The rift in Antarctica’s Larsen C ice shelf continues to rip. Researchers from Project MIDAS, which tracks the effects of a warming climate on the ice shelf, report that the crack grew 17 kilometers between May 25 and May 31.
The crack has now turned toward the water and is within 13 kilometers of the edge of the shelf. Within days, the crack could reach the edge. When that happens, one of the largest icebergs ever recorded will fall into the ocean.
“There appears to be very little to prevent the iceberg from breaking away completely,” the researchers write.
After calving such a massive section, the shelf won’t be stable. It may experience the same fate as Larsen B, which disintegrated in 2002, after a crack there broke off a huge chunk of ice.
A weird new particle imitator flouts the established rules of particle physics. The discovery could help scientists simulate how particles behaved just after the Big Bang or lead to the development of new devices with unusual electromagnetic properties.
The curious new phenomenon involves a particle-like entity called a quasiparticle, formed from a jostling mosh pit of electrons that collectively act like a single particle in a solid. Found in a compound of lanthanum, aluminum and germanium, the new quasiparticle is a bit of a renegade, physicist M. Zahid Hasan of Princeton University and colleagues report June 2 in Science Advances. Known as a type-II Weyl fermion, the quasiparticle breaks a rule called Lorentz symmetry, which states that the laws of physics are the same no matter the observer’s perspective, whether moving or stationary. Lorentz symmetry is the foundation of Einstein’s special theory of relativity, which details the physics of observers zipping along near the speed of light. For a real particle, violating Lorentz symmetry would be an unallowable faux pas, but for quasiparticles, the rules are looser, so type-II Weyl fermions can behave in a way a normal particle wouldn’t.
Fermions are a class of elementary particle that includes quarks, which make up protons and neutrons, and electrons. There are three different types of fermions: Dirac, Majorana and Weyl. Dirac fermions are the garden-variety type and include electrons and quarks. Majorana fermions are their own antiparticles. Neutrinos, notoriously lightweight and elusive particles, could be either Majorana or Dirac fermions; scientists aren’t yet sure which.
Weyl fermions are a massless variety of fermion. No examples have been found in particle physics. But the quasiparticle version of Weyl fermions burst onto the scene in 2015, when scientists first discovered them in a compound made of tantalum and arsenic (SN: 8/22/15, p. 11). Soon, scientists realized that their Lorentz-violating relatives, type-II Weyl fermions, might likewise pop up in solids.
In the new study, Hasan and colleagues measured the relationship between the energy and momentum of the quasiparticles, showing that they were consistent with type-II Weyl fermions. Although previous experiments have shown hints of the unusual quasiparticles, those measurements were skin-deep, assessing particles only on the surface of the material, Hasan says. With surface measurements alone, it’s hard to confirm the type-II Weyl fermions are there, says physicist Alexey Soluyanov of ETH Zurich. But Hasan and colleagues peered inside the material. “Experimentally, this work really is a nice example,” Soluyanov says.
In solids, Weyl fermions lead to unusual behavior. Put a normal material in a magnetic field, and resistance to the flow of electricity grows, but in a solid with Weyl fermions, a magnetic field makes current flow more easily. Type-II Weyl fermions are even stranger, due to their Lorentz-violating properties. In a material with these quasiparticles, a magnetic field in one direction can increase conductivity, while in another direction it can decrease conductivity. “This type of thing can have interesting applications,” says Hasan. “In a single material, just by changing the direction of the field, now we can get different behaviors,” flipping between insulating and conducting, for example. The new material could also provide insight for particle physicists. “Of course, people have wondered what happens when you break Lorentz invariance,” says physicist Adolfo Grushin of Institut Néel in Grenoble, France. Type-II Weyl fermions could help scientists better understand theories that violate the rule. “It’s a good test-bed,” says Grushin.
For example, Hasan says, “we can test theoretical ideas in the early universe,” simulating how particles may have behaved just after the Big Bang, when Lorentz symmetry may not have been obeyed.
In pumped-up sequels for scary beach movies, each predator is bigger than the last. Turns out that predators in real-world oceans may have upsized over time, too.
