Blame oxidation for rusted bridges and browned avocados. But this fundamental process can be harnessed for good, too — and now scientists have scored front-row seats that could show them how.

Researchers watched at near-atomic resolution as iron nanoparticles transformed into iron oxide — not rust in this case, but related compounds. That closeup view could help scientists better control oxidation and design corrosion-resistant materials or new kinds of catalysts, the researchers report in the April 21 Science.
This is the first time the oxidation process has been observed in such detail, says Andreu Cabot, a physicist at the Catalonia Institute for Energy Research in Barcelona who wasn’t part of the study.

When a metal oxidizes, its atoms mix and mingle with oxygen atoms to create a new material. That process is perhaps most famous for creating rust, which flakes and corrodes. But iron can oxidize in a variety of ways, some of which are useful.

For instance, chemist Yugang Sun and his colleagues at Temple University in Philadelphia are trying to create hollow iron oxide nanoparticles that could serve as catalysts to speed up chemical reactions or as vessels to deliver drugs or store energy in chemical form. But making these “nanoshells” from iron nanoparticles requires precise control over the oxidation process.

If oxygen atoms work their way into an iron nanoparticle faster than the iron atoms can diffuse out, that nanoparticle becomes a tight, solid ball, Sun says. If the iron diffuses out faster than the oxygen comes in, on the other hand, it becomes the hollow sphere that Sun’s lab wants.

Controlling that process is difficult because it has been unclear exactly how these shells form on an atomic level, Sun says. Scientists haven’t been able to watch it happen, because high-powered microscopy techniques can disrupt the reaction or show the action in only two dimensions.
Sun’s team tried a different approach to observe the reaction, by shooting X-rays at many identical iron nanoparticles suspended in a liquid. Each time the X-rays hit a different material — moving from the liquid to the solid, for instance — they scattered.
By tracking how the X-rays bounced off many small, uniform iron nanoparticles, the researchers were able to reconstruct where individual atoms were going as the particles oxidized into hollow shells over the course of several hours.

The researchers watched as the iron moved out of the center of the nanoparticle to react with the oxygen, initially forming many small holes inside the nanoparticle. Eventually, those empty spaces merged together to form one big void in the middle of the nanoparticle.

“The impact of this paper is more than just the hollow [nanoparticles],” says Yadong Yin, a chemist at the University of California, Riverside who wasn’t involved in the research. The imaging technique itself will be a useful way to study how other types of nanoparticles form — something scientists still don’t understand well, he says. It can be used to gain insight into other types of oxidation, too.

An experimental drug touted as “exercise in a pill” has dramatically increased endurance in couch potato mice, even after a lifetime of inactivity. It appears to work by adjusting the body’s metabolism, allowing muscles to favor burning fat over sugar, researchers report in the May 2 Cell Metabolism.

Sedentary mice prodded into exercising ran for an average of about 160 minutes on an exercise wheel before reaching exhaustion. But mice given the drug for eight weeks could run for 270 minutes on average. These mice were burning fat like conditioned athletes, even though they had spent their whole lives taking it easy, molecular biologist Michael Downes and colleagues found.
Normally, running, cycling or other prolonged exercise eventually depletes available glucose in the blood, leaving the brain short of energy. The brain then sends an emergency stop signal. Athletes call this “hitting the wall.” Training and conditioning shift the body to burning fat for energy, leaving an ample supply of glucose for the brain and other organs.

Scientists at the Salk Institute for Biological Studies in La Jolla, Calif., developed the drug to activate a protein that regulates genes triggered during exercise. “We believe it’s tricked the body into thinking it’s done some training,” says Downes.

Called GW501516, the drug has been under study for more than a decade. Previous research had found that it could improve endurance, but only when combined with regular exercise (SN: 7/3/10, p. 18). The goal is not to boost athlete performance, though, but to help those who can’t exercise: people who are sick, disabled or elderly. It may also aid people who are obese or diabetic and do not have the stamina for even short-term exercise, Downes says.

“We know a lot about exercise, but we still don’t know how we obtain all the benefits,” says Rick Vega, a molecular and cellular biologist at Sanford Burnham Prebys Medical Discovery Institute in Orlando, who was not involved in the experiment. He praised the work as adding valuable information to the understanding of exercise and the drug in development. “The next step is really to show this has value in a medical application. To state the obvious, mice are not humans.”

Chaco Canyon is a land of extremes. Summer heat scorches the desert canyon, which is sandwiched between sandstone cliffs nearly two kilometers above sea level in New Mexico’s northwestern corner. Bitter cold sweeps in for winter. Temperatures can swing as many as 28 degrees Celsius during the course of a day. Through it all, Chaco Canyon maintains a desolate beauty and a craggy pride as home to one of ancient America’s most enigmatic civilizations.

Scientists have struggled to understand Chaco society since its first excavations in the late 1800s. Who first settled Chaco Canyon around 1,200 years ago is still a mystery. Many researchers suspect that it took a few hundred years for a fledgling city-state run by an elite social class to emerge. Political and cultural ties between the ancient society and Chaco-style communities outside the canyon also perplex. Then there’s the puzzle of how people survived from about 800 to around 1300 on the rough, parched terrain.
A new generation of Chaco studies and discoveries is under way, partly thanks to a young researcher’s skeleton reassembly project. This jigsaw job required a lot of travel, but not to Chaco Canyon.

