Great tits sing with syntax

Great tits use syntax to compose their tunes.

Japanese great tits (Parus minor) communicate using at least 10 different notes on their own and in combination. Researchers played different calls for Japanese great tits in a forest in Nagano, Japan, to see how the birds responded — an indication of what the call might mean. The birds responded differently to individual notes than they did when played the same note in combination with other notes. And, when researchers reversed the note order, the birds didn’t respond the same way.
By itself, a note means one thing to great tits, but in combination, it means something different, the team argues March 8 in Nature Communications. Similarly, among humans, the order of words in a sentence, its compositional syntax, matters.

Some primates combine calls to convey different messages, but individual notes don’t carry unique meaning in these species. Great tits are the first nonhuman species shown to use compositional syntax, the researchers write.
In this recording, researchers played three types of calls for Japanese great tits: First, a call with three notes — A, B, and C — which signals danger; second, a one-note call (D), which attracts mates; and finally, a combination call, ABC-D, which causes the birds to scan the skies for predators and fly to the source of the sound.
Researchers played an ABC-D call for great tits, and then reversed an ABC-D call. Birds responded differently in each case.

Brain holds more than one road to fear

In a pair of twin sisters, a rare disease had damaged the brain’s structures believed necessary to feel fear. But an injection of a drug could nevertheless make them anxious.

The results of that experiment, described in the March 23 Journal of Neuroscience, add to evidence that the amygdalae, small, almond-shaped brain structures tucked deep in the brain, aren’t the only bits of the brain that make a person feel afraid. “Overall, this suggests multiple different routes in the brain to a common endpoint of the experience of fear,” says cognitive neuroscientist Stephan Hamann of Emory University in Atlanta.
The twins, called B.G. and A.M., have Urbach-Wiethe disease, a genetic disorder that destroyed most of their amygdalae in late childhood. Despite this, the twins showed fear after inhaling air laden with extra carbon dioxide (an experience that can create the sensation of suffocating), an earlier study showed (SN: 3/23/13, p. 12). Because carbon dioxide affects a wide swath of the body and brain, scientists turned to a more specific cause of fear that stems from inside the body: a drug called isoproterenol, which can set the heart racing and make breathing hard. Sensing these bodily changes provoked by the drug can cause anxiety.

“If you know what adrenaline feels like, you know what isoproterenol feels like,” says study coauthor Sahib Khalsa, a psychiatrist and neuroscientist at the Laureate Institute for Brain Research in Tulsa, Okla.

After injections of isoproterenol, both twins felt shaky and anxious. B.G. experienced a full-blown panic attack, a result of the drug that afflicts about a quarter of people who receive it, says Khalsa. In a second experiment, researchers tested the women’s ability to judge their bodies’ responses to the drug. While receiving escalating doses, the women rated the intensity of their heartbeats and breathing. A.M., the woman who didn’t have a panic attack, was less accurate at sensing the drug’s effects on her body than both her sister and healthy people, researchers found.

It’s not clear why the twins responded differently, Khalsa says. Further experiments using brain scans may help pinpoint neural differences that could be behind the different reactions.

The results suggest that the amygdala isn’t the only part of the brain involved in fear and anxiety, but there’s more work to do before scientists understand how the brain creates these emotions, Khalsa says. “It’s definitely a complicated question and a debate that’s unresolved,” he says.

Global obesity rates continue to climb

Despite massive public health campaigns, the rise in worldwide obesity rates continues to hurtle along like a freight train on greased tracks.

In 2014, more than 640 million men and women were obese (measured as a body mass index of 30 or higher). That’s up from 105 million in 1975, researchers estimate in the April 2 Lancet. The researchers analyzed four decades of height and weight data for more than 19 million adults, and then calculated global rates based on population data. On average, people worldwide are gaining about 1.5 kilograms per decade — roughly the weight of a half-gallon of ice cream.
But the road isn’t entirely rocky. During the same time period, average life expectancy also jumped: from less than 59 years to more than 71 years, George Davey Smith points out in a comment accompanying the new study. Smith, an epidemiologist at the University of Bristol in England, boils the data down to a single, seemingly paradoxical sentence: “The world is at once fatter and healthier.”

Pollen becoming bee junk food as CO2 rises

Bees may need their own supplemental protein shakes as increasing carbon dioxide in the atmosphere saps the nutritional quality of pollen.

Pollen collected from plants gives bees their only natural source of protein (nectar is a sugar-shot for energy). Yet protein content in pollen of a widespread goldenrod species (Solidago canadensis) dwindled by a third, from about 18 percent to 12 percent, over 172 years, according to analysis of recently collected flowers and of preserved specimens at the Smithsonian Institution’s National Museum of Natural History. During those same years, CO2 concentrations in the atmosphere increased from about 280 parts per million to 398 ppm, researchers report April 12 in Proceedings of the Royal Society B.
The same themes also showed up in two years of growing the goldenrod at CO2 concentrations up to 500 ppm. More CO2 meant less concentrated protein in pollen, say Lewis Ziska of the U.S. Department of Agriculture’s Bee Research Laboratory in Beltsville, Md., and his colleagues.

