For the first time, humans have built a set of pushy, destructive genes that infiltrated small populations of mosquitoes and drove them to extinction.

But before dancing sleeveless in the streets, let’s be clear. This extermination occurred in a lab in mosquito populations with less of the crazy genetic diversity that an extinction scheme would face in the wild. The new gene drive, constructed to speed the spread of a damaging genetic tweak to virtually all offspring, is a long way from practical use. Yet this test and other news from 2018 feed one of humankind’s most persistent dreams: wiping mosquitoes off the face of the Earth.

For the lab-based annihilation, medical geneticist Andrea Crisanti and colleagues at Imperial College London focused on one of the main malaria-spreading mosquitoes, Anopheles gambiae. The mosquitoes thrive in much of sub-Saharan Africa, where more than 400,000 people a year die from malaria, about 90 percent of the global total of malaria deaths.

To crash the lab population, the researchers put together genes for a molecular copy-and-paste tool called a CRISPR/Cas9 gene drive. The gene drive, which in this case targeted a mosquito gene called doublesex, is a pushy cheat. It copies itself into any normal doublesex gene it encounters, so that all eggs and sperm will carry the gene drive into the next generations. Female progeny with two altered doublesex genes develop more like males and, to people’s delight, can’t bite or reproduce.

In the test, researchers set up two enclosures, each mixing 150 males carrying the saboteur genes into a group of 450 normal mosquitoes, males and females. Extinction occurred in eight generations in one of the enclosures and in 12 in the other (SN: 10/27/18, p. 6).

This is the first time that a gene drive has forced a mosquito population to breed itself down to zero, says Omar Akbari of the University of California, San Diego, who has worked on other gene drives. However, he warns, “I believe resistance will be an issue in larger, diverse populations.” More variety in mosquito genes means more chances of some genetic quirk arising that counters the attacking gene drive.

But what if a gene drive could monkey-wrench a wild population, or maybe a whole species, all the way to extinction? Should people release such a thing? To make sense of this question, we humans will have to stop talking about “mosquitoes” as if they’re all alike. The more than 3,000 species vary considerably in what they bite and what ecosystem chores they do.

The big, iridescent adults of Toxorhynchites rutilus, for instance, can’t even drink blood. And snowmelt mosquitoes (Ochlerotatus communis) are pollinators of the blunt-leaved orchid (Platanthera obtusata), ecologist Ryo Okubo of the University of Washington in Seattle said at the 2018 meeting of the Society for Integrative and Comparative Biology.
Estimating what difference it would make ecologically if a whole mosquito species disappeared has stirred up plenty of speculation but not much data. “I got pretty fed up with the hand-waving,” says insect ecologist Tilly Collins of Imperial College London. So she and colleagues dug through existing literature to see what eats An. gambiae and whether other mosquitoes would flourish should their competitor vanish.

So far, extermination of this particular mosquito doesn’t look like an ecological catastrophe, Collins says. Prey information is far from perfect, but diets suggest that other kinds of mosquitoes could compensate for the loss. The species doesn’t seem to be any great prize anyway. “As adults, they are small, not juicy, and hard to catch,” she says. The little larvae, built like aquatic caterpillars with bulging “shoulders” just behind their heads, live mostly in small, temporary spots of water.
The closest the researchers came to finding a predator that might depend heavily on this particular mosquito was the little East African jumping spider Evarcha culicivora. It catches An. gambiae for about a third of its diet and likes the females fattened with a human blood meal. Yet even this connoisseur “will readily consume” an alternative mosquito species, the researchers noted in July in Medical and Veterinary Entomology.

Collins also thinks about the alternatives to using genetically engineered pests as pest controls. Her personal hunch is that saddling mosquitoes with gene drives to take down their own species is “likely to have fewer ecological risks than broad-spectrum use of pesticides that also kill other species and the beneficial insects.”

Gene drives aren’t the only choice for weaponizing live mosquitoes against their own kind. To pick just one example, a test this year using drones to spread radiation-sterilized male mosquitoes in Brazil improved the chances that the old radiation approach will be turned against an Aedes mosquito that can spread Zika, yellow fever and chikungunya.

Old ideas, oddly enough, may turn out to be an advantage for antimosquito technologies in this era of white-hot genetic innovation. Coaxing the various kinds of gene drives to work is hard enough, but getting citizens to sign off on their use may be even harder.

For three years, a team of scientists kept a big secret: They had discovered a giant crater-shaped depression buried beneath about a kilometer of ice in northwestern Greenland. In November, the researchers revealed their find to the world.

They hadn’t set out to find a crater. But in 2015, glaciologists studying ice-penetrating radar images of Greenland’s ice sheet, part of an annual survey by NASA’s Operation IceBridge mission, noticed an oddly rounded shape right at the northern edge of Hiawatha Glacier. If the 31-kilometer-wide depression is confirmed to be the remnant of a meteorite impact — and the team has produced a wealth of evidence suggesting that it is (SN: 12/8/18, p. 6) — the discovery is exciting in and of itself. It’s rare to find a new crater, let alone one on land that has retained its perfect bowl shape.

“This is just a straight-up exciting discovery that starts with this wonderful element of serendipity,” says team member Joseph MacGregor, a glaciologist with Operation IceBridge.

But the crater — let’s call it that, for the sake of discussion — may have also reignited a debate over a controversial hypothesis about a mysterious cold snap known as the Younger Dryas. This cold period began abruptly about 12,800 years ago and ended just as abruptly about 11,700 years ago. For more than a decade, a small group of researchers, unconnected with the group behind the new discovery, has suggested that a cosmic impact triggered the cooling (SN: 7/7/18, p. 18).
Proponents of the Younger Dryas impact hypothesis say that the remnants of a comet exploded in Earth’s atmosphere and that the airbursts sparked wildfires across North America. Soot and other particles from the fires blocked out the sun, causing the cold snap, which has been blamed for everything from the extinction of the mammoths to the disappearance of a group of people known as the Clovis.

