Blobs of gas near the Milky Way’s center may be just the right mass to harbor young stars and possibly planets, too. Any such budding stellar systems would face an uphill battle, developing only about two light-years from the galaxy’s central supermassive black hole with its intense gravity and ultraviolet radiation. But it’s not impossible for the small stars to survive in the hostile place, a new study suggests.
“Nature is very clever. It finds ways to work in extreme environments,” says Farhad Yusef-Zadeh, an astrophysicist at Northwestern University in Evanston, Ill. Four blobs of gas near the galactic center have the right amount of mass to be planetary systems with small, young stars, Yusef-Zadeh and colleagues report online January 20 at arXiv.org. The paper is also slated for publication in the Monthly Notices of the Royal Astronomical Society. “It is fairly likely that planets and low-mass stars do form near the galactic center. But we do not know it for sure at the moment,” says Avi Loeb, an astrophysicist at Harvard University. Loeb, who was not involved in the study, says the new evidence is “tentative at best.”
Yusef-Zadeh and colleagues used ALMA, the Atacama Large Millimeter/submillimeter Array, in Chile to study emissions from five of the 44 blobs of gas that the team discovered in 2014 (SN Online: 3/24/15). Four of the clouds had between 0.03 and 0.05 as much mass as the sun, the team calculated. That’s right in line with what’s needed to generate low-mass stars — ones about the size of the sun or a little bigger — and the planets that orbit them, Yusef-Zadeh says. He points out that the team has not detected these stars or planets, just that conditions are ripe for them to exist.
Loeb notes that the team had to infer the clouds’ entire masses from the ALMA measurements, which may reveal only a surface look at the blobs. The clouds may actually be denser; as a result, they would form more massive stars, challenging the team’s claim that low-mass stars are forming.
Yusef-Zadeh and colleagues are planning additional studies with ALMA and are also working on research that suggests that black holes may, in fact, help star formation. “It’s paradoxical,” Yusef-Zadeh says. “Black holes eat everything that comes too close to them. They tear everything apart. But they may actually make the formation of stars more efficient.”
The breath of oxygen that enabled the emergence of complex life kicked off around 100 million years earlier than previously thought, new dating suggests.
Previous studies pegged the first appearance of relatively abundant oxygen in Earth’s atmosphere, known as the Great Oxidation Event, or GOE, at a little over 2.3 billion years ago. New dating of ancient volcanic outpourings, however, suggests that oxygen levels began a wobbly upsurge between 2.460 billion and 2.426 billion years ago, researchers report the week of February 6 in Proceedings of the National Academy of Sciences.
That time difference is a big deal, says study coauthor and sedimentary geologist Andrey Bekker of the University of California, Riverside. The new date shakes up scientists’ understanding of the environmental conditions that led to the GOE, which prompted the evolution of oxygen-dependent life-forms called eukaryotes. Voluminous volcanic eruptions at the time poured fresh rock over a supercontinent near the equator, and the planet dipped into a frigid period known as a Snowball Earth.
A similar series of geologic events around 700 million years ago coincided with a second rise of oxygen, to near-modern levels, and some eukaryotes evolving into the first animals. Both oxygen upswings pushed life toward complexity and the ultimate emergence of humans, Bekker says. “For the first time, we see parallels between these two time intervals,” he says. Oxygen-producing microbes probably first appeared more than 3 billion years ago (SN Online: 9/8/15). But oxygen remained scant until the GOE when, for unknown reasons, atmospheric concentrations of the gas rose from near zero to around 0.1 percent of modern levels.
Dating the GOE’s start has been tricky, though, because few rocks from back then remain. Geologist Ashley Gumsley of Lund University in Sweden, Bekker and colleagues studied ancient volcanic rocks from South Africa that neighbor a layer of minerals that could have formed only in the presence of oxygen. Using an old technique, geologists had previously determined those volcanic rocks to be from around 2.222 billion years ago, well after the GOE’s start.
Applying modern techniques that measure the gradual decay of radioactive uranium in the rocks, the researchers revised the volcanism’s timing to about 2.426 billion years ago. That new date — plus a separate volcanic eruption previously dated to around 2.460 billion years ago that clearly happened before the oxygen rise — helps constrain the potential GOE start date.
The GOE isn’t the only global event to have its timeline tweaked. The oldest known evidence of global glaciation, called a Snowball Earth, lies underneath and alongside the South African rocks. The new eruption dating pushes that Snowball Earth event earlier as well — to around the same time as the start of the GOE.