“It’s like you’re eating a starchier diet — what would that do to us?” says study coauthor Joan Edwards of Williams College in Williamstown, Mass. “Bees aren’t so different.”

Bees, wild or domesticated, need adequate protein to feed their larvae, maintain their immune systems and for many more functions, says bee biologist Cédric Alaux of the French agricultural research agency INRA in Avignon. Canada goldenrod is an example of a species known to offer pollen that can be stored to tide honeybees over the winter. The one-third decrease in protein concentration reported in the new study is big enough to shorten bee life spans, he says.

Lower quality in bee food sources could be contributing to global bee declines observed in recent years and the uncertain state of pollination for crops, Edwards says. “The health of the bee population is not just for the flowers and the bees and biodiversity, but also for human health and well-being.”

Humans have pondered aliens since medieval times

For beings that are supposedly alien to human culture, extraterrestrials are pretty darn common. You can find them in all sorts of cultural contexts, from comic books, sci-fi novels and conspiracy theories to Hollywood films and old television reruns. There’s Superman and Doctor Who, E.T. and Mindy’s friend Mork, Mr. Spock, Alf, Kang and Kodos and My Favorite Martian. Of course, there’s just one hitch: They’re all fictional. So far, real aliens from other worlds have refused to show their faces on the real-world Earth — or even telephone, text or tweet. As the Italian physicist Enrico Fermi so quotably inquired during a discussion about aliens more than six decades ago, “Where is everybody?”
Scientific inquiry into the existence of extraterrestrial intelligence still often begins by pondering Fermi’s paradox: The universe is vast and old, so advanced civilizations should have matured enough by now to send emissaries to Earth. Yet none have. Fermi suspected that it wasn’t feasible or that aliens didn’t think visiting Earth was worth the trouble. Others concluded that they simply don’t exist. Recent investigations indicate that harsh environments may snuff out nascent life long before it evolves the intelligence necessary for sending messages or traveling through space.
In any event, Fermi’s question did not launch humankind’s concern with visitors from other planets. Imagining other worlds, and the possibility of intelligent life-forms inhabiting them, did not originate with modern science or in speculative fiction. In the ancient world, philosophers argued about the possibility of multiple universes; in the Middle Ages the question of the “plurality of worlds” and possible inhabitants occupied the deepest of thinkers, spawning intricate and controversial philosophical, theological and astronomical debate. Far from being a merely modern preoccupation, life beyond Earth has long been a burning issue animating the human race’s desire to understand itself, and its place in the cosmos.

Other worlds, illogical
From ancient times Earth’s place was widely regarded to be the center of everything. As articulated by the Greek philosopher Aristotle, the Earth was the innermost sphere in a universe, or world, surrounded by various other spheres containing the moon, sun, planets and stars. Those heavenly spheres, crystalline and transparent, rotated about the Earthly core comprising four elements: fire, air, water and earth. Those elements layered themselves on the basis of their essence, or “nature” — earth’s natural place was at the middle of the cosmos, which was why solid matter fell to the ground, seeking the inaccessible center far below.

On the basis of this principle, Aristotle deduced the impossibility of other worlds. If some other world existed, its matter (its “earth”) would seek both the center of its world and of our world as well. Such opposite imperatives posed a logical contradiction (which Aristotle, having more or less invented logic, regarded as a directly personal insult). He also applied further reasoning to point out that there is no space (no void) outside the known world for any other world to occupy. So, Aristotle concluded, two worlds cannot both exist.

Some Greeks (notably those advocating the existence of atoms) believed otherwise. But Aristotle’s view prevailed. By the 13th century, once Aristotle’s writings had been rediscovered in medieval Europe, most scholars defended his position.
But then religion leveled the philosophical playing field. Fans of other worlds got a chance to make their case.

In 1277, the bishop of Paris, Étienne Tempier, banned scholars from teaching 219 principles, manny associated with Aristotle’s philosophy. Among the prohibited teachings on the list was item 34: that God could not create as many worlds as he wanted to. Since the penalty for violating this decree was excommunication, Parisian scholars suddenly discovered rationales allowing multiple worlds, empowering God to defy Aristotle’s logic. And since Paris was the intellectual capital of the European world, scholars elsewhere followed the Parisian lead.
While several philosophers asserted that God could make many worlds, most intimated that he probably wouldn’t have bothered. Hardly anyone addressed the likelihood of alien life, although both Jean Buridan in Paris and William of Ockham in Oxford did consider the possibility. “God could produce an infinite [number of] individuals of the same kind as those that now exist,” wrote Ockham, “but He is not limited to producing them in this world.”
Populated worlds showed up more prominently in writings by the renegade thinkers Nicholas of Cusa (1401–1464) and Giordano Bruno (1548–1600). They argued not only for the existence of other worlds, but also for worlds inhabited by beings just like, or maybe better than, Earth’s humans.