Most scientists reject that an impact was responsible, refuting the idea that there were vast wildfires at the time or that the Clovis people even disappeared. Another big objection: the lack of a smoking gun, a crater dating to the onset of the Younger Dryas.
The “mammoth in the room,” therefore, is whether the Greenland crater might be that smoking gun. But a large, recent impact would be extremely unlikely, given the rarity of such impacts on Earth, particularly on land, says planetary scientist Clark Chapman of the Southwest Research Institute in Boulder, Colo., who was not involved with the discovery.

Indeed, one sticking point is that there are no direct dates for the newly discovered crater, because it is still buried beneath all that ice. The radar data offer only tantalizing clues to the age, suggesting that the crater is between 2.6 million and 11,700 years old.

That’s a huge time range, but the proponents of the hypothesis are convinced that this crater is what they’ve been waiting for. “I think it’s transformational in terms of convincing a lot of skeptics,” says James Kennett, a geologist at the University of California, Santa Barbara.
There’s another big sticking point when it comes to linking this crater to the impact hypothesis: Instead of a fragment of a comet, the discoverers think the Hiawatha impactor was an iron meteorite. That determination is based on measurements of platinum and other elements in glacial outwash, sediments carried by meltwater from beneath the ice. An iron meteorite impact would probably not produce the kinds of explosive airbursts that could ignite continent-scale wildfires, says Michail Petaev, a geochemist at Harvard University.
Petaev and colleagues previously found a hint that an iron meteorite might have smacked into Greenland about 13,000 years ago. In 2013, his group examined Greenland ice cores and found a strange platinum anomaly dating to right before the Younger Dryas. The ratio of platinum to iridium measured in the ice cores points to an iron meteorite, the team reported.

Despite the platinum data, the impact hypothesis proponents hold firmly to the idea that the Hiawatha impactor was a comet. Because little is known about comet compositions, Kennett says, a comet might well have been the source for the platinum found in the glacial outwash and the ice cores. But Petaev maintains that the observed platinum ratios just wouldn’t occur in a comet, which is made of the primitive stuff of the universe. Instead, he says, those ratios require the cycles of melting and recrystallizing that form iron meteorites, the ancient cores of asteroids or planets.
Glaciologist Kurt Kjær of the University of Copenhagen, who led the team that identified the crater, and his colleagues don’t want to weigh in on the Younger Dryas debate. “We can’t prove it,” Kjær says. “But we can certainly not disprove it.”

Instead, the crater’s discoverers are planning to collect more sediments from the glacial outwash, and perhaps even drill directly into the crater to retrieve sediment cores that can be dated. And there may be other craters lurking beneath Greenland’s ice, or even Antarctica’s — perhaps more easily identifiable once you know what to look for, says MacGregor.

Asked whether the team has actually identified any other round shapes of interest, he pauses. Then MacGregor says, cryptically, “stay tuned.”

Quantum physics has earned a reputation as a realm of science beyond human comprehension. It describes a microworld of perplexing, paradoxical phenomena. Its equations imply a multiplicity of possible realities; an observation seems to select one of those possibilities for accessibility to human perception. The rest either disappear, remain hidden or weren’t really there to begin with. Which of those explanations pertains is debated by competing interpretations of the quantum math, pursued in a field of study known as quantum foundations.

Numerous quantum interpretations have been proposed — and an even greater number of books have been written about them. Two of the latest such books offer very different perspectives.
Philip Ball, in Beyond Weird, argues that much of the famous quantum weirdness lies in the popular descriptions of it, rather than in the math itself. Adam Becker’s What is Real? insists that the traditional “Copenhagen interpretation” is misguided; he extols the work of several physicists who reject it. Becker writes with exuberance and self-assuredness, often focusing on the personal stories of the scientists he discusses. Ball’s approach is less personal but more conversational, although he does not try to evade the sticky technicalities that illustrate and partially explain the quantum mysteries.
Ball contends that many of the analogies and illustrations used by popularizers (and physicists) to convey the weirdness of quantum theory (like a particle being in two places at once) are actually misleading. With less flamboyant phrasing, in Ball’s view, quantum physics can seem less perplexing, even almost understandable.

Without fully endorsing it, Ball gives a fairly sound presentation of the Copenhagen interpretation, based on the ideas of the Danish physicist Niels Bohr. Bohr held that quantum reality cannot be described apart from the experiments designed to probe it. A particle has many possible locations before you experimentally observe it; once observed, the location is established and the other possibilities vanish. And an electron will seem to behave as a particle or wave, depending on what sort of experimental apparatus you use to observe it.

Bohr expressed these truths by a principle he called complementarity — mutually exclusive concepts (such as wave or particle) are required to explain reality, but both concepts cannot be observed in any individual experiment. Bohr’s elaborations on this idea are famously convoluted and expressed rather obscurely. (When asked what is complementary to truth, Bohr replied, “clarity.”)

Bohr’s lack of clarity has led to many misinterpretations of what he meant, and it is those misinterpretations that Becker criticizes, rather than Bohr’s actual views. Becker’s main argument insists that the Copenhagen interpretation embraces the philosophy known as positivism (roughly, nothing unobservable is real, and sensory perceptions are the realities on which science should be based), and then demonstrates positivism’s fallacies. He does a fine job of demolishing positivism. Unfortunately, the Copenhagen interpretation is not positivistic, as its advocates have often pointed out. Bohr’s colleague Werner Heisenberg said so quite clearly: “The Copenhagen interpretation of quantum theory is in no way positivistic,” he wrote. And the philosopher Henry Folse’s 1985 book on Bohr’s philosophy thoroughly dispelled the mistaken belief that Bohr’s view was positivistic or opposed to the existence of an underlying reality.

