Young blood to be used in ultimate rejuvenation trial

In California, people with Alzheimer’s will be given transfusions of young blood to see if improves their cognition – there's good reason to hope it might

IT SOUNDS like the dark plot of a vampire movie. In October, people with Alzheimer's disease will be injected with the blood of young people in the hope that it will reverse some of the damage caused by the condition.

The scientists behind the experiment have evidence on their side. Work in animals has shown that a transfusion of young mouse blood can improve cognition and the health of several organs in older mice. It could even make those animals look younger. The ramifications for the cosmetics and pharmaceutical industries could be huge if the same thing happens in people.

Disregarding vampire legends, the idea of refreshing old blood with new harks back to the 1950s, when Clive McCay of Cornell University in Ithaca, New York, stitched together the circulatory systems of an old and young mouse – a technique called heterochronic parabiosis. He found that the cartilage of the old mice soon appeared younger than would be expected.

It wasn't until recently, however, that the mechanisms behind this experiment were more clearly understood. In 2005, Thomas Rando at Stanford University in California and his team found that young blood returned the liver and skeletal stem cells of old mice to a more youthful state during heterochronic parabiosis. The old mice were also able to repair injured muscles as well as young mice (Nature, doi.org/d4fkt5).

Spooky things seemed to happen in the opposite direction, too: young mice that received old blood appeared to age prematurely. In some cases, injured muscles did not heal as fast as would be expected.

Several other experiments have shown similar effects. In 2012, Amy Wagersat Harvard University showed that young blood can reverse heart decline in old mice. Her team paired healthy young mice with old mice that had cardiac hypertrophy – a condition which swells the size of their heart – and connected their circulatory systems. After four weeks, the old mouse's heart had shrunk to the same size as its younger partner. In this experiment, the young mouse was seemingly unaffected by the old blood, its heart not changing in size.

Once the researchers had ruled out the effect of reduced blood pressure on the older mice, they identified a protein in the blood plasma called growth differentiation factor 11 (GDF11) that appeared to fall with age. To see if it was linked to the rejuvenating effects, the team gave old mice with enlarged hearts daily injections of GDF11 for 30 days. Their hearts decreased in size almost as much as they had in the parabiosis experiments (Cell, doi.org/q2f).

A year later, the same team showed in mice that daily injections of GDF11 also increases the number of blood vessels and the number of stem cells in the brain – both factors known to improve brain function. A separate team led by Tony Wyss-Coray at Stanford performed similar experiments. His team injected blood plasma from young mice into old mice and showed animprovement in the old mice's physical endurance and cognitive function(Nature Medicine, DOI: 10.1038/nm.3569).

In both mice and humans, GDF11 falls with age. We don't know why it declines, but we know it is involved in several mechanisms that control growth. It is also thought to mediate some age-related effects on the brain, in part by activation of another protein that is involved in neuronal growth and long-term memory.

So the billion-dollar question is: would a GDF11 boost have the same effect in humans? Wyss-Coray thinks it will, having taken the next step of injecting young human blood plasma into old mice. His preliminary results suggest that human blood has similar rejuvenating benefits for old mice as young mouse blood does.

"We saw these astounding effects," he says. "The human blood had beneficial effects on every organ we've studied so far."

Now, the final step – giving young human blood plasma to older people with a medical condition – is about to begin. Getting approval to perform the experiment in humans has been relatively simple, says Wyss-Coray, thanks to the long safety record of blood transfusions. He warns against swapping blood at home because transfusions need to be screened for disease, matched for blood type and the plasma needs to be separated out. "Certainly you can't drink the blood," he says. "Although obviously we haven't tried that experiment."

So in early October, a team at Stanford School of Medicine will give a transfusion of blood plasma donated by people under 30 to older volunteers with mild to moderate Alzheimer's.

Following the impressive results in animal experiments, the team hopes to see immediate improvements in cognition, but Wyss-Coray cautions that it is still very experimental. "We will assess cognitive function immediately before and for several days after the transfusion, as well as tracking each person for a few months to see if any of their family or carers report any positive effects," he says. "The effects might be transient, but even if it's just for a day it is a proof of concept that is worth pursuing."

All researchers involved in the work agree that GDF11 is unlikely to be the only factor that keeps organs youthful. "It's too optimistic to think there would be just one factor," says Francesco Loffredo, who studies the effects of young blood in old animals at Harvard University. "It's much more likely to be several factors that exert these effects in combination."

Loffredo says the approach of testing the effects of young blood in people with Alzheimer's is fascinating, but reckons in the long-term it is best to continue to strive to identify the individual factors that are exerting the rejuvenating effects so that they can be translated to humans more easily. "Imagine if you had to be transfused with young blood all the time – it's hard to imagine as a therapy. Who is going to be donating all this blood?" he asks.