“In every region inhabitants of diverse nobility of nature proceed from God,” wrote Nicholas, who argued that space had no center, and therefore the Earth could not be central or privileged with respect to life. Bruno, an Italian friar, asserted that God’s perfection demanded an infinity of worlds, and beings. “Infinite perfection is far better presented in innumerable individuals than in those which are numbered and finite,” Bruno averred.

Burned at the stake for heretical beliefs (though not, as often stated, for his belief in other worlds), Bruno did not live to see the triumph of Copernicanism during the 17th century. Copernicus had placed the sun at the hub of a planetary system, making the Earth just one planet of several. So the existence of “other worlds” eventually became no longer speculation, but astronomical fact, inviting the notion of otherworldly populations, as the prominent Dutch scientist Christiaan Huygens pointed out in the late 1600s. “A man that is of Copernicus’ opinion, that this Earth of ours is a planet … like the rest of the planets, cannot but sometimes think that it’s not improbable that the rest of the planets have … their inhabitants too,” Huygens wrote in his New Conjectures Concerning the Planetary Worlds, Their Inhabitants and Productions.

A few years earlier, French science popularizer Bernard le Bovier de Fontenelle had surveyed the prospects for life in the solar system in his Conversations on the Plurality of Worlds, an imaginary dialog between a philosopher and an uneducated but intelligent woman known as the Marquise.

“It would be very strange that the Earth was as populated as it is, and the other planets weren’t at all,” the philosopher told the Marquise. Although he didn’t think people could live on the sun (if there were any, they’d be blinded by its brightness), he sided with those who envisioned inhabitants on other planets and even the moon.

“Just as there have been and still are a prodigious number of men foolish enough to worship the Moon, there are people on the Moon who worship the Earth,” he wrote.

From early modern times onward, discussion of aliens was not confined to science and philosophy. They also appeared in various works of fiction, providing plot devices that remain popular to the present day. Often authors used aliens as stand-ins for evil (or occasionally benevolent) humans to comment on current events. Modern science fiction about aliens frequently portrays them in the role of tyrants or monsters or victims, with parallels to real life (think Flash Gordon’s nemesis Ming the Merciless, a 1930s dictator, or the extraterrestrials of the 1980s film and TV show Alien Nation — immigrants encountering bigotry and discrimination). When humans look for aliens, it seems, they often imagine themselves.

Serious science
While aliens thrived in fiction, though, serious scientific belief in extraterrestrials — at least nearby — diminished in the early 20th century, following late 19th century exuberance about possible life on Mars. Supposedly a network of lines interpreted as canals signified the presence of a sophisticated Martian civilization; its debunking (plus further knowledge about planetary environments) led to general agreement that finding intelligent life elsewhere in the solar system was not an intelligent bet.
On the other hand, the universe had grown incredibly vaster than the early Copernicans had imagined. The sun had become just one of billions of stars in the Milky Way galaxy, which in turn was only one of billions of other similar galaxies, or “island universes.” Within a cosmos so expansive, alien enthusiasts concluded, the existence of other life somewhere seemed inevitable. In 1961, astronomer Frank Drake developed an equation to gauge the likelihood of extraterrestrial life’s existence; by the 1990s he estimated that 10,000 planets possessed advanced civilizations in the Milky Way alone, even before anybody really knew for sure that planets outside the solar system actually existed.

But now everybody does. In the space of the last two decades, conclusive evidence of exoplanets, now numbering in the thousands, has reconfigured the debate and sharpened Fermi’s original paradox. No one any longer doubts that planets are plentiful. But still there’s been not a peep from anyone living on them, despite years of aiming radio telescopes at the heavens in hope of detecting a signal in the static of interstellar space.

Maybe such signals are just too rare or too weak for human instruments to detect. Or possibly some cosmic conspiracy is at work to prevent civilizations from communicating — or arising in the first place. Or perhaps civilizations that do arise are eradicated before they have a chance to communicate.

Or maybe the alien invasion has merely been delayed. Fermi’s paradox implicitly assumes that other civilizations have been around long enough to develop galactic transportation systems. After all, the universe, born in the Big Bang 13.8 billion years ago, is three times as old as the Earth. So most analyses assume that alien civilizations had a head start and would be advanced enough by now to go wherever they wanted to. But a new paper suggests that livable galactic neighborhoods may have developed only relatively recently.
In a young, smaller and more crowded universe, cataclysmic explosions known as gamma-ray bursts may have effectively sterilized otherwise habitable planets, Tsvi Piran and collaborators suggest in a paper published in February in Physical Review Letters.

