Psychobiotics: How gut bacteria mess with your mind

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Gut bugs can change the way our brains work, offering new ways to relieve problems like stress, anxiety and depression, say two leading professors

Leader: "Counting the hidden victims of medicine"

WE HAVE all experienced the influence of gut bacteria on our emotions. Just think how you felt the last time you had a stomach bug. Now it is becoming clear that certain gut bacteria can positively influence our mood and behaviour. The way they achieve this is gradually being uncovered, raising the possibility of unlocking new ways to treat neurobehavioural disorders such as depression and obsessive-compulsive disorder (OCD).

We acquire our intestinal microbes immediately after birth, and live in an important symbiotic relationship with them. There are far more bacteria in your gut than cells in your body, and their weight roughly equals that of your brain. These bacteria have a vast array of genes, capable of producing hundreds if not thousands of chemicals, many of which influence your brain. In fact, bacteria produce some of the same molecules as those used in brain signalling, such as dopamine, serotonin and gamma-aminobutyric acid (GABA). Furthermore, the brain is predominantly made of fats, and many of these fats are also produced by the metabolic activity of bacteria.

In the absence of gut bacteria, brain structure and function are altered. Studies of mice reared in a germ-free environment, with no exposure to bacteria, show that such mice have alterations in memory, emotional state and behaviour. They show autistic patterns of behaviour, spending as much time focusing on inanimate objects as on other mice. This behavioural change is driven by alterations in the underlying brain chemistry. For example, dramatic changes in serotonin transmission are seen, together with changes in key molecules such as brain-derived neurotrophic factor, which plays a fundamental role in forming new synapses.

These findings give weight to the notion of probiotics – bacteria with a health benefit. Probiotics were first proposed by Russian biologist Élie Metchnikoff who, in the early 1900s, observed that people living in a region of Bulgaria who consumed fermented food tended to live longer. However, it now seems that certain bacteria – dubbed psychobiotics – might have a mental-health benefit, too.

Although the field of psychobiotics is in its infancy, there are already promising signs. Last year, for instance, researchers from the California Institute of Technology in Pasadena showed that when the bacterium Bacteroides fragilis was given early in life, it corrected some of the behavioural and gastrointestinal deficits in a mouse model of autism. And previous reports indicate that Bifidobacterium infantis is effective in an animal model of depression.

How exactly do gut bacteria influence the brain? The mechanisms are becoming clear. The bacterium Lactobacillus rhamnosus, which is used in dairy products, has potent anti-anxiety effects in animals, and works by changing the expression of GABA receptors in the brain. These changes are mediated by the vagus nerve, which connects the brain and gut. When this nerve is severed no effect on anxiety or on GABA receptors is seen following psychobiotic treatment with L. rhamnosus.

L. rhamnosus has also been shown to alleviate OCD-like behaviours in mice. Interestingly, this bacterium not only alters GABA receptors in the brain but has been shown to synthesise and release GABA. Other evidence supports the view that gut bacteria may influence the brain in routes other than the vagus nerve – by altering the immune system and via the manufacture of short-chain fatty acids, for example.

Just as certain genes render bacteria pathogenic, it is likely that clusters of genes within gut bacteria provide mental health benefits. However, the essential genes for effective psychobiotics have yet to be established. It may be that, in the future, the ideal psychobiotic will be a genetically modified organism containing genes from several different bacteria.

In the meantime, cocktails of bacteria are likely to be more effective than single strains in producing health benefits. For example, a 2011 study showed that a combination of Lactobacillus helveticus and Bifidobacterium longum reduced anxiety and depressive symptoms in healthy volunteers. A 2013 neuroimaging study showed that a fermented milk product containing four different probiotic bacteria was associated with the reduced response of a brain network involved in the processing of emotion and sensation. And certain strains of bacteria can reduce the symptoms of irritable bowel syndrome, a common stress-related disorder of the brain-gut axis. This is probably achieved through a reduction in levels of the "stress hormone" cortisol and of inflammatory molecules produced by the immune system.

These findings are promising, but we are still a long way from the development of clinically proven psychobiotics and it remains to be seen whether they are capable of acting like – or perhaps even replacing – antidepressants. At a time when prescriptions for antidepressants have reached record levels, effective natural alternatives with fewer side effects would be welcome. We are currently completing a study of the gut microbiota in people with severe depression. If we find consistent alterations, this will provide a strong rationale for targeting depression with a suitable psychobiotic. We are also about to start a placebo-controlled study of Lactobacillus brevis in treating anxiety in healthy volunteers.

