In a chorus of indris, young males vie for the spotlight, riffing in alternation rather than singing in unison. Not content to be the Joey Fatone of the group, these guys strive for Justin Timberlake status.

Indris (Indri indri), the only singing lemur species, begin their songs with roars that descend into long, phrased howls. These choirs are composed of males and females, with one dominant pair. Marco Gamba of the University of Turin in Italy and his colleagues wanted to analyze variation among individual singers.

Listening to 496 indri songs recorded over 10 years in the dense forests of Madagascar, the team found that pitch varies between males and females. And indri groups typically sing in synchrony, amplifying their tunes and vocally marking their territory to other groups. When one singer starts to croon, the others join in and match rhythm.

Solos are rare, but young male singers tend to sing out of sync — probably to stand out and advertise their masculinity, Gamba and his colleagues propose June 14 in Frontiers in Neuroscience.

There are degrees of slothfulness, it turns out, even when it comes to sloths. And three-toed sloths may be the most slothful of them all: A species of the animal has a field metabolic rate that is the lowest ever recorded for any mammal in the world.

Jonathan Pauli, an ecologist at the University of Wisconsin-Madison, got interested in sloths not because they’re adorable but because “other things eat them,” he says. And he stayed interested in the animals because they are “biologically fascinating.”

Sloths are a type of arboreal folivore, a group that includes all animals that live in trees and eat only leaves. What most people lump into the category of “sloth” are really six species in two families (two-toed and three-toed) separated by millions of years of evolution. Both families live in trees in Central and South America and eat leaves, but three-toed sloths tend to have smaller ranges and more constricted diets, eating from only a few species of trees and only a limited number of them. Studies have also shown that these sloths have a very slow metabolic rate.

But how slow? To find out, Pauli and his colleagues captured 10 brown-throated three-toed sloths (Bradypus variegatus) and 12 Hoffmann’s two-toed sloths (Choloepus hoffmanni) from a study site in northeastern Costa Rica. There, the sloths live among a variety of habitat types, ranging from pristine forest to cacao agroforest to monocultures of banana and pineapple. “It’s really a quilt of different habitat types,” Pauli says, and one that allows the researchers to not only study many habitats at once but also more easily capture and track sloths than if they were in dense jungle.

The researchers injected the sloths with water labeled with isotopes of oxygen and hydrogen and released the animals, tracking them with radiotelemetry. After a week to a week and a half, the scientists again captured the sloths and took blood samples. By seeing how much of the oxygen and hydrogen isotopes remained, the scientists could calculate the sloths’ field metabolic rate — the energy that an organism uses throughout the day.

The field metabolic rate for the three-toed sloths was 31 percent lower than that of two-toed sloths and lower than that found in any mammal outside of hibernation, the researchers report May 25 in the American Naturalist.

“There seems to be kind of a cool combination of behavior and physiological characteristics that lead to these tremendous cost savings for three-toed sloths,” Pauli says. Three-toed sloths spend a lot of time in the canopy eating and sleeping, he notes. “They don’t do a lot of movement, whereas two-toed sloths are much more mobile. They’re moving around a lot more.”

But it’s more than just that. “Three-toed sloths have the capacity to fluctuate their body temperature,” he says. Unlike humans, who need to keep their temperature within a few degrees to function properly, the sloths can let theirs rise and fall with the ambient temperature, a bit like how a lizard or snake might regulate its body temperature. “Those are big cost savings to let your body change with your surroundings.”

The results of the study help explain why there aren’t more kinds of sloths and other arboreal folivores, Pauli and his colleagues argue. “Being an arboreal folivore is really tough living,” Pauli says. Leaf eaters tend to be big because they need to accommodate a large digestive system capable of processing all the leaf matter they need to survive. But to live in the trees, an animal can’t be too big. And this could be why arboreal folivory is one of the world’s rarest lifestyles. The need for all the various adaptations for that lifestyle could prevent the rapid diversification seen among other groups, such as Darwin’s finches.

Fierce combat erupted in February 2016 at the northern Iraqi village of Kudilah. A Western-backed coalition of Arab Sunni tribesmen, Kurds in the Iraqi army and Kurdish government forces advanced on Islamic State fighters who had taken over the dusty outpost.

