To make this happen, microorganisms have evolved adaptations that help them survive their forever winter – whether it’s because they prefer cold environments (known as psychrophiles) or they can tolerate them (psychrotolerants) until more favorable conditions arise.

One example of cryosphere adapted fungi are a genus of single celled, pink pigmented yeast called Rhodotorula, which have been isolated and characterized from a range of cold ecosystems. In order to survive the coldest and driest parts of the Earth, they’ve evolved unique strategies to handle the elements. In a recent study by scientists at McGill University, a novel species of Rhodotorula yeast is changing our understanding of fungal cold adaptations in new and unexpected ways.

The newly identified psychrotolerant yeast, Rhodotorula frigidialcoholis, was isolated from 150,000-year-old ice cemented permafrost in the McMurdo Dry Valleys of Antarctica. The researchers found it has two novel responses to extreme cold temperatures: it can switch its metabolism from respiration to ethanol fermentation as its main pathway, and can overexpress molecules called small non-coding RNAs (sRNAs) that help regulate which genes are expressed after transcription. R. frigidialcoholis now also holds the record for the lowest temperature reported for ethanol production by any microorganism.

Scientists are still working to understand the precise role of sRNA expression in cold adaptation, but the metabolic switch from respiration to ethanol fermentation by R. frigidialcoholis may help the novel yeast – and potentially others like it – save energy, slowing down the freezing point in their cells as a long-term survival strategy.

Hoy en día, hay muy poca información disponible sobre que les pasó a aquellos walabíes introducidos. Dos científicos, Holly English y Anthony Caravaggi, decidieron investigar qué pasó con aquellos animales. Recogieron información sobre avistamientos de walabíes en los registros oficiales, las redes sociales, y los periódicos. Gracias a lo monos e inusuales que son, los avistamientos suelen ser mencionados en los periódicos locales.

En su artículo reciente publicado en la revista científica Ecologia y Evolución, los investigadores encontraron pequeñas poblaciones de walabíes viviendo a lo largo del sur de Inglaterra. Aunque alguno de estos animales es probablemente un fugitivo moderno de una colección privada o un zoo, es improbable que tales escapadas sean el origen de todos los avistamientos de la región. Por ello, los investigadores creen que las poblaciones del sur de Inglaterra se están reproduciendo en libertad.

Así que, si alguna vez estas en el sur de Inglaterra y crees que has visto a un walabí, ¡no te sorprendas demasiado!

Among these moving giants rises St. Lawrence Island. Closer to Russia than the United States, its granite cliffs uplift rock as old as the Palezoic era, when an explosion of life spilled over the Earth. Waves have since cut away lake-dotted plains, and its headlands, once hugged by ice for much of the year, are rugged, with spare, bouldered beaches.

When Delbert Pungowiyi was born in 1959, the island had no electricity or cars. People were just beginning to use heaters. His family and their Yupik community relied on dog teams to travel, and ate what the land and sea gave them. When he was six, Pungowiyi’s father passed away in a hunting accident. “We had to grow up real fast to contribute,” he says. The winters were long and hard, and Pungowiyi’s family worried about running out of food. But the light always crept back. The sea would unlock, fast ice clinging to the shore. Then one day, the birds would come.

“It was a spectacle,” Pungowiyi says. “They would literally blacken the skies, swarms and swarms, circling.” A critical nesting ground, St. Lawrence Island draws millions of seabirds — puffins and auklets and murres — in migratory flocks, traveling vast distances to arrive precisely with the last of the ice. Pungowiyi could hear their calls from his bed, and ventured out to the cliffs with a homemade slingshot to harvest what his family needed. He was a good shot, but “a lot of times, I’d just lay there and look up at the sky, and watch the birds go around and around.” He marveled how, despite their careening speeds, the birds never seemed to collide. The air would still to the whoosh and thump of wings.

But the Bering Sea, the only marine gateway between the icy Arctic and the Pacific Ocean, is warming. More and more of its multi-year ice has melted. Normally, more than 193,000 square miles of ice would form across the Bering Strait each winter. In 2018, there was almost none, a development that scientists originally didn’t forecast until the end of the century. “That’s about two Texas’s worth of ice that is missing,” wrote Walter Meier, a scientist at the National Snow and Ice Data Center. The sea’s winter ice extent in 2018 and 2019 was the lowest it has been for 5,500 years.