A planet near the core of a galaxy would be especially susceptible to gamma-ray catastrophes. And in a young universe, planets closer to the galactic edge (like Earth) would also be in danger from gamma-ray bursts in neighboring satellite galaxies. Only as the expansion of the universe began to accelerate — not so long before the birth of the Earth — would galaxies grow far enough apart to provide safety zones for life.

“The accelerated expansion induced by a cosmological constant slows the growth of cosmic structures, and increases the mean inter-galaxy separation,” Piran and colleagues write. “This reduces the number of nearby satellites likely to host catastrophic” gamma-ray bursts. So most alien civilizations would have begun to flourish not much before Earth’s did; those aliens may now be wondering why nobody has visited them.

Still, the radio silence from the sky makes some scientists wonder whether today’s optimism about ET’s existence will go the way of the Martian canal society. From one sobering perspective, aliens aren’t sending messages because few planets remain habitable long enough for life to develop an intelligent civilization. One study questions, for instance, how likely it is that life, once initiated on any planet, would shape its environment sufficiently well to provide for lasting bio-security.

In fact, that study finds, a wet, rocky planet just the right distance from a star — in the Goldilocks zone — might not remain habitable for long. Atmospheric and geochemical processes would typically drive either rapid warming (producing an uninhabitable planet like Venus) or quick cooling, freezing water and leaving the planet too cold and dry for life to survive, Aditya Chopra and Charles Lineweaver conclude in a recent issue of Astrobiology. Only if life itself alters these processes can it maintain a long-term home suitable for developing intelligence.

“Feedback between life and environment may play the dominant role in maintaining the habitability of the few rocky planets in which life has been able to evolve,” wrote Chopra and Lineweaver, both of the Australian National University in Canberra.

Yet even given such analyses — based on a vastly deeper grasp on astronomy and cosmology than medieval scholars possessed — whether real aliens exist remains one of those questions that science cannot now answer. It’s much like other profound questions also explored in medieval times: What is the universe made of? Is it eternal? Today’s scientists may be closer (or not) to answering those questions than were their medieval counterparts. Nevertheless the answers are not yet in hand.

Maybe we’ll just have to pose those questions to the aliens, if they exist, and are ever willing to communicate. And if those aliens do arrive, and provide the answers, humankind may well discover how medieval its understanding of the cosmos still is. Or perhaps the aliens will be equally clueless about nature’s deepest mysteries. As Fontenelle’s philosopher told the Marquise: “There’s no indication that we’re the only foolish species in the universe. Ignorance is quite naturally a widespread thing.”

Gun research faces roadblocks and a dearth of data

Buying a handgun in Connecticut means waiting — lots of waiting. First comes an eight-hour safety course. Then picking up an application at a local police department. Review of the application (which includes a background check and fingerprinting) can take up to eight weeks. If approved, the state issues a temporary permit, which the buyer trades in at state police headquarters for a permanent one. Then it’s back to the store for the gun.

Head west to Missouri, though, and buying a handgun is practically a cakewalk. Customers at Osage County Guns in Belle, Mo., for example, can walk into the store and walk out with a gun if they pass the FBI’s instant background check, says John Dawson, the store’s chief technical officer.
“If a person knew exactly what they wanted,” he says, the store could, “in theory, complete the transaction in about 15 minutes.”

Missouri and Connecticut have staked out opposite ends of the gun law spectrum. Connecticut didn’t require handgun buyers to get a permit until 1995. Missouri had a tough law on the books, but repealed it in 2007. The states’ laws have flip-flopped, making for a fascinating natural experiment on gun laws’ effects on gun violence.

The states “had mirror image policy changes, and mirror image results,” says Daniel Webster, a health policy researcher at Johns Hopkins University.

Flipping the laws was associated with 15 percent fewer gun suicides in Connecticut and 16 percent more in Missouri, a statistical analysis by Webster and colleagues, published last year in Preventive Medicine, estimated. Similar analyses by Webster in 2014 and 2015 indicated a 40 percent reduction in Connecticut gun homicide numbers, and an 18 percent rise in Missouri.
The evidence is very suggestive, says Harvard University researcher David Hemenway. But it’s not extensive enough to persuade everyone — or to move national policy.

In fact, questions loom about the impact of all sorts of policies, from background checks to assault weapons bans to gun buybacks. That’s partly because gun research faces roadblocks at every turn: Scientists have to deal with data shutouts, slashed funding and, occasionally, harassment.

For a few questions, however, researchers have come up with solid answers: There’s a convincing link between gun availability and gun suicide, for one. And studies from the United States and abroad suggest that some gun laws do rein in gun violence. To make firm conclusions, though, scientists are desperate for more data.

But the U.S. Centers for Disease Control and Prevention can’t collect gun data like it used to, and information about guns used in individual crimes is locked up tight. Under current federal laws, Hemenway says, “It’s almost impossible for researchers to get even the data that are available.”

