Pigs are a step closer to becoming organ donors for people.

Researchers used molecular scissors known as CRISPR/Cas9 to snip embedded viruses out of pig DNA. Removing the viruses — called porcine endogenous retroviruses, or PERVs — creates piglets that can’t pass the viruses on to transplant recipients, geneticist Luhan Yang and colleagues report online August 10 in Science.

Yang, a cofounder of eGenesis in Cambridge, Mass., and colleagues had previously sliced 62 PERVs at a time from pig cells grown in the lab (SN: 11/14/15, p. 6). Many of the embedded viruses are already damaged and can’t make copies of themselves to pass on an infection. So in the new study, the researchers removed just 25 viruses that were still capable of infecting other cells.
The team had to overcome several technical hurdles to make PERV-less pig cells that still had the normal number of chromosomes. In a process similar to the one that created Dolly the Sheep (SN: 3/1/97, p. 132), researchers sucked the DNA-containing nuclei from the virus-cleaned cells and injected them into pig eggs. The technique, called somatic cell nuclear transfer, is better known as cloning. Embryos made from the cloned cells were transplanted to sows to develop into piglets.

The process is still not very efficient. Researchers placed 200 to 300 embryos in each of 17 sows. Only 37 piglets were born, and 15 are still living. The oldest are about 4 months old. Such virus-free swine could be a starting point for further genetic manipulations to make pig organs compatible with humans.

As the moon’s shadow races across North America on August 21, hundreds of radio enthusiasts will turn on their receivers — rain or shine. These observers aren’t after the sun. They’re interested in a shell of electrons hundreds of kilometers overhead, which is responsible for heavenly light shows, GPS navigation and the continued existence of all earthly beings.

This part of the atmosphere, called the ionosphere, absorbs extreme ultraviolet radiation from the sun, protecting life on the ground from its harmful effects. “The ionosphere is the reason life exists on this planet,” says physicist Joshua Semeter of Boston University.
It’s also the stage for brilliant displays like the aurora borealis, which appears when charged material in interplanetary space skims the atmosphere. And the ionosphere is important for the accuracy of GPS signals and radio communication.

This layer of the atmosphere forms when radiation from the sun strips electrons from, or ionizes, atoms and molecules in the atmosphere between about 75 and 1,000 kilometers above Earth’s surface. That leaves a zone full of free-floating negatively charged electrons and positively charged ions, which warps and wefts signals passing through it.
Without direct sunlight, though, the ionosphere stops ionizing. Electrons start to rejoin the atoms and molecules they abandoned, neutralizing the atmosphere’s charge. With fewer free electrons bouncing around, the ionosphere reflects radio waves differently, like a distorted mirror.
We know roughly how this happens, but not precisely. The eclipse will give researchers a chance to examine the charging and uncharging process in almost real time.

“The eclipse lets us look at the change from light to dark to light again very quickly,” says Jill Nelson of George Mason University in Fairfax, Va.

Joseph Huba and Douglas Drob of the U.S. Naval Research Laboratory in Washington, D.C., predicted some of what should happen to the ionosphere in the July 17 Geophysical Research Letters. At higher altitudes, the electrons’ temperature should decrease by 15 percent. Between 150 and 350 kilometers above Earth’s surface, the density of free-floating electrons should drop by a factor of two as they rejoin atoms, the researchers say. This drop in free-floating electrons should create a disturbance that travels along Earth’s magnetic field lines. That echo of the eclipse-induced ripple in the ionosphere may be detectable as far away as the tip of South America.

Previous experiments during eclipses have shown that the degree of ionization doesn’t simply die down and then ramp back up again, as you might expect. The amount of ionization you see seems to depend on how far you are from being directly in the moon’s shadow.

For a project called Eclipse Mob, Nelson and her colleagues will use volunteers around the United States to gather data on how the ionosphere responds when the sun is briefly blocked from the largest land area ever.
About 150 Eclipse Mob participants received a build-it-yourself kit for a small radio receiver that plugs into the headphone jack of a smartphone. Others made their own receivers after the project ran out of kits. On August 21, the volunteers will receive signals from radio transmitters and record the signal’s strength before, during and after the eclipse.
Nelson isn’t sure what to expect in the data, except that it will look different depending on where the receivers are. “We’ll be looking for patterns,” she says. “I don’t know what we’re going to see.”

Semeter and his colleagues will be looking for the eclipse’s effect on GPS signals. They would also like to measure the eclipse’s effects on the ionosphere using smartphones — eventually.