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Stem cell power unleashed after 30 minute dip in acid

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A mouse embryo made with reprogrammed cells (Image: Haruko Obokata)

A LITTLE stress is all it took to make new life from old. Adult cells have been given the potential to turn into any type of body tissue just by tweaking their environment. This simple change alone promises to revolutionise stem cell medicine.

Yet New Scientist has also learned that this technique may have already been used to make a clone. "The implication is that you can very easily, from a drop of blood and simple techniques, create a perfect identical twin," says Charles Vacanti at Harvard Medical School, co-leader of the team involved.

Details were still emerging as New Scientist went to press, but the principles of the new technique were outlined in mice in work published this week. The implications are huge, and have far-reaching applications in regenerative medicine, cancer treatment and human cloning.

In the first few days after conception, an embryo consists of a bundle of cells that are pluripotent, which means they can develop into all cell types in the body. These embryonic stem cells have great potential for replacing tissue that is damaged or diseased but, as their use involves destroying an embryo, they have sparked much controversy.

To avoid this, in 2006 Shinya Yamanaka at Kyoto University, Japan, and colleagues worked out how to reprogram adult human cells into what they called induced pluripotent stem cells (iPSCs). They did this by introducing four genes that are normally found in pluripotent cells, using a harmless virus.

The breakthrough was hailed as a milestone of regenerative medicine – the ability to produce any cell type without destroying a human embryo. It won Yamanaka and his colleague John Gurdon at the University of Cambridge a Nobel prize in 2012. But turning these stem cells into therapies has been slow because there is a risk that the new genes can switch on others that cause cancer.

Now, Vacanti, along with Haruko Obokata at the Riken Center for Developmental Biology in Kobe, Japan, and colleagues have discovered a different way to rewind adult cells – without touching the DNA. The method is striking for its simplicity: all you need to do is place the cells in a stressful situation, such as an acidic environment.

The idea that this might work comes from a phenomenon seen in the plant kingdom, whereby drastic environmental stress can change an ordinary cell into an immature one from which a whole new plant can arise. For example, the presence of a specific hormone has been shown to transform a single adult carrot cell into a new plant. Some adult cells in reptiles and birds are also known to have the ability to do this.

To investigate whether the process could occur in mammals, Obokata and colleagues used mice that were bred to carry a gene that glows green in the presence of Oct-4, a protein that is only found in pluripotent cells. The team took a blood sample from the spleenof these mice when they were one week old, isolated white blood cells called lymphocytes, and exposed them to various strong but fleeting physical and chemical stresses.

One batch of cells was exposed to a "sub-lethal" acidic environment, with a pH of 5.7, for 30 minutes. The team then tried to grow the cells in the lab.

Not much happened at first – some cells died, and the rest still looked like white blood cells. But on day 2, a number of cells began to glow green, meaning they were producing Oct-4. By day 7, two-thirds of the surviving cells showed this pluripotent marker, together with other genetic markers of pluripotency – many of which are also seen in embryonic stem cells. In contrast, iPS cells can take four weeks to reach this stage.

The team call their new cells "stimulus-triggered acquisition of pluripotency", or STAP cells.

To make sure they really were pluripotent, the team injected the STAP cells from the spleen into an early-stage mouse embryo, or blastocyst. These are typically five or six days old with about eight cells already formed inside. The STAP cells seemed to integrate themselves into the structure, and the embryo went on to form the three "germ layers" that eventually give rise to all cell types in the body. The embryos developed into pups that incorporated STAP cells into every tissue in their body. These pups subsequently gave birth to offspring that also contained STAP cells – showing that the cells incorporated themselves into the animal's sperm or eggs, and were inherited.

In a second test, the team injected STAP cells into an adult mouse. They wanted to see if the cells formed a type of embryonic tumour called a teratoma – another gold standard test of pluripotency. They did.

The team wondered whether other adult cells might behave in a similar way. So they tried the acid-bath technique on brain, skin, muscle, fat, bone marrow, lung and liver tissues from one-week-old mice. Although the efficiency varied, the same thing happened in each case. In unpublished results, Vacanti says they have now found the procedure appears to work on cells from much older animals, including some from adult primates. He cautions though that these studies have yet to be completed.

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Astrophile: Jellyfish galaxies found spawning in clusters

Object: Jellyfish galaxies

Habitat: Crowded clusters of cosmic blobs

The large spiral galaxy was tired of being alone. It had been ages since its last relationship with another galaxy, and they had enjoyed a long, slow dance in each other's orbit. When they finally merged, the spiral felt like it had done some serious growing, and it wanted even more social interaction. But it turns out that spiral galaxies need to change in a much more fundamental way if they want to move in with groups of friends.