The oxygen rise and the temperature drop may have been related, the researchers propose.
The new data and existing chemical evidence suggest that oxygen levels during the GOE wavered between pitiful and plentiful several times, rather than steadily rising (SN: 2/18/17, p. 16). (Oxygen concentrations stabilized around 2.250 billion years ago and remained largely unchanged until levels rose again more than a billion years later.) These oscillations coincided with Snowball Earths and volcanic eruptions, Gumsley says.
Climate, oxygen and volcanism were intertwined during the GOE, the researchers propose. Volcanic eruptions covered the supercontinent with fresh rock. That rock formed near the equator where heavy precipitation weathered the rock, drawing carbon dioxide from the air and washing nutrients into the ocean. Those nutrients nourished photosynthetic microbes, which produced an abundance of oxygen. Oxygen built up in the atmosphere and reacted with methane, reducing levels of that greenhouse gas (SN: 10/29/16, p. 17).
With less CO2 and methane warming the climate, Earth froze and oxygen-producing biological activity decreased. The ongoing volcanism spewed replacement CO2 into the atmosphere over time and eventually reheated the planet.
“This is further evidence that oxygen’s history has really been a roller coaster ride rather than a unidirectional rise,” says Yale University geochemist Noah Planavsky. While he’s uncertain about the role rock weathering played in controlling ancient oxygen levels, Planavsky believes the new age will allow scientists to delve into the question of why the GOE began when it did. “Without dates,” he says, it’s impossible “to have any real grounding to tackle these problems.”
People who undergo gastric bypass surgery are more likely to experience a remission of their diabetes than patients who receive a gastric sleeve or intensive management of diet and exercise, according to a new study. Bypass surgery had already shown better results for diabetes than other weight-loss methods in the short term, but the new research followed patients for five years.
“We knew that surgery had a powerful effect on diabetes,” says Philip Schauer of the Bariatric & Metabolic Institute at the Cleveland Clinic. “What this study says is that the effect of surgery is durable.” The results were published online February 15 in the New England Journal of Medicine. The study followed 134 people with type 2 diabetes for five years in a head-to-head comparison of weight-loss methods. At the end of that time, two of 38 patients who only followed intensive diet and exercise plans were no longer in need of insulin to manage blood sugar levels. For comparison, 11 of 47 patients who had a gastric sleeve, which reduces the size of the stomach, and 14 of 49 who underwent gastric bypass, a procedure that both makes the stomach smaller and shortens digestion time, did not need the insulin anymore. In general, patients who had been diabetic for fewer than eight years were more likely to be cured, Schauer says.
Even those surgical patients who still needed to take insulin had greater weight loss and lower median glucose levels than others in the study. This study was also one of the few to show that bariatric surgery could help those with only mild obesity, defined as a body mass index between 27 and 34. How bariatric surgery might improve diabetes is still unknown, but scientists have pointed to effects on the body’s metabolism (SN: 8/24/13, p. 14) and gut microbes (SN: 9/5/15, p. 16). The same research team had published similar results at one and three years after surgery, but few studies looked further, says Kristoffel Dumon, a bariatric surgeon with the University of Pennsylvania Health System in Philadelphia. “The criticism of bariatric research has been that there are no good long-term results. With weight-loss surgery, you often see rapid initial results, but you want to see that to a five-year time point.” Dumon also notes that the patients who received only intensive medical therapy did not report an improvement in their quality of life, and their emotional well-being worsened. People in the surgical group reported improvements in quality of life, but not in emotional well-being, a finding that Schauer says has more to do with stress management and other characteristics that wouldn’t necessarily be affected by surgery.
Schauer hopes to have even longer-term data in the future. His team will combine their results with those from similar research at three other U.S. sites with the goal of following patients for up to 10 years.
Eijiro Miyako gets emotional about the decline of honeybees.
“We need pollination,” he says. “If that system is collapsed, it’s terrible.”
Insects, especially bees, help pollinate both food crops and wild plants. But pollinators are declining worldwide due to habitat loss, disease and exposure to pesticides, among other factors (SN: 1/23/16, p. 16).
Miyako, a chemist at the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan, became passionate about the loss of pollinators after watching a TV documentary. He remembers thinking: “I need to create something to solve this problem.” His answer was in an 8-year-old jar in his lab.