Islamic State combatants, led by young men wearing explosive vests, fought back. The well-trained warriors scurried through battle lines until they reached their enemy. Then they blew themselves up along with a few coalition soldiers, setting the stage for an Islamic State victory. These suicide bombers are called inghamasi, meaning “those who dive in deep.”
The inghamasi’s determination and self-sacrifice inspires their comrades to fight to the death, says anthropologist Scott Atran of the University of Michigan in Ann Arbor. Outnumbered about 6-to-1, Islamic State fighters still retained control of Kudilah after two days of heavy fighting. Coalition forces retreated, unwilling to lose more soldiers.

Atran and colleagues arrived in northern Iraq a couple of weeks later. Their plan: study “the will to fight” among soldiers on both sides of the Kudilah clash, even as fighting in the area continued. Their goals: try to understand what motivates people to join brutal organizations such as the Islamic State, and describe the personal transformations that push people leading comfortable, peaceable lives to commit acts of incredible violence and self-destruction.

Atran wondered whether there were common individual traits that explain the fierce devotion held by fighters for the Islamic State (also known as ISIS, ISIL or Daesh) as well as troops trying to take down ISIS. Scientists typically treat extreme sacrifice for others as premised on a careful weighing of pros and cons by “rational actors” who behave in a way that best satisfies their own interests even if others benefit as well. But it’s hard to see how a “what’s in it for me” formula applies to inghamasi, Atran says, much less someone who operates in a more conventionally altruistic way, such as a Navy SEAL. It’s a mistake to write off ISIS fighters as lonely losers, each seeking death as a gateway to a heavenly rendezvous with a private stock of virgins, he contends.
To break out of the rational-actor rut, Atran shifted his experimental focus nearly a decade ago to examine cherished values that mobilize people to take collective action, regardless of risks or rewards. In the last several years, he has moved his studies to the field, to focus on combatants in current conflicts and their sympathizers. And he’s finding that extreme personal sacrifices made for outfits such as the Islamic State can be understood, but only by accounting for values he describes as “sacred” and by tracking the way in which individuals identify with like-minded comrades.

Collective identity
Academics who study warfare and terrorism typically don’t conduct research just kilometers from the front lines of battle. But taking the laboratory to the fight is crucial for figuring out what impels people to make the ultimate sacrifice to, for example, impose Islamic law on others, says Atran, who is affiliated with the National Center for Scientific Research in Paris.

Atran’s war zone research over the last few years, and interviews during the last decade with members of various groups engaged in militant jihad (or holy war in the name of Islamic law), give him a gritty perspective on this issue. He rejects popular assumptions that people frequently join up, fight and die for terrorist groups due to mental problems, poverty, brainwashing or savvy recruitment efforts by jihadist organizations.

Instead, he argues, young people adrift in a globalized world find their own way to ISIS, looking to don a social identity that gives their lives significance. Groups of dissatisfied young adult friends around the world — often with little knowledge of Islam but yearning for lives of profound meaning and glory — typically choose to become volunteers in the Islamic State army in Syria and Iraq, Atran contends. Many of these individuals connect via the internet and social media to form a global community of alienated youth seeking heroic sacrifice, he proposes.

Preliminary experimental evidence suggests that not only global terrorism, but also festering state and ethnic conflicts, revolutions and even human rights movements —  think of the U.S. civil rights movement in the 1960s — depend on what Atran refers to as devoted actors. These individuals, he argues, will sacrifice themselves, their families and anyone or anything else when a volatile mix of conditions are in play. First, devoted actors adopt values they regard as sacred and nonnegotiable, to be defended at all costs. Then, when they join a like-minded group of nonkin that feels like a family — a band of brothers — a collective sense of invincibility and special destiny overwhelms feelings of individuality. As members of a tightly bound group that perceives its sacred values under attack, devoted actors will kill and die for each other.

His team’s studies of devoted actors may help to explain why a growing number of people from around the world are leaving their families and home nations to join ISIS. Congressional and United Nations reports suggest that by October 2015, nearly 30,000 recruits from more than 100 countries had become fighters in Syria and Iraq, primarily for the Islamic State.