A hunt through images from the Hubble Space Telescope has turned up half a dozen spiral galaxies that are being ripped apart and remade into jellyfish – with blobby bodies and glowing tendrils of stars – as they move towards joining galaxy clusters. It is thought that this process ultimately turns spirals into elliptical-shaped galaxies. That means the discovery, which more than doubles the number of known jellyfish galaxies, should help researchers better understand why such "ellipticals" are more common in clusters than their spiral cousins.

Galaxies can live in relative isolation, like our Milky Way, and only change shape significantly if they happen to collide with another galaxy. But in denser parts of the universe, gravity pulls galaxies together into enormous clusters. Previously, researchers had noticed that these clusters contain many more elliptical galaxies than spirals, hinting that newcomer spirals were somehow being transformed.

Blasted gas

Harald Ebeling at the University of Hawaii in Honolulu and his colleagues think jellyfish galaxies capture the process in action. "We see them turning one into the other," says Ebeling. "They're caught in the act."

The space between the galaxies in a cluster is laced with dark matter and gas, which reaches searing hot temperatures due to the pressure from its crowded surroundings. That means when new galaxies join a cluster, they can't just slip in quietly, says Ebeling.

Hot gas in the cluster smacks into cold gas within a new arrival, blasting the cold gas outwards in long streams. The stripped body of the galaxy settles into a blobby shape, while cold gas in the tendrils compresses enough to ignite new stars.

Ebeling and colleagues unexpectedly caught their first jellyfish in late 2005 and have been hunting for more extreme examples in Hubble images since then. Until recently, though, the transformation had been spotted only a few times in relatively nearby clusters. That's probably because the change is over too fast, says Alastair Edge at the University of Durham, UK. And once a spiral galaxy has been stripped if its cold gas, it won't experience another drastic transformation.

Orphan stars

"You've defused the bomb," says Edge, "and it will settle down to be much more sedate and much more like all the other galaxies we see. This is a very rough period that it undergoes, and observationally it's quite hard to see." Now Ebeling's team has caught six obvious jellyfish, clearly visible in Hubble images, which should help them better understand this unique galactic morphing.

"These images are stunning – you can see what's happening," says Ebeling. "You take a spiral galaxy, and it's getting completely annihilated and destroyed by the gas that it's running into."

Studying jellyfish in detail could help solve another mysterious feature of galaxy clusters: why they contain relatively young "orphan" stars that do not belong to any particular galaxy. The gas inside clusters is too hot to collapse into new stars, so the stars must come from outside – possibly from the tentacles of jellyfish galaxies.

Journal reference: Astrophysical Journal Letters, DOI: 10.1088/2041-8205/781/2/L40

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Parched California hunts for water in unusual places

Water is running low in California. Reservoirs are receding, leaving lake beds cracking in the warm winter sun. Snowpack in the Sierra Nevada mountains, traditionally a third of the state's water supply, has dropped to 12 per cent of its normal level. 2013 was the driest year in more than a century, and the resulting water shortages are providing a glimpse of California's future in a warming world.

Alexander Gershunov of the Scripps Institution of Oceanography in San Diego points out that uneven warming of the planet – which is heating faster at the poles than at the equator – is changing the north-south temperature gradient, and weather patterns are changing accordingly. That has pushed some of the winter storms that usually soak the state further north. "Most models agree that the frequency of winter storms will decrease, although the intensity of the largest storms will also increase, so annual average precipitation doesn't change too much," Gershunov says.

A shorter, more intense storm season means that the chance of either a very dry or very wet winter goes up. Either way, that is a problem, because as temperatures warm, more precipitation will fall as rain than snow. Unlike snow, rain will come gushing down out of the mountains in one fell swoop – making it difficult for water managers to capture and store for later use.

That means more precipitation flows into the Pacific Ocean, and less is available for farmers in California's fertile Central Valley, which produces 8 per cent of the US's food by value.

New sources

Heather Cooley of the Pacific Institute in Oakland, California, says the state's future water supply will need to be bolstered by new sources, and better conservation. Catching and treating storm water and pushing it into underground aquifers; cleaning and reusing domestic and industrial waste water; even sucking fresh water from a salty ocean will all be important sources of supply in future. All over the state, work to secure these new sources is already beginning.