That’s because bones of people excavated at Chaco in the 1890s and 1920s were packed away in boxes and drawers at museums in New York City, Chicago and Washington, D.C. Kerriann Marden visited all of these places to retrieve far-flung body parts from one site in particular — Pueblo Bonito, the oldest and largest of a dozen huge stone great houses in Chaco Canyon. The structure was built, along with a range of smaller structures, between about 800 and 1130.
Pueblo Bonito was massive, rising at least five stories with around 650 rooms. It has yielded more human bones and artifacts than any other Chaco site. Research has focused on this great house presumably reserved for Chaco’s elite families; the lives of workaday folk have been largely unexplored, even in the latest studies.
During Chaco society’s heyday, other civilizations peaked elsewhere in the Americas, including the Maya in Central America. Just as present-day Maya groups trace their ancestry back to that ancient civilization, today’s Pueblo tribes, such as the Hopi and Zuni, consider Chaco people to have been their forebears. Navajo Nation also claims an ancestral tie to Chaco society.
Reassembly required
Archaeological excavations a century or more ago — at Pueblo Bonito and elsewhere — didn’t follow today’s rigorous standards for excavating and preserving remains. The work consisted of little more than mining for bones and artifacts, then carting the discoveries off to museums. As an anthropology graduate student at Tulane University in New Orleans, Marden journeyed back and forth between New York’s American Museum of Natural History, Chicago’s Field Museum and Washington’s Smithsonian National Museum of Natural History from 2005 to 2011. She painstakingly reunited long-dead Chaco individuals’ skulls with arms, legs with feet and so on. Marden is now a forensic anthropologist at Eastern New Mexico University in Portales.

As skeletons assumed their former shapes, a couple of peculiar things stood out. First, many individuals bore signs of disease, including tuberculosis and syphilis. That seemed peculiar for people who were buried in a great house typically thought to have been reserved primarily for society’s upper crust, not for the ill. Second, bodies had been manipulated in unusual ways and for unknown reasons. Comparisons of restored skeletons with field notes and photographs from original excavations indicated, for instance, that one woman was originally found with a fetus’s fragile remains in her pelvic cavity and her own bones below the knees missing. Her body lay across a room from several intact bodies.

“Nothing is simple at Pueblo Bonito,” Marden says. Her campaign to put Pueblo Bonito skeletons back together has enabled a couple of provocative new investigations. One concludes that members of a single maternal line wielded power in Chaco society from the start through an unexpected stretch of at least 330 years and perhaps 10 generations. Another study proposes that Chaco society’s founders were not outsiders with experience constructing huge buildings, as many researchers have assumed. People living in and near Chaco Canyon may have established a cliff-bordered society all on their own.
Other new findings suggest that Chaco residents contacted and traded with people living as far as 2,500 kilometers to the south in Central America and as close as 75 kilometers to the west and south. It’s debatable, though, whether Chaco Canyon’s 2,000 to 3,000 residents could raise enough crops to feed themselves or whether they had to trade for staples such as maize.

Less contentious — but far weirder — is evidence from graves and artwork that Chaco people revered community members with six toes and often created images of human feet and footprints with and without extra digits.

DNA dynasty
Fittingly, Chaco society’s archaeological footprint covers what was once an extensive regional system of buildings and roads. The largest great houses were clustered in a 2-kilometer-diameter downtown zone at the center of Chaco Canyon. Smaller great houses, ritual structures called kivas, groups of small family houses and other urban features, connected by a network of straight dirt roads, fanned out from the canyon across an area the size of Ireland.

After Chaco society dissolved around 1300, Pueblo groups may have rejected its centralized political system and social classes, says archaeologist Stephen Lekson of the University of Colorado Boulder. Pueblo people today live in small communities oriented around clans based on maternal lines of descent.

Therein lies a connection between past and present, says archaeologist Stephen Plog of the University of Virginia in Charlottesville. Many individuals buried in one of Pueblo Bonito’s oldest rooms, known to researchers as Room 33, shared maternal ancestry (SN Online: 2/21/17). Plog and colleagues — led by Penn State archaeologist Douglas Kennett — extracted mitochondrial DNA, which is typically passed from mother to child, from skeletons of nine of 14 individuals interred in Room 33. Marden’s reassembly project was crucial to identifying individuals whose DNA was analyzed.

Members of this Pueblo Bonito group, the researchers reported February 21 in Nature Communications, inherited mitochondrial DNA that was similar enough to signal shared kinship with a female line. Nuclear DNA recovered from six Room 33 skeletons identified two as mother and daughter and two others as a grandmother and grandson. Children inherit nuclear DNA from both parents.
Room 33 is a crypt with a complex history. Two men were buried beneath the chamber’s wooden floor, one below the other. The lowermost body had a gash in the head. Plog suspects the man was bashed on the noggin during a fight. Marden thinks it’s more likely that someone with a shovel, perhaps a looter, broke the skull after the man had been buried.