“The rise of the Islamic State is a revolutionary movement of historic proportions,” Atran says. “Many of its members are devoted actors with an apocalyptic belief that they must destroy the world to save it.” That uncompromising vision feeds off the promise of a global caliphate — a joint political and Islamic entity that kills or controls nonbelievers — that will bring on the end of the world and replace it with God’s true kingdom. Volunteers to that cause have participated in more than 50 terror attacks in 20 countries since June 2014. Muslim militants carried out 450 suicide bombing attacks in 2015, with 174 attributed to the Islamic State.

Atran’s research may provide a rare tool to study soldiers’ will to fight, whether or not they’re Islamic State adherents, says psychologist and terrorism researcher John Horgan of Georgia State University in Atlanta. Too many investigators have dismissed those deemed to be terrorists “as either incomprehensible or not even worthy of understanding,” Horgan says.

At the time of the Kudilah battle, the Islamic State controlled hundreds of thousands of square kilometers in the Middle East. It had successfully defended a 3,000-kilometer-long military front stretching from Iraq to Syria against multi-national forces. It’s certainly possible to destroy the Islamic State with overwhelming military might, Atran says, but that approach would come at a price. It would leave a fragmented Sunni Muslim world, from which the Islamic State arose, as well as a global pool of passionate young men and women seeking liberation through sacrifice and martyrdom. A military takedown alone might trigger “a volcanic resurgence of rebels with a cause, even readier for doomsday,” he predicts.

Sacred apocalyptic values are best opposed by the spread of deeply held, life- and freedom-affirming values that supporters are willing to defend unconditionally, Atran argues. The Kurds have had success with this approach.

Sacred kin
In the Middle East, only Kurdish people living in northern Iraq have consistently held off Islamic State attacks. The Kurds, Atran finds, display a will to fight equal to that of captured Islamic State fighters. As important as guns and other material support are to a military operation, an indomitable will to fight may be even more crucial, he says. Both the Islamic State and the Kurdish army have achieved considerable military success without all the hardware of Western armies.

At Kudilah, Kurdish soldiers showed their mettle in a fierce clash. Several of these men later described the event to Atran. As Iraqi army units withdrew, Islamic State forces rapidly pushed forward. A small company of Kurds stood their ground. After the fight raged for several hours, Iraqi army reinforcements arrived, enabling the Kurds to live to fight another day.

Atran’s team interviewed 28 Kurdish soldiers plus 10 Kurds who provided supplies, medical care and other frontline assistance. Seven Islamic State fighters, six of them prisoners, also agreed to be interviewed. One had been freed and changed sides, working with groups opposed to the Islamic State.

Among the 38 Kurdish volunteers, 22 reported devotion to a homeland of “Kurdistan” as a sacred value that they would fight and die for, even overriding family ties and their Islamic religion, Atran reports in the June Current Anthropology. All but one of the 22 reported feeling a collective bond, or what Atran calls identity fusion, with the Kurdish people.

Captured ISIS members reported visceral, family-like bonds with their fellow fighters. All Islamic State prisoners cited an absolute commitment to an imposition of Islamic law, or Sharia, on nonbelievers.

Investigators measured identity fusion by presenting participants with touch-screen computer tablets showing a small circle labeled “me” and a large circle with a group label, such as “Kurds” or “family.” To represent their relationship to a particular group, individuals could move the circles together so that they partly or completely overlapped. Those who moved the small circle inside the large circle were regarded as fully fused with that group.
Atran adopted this test from ongoing research initiated nearly a decade ago by psychologist William Swann of the University of Texas at Austin. An international team led by social anthropologist Harvey Whitehouse of the University of Oxford, including Swann, studied Libyan men who tried to overthrow their government in 2011. The researchers found that nearly all the men reported intense, family-like bonds with fellow combatants. Revolutionary leaders granted the researchers access to 42 Libyan soldiers and 137 support personnel, including mechanics and ambulance drivers, as hostilities wound down in late 2011.

On the overlapping circles test, 45 percent of fighters reported being more strongly bonded to their battalions of three to five comrades than to their families, the researchers reported in 2014 in the Proceedings of the National Academy of Sciences. A smaller portion of support personnel, 28 percent, identified more with revolutionary battalions than with their families. That’s consistent with the idea that frontline fighters most often bond tightly to their units, upping their readiness to give their lives for comrades.