Ice is the keystone of this ecosystem: When it melts, it releases fresh water and nutrients, sustaining algae and phytoplankton blooms, which in turn support some of the biggest fisheries on the planet. When floes form, they shed briny, cold water, forming a frigid ocean curtain that supported Arctic species and kept southern ones, like pollock and cod, out of the Arctic Ocean. This cold pool has been shrinking. In 2018, researchers were shocked when it vanished almost entirely.

The Bering Sea is now trapped in a feedback loop: Open water absorbs more heat from the sun, warming the dark waters, and making it harder for ice to form the next year. Summer sea-bottom temperatures have increased by more than 12 degrees in less than a decade, impacting everything from the patterns of currents to nutrient availability to what fish thrive where. Even the salinity of the water itself is changing as older ice melts. Before, Pungowiyi says, “Young ice — we call it sikuliaq — was almost like a water bed, every step bends.” Hunters trusted it when they ventured out to fish or crab. But thinner, newer ice, he says, “is brittle, and breaks up.”

This loss is echoing up the food chain. The Alaska snow crab population has crashed. Ice seal carcasses have increased five-fold. Emaciated gray whales are stranding themselves. And in 2021, for the fifth consecutive summer, communities all over western Alaska reported dead seabirds washing ashore. Residents from small towns along the Bering Sea have been mailing corpses to biologists in boxes, hoping the scientists can figure out what’s killing them.

At times on St. Lawrence Island, Pungowiyi says, “The beaches have been literally littered with carcasses.” He mourns over the bodies of crested auklets, slick, black diving birds with a splash of feathers like bangs. When they wash up, their keels curve out of gaunt chests. “Since the cold curtain lifted, the impact has been accelerating,” Pungowiyi says. “It literally sends chills down my spine to see this in my lifetime.” These changes are altering peoples’ relationship with the food they depend on. In town, the constant murmur and chatter from the cliffs is eerily quiet.

“As a young man growing up, I thought this will always be. And now I see that what I thought is really not…” he trails off. “It’s heart-wrenching.”

A crested auklet colony can be smelled before it's seen: The chunky, raucous birds give off the smell of tangerines from a hundred yards. In the thrill of spring, males will puff up their distinctive crest. If a potential partner is interested, she’ll bury her beak in his neck feathers, where the citrus scent is strongest. Then the pair twist their necks together and rub, cackling. Onlookers egg them on in a scrum, pressed close as if on a crowded dance floor.

Although seabirds of many species gravitate to St. Lawrence, Alexis Will, a biologist at the Institute of Arctic Biology, says the extent of the island’s crested and least auklet colonies make it unique. They are so large that she needs an ATV to survey them. “You’re driving along and it’s just these clouds of birds,” she says. Bumping over the tundra, the nesting cliffs dropping off to the ocean look like the edge of the world. The island is one of only about 100 known crested auklet nesting sites. “You just see these swirls of birds for kilometers. They go on forever.” Her voice breaks. “It’s hard to see how amazing it is — and then to see that start to fall apart.”

The lives of seabirds are perilous, and occasional die-offs are normal. But recent events are different: They’re happening more frequently, lasting longer, impacting more species, and covering larger geographic areas.

In 2015, as many as a million common murres — a highly adaptive species — died in the Gulf of Alaska after an unusual marine heat wave. That catastrophic event was soon followed by many others, with die offs happening year after year around the Bering Sea. This September alone, 650 dead birds — shearwaters and common murres and horned puffins — were reported around St. Lawrence Island; Will says that since most birds die unobserved at sea, that’s likely a large underestimate of the true mortality.

There isn’t a single, easily explainable cause. Rather, the likely culprit, climate change, is impacting each location and species differently. “There are lots of ways to die off,” Will says.

Seabirds like the crested auklet eat small zooplankton called copepods, tiny shrimp-like creatures. Kathy Kuletz, a seabird biologist with the U.S. Fish & Wildlife Service, explains that as the Bering Sea warms, large, lipid-rich copepods have declined. While smaller copepods are proving more resilient, they provide less energy for the fish and birds who rely on them. The collapse of the Bering Sea’s cold pool may have also increased competition for prey, as predatory fish like pollock move north. “To feed a chick, a bird might have to catch three pollock, instead of one arctic cod, which is richer in lipids,” Kuletz says, causing chicks to mature slower, or fledge late, with fewer surviving to breed. “Things are changing, probably faster than some species of birds can respond.”