Thousands of offerings, including turquoise and shell beads and pendants, were heaped around the two bodies under Room 33’s floor, with the lion’s share surrounding the bottommost man. Chaco people laid a wooden plank floor over the two men’s graves before additional bodies were buried in the chamber.

Radiocarbon dating conducted by Plog’s group gives a rough timeline for Room 33’s burials. The first two men were placed there as early as 800. Construction of the wooden floor occurred by about 900. Additional burials took place intermittently up to 1130, the new dating indicates. Activity in Room 33 occurred as civilizations flourished throughout the Americas, from what’s now the U.S. Midwest to Central and South America.

Plog regards the extravagantly buried man at the base of Room 33 as an early leader from a prominent Chaco family dynasty. Based on the exceptional treatment given to all deceased individuals placed in the special room in Chaco’s first and largest great house, Plog suspects these folks belonged to a maternal line in which leadership was handed down from the ninth to the 12th century. At that point, researchers suspect, many Chaco residents and possibly members of nearby communities moved to a settlement 50 kilometers north of Chaco Canyon. A Chaco-style great house there was occupied from 1140 to the 1290s, consistent with an influx of people familiar with Chaco architecture.

“Our findings reinforce the possibility that a complex society existed in Chaco by the ninth century, about 200 years earlier than has often been assumed,” Plog says. If so, Chaco society consisted of a few powerful families and lots of commoners from the start.

Local founders
That’s not the only surprise encased in Pueblo Bonito’s skeletal trove. Chemical analyses of teeth from 61 individuals interred in two sections of the great house indicate that most of these people grew up eating food and drinking water from Chaco Canyon or nearby areas to the south. These results challenge an influential idea established over the last decade that people from ancient settlements that included large structures, located more than 160 kilometers north of Chaco Canyon, migrated south and brought with them knowledge of how to design great houses.

Archaeologist T. Douglas Price of the University of Wisconsin–Madison, Plog and colleagues made a case for local origins of Chaco society in the February issue of the Journal of Archaeological Science: Reports.

The researchers focused on the two sections of Pueblo Bonito where human skeletons were found in previous excavations. Room 33 and three adjacent chambers on the great house’s northern side contained burials of about 25 individuals. Four rooms on the structure’s western side produced remains of more than 80 bodies.

Radiocarbon analyses of 12 skeletons from the western chambers, led by Marden during her graduate work, dates the bodies to between the years 687 and 949. Further radiocarbon dating is needed to narrow that wide age range for western interments, Marden says.

Ratios of certain forms of chemical elements — strontium, oxygen and lead — suggest that 58 of 61 people buried in Pueblo Bonito had grown up eating plants and animals and drinking water that came from the Chaco Canyon area.

Plog suspects that the few Chaco Canyon outsiders that have been identified at Pueblo Bonito came from somewhere nearby. It’s unclear what roles those outsiders assumed in Chaco society. But finding a majority of locals buried in the great house challenges a previous proposal that Chaco Canyon was first settled by people from the north, Plog says. Design similarities between some northern stone buildings and Chaco great houses fueled that suspicion.

The new DNA and chemical results aren’t entirely consistent. Although the two men placed beneath the floor of Room 33 belonged to a maternal line interred at Pueblo Bonito, the chemical makeup of their bones suggests they might have grown up outside Chaco Canyon. For now, where the men were raised and how they ended up in Pueblo Bonito remains a mystery. “It will take a while to make sense of both datasets,” Plog says.
Chaco lot
Ancient Chaco society was based in northwestern New Mexico’s Chaco Canyon (green rectangle). Chaco-style great houses (red) appear throughout the region. Roads (some shown here in yellow) radiated out from Chaco Canyon.

Click the dots for more.
Sources: Map: T.D. Price et al/J. Archaeol. Sci.: Reports 2017; feet: P. Crown and H. Mattson/Amer. Antiquity 2016; wood: C. Guiterman et al/PNAS 2016; macaws: A. Watson et al/PNAS 2015; Aztec Ruin: H. Mattson/J. Anthro. Archaeo. 2016.

Reign fall
Marden says it’s too early to say much of anything about how Chaco society was organized based on initial genetic evidence from Pueblo Bonito skeletons. “Huge pronouncements about Chaco social structure are being made based on partial, flawed data,” she says. “It’s like excavating only human foot bones and concluding that people at that time had no hands.”

DNA from a mere nine folks can’t support a sweeping conclusion that Pueblo Bonito housed the dead of a Chaco maternal dynasty, Marden argues. Additional genetic samples are needed to determine, for instance, whether people buried elsewhere in Pueblo Bonito, in other great houses in and near Chaco Canyon and in smaller Chaco buildings belonged to the same maternal line as those from Room 33, she holds.

DNA studies of more Chaco skeletons are unlikely in the near future. Some Pueblo groups have complained that scientists didn’t consult with them before removing genetic material from the bones of people regarded as ancestors. In a related case, scientists have collaborated with Native Americans in the Pacific Northwest, who provided DNA for comparisons to Kennewick Man’s DNA (SN: 7/25/15, p. 6).