Locked up
In a squat brick building tucked in the hills of Martinsburg, W. Va., gun data are overflowing.

Thousands of cardboard boxes, stacked high in tidy columns, line the hallways of the federal government’s National Tracing Center. In the parking lot, steel shipping containers hold even more boxes. Each box contains about 2,000 pages of gun purchase records. To trace a gun, the center’s employees often search through these records by hand.

That’s their job: tracking when and where guns used in crimes were originally purchased, and by whom. It’s a huge undertaking: In 2015, the center, part of the Bureau of Alcohol, Tobacco, Firearms and Explosives, or ATF, received more than 373,000 gun trace requests from law enforcement.
Such a mass of data is a researcher’s dream. But current laws keep gun traces secret. The agency shares traces only with law enforcement. The public can see just summaries or aggregate data.

Webster has used this data to paint a rough picture of how Missouri’s repeal affected the flow of guns to criminals. In 2006, when buying a handgun required a permit, 56.4 percent of guns recovered by police had been originally sold by a Missouri gun dealer. In 2012, five years after the state nixed the permit requirement, the number rose to 71.8 percent, Webster and colleagues reported in the Journal of Urban Health in 2014.

The findings suggest that it’s easier now for criminals in Missouri to get their hands on legally purchased guns. But Webster can’t say for certain whether more guns are moving to criminals — or whether legal gun owners are committing more crimes. For that, he’d need to see the individual gun traces.

About a decade ago, researchers who wanted such detailed data could get it. “We’d just hand them a DVD,” says ATF information specialist Neil Troppman. “Those days are long over.”

A handful of laws snarl the process, from how a gun trace begins to who can see the data.

One big hitch in the system: Police officers who find a gun at a crime scene can’t always look up the owner’s name on a computer. That’s because there is no national registry — no searchable database of guns and their owners. To set one up would be illegal. So police have to submit a request to the tracing center, which tracks the gun’s movement from manufacturer or importer to dealer. Then the ATF can ask the dealer who bought the gun. If the dealer has gone out of business, ATF employees dig for the answer themselves, in old gun purchase records stockpiled at the tracing center. The process takes an average of five days. And after law enforcement gets the data, federal law makes sure no one else can see it.

Federal constraints
In 2003, Congress unleashed a beast of a bill with an amendment that effectively tore out the ATF’s tongue. The Tiahrt amendment was the first in a series of provisions that drastically limited the agency’s ability to share its crime gun data — no giving it to researchers, no making it public, no handing it over under Freedom of Information Act requests (the public’s channel for tapping into information from the federal government).

Funding for gun control research had dried up a few years earlier. There’s no outright ban, but a 1996 amendment had nearly the same effect. It’s known as the Dickey amendment, and it barred the CDC from using funds to “advocate or promote gun control.” According to a 2013 commentary in JAMA, that meant almost any research on guns.
If the 1996 law’s language was vague, Congress made the message clear by cutting the CDC’s budget by $2.6 million — exactly the same amount the agency had spent the previous year on gun violence research. The funds were later reinstated, but earmarked for other things. So the CDC largely backed off, except for some basic tallying, says spokesperson Courtney Lenard, because of the funding cuts and because Congress “threatened to impose further cuts if that research continued.”

In 2011, Congress hit the National Institutes of Health with similar restrictions. About a year later, President Obama tried to ease the choke hold: He ordered the CDC to research the causes and prevention of gun violence, and called on Congress to provide $10 million in funding. Finally, 17 years after the CDC cuts, news reports proclaimed that the ban had been lifted and research could resume. But Congress never authorized the money, and the CDC remained on the sidelines. This April, nearly 150 health and science organizations, universities and other groups signed a letter urging Congress to restore the CDC’s funding.

Meanwhile, research on gun violence and gun control trudges forward: Researchers can sometimes convince law enforcement agencies to share data on guns linked to crimes, and grants can come from private foundations. Yet even with limits on research, the science in some cases is solid: A gun in the home, for example, increases the odds a person will commit suicide by about 3-to-1. Here, Hemenway says, “The weight of the evidence is overwhelming.”

But how to use laws to reduce gun violence remains hotly contested, and opinions among the public, and even scientists, are polarized.

Critics of gun control laws think the matter is clear: Again and again studies show that gun control policies just don’t work, says economist John Lott, who has written extensively on the subject. Take background checks, he says, “Given that these laws are costly, you’d like to believe there’s some evidence that they produce a benefit.”

Webster acknowledges the divisive split in opinions. “The vast majority of people are on one side of the fence or the other,” he says. “They’ll point to a study that is convenient to their political arguments and call it a day.”

Bad for your health
For researchers who manage to navigate the legal tangles and funding troubles of gun research, actually doing the research itself isn’t easy.