Attack holes in nearly 7,000 fossil shells suggest that drilling predators have outpaced their prey in evolving ever larger bodies and weapons, says paleontologist Adiël Klompmaker of the University of California, Berkeley. The ability to drill through a seashell lets predatory snails, octopuses, one-celled amoeba-like forams and other hungry beasts reach the soft meat despite prey armor. Millions of years later, CSI Paleontology can use these drill holes to test big evolutionary ideas about the power of predators. “Predators got bigger — three words!” is Klompmaker’s bullet point for the work. Over the last 450 million years or so, drill holes have grown in average size from 0.35 millimeters to 3.25 millimeters, Klompmaker and an international team report June 16 in Science. Larger holes generally mean larger attackers, the researchers say, after looking at 556 modern drillers and the size of their attack holes.
Prey changed over millennia, too, but there’s no evidence for a shift in body size. The ratio of drill-hole size to prey size became 67 times greater over time, the researchers conclude.
It’s “the rise of the bullies,” says coauthor Michal Kowalewski of the University of Florida in Gainesville.
All these data on shell holes allow researchers to test a key part of what’s called the escalation hypothesis. In 1987, Geerat Vermeij proposed a top-down view of evolutionary change, where predators, competitors and other enemies growing ever more powerful drive the biggest changes in their victims. This wasn’t so much an arms race between predators trading tit for tat with their prey as a long domination of underdogs repeatedly stomped by disproportionate menace. (Unless the prey somehow flips the relationship and can do deadly harm in return.) Vermeij, now at the University of California, Davis, and others have drawn on escalating threats to explain prey evolutionary innovations in thick shells, spines and spikes, mobility, burrowing lifestyles and toxins. One aspect of escalation scenarios has been especially hard to test: the idea that predators can become more dangerous and a stronger evolutionary force over time. Drill holes suggesting bigger, more powerful attackers allowed a rare way of exploring the idea, Klompmaker says. He now reads the deep history as showing predators escalated in size, but prey didn’t.
The energetics worked out, in large part, because early hard-shelled prey called brachiopods — a bit like clams but with one shell-half larger than the other — became scarcer over time, while clams and their fellow mollusks grew abundant. Mollusks typically have more flesh inside their shells than brachiopods, and prey overall grew denser on the ocean bottom. Killer drillers, able to dine at this buffet, could thus support bigger bodies even when prey size wasn’t rising, too.
Prey don’t make drilling easy, Klompmaker says. An hour’s work gets a typical modern predatory snail only about 0.01 to 0.02 millimeters deeper into a mollusk shell. So finally striking lunch could take days of effort with the thickest shells. And that’s with specialty equipment: A snail alternates grinding away using a hard, rasplike driller and then switching to its accessory boring organ that releases acids and enzymes, weakening the drilling spot for the next bout.
The role of such animal clashes in evolution has been notoriously difficult to study, says marine ecologist Nick Dulvy of Simon Fraser University in Burnaby, Canada. Nutrients, climate and other factors that don’t swim away into the blue are much easier to measure. Even after a robust century of ecological study, “the discoveries that otters propped up kelp forests, triggerfishes garden coral reefs, and wolves and cougars create lush diverse watersheds are comparatively recent,” Dulvy says. Until the new drill-hole study, he could think of only one earlier batch of evidence (crabs preying on mollusks) for the long rise of predators as an evolutionary force.
The story from drill holes, says Vermeij, is “very convincing.”
PORTLAND, ORE. — A great flower shape for a moth trying to get a drink in the dark turns out to be awful from the plant’s point of view.
Offering hawk moths (Manduca sexta) a range of 3-D printed flowers with different curvatures shows that a moderately curved trumpet shape lets moths sip most efficiently, Foen Peng reported June 24 at the Evolution 2017 meeting. That’s a win for a nocturnal flying insect searching for nectar. Yet drinking ease wasn’t best for the plant. During swift sips, the moths did less inadvertent bumping against the artificial flowers’ simulated sex organs than moths struggling to sip from an inconvenient shape. Less contact with real flower parts would mean less delivery and pickup of pollen.