Libyan soldiers who felt intense connections to their battalions probably qualified as devoted actors, says psychologist Hammad Sheikh of the New School for Social Research in New York City, who was not involved in Whitehouse’s study. The soldiers’ commitment to the revolution’s goals probably transcended even family loyalties, Sheikh suspects. He bases that opinion on Atran’s findings. Whitehouse’s team did not try to identify devoted actors among Libyan fighters.

People willing to sacrifice everything in defense of the Islamic State’s sacred values also exist outside of the war zone. Among 260 Moroccans who lived in either of two city neighborhoods known as pro-ISIS hotbeds, testing indicated that about 30 percent were devoted actors. They described the imposition of Sharia as a nonnegotiable necessity, Sheikh and his colleagues, including Atran, report in a second paper in the June Current Anthropology.

On the overlapping circles test, devoted actors in Morocco depicted especially close bonds with family-like groups of friends, ranging from Islamic State supporters to soccer buddies.
Western weakness
Such dedication to collective values may be tougher to come by in Western nations. Online testing of 644 people in Spain identified only 12 percent as devoted actors willing to sacrifice all for democracy, even after being reminded of threats by ISIS and Al Qaeda. Frequent corruption scandals have left many Spaniards disillusioned with democracy, Sheikh says. Whether a similarly weak devotion to democratic values applies to citizens of other European countries or the United States remains to be tested.

Field research suggests that collective commitments to democratic values may be weaker in the West. When devoted actors among Islamic State fighters, Kurds and members of a Kurdish-speaking religious community known as Yazidis were given a hypothetical choice between abandoning their sacred values if others in their group do, or leaving the group to fight on for their sacred values, they nearly always opted to fight on for their values, Atran says.

Devoted actors in Spain, however, typically say they’d follow their group if it rejected democratic values. People in France and Spain tested by Atran’s team also rate their own society’s “spiritual force,” or the strength of collective beliefs and commitments, as much weaker than that of ISIS.

Among U.S., British and former Soviet soldiers, there have long been indications from interviews, field reports and personal letters of a stronger willingness to die for close comrades in war than in defense of broader values, Atran says. Historical evidence, however, suggests that certain relentless fighters, including Nazi troops during World War II and Viet Cong soldiers in the Vietnam War, were devoted actors inspired by beliefs in a higher cause, he says, adding that the same may have been true for soldiers on both sides of the U.S. Civil War.
Sacrificial appeal
Atran and his colleagues now have their own cause: describing more fully how some people go from holding extreme beliefs on the sidelines to becoming devoted actors at the front lines of extreme movements.

It would help, says political psychologist Clark McCauley of Bryn Mawr College in Pennsylvania, if researchers could clarify what counts as a sacred value and why some sacred values outweigh others. Identity fusion is also a tricky concept to pin down, McCauley says. Further research needs to determine whether a person who moves a “me” circle inside a circle representing a fighting unit still feels a sense of individuality or totally buys into a collective identity, he suggests.

Only by venturing into war zones can researchers begin to understand the will to fight on all sides, from the perspectives of the fighters themselves, Atran argues. It’s daunting work. He has seen ISIS fighters advancing on an Iraqi army outpost, then detonating their explosive vests in the ultimate show of commitment to their cause. He has spoken to Kurdish veterans missing arms or legs and men who had joined the Kurdish army back in the 1950s, all of them now fighting at the front to defend their homeland.

A young Yazidi fighter told Atran that he used vacation time from college to train for a week with Kurdish Marxists in Syria to defend his Kurdish religious community against the Islamic State. Fighting with a few comrades in August 2014, the student-soldier fended off ISIS attackers long enough for reinforcements to arrive. He helped save thousands of Yazidis from slaughter. The young man then returned to his studies. He wanted to be an archaeologist.

“You learn more in five minutes in the field than in five years of analysis from afar,” Atran says.

Despite careful planning, Atran’s team sometimes gets distressingly close to warring parties while conducting research in Iraq. It’s an unavoidable risk but not a deal breaker for the researchers. “There’s something so compelling,” he says, “about trying to figure out humans in extreme circumstances such as war.”
This article appears in the July 9, 2016, issue of Science News under the headline “Deadly devotion: New studies explore why ordinary people turn terrorist.”