Wyss-Coray agrees. "It would be great if we could identify several factors that we could boost in older people," he says. "Then we might be able to make a drug that does the same thing. We also want to know what organ in the body produces these factors. If we knew that, maybe we could stimulate that tissue in older people."

Chemotherapy aid

Alessandro Laviano at the Sapienza University of Rome in Italy says that the research on diseases of ageing certainly holds promise, but he is more interested in the potential use of young blood in chronic disease. People with cancer who resist muscle loss have better chances of survival, he says. "So I'd like to consider the possibility of using these youthful factors in young blood to reduce the muscle wasting that occurs during chemotherapy."

Before moving to clinical trials in people with cancer we need to learn more about the dynamics of the beneficial factors in blood, says Laviano, such as when they are at their peak. Do we reach a peak at 5 or 35 years? "We just don't know," he says. He would also like to investigate what happens when you give "too much" GDF11 – does it result in extra benefit or a negative outcome?

Laviano is currently looking at the effect of GDF11 on tumours in animals to see if it inhibits their growth, but he would also like to start an observational trial in humans. It would be very simple, he says, to find the age of the blood given to people receiving transfusions and test whether it has any effect.

"I certainly think that this therapy might be beneficial in a number of different conditions," says Wyss-Coray. "Blood might contain the fountain of youth after all. And it is within us all – that's the crazy thing. It just loses its power as we age."

This article appeared in print under the headline "Young blood turns back time"

Neanderthal demise traced in unprecedented detail

GUILTY as charged. Over the years, humans have often been accused of killing off our Neanderthal cousins, although climate change, stupidity and even bad luck have been blamed too. Now we are back in the frame.

A reassessment of major archaeological sites suggests that instead of dying out 23,000 years ago, Neanderthals were gone as early as 39,000 years ago. It also looks like we shared their territory for 5000 years, steadily replacing them as we spread across Europe.

Some say the findings support the idea that our direct ancestors pushed Neanderthals out: humans were an invasive species.

Neanderthals came to Europe some 300,000 years ago. They hunted big game with stone tools. Their territory spanned Europe and Asia. They left distinctive "Mousterian" artefacts.

What has not been clear is when and how they died out. Tom Higham of the University of Oxford and his colleagues used improved techniques to date material from 40 key sites in Europe, spanning the period when humans reached Europe and Neanderthals vanished. They studied three types of artefact. Two of them, Mousterian and Châtelperronian, are probably Neanderthal. The third kind, Uluzzian, were once attributed to late Neanderthals, but recent work suggests they were made by humans (Nature, doi.org/bxh255).

Higham and his team found that every possible or definite Neanderthal site – Mousterian and Châtelperronian – was at least 40,000 years old (Nature, DOI: 10.1038/nature13621).

"Until recently, I and many with me had thought that Neanderthals survived until 30,000 years ago, or perhaps even slightly later," says Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. "The new dates make it clear that they disappeared 10,000 years earlier."

For Chris Stringer of the Natural History Museum in London, the findings look clear. "Neanderthals had largely, and perhaps entirely, vanished from their known range by 39,000 years ago."

Nevertheless some still believe Neanderthals lasted longer. "It is highly unlikely that all the dates are of Neanderthals about to become instantaneously extinct," says Clive Finlayson of the Gibraltar Museum.

There are Neanderthal artefacts claimed to be 23,000 years old, but Higham could not get any solid dates from them, so while a late survival is possible, there is no real evidence.

Work on material from Italy seems to show human settlers pushing Neanderthals out (see maps). Mousterian tools were common there 45,000 years ago, when human-made Uluzzian material first appeared. By 44,000 years ago, humans were sharing Italy with a dwindling Neanderthal population. By 42,000 years ago, the Neanderthals were gone.

For Pat Shipman of Penn State University, this supports her theory that modern humans acted like an invasive species in Europe, beating the Neanderthals in a competition for resources. That's a "distinct possibility", Higham says.

But that does not mean we murdered our cousins. There is no evidence humans ever killed Neanderthals, and they probably didn't meet often, says Higham.

So what role did we play? Many now suspect we were the last straw for an already fragile species. Genetics suggests Neanderthal numbers dropped sharply around 50,000 years ago. This coincides with a sudden cold snap, hinting climate struck the first blow.

By 45,000 years ago, they were probably living in small isolated groups, so were less resilient. If only one person knows how to make a certain tool, orgather medicinal plants, losing them harms the entire tribe. "The death of a few individuals might mean the death of key survival skills," says Shipman. "Neanderthals need not have been stupid or inept, just thin on the ground."