Peng, of the University of Washington in Seattle, offered the moths three other shapes besides the gently curved trumpet. The best for the plant was a flat-topped “flower” with a right angle drop to a nectar well in the center. Previous work suggested that lack of curves made it very difficult for hawk moths hovering above a flower and extending their tonguelike proboscises to tap and probe the way to nectar in dim light.
Pollination at first glance may look like an easy mutualism evolving with the best interests of both plant and pollinator. But these experiments reveal a hidden, underlying conflict, Peng said.
Out-of-whack microbes in the vagina can raise HIV risk — and now there’s evidence that the makeup of the penis microbiome matters, too. The greater the number of anaerobic bacteria tucked under the foreskin, the more likely an uncircumcised man is to become infected with the virus, researchers report July 25 in mBio.
“This mirrors what’s been seen in women, but it’s the first study of its kind in men,” says Deborah Anderson, a microbiologist and gynecologist at Boston University School of Medicine. The data come from heterosexual Ugandan men followed for two years as part of a larger study on circumcision. Researchers swabbed the men’s penises to collect bacteria samples at the beginning of the two-year study. Then they compared the penile bacterial composition of the 46 uncircumcised men who became infected with HIV over the course of the study with that of 136 uncircumcised men who didn’t.
The total amount of penile bacteria didn’t differ, but men with higher levels of anaerobic bacteria were more likely to have contracted HIV, researchers found. Having 10 times more Prevotella, Dialister, Finegoldia and Peptoniphilus bacteria raised the risk of contracting HIV by 54 to 63 percent after controlling for other factors that might affect risk, such as condom use habits and number of sexual partners.
The results might help explain why circumcision cuts the risk of HIV, says Thomas Hope, a cell biologist at Northwestern University Feinberg School of Medicine in Chicago: Removing the flap of foreskin takes away a moist hideout for bacteria that thrive in oxygen-starved environments. But, Hope cautions, the study only draws an association between the microbiome and HIV — not necessarily a cause and effect.
It’s not clear how certain bacteria might raise HIV risk, but the new study revealed one possible clue: Men with more anaerobic penis bacteria also had higher levels of inflammatory cytokine proteins, which call immune cells to the scene.
“Specific bacteria might cause inflammatory response that would cause the immune cells to congregate in the penis, where they’re more likely to be exposed to the virus,” says study coauthor Cindy Liu, a pathologist at George Washington University in Washington, D.C. HIV targets particular immune cells, so recruiting an immune response to the penis might have an unintended consequence — a free ferry ride for the virus into the bloodstream. Liu and colleagues hope to test that explanation more thoroughly by looking at tissue samples from circumcised foreskins, and seeing whether there’s a relationship between the penis microbiome and the kinds of immune cells found in the foreskin.
Some of these same bacteria are also linked to increased HIV risk in women, and the microbes can be swapped between partners during sex. While practicing safe sex is still the best HIV-prevention strategy, topical creams that adjust the bacterial balance on the penis might someday help lower the risk of infection, Liu says.
In fishes as familiar as tunas, humans have managed to find some unknown anatomy: a hydraulic system based on lymph.
Often the underdogs of body parts, vertebrate lymph systems can do vital chores such as fight disease but rarely get the attention that blood systems do. Yet it turns out to be lymph, not blood, that rushes into two sickle-shaped tuna fins and fans them wide during complex swimming maneuvers, says Barbara Block of Stanford University. Tuna bodies are relatively “stiff and only wag at the tail,” she says. That’s efficient for long-distance cruising. For zigs and zags, Pacific bluefin and yellowfin tunas get extra control from muscles, bones and lymph tweaking the shape of a fin on the back and its counterpart underneath, Block and colleagues report in the July 21 Science.
Among other tests, the researchers injected a tuna specimen with blue liquid that highlighted a complex of channels near and within the fins. Injecting a saline solution into the channels raised or lowered the fins depending on the pressure. Immunological and other tests confirmed that it’s lymph that changes the fin shape.