For this year’s solar eclipse, they will observe radio signals using an existing network of GPS receivers in Missouri, and intersperse it with small, cheap GPS receivers that are similar to the kind in most phones. The eclipse will create a big cool spot, setting off waves in the atmosphere that will propagate away from the moon’s shadow. Such waves leave an imprint on the ionosphere that affects GPS signals. The team hopes to combine high-quality data with messier data to lay the groundwork for future experiments to tap into the smartphone crowd.

“The ultimate vision of this project is to leverage all 2 billion smartphones around the planet,” Semeter says. Someday, everyone with a phone could be a node in a global telescope.

If it works, it could be a lifesaver. Similar atmospheric waves were seen radiating from the source of the 2011 earthquake off the coast of Japan (SN Online: 6/16/11). “The earthquake did the sort of thing the eclipse is going to do,” Semeter says. Understanding how these waves form and move could potentially help predict earthquakes in the future.

Carbondale, Ill., is just a few kilometers north of the point where this year’s total solar eclipse will linger longest — the city will get two minutes and 38 seconds of total darkness when the moon blocks out the sun. And it’s the only city in the United States that will also be in the path of totality when the next total solar eclipse crosses North America, in 2024 (SN: 8/5/17, p. 32). The town is calling itself the Eclipse Crossroads of America.
“Having a solar eclipse that goes through the entire continent is rare enough,” says planetary scientist Padma Yanamandra-Fisher of the Space Science Institute’s branch in Rancho Cucamonga, Calif. “Having two in seven years is even more rare. And two going through the same city is rarer still.”

That makes Carbondale the perfect spot to investigate how the sun’s atmosphere, or corona, looks different when solar activity is high versus low.

Every 11 years or so, the sun cycles from periods of high magnetic field activity to low activity and back again. The frequency of easy-to-see features — like sunspots on the sun’s visible surface, solar flares and the larger eruptions of coronal mass ejections — cycles, too. But it has been harder to trace what happens to the corona’s streamers, the long wispy tendrils that give the corona its crownlike appearance and originate from the magnetic field.
The corona is normally invisible from Earth, because the bright solar disk washes it out. Even space telescopes that are trained on the sun can’t see the inner part of the corona — they have to block some of it out for their own safety (SN Online: 8/11/17). So solar eclipses are the only time researchers can get a detailed view of what the inner corona, where the streamers are rooted, is up to.
Right now, the sun is in a period of exceptionally low activity. Even at the most recent peak in 2014, the sun’s number of flares and sunspots was pathetically wimpy (SN: 11/2/13, p. 22). During the Aug. 21 solar eclipse, solar activity will still be on the decline. But seven years from now during the 2024 eclipse, it will be on the upswing again, nearing its next peak.

Yanamandra-Fisher will be in Carbondale for both events. This year, she’s teaming up with a crowdsourced eclipse project called the Citizen Continental-America Telescope Eclipse experiment. Citizen CATE will place 68 identical telescopes along the eclipse’s path from Oregon to South Carolina.

As part of a series of experiments, Yanamandra-Fisher and her colleagues will measure the number, distribution and extent of streamers in the corona. Observations of the corona during eclipses going back as far as 1867 suggest that streamers vary with solar activity. During low activity, they tend to be more squat and concentrated closer to the sun’s equator. During high activity, they can get more stringy and spread out.

Scientists suspect that’s because as the sun ramps up its activity, its strengthening magnetic field lets the streamers stretch farther out into space. The sun’s equatorial magnetic field also splits to straddle the equator rather than encircle it. That allows streamers to spread toward the poles and occupy new space.

Although physicists have been studying the corona’s changes for 150 years, that’s still only a dozen or so solar cycles’ worth of data. There is plenty of room for new observations to help decipher the corona’s mysteries. And Yanamandra-Fisher’s group might be the first to collect data from the same point on Earth.

“This is pure science that can be done only during an eclipse,” Yanamandra-Fisher says. “I want to see how the corona changes.”

Cube-shaped ice is rare, at least at the microscopic level of the ice crystal. Now researchers have coaxed typically hexagonal 3-D ice crystals to form the most cubic ice ever created in the lab.

Cubed ice crystals — which may exist naturally in cold, high-altitude clouds — could help improve scientists’ understanding of clouds and how they interact with Earth’s atmosphere and sunlight, two interactions that influence climate.