In a written statement, the American Museum of Natural History says it approved the new DNA analysis of Chaco bones from its collection based on discussions with 20 Native American tribes in the U.S. Southwest during the 1990s. No claims of cultural ties to Chaco people were lodged then or since, making the new investigation legal, the museum statement concludes.

A formal inquiry to the museum about its decision will be filed soon, says Leigh Kuwanwisiwma, director of the Hopi Cultural Preservation Office in Kykotsmovi, Ariz.

So for now, DNA from nine Chaco individuals raises only provocative possibilities. The two men interred beneath Room 33’s floor appear to have been important, Marden acknowledges, but that doesn’t make them founding fathers of a Chaco dynasty that traced descent through a female line. Room 33 may simply have housed deceased members of a prominent family.
Relatives probably visited the men’s graves in Room 33 on occasion, leaving offerings that piled up over time. Those items, including turquoise frog ornaments and seashells, often refer to water, a precious commodity in Chaco society. However, researchers can easily see signs of symbolic rituals where they don’t exist, Marden warns. For instance, for more than a century, many researchers have assumed that a hole cut into Room 33’s floor represented an entrance to a supernatural underworld for the dead. The floor opening was more likely used as a handle to remove surrounding planks to reach the graves below, she suspects

“There’s undoubtedly symbolism at Pueblo Bonito, but as a forensic anthropologist, I’m looking for practical explanations,” Marden says.

Southern influences
What appears clear at Pueblo Bonito is that connections existed between Chaco society and populations extending as far south as Central America.

Recovered pottery tells a similar story to Price’s teeth analysis suggesting local as well as southern origins for Pueblo Bonito’s dead. Vessels recovered at that great house and other Chaco sites resemble pottery from comparably ancient sites about 50 kilometers to the southwest. Anthropological archaeologist Barbara Mills of the University of Arizona in Tucson reported the finding March 30 in Vancouver at the annual meeting of the Society for American Archaeology.

The Zuni Mountains, about 75 kilometers to the south, and the Chuska Mountains, about the same distance to the west of Chaco Canyon, provided close to 70 percent of the more than 240,000 trees that were used for roof beams, doorframes and other features of Chaco great houses. A team led by dendrochronologist Christopher Guiterman at the University of Arizona reported those findings, based on matching tree ring configurations at Chaco and in the two mountain ranges, last year in Proceedings of the National Academy of Sciences.

Chaco people also apparently traded turquoise objects for goods from societies in southern Mexico and Central America. Residue on Pueblo Bonito jars and pitchers comes from a chocolate beverage made from cacao that grows in those tropical areas (SN Online: 3/17/11). Exotic birds — scarlet macaws — from the same region turned up at Pueblo Bonito starting in the late 800s.

Colorado’s Lekson thinks southern influences on Chaco society run deep. Chaco’s social and political structure drew on a type of small city-state in what’s now southern Mexico and Central America called an altepetl, Lekson proposes. An altepetl consisted of seven or eight related noble families, each ruling over commoners who cultivated crops and paid tribute in food and labor. Leading noble families took turns ruling an altepetl and elected a figurehead king.

Chaco’s seven great houses served as elite families’ residences, as in an altepetl, Lekson proposes. Other Chaco structures housed minor nobles, priests and commoners, from this perspective.

That’s a minority view, though. Mills, Plog and several other Chaco researchers suspect that Chaco society was organized around houses of varying social status. A structure’s status would have been based on its age and ritual connections to ancestors. Differences in architecture among great houses suggest that they were ranked as well, Mills says. If that’s how the system worked, heads of various Chaco houses probably led their respective extended families.

“Chaco was a hierarchically organized society from the start,” Plog says.

It helped that Chaco Canyon’s soil, although salty, was able to support widespread maize cultivation with the help of irrigation ditches, Plog and his colleagues, led by University of Cincinnati geoarchaeologist Kenneth Tankersley, reported in the October 2016 Journal of Archaeological Science: Reports.

University of Colorado hydrologist and geochemist Larry Benson says that’s unlikely. Chaco Canyon soil was too salty and annual rainfall too low to feed more than a few hundred people, Benson reported online last December in the same journal. He suspects that the Chaco crowd imported maize grown near the Chuska Mountains.

Special feet
Chaco society’s puzzles go beyond who was in charge and where meals came from. One of the ancient population’s most vexing oddities concerns feet.
Six-toed individuals appear to have held special status at Pueblo Bonito, says archaeologist Patricia Crown of the University of New Mexico in Albuquerque. “Having six toes brought social honor in Chaco society,” Crown holds. “We don’t know why Chaco people were so interested in feet or what feet symbolized to them.”
A review of Pueblo Bonito skeletons and artifacts conducted by Crown and her colleagues, published in the July 2016 American Antiquity, identified three six-toed individuals among the burials. Only one case had previously been noticed — the less-decorated man placed beneath Room 33’s floor.

It’s not known how common it was to be born with more than five toes or fingers in the ancient U.S. Southwest. This condition affects about 2.4 of every 1,000 Native Americans today.

Footprints and handprints sporting six digits also appear on several plastered walls at Pueblo Bonito. Rock art in Chaco Canyon depicts almost 800 human feet, with anywhere from three to eight toes.