Lymph shape-changing also evolved in birds — but in a different way. Lymph, not blood, inflates the penis in ducks, emus, chickens and probably other birds that have such an organ, notes Patricia Brennan of the University of Massachusetts Amherst, who studies the evolution of sexual organs. Whether a male tuna would similarly use lymph, however, is a hypothetical question: Tunas didn’t evolve a penis.
For flowers, too much light at night could lead to a pollination hangover by day.
Far from any urban street, researchers erected street lights in remote Swiss meadows to mimic the effects of artificial light pollution. In fields lit during the night, flowers had 62 percent fewer nocturnal visitors than flowers in dark meadows, researchers report August 2 in Nature.
For one of the most common flowers, daytime pollination didn’t make up for nightly losses, says ecologist Eva Knop of the University of Bern in Switzerland. In a detailed accounting of the pollination life of cabbage thistles (Cirsium oleraceum), Knop and colleagues found that night-lit plants produced 13 percent fewer seeds overall than counterparts in naturally dark places. Night lights could affect the entire network of plants and pollinators, the team suggests. In the test fields, nighttime pollination wasn’t just the business of a few kinds of specialized moth-loving plants. Flowers that fed a wide range of nighttime visitors also attracted a broad buzzing circus of different kinds of daytime pollinators. If the daytime insects don’t make up for nocturnal losses, a flower’s population might dwindle. And a lot of insects, both day and night, might then feel the loss of nectar and foliage, Knop says.
More than 80 percent of flower species get some help from animals in making seeds, and none evolved with light after sundown. “I hope people start to realize that it’s really something that changes the whole ecosystem,” Knop says. The new study is the first to show how artificial light affects plants’ ability to make seeds, she says. The test is also unusual because it considers all kinds of insect pollinators instead of focusing on, say, only night-flying moths. This big-picture view was so not easy to achieve. Finding possible dead-dark sites in highly developed Europe to set up LED lamps was impossible, so researchers worked in 14 dark-as-possible, remote meadows in land rising toward the Alps. But that created a problem. “If you don’t have light, you don’t have power,” Knop points out. To avoid generator growls and smells confounding their results, researchers painstakingly scouted sites where possible near water-powered energy sources and overall used “really long cables.” For the sites with natural night, researchers measured pollination by patrolling set paths and catching any insect wriggling on a flower — in complete darkness, of course. The team used night-vision goggles but still didn’t have a perfect view, she says. It’s “not that easy to catch insects without three-dimensional vision.”
Besides paying special attention to the commonly visited cabbage thistle, researchers pieced together the whole network of which pollinator species visited which plant species day or night. Analysis of this Matterhorn of data suggested that changes in the night crew could affect daytime meadows.
The idea that night light could have broad knock-on effects on daytime pollinators is still speculation at this point, says ecologist Darren Evans of Newcastle University in England, who also studies light pollution and pollination. But the risk of such spillover warrants more attention.
A string of state-directed, targeted mass killings left a bloody stain on the 20th century. A genocide more recent than the Holocaust is providing new insights into why some people join in such atrocities.
Adolf Hitler’s many accomplices in his campaign to exterminate Jews throughout Europe have justifiably attracted the attention of historians and social scientists. But a 100-day spasm of unprecedented violence in 1994 that wiped out about three-quarters of the ethnic Tutsi population in the African nation of Rwanda has the potential to reveal much about how mass killings unfold at ground level. There is no guarantee that a better, although inevitably incomplete, understanding of why certain members of Rwanda’s majority Hutu population nearly eliminated a Tutsi minority will prevent future large-scale slaughters. The research is worth the effort, though, especially in a 21st century already marked by massacres of hundreds of thousands of people in western Sudan’s Darfur region and in Syria.
Researchers have an advantage in Rwanda. When hostilities ended, Rwanda’s government gathered extensive data on genocide victims and suspected perpetrators through a national survey. And local courts tried more than 1 million cases of alleged involvement in the violence, making the case documents available to researchers.