"Ultimately, there were more of us than there were of them, and we were doing similar things and hunting similar animals," says Higham. "Neanderthals became isolated and ultimately were pushed to extinction."

Seals, not Spaniards, first brought TB to Americas

BLAME the marine mammals. Seals and sea lions may have brought a form of tuberculosis to the Americas, centuries before the Spanish did so.

There's little doubt that the Spanish carried measles, malaria, influenza and smallpox to the New World, when the conquistadores followed in Columbus's wake and began conquering the native peoples. Many assumed that they also brought Mycobacterium tuberculosis, the bacterium behind TB. But in the 1970s, 1000-year-old skeletons were found in Peru with apparent signs of TB. The Spanish didn't arrive until 1492, so how they became infected was a mystery.

Johannes Krause of the University of Tübingen in Germany and his colleagues have taken a close look at three of the skeletons. Radiocarbon dating showed that they lived between 1028 and 1280.

Krause found that the bacteria in the skeletons were closely related to a TB strain called Mycobacterium pinnipedii, which infects sea lions and seals, and not to the strains infecting humans today. That suggests marine animals picked up the disease in Africa and carried it to the Americas (Nature, DOI: 10.1038/nature13591).

Krause says the ancient Peruvians were probably infected while hunting and handling seals. "If you have infected sea mammals, there are lots of potential connections," he says. "It's a very robust result, and it solves this age-old puzzle."

However, they cannot rule out the possibility that the seals transmitted the disease to an unknown host, which then infected people.

The seal TB may not have been transmitted between people, making it less harmful than the later strain, says Stewart Cole of the Swiss Federal Institute of Technology in Lausanne.

It has since been replaced by the virulent strain the Spaniards brought. "The one in these three people is now extinct in the Americas," says Krause.

First samples of Antarctic lake reveal thriving life

THE popular image of Antarctica as a frozen, almost lifeless desert needs a makeover. For the first time, water from a lake beneath the ice has been found to harbour a vibrant microbial ecosystem.

"Our discovery proves that water is habitable space, even if it's at sub-zero temperatures and there is no sunlight," says John Priscu of Montana State University in Bozeman. He co-led the US team that drilled into Lake Whillans, 800 metres beneath the west Antarctic ice sheet.

The finding is good news for astrobiologists hoping to discover life elsewhere in the solar system: in the ocean beneath the frozen surface of Jupiter's moon Europa, for instance, or clinging on under the Martian polar ice caps.

Antarctica is home to about 400 subglacial lakes, many of which are linked in drainage basins. Priscu calls it "the planet's largest wetland".

Lake Whillans (see map) is one such lake. As it fills up with water from inland, the ice above swells. About every three years, the pressure builds up so much that water rushes out into the Southern Ocean, like fuel being siphoned from a car's tank.

Priscu's team broke into Lake Whillans in January 2013, using hot water to melt a 60-centimetre-diameter hole through the ice. The water used was kept sterile using filters, heating, ultraviolet light and hydrogen peroxide. That should lay to rest any suggestion that the microbes found were contaminants from the surface.

Such doubts have dogged claims about life in Lake Vostok in eastern Antartica. A Russian team took samples from the lake in 2012, but they used non-sterile kerosene as the drilling fluid.

In any case, the sheer numbers of microbes found in the samples from Lake Whillans argue against contamination. "We were surprised by the cell densities we observed," says Priscu's colleague Brent Christner of Louisiana State University in Baton Rouge. "They are very similar to what you'd find in low-nutrient lakes on the surface or in the open ocean."

The team found almost 4000 species of single-celled organisms (Nature, DOI: 10.1038/nature13667). Most seem to be feeding on sediments on the lake bed, laid down when the area was last ice-free and under the ocean, at least 120,000 years ago.

Many of the microbes convert ammonium to nitrite. The most common species, accounting for about 13 per cent of the DNA sequences found, takes that nitrite and converts it to nitrate. Others seem to feed on methane.

Whillans is not necessarily representative of other subglacial lakes. For instance, Lake Vostok is thought to have been completely cut off, including from other lakes, for at least 15 million years. That means any microbes there may have to feed instead on chemicals released as bedrock is ground away by the surrounding ice. "What we have is one point on the map. We need more," says Martin Siegert of Imperial College London.

"We've got to get down and sample these lakes," says Priscu. But it will be hard to reach lakes nearer the centre of Antarctica, where conditions are harsher, without contaminating them with drilling fluid. Siegert heads a team that was thwarted in its 2012 efforts to reach Lake Ellsworth by boring through 3 km of ice. He hopes to try again in a few years.

