case. They are now analysing geological records from Madagascar, to the Cook Islands and Vanuatu. "We're working on the whole southern hemisphere," he says.

Journal reference: Nature, DOI: 10.1038/nature12882

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Neanderthal-human sex bred light skins and infertility

IT IS surprising what a little hanky-panky can do. A handful of sexual encounters between humans and Neanderthals made many of us what we are today, affecting both our appearance and our vulnerability to disease. But the genetic legacy left by the Neanderthals also highlights just how different we are from our sister species.

Neanderthals lived in Europe and Asia between about 200,000 and 30,000 years ago. Our species – sometimes dubbed "modern humans" – made it to Eurasia about 65,000 years ago, and so the two species had plenty of time to cosy up. In 2010, geneticists discovered that they had been very close neighbours indeed. They sequenced a Neanderthal genome and discovered it carried genes that also appear in the genomes of people of European and Asian descent: our species must have interbred with Neanderthals.

Now, by studying Neanderthal genes in people alive today, researchers are beginning to appreciate how that interbreeding influenced our species.

In one new study of 1000 human genomes, Sriram Sankararaman and David Reich of Harvard Medical School and colleagues found that Neanderthal DNA is most common in regions of the genome with the greatest genetic variability, making them a prime target for natural selection. While Neanderthal DNA may make up only 1.6 to 1.8 per cent of the Eurasian genome, it punches above its weight in terms of biological impact, says Reich (Nature, DOI: 10.1038/nature12961).

Joshua Akey and Ben Vernot of the University of Washington in Seattle have analysed the Neanderthal DNA in a further 665 humans (Science, DOI: 10.1126/science.1245938). Both their study and the Harvard one found a hotspot of Neanderthal ancestry in genes relating to keratin, a fibrous protein found in our hair, skin and nails.

One of the genes, BNC2, is involved in skin pigmentation. That implies that Eurasians owe their paler skins partly to Neanderthals. Light skin is an advantage at higher latitudes because it is more efficient at generating vitamin D from sunlight, so Neanderthal DNA may have helped modern humans to adapt to life outside Africa.

If so, the adaptation took thousands of years to become universal. A third study published this week describes a DNA analysis of one person who lived in Stone Age Europe about 7000 years ago – 40,000 years after any Neanderthal interbreeding. His genes suggest his skin was dark (Nature, doi.org/q74). It may be that the Neanderthal keratin affected early Eurasians' hair instead, perhaps straightening it.

Not all of the Neanderthal genes are beneficial. Sankararaman and Reich found that our Neanderthal inheritance includes several genes that make us susceptible to diseases including type 2 diabetes, lupus and Crohn's disease.

Some of the genes, meanwhile, appear to have led to fertility problems. For instance, Sankararaman found that the X chromosome is almost devoid of Neanderthal DNA. This suggests that most Neanderthal DNA that wound up on the X chromosome made the bearer less fertile – a common occurrence when related but distinct species interbreed – and so it quickly disappeared from the human gene pool. "Neanderthal alleles were swept away," says Sankararaman.

"This underlines that modern humans and Neanderthals are indeed different species," says Fred Spoor of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who was not involved in any of the studies.

The genetic evidence further backs this up. Neanderthal DNA is irregularly spaced through the modern human genome rather than being fully mixed. That implies that interbreeding occurred very rarely. Sankararaman estimates it may have happened just four times.

"But these relatively few matings obviously were an important event in the history of non-Africans," says Reich.

This article appeared in print under the headline "Neanderthal sex, the aftermath"

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