Genocide studies have often split offenders into organizers — mainly political and community leaders — and “ordinary men” who kill out of blind obedience to central or local authorities and hatred of those deemed enemies. But the extensive data from Rwanda tell a different story: An individual’s willingness to take part in genocidal violence depends on many personal and social factors that influence whether and how deeply a person participates, says sociologist and Rwanda genocide researcher Hollie Nyseth Brehm of Ohio State University in Columbus.
Nyseth Brehm’s findings may not apply to some of Rwanda’s most avid killers, who eluded capture and fled the country as soon as hostilities stopped. But when it comes to the ordinary citizens swept up in the deadly campaign, involvement was not primarily about following political leaders’ orders to eliminate Tutsis.
New reports by Nyseth Brehm and others fuel skepticism about the popular idea that regular folks tend to do as they’re told by authorities. And a fresh look at a famous 1960s psychology study adds further doubt that people will blindly follow orders to harm or kill others. In reality, only about 20 percent of Hutu men, an estimated 200,000, seriously injured or killed at least one person during the genocidal outbreak, estimates Rwanda genocide researcher Omar McDoom of the London School of Economics and Political Science.
“Why did four in five Hutu men not engage in the killing?” McDoom asks. That puzzle goes against the ordinary man thesis that “implies there are no individual differences in genocide participation,” he says. He suspects participation hinged on personal motivations, such as wanting to defend Rwanda from enemies or make off with a Tutsi neighbor’s possessions. Social circumstances, such as living in high-violence areas or having friends or family members who had already murdered Tutsis, probably played a role too. Nyseth Brehm agrees.
Local triggers Genocides often fester before exploding. In Rwanda, Tutsi rebels attacked the Hutu-led government and set off a civil war several years before mass killings started. A turning point came when unidentified forces killed Rwanda’s president, shooting down his plane on April 6, 1994. Over the next three months, the government orchestrated a massacre of Tutsis and any Hutus deemed friendly or helpful to Tutsis. Most scholars place the death toll at around 800,000, although estimates range from 500,000 to 1.2 million. Bands of Hutus scoured the countryside for their sworn enemies. Killings took place at roadblocks and in raids on churches, schools and other community facilities. Hutu women killed on a much smaller scale than men did, although they often aided those involved in the carnage.
In many parts of Rwanda, local authorities appointed by the national government recruited Hutu men into groups that burned and looted homes of their Tutsi neighbors, killing everyone they encountered, says political scientist Scott Straus of the University of Wisconsin–Madison. In his 2016 book Fundamentals of Genocide and Mass Atrocity Prevention, Straus describes how Rwandan recruitment efforts coalesced into a killing machine. Politicians, business people, soldiers and others encouraged Hutu farmers to kill an enemy described as “cockroaches” in need of extermination. Similarly, Nazis portrayed Jews as cockroaches and vermin.
Despite the Rwandan state’s best efforts to encourage nationwide Tutsi annihilation, local conditions shaped how the 1994 genocide unfolded, Nyseth Brehm reported in February in Criminology. She looked at 142 of the nation’s 145 municipalities, known as communes. Some experienced as few as 71 killings, while in others, as many as 54,700 people were murdered, she found.
Communes with the fewest killings were those that had the highest marriage and employment rates, Nyseth Brehm says. In those settings, mainly farming communities where people knew and trusted each other, most citizens valued a peaceful status quo and discouraged a descent into mass killing, she suspects. Curiously, violence was worse in areas with the largest numbers of educated people. That points to the effectiveness of anti-Tutsi teachings in Rwandan schools, Nyseth Brehm suggests.
Her study relied on data from a postgenocide survey, published in 2004 by Rwanda’s government, intended to document every person killed during the atrocity. Citizens throughout Rwanda told interviewers about individuals in their communities who had been killed during the outburst of slaughter. Reported and confirmed deaths were checked against records of human remains linked to the 1994 genocide. Comparisons were also made to Rwanda’s 1991 census.
However, any data on killings during mass violence, including from the Rwandan survey, will be incomplete, Nyseth Brehm cautions. So she also analyzed data from 1,068,192 genocide-related cases tried in local Rwandan courts from 2002 to 2012. Of particular note, although most nongenocidal murders in Rwanda are carried out by men in their 20s, the average age of accused genocide perpetrators was 34.7 years old, Nyseth Brehm reported in the November 2016 Criminology.