In February a committee at the California Department of Public Health will meet to examine the possibility of permitting treated wastewater to be used as drinking water. New treatment plants are already running across California, although they are currently legally prevented from supplying the water for human use.

Behzad Ahmadi, who manages the groundwater programme for the Santa Clara Valley Water District, says that waste water treatment will play a key role in ensuring the state's future water supply. Santa Clara county's own treatment facility, the Silicon Valley Advanced Water Purification Center, will produce 36 million litres of water a day when it comes online later this year.

Filthy Walk of Fame

Water engineer Mark Hanna at GeoSyntec in Los Angeles is working on a way to gather storm water in the midst of the city's concrete jungle, water that would otherwise run off into the Pacific Ocean – carrying with it pollutants that close LA's beaches for days after big storms. In July, engineers will start punching holes in the city's concrete skin to make 15-metre-deep wells that will be filter-lined to ensure that contaminants from the street don't get washed into the groundwater below.

"Some people call it urban acupuncture," Hanna says. "We've figured out a way for a 30-acre neighbourhood to give 43 acre feet a year recharged on average." In metric terms, that's over 50,000 cubic metres of water every year, collected by a neighbourhood covering 12 hectares.

Desalination is happening too, using electricity to pull salt out of seawater. The Carlsbad Project in San Diego County is expected to be the largest desalination plant in the Western hemisphere when it starts pumping water in 2016. The project's website advertises the future water supply as "drought-proof" – precisely what California is going to need.

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Black Death may have scuppered Roman Empire

Video: Ancient teeth reveal origin of the Justinian plague

What caused the fall of the Roman Empire? A devastating plague that struck during the reign of Emperor Justinian in 541 AD, killing a quarter of the population, seems to have landed the final blow, but the identity of the infection was a mystery.

Now sequencing of DNA taken from two skeletons buried in Bavaria, Germany, in the 6th century has uncovered the complete genome of Yersinia pestis, the bacteria also blamed for the Black Death that struck Europe in 1348. The find suggests that Y. pestis may have emerged to ravage humanity several times.

Hendrik Poinar at McMaster University in Hamilton, Canada, who led the team that sequenced the German bacteria, also helped sequence Y. pestis bacteria from Londoners killed by the Black Death. He says the new finds don't prove Y. pestis was the sole cause of both plagues, but "make it more likely Yersinia was part of the larger story".

Ancient cemetery

The team analysed 12 skeletons from a large Iron Age cemetery at Aschheim in Bavaria. While there were low levels of Y. pestis DNA in 10 of them, says Poinar, the teeth of two skeletons had enough to allow the team to reconstruct the entire DNA sequence of the bacteria.

The beads buried with women in the cemetery were used to date the burials – previous work had shown that fashions changed quickly in Iron Age Bavaria, fast enough that the styles can date graves to the nearest 25 years with them. Such beads date one of the two skeletons to 525-550 AD, very close to the first wave of Justinian's plague. The position of the other grave, says Poinar, suggests a similar date.

Bavaria was outside the Roman Empire, but records of the time report that the highly contagious disease spread beyond its borders, into Persia and across the Roman frontier at the Rhine.

With the complete sequence the team can position the bacteria on the family tree of all Y. pestis taken from human infections. They were surprised to find that the German bacteria merit their own branch, with no known descendants. In contrast, the Y. pestis DNA from a mass grave dug during the 1348 plague in Spitalfields, London, suggest those bacteria are ancestors of all modern human infections worldwide.

This suggests the plagues emerged separately, and repeatedly, from the bacteria's usual hosts, ground-dwelling rodents such as marmots. That also means, the team warns, that Y. pestis could emerge again.

Different character

But the gene sequences cannot yet explain why both plagues behaved so differently from disease caused by modern Y. pestis .

Both the plague of Justinian and the Black Death raced across Europe, as if spreading from human to human. When Y. pestis travelled worldwide in the so-called "third pandemic" at the turn of the 20th century, however, it spread slowly, and rarely from person to person. This remains the case today in places such as Madagascar where the bacteria frequently cause human disease.

It could be, says Poinar, that Y. pestis was not the sole cause of the two devastating plagues, but merely the "final straw" that killed people weakened by another, fast-spreading infection – the way bacterial pneumonia often strikes after flu. "We are looking at other, co-infecting pathogens as well," says Poinar. "That is the million dollar question."

The team has developed a method to screen for 1000 human pathogens at once, he says, which will allow them to search for causes of death in ancient bones comprehensively.