There’s an osprey nest just outside Jeffrey Brodeur’s office at the Woods Hole Oceanographic Institution in Massachusetts. “I literally turn to my left and they’re right there,” says Brodeur, the organization’s communications and outreach specialist. WHOI started live-streaming the osprey nest in 2005.

For the first few years, few people really noticed. All that changed in 2014. An osprey pair had taken up residence and produced two chicks. But the mother began to attack her own offspring. Brodeur began getting e-mails complaining about “momzilla.” And that was just the beginning.

“We became this trainwreck of an osprey nest,” he says. In the summer of 2015, the osprey family tried again. This time, they suffered food shortages. The camera received an avalanche of attention, complaints and e-mails protesting the institute’s lack of intervention. One scolded, “it is absolutely disgusting that you will not take those chicks away from that demented witch of a parent!!!!! Instead you let them be constantly abused and go without [sic] food. Yes this is nature but you have a choice to help or not. This is totally unacceptable. She should be done away with so not to abuse again.” By mid-2015, Brodeur began to receive threats. “People were saying ‘we’re gonna come help them if you don’t,’” he recalls.

The osprey cam was turned off, and remains off to this day. Brodeur says he’s always wondered why people had such strong feelings about a bird’s parenting skills.

Why do people spend so much time and emotion attempting to apply their own moral sense to an animal’s actions? The answer lies in the human capacity for empathy — one of the qualities that helps us along as a social species.

When we are confronted with another person — say, someone in pain — our brains respond not just by observing, but by copying the experience. “Empathy results in emotion sharing,” explains Claus Lamm, a social cognitive neuroscientist at the University of Vienna in Austria. “I don’t just know what you are feeling, I create an emotion in myself. This emotion makes connections to situations when I was in that emotional state myself.”

Lamm and his colleagues showed that viewing someone in pain activates certain brain areas such as the insula, anterior cingulate cortex and medial cingulate cortex, regions that are active when we ourselves are in pain. “They allow us to have this first person experience of the pain of the other person,” Lamm explains.
When participants viewed someone reacting as though they were in pain to a stimulus that wasn’t painful for the viewer, the participants showed activity in the frontal cortex in areas important for distinction between “self” and “other.” We can still sympathize with someone else’s pain, even if we don’t know what it feels like, Lamm and his colleagues reported in 2010 in the Journal of Cognitive Neuroscience.

This works for animals, too: We ascribe certain emotions or feelings to animals based on their actions. “You know you have a mind, thoughts and feelings,” says Kurt Gray, a psychologist at the University of North Carolina in Chapel Hill. “You take it for granted that other people do too, but you can never really know. With animals, you can’t know for sure, so your best guess is what you would do in that situation.”

When people see an animal suffering — such as, say, a suffering osprey chick — they feel empathy. They then categorize that sufferer into a “feeler,” or a victim. But that suffering chick can’t exist in a vacuum. “When there’s a starving chick, we think, ‘oh, it’s terrible!’” Gray says. “It’s not enough for us to say nature is red in tooth and claw. There must be someone to blame for this.”
In a theory he calls dyadic completion, he explains that we think of moral situations — situations in which there is suffering — as dyads or pairs. Every victim needs a perpetrator. A sufferer with no one responsible is psychologically incomplete, and viewers will fill in a perpetrator in response. In the case of suffering osprey chicks, he notes, that perpetrator might be an uncaring osprey mom, or the camera operator who refuses to intervene in a natural process. Gray and his colleagues published their ideas on dyadic completion in 2014 in the Journal of Experimental Psychology.

Anthropomorphizing animals — whether or not it is logical or realistic — is usually pretty harmless. “It’s probably OK to say a cat is content,” says John Hadley, an ethicist at Western Sydney University in Australia. Similarly, it’s OK to say that a mother osprey is being violent when she attacks her own young. People are describing what they see in emotional terms they recognize. But this doesn’t mean that these animals should be held responsible for their actions, he says. When we judge an animal for its parenting skills, “in one sense it implies we want to hold these animals up as objects of praise or blame.” The natural tendency to ascribe emotions to animals, he says, is “only really problematic if [the emotions] are inaccurate or if they lead to some kind of ethical problem.”