Hutu men in their 30s joined the genocidal fray as a way to fulfill adult duties by defending their communities against an outside threat, she suggests. Preliminary analyses show that perpetrators tended to cluster in families; if one of several brothers killed Tutsis, the others were far more likely to follow suit.
Additional scouring of court data indicated that Rwandans who had siblings convicted of genocide killings were especially likely to have murdered Tutsis themselves. In earlier interviews of 130 Rwandans, some who had killed Tutsis and others who hadn’t, McDoom similarly found that perpetrators tended to cluster in families.
Missing murderers Unfortunately, the Rwandan genocide’s most prolific players have eluded both the law and science, says political scientist Cyanne Loyle of Indiana University Bloomington. Investigators have so far interviewed only a handful of the powerful “big fish” who orchestrated the genocide, plus several hundred people tried and imprisoned for genocide participation. Survey and court data are limited to killers who either stayed in Rwanda after atrocities ended or were caught trying to flee the country.
But perpetrators with the most blood on their hands traveled in bands, wiping out tens of thousands of people at a time before hiding abroad, Loyle says. For instance, local officials lured large numbers of Tutsis to a school near the town of Murambi, where Hutu militias used machine guns, explosives and other weapons to kill more than 40,000 people in just three days.
“Scholars have studied Rwandans who killed on the sidelines while a larger and deadlier campaign was under way,” Loyle says. “They have mistaken a sideshow for the main event.”
Perpetrators of colossal atrocities at Murambi and elsewhere were less powerful than the government’s genocide masterminds, Loyle says. These “murderers in the middle,” however, were better equipped and far more effective at killing than common folk who got caught up in events, she contends.
There are no good estimates of how many members of large-scale killing squads escaped Rwanda and now live elsewhere. From 15,000 to 22,000 members of the Rwandan army and local militia groups were at large in the Democratic Republic of the Congo, near Rwanda’s border, in January 2003, according to a report by the International Crisis Group, a nonprofit organization.
Nyseth Brehm acknowledges the difficulty of accounting for genocide perpetrators who eluded justice. She and others, including Straus, have interviewed genocide offenders who stayed in Rwanda, often imprisoned for their crimes. Many of those who fled must have traveled in groups that murdered on a grand scale, she says. Those mass killers represent crucial missing data on who participates in genocide, and for what reasons. Vicious virtue In interviews by Nyseth Brehm, McDoom and others, perpetrators listed many reasons for joining the 1994 killing spree — hatred of Tutsis, a perceived need to protect nation and family, a desire to claim a neighbor’s property or a decision to join a suddenly popular cause, to name a few. Blind obedience to brutal leaders was far from the only reason cited.
That finding conflicts with the late psychologist Stanley Milgram’s interpretation of his famous “obedience to authority” experiments. Milgram described those trials, in which volunteers were told to administer increasingly intense shocks to another person, as a demonstration of people’s frequent willingness to follow heinous commands. He saw the experiments as approximating the more extreme situations in which Germans had participated in the Holocaust. On closer inspection, though, Milgram’s study aligns closely with what’s known about Rwandan genocide perpetrators, says S. Alexander Haslam, a psychologist at the University of Queensland in Australia. In Milgram’s experiments, as in Rwanda and Nazi Germany, “those willing to harm others were not so much passive ciphers as motivated instruments of a collective cause,” Haslam says. “They perceived themselves as acting virtuously and doing good things.”
Although Milgram’s tests upset some volunteers, most participants identified with his scientific mission to understand human behavior and wanted to prove themselves as worthy of the project, Haslam and psychologist Stephen Reicher of the University of St. Andrews in Fife, Scotland, conclude in a research review scheduled to appear in the 2017 Annual Review of Law and Social Science.