Of 13 ancient sandals recovered at Pueblo Bonito, seven include woven extensions on the outer border for a sixth toe.

Ancient cultures of Southern Mexico and Central America sometimes depicted their gods with six toes. Chaco folk probably regarded extra-toed peers as special but not divine, Crown says. Of the three six-toed individuals given the presumed honor of a Pueblo Bonito burial, only one lay in an elaborate grave. Such treatment would have applied to all three if an extra toe signified godlike status, she says.

That’s a preliminary conclusion, though. Chaco residents constantly reworked and rebuilt Pueblo Bonito for more than 300 years, so deciphering precisely what happened in the great house’s many rooms and at particular times is daunting.

Pinning down Chaco’s origins is equally challenging, Plog says. Pueblo Bonito and many other Chaco structures were built on soil that accumulated when Chaco Canyon streams occasionally flooded. No one has looked for possible forerunners of the ancient society buried underneath all that earth.

Researchers trying to crack Chaco’s secrets while burdened with so many crucial unknowns can be excused for feeling like the pregnant woman buried inside Pueblo Bonito — cut off at the knees.

A stone tool found in Syria more than 80 years ago has sharpened scientists’ understanding of Stone Age networking.

Small enough to fit in the palm of an adult’s hand, this chipped piece of obsidian dates to between 41,000 and 32,000 years ago, say archaeologists Ellery Frahm and Thomas Hauck. It was fashioned out of volcanic rock from outcrops in central Turkey, a minimum of 700 kilometers from where the artifact was found, the researchers report in the June Journal of Archaeological Science: Reports. Until now, the earliest transport of obsidian into the Middle East was thought to have occurred between 14,500 and 11,500 years ago, when Natufian foragers began to live in year-round settlements (SN: 9/25/10, p. 14).
Someone probably shaped the obsidian chunk into a usable tool near its Turkish source, say Frahm, of Yale University, and Hauck, of the University of Cologne in Germany. The tool, which could have been used for various cutting and scraping tasks, was then passed from one mobile group to another, perhaps several times, before reaching Syria’s Yabroud II rock-shelter. Along the way, the implement underwent reshaping and resharpening.

The most direct path between the Turkish and Syrian sites stretches about 700 kilometers. But hunter-gatherers meander, following prey animals and searching for other food. So, Stone Age bearers of the obsidian tool probably traveled considerably farther to reach one of several rock-shelters clustered near what’s now the Syrian town of Yabroud, the investigators say. “They didn’t type ‘Yabroud’ into a GPS unit and make their way to the rock-shelter as fast as possible,” Frahm says.
Excavations at the Yabroud sites between 1930 and 1933 yielded the obsidian tool and hundreds of artifacts made from a type of rock called chert found a mere five to 10 kilometers away. Some researchers suspect the obsidian tool was mistakenly included among much older finds shortly after being excavated. But a copy of the lead excavator’s book describing his fieldwork, housed at Yale, confirms that the implement was found in sediment dating to around the time ancient humans and Neandertals inhabited the Middle East, Frahm says. Since excavators did not collect material for radiocarbon dating, Frahm and Hauck estimated the Syrian rock-shelter’s age by comparing its sediment layers and artifacts with those at several nearby, better-dated sites.
Neandertals survived in the Middle East and elsewhere until at least 40,000 years ago (SN: 9/20/14, p. 11), so they might have been the final recipients of the obsidian tool. But Frahm considers Homo sapiens a better candidate. Humans occupied the Middle East and nearby regions throughout the period when the tool may have been used. No hominid fossils have been recovered at the Syrian site.

Using a portable X-ray device, Frahm and Hauck determined the chemical composition of the obsidian tool and 230 obsidian samples from known sites throughout southwestern Asia. That let the researchers match the Syrian find to its Turkish source.

Outside the Middle East, previous evidence suggested that long-distance obsidian transport occurred in Stone Age Eurasia. Researchers reported in 1966 that two obsidian pieces with sharpened edges found at northern Iraq’s Shanidar Cave originated roughly 450 kilometers to the north. That analysis used an earlier technique for measuring a stone’s chemical composition. Shanidar’s obsidian finds date to about the same time as that of the Yabroud II obsidian tool, perhaps to as early as 48,000 years ago, Frahm says.

Recent investigations of obsidian artifacts at late Stone Age sites in Eurasia not far from Shanidar Cave, in what’s now Armenia and Georgia, indicate that hunter-gatherers there also exploited vast territories, says archaeologist Daniel Adler of the University of Connecticut in Storrs. Frahm has contributed to some of that research. As for the Yabroud II obsidian tool, “a 700-kilometer transport distance is fully within the realm of possibility for a single person over an extended period of time,” Adler says.

Eurasia may have a far older tradition of extensive hunter-gatherer networking than the Middle East does. Evidence of long-distance obsidian transport in Armenia dates to as early as around 500,000 years ago, notes archaeologist Andrew Kandel of the University of Tübingen in Germany. That means Neandertals or other now-extinct hominid species first transported obsidian across hundreds of kilometers, he says.