Starting in 2017, Will found that copepods nearly disappeared from both auklet species’ diets. This summer, when a friend of Pungowiyi’s went to harvest birds, he was devastated by their condition: The stomachs of the emaciated birds weren’t the usual color — they clearly weren’t eating their normal prey. Punguk Shoogukwruk, a St. Lawrence resident, has been collaborating with Will for the last three years, catching and measuring birds. He has noticed chicks dying of hunger, as well as starving fledglings abandoning their nests prematurely. “To be going around checking nests and seeing one dead chick after another is pretty much the worst thing,” Will says. Neither auklet species produced any surviving chicks in 2018 or 2019; the pandemic has limited her field research since.

Scientists have found that shifting wind patterns have broken down the normal transport of sea ice and currents, impacting how nutrients are dispersed through the ocean, and possibly changing where auklets can find their staple prey. Strong, warm southerly winds have been forcing the remaining ice north, redistributing zooplankton — and everything that depends on them.

It’s difficult to track the rapid changes occurring in this critical habitat, much less predict their consequences. The thick-billed murre, for example, which also nests on St. Lawrence Island, mostly eats small fish that live near the sea bottom. These fish populations appear stable, for now. But even though the murres seem to have enough food, they died in droves around St. Lawrence in 2018. The number of returning thick-billed murres fell the following summer by 25 percent. Scientists wonder whether their prey moved to unusual or harder to access locations. Worsening toxic algae blooms and avian disease could also be contributing factors, but so far, research has been inconclusive. “The Bering Sea is in such a state of flux right now that there’s not necessarily any established pattern,” Will says. “It’s all broken down — the system is in a state of freefall.”

Will has been studying seabirds that nest on St. Lawrence since 2016. By measuring a stress hormone called corticosterone, she recently found that all five of the species she examined on the island are experiencing high nutritional stress. Each dives to a different depth, and targets different prey, but starvation is their common suspected enemy. “The seabirds we’ve been tracking encompass pretty much the range of how you can make a living in a marine environment,” Will says. “Basically, none of the birds are winning.”

Some seabirds live for a long time. Kittiwakes, for example, can live to 30 years old. But crested auklets have flash-in-the-pan lives; they sport their tangerine smiles for less than a decade, intensifying pressure on the efforts to understand what is going wrong. Least auklets live for even shorter periods. After two years with a complete failure to breed, their population may already be slipping away. On St. Lawrence Island, if this trend continues “we have about a decade for least auklets, maybe less,” Will says. “And there’s really nothing we can do — it’s climate change.”

In 1983, Pungowiyi was sitting in his grandfather’s house, the home he inherited and lives in today. “Things were pretty normal back then,” he says. They were on the couch watching TV when his grandfather turned to him. “Remember what I tell you,” he said in Yupik. “I will not be here, but you will witness the loss of ice.” Although Pungowiyi’s grandfather didn’t use scientific terms like “climate change” or “unusual mortality events,” he knew through close observation that the weather had begun to shift.

By the 1990s, Indigenous reports that the Arctic was changing made it into a few academic studies. It took another decade for the wider scientific community to pay attention. “Our ancestors believed all oceans were connected,” Pungowiyi says. The Bering Sea plays a crucial role in the marine conveyor belt that regulates the world’s oceans. Changes here can possibly interfere with the jet stream, weakening the polar vortex and affecting everything from drought in the American West to record-breaking rainfall in Europe. “I fear if the Bering Sea ecosystem collapses, it will have a domino effect,” he says.

When Pungowiyi learned to hunt from his grandfather, the island saw nine months of solid winter, with freeze up starting in October and break up extending into June. He learned to predict the weather by ocean ripples, and the formation of drifting snow. The long cold thickened the ice, making it possible to hunt and travel. Village monitors on St. Lawrence Island began recording the daily ice extent in 2000, when gleaming, multi-year bergs still blued the islands’ beaches. Now, winter lasts for three months, Pungowiyi says, four “if we’re lucky.” When it snows, he hears kids saying that it’s winter, and explains to them that the season, uksuq, only begins when “the whole of the sea is locked up, and there’s no more open water. That’s winter.” Some years now, uksuq doesn’t come at all.