Milgram conducted 23 obedience experiments with New Haven, Conn., residents in 1961 and 1962 (SN: 9/21/13, p. 30). Most attention has focused on only one of those experiments. Volunteers designated as “teachers” were asked by an experimenter to continue upping the intensity of what they thought were electric shocks to a “learner” — who was actually in league with Milgram — who erred time and again on a word-recall test. Through screams, shouts and eventually dead silence from the learner, 26 of 40 volunteers, or 65 percent, administered shocks all the way to a maximum of 450 volts.
But experiments that undermined participants’ identification with the scientific mission lowered their willingness to deliver the harshest shocks, Haslam and Reicher say. Fewer volunteers shocked to the bitter end if, for instance, the study was conducted in an office building rather than a university laboratory or if the experimenter was not physically present. An analysis of data available from 21 of the 23 experiments finds that 43.6 percent of 740 volunteers shocked learners to the limit. Participants were most compliant when an experimenter encouraged them to continue shocking for the sake of the experiment (by saying, “The experiment requires that you continue”), the psychologists add. Participants never followed the order: “You have no choice, you must continue.”
Milgram’s archives at Yale University contain letters and survey responses from former participants reporting high levels of support for Milgram’s project and for science in general. Many former volunteers told Milgram that they administered shocks out of a duty to collaborate on what they viewed as important research, even if it caused them distress at the time. Still, Milgram’s recruits often admitted having had suspicions during the experiments that learners were not really being zapped.
Milgram was right that his experiments applied to real-world genocides, Haslam concludes, but erred in assuming that obedience to authority explained his results. From Milgram’s laboratory to Rwanda’s killing squads and Nazi concentration camps, orders to harm others are carried out by motivated followers, not passive conformists, he asserts.
If anything, that makes genocide all the more horrifying.
When the Aug. 21 solar eclipse unveils the sun’s normally dim atmosphere, the corona will look like an intricate, orderly network of loops, fans and streamers. These features trace the corona’s magnetic field, which guides coronal plasma to take on the shape of tubes and sheets.
These wispy coronal structures arise from the magnetic field on the sun’s visible surface, or its photosphere. Unlike the corona, the photosphere’s magnetism is a complete mess. “It’s not a static surface like the ground, it’s more like an ocean,” says solar physicist Amir Caspi of the Southwest Research Institute in Boulder, Colo. “And not just an ocean. It’s like a boiling ocean.”
Because the corona’s loops and streamers all originate in the turbulent photosphere, their roots should get twisted and turned around.
“And yet these structures in the corona are not tangled and snarled and matted like kelp or seaweed in the ocean,” Caspi says. “They seem to still be these organized, smooth loops. Nobody understands why.”
To unknot the photosphere’s tangled mats, the corona must release some of the energy stored there, Caspi says. So during the eclipse, he and his colleagues will be looking for the release valves that set the corona free. One possibility is that wave motion in the corona’s magnetic field lines helps untie the snarls. Magnetic waves in plasma, called Alfvén waves, are thought to ripple through the sun’s magnetic field lines like vibrations in a guitar string. Researchers have directly observed Alfvén waves in the lower corona, within about half a solar radius of the surface (SN: 4/11/09, p. 12), but not farther out where similar waves with higher amplitudes would travel. Those close-in waves were too weak to explain the corona’s features, but perhaps more distant waves could shake things up enough. Another option is that little hypothetical spurts of magnetic energy could help release the tangles. These nanoflares and nanojets would be like solar flares but with a billionth of the energy. By going off all the time, nanoflares and nanojets could collectively release enough energy to give the corona some structure, simulations have shown.
“Both are symptoms of tiny rearrangements of the magnetic field — magnetic reconnection,” says solar physicist Craig DeForest, also at the Southwest Research Institute. Solar flares and bigger outbursts called coronal mass ejections are also signs of magnetic reconnection, but they’re not frequent enough to account for the corona’s smoothness. “Nanojets and/or nanoflares in the middle corona would be a smoking gun that would explain why the corona is so organized,” DeForest says.
No one has actually seen any nanoflares or nanojets. Theories suggest that they’re too small and quick to see individually — but they should be visible as a cacophony of little pops when the solar eclipse reveals the lower corona.