Exploring beneath the ice of other bodies in our solar system will be an even tougher challenge. Still, finding a flourishing ecosystem beneath Antarctica boosts the idea that life may exist beyond Earth. "I believe the implications for life elsewhere in our solar system are significant," saysEdward Goolish of the NASA Ames Research Center in Mountain View, California.

Digital textbooks adapt to your level as you learn

Struggling with chapter 3? Adaptive textbooks will give you extra, personalised help when you need it

TIRED of learning from a dusty old textbook? Try a book that learns from you. Students in Houston, Texas, are about to get their hands on the first digital schoolbooks that use artificial intelligence to personalise lessons. The aim, says the books' creator, is to "explode the book" and rethink how students learn from texts.

"We want to be able to create the perfect book for every person," saysRichard Baraniuk, director of the OpenStax project at Houston's Rice University, which is behind the books. "Ultimately, we want a system that turns reading the book into an exploration of knowledge."

OpenStax already offers an array of online and printed textbooks on subjects including economics, biology and history. For the past three years, researchers have tracked how students in 12 US schools use the books in their studies, including information on how they scored on questions.

That work is now being used to train machine-learning algorithms that give OpenStax's biology and physics textbooks the ability to adapt to individuals. If a reader seems to be struggling with a particular topic – acceleration, say – the book will slot in additional explanations and practice questions, and increase emphasis on related subjects, such as centripetal force, that could otherwise trip that person up.

The adaptive textbooks also incorporate a learning method called retrieval practice, in which material that students have already learned pops up again in occasional quizzes. This method has been shown to enhance students' ability to retain material, and the algorithmic textbooks will be able to decide when to ask questions based on past exercises.

Digital textbooks are not new – but despite their potential, they have yet to be widely adopted.

"Universities are just not suited for developing and serving such large-scale products. We need start-ups for that," says Peter Brusilovsky of the University of Pittsburgh in Pennsylvania, one of the designers of the interactive learning system ELM-ART (Episodic Learner Model – The Adaptive Remote Tutor). "If done right, adaptive textbooks could help us to learn faster and better."

Such personalised learning is designed to give students who are struggling time to understand subjects, while faster learners can surge ahead without getting bored. Software is a great way to do this – at Summit Preparatory Charter High School in Redwood City, California, students spend a portion of each week working independently with a computer program that suggests assignments and tracks progress, but students choose how to spend their time and set their own pace. This approach has helped Summit to becomeone of the top 20 schools in California, according to US News and World Report.

The initial roll-out of OpenStax in Houston high schools will be relatively small, but large institutions have also expressed interest.

Salt Lake Community College, which has more than 60,000 students and is the largest higher-education institution in Utah, wants to pilot OpenStax's algorithm-enhanced textbooks next year in political science, business and mathematics classes. Jason Pickavance, director of educational initiatives at the college, says he is curious to see whether the books improve student performance.

"We have such a varied student body in terms of college readiness," Pickavance says. "What they need is more individualised attention, more tutoring. The courseware has the potential for us to get that mix right."

Whether the books are successful will depend on teachers, says Ben du Boulay, who works on artificial intelligence at the University of Sussex, UK. They are the ones who will ensure that students make the most of their books – for instance, by working out what to do when the books identify a common problem area among their students.

"If all we needed was books, why have teachers?" de Boulay says. "It's the educational interactions around private study that make the difference."

Non-fatal diseases increasingly drive assisted suicide

It's a tourism boom, but not one to crow about. The number of people travelling to Switzerland to end their lives is growing. And it seems more and more people with a non-fatal disease are making the trip.

An ongoing study of assisted suicide in the Zurich area has found that the number of foreign people coming to the country for the purpose is rising. For example, 123 people came in 2008 and 172 in 2012. In total 611 people came over that period from 31 countries, with most coming from Germany or the UK, with 44 per cent and 21 per cent of the total respectively.

Neurological diseases, only some of which are fatal, were given as the reason for 47 per cent of assisted suicides for the years 2008 to 2012, up from 12 per cent in a similar study of the same region between 1990 and 2000. Rheumatic or connective tissue diseases, generally considered non-fatal, such as rheumatoid arthritis and osteoporosis, accounted for 25 per cent of cases in the new study. Between 1990 and 2000, they were cited in only 10 per cent of cases. There was also a tiny rise in the number of people coming to Switzerland because of mental health problems – 3.4 per cent in the latest study, up from 2.7 per cent.

Cancer, on the other hand, was cited in 37 per cent of cases between 2008 and 2012, a decrease of 10 per cent.