People can’t put an osprey on trial for being a bad parent. But as in the case of an abandoned bison calf in Yellowstone, people do sometimes intervene — even though their actions might not be helpful. “That’s a question of ethical systems coming in to conflict,” Hadley says. “National parks apply a holistic ethic, try to let nature run its course…. But a more common-sense approach would be that you can intervene, there’s suffering you can stop and you should try and stop it.”

The feelings of pity and the desire to intervene is really all about us. “When we look at nonhuman animals and we read them as if they are humans … that might just be our being narrow and unable to imagine any creature that is not somehow a reflection of us,” says Janet Stemwedel, a philosopher at San Jose State University in California. “There’s a way in which looking at animals and reading them as human and imagining them as having emotions and inner lives is maybe a gateway to caring,” Stemwedel says. This caring might be erring on the side of caution, she explains, “acknowledging the limits of what we can know about how [animals] experience the world.” If we fail to imagine what animals might be feeling, “we could do a great deal of harm, [and] put suffering in the world that doesn’t need to be there,” she notes.

Our caring for the suffering and the lonely is part of what makes us a social species. “Evolution endowed us with a moral sense because it was useful for living in groups,” Gray notes. “It’s not crazy. It’s the same impulse that leads us to protect children from child abuse, and it so happens that we extend that to osprey children.” Those anthropomorphizing impulses aren’t stupid or useless. Instead, they tell us something, not about animals, but about ourselves.

Taking a combo of HIV drugs can make unprotected sex a whole lot safer.

Antiretroviral therapy cut HIV transmission between partners to zero, researchers report July 12 in JAMA.

That doesn’t mean there’s no risk, says infectious disease researcher Alison Rodger of University College London. But for heterosexual couples with an HIV-positive member who is on therapy and has low levels of virus in the blood, “the risk is extremely low — likely negligible,” she says. That may also be true for homosexual couples, Rodger says, but her team needs more data to say for sure.
Antiretroviral therapy curbs the amount of HIV circulating in the bloodstream. Scientists knew that HIV-positive people taking this therapy were less infectious than normal, but no one had nailed down their risk of spreading the virus through condom-free, penetrative sex.

Rodger and colleagues analyzed data from 1,166 couples enrolled in an observational study to assess HIV transmission risks. All couples had reported having unprotected sex, and one member of each couple was HIV-positive and on therapy. Researchers tested the negative partner for HIV every six to 12 months.

Among 888 couples eligible for follow-up, researchers didn’t find a single case of partner-to-partner HIV transmission for about one and a half years, despite frequent unprotected sex.

ORLANDO, Fla. — Organisms as different as plants, bacteria, yeast and humans could hold genetic swap meets and come away with fully functional genes, new research suggests.

Researchers have known for decades that organisms on all parts of the evolutionary tree have many of the same genes. “How many of these shared genes are truly functionally the same thing?” wondered Aashiq Kachroo, a geneticist at the University of Texas at Austin, and colleagues. The answer, Kachroo revealed July 15 at the Allied Genetics Conference, is that about half of shared genes are interchangeable across species.
Last year, Kachroo and colleagues reported that human genes could substitute for 47 percent of yeast genes that the two species have in common (SN: 6/27/15, p. 5). Now, in unpublished experiments, the researchers have swapped yeast genes with analogous ones from Escherichia coli bacteria or with those from the plant Arabidopsis thaliana. About 60 percent of E. coli genes could stand in for their yeast counterparts, Kachroo reported. Plant swaps are ongoing, but the researchers already have evidence that plant genes can substitute for yeast genes involved in some important biological processes.

In particular, many organisms share the eight-step biochemical chain reaction that makes the molecule heme. The researchers found that all but one of yeast’s heme-producing genes could be swapped with one from E. coli or plants.

Human eyes are capable of detecting a single photon — the tiniest possible speck of light — new research suggests.

The result, published July 19 in Nature Communications, may settle the debate on the ultimate limit of the sensitivity of the human visual system, a puzzle scientists have pondered for decades. Scientists are now anticipating possibilities for using the human eye to test quantum mechanics with single photons.