Unlike clinical trials in medicine, where scientists can give, for example, a cholesterol drug to half a study’s participants and then compare the effects between users and nonusers, scientists studying gun violence can’t dole out new handguns to one group and none to another and see what happens.

Instead, researchers turn to observational studies. That means looking at how — and if — suicides track with gun ownership in different groups of people and over time, for example. Finding a link between two observations doesn’t necessarily mean they’re connected. (People have linked the yearly number of Nicolas Cage movies to swimming pool drownings, after all.) But finding a lot of links can be telling.

For suicides, the link to gun access holds strong — among old people, young people, women, adolescents, “you name it,” Hemenway says. Lots of guns means lots of suicides by gun, he says.
In 2007, Hemenway and colleagues examined gun ownership rates and statewide suicide data from 2000 to 2002. People in states with a high percentage of gun owners (including Wyoming, South Dakota and Alaska) were almost four times as likely to kill themselves with guns as people living in states with relatively few gun owners (such as Hawaii, Massachusetts and Rhode Island), the researchers reported in the Journal of Trauma Injury, Infection and Critical Care.

More recently, a 2013 study in Switzerland compared suicide rates before and after an army reform that cut the number of Swiss soldiers by half. After the reform, fewer people had access to army-issued guns — and the suicide rate dipped down by about two per 100,000 men age 18–43. That’s about 30 men each year who didn’t die from suicide, the study’s authors estimated in the American Journal of Psychiatry.

A 2014 review of 16 such studies, published in the Annals of Internal Medicine, came to the same conclusion, again: Access to guns meant higher risk of suicide.

“The evidence is unassailable,” says Stanford University criminologist John Donohue. “It’s as strong as you can get.”

Mental illness factors into suicide too, says Jeffrey Swanson, a medical sociologist at Duke University. (Some 21 to 44 percent of suicides reported to the CDC are committed by people with mental health problems.) And federal laws aren’t particularly good at keeping guns away from mentally ill people. A 1968 law prohibits gun sales to a narrow slice of people with a history of mental illness, but it’s easy for others to slip through the cracks. Even people the law does target can end up with guns — because states don’t have to report mental health records to the FBI’s national background-check system.

“You’ve got tons of records that would disqualify people from buying guns,” Swanson says, but they don’t necessarily make it into the system.
Even if the United States had a perfect mental health care system and cured schizophrenia and bipolar disorder and depression, he says, the overall problem of gun violence would still exist. Mentally ill people just aren’t that violent toward others, Swanson noted in the Annals of Epidemiology in 2015. In fact, people with mental illness committed fewer than 5 percent of U.S. gun killings between 2001 and 2010, according to the CDC.

“People think that in order to fix gun violence, we need to fix the mental health care system,” Swanson says. That’s wrong, he argues. “It’s a diversion from talking about guns.”

Weak laws
After Sandy Hook, San Bernardino and other high-profile mass shootings, people have been talking about what gun control laws, if any, actually work.

Unfortunately, there’s just not enough evidence to make strong conclusions about most laws, Hemenway says. In 2005, for example, a federal task force reviewed 51 studies of gun laws, mostly in the United States, and came up empty-handed. The task force couldn’t say whether any one of the laws made much of a difference. The efficacy of U.S. gun laws is hard to pin down for two main reasons, Hemenway says: Gun laws aren’t typically very strong, and studies tend to look at overall effects on violence.

One major study published in JAMA in 2000 analyzed suicide and homicide data from 1985 to 1997 to evaluate the impact of the Brady Act, a 1994 federal law that requires background checks for people buying guns.

Eighteen states and the District of Columbia already followed the law. So researchers compared suicide and homicide rates with those in the 32 states new to the law. If Brady curbed gun violence, those 32 states should see dips in deaths.
That didn’t happen (with one exception: Gun suicides in those states dropped in people age 55 and older — by about 1 per 100,000 people).

“I don’t think anybody was really shocked,” Webster says. After all, Brady had a gaping hole: It didn’t require background checks for guns bought from private sellers (including those at gun shows). The loophole neutered Brady: People who didn’t want a background check could simply find a willing private seller. That’s just too easy, Webster says: It’s like letting people decide whether they want to go through the metal detector at the airport.

Like the Brady Act, the 1994 Federal Assault Weapons Ban didn’t seem to do much to prevent violence, criminologist Christopher Koper and colleagues concluded in a 2004 report to the U.S. Department of Justice. The law, which expired in 2004, imposed a 10-year ban on sales of military-style semiautomatic guns. These weapons fire one bullet per trigger squeeze and have features like threaded barrels (which can be used for screwing on silencers) or barrel mounts (for attaching bayonets). The 1994 law also banned most large-capacity magazines (storage devices that feed guns more than 10 rounds of ammo).

But like Brady, the ban came with a catch: It didn’t apply to weapons and magazines made before September 13, 1994. That’s a lot of exemptions. At the time, the United States had more than 1.5 million assault weapons and nearly 25 million guns with large-capacity magazines, reported Koper, of George Mason University in Fairfax, Va.