The researchers write that figures such as these suggest that diseases which are non-fatal, or those which could be terminal but have yet to reach their final stages, could be becoming increasingly common reasons to seek assisted suicide in Switzerland – although they also note that the earlier study looked at Swiss residents whereas theirs looks at foreign visitors.

Travelling while they can

One reason that people with non-terminal conditions might be travelling to Switzerland to die could be down to the fact that people with late-stage diseases, for example, are less mobile, according to Michael Charouneau of UK campaign group Dignity in Dying. "We know that many of those who travel do so earlier than they would wish, whilst they are still physically well enough to make the journey," he says.

"The idea of assisted suicide is more acceptable today than it was 10 or 20 years ago," says Ruth Horn, a medical ethics researcher at the University of Oxford. She suggests that this might be one reason why more people with non-fatal diseases are choosing to end their lives. "Subsequently it appears to have become more and more acceptable to extend the right to assisted death to patients with non-terminal conditions."

The legal standing of relatives and doctors implicated in euthanasia has been debated in both Germany and the UK in recent years. While efforts to change Germany's criminal code have stalled, in the UK a private member's bill on assisted dying is being debated in the House of Lords. "People choosing to go to Switzerland for assistance to die is one signal that the law is not working here in the UK," says Charouneau.

Race to electrify rural Africa could help the West too

Investments in mini grid systems aimed at powering up remote parts of Africa may provide a test bed for rural energy infrastructure elsewhere in the world

TURNING on the lights in Africa may help to power up the rest of the world sustainably. New investments in mini grid systems aimed at bringing power to rural Africa and other remote areas may provide a test bed for the rural energy infrastructure of the future.

Rich nations are taking an increasing interest in electrifying the rest of the world. At the Africa Leaders Summit in Washington DC this month, US president Barack Obama announced an additional $12 billion in funding for his administration's Power Africa initiative, which aims to help bring power to at least 60 million households and businesses across the continent.

But 85 per cent of the 1.3 billion people lacking electricity worldwide live in rural areas. That means powering Africa won't be as simple as hooking up villages to a centralised power grid. Localised "micro-grids" are beginning to take off. They can generate anything from a few watts to a few megawatts and provide power for tens to thousands of households at a time.

An increasing amount of this power is coming from renewable sources, such as wind, solar and hydro. "It creates an opportunity," says Subhes Bhattacharyya at De Montfort University in Leicester, UK. "You don't have to follow the old-fashioned way of doing things. You can jump the queue to new technologies."

For instance, international group Practical Action is building micro-hydro-power plants in Zimbabwe and Kenya, which harness falling water such as that in mountain rivers.

Another group, a Kenyan start-up called Access:energy, developed a model to teach Kenyans to make parts of wind turbines out of scrap metal and car parts, reducing the need for outside help should a part of the system break. A single turbine can generate about 2.5 kilowatt-hours per day, enough to power a micro-grid for 50 homes.

These sorts of local efforts are important – and not just for getting electricity to rural Africa. The continental US and other rich parts of the world have set goals for switching to renewable power and reinventing electricity grids as well. Lessons learned in Africa could help get parts of the US running on renewables and micro-grids.


"There are vulnerabilities because of the way our US grid is based on big, centralised power stations that are all very interdependent," says Gwen Holdmann at the Alaska Center for Energy and Power in Fairbanks. "If one component goes down, it can cause a cascading effect." Switching to local grids can ultimately help make the whole power infrastructure more robust in emergencies such as hurricanes or solar storms.

Not everyone agrees that renewable energy is the best option for Africa, however. Micro-grids may not be the cheapest option in the long run, as electricity from small grids tends to be three or four times as expensive per unit than that from centralised sources.

It hardly seems fair that the people who can least afford energy must use a more expensive system, says Bhattacharyya. "On the other hand, if they don't get electricity and remain in darkness, then it's unfair for them as well. That's the choice one has to make, and there's no single solution for all."

This article appeared in print under the headline "Africa's power surge"

Swelling Australian cities harbour ever bigger spiders

As if Australia's spiders weren't big and scary enough, it turns out denser, busier cities are allowing some of them to grow even bigger. The same thing could be happening the world over.

Most Australians will have seen the large but mostly harmless golden orb-weavers that sometimes congregate in people's gardens. Elizabeth Loweof the University of Sydney was surprised at just how large some were growing, and began investigating what could be behind this.