Engineer Barbara Wyslouzil of Ohio State University and colleagues made the cubed ice by shooting nitrogen and water vapor through nozzles at supersonic speeds. The gas mixture expanded and cooled, and then the vapor formed nanodroplets. Quickly cooling the droplets further kept them liquid at normally freezing temperatures. Then, at around –48° Celsius, the droplets froze in about one millionth of a second.

The low-temperature quick freeze allowed the cubic ice to form, the team reports in the July 20 Journal of Physical Chemistry Letters. The crystals weren’t perfect cubes but were about 80 percent cubic. That’s better than previous studies, which made ice that was 73 percent cubic.

Neandertals took stick-to-itiveness to a new level. Using just scraps of wood and hot embers, our evolutionary cousins figured out how to make tar, a revolutionary adhesive that they used to make formidable spears, chopping tools and other implements by attaching sharp-edged stones to handles, a new study suggests.

Researchers already knew that tar-coated stones date to at least 200,000 years ago at Neandertal sites in Europe, well before the earliest known evidence of tar production by Homo sapiens, around 70,000 years ago in Africa. Now, archaeologist Paul Kozowyk of Leiden University in the Netherlands and colleagues have re-created the methods that these extinct members of the human genus could have used to produce tar.
Three straightforward techniques could have yielded enough adhesive for Neandertals’ purposes, Kozowyk’s team reports August 31 in Scientific Reports. Previous studies have found that tar lumps found at Neandertal sites derive from birch bark. Neandertal tar makers didn’t need ceramic containers such as kilns and didn’t have to heat the bark to precise temperatures, the scientists conclude.
These findings fuel another burning question about Neandertals: whether they had mastered the art of building and controlling a fire. Some researchers suspect that Neandertals had specialized knowledge of fire control and used it to make adhesives; others contend that Neandertals only exploited the remnants of wildfires. The new study suggests they could have invented low-tech ways to make tar with fires, but it’s not clear whether those fires were intentionally lit.

“This new paper demystifies the prehistoric development of birch-bark tar production, showing that it was not predicated on advanced cognitive or technical skills but on knowledge of familiar, readily available materials,” says archaeologist Daniel Adler of the University of Connecticut in Storrs, who did not participate in the study.
Kozowyk’s group tested each of three tar-making techniques between five and 11 times. The lowest-tech approach consisted of rolling up a piece of birch bark, tying it with wood fiber and covering it in a mound of ashes and embers from a wood fire. Tar formed between bark layers and was scraped off the unrolled surface. The experimenters collected up to about one gram of tar this way.

A second strategy involved igniting a roll of birch bark at one end and placing it in a small pit. In some cases, embers were placed on top of the bark. The researchers either scraped tar off bark layers or collected it as it dripped onto a rock, strip of bark or a piece of bark folded into a cup. The most tar gathered with this method, about 1.8 grams, was in a trial using a birch-bark cup placed beneath a bark roll with its lit side up and covered in embers.

Repeating either the ash-mound or pit-roll techniques once or twice would yield the relatively small quantity of tar found at one Neandertal site in Europe, the researchers say. Between six and 11 repetitions would produce a tar haul equal to that previously unearthed at another European site.

In a third technique, the scientists placed a birch-bark vessel for collecting tar into a small pit. They placed a layer of twigs across the top of the pit and placed pebbles on top, then added a large, loose bark roll covered in a dome-shaped coat of wet soil. A fire was then lit on the earthen structure. This method often failed to produce anything. But after some practice with the technique, one trial resulted in 15.7 grams of tar — enough to make a lump comparable in size to the largest chunks found at Neandertal sites.

An important key to making tar was reaching the right heat level. Temperatures inside bark rolls, vessels, fires and embers varied greatly, but at some point each procedure heated bark rolls to between around 200˚ and 400˚ Celsius, Kozowyk says. In that relatively broad temperature range, tar can be produced from birch bark, he contends.

If they exploited naturally occurring fires, Neandertal tar makers had limited time and probably relied on a simple technique such as ash mounds, Kozowyk proposes. If Neandertals knew how to start and maintain fires, they could have pursued more complex approaches.

Some researchers say that excavations point to sporadic use of fire by Neandertals, probably during warm, humid months when lightning strikes ignited wildfires. But other investigators contend that extinct Homo species, including Neandertals, built campfires (SN: 5/5/12, p. 18).