In 2007, he had tried to make a gel that conducts electricity, but it was “a complete failure,” he says. So he poured the liquid into a jar, put it in a drawer and forgot about it. Cleaning out his lab in 2015, he accidentally dropped and broke the jar. Surprisingly, the gel was still sticky and picked up dust from the floor. Miyako realized that the gel’s ability to capture the tiny particles was similar to how honeybee body hairs trap pollen. His thoughts jumped to artificial pollination.
First, he investigated whether non-pollinating insects could help do the job. He dabbed his gel onto ants and set them loose in a box of tulips. The ants were coated with pollen after three days.
Still, Miyako worried that predators would snack on his insect pollinators. To give them camouflage, he mixed four light-reactive compounds into the gel. He tested the new concoction on flies, placing a droplet on their backs and setting the insects in front of blue paper. Under ultraviolet light, the gel changed from clear to blue, mimicking the color of the backdrop.
Though this chemical invisibility cloak might protect the insects, Miyako wanted a pollinator that could be controlled and wouldn’t wander off at the first scent of a picnic.
He bought 10 kiwi-sized drones and taught himself to fly them, breaking all but one in the process. Miyako covered the bottom of the surviving drone with short horsehair, using electricity to make the hair stand up. Adding his gel made the horsehair work like bee fuzz. In tests so far, the drone has successfully pollinated Japanese lilies more than a third of the time, brushing up against one flower to collect pollen, then flying into another to knock the grains off, his team reports in the Feb. 9 Chem. Glad he saved that failed gel, Miyako thinks it is possible to automate a fleet of 100 drones, using GPS and artificial intelligence, to pollinate alongside bees and other insects. “It’s not science fiction,” he says.
One of Jupiter’s companions is a bit of a nonconformist.
The gas giant shares its orbit around the sun with a slew of asteroids, but scientists have now discovered one that goes against the flow. It journeys around the solar system in reverse — in the opposite direction of Jupiter and all the other planets. Asteroid 2015 BZ509 is the first object found that orbits in the same region as a planet but travels backward, researchers from Canada and the United States report March 30 in Nature. The asteroid was discovered with the Pan-STARRS observatory in Hawaii in 2015, and the researchers made additional observations with the Large Binocular Telescope Observatory in Arizona.
Backward-going asteroids are rare — only 0.01 percent of known asteroids are in retrograde orbits. Until now, none were known to share a planet’s orbit. It was thought that asteroids going in reverse couldn’t coexist with a planet because interactions with the celestial body, twice each orbit, would knock the asteroid off track. But because 2015 BZ509 passes on alternating sides of Jupiter, the interactions cancel each other out, the researchers say. The first flyby in orbit pulls the asteroid outward, and the next tugs it inward — keeping the maverick asteroid in line.
The asteroid’s relationship with Jupiter is no short-term fling: The researchers determined that the two have shared an orbit for a million years.
The oldest known specimens of bedbug relatives have been unearthed in an Oregon cave system where ancient humans once lived. The partial fossils from three different species in the bedbug family date back 5,000 to 11,000 years, predating a previous find from 3,500 years ago, researchers report April 4 in the Journal of Medical Entomology.
“The bedbugs that we know in modern times originated as bat parasites, and it’s believed that they became human parasites when humans lived in caves with bats,” says study coauthor Martin Adams of Paleoinsect Research in Portland, Ore. When humans moved elsewhere, bedbugs came along for the ride.
These three species (Cimix antennatus, Cimex latipennis and Cimex pilosellus) probably coexisted with humans in Oregon’s Paisley Five Mile Point Caves, and probably snacked on people at least occasionally, Adams says. Even though all three species are still around today, they still feast mostly on bats.
Archaeologists think that ancient humans lived in the Paisley Caves only seasonally, which could explain why these particular species of bedbugs didn’t switch to a human-centric diet.
The solar system doesn’t have a long, twisted tail after all.
Data from the Cassini and Voyager spacecraft show that the bubble of particles surrounding the solar system is spherical, not comet-shaped. Observing a spherical bubble runs counter to 55 years of speculation on the shape of this solar system feature, says Tom Krimigis of the Johns Hopkins Applied Physics Laboratory in Laurel, Md. He and colleagues report the result online April 24 in Nature Astronomy. “You can’t really argue with the new result,” says Merav Opher of Boston University, who was not involved in the study. “The data so loudly say that there is no tail.”