“The more complete the bans are, the better the effects seem to be,” Donohue says. Take Australia: In 1996, the country enacted strict laws and a gun buyback program after a mass shooting killed 35 people in Tasmania. The ban made certain long-barreled guns illegal (including semiautomatic rifles and pump-action shotguns — weapons that let people fire lots of rounds quickly), and the country bought back and destroyed more than 650,000 guns.

With the law, Donohue says, “Australia effectively ended the problem of mass shootings.”

And as economists Christine Neill and Andrew Leigh found, the law drastically cut down the number of gun suicides, too.
Tough laws
Eleven years after Australia launched its tough gun control legislation, Neill, of Wilfrid Laurier University in Canada, and Leigh, then at Australian National University in Canberra, announced that the law might actually be saving lives.

Critics attacked. One petitioned Neill’s university to reprimand her. Then they came for Leigh’s e-mails. He had to hand over any that mentioned firearms or guns. Had there been anything improper — any whiff that the researchers were biased — Neill believes gun advocates would have pounced.

Neill and Leigh, now an Australian politician, had uncovered telling changes in different regions’ suicide rates between 1990–1995 and 1998–2003. “Firearms suicides fell most in Tasmania, by a long shot,” Neill says, almost 70 percent, the team later reported in 2010 in the American Law and Economics Review.

Australia’s law, called the National Firearms Agreement, or NFA, applied to all of the country’s states and territories, but some had more guns than others. Tasmania, for example, had the most guns bought back, Neill says: 7,302 guns per 100,000 people. More guns bought back meant bigger drops in suicide rates, she says.
Instead, the United States goes for smaller laws, fashioned mostly state-by-state. Still, some may be effective. Blocking domestic violence offenders’ access to guns seems to cut down on homicides, for example. From 1982 to 2002, states with restraining order laws that bar offenders from buying guns had rates of intimate partner homicide that were 10 percent lower than in states lacking the laws, researchers reported in 2006 in Evaluation Review.It’s a stark result, and suggests that tough laws can have big impacts. Australia “did an outright ban and something akin to a confiscation of guns,” Webster says. “That’s never going to happen in the United States.”

In 2010, Webster and colleagues reported similar results at the city level. He and colleagues tracked intimate partner homicides from 1979 to 2003 in 46 U.S. cities. Those that made it hard for people with domestic violence restraining orders to get guns had 19 percent fewer intimate partner homicides compared with cities with less stringent laws, the team reported in Injury Prevention.

“These are pretty consistent findings,” Webster says. Those state policies seem to be working.

Conclusions about other, more well-known laws, such as “right-to-carry,” are less convincing. Such laws, which allow people to carry concealed handguns in public, could offer people a means of defense. Or they could make it easier for people in an argument to whip out a gun.
“The findings are all over the map,” Hemenway says. A report from the National Research Council in 2005 found no causal link between right-to-carry laws and crime. It also concluded that people do use guns to protect themselves (say, by threatening or shooting an attacker) but how often is hard to say. Estimates vary from 100,000 to 2.5 million times per year in the United States.

Economist Mark Gius of Quinnipiac University in Hamden, Conn., estimated that restricting people’s right to carry boosts a state’s murder rate by 10 percent, he reported in 2014 in Applied Economics Letters.

Donohue’s 2014 results lean a different way. The Stanford researcher updated the NRC analysis with more than a decade of new data and found that laws letting people carry concealed weapons boost violent crime — a bit. Based on data from 1979 to 2012, his statistical modeling showed that a state with a right-to-carry law would experience 8 percent more aggravated assaults than a state without such a law, for example.

“More and more evidence is amassing that these laws are harmful,” Donohue says, but he concedes that there’s still uncertainty. “I’m not quite ready to say that we’ve nailed it down.”

Less uncertainty would require more analyses and more data. But in this field, even that doesn’t guarantee consensus.

“The problem is that there are many ways to slice the data,” Donohue says. “Almost nothing is as clear as the advocates make it — on both sides.”

Remnants from Earth’s birth linger 4.5 billion years later

Shaken-but-not-stirred remnants of Earth’s earliest years still exist nearly 4.6 billion years later.

Researchers traced the shadowy footprints of an isotope that hasn’t existed for over 4.5 billion years to much younger lava rocks from the Pacific and Atlantic oceans. That suggests that reservoirs of the ancient mantle may be hidden deep inside the planet, geochemist Hanika Rizo and colleagues report May 13 in Science.