Becker’s book commits many other more specific errors. He says Heisenberg found his famous uncertainty principle “buried in the mathematics of [Erwin] Schrödinger’s wave mechanics.” But Heisenberg despised wave mechanics and did his work on uncertainty wholly within his own matrix mechanics. Becker claims that physicists Murray Gell-Mann and James Hartle “had long been convinced that the Copenhagen interpretation had to be wrong.” But Gell-Mann and Hartle are on record stating that the Copenhagen view is not wrong, merely limited to special cases and not general enough to tell the whole quantum story.

Becker’s book does offer engaging discussions of the physicists who have questioned Bohr’s ideas and proposed alternate ways of interpreting quantum physics. But he allows the opponents to frame Bohr’s position rather than devoting any effort of his own to examining the subtlety and depth of Bohr’s philosophy and arguments. And Becker fails to address the important point that every quantum experiment’s results, no matter how bizarre, are precisely what Bohr would have expected them to be.

Becker does not engage deeply with the more recent body of work on quantum foundations, an area where Ball excels. Ball especially favors the perspective on quantum physics offered by the notion of quantum decoherence. Very roughly, the decoherence process dissipates various possible quantum realities into the environment, and only those versions of reality that are robustly recorded in the environment present themselves to observers. It’s of course much more complicated than that, and Ball admirably conveys those complications even at the occasional expense of clarity. Which puts his account closer to the truth.

The monarch butterfly isn’t the only insect flying up and down North America in a mind-boggling annual migration. Tests show a big, shimmering dragonfly takes at least three generations to make one year’s migratory loop.

Ecologist Michael Hallworth and his colleagues pieced together the migration of the common green darner, described December 19 in Biology Letters, using data on forms of hydrogen in the insects’ wings, plus records of first arrivals spotted by citizen scientists.
The study reveals that a first generation of insects emerges in the southern United States, Mexico and the Caribbean from about February to May and migrates north. Some of those Anax junius reach New England and the upper Midwest as early as March, says Hallworth, of the Smithsonian Migratory Bird Center headquartered in Washington, D.C.

Those spring migrant darners lay eggs in ponds and other quiet waters in the north and eventually die in the region. This new generation migrates south from about July until late October, though they have never seen where they’re heading. Some of these darners fly south in the same year their parents arrived and some the next year, after overwintering as nymphs.

A third generation emerges around November and lives entirely in the south during winter. It’s their offspring that start the cycle again by swarming northward as temperatures warm in the spring. With a wingspan as wide as a hand, they devote their whole lives to flying hundreds of kilometers to repeat a journey their great-grandparents made.
Scientists knew that these dragonflies migrated. Dragonfly enthusiasts have spotted swarms of the green darners in spring and in fall. But which generations were doing what has been tricky to demonstrate. “Going in, we didn’t know what to expect,” Hallworth says.
Tracking devices that let researchers record animals’ movements for more than a week or two haven’t been miniaturized enough to help. The smallest still weigh about 0.3 grams, which would just about double a darner’s weight, Hallworth says. So researchers turned to chemical clues in darner tissues. Conservation biologist and study coauthor Kent McFarland succeeded at the delicate diplomacy of persuading museums to break off a pinhead-sized wing tip fragment from specimens spanning 140 years.

Researchers checked 800 museum and live-caught specimens for the proportion of a rare heavy form of hydrogen that occurs naturally. Dragonfly wings pick up their particular mix of hydrogen forms from the water where the aquatic youngsters grow up. Scientists have noticed that a form called hydrogen-2 grows rarer along a gradient from south to north in North America. Looking at a particular wing in the analysis, “I can’t give you a zip code” for a darner, Hallworth says. But he can tell the native southerners from Yankees.

An adult darner, regardless of where it was born, is “a green piece of lightning,” says McFarland, of the Vermont Center for Ecostudies in White River Junction. Darners maneuver fast enough to snap insect prey out of the air around ponds across North America. The front of an adult’s large head is “all eye,” he says, and trying to catch samples for the study was “like hitting a knuckleball.”

Although the darners’ north-south migration story is similar to that of monarchs (Danaus plexippus), there are differences, says evolutionary biologist Hugh Dingle of the University of California, Davis, who has long studied these butterflies. Monarchs move northward in the spring in stepwise generations, instead of one generation sweeping all the way to the top of its range.

Also, Dingle says, pockets of monarchs can buck the overall scheme. Research suggests that some of the monarchs in the upper Midwest do a whole round trip migration in a single generation. As researchers discover more details about green darners, he predicts, the current basic migration scheme will turn out to have its quirky exceptions, too.

The adolescent saber-toothed cat on a summertime hunt realized too late that she had made a terrible miscalculation.

Already the size of a modern-day tiger, with huge canine teeth, she had crept across grassy terrain to ambush a giant ground sloth bellowing in distress. Ready to pounce, the cat’s front paw sank into sticky ground. Pressing down with her other three paws to free herself, then struggling in what has been called “tar pit aerobics,” she became irrevocably mired alongside her prey.

Scenarios much like this played out repeatedly over at least the last 35,000 years at California’s Rancho La Brea tar pits. Entrapped herbivores, such as the sloth, attracted scavengers and predators — including dire wolves, vultures and saber-toothed Smilodon cats — to what looked like an easy meal. Eventually the animals would disappear into the muck, until paleontologists plucked their fossils from the ground in huge numbers over the last century.

Five million or so fossils have been found at the site. But “it’s not like there was this orgy of death going on,” says Christopher Shaw, a paleontologist and former collections manager at the La Brea Tar Pits and Museum in Los Angeles. He calculates that such an entrapment scenario, dooming 10 or so large mammals and birds, would have needed to occur only once per decade over 35,000 years to account for that bounty of fossils.