Whatever the case, Kozowyk says, “Neandertals could have invented tar with only basic knowledge of fire and birch bark.”

Walls can get the best of clumsy TV sitcom characters and bats alike.

New lab tests suggest that smooth, vertical surfaces fool some bats into thinking their flight path is clear, leading to collisions and near misses.

The furry fliers famously use sound to navigate — emitting calls and tracking the echoes to hunt for prey and locate obstacles. But some surfaces can mess with echolocation.

Stefan Greif of the Max Planck Institute for Ornithology in Seewiesen, Germany, and colleagues put bats to the test in a flight tunnel. Nineteen of 21 greater mouse-eared bats (Myotis myotis) crashed into a vertical metal plate at least once, the scientists report in the Sept. 8 Science. In some crashes, bats face-planted without even trying to avoid the plate.
Smooth surfaces act as acoustic mirrors, the team says: Up close, they reflect sound at an angle away from the bat, producing fuzzier, harder-to-read echoes than rough surfaces do. From farther away, smooth surfaces don’t produce any echoes at all.

Infrared camera footage of wild bat colonies showed that vertical plastic plates trick bats in more natural settings, too.

Crash reel
This video shows three experiments into how smooth surfaces affect bat flight. In one lab test, a vertical metal plate gave a bat the illusion of a clear flight path, causing it to crash into the barrier. In a second lab test, a horizontal metal plate created the illusion of water; the bat dips to surface to take a sip. Finally, near a natural bat colony, a bat collides with a vertically hung plastic plate, showing that smooth surfaces could impact bats in the wild, as well.

After one last swing past Titan, the Cassini spacecraft is now plunging to its doom. At 3:04 p.m. EDT (12:04 p.m. PDT) on September 11, the spacecraft used a gravitational nudge from Saturn’s largest moon to set itself on a collision course with the giant planet’s atmosphere on September 15.

Cassini’s last close flyby of Titan on April 21 curved the spacecraft’s orbit to send it on a series of dives between Saturn and its rings. That approach took the probe to about 979 kilometers above the moon’s surface. This final flyby, which the mission team calls the “kiss goodbye,” is a more distant 119,049 kilometers — but that’s enough to slow the spacecraft down and send it into Saturn’s atmosphere, where it will ultimately melt and disintegrate.

“There is no coming out of it,” Cassini project manager Earl Maize said in a press conference on August 29. “That final kiss goodbye, I don’t want to get too romantic about it, but that really is our last flyby.”

Titan is home to lakes and rivers made of liquid hydrocarbons, which may be hospitable to life unlike that on Earth. Mission engineers decided to send Cassini to burn up in Saturn’s atmosphere in part to protect any potential life-forms from contamination if Cassini accidentally crashed into Titan.

Cassini has been orbiting Saturn since 2004 and has revolutionized our understanding of Saturn’s atmosphere, rings, moons, and of the outer solar system in general.

To the residents of Donora, Pa., a mill town in a crook of the Monongahela River, the daily haze from nearby zinc and steel plants was the price of keeping their families fed. But on October 27, 1948, the city awoke to an unusually sooty sky, even for Donora. The next day, the high school quarterbacks couldn’t see their teammates well enough to complete a single pass.

The town was engulfed in smog for five days, until a storm finally swept the pollution out of the valley. By then, more than one-third of the population had fallen ill and 20 people were dead. Another 50 perished in the following months.

After the Donora tragedy, the federal government began to clamp down on industries that release pollutants into the air. Environmental advocates in the coming decades fought for, and won, tighter regulations. As a result, combined emissions of six common air pollutants have dropped by about 70 percent nationwide since the 1970 passage of the Clean Air Act, which regulates U.S. emissions of hazardous air pollutants. In 35 major U.S. cities, the total number of days with unhealthy air has fallen by almost two-thirds just since 2000. “It’s one of the great success stories of public health,” says Joel Kaufman, a physician and epidemiologist at the University of Washington School of Public Health in Seattle.