People may think they act independently. But we catch social behaviors faster than colds. Whether or not we vote, try a new food or wear clear plastic pants will have something to do with whether other people are doing it. Unfortunately, it’s often hard to prove exactly how contagious a particular behavior is, or which behaviors will actually spread.

A new study shows that among runners using a fitness social network, logging miles is infectious — if the runner you’re comparing yourself to is slightly worse than you. The work shows a clever new way to determine if a behavior is socially contagious. But the results also confirm something about runners: We might be a little too competitive.

Glance at any group of kids with fidget spinners or teens wearing the same brand of shoes, and it’s easy to buy into the idea of social contagions. But it’s actually not so simple to distinguish between that kind of peer influence and other outside factors. says Johan Ugander, an applied mathematician at Stanford University. It’s easy for marketers to say they want something to go viral. But it’s a lot harder to be confident that the thing that’s spreading is really a social contagion and not a common factor like location or a group of people with common interests.

For one thing, birds of a feather really do flock together. People become friends because they have things in common. You might share an important article to Facebook, and find a friend has shared the same article 20 minutes later. But is that because you influenced your friend? Or because you have the same interests and read the same kind of articles, and you just happened to see it 20 minutes before they did?

Similarly, people tend to have friends who are near them geographically. So if two neighbors gain weight, Ugander notes, it could be “because the McDonald’s opened down the street, not because I gained weight then you gained weight.”

To get around this problem of homophily, Sinan Aral, a computational social scientist at MIT, decided to look at a single behavior — running. “Running is one of the most pervasive forms of this type of exercise,” he says. “I thought it would be most generalizable.”

Runners also like to log their miles and share them with their peers. Aral was able to get data from one of several social media platforms designed for jogging buffs. Aral can’t disclose the exact app or program he used in the study (and received some funding from), but there are a few social apps out there that fit the bill, including MapMyRun, RunKeeper and Strava. Aral ended up with a vast, anonymized dataset of more than 1.1 million runners who logged more than 359 million kilometers (223 million miles) over five years.
To figure out if running is contagious, there would have to be a way to make some people run and other people stay home. “The ideal study to show [a causal effect] would be to go around with a cattle prod, prodding some people to exercise more,” but leaving others alone, Aral says. “But that’s not an experiment you can run.” (Obviously.)

So Aral and colleagues used the weather as their cattle prod. Good weather beckons a runner outdoors. Rain, snow, sleet or hail will keep a runner off the street. The researchers combed through data, noting what the weather was like on a given day and how far a runner went. They then compared that runner’s logs to their friends in other cities — places far enough away that the weather would be different. With the weather serving as the prod for some to put on their running shoes or keep others at home, the scientists got a good idea of who socially infected who with the running bug.

They found that for every additional kilometer run by someone’s distant friends, the runner would add another 0.3 km (0.18 mi). Timewise, a friend spending an additional 10 minutes running will inspire an extra three minutes in someone else, Aral and his group reported April 18 in Nature Communications.

But social contagion didn’t affect everyone the same way. The runners most influenced were those who compared themselves to runners slightly worse than they were. “In the loose analogy of a race, I’m more motivated by the guy behind me than I am motivated by the person ahead of me,” Aral says.

The study also showed some gender effects. Men were most influenced by other men, but were also ready to outrace the women. In contrast, women did not tend to be influenced by men. “There have been experimental studies showing men are more competitive with one another, while women are more self-directed and motivated by internal factors,” Aral says. But that doesn’t mean that women aren’t competitive. Women were just influenced by other women.

“It’s usually very difficult to identify causal effects from correlational data, in the absence of a randomized controlled trial,” says Edoardo Airoldi, a statistician at Harvard University. The data in this study may not translate to other behaviors — even to other forms of exercise. But that isn’t the point. The beauty, Airoldi says, is in the methods. “People should know you can use the weather as an instrument to uncover patterns of human behavior that are otherwise hard to elicit,” he says.

Ugander is also a fan of the new study, but he notes that this doesn’t mean all social behaviors, or even all sports, will prove similarly contagious, especially with regard to the gender differences. “It’s not clear that that will generalize to yoga or some other sport with other gender norms,” he says.

We don’t really know what exactly drives social contagion. One theory — the complex contagion theory — posits that costly behaviors (like going for an exhausting run) require a lot of signals from a lot of people. In other words, the more people in your network are running, the more likely you are to run.

Another theory developed by Ugander’s group posits that it’s not quantity that matters, but variety, a theory called structural diversity. Your family all going running is one thing. A family member, a friend and coworker is another. “If you’re getting it from two people from different parts of your life, say sibling and coworkers, it carries more weight,” Ugander says. “But two coworkers probably got it from each other.”

A third theory suggests that embeddedness — the number of mutual connections — matters most. After all, seeing all your friends virtuously running and knowing that they are also seeing each other live the wholesome life is a lot of peer pressure.

The data from Aral’s group suggests that for running, embeddedness and structural diversity may prove the most catching. “This doesn’t mean the complex theory is wrong,” Aral notes. “We just didn’t see it for running.”