Earth formed about 4.6 billion to 4.5 billion years ago as planetary bodies collided, disintegrating and melting to accrete into one mass like a hot, rocky lint ball. Geologists have assumed that any relics of this bumpy beginning were mixed beyond recognition.
Instead, Rizo’s team found a surprise: Some modern flood basalts have unusually high concentrations of tungsten-182. That’s significant because that isotope forms only from radioactive decay of hafnium-182. And hafnium-182 only existed during Earth’s first 50 million years. “These isotopes had to be created early,” says Rizo, of the University of Quebec in Montreal.
It is “spectacular” that some of Earth’s earliest materials may still be preserved, says Matthias Willbold, a geochemist at the University of Manchester in England. “We may have to revise our view of the Earth’s internal structure.”

Rizo and colleagues measured the tungsten-182 in flood basalts from two locations: Canada’s Baffin Bay, part of the 60-million-year-old North Atlantic Igneous Province, and near the Solomon Islands, part of the 120-million-year-old Ontong Java Plateau in the Pacific Ocean. “Flood basalts are not normal eruptions,” Rizo says. “They are capable of tapping into the deep mantle.”
Her team found that levels of tungsten-182 in the lavas varied, suggesting that the deep sources of these younger rocks were different pieces of Earth’s oldest material, each with their own isotopic signature and history. These results also show that the ancient remnants have somehow escaped being mixed by convection currents.

Geophysicists have identified two large “blobs” in the deep mantle, called large low-shear velocity provinces. Those blobs “could be candidates” for the remnants of the ancient mantle, Rizo says.

Scientists find way to break through bad bacteria’s defenses

What builds up can also tear down, a new study of bacteria suggests.

Bacteria build biofilms, communities of the microorganisms encased in a protective goo that shields the microbes from antibiotics and immune system attacks. But the very enzymes bacteria use to construct that shield can also destroy some of its molecules and strip away the protection, researchers report May 20 in Science Advances.

“We’re weaponizing the bacteria against themselves,” says P. Lynne Howell, a structural microbiologist at the Hospital for Sick Children in Toronto. Howell and colleagues studied Pseudomonas aeruginosa bacteria, which can cause pneumonia and other infections and is particularly problematic for people with the lung disease cystic fibrosis.
The researchers discovered that two enzymes, PelAh and PslGh, which the bacteria use to build two different sugar polymers, can degrade those same polymers. That delete function, supplied by parts of the enzymes known as glycoside hydrolase domains, normally helps correct mistakes or prevents buildup of the sugar chains inside bacterial cells, Howell says.

In laboratory tests, synthetic versions of the glycoside hydrolase domains applied to P. aeruginosa cultures stopped the bacteria from forming new biofilms and melted existing ones. Stripping away sugar polymers did not kill the bacteria but did make them more vulnerable to antibiotics and immune cells. Human lung cells grown in dishes containing the enzymes suffered no harm, suggesting the enzymes wouldn’t damage human tissues.

Animal tests are needed to determine whether the enzymes are safe and can fight biofilm infections in the body, Howell says. Similar enzymes from other bacteria and fungi may also fight biofilm infections caused by those organisms, she says.

Pandas have ultrasonic hearing

Giant pandas have better ears than people — and polar bears. Pandas can hear surprisingly high frequencies, conservation biologist Megan Owen of the San Diego Zoo and colleagues report in the April Global Ecology and Conservation.

The scientists played a range of tones for five zoo pandas trained to nose a target in response to sound. Training, which took three to six months for each animal, demanded serious focus and patience, says Owen, who called the effort “a lot to ask of a bear.”

Both males and females heard into the range of a “silent” ultrasonic dog whistle. Polar bears, the only other bears scientists have tested, are less sensitive to sounds at or above 14 kilohertz. Researchers still don’t know why pandas have ultrasonic hearing. The bears are a vocal bunch, but their chirps and other calls have never been recorded at ultrasonic levels, Owen says. Great hearing may be a holdover from the bears’ ancient past.

A third of the population can’t see the Milky Way at night

At night, a river of stars cuts through the dense darkness of space. These celestial bodies form our galaxy’s core and their soft glow earned our galaxy the moniker “Milky Way.” But for more than a third of Earth’s population, the glare of artificial lights conceals this cosmic wonder from view, researchers report June 10 in Science Advances. Nearly 80 percent of North Americans and 60 percent of Europeans can no longer see the galactic core at night, the researchers estimate.

Using a combination of satellite measurements and on-the-ground observations, the researchers assembled the first global atlas of artificial sky luminance, recording light pollution from everything from streetlamps to spotlights. Nearly four in five people worldwide live under light-polluted skies, the atlas reveals. Singapore boasts the brightest nights, the team found, with skies so luminous that no one living there can fully adapt to night vision. Nights are darkest in Chad, the Central African Republic and Madagascar, where more than three-quarters of inhabitants can gaze up at the stars under pristine viewing conditions.
Bright nights aren’t just an eyesore for stargazers. Artificial lights can disrupt wildlife by, for example, confounding sex-seeking fireflies (SN Online: 8/12/15) and misguiding moths (SN: 6/13/15, p. 9).