Our bodies feel the difference. One study, reported in JAMA last year, followed 4,602 children in Southern California between 1993 and 2012 to see how lung health correlated with three common air pollutants. As levels of ozone, nitrogen dioxide and particulate matter fell over time, so did the number of children who reported a daily cough, persistent congestion and other symptoms of irritated lungs. At the start of the study, 48 percent of children with asthma had reported bronchitis symptoms in the previous year. In communities with the greatest drop in pollutants during the study period, bronchitis prevalence fell by as much as 30 percent in children with asthma.
But the air pollution story isn’t over. Researchers from the Harvard T.H. Chan School of Public Health in Boston recently reported on links between air quality and mortality throughout the entire U.S. Medicare population (more than 60 million people who are age 65 and older or disabled). The analysis looked at levels of two common air pollutants and death rates from 2000 to 2012, while accounting for factors that might confound the results, such as race and socioeconomic status. The analysis, published in June in the New England Journal of Medicine, found that when pollutant levels rose (but remained at levels below national standards), so did death rates.

Even with vast improvements in air quality since the ’70s, people haven’t stopped dying from the air they breathe. An analysis published in 2013 from researchers at MIT estimated that about 200,000 premature deaths occur each year in the United States because of fine particulate air pollution. A study published in January in Environmental Health Perspectives reported that daily deaths over a decade in metropolitan Boston peaked on days when concentrations of three common air pollutants were at their highest, even though those levels would currently satisfy the U.S. Environmental Protection Agency.

“We’ve made these improvements in exposure,” Kaufman says, “but what more do we need to clean up?”

So despite a half-century of progress, airborne grime is still a menace — probably in ways the people of Donora never imagined. Researchers are now finding that more than the lungs are at risk, as dirty air may in fact be an accomplice to some of the greatest threats to public health, including diabetes, obesity and even dementia. Those studies are likely to inform the ongoing debate over antismog rules. The U.S. House of Representatives voted this summer to delay implementation of updated standards for the Clean Air Act.

Slow burn
As it has for more than a century, air pollution in America largely arises from power plants, industries, vehicles and other sources of fuel burning. The pollution is generally a mixture of gases — such as carbon monoxide, sulfur dioxide and nitrogen oxides — and particulate matter, microscopic solids or droplets that can be inhaled into the lungs. The pollutant that has declined the least is ozone, a hard-to-control noxious gas formed when nitrogen oxides and volatile organic compounds react with sunlight. Ozone pollution tends to soar on hot, windless summer days as the sun blazes.

Particulates come from tail pipes and smokestacks, but also consist of tiny fragments shed from tires, roads and brake pads. Fine particulates (less than 2.5 micrometers wide, or about a quarter of the width of the smallest grain of pollen) are of greatest concern because they can penetrate deeply into the lungs to reach the body’s innermost nooks and crannies. A study in April in the journal ACS Nano demonstrated that fact. Fourteen healthy volunteers intermittently riding exercise bikes inhaled gold nanoparticles — stand-ins for particulates — and 15 minutes later, the nanoparticles were detected in the bloodstream and remained present in the body for as long as three months.

While events in Donora showed that air pollution can have immediate consequences, it took decades for researchers to realize that deaths from smog could be going undetected, lost in the background noise of mortality statistics. In 1993, Harvard University scientists published a study in the New England Journal of Medicine looking at mortality rates among adults in six U.S. cities. The researchers studied more than 8,000 people for 14 to 16 years. In areas with higher levels of sulfate particles in the air, a measure of pollution, mortality rates were higher. Dozens of similar studies have followed, including one published in 2003 that looked at death rates across 20 of the largest U.S. cities. That research found that the highest death rates occurred the day after particulate concentrations reached their highest levels, though the levels were subtle enough to go unnoticed at the time.
Scientists now know that inhaling pollutants triggers a flurry of physiological coping mechanisms throughout the body. “Until 20 years ago, we thought that air pollution affected only the respiratory system,” says Petros Koutrakis, an environmental chemist who heads the EPA Harvard Center for Ambient Particle Health Effects. By 2004, the American Heart Association published a consensus statement in Circulation laying out “a strong case that air pollution increases the risk of cardiovascular disease,” the leading cause of U.S. deaths.
More studies followed that statement, including one from Kaufman and colleagues in the New England Journal of Medicine in 2007. The researchers studied 65,893 women, looking for a link between exposure to fine particulates and death from heart attack or stroke, or even nonfatal heart attacks or the need for artery-clearing procedures. In the end, each increase of 10 micrograms of fine particulates per cubic meter of air increased the risk of any cardiovascular health event by 24 percent and the risk of dying from heart attack or stroke by 76 percent. In 2010, the American Heart Association updated its position: “The overall evidence is consistent with a causal relationship between [fine particulate] exposure and cardiovascular morbidity and mortality.” While the mechanism is still under study, research points to inflammation, heart rate variability and blood vessel damage.