Lowe and colleagues found one species of this genus, Nephila plumipes, is gaining weight the more built-up Sydney gets. Examining more than 200 specimens around Sydney, they found that the more concrete there was, the further they were from bushland and the less leaf litter there was, the bigger the spiders tended to be. Lowe says the spiders in the bushland of Brisbane Water National Park, north of Sydney, had an average mass of 0.5 grams. But those in an inner-city park near Bondi Beach averaged 1.6 grams.

"It's probably because of the urban heat-island effect and prey availability," says Lowe. "Most invertebrates will grow to larger sizes if they are warmer. They are very sensitive to temperatures."

Urbanisation probably benefits these spiders in several ways, she says. The insects the spiders prey on tend to do very well in small fragments of bushland like urban parks, and even better when there is lighting at night. "The spiders have more to prey on and can put more energy into growing bigger."

Wealth effect

Surprisingly, the researchers also found that wealthier areas tended to have larger spiders. Lowe isn't sure why. It might be that wealthier areas tend to have more parks or more hard surfaces like concrete that heat up readily.

Lowe says this is probably also happening with other spiders in Australia likehuntsmen and redbacks, and is almost certainly happening elsewhere in the world. What's more, global warming will encourage spiders to grow bigger – although very hot weather will kill them, she says. "During the hot summer last year, most of these spiders died out in Sydney."

Michael Kasumovic from the University of New South Wales in Sydney said he is surprised by the results and expected the opposite would be true. "If it is an increase in heat, what that usually means is it increases development rates. Metabolic functions are going faster and they mature earlier – at a smaller size," he says.

Lowe notes the relationship between heat and body size is complicated. The heat could allow the spiders to hatch earlier in the year, giving them a longer growing season.

In any case, she says healthy spider populations in cities should be celebrated: they are mostly harmless to people, they eat pests and they provide food for birds. "I'm all about encouraging spiders in urban areas," she says.

China sting shows censors fear posts that incite unrest

Last year, violence broke out in a north-western corner of China, whenmembers of the local Uighur population – an ethnic minority in China – faced off against the police. Dozens of people were reportedly killed, and social media lit up with posts about the riots. But as China's many censors got to work, many posts also quickly disappeared. But how did the government decide which could stay and which had to go?

A group of US researchers can help answer that question. They have lifted the lid on Chinese online censorship – by pretending to be censors themselves. They found that the censors of China's social media sites are only worried about posts that may incite mass protests, rather than ones that poke fun at individual politicians, for example.

Acting like a social media start-up, Gary King at Harvard University and his colleagues built a fake website, bought a domain name and server space inside China, and populated the site with their own posts. Then, they obtained a copy of the software that helps Chinese website administrators censor their content so they stay out of trouble with the authorities. When questions about how the software worked came up, answers were just a phone call to customer service away.

"We could call customer service and say, 'How do we stay out of trouble with the Chinese government?' They would say, 'Let me tell you,'" says King. "Customer service was pretty good at their job."

Reverse engineering

The software could automatically block posts that came from banned IP addresses or contained problematic keywords. But many of the censorship choices were still deferred to human judgment. Some sites held posts for manual review within 24 hours; others automatically published the post, and a person would check in later to decide if it was OK.

If in-house human censors, rather than software, were calling the shots, then perhaps the researchers could divine insight into the minds of both government and independent censors by examining their choices carefully. King's team went back to real social media sites such as Sina Weibo. Of the 100 sites, 20 were run by central government, 25 were by overseen by local authorities, and 55 were privately owned.

The researchers wrote more than 1000 comments about controversial topics, such as artist Ai Weiwei's music, a village protest in Panxu, and the Uighur riots in Xinjiang. The researchers tracked if and when the posts were taken down.

"The censorship programme is like an elephant tiptoeing around. It leaves big footprints," says King. "We can look at those footprints and learn things about the intentions of the Chinese government that would be difficult to learn otherwise."

Collectivism a no-no

To their surprise, the posts that were most likely to be censored were those that mentioned collective action in the real world, like a protest or a boycott. Even posts that praised the government could be censored if they also referenced collective action.

Meanwhile, criticism and complaints often made it through to publication. A satirical post about the Uighur situation went viral, and only got censored about 10 per cent of the time.

King suspects this is because the government is more worried about regime stability than anything else, so they exert most of their pressure on posts that could jeopardise their power. "They don't care what anybody says about them in and of itself. They care what people will do with that information," he says.

Degrees of criticism

Before this study, we only had "very impressionistic understandings" of the Chinese government's priorities, says Susan Shirk, director of the 21st Century China Program at the University of California, San Diego. The findings suggest that censorship decisions are more nuanced than previously thought.

"It's really an amazing piece of work, to be able to do that kind of intervention and look at the impact of the intervention. Nobody has ever done anything quite like that before," Shirk says. In some ways, the censorship system is tighter than we thought, she says, and in some ways looser.