At La Brea, the collection of Smilodon fatalis fossils alone includes more than 166,000 bones, from an estimated 3,000 of the ill-fated prehistoric cats. Famed for their fearsome canines, which grew up to 18 centimeters long, S. fatalis weighed as much as 280 kilograms, bigger than most of today’s largest lions and tigers.
Fossils of S. fatalis, the second largest of three Smilodon species that roamed the Americas during the Pleistocene Epoch, have been found across the United States and in South America, west of the Andes as far south as Chile. And a recent study put S. fatalis in Alberta, Canada, about 1,000 kilometers north of its previously known range.

But the La Brea fossil site, unique in offering up so many specimens, is the source of the vast majority of knowledge about the species. There, fossils of dire wolves and saber-toothed cats together outnumber herbivores about 9-to-1, leading scientists to speculate that both predators may have formed prides or packs, similar to modern lions and wolves. Yet a small number of experts argue against cooperative behavior for Smilodon, reasoning that pack-living animals would have been too intelligent to get mired en masse.
New studies may help settle the debate about Smilodon’s sociality, and answer questions about how the cat lived and why it died out 10,000 to 12,000 years ago.

“We have an innate curiosity to understand what it was doing and why it went extinct,” says Larisa DeSantis, a vertebrate paleontologist at Vanderbilt University in Nashville. Now, she says, “we can answer these questions.”

DeSantis is studying microscopic wear on fossil teeth and chemical signatures in the enamel to reveal Smilodon’s diet. Other scientists are doing biomechanical studies of the skull, fangs and limbs to understand how the powerful cat captured and killed its prey. Some researchers are extracting DNA from fossils, while others are gathering data on the paleoclimate to try to piece together why Smilodon died out.

“It’s the T. rex of mammals … a big, scary predator,” says Ashley Reynolds, a paleontology Ph.D. student and fossil cat researcher at the University of Toronto. She presented the Alberta fossil find in October in Albuquerque at the Society of Vertebrate Paleontology conference. Explaining why Smilodon cats continue to excite researchers, she says, “They’re probably the baddest of all the cats that have ever existed.”
Safety in numbers
Whether Smilodon was a pack hunter has long been debated (SN: 10/28/17, p. 5) because living in groups is rare among large cats today. But an unusual number of healed injuries in the Smilodon bones at La Brea makes it unlikely that these cats were solitary, DeSantis and Shaw reported in November in Indianapolis at a meeting of the Geological Society of America.

More than 5,000 of the Smilodon bones at La Brea have marks of injury or illness: tooth decay, heavily worn arthritic joints, broken legs and dislocated elbows that would have occurred before the animals’ tar burial. Dramatic examples include crushed chests and spinal injuries, which the cats somehow survived. “You would actually wince to see these horribly, traumatically injured specimens,” says Shaw, who is also coeditor of the 2018 book Smilodon: The Iconic Sabertooth.

One particularly debilitating injury was a crippled pelvis, but evidence of new bone growth shows that the animal lived long enough for healing to occur. “There was a lot of infection, pain and smelly stuff, and just a really awful situation for this animal, but it survived well over a year,” Shaw says. “To me that indicates [the injured cat] was part of a group that helped it survive by letting it feed at kills and protecting it.”

Shaw and DeSantis looked at a series of specimens with what were probably agonizing maladies in the teeth and jaws, including fractured canines and massive infections that left animals with misshapen skulls.

“These animals probably couldn’t have gone out … to kill anything,” Shaw says. “You know how it is when you have a toothache. This is like that times 100.”
DeSantis compared microscopic pits and scratches on the surface of the teeth of injured animals with microwear on the teeth of seemingly healthy Smilodon cats. The injured cats’ dental surfaces indicated that the animals were eating softer foods, which would have been less painful to chew, “likely a higher proportion of flesh, fat and organs, as opposed to bone,” she says.

The findings are consistent with the interpretation that Smilodon was a group-living animal, she says, and that the cats “allowed each other access to food when [injured pack members] couldn’t necessarily take down their own prey.”

Reynolds agrees that the healed injuries are persuasive evidence that Smilodon lived in groups. “When you see an animal with really nasty injuries that healed somehow, it does make you wonder if they were cared for.”

Not everyone is convinced, however. Ecologist Christian Kiffner of the Center for Wildlife Management Studies in Karatu, Tanzania, has studied modern carnivores such as African lions and spotted hyenas. “Relatively long survival of Smilodon fatalis individuals after dental injuries had occurred does not necessarily provide airtight evidence for a specific social system in this species,” he says. “It is very, very difficult to use patterns in Pleistocene carnivore [fossil] assemblages to make inferences about behavior of an extinct species.”

Even if the saber-toothed cats did live in groups, the animals’ exact social structure remains an open question, Reynolds says. Modern lion prides have numerous females and several younger males led by an alpha male, with intense competition between male lions. As a result, males are much bigger than females, as the males must work hard to defend their positions.

Despite searching, scientists have not found obvious evidence of a size difference between the sexes in Smilodon; researchers can’t even tell which La Brea fossils are male or female. Size differences between the sexes, if they existed, may have been small.

“That lack of sexual dimorphism is odd,” says Blaire Van Valkenburgh, a UCLA paleontologist who studies fossil carnivores. Sex-related size differences are seen in many big cats today, most particularly lions. She thinks the lack of sexual dimorphism in Smilodon might hint at a different social structure. Perhaps males weren’t competing quite so intensely for access to females. Maybe there was no single alpha male preventing the majority of males from making a move.