Evidence keeps accumulating. A study by Koutrakis and colleagues, published in 2012 in Archives of Internal Medicine, found similar results. When particulate concentrations rose even to mild levels — those classified as a “moderate health concern for a very small number of people” by EPA standards — the risk of stroke rose by 34 percent within a day of exposure.

Pounds and pollution
Lately, studies have moved from cardiovascular disease into more unexpected territory. And they’ve turned up compelling evidence that air quality may contribute to excess body weight. Frank Gilliland, an environmental epidemiologist at the University of Southern California in Los Angeles, became intrigued when laboratory studies suggested that certain pollutants in the environment might function as “obesogens,” contributing to weight gain by mimicking or disrupting the action of hormones, or having other effects. Still, he says, “I was very skeptical.”

Out of curiosity, he began to look for a link between childhood obesity and living close to a major roadway. His first study, published in 2010, examined over 3,000 children across California. Although the researchers found an association, they couldn’t rule out other explanations that would also lead back to cars. “Maybe the kids aren’t getting exercise because there’s a lot of traffic out,” he says.
Newer findings are more convincing, including a 2014 study by Gilliland and colleagues. They studied body mass index among children exposed to traffic-related air pollution. Of course, as the children grew over the five-year study period, their BMIs increased from an average of 16.8 to 19.4 kilograms per square meter. But children exposed to the most air pollution, compared with those least exposed, had a 14 percent larger BMI increase, which meant an additional 0.4 kg/m2 increase in BMI by age 10. Adults, too, appear to be affected. Researchers from Harvard Medical School and elsewhere published a study in 2016 in the journal Obesity looking at whether adults living with constant exposure to traffic are more likely to be overweight. In particular, people who lived within 60 meters of a major road had a higher BMI, by 0.37 kg/m2, and more fat tissue than those who lived 440 meters from a busy road. The healthy range for an adult’s BMI is 18.5 to 25 kg/m2.

Studies in animals have started to offer hints why this might be the case. Last year in the FASEB Journal, Chinese researchers described an experiment in which one group of pregnant rats was raised in filtered air scrubbed of pollutants, while another breathed the usual Beijinghaze. Though they were fed the same diet, the animals living in Beijing air were heavier at the end of their pregnancies, as were their offspring that continued to breathe the dirty air eight weeks after birth. Among later autopsy findings: Rats exposed to pollution experienced higher levels of inflammation, which is thought to be a contributor to weight gain and metabolic disruption.

The relationship is probably subtle, and interwoven with genetics and lifestyle. UCLA researchers who followed a large group of African-American women over 16 years found no association between weight and exposure to particulates. For now, the connection between obesity and pollution is still a subject of investigation. But given that 11 million Americans live along major roadways, even a small effect could have widespread consequences.

Links to diabetes
For many people, diabetes goes hand in hand with obesity. One of the earliest compelling studies to suggest a relationship between diabetes and air pollution was an animal experiment published in 2009 in Circulation from researchers at Ohio State University and other institutions. The test was relatively simple: Two groups of mice were fed a high-fat diet for 24 weeks. One lived in clean, filtered air; the other group was housed in enclosures polluted with air containing fine particulates, at concentrations still within EPA standards. The mice breathed the polluted air for six hours per day, five days a week for 128 days. Even though they ate the same food, the mice living in dirty air developed metabolic changes characteristic of insulin resistance while the other mice did not. Similarly, a 2013 study from EPA scientists found that mice exposed to ozone can develop glucose intolerance, a precursor for diabetes.

In July in Diabetes, Gilliland and colleagues published data not only finding links between air pollution and diabetes in children, but also insight into the body’s physiological response. In the study, 314 overweight or obese children in Los Angeles were followed for an average of three years. At the end of the study, children who lived in neighborhoods with the highest concentrations of nitrogen dioxide and particulates had experienced greater declines in insulin sensitivity and had signs of impaired pancreatic beta cells, which produce insulin.
As for adults, a study this year in Environment International, conducted by researchers from eight institutions, tracked more than 45,000 African-American women across the United States. Those who were exposed to the highest concentrations of ozone were about 20 percent more likely to develop diabetes, even after adjusting for other possible explanations such as diet and exercise levels.

Brain drain
One of the latest lines of research suggests that poisons in the air might accelerate aging in the brain. Studies have long documented the connection between the nose and brain function. For reasons not yet known, for instance, one of the early signs of Parkinson’s disease is a loss of the ability to distinguish smells.