The bubble, called the heliosphere, is inflated by particles streaming from the sun and envelops all of the material in the solar system. Its shape is important because it provides clues about how the solar system interacts with interstellar space.
In the 1960s, researchers proposed that the heliosphere was either shaped like a comet or was spherical. Magnetic fields surrounding the sun and the planets look sort of like comets, with long tails extending behind them. So, scientists speculated that the heliosphere would have a tail, too. In 2013, data from the Interstellar Boundary Explorer, or IBEX, spacecraft found signs that the tail assumption was right. The probe counted the number of fast-moving atoms that are thought to be kicked inward from the edge of the solar system when they collide with charged particles from the sun. Detecting those atoms offers clues to the shape of the heliosphere, and the images suggested that solar system had a long, twisted tail that looked like a four-leaf clover (SN: 8/24/13, p. 9).
But it wasn’t clear from the data exactly how far away from the spacecraft the atoms were and therefore how far the heliosphere’s tail extended, Krimigis says. By combining more than a decade’s worth of data from the Voyager and Cassini probes, he and colleagues sought a clearer picture. The team specifically tracked how the abundance of the speedy atoms changed in different parts of the heliosphere as the intensity of charged particles streaming from the sun, the solar wind, waxed and waned.
At the front of the heliosphere, where the Voyager probes sit, when the intensity of the solar wind decreased, so did the abundance of speedy atoms. When it increased, the number went up, in lockstep. Looking at speedy atoms at the back of the heliosphere, the team saw the same changes. If there were a long tail, Krimigis says, the changes in the number of atoms wouldn’t be the same in both directions. Because the atoms would have farther to travel in a tail, it would take longer for their abundance to build up there again.
While the observational evidence now favors a spherical shape for the heliosphere, recent simulations suggest something more exotic. The bubble might actually be shaped like a croissant, Opher says. The simulations, which incorporate data from Voyager 1, show that the interaction of the magnetic fields from the sun and interstellar space squish the solar wind into two jets — what might be observed as two short tails. These jets haven’t been detected yet. But if they are, she says, they could give clues to other sets of jets seen in the universe such as those shooting from young stars or possibly even black holes.
Most people who eat octopus prefer it immobile, cut into pieces and nicely grilled or otherwise cooked. For some, though, the wiggly, sucker-covered arms of a live octopus are a treat — even though those arms can stick to the throat and suffocate the diner if they haven’t been chopped into small enough pieces.
Dolphins risk the same fate when eating octopus — and they can’t cook it or cut it up with a chef’s knife. “Octopus is a dangerous meal,” notes Kate Sprogis of Murdoch University in Australia. Even if a dolphin manages to remove an octopus’ head, it still has to deal with those sucker-covered tentacles. “The suckered arms would be difficult to handle considering dolphins don’t have hands to assist them,” Sprogis says.
A group of hungry dolphins off the coast of Western Australia have figured out a solution. They shake and toss their prey until the head falls off, the animal is in pieces and its arms are tender and not wiggling anymore, Sprogis and her colleagues report April 2 in Marine Mammal Science.
The behavior, never before reported, was discovered during observations between March 2007 and August 2013 of bottlenose dolphins living in the waters off Bunbury, Western Australia. During that time, researchers witnessed 33 events in which dolphins handled an octopus with two different methods.
In one technique, a dolphin held an octopus in its mouth and shook it, slamming its prey into the water’s surface until the meal was in pieces. Each dolphin would repeat its preferred motion, or combine the two, usually around a dozen times, over several minutes until the octopus was safe to eat. (See video below.)
“If the dolphins haven’t prepared their meal enough, then this can cause problems,” Sprogis notes. There have been two dead dolphins found in this area with whole octopuses lodged in their throats. The researchers assume that the dolphins suffocated.
Dolphins have garnered a reputation for tackling difficult-to-eat foods in creative ways. Some have been spotted using cone-shaped sponges to flush out little fish from the sandy ocean floor. Others use a six-step process to prepare a cuttlefish meal. The Bunbury dolphins eat both octopus and cuttlefish, and those meals appear to be more common in the winter and spring, when waters are cooler, Sprogis notes. That may be when the octopus and cuttlefish breed and lose some of their camouflage abilities — making them easy prey for dolphins brave or knowledgeable enough to take advantage of the potential meal.
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.