Researchers also found that the human eye is more sensitive to single photons shortly after it has seen another photon. This was “an unexpected phenomenon that we just discovered when we analyzed the data,” says physicist Alipasha Vaziri of Rockefeller University in New York City.
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Previous experiments have indicated that humans can see blips of light made up of just a few photons. But there hasn’t been a surefire test of single photons, which are challenging to produce reliably. Vaziri and colleagues used a quantum optics technique called spontaneous parametric down-conversion. In this process, a high-energy photon converts into two low-energy photons inside of a crystal. One of the resulting photons is sent to someone’s eye, and one to a detector, which confirms that the photons were produced.

During the experiment, subjects watched for the dim flash of a photon, which arrived at one of two times, with both times indicated by a beep. Subjects then chose which beep they thought was associated with a photon, and how confident they were in their decision.

In 2,420 trials, participants fared just slightly better than chance overall. That seemingly unimpressive success rate is expected. Because most photons don’t make it all the way through the eye to the retina where they can be seen, in most trials, the subject wouldn’t be able to see a photon associated with either beep. But in trials where the participants indicated they were most certain of their choice, they were correct 60 percent of the time. Such a success rate would be unlikely if humans were unable to see photons — the chance of such a fluke is 0.1 percent.

“It’s not surprising that the correctness of the result might rely on the confidence,” says physicist Paul Kwiat of the University of Illinois at Urbana-Champaign, who was not involved with the research. The high-confidence trials may represent photons that made it through to the retina, Kwiat suggests.

Additionally, the data indicate that single photons may be able to prime the brain to detect more dim flashes that follow. When participants had seen another photon in the preceding 10 seconds, they had better luck picking out the photon.
Scientists hope to use the technique to test whether humans can directly observe quantum weirdness. Photons can be in two places at once, a state known as a quantum superposition. The technique could be adapted to send such quantum states to a subject’s eye. But, says Leonid Krivitsky, a physicist at the Agency for Science, Technology and Research in Singapore, “I’m pretty skeptical about this idea of observing quantumness in the brain.” The signals, he suggests, will have lost their quantum properties by the time they reach the brain.

Whether humans can see individual photons may seem to be a purely academic question. But, Vaziri says, “If you are somewhere outside of a city in nature and on a moonless night and you have only stars to navigate, on average the number of photons that get into your eye is approaching the single photon regime.” So, he says, having eyes sensitive enough to see single photons may have some evolutionary advantage.

About 20,000 kilometers beneath the sun’s surface, magnetic fields rise no faster than about 500 kilometers per hour. That speed (roughly one-third of previous estimates) is about the same speed that gas rises and falls within the sun, implying that moving parcels of gas help steer magnetic fields toward the surface, researchers report July 13 in Science Advances.

Aaron Birch of the Max Planck Institute for Solar System Research in Göttingen, Germany, and colleagues estimated the speed by combining observations of the sun’s surface with computer simulations of how gas moves within the hot orb. By studying the sun’s inner workings, researchers hope to understand what drives sunspots and flares — the blemishes and eruptions triggered by magnetic fields punching through the surface.

A new genetic discovery could equip researchers to fight a superbug by stripping it of its power rather than killing it outright.

Scientists have identified a set of genes in Clostridium difficile that turns on its production of toxins. Those toxins can damage intestinal cells, leading to diarrhea, abdominal pain and potentially life-threatening disease. Unlocking the bug’s genetic weapon-making secret could pave the way for new nonantibiotic therapies to disarm the superbug while avoiding collateral damage to other “good” gut bacteria, researchers report August 16 in mBio.
Identifying a specific set of genes that control toxin production is a big step forward, says Matthew Bogyo. Bogyo, a chemical biologist at Stanford University, also studies ways to defuse C. difficile’s toxin-making.

C. difficile bacteria infect a half million people and kill about 29,000 each year in the United States. In some individuals, though, the microbe hangs out in the gut for years without causing trouble. That’s because human intestines normally have plenty of good bacteria to keep disease-causing ones in check. However, a round of antibiotics can throw the system off balance, and if enough good bugs die off, “C. difficile takes over,” says lead author Charles Darkoh, a molecular microbiologist at the University of Texas Health Science Center at Houston. As infection rages, C. difficile can develop resistance to antibiotic drugs, turning it into an intractable superbug.