Family affair
Perhaps Smilodon groups had an alpha female rather than an alpha male, or an alpha pair. Such is the case in modern wolves and coyotes, which have less pronounced size differences between sexes than lions do. The prehistoric cats “could have had extended family structures [similar to wolves] where uncles and aunts hung around, because it probably took a while to raise the young saber-toothed cats,” Van Valkenburgh suspects.

Kittens may have taken a long time, as long as 22 months, to get most of their adult teeth, she says. The upper canines took even longer, as much as three years or more, to reach their massive size, researchers reported in PLOS ONE in 2015. Modern lions, in contrast, typically have all of their adult teeth by 17 months, Van Valkenburgh says.

Smilodon kittens also probably went through a substantial learning curve before attempting to take down large prey. “It took longer for them to learn how to safely kill something without breaking their teeth or biting in the wrong place and hurting themselves,” Van Valkenburgh speculates.

Pack living would enable this slower development: “If you’re a social species, you can afford to grow at a slower rate than a nonsocial species because you have a family safety net,” Reynolds says. She is studying Smilodon fossils from Peru’s Talara tar pits for evidence of slow bone development using bone histology, examining thin cross sections under a microscope to determine such things as age and growth rate.
To understand how saber-toothed cats eventually took down prey, Van Valkenburgh joined paleobiologist Borja Figueirido of the University of Málaga in Spain and others. The group studied the biomechanics of Smilodon’s killing bite and how the animal used its sabers. That work, published in the October 22, 2018 Current Biology, adds to a consensus that the cat used its powerful forelimbs, which existed even in the youngsters (SN Online: 9/27/17), to pin prey before applying a lethal bite to the neck.

“The specialization of being a saber-toothed appears to have been partly to effectively take prey larger than yourself and to do that very quickly,” Van Valkenburgh says. With the prey tightly gripped, a Smilodon cat would position itself so that one or two really strong canine bites would rip open the pinned animal’s throat.

In contrast, lions suffocate prey — one lion may clamp its jaws around the neck, crushing the windpipe, while another uses its mouth to cover the victim’s nose and mouth. Using this slower method would have increased Smilodon’s chances of injuring or damaging those precious canine teeth.

Diverging senses
Smilodon and its extinct saber-toothed relatives are on a branch of the cat family tree that is far from today’s cats. Scientists think Smilodon’s branch diverged from the ancestors of all living cats about 20 million years ago. Given the evolutionary distance, researchers are still trying to determine how similar — or different — Smilodon was from its living feline cousins. A recent focus has been the cat’s sounds and senses.

At the October vertebrate paleontology conference, Shaw presented evidence that Smilodon may have roared, as do lions, tigers, leopards and their close relatives. The clues come from 150 La Brea fossils that were once part of the hyoid arch, or larynx, in the Smilodon throat. (Tar pits stand out for preserving tiny bones rarely found elsewhere.) The small fossils are very similar in shape and style to those of roaring cats. House cats and others that purr have a different arrangement of bones.
Smilodon may have “used this type of communication as an integral part of social behavior,” Shaw says. Roaring, however, is not a sure sign of pack living, Reynolds notes; most roaring cats today do not live in large groups.

How Smilodon’s sense of smell compared with living cats’ is something else researchers wonder about. To probe this part of the extinct animal’s biology, a team lead by Van Valkenburgh looked at Smilodon’s cribriform plate — a small, perforated bone inside the skull. Smell-sensing nerve cells pass through holes in the plate from the olfactory receptors in the nose to the brain. The size and number of holes are thought to correlate with the number of receptors and, therefore, the extent of an animal’s sense of smell.

To confirm this link, Van Valkenburgh’s team combined CT scans and 3-D images of skulls from 27 species of living mammals with information on the number of olfactory receptor genes. A CT scan of a skull revealed that Smilodon may have had slightly fewer olfactory receptor nerve cells than a domestic cat, the researchers reported at the paleontology conference. Smilodon’s sense of smell was perhaps 10 to 20 percent less keen than a modern lion’s, says Van Valkenburgh, whose team reported the findings in the March 14, 2018 Proceedings of the Royal Society B.

Smilodon “might have relied more heavily on their eyes and their ears,” she says. Perhaps, in an ancient evolutionary divergence, Smilodon’s level of reliance on smell went in a slightly different direction than in modern big cats.

Saber-toothed swan song
As the pieces of the Smilodon puzzle fall into place, perhaps the biggest remaining mystery is why the animal disappeared 10,000 to 12,000 years ago. Debate about the extinction of some of North America’s large mammal species swings between blaming humans and climate change (SN: 11/10/18, p. 28). While humans, who probably arrived on the continent more than 15,000 years ago, and Smilodon certainly knew one another in the Americas, they may not have overlapped at La Brea, Shaw says. The earliest evidence of people in the Los Angeles Basin is about 11,000 years ago, by which time Smilodon may or may not already have gone. Nevertheless, human hunting of large prey elsewhere in the Americas could have led to a scarcity of food for the big cats, he says.

One theory holds that Smilodon went through tough times at La Brea when lack of prey forced the saber-toothed cats to consume entire carcasses including bones. This has been posited as the reason for all those broken teeth among the La Brea fossils. But DeSantis isn’t convinced; she thinks breakages happened during scuffles with prey. She says dental microwear suggests that Smilodon was not eating great quantities of bone.
Some opportunistic carnivores, such as cougars, did eat bone and managed to survive to the modern day. Perhaps Smilodon couldn’t adapt to hunting smaller prey when larger herbivores disappeared, also around 10,000 to 12,000 years ago (SN: 11/24/18, p. 22).

“A lot of the large prey on the landscape go extinct,” DeSantis says. “You lose out on the horses, camels, giant ground sloths, mammoths and mastodon. That’s got to have had an impact.”