During her graduate studies at Harvard, Jennifer Weuve, now an epidemiologist at the Boston University School of Public Health, wondered if airborne pollutants might be bad for the brain. “There was really intriguing data from animal studies,” she says, which showed that inhaled pollutants had toxic effects on nerve cells. In 2012, she published the first study to note a faster-than-normal cognitive decline among people exposed to higher levels of particulates, both those smaller than 2.5 micrometers and even larger ones that are thought to be less harmful. Her study, published in Archives of Internal Medicine, analyzed data from the Nurses’ Health Study Cognitive Cohort, which included almost 20,000 women ages 70 to 81, and used geographic information and air-monitoring data to estimate pollution exposure.

More recently, researchers from Sweden examined the relationship between pollution exposure and dementia, studying the records of people in northern Sweden participating in a long-term study of memory and aging. In 2016 in Environmental Health Perspectives, the researchers reported that people with the most exposure to air pollution were also the most likely to be diagnosed with Alzheimer’s or other forms of dementia. In all, more than a dozen human studies have examined pollution’s link to dementia. Last year in NeuroToxicology, Weuve and colleagues reviewed 18 human studies published as of late 2015, and concluded that as a whole, the evidence was “highly suggestive” and in need of more exploration. “What is it going to take for more people to take this seriously?” Weuve asks.

While the relationship is far from established, animal data may help clarify the results. One study published this year in Neurobiology of Aging, from researchers at the University of Southern California, examined brain changes in mice exposed to particulate air pollution at levels commonly found near freeways. After exposure to the pollution for five hours per day, three days a week for 10 weeks, the animals showed accelerated aging in the hippocampus, a region of the brain associated with memory. And a 2015 study of older women exposed to high levels of particulate matter, at levels common in the eastern half of the United States and in parts of California, showed a small decrease in the volume of white matter, the myelin-coated nerve cell projections called axons.
Parkinson’s disease may also be linked to pollution. Danish researchers, with colleagues in the United States and Taiwan, published a study last year in Environmental Health Perspectives looking at people with and without Parkinson’s and their exposure to nitrogen dioxide, a marker for traffic-polluted air. The scientists identified 1,828 people in Denmark with Parkinson’s diagnosed between 1996 and 2009, and compared them with about the same number of randomly selected healthy people. Those exposed to the highest levels of air pollution had the greatest risk of developing the disease. The data, the researchers wrote, “raise concern given the increase in vulnerable aging populations.”

If science bears out the connection between pollution and brain health, or pollution and metabolism, environmental advocates and businesses may have even more reason to push for cleaner air. Researchers hope in the future to have more data on which pollutants cause the greatest harm, and why. In Donora, the site of one of the country’s biggest air pollution disasters, a sign at the Smog Museum now reads “Clean Air Started Here.” No one can yet say how clean is clean enough.

Saber-toothed kittens were the spitting image of their parents. Even as babies, the cats not only had the oversized canine teeth but also unusually powerful forelimbs, Katherine Long, a graduate student at California State Polytechnic University in Pomona, and colleagues report September 27 in PLOS ONE.

As adults, the ferocious felines used those strong forelimbs to secure wriggling prey before slashing a throat or belly (thereby avoiding breaking off a tooth in the struggle). Paleontologists have puzzled over whether saber-toothed cats such as Smilodon fatalis developed those robust limbs as they grew.

To compare the growth rate of Smilodon with that of similar-sized non‒saber-toothed cats that lived alongside it, Long and her team turned to fossils collected from the La Brea Tar Pits in Los Angeles. The ancient asphalt traps hold a wealth of species and specimens from juveniles to adults, dating to between 37,000 and 9,000 years ago.

The Smilodon bones, they found, did not show any evidence of an unusual growth spurt. Instead, the bones grew longer and slimmer as the kittens grew up, following the same developmental pattern as the other large cats. That suggests that when it comes to their mighty forelimbs, Smilodon kittens were just born that way.

In a pitch-black rainforest with fluttering moths and crawling centipedes, Christina Warinner dug up her first skeleton. Well, technically it was a full skeleton plus two headless ones, all seated and draped in ornate jewelry. To deter looters, she excavated through the night while one teammate held up a light and another killed as many bugs as possible.