Darkoh’s team reported last year that C. difficile regulates toxin production with quorum sensing — a system that lets bacteria conserve resources and launch an attack only if their numbers reach a critical threshold. That study identified two sets of quorum-signaling genes, agr1 and agr2, that could potentially activate toxin production.

In the new analysis, Darkoh and colleagues tested the ability of a series of C. difficile strains to make toxins when incubated with human skin cells. Some C. difficile strains had either agr1 or agr2 deleted; others had all their quorum-sensing genes or lacked both gene sets. Agr1 is responsible for packing the superbug’s punch, the researchers found. C. difficile mutants without that set of genes made no detectable toxins, and skin cells growing in close quarters stayed healthy. Feeding those mutant bugs to mice caused no harm, whereas mice that swallowed normal C. difficile lost weight and developed diarrhea within days. In the skin cell cultures, agr2-deficient strains were just as lethal as normal C. difficile, showing that only agr1 is essential for toxin production.

Based on their new findings, Darkoh and colleagues have identified several compounds that inactivate C. difficile toxins or block key steps in the molecular pathway controlling their production. The researchers are testing these agents in mice.

In a mouse study published in Science Translational Medicine last year, Bogyo and colleagues found a different compound that could disarm C. difficile by targeting its toxins. And several companies are trying to fight C. difficile with probiotics — cocktails of good bacteria. Results have been mixed.

How the seafloor quivers under an intense storm called a “weather bomb” could help reveal Earth’s innermost secrets.

Using a network of seismic sensors, researchers in Japan detected a rare type of deep-Earth tremor originating from a rapidly strengthening cyclone over the North Atlantic Ocean. Tracking how these newfound shakes ripple through the globe will help geoscientists map the materials that make up the planet’s depths, the researchers report August 26 in Science.

“We’re potentially getting a suite of new seismic source locations that can be used to investigate the interior of the Earth,” says Peter Bromirski, a geophysical oceanographer at the Scripps Institution of Oceanography in La Jolla, Calif., who wrote a commentary on the new research in the same issue of Science. “Further investigations will refine our understanding of how useful these particular waves will be.”
Tremors traveling through the ground speed up, slow down or change direction depending on the type of material they pass through. Carefully measuring these movements from earthquake waves has allowed scientists to gather clues about the structure and composition of Earth’s deepest layers.

Some regions — the middle of tectonic plates under the ocean, for instance — don’t see many earthquakes, though. Luckily, weather bombs can generate their own seismicity. Whipping winds can stir up towering ocean swells. When two opposing ocean swells collide, the meet-up can send a pressure pulse down to the ocean floor. The pulse thumps the seafloor, producing seismic waves that penetrate deep into the planet.
Scientists had previously detected only one type —called P waves —of these storm-generated seismic waves. P waves cause a material to compress and stretch like an accordion in the same direction that the wave travels. The other variety, called S waves, has proved more elusive. S waves formed by storms are typically weaker than P waves and cause material to ripple perpendicular to the wave’s path. The effect is similar to when one end of a garden hose is jerked up and down, producing waves that travel along the hose’s length.
Seismologists Kiwamu Nishida of the University of Tokyo and Ryota Takagi of Tohoku University in Sendai, Japan, hunted for the elusive S waves using a network of 202 seismic stations in Japan. Typically, the waves are lost within Earth’s natural seismic background noise. By combining and analyzing the data collected by the extra-sensitive seismometers, however, the researchers were able to tease out the S wave signals.

The waves originated from a North Atlantic cyclone, the researchers found. That storm actually produced two types of S waves. SV waves shift material vertically relative to Earth’s surface and can form from P waves. SH waves shift material horizontally and their origins are more of a mystery. Those SH waves may form from complex interactions between the ocean and seafloor, Nishida says.

Combining measurements of P, SV and SH waves will “ultimately provide better maps of Earth’s mantle and maybe even the core,” says Keith Koper, a seismologist at the University of Utah in Salt Lake City. Koper and colleagues report similar observations of S waves generated in the Pacific Ocean and detected by a Chinese seismic network in the Sept. 1 Earth and Planetary Sciences Letters. “It’s nice to see someone else get similar results —it makes me feel more confident about what we observed,” Koper says.