The challenge of dating fossils from the tar pits has been one hurdle to understanding exactly what was going on with Smilodon over time. Bones deposited over many thousands of years get jumbled by movement in the tar, for reasons experts don’t fully understand. Plus, the tar itself becomes embedded in each specimen, complicating carbon dating.

However, new methods of chemically pretreating fossils to remove the tar have made carbon dating much easier and cheaper — and a multi-institutional project is now dating hundreds of Smilodon and other bones. Researchers will soon be able to track changes in Smilodon over the 35,000 years of prehistory recorded at La Brea and correlate fossil changes to known changes in climate over that time.

“We’re going to have a much better handle,” Van Valkenburgh says, “on what was going on towards the end of their existence.”

This article appears in the March 30, 2019 issue of Science News with the headline, “The Baddest Cat of All: Fresh details say saber-toothed Smilodon helped injured pack members.”

Like a quantum version of a whirling top, protons have angular momentum, known as spin. But the source of the subatomic particles’ spin has confounded physicists. Now scientists have confirmed that some of that spin comes from a frothing sea of particles known as quarks and their antimatter partners, antiquarks, found inside the proton.

Surprisingly, a less common type of antiquark contributes more to a proton’s spin than a more plentiful variety, scientists with the STAR experiment report March 14 in Physical Review D.
Quarks come in an assortment of types, the most common of which are called up quarks and down quarks. Protons are made up of three main quarks: two up quarks and one down quark. But protons also have a “sea,” or an entourage of transient quarks and antiquarks of different types, including up, down and other varieties (SN: 4/29/17, p. 22).

Previous measurements suggested that the spins of the quarks within this sea contribute to a proton’s overall spin. The new result — made by slamming protons together at a particle accelerator called the Relativistic Heavy Ion Collider, or RHIC — clinches that idea, says physicist Elke-Caroline Aschenauer of Brookhaven National Lab in Upton, N.Y., where the RHIC is located.

A proton’s sea contains more down antiquarks than up antiquarks. But, counterintuitively, more of the proton’s spin comes from up than down antiquarks, the researchers found. In fact, the down antiquarks actually spin in the opposite direction, slightly subtracting from the proton’s total spin.

“Spin has surprises. Everybody thought it’s simple … and it turns out it’s much more complicated,” Aschenauer says.
Editor’s note: This story was updated April 3, 2019, to correct the subheadline to say that up antiquarks (not up quarks) add more angular momentum than do down antiquarks (not down quarks).

Life after shingles
In “With its burning grip, shingles can do lasting damage” (SN: 3/2/19, p. 22), Aimee Cunningham described the experience of Nora Fox, a woman whose bout with shingles nearly 15 years ago left her with a painful condition called postherpetic neuralgia. Fox hadn’t found any reliable treatments, Cunningham reported.

Fox praised Science News for our portrayal of shingles-related pain. “The cover is excellent and looks just like I felt,” she wrote.

As the story went to press, Fox had a surgery during which doctors placed electrodes under the skin near sites of pain. A device lets Fox control when stimulation is delivered to those areas. But the treatment, called peripheral nerve stimulation, may not work for all patients with postherpetic neuralgia. There are reports in scientific journals of individual patients experiencing relief from their neuropathic pain after the procedure, Cunningham says.
Fox’s husband, Denver C. Fox, sent Science News an update on her pain since the procedure: “There [has] been a significant change to the unbearable pain my wife has endured EVERY afternoon and evening for 14 years, despite trying every possible treatment the MDs knew of.” Shortly after the procedure, “her pain is greatly and markedly diminished.”
Stone Age throwback
Tests with replicas of a 300,000-year-old wooden spear suggest that Neandertals could have hunted from a distance, Bruce Bower reported in “Why modern javelin throwers hurled Neandertal spears at hay bales” (SN: 3/2/19, p. 14).

Reader Brenda Gray suggested that Neandertals’ spears could have been used for fighting instead of hunting.

The ancient spear found in Germany, on which the spear replicas were based, came from sediment that also contained stone tools and thousands of animal bones displaying marks made by stone tools, Bower says. “Such evidence indicates that the spears were used as hunting weapons. Neandertals could have used wooden spears in different ways, but there is no evidence that I know of for Neandertals using spears in warfare,” he says.

Young and restless
Earth’s inner core began hardening sometime after 565 million years ago, Carolyn Gramling reported in “Earth’s core may have hardened just in time to save its magnetic field” (SN: 3/2/19, p. 13). The core may have solidified just in time to strengthen the planet’s magnetic field, saving it from collapse.

Reader John Bunch thought that the timing of the inner core’s solidification “lines up nicely” with the Cambrian explosion, when life rapidly diversified about 542 million years ago. “It leads me to wonder if there may be some cause and effect or some other relationship between the two that’s going on here.”

That extremely low-intensity magnetic field actually roughly lines up with the Avalon explosion, an earlier proliferation of new life forms called the Ediacaran biota, between about 575 million and 542 million years ago, Gramling says. It’s an intriguing coincidence that researchers noted.

Earth’s magnetic field helps protect the planet from radiation. So a weak magnetic field might somehow be linked with the Avalon explosion. One idea is that increased radiation reaching Earth’s surface hundreds of millions of years ago might have increased organisms’ mutation rates, Gramling says. But there just isn’t any evidence to support a causal link at the moment.

Multiplying 2 x 2 is easy. But multiplying two numbers with more than a billion digits each — that takes some serious computation.

The multiplication technique taught in grade school may be simple, but for really big numbers, it’s too slow to be useful. Now, two mathematicians say that they’ve found the fastest way yet to multiply extremely large figures.