Aral himself is a runner, and admits he’s not immune to the social contagion he found. “When I have friends who are close to me in fitness in terms of their level of activity, I may be influenced,” he says. “I also feel like I’d be more influenced by someone who was slightly less of a runner than I am. If they were running more, I would think, ‘Wow, even so-and-so is out there, I need to get out there.’” This social behavior might be catching, but the vulnerable population already has a raging competition infection.

The rift in Antarctica’s Larsen C ice shelf continues to rip. Researchers from Project MIDAS, which tracks the effects of a warming climate on the ice shelf, report that the crack grew 17 kilometers between May 25 and May 31.

The crack has now turned toward the water and is within 13 kilometers of the edge of the shelf. Within days, the crack could reach the edge. When that happens, one of the largest icebergs ever recorded will fall into the ocean.

“There appears to be very little to prevent the iceberg from breaking away completely,” the researchers write.

After calving such a massive section, the shelf won’t be stable. It may experience the same fate as Larsen B, which disintegrated in 2002, after a crack there broke off a huge chunk of ice.

A weird new particle imitator flouts the established rules of particle physics. The discovery could help scientists simulate how particles behaved just after the Big Bang or lead to the development of new devices with unusual electromagnetic properties.

The curious new phenomenon involves a particle-like entity called a quasiparticle, formed from a jostling mosh pit of electrons that collectively act like a single particle in a solid. Found in a compound of lanthanum, aluminum and germanium, the new quasiparticle is a bit of a renegade, physicist M. Zahid Hasan of Princeton University and colleagues report June 2 in Science Advances. Known as a type-II Weyl fermion, the quasiparticle breaks a rule called Lorentz symmetry, which states that the laws of physics are the same no matter the observer’s perspective, whether moving or stationary.
Lorentz symmetry is the foundation of Einstein’s special theory of relativity, which details the physics of observers zipping along near the speed of light. For a real particle, violating Lorentz symmetry would be an unallowable faux pas, but for quasiparticles, the rules are looser, so type-II Weyl fermions can behave in a way a normal particle wouldn’t.

Fermions are a class of elementary particle that includes quarks, which make up protons and neutrons, and electrons. There are three different types of fermions: Dirac, Majorana and Weyl. Dirac fermions are the garden-variety type and include electrons and quarks. Majorana fermions are their own antiparticles. Neutrinos, notoriously lightweight and elusive particles, could be either Majorana or Dirac fermions; scientists aren’t yet sure which.

Weyl fermions are a massless variety of fermion. No examples have been found in particle physics. But the quasiparticle version of Weyl fermions burst onto the scene in 2015, when scientists first discovered them in a compound made of tantalum and arsenic (SN: 8/22/15, p. 11). Soon, scientists realized that their Lorentz-violating relatives, type-II Weyl fermions, might likewise pop up in solids.

In the new study, Hasan and colleagues measured the relationship between the energy and momentum of the quasiparticles, showing that they were consistent with type-II Weyl fermions. Although previous experiments have shown hints of the unusual quasiparticles, those measurements were skin-deep, assessing particles only on the surface of the material, Hasan says. With surface measurements alone, it’s hard to confirm the type-II Weyl fermions are there, says physicist Alexey Soluyanov of ETH Zurich. But Hasan and colleagues peered inside the material. “Experimentally, this work really is a nice example,” Soluyanov says.

In solids, Weyl fermions lead to unusual behavior. Put a normal material in a magnetic field, and resistance to the flow of electricity grows, but in a solid with Weyl fermions, a magnetic field makes current flow more easily. Type-II Weyl fermions are even stranger, due to their Lorentz-violating properties. In a material with these quasiparticles, a magnetic field in one direction can increase conductivity, while in another direction it can decrease conductivity. “This type of thing can have interesting applications,” says Hasan. “In a single material, just by changing the direction of the field, now we can get different behaviors,” flipping between insulating and conducting, for example.
The new material could also provide insight for particle physicists. “Of course, people have wondered what happens when you break Lorentz invariance,” says physicist Adolfo Grushin of Institut Néel in Grenoble, France. Type-II Weyl fermions could help scientists better understand theories that violate the rule. “It’s a good test-bed,” says Grushin.

For example, Hasan says, “we can test theoretical ideas in the early universe,” simulating how particles may have behaved just after the Big Bang, when Lorentz symmetry may not have been obeyed.

In pumped-up sequels for scary beach movies, each predator is bigger than the last. Turns out that predators in real-world oceans may have upsized over time, too.

Attack holes in nearly 7,000 fossil shells suggest that drilling predators have outpaced their prey in evolving ever larger bodies and weapons, says paleontologist Adiël Klompmaker of the University of California, Berkeley. The ability to drill through a seashell lets predatory snails, octopuses, one-celled amoeba-like forams and other hungry beasts reach the soft meat despite prey armor. Millions of years later, CSI Paleontology can use these drill holes to test big evolutionary ideas about the power of predators.
“Predators got bigger — three words!” is Klompmaker’s bullet point for the work. Over the last 450 million years or so, drill holes have grown in average size from 0.35 millimeters to 3.25 millimeters, Klompmaker and an international team report June 16 in Science. Larger holes generally mean larger attackers, the researchers say, after looking at 556 modern drillers and the size of their attack holes.