As Warinner worked, unanswerable questions about the people whose skeletons she was excavating flew through her mind. “There’s only so much you can learn by looking with your own eyes at a skeleton,” she says. “I became increasingly interested in all the things that I could not see — all the stories that these skeletons had to tell that weren’t immediately accessible, but could be accessible through science.”

At age 21, Warinner cut her teeth on that incredibly complex sacrificial burial left behind by the Maya in a Belize rainforest. Today, at age 37, the molecular anthropologist scrapes at not-so-pearly whites to investigate similar questions, splitting her time between the University of Oklahoma in Norman and the Max Planck Institute for the Science of Human History in Jena, Germany.
In 2014, she and colleagues reported a finding that generated enough buzz to renew interest in an archaeological resource many had written off decades ago: fossilized dental plaque, or calculus. Ancient DNA and proteins in the plaque belong to microbes that could spill the secrets of the humans they once inhabited — what the people ate, what ailed them, perhaps even what they did for a living.

Bacteria form plaque that mineralizes into calculus throughout a person’s life. “It’s the only part of your body that fossilizes while you’re still alive,” notes Warinner. “It’s also the last thing to decay.”

Though plaque is prolific in the archaeological record, most researchers viewed calculus as “the crap you scraped off your tooth in order to study it,” says Amanda Henry, an archaeologist at Leiden University in the Netherlands. With some exceptions, molecular biologists saw calculus as a shoddy source of ancient DNA.

But a few researchers, including Henry, had been looking at calculus for remnants of foods as potential clues to ancient diets. Inspired by some of Henry’s images of starch grains preserved in calculus, Warinner wondered if the plaque might yield dead bacterial structures, perhaps even bacteria’s genetic blueprints.

Her timing couldn’t have been better. Warinner began her graduate studies at Harvard in 2004, just after the sequencing of the human genome was completed and by the time she left in 2010, efforts to survey the human microbiome were in full swing. As a postdoc at the University of Zurich, Warinner decided to attempt to extract DNA from the underappreciated dental grime preserved on the teeth of four medieval skeletons from Germany.
At first, the results were dismal. But she kept at it. “Tina has a very interested, curious and driven personality,” Henry notes. Warinner turned to a new instrument that could measure DNA concentrations in skimpy samples, a Qubit fluorometer. A surprising error message appeared: DNA too high. Dental calculus, it turned out, was chock-full of genetic material. “While people were struggling to pull out human DNA from the skeleton itself, there’s 100 to 1,000 times more DNA in the calculus,” Warinner says. “It was sitting there in almost every skeletal collection untouched, unanalyzed.”
To help her interpret the data, Warinner mustered an army of collaborators from fields ranging from immunology to metagenomics. She and her colleagues found a slew of proteins and DNA snippets from bacteria, viruses and fungi, including dozens of oral pathogens, as well as the full genetic blueprint of an ancient strain of Tannerella forsythia, which still infects people’s gums today. In 2014, Warinner’s team revealed a detailed map of a miniature microbial world on the decaying teeth of those German skeletons in Nature Genetics.

Later in 2014, her group found the first direct protein-based evidence of milk consumption in the plaque of Bronze Age skeletons from 3000 B.C. That same study linked milk proteins preserved in the calculus of other ancient human skeletons to specific animals — providing a peek into long-ago lifestyles.

“The fact that you can tell the difference between, say, goat milk and cow milk, that’s kind of mind-blowing,” says Laura Weyrich, a microbiologist at the University of Adelaide in Australia, who also studies calculus.
Since then, Warinner has found all sorts of odds and ends lurking on archaic chompers from poppy seeds to paint pigments. Warinner’s team is still looking at the origins of dairying and its microbial players, but she’s also branching out to the other end of the digestive spectrum. The researchers are looking at ancient DNA in paleofeces, which is exactly what it sounds like — desiccated or semifossilized poop. It doesn’t stay as fresh as plaque in the archaeological record. But she’s managed to find some sites with well-preserved samples. By examining the array of microbes that lived in the excrement and plaque of past humans and their relatives, Warinner hopes to characterize how our microbial communities have changed through time — and how they’ve changed us.

The research has implications for understanding chronic, complex human diseases over time. Warinner’s ancient DNA work “opens up a window on past health,” says Clark Larsen, an anthropologist at Ohio State University.

It’s all part of what Warinner calls “the archaeology of the unseen.”

Editor’s note: This story was corrected on October 4, 2017, to note that the 2014 report on milk consumption was based on protein evidence, not DNA.