The duo claim to have achieved an ultimate speed limit for multiplication, first suggested nearly 50 years ago. That feat, described online March 18 at the document archive HAL, has not yet passed the gauntlet of peer review. But if the technique holds up to scrutiny, it could prove to be the fastest possible way of multiplying whole numbers, or integers.
If you ask an average person what mathematicians do, “they say, ‘Oh, they sit in their office multiplying big numbers together,’” jokes study coauthor David Harvey of the University of New South Wales in Sydney. “For me, it’s actually true.”

When making calculations with exorbitantly large numbers, the most important measure of speed is how quickly the number of operations needed — and hence the time required to do the calculation — grows as you multiply longer and longer strings of digits.

That growth is expressed in terms of n, defined as the number of digits in the numbers being multiplied. For the new technique, the number of operations required is proportional to n times the logarithm of n, expressed as O(n log n) in mathematical lingo. That means that, if you double the number of digits, the number of operations required will increase a bit faster, more than doubling the time the calculation takes.
But, unlike simpler methods of multiplication, the time needed doesn’t quadruple, or otherwise rapidly blow up, as the number of digits creeps up, report Harvey and Joris van der Hoeven of the French national research agency CNRS and École Polytechnique in Palaiseau. That slower growth rate makes products of bigger numbers more manageable to calculate.

The previously predicted max speed for multiplication was O(n log n), meaning the new result meets that expected limit. Although it’s possible an even speedier technique might one day be found, most mathematicians think this is as fast as multiplication can get.

“I was very much astonished that it had been done,” says theoretical computer scientist Martin Fürer of Penn State. He discovered another multiplication speedup in 2007, but gave up on making further improvements. “It seemed quite hopeless to me.”

The new technique comes with a caveat: It won’t be faster than competing methods unless you’re multiplying outrageously huge numbers. But it’s unclear exactly how big those numbers have to be for the technique to win out — or if it’s even possible to multiply such big numbers in the real world.

In the new study, the researchers considered only numbers with more than roughly 10214857091104455251940635045059417341952 digits when written in binary, in which numbers are encoded with a sequence of 0s and 1s. But the scientists didn’t actually perform any of these massive multiplications, because that’s vastly more digits than the number of atoms in the universe. That means there’s no way to do calculations like that on a computer, because there aren’t enough atoms to even represent such huge numbers, much less multiply them together. Instead, the mathematicians came up with a technique that they could prove theoretically would be speedier than other methods, at least for these large quantities.

There’s still a possibility that the method could be shown to work for smaller, but still large, numbers. That could possibly lead to practical uses, Fürer says. Multiplication of these colossal numbers is useful for certain detailed calculations, such as finding new prime numbers with millions of digits (SN Online: 1/5/18) or calculating pi to extreme precision (SN Online: 12/10/02).

Even if the method is not widely useful, making headway on a problem as fundamental as multiplication is still a mighty achievement. “Multiplying numbers is something people have been working on for a while,” says mathematical physicist John Baez of the University of California, Riverside. “It’s a big deal, just because of that.”

A week after two large earthquakes rattled southern California, scientists are scrambling to understand the sequence of events that led to the temblors and what it might tell us about future quakes.

A magnitude 6.4 quake struck July 4 near Ridgecrest — about 194 kilometers northeast of Los Angeles — followed by a magnitude 7.1 quake in the same region on July 5. Both quakes occurred not along the famous San Andreas Fault but in a region of crisscrossing faults in the state’s high desert area, known as the Eastern California Shear Zone.

The San Andreas Fault system, which stretches nearly 1,300 kilometers, generally takes center stage when it comes to California’s earthquake activity. That’s where, as the Pacific tectonic plate and the North American tectonic plate slowly grind past each other, sections of ground can lock together for a time, slowly building up strain until they suddenly release, producing powerful quakes.

For the last few tens of millions of years, the San Andreas has been the primary origin of massive earthquakes in the region. Now overdue for a massive earthquake, based on historical precedent, many people fear it’s only a matter of time before the “Big One” strikes.
But as the July 4 and July 5 quakes — and their many aftershocks — show, the San Andreas Fault system isn’t the only source of concern. The state is riddled with faults, says geophysicist Susan Hough of the U.S. Geological Survey in Pasadena, Calif. That’s because almost all of California is part of the general boundary between the plates. The Eastern California Shear Zone alone has been the source of several large quakes in the last few decades, including the magnitude 7.1 Hector Mine quake in 1999, the magnitude 6.7 Northridge quake in 1994 and the magnitude 7.3 Landers quake in 1992 (SN Online: 8/29/18).

Here are three questions scientists are trying to answer in the wake of the most recent quakes.

Which faults ruptured, and how?
The quakes appear to have occurred along previously unmapped faults within a part of the Eastern California Shear Zone known as the Little Lake Fault Zone, a broad bunch of cracks difficult to map, Hough says. “It’s not like the San Andreas, where you can go out and put your hand on a single fault,” she says. And, she adds, the zone also lies within a U.S. Navy base that isn’t generally accessible to geologists for mapping.

But preliminary data do offer some clues. The data suggest that the first rupture may actually have been a twofer: Instead of one fault rupturing, two connected faults, called conjugate faults, may have ruptured nearly simultaneously, producing the initial magnitude 6.4 quake.

It’s possible that the first quake didn’t fully release the strain on that fault, but the second, larger quake did. “My guess is that they will turn out to be complementary,” Hough says.

The jury is still out, though, says Wendy Bohon, a geologist at the Incorporated Research Institutions for Seismology in Washington, D.C. “What parts of the fault broke, and whether a part of the fault broke twice … I’m waiting to see what the scientific consensus is on that.”
And whether a simultaneous rupture of a conjugate fault is surprising, or may actually be common, isn’t yet clear, she says. “In nature, we see a lot of conjugate fault pairs. I don’t think they normally rupture at the same time — or maybe they do, and we haven’t had enough data to see that.”