Prey changed over millennia, too, but there’s no evidence for a shift in body size. The ratio of drill-hole size to prey size became 67 times greater over time, the researchers conclude.

It’s “the rise of the bullies,” says coauthor Michal Kowalewski of the University of Florida in Gainesville.

All these data on shell holes allow researchers to test a key part of what’s called the escalation hypothesis. In 1987, Geerat Vermeij proposed a top-down view of evolutionary change, where predators, competitors and other enemies growing ever more powerful drive the biggest changes in their victims. This wasn’t so much an arms race between predators trading tit for tat with their prey as a long domination of underdogs repeatedly stomped by disproportionate menace. (Unless the prey somehow flips the relationship and can do deadly harm in return.) Vermeij, now at the University of California, Davis, and others have drawn on escalating threats to explain prey evolutionary innovations in thick shells, spines and spikes, mobility, burrowing lifestyles and toxins.
One aspect of escalation scenarios has been especially hard to test: the idea that predators can become more dangerous and a stronger evolutionary force over time. Drill holes suggesting bigger, more powerful attackers allowed a rare way of exploring the idea, Klompmaker says. He now reads the deep history as showing predators escalated in size, but prey didn’t.

The energetics worked out, in large part, because early hard-shelled prey called brachiopods — a bit like clams but with one shell-half larger than the other — became scarcer over time, while clams and their fellow mollusks grew abundant. Mollusks typically have more flesh inside their shells than brachiopods, and prey overall grew denser on the ocean bottom. Killer drillers, able to dine at this buffet, could thus support bigger bodies even when prey size wasn’t rising, too.

Prey don’t make drilling easy, Klompmaker says. An hour’s work gets a typical modern predatory snail only about 0.01 to 0.02 millimeters deeper into a mollusk shell. So finally striking lunch could take days of effort with the thickest shells. And that’s with specialty equipment: A snail alternates grinding away using a hard, rasplike driller and then switching to its accessory boring organ that releases acids and enzymes, weakening the drilling spot for the next bout.

The role of such animal clashes in evolution has been notoriously difficult to study, says marine ecologist Nick Dulvy of Simon Fraser University in Burnaby, Canada. Nutrients, climate and other factors that don’t swim away into the blue are much easier to measure. Even after a robust century of ecological study, “the discoveries that otters propped up kelp forests, triggerfishes garden coral reefs, and wolves and cougars create lush diverse watersheds are comparatively recent,” Dulvy says. Until the new drill-hole study, he could think of only one earlier batch of evidence (crabs preying on mollusks) for the long rise of predators as an evolutionary force.

The story from drill holes, says Vermeij, is “very convincing.”

PORTLAND, ORE. — A great flower shape for a moth trying to get a drink in the dark turns out to be awful from the plant’s point of view.

Offering hawk moths (Manduca sexta) a range of 3-D printed flowers with different curvatures shows that a moderately curved trumpet shape lets moths sip most efficiently, Foen Peng reported June 24 at the Evolution 2017 meeting. That’s a win for a nocturnal flying insect searching for nectar.
Yet drinking ease wasn’t best for the plant. During swift sips, the moths did less inadvertent bumping against the artificial flowers’ simulated sex organs than moths struggling to sip from an inconvenient shape. Less contact with real flower parts would mean less delivery and pickup of pollen.

Peng, of the University of Washington in Seattle, offered the moths three other shapes besides the gently curved trumpet. The best for the plant was a flat-topped “flower” with a right angle drop to a nectar well in the center. Previous work suggested that lack of curves made it very difficult for hawk moths hovering above a flower and extending their tonguelike proboscises to tap and probe the way to nectar in dim light.

Pollination at first glance may look like an easy mutualism evolving with the best interests of both plant and pollinator. But these experiments reveal a hidden, underlying conflict, Peng said.

BOSTON — Guidebook claims about the superior acoustics of the ancient Greek amphitheater of Epidaurus are a tad melodramatic. An actor’s voice can be heard in the back row, but whispers and other quiet noises cannot, acoustician Remy Wenmaekers reported June 28 at a meeting of the Acoustical Society of America.

The acoustics of the 14,000-seat theater, which dates to the fourth century B.C., are often touted as carrying faint sounds with extraordinary clarity. Wenmaekers and colleagues at Eindhoven University of Technology in the Netherlands positioned microphones at 264 spots throughout the theater and recorded a slow whooping sound projected from the stage that went from low to high frequency with time like a fire truck siren. The team also recorded sounds made by a voice simulator that mimics the frequency spectrum of a male speaker. These tests provided acoustic parameters such as sound strength and reverberation time for various spots in the audience. Then, in a lab, researchers determined the threshold for hearing noises such as a pin dropping or person whispering against the background noise of the theater.

With no roads of humming traffic nearby, the theater, which is still in use today, is remarkably quiet, especially when there’s no wind, Wenmaekers said. But sounds like tearing a sheet of paper or striking a match would be discernable only for someone sitting near the stage. The sound of a dropped coin would just barely be audible for someone seated in the back, but a dropped pin would be too quiet to hear. It’s still unknown just how far noise made by an audience member unwrapping a piece of candy carries.