Journal reference: The Lancet Infectious Diseases, DOI: 10.1016/S1473-3099(13)70323-2

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China's Jade Rabbit rover may be victim of moon dust

A plucky bunny on the moon may have just met an untimely end. Reports from Chinese state media suggest the country's Yutu – or Jade Rabbit – lunar rover has stopped working just six weeks into its three-month mission.

China's Chang'e-3 lander touched down on the moon on 14 December and released the Yutu rover about 7 hours later. Both machines successfully entered hibernation mode during their first lunar night. On the moon, night lasts for half of each Earthly month and plunges surface temperatures from daytime highs of about 90ºC to below -180ºC.

The second lunar night rolled around on Saturday, and while the lander is once again successfully sleeping, Yutu appears to have failed. The Xinhua news agency reports that the rover has experienced a mechanical control fault due to the "complicated lunar surface environment". No further details were given by China's State Administration for Science, Technology and Industry for National Defence.

During the deep freeze of lunar night, the most critical moving parts on Yutu are its mast and solar panels. When temperatures plunge, the mast is designed to fold down to protect delicate instruments, which can then be kept warm by a radioactive heat source. Yutu also needs to angle a solar panel towards the point where the sun will rise to maintain power levels. A mechanical fault in these systems could leave the rover fatally exposed to the dark and bitter cold.

Long, hard wait

As for what caused the malfunction, abrasive lunar dust is a top suspect. Moon soil gets ground up by micrometeoroid impacts into a glassy dust that can then become charged as it is bombarded by solar particles. During the Apollo program the sharp-edged dust grains wore through astronaut space suits, scratched up mirrors used for laser ranging experiments and caused moon buggies to overheat.

Rover designers can take measures to avoid getting this damaging dust inside important systems, says Bernard Foing, director of the International Lunar Exploration Working Group. "However, lunar dust can be electrostatically charged and can stick on sensitive parts," he says. The abrupt temperature change when the airless moon goes from day to night can also put a huge stress on mechanical systems and could have damaged the rover's moving parts, says Foing.

It is not possible to communicate with the rover during lunar night, so mission operators will have to wait until about 8 February to determine the extent of the damage. "I am sure that they are not going to give up," says Foing. "They are analysing the problem in depth and are working hard to assess safe recovery strategies."

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Drone with legs can perch, watch and walk like a bird

Video: Drone with legs can perch on a branch

Is that a bird or a drone watching you from the telephone wire? A drone with legs can perch just like a bird – or land and walk on flat surfaces. Bhargav Gajjar of Vishwa Robotics in Brighton, Massachusetts, designed the legs as an add-on for small US air force drones.

Small drones generally lack landing gear. Many rely on a controlled crash-landing, a somewhat crude approach compared with the elegant precision landing of a perching bird. Gajjar studied dozens of bird species and recorded their landings using a high-speed camera. His drone's legs are based on those of the American kestrel.

The drone perches in an upright position with a powerful gripping action from an electric motor. Its claws are extremely sharp so that its grip is difficult to break.

A remote computer uses footage from a camera fitted to the drone to control flight and get the drone into the correct position for landing. Just like a real bird, the drone has to brake sharply just above its landing site and perform a controlled stall in order to touch down. Birds' legs also act as shock absorbers, and the mechanical version mimics this.

Gajjar's perching legs can waddle short distances, so the drone can explore indoor spaces.

Stealthy watcher

A perching drone can occupy any convenient vantage point, making it stealthier and giving a closer view than one circling overhead. Perching uses no power, and a perching drone recharging from solar cells could operate indefinitely. Gajjar has flown his legs on fixed-wing drones, but is using a quadrotor inside the laboratory.

Copying animals in ways like this appeals to Justin Thomas of the University of Pennsylvania's General Robotics, Automation, Sensing and Perception (GRASP) Laboratory. "Such a biomimetic approach would have advantages in extending the working time of an aerial robot by allowing it to perch and save energy," he says. His team has previously created a drone that can grab objects on the ground.

"This could be particularly advantageous for applications such as environmental monitoring and establishing temporary communication networks, such as in the case of a natural disaster," Thomas says.

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Mini space shuttle gears up to chase astronaut dreams

(Artist's impression: Sierra Nevada Corp)

NASA astronauts may be getting a sweet new ride. Engineers at Sierra Nevada Corporation have announced that the Dream Chaser will make its first orbital flight on 1 November 2016.