Is the center of tectonic action moving away from the San Andreas Fault?
GPS data have revealed exactly how the ground is shifting in California as the giant tectonic plates slide past one another. The San Andreas Fault system bears the brunt of the strain, about 70 percent, those data show. But the Eastern California Shear Zone bears the other 30 percent. And the large quakes witnessed in that region over the last few decades raise a tantalizing possibility, Hough says: We may be witnessing the birth pangs of a new boundary.

“The plate boundary system has been evolving for a long time already,” Hough says. For the last 30 million years or so, the San Andreas Fault system has been the primary locus of action. But just north of Santa Barbara lies the “big bend,” a kink that separates the northern from the southern portion of the fault system. Where the fault bends, the Pacific and North American plates aren’t sliding sideways past one another but colliding.

“The plates are trying to move, but the San Andreas is actually not well aligned with that motion,” she says. But the Eastern California Shear Zone is. And, Hough says, there’s some speculation that it’s a new plate boundary in the making. “But it would happen over millions of years,” she adds. “It’s not going to be in anyone’s lifetime.”

Will these quakes trigger the Big One on the San Andreas?
Such large quakes inevitably raise these fears. Historically, the San Andreas Fault system has produced a massive quake about every 150 years. But “for whatever reason, it has been pretty quiet in the San Andreas since 1906,” when an estimated magnitude 7.9 quake along the northern portion of the fault devastated San Francisco, Hough says. And the southern portion of San Andreas is even more overdue for a massive quake; its last major event was the estimated magnitude 7.9 Fort Tejon quake in 1857, she says.

The recent quakes aren’t likely to change that situation. Subsurface shifting from a large earthquake can affect strain on nearby faults. But it’s unlikely that the quakes either relieved stress or will ultimately trigger another earthquake along the San Andreas Fault system, essentially because they were too far away, Hough says. “The disruption [from one earthquake] of other faults decreases really quickly with distance,” she says (SN Online: 3/28/11).

Some preliminary data do suggest that the magnitude 7.1 earthquake produced some slippage, also known as creep, along at least one shallow fault in the southern part of the San Andreas system. But such slow, shallow slips don’t produce earthquakes, Hough says.

However, the quakes could have more significantly perturbed much closer faults, such as the Garlock Fault, which runs roughly west to east along the northern edge of the Mojave Desert. That’s not unprecedented: The 1992 Landers quake may have triggered a magnitude 5.7 quake two weeks later along the Garlock Fault.

“Generations of graduate students are going to be studying these events — the geometry of the faults, how the ground moved,” even how the visible evidence of the rupture, scarring the land surface, erodes over time and obscures its traces, Bohon says.

At the moment, scientists are eagerly trading ideas on social media sites. “It’s the equivalent of listening in on scientists shouting down the hallway: ‘Here’s my data — what do you have?’ ” she says. Those preliminary ideas and explanations will almost certainly evolve as more information comes in, she adds. “It’s early days yet.”

The James Webb Space Telescope’s first peek at the distant universe unveiled galaxies that appear too big to exist.

Six galaxies that formed in the universe’s first 700 million years seem to be up to 100 times more massive than standard cosmological theories predict, astronomer Ivo Labbé and colleagues report February 22 in Nature. “Adding up the stars in those galaxies, it would exceed the total amount of mass available in the universe at that time,” says Labbé, of the Swinburne University of Technology in Melbourne, Australia. “So you know that something is afoot.”
The telescope, also called JWST, released its first view of the early cosmos in July 2022 (SN: 7/11/22). Within days, Labbé and his colleagues had spotted about a dozen objects that looked particularly bright and red, a sign that they could be massive and far away.

“They stand out immediately, you see them as soon as you look at these images,” says astrophysicist Erica Nelson of the University of Colorado Boulder.

Measuring the amount of light each object emits in various wavelengths can give astronomers an idea of how far away each galaxy is, and how many stars it must have to emit all that light. Six of the objects that Nelson, Labbé and colleagues identified look like their light comes from no later than about 700 million years after the Big Bang. Those galaxies appear to hold up to 10 billion times the mass of our sun in stars. One of them might contain the mass of 100 billion suns.

“You shouldn’t have had time to make things that have as many stars as the Milky Way that fast,” Nelson says. Our galaxy contains about 60 billion suns’ worth of stars — and it’s had more than 13 billion years to grow them. “It’s just crazy that these things seem to exist.”

In the standard theories of cosmology, matter in the universe clumped together slowly, with small structures gradually merging to form larger ones. “If there are all these massive galaxies at early times, that’s just not happening,” Nelson says.

One possible explanation is that there’s another, unknown way to form galaxies, Labbé says. “It seems like there’s a channel that’s a fast track, and the fast track creates monsters.”

But it could also be that some of these galaxies host supermassive black holes in their cores, says astronomer Emma Curtis-Lake of the University of Hertfordshire in England, who was not part of the new study. What looks like starlight could instead be light from the gas and dust those black holes are devouring. JWST has already seen a candidate for an active supermassive black hole even earlier in the universe’s history than these galaxies are, she says, so it’s not impossible.
Finding a lot of supermassive black holes at such an early era would also be challenging to explain (SN: 3/16/18). But it wouldn’t require rewriting the standard model of cosmology the way extra-massive galaxies would.

“The formation and growth of black holes at these early times is really not well understood,” she says. “There’s not a tension with cosmology there, just new physics to be understood of how they can form and grow, and we just never had the data before.”

To know for sure what these distant objects are, Curtis-Lake says, astronomers need to confirm the galaxies’ distances and masses using spectra, more precise measurements of the galaxies’ light across many wavelengths (SN: 12/16/22).

JWST has taken spectra for a few of these galaxies already, and more should be coming, Labbé says. “With luck, a year from now, we’ll know a lot more.”