Artists protest in Hong Kong, demanding the release of then-detained Chinese artist Ai Weiwei on 23 April, 2011 (Image: Laurent Fievet/AFP/Getty)

Min Jiang at the University of North Carolina at Charlotte is more sceptical of the results. She suspects there are still some kinds of complaints that the government would want to censor, like Western media reports that expose abuses of power. "Criticism has many different degrees," she notes.

Earliest stars lived short, fiery lives

The first stars may have been big shots that went out in a blaze of glory. A stellar fossil has revealed new insights into a long-extinct species of primordial stars.

This group, sometimes called population III stars, were the first to form in the early universe. They forged the first elements heavier than the hydrogen and helium made in the big bang. Then they exploded as supernovae, expelling these elements into their surroundings, to be incorporated into the next generation of stars.

But the details depend on the masses of these first stars. Computer models suggested that they could be as much as 100 times the mass of our sun, meaning they would die too quickly to build anything heavier than iron. But they could also be as light as 10 times the mass of our sun and live longer. With no population III stars around today, it's hard to know what they looked like.

Now we have hints from a star named SDSS J0018-0939, that appears to have been born out of the dust left behind by an exploding primordial star. A team led by Wako Aoki of the National Astronomical Observatory (NAO) of Japan in Tokyo, analysed the different elements in the star's outer shell for clues to how the mysterious population III stars lived and died.

"It's a bit like a DNA fingerprint," says Volker Bromm of the University of Texas in Austin. "This study answers the overall question of how the cosmic dark ages ended."

Even-numbered clue

The fossil star, which was discovered via the NAO's Subaru telescope in Hawaii, appears to contain a fair amount of iron, but little by way of heavier metals like strontium and barium. It also has far more even-numbered elements than odd ones. Both of these features indicate that population III stars were short-lived, as building heavier and odd-numbered elements is a slower process.

This means the population III stars were probably even bigger than we thought – hundreds of times more massive than the sun. The "parent" star of SDSS J0018-0939 was about 140 times the sun's mass.

Its huge size means that the star probably exploded in a fiery thermonuclear explosion 10 to 100 times more powerful than typical supernovae we see today. Bromm thinks these explosions may have been bright enough that their embers will be seen by the James Webb Space Telescope, due to launch in 2018.

But it's not a dead certainty that the fossil star formed from the remnants of a single supernova, says John Wise of the Georgia Institute of Technology in Atlanta. It could instead contain dust from a few supernovae.

"It's not exactly a smoking gun," he says. "It is exciting that it's different from any of the other metal-poor stars that we've discovered in the Milky Way."

Hummingbirds turned savoury into sweet to taste nectar

It's the strangest sweet tooth in the world. Birds lost the ability to taste sugars, but nectar-feeding hummingbirds re-evolved the capacity by repurposing receptors used to taste savoury food.

To differentiate between tastes, receptors on the surface of taste buds on the tongue, known as T1Rs, bind to molecules in certain foods, triggering a neurological response.

In vertebrates such as humans, a pair of these receptors – T1R2 and T1R3 – work together to deliver the sweet kick we experience from sugar. But Maude Baldwin at Harvard University and her colleagues found that birds don't have the genes that code for T1R2. They are found in lizards, though, suggesting that they were lost at some point during the evolution of birds or the dinosaurs they evolved from.

But hummingbirds clearly can detect sugar: not only do they regularly sup on nectar, taste tests show they prefer sweet tasting foods over blander options. Now Baldwin and her team have worked out why: another pair of receptors – T1R1 and T1R3 – work together to detect sugar.

Savoury to sweet

Other vertebrates use T1R1 to taste savoury foods. It seems that in hummingbirds the proteins on the surface of the two receptors have been modified so that they respond to sugars instead.

"The change in the taste receptor was certainly not the only factor or aspect of hummingbird biology that was important [for them to feed on nectar], but it seems like it played an important role," says Baldwin. "There are many behavioural and physiological changes that have occurred between hummingbirds and their ancestors: small body size, a long bill and changes in the wing which allowed them to hover."

"We know a lot about bird vision and smell, but until recently very little was known about the genetic basis of taste in any bird species," says Hannah Rowland at the University of Cambridge, who was not involved in the study. "These findings should help researchers test sweet perception in other birds that eat fruit and nectar. The question for me is whether other nectar eating birds and frugivores have evolved this same capacity."

The re-evolution of sugar receptors may have happened multiple times, says study member Stephen Liberles, also at Harvard. "It will be exciting to see how other nectar feeding birds taste sugar, to compare whether evolution used the same or different strategies to solve the problem of sugar detection," he says.