The Dream Chaser will launch attached to an Atlas V rocket as shown in this artist's impression. In previous flight tests, the craft was "flown" suspended from a helicopter. Its first free flight ended badly when it crash-landed after successfully gliding on autopilot from an altitude of 3.8 kilometres.

The Dream Chaser is one of three spacecraft vying to replace NASA's retired space shuttle and restore the US's ability to send astronauts into orbit. Currently, astronauts must hitch a ride to the International Space Station in Russian Soyuz capsules. Other contenders being developed with NASA's support are Boeing's CST-100and SpaceX's Dragon.

(Artist's impression: Sierra Nevada Corp)

Though the Dream Chaser small – about 9 metres long, compared with 37 metres for the space shuttle – it can nevertheless carry up to seven astronauts and their equipment.

The uncrewed flight in 2016 will launch from Cape Canaveral, Florida, and spend about a day in orbit. Sierra Nevada is planning a crewed mission for 2017.

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One-parent families: US social mobility's main barrier?

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What is the most important factor blocking social mobility in the US? It could be single parents, not economic inequality

This week, in his State of the Union address, President Obama is expected to return to a theme he and many progressives have been hitting hard in recent months: namely that the American Dream is in trouble and that growing economic inequality is largely to blame. In a speech to the Center for American Progress last month, Obama said: "The combined trends of increased inequality and decreasing mobility pose a fundamental threat to the American Dream." Likewise, New York Times columnist Paul Krugman recently wrote that the nation "claims to reward the best and brightest regardless of family background" but in practice shuts out "children of the middle and working classes".

Obama and Krugman are clearly right to argue that the American Dream is in trouble. Today, poor children have a limited shot at moving up the economic ladder into the middle or upper class. One study found that the nation leaves 70 per cent of poor children below the middle class as adults. Equally telling, poor children growing up in countries like Canada and Denmark have a greater chance of moving up the economic ladder than do poor children from the United States. As Obama noted, these trends call into question the "American story" that our nation is exceptionally successful in delivering equal opportunity to its citizens.

But the more difficult question is, why? What are the factors preventing poor children from getting ahead? An important new Harvard study that looks at the best community data on mobility in America – released this past weekend – suggests a cause that progressives may find discomforting, especially if they are interested in reviving the American Dream for the 21st century.

The study, Where is the Land of Opportunity?: The geography of intergenerational mobility in the United States , authored by Harvard economist Raj Chetty and colleagues from Harvard and Berkeley, explores the community characteristics most likely to predict mobility for lower-income children. It specifically focuses on two outcomes: absolute mobility for lower-income children – how far up the income ladder they move as adults &ndash and relative mobility – how far apart children who grew up rich and poor in the same community end up on the economic ladder as adults. When it comes to these measures, the Harvard study asks which factors are the strongest predictors of upward mobility.

1. Family structure. Of all the factors most predictive of economic mobility in America, one factor clearly stands out in their study: family structure. By their reckoning, when it comes to mobility, "the strongest and most robust predictor is the fraction of children with single parents". They find that children raised in communities with high percentages of single mothers are significantly less likely to experience absolute and relative mobility. Moreover, "children of married parents also have higher rates of upward mobility if they live in communities with fewer single parents". In other words it looks like a married village is more likely to raise the economic prospects of a poor child.

What makes this finding particularly significant is that this is the first major study showing that rates of single parenthood at the community level are linked to children's economic opportunities over the course of their lives. A lot of research – including new research from the Brookings Institution – has shown us that kids are more likely to climb the income ladder when they are raised by two, married parents. But this is the first study to show that lower-income kids from both single and married-parent families are more likely to succeed if they hail from a community with lots of two-parent families.

2. Racial and economic segregation. According to the study, economic and racial segregation are also important characteristics of communities that do not foster economic mobility. Children growing up in communities that are racially segregated, or cluster lots of poor kids together, do not have a great shot at the American Dream. In fact, in this study, racial segregation is one of only two key factors – the other is family structure – that is consistently associated with both absolute and relative mobility in America.

3. School quality. Another powerful predictor of absolute mobility for lower-income children is the quality of schools in their communities. Chetty and his colleagues measure this by looking at high-school dropout rates. Their takeaway is that poor kids are more likely to make it in America when they have access to schools that do a good job of educating them.

4. Social capital. In a finding that is bound to warm the heart of their colleague, Harvard political scientist Robert Putnam, Chetty and his team find that communities with more social capital enjoy significantly higher levels of absolute mobility for poor children. That is, communities that have high levels of religiosity, civic engagement, and voter involvement are more likely to lift the fortunes of their poorest members.

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