The shaking from Alfvén waves and the flickers of nanoflares could not only loosen up the tangled skein of magnetism, but also transfer heat high up into the corona. Caspi, DeForest and their colleagues hope to see both effects on August 21, when they fly a pair of telescopes on twin NASA WB-57 high-altitude research jets along the path of the eclipse (SN Online: 8/14/17).
“We’re taking high-speed movies of the sun and analyzing them for things that look like waves,” Caspi says. “We’re just overall looking at the structure of the corona.”
A boy who lived in what’s now South Africa nearly 2,000 years ago has lent a helping genome to science. Using the long-gone youngster’s genetic instruction book, scientists have estimated that humans emerged as a distinct population earlier than typically thought, between 350,000 and 260,000 years ago.
The trick was retrieving a complete version of the ancient boy’s DNA from his skeleton to compare with DNA from people today and from Stone Age Neandertals and Denisovans. Previously documented migrations of West African farmers to East Africa around 2,000 years ago, and then to southern Africa around 1,500 years ago, reshaped Africans’ genetics — and obscured ancient ancestry patterns — more than has been known, the researchers report online September 28 in Science. The ancient boy’s DNA was not affected by those migrations. As a result, it provides the best benchmark so far for gauging when Homo sapiens originated in Africa, evolutionary geneticist Carina Schlebusch of Uppsala University in Sweden and her colleagues conclude.
In line with the new genetically derived age estimate for human origins, another team has proposed that approximately 300,000-year-old fossils found in northwestern Africa belonged to H. sapiens (SN: 7/8/17, p. 6). Some researchers suspect a skull from South Africa’s Florisbad site, dated to around 260,000 years ago, qualifies as H. sapiens. But investigators often place our species’ origins close to 200,000 years ago (SN: 2/26/05, p. 141). There is broad consensus that several fossils from that time represent H. sapiens.
Debate over the timing of human origins will continue despite the new evidence from the child, whose remains came from previous shoreline excavations near the town of Ballito Bay, says Uppsala University evolutionary geneticist and study coauthor Mattias Jakobsson. “We don’t know if early Homo sapiens fossils or the Florisbad individual were genetically related to the Ballito Bay boy,” he says.
Thus, the precise timing of humankind’s emergence, and exact patterns of divergence among later human populations, remain unclear. Researchers have yet to retrieve DNA from fossils dating between 200,000 and 300,000 years old that either securely or possibly belong to H. sapiens. However early human evolution played out, later mixing and mingling of populations had a big genetic impact. DNA evidence from more recent fossils, including those studied by Schlebusch’s group, increasingly suggests that Stone Age human groups migrated from one part of Africa to another and mated with each other along the way (SN: 10/20/12, p. 9), says Harvard Medical School evolutionary geneticist Pontus Skoglund. In the Sept. 21 Cell, he and his colleagues report that DNA from 16 Africans, whose remains date to between 8,100 and 400 years ago, reveals a shared ancestry among hunter-gatherers from East Africa to South Africa that existed before West African farmers first arrived 2,000 years ago.
That ancient set of common genes still comprises a big, varying chunk of the DNA of present-day Khoisan people in southern Africa, Skoglund’s group found. Earlier studies found that the Khoisan — consisting of related San hunter-gatherer and Khoikhoi herding groups — display more genetic diversity than any other human population.
Schlebusch’s team estimates that a genetic split between the Khoisan and other Africans occurred roughly 260,000 years ago, shortly after humankind’s origins and around the time of the Florisbad individual. Khoisan people then diverged into two genetically distinct populations around 200,000 years ago, the researchers calculate.
Ancient DNA in Schlebusch’s study came from seven individuals unearthed at six South African sites. Three hunter-gatherers, including the Ballito Bay boy, lived about 2,000 years ago. Four farmers lived between 500 and 300 years ago.
Comparisons to DNA from modern populations in Africa and elsewhere indicated that between 9 percent and 30 percent of Khoisan DNA today comes from an East African population that had already interbred with Eurasian people. Those East Africans were likely the much-traveled farmers who started out in West Africa and reached southern Africa around 1,500 years ago, the researchers propose.