Searching for survivors in Hiroshima's shattered homes

Rescue workers are searching for survivors in debris left by a landslide that hit Hiroshima, Japan, on Wednesday. People are still missing under the collapsed buildings, mud and rock that litter the base of the mountain on the outskirts of the city.

According to Hiroshima police, at least 39 people have been killed in the landslide, and 52 more are still missing. The slide was triggered by a sudden deluge: a month's worth of rain fell in 24 hours between Tuesday and Wednesday morning, causing whole hillsides to collapse.

One of those killed was a 53-year-old firefighter, Noriyoshi Masaoka, who died rescuing five people.

Around 3000 rescue personnel are working in the area, although further heavy rain halted search efforts on Thursday evening. There are now fears of a fresh collapse, with rain due to continue through to Saturday evening and the surrounding mountains becoming "misshapen", said a police spokesman.

Up to 100,000 residents have evacuated surrounding districts, fearing further landsides and floods. According to Fuji TV, 1100 residents have been unable to return to their homes and are sleeping in local schools.

Chimps show empathy by mimicking pupil size

Chimpanzees and humans may share the same ability to empathise with other individuals by involuntarily matching their pupil size. The mimicry only appears to work between two humans or between two chimpanzees but not between species, suggesting the signalling reinforces social bonds within species.

We already know that pupils change shape in response to a new, unfamiliar target: they tend to constrict initially and, after a fraction of a second, readjust and dilate. There's evidence that human pupils dilate more rapidly while adjusting if their owner is interacting with another human whose pupils are also dilating. The dilation-adjustment happens more slowly if the other human's pupils are constricting. But it is unclear when this pupil mimicry began in evolutionary terms.

To investigate, Mariska Kret at the University of Amsterdam in the Netherlands and her colleagues studied pupil mimicry in humans and, for the first time, looked for the phenomenon in chimps too. Chimps and human volunteers viewed images of pairs of chimp or human eyes for 4-second-long periods. Kret and her colleagues digitally manipulated the eye images so that after one-sixth of a second, the pupils on view started either dilating or constricting by a fixed amount, reaching their new size within a second and staying that size for the remaining 3 seconds of viewing time.

Unobtrusive binocular eye-trackers monitored and recorded whether pupil size in the viewer – whether chimp or human – changed as they gazed at the various images.

The pupil dilation in humans and chimpanzees did indeed subtly alter in response to the different images. In keeping with expectations, after initially constricting, a human's pupils dilated more slowly when they viewed a human whose pupils were constricting. If the human on view's pupils were dilating, the volunteer's pupils dilated more rapidly after the initial constriction. At the end of the 4-second-long viewing period there was a 0.2 millimetre difference in the volunteers' pupil size, on average, depending on whether the eyes in the image had dilated or constricted.

Mother phenomenon

Interestingly, the same applied to the chimpanzees: their pupils, too, dilated more slowly when they viewed a chimp with constricting pupils. The effect was a great deal more subtle in the chimps, but a statistical analysis showed the differences were nonetheless significant. The most striking effects in chimps were seen in three mothers, suggesting that motherhood increases a chimp's subconscious awareness of pupil size.

The experiments also revealed something else: pupil dilation in humans is not altered by viewing images of chimps with either dilating or constricting pupils, and vice versa.

The results suggest that pupil mimicry might have a long evolutionary history, says Kret, because if the phenomenon is present in both humans and chimps it is possible it originally evolved in a common ancestor of the two species.

Neil Harrison at the Brighton and Sussex Medical School at the University of Sussex, UK, says that finding pupil mimicry for the first time in chimps is extremely significant, especially the accentuated effect observed in the three chimp mothers, as this suggests they are more sensitive empathetically.

All white now

The findings might even hint at a new reason for why humans evolved sclera, the whites of our eyes. "Traditionally, it's been thought that the evolution of white sclera was driven by its enhanced ability to indicate gaze direction, and hence share attention," says Harrison.

In a landmark paper in 2006, he showed that the pupils of human viewers tend to match those in images of people expressing sadness – but not other emotions.

Given that the human volunteers in Kret's study were more responsive than the chimps to changes in pupil size, it might be that the whites of our eyes evolved to help us subconsciously spot those changes more readily, says Harrison.

Pupils also dilate when someone is aroused, stressed, making decisions or – obviously – in darker conditions. Kret speculates that the involuntary changing of pupil size in response to looking at someone else may be a subconscious attempt to reinforce bonding by showing you are interested in them, or share an emotional state.

I feel you, fellow chimp (Image: Brad Wilson/Getty)