In the old patterns of life, animal behavior was once so habitual that the Yupik word for July is alpaarusvik, literally “time when the murres leave.” But in 2007, for the first time in the elders’ memory, flying cormorants arrived in mid-winter. The seals come early, and the whales late. “We’re seeing big shifts in availability and abundance of species,” says Lisa Sheffield Guy, a biologist and the project manager at the Arctic Research Consortium of the U.S. Hunting requires an intricate understanding of the weather, but travel on thin ice is perilous, and recently, warm, dangerous winds rise out of nowhere, sweeping ice and anyone on it offshore. “One thing we do still rely on is clouds,” Pungowiyi says. “They always tell the truth.” For everything else, the changes are so fast, and so fundamental, they are outstripping traditional knowledge.

These shifts are driving food insecurity on the island. “People depend on the yearly harvest of eggs, and lately there have been less and less,” Shoogukwruk says. In addition to hunting birds, residents collect eggs during the brief nesting window, and then freeze them. But as access to these kinds of food sources change, many are having to increasingly rely on imported food. The cost of shipping goods out to St. Lawrence is high, and grocery prices are steep; a half-gallon of milk costs over $10 and a box of cereal can cost $8. Pungowiyi is among the many residents who visit the food bank in town, but it struggles to keep up with demand.

Pungowiyi has spent the last few years trying everything he can think of to get people to pay attention, including inviting Senator Lisa Murkowski out to the island. Yet scientific and governmental responses have been slow. As the former tribal president, Pungowiyi recently traveled to an Arctic Council meeting, where he was excited to speak to some of the world’s top scientists. He planned a talk, hoping to describe the die-offs he’d witnessed, but “they had us in a tiny little room on the second floor,” during the lunch hour. He decided he was going to find a way to speak to the full gathering, in the big room. In a break for questions, he walked up to one of the microphones, wearing a hat his mother had embroidered with two polar bear heads. “I had made up my mind to speak as quick as I can, until they cut me off,” he says. And then he told the room about his grandfather’s warning, and the island’s birds dying.

Pungowiyi hoped sharing what he’d seen would wake people up, get them to do something. Instead, it became clear no one was grasping the urgency of the crisis. “I feel at the end of my rope,” he says. He was distressed by the recent international climate talks in Glasgow, which he felt failed to recognize either Indigenous voices or the major impact he’s seen on the oceans. “The table they are talking at was our table,” he says. “But they have just pushed us aside.”

Igor Krupnik, an anthropologist and Arctic ethnology curator at the Smithsonian’s National Museum of Natural History, has known Pungowiyi for years, and watched him grow more and more desperate. Drama is antithetical to a culture where people had to tolerate each other through long winters, Krupnik says, so Pungowiyi’s outward-facing advocacy is particularly striking. “Delbert is a very strong person, who is now in a moment of hopelessness,” Krupnik says. He, too, seems troubled. “Is this what our life is going to be, without birds, and without ice?”

As I continued reporting, I kept hearing the same story. “Yeah, Delbert called me too,” says Jon Rosales, a climate scientist at St. Lawrence University in New York who has been documenting the impacts of global warming on Native peoples in the Arctic, and whose mother-in-law is from St. Lawrence Island. “You feel helpless, that’s where the despair comes in,” he says. “You hear these stories from the frontlines, and yet the solutions are really global.”

Even if every country meets its current climate targets, there will still be catastrophic amounts of warming. Scientists recently found that if the world continues business-as-usual, likely temperature increases will cause biological and chemical conditions in more than half the ocean to become “new and significantly different.” Not everything will suffer: Without ice, a different kind of plankton will bloom, supporting fish that swim near the ocean surface, and the animals that eat them. But the balance has shifted. Far short of extinction, the island’s old ecology is unraveling. “The biggest realization for me is it’s not done,” says Will. “We’re in this wobbly state, where the system probably won’t ever go back to how it functioned before, but it also hasn’t settled into a new steady state of being.”

Everyone is handling these changes differently. Shoogukwruk says he knows the island’s residents can adapt, because they have before: when the Russians came, when their land was sold to the United States, and when they were forced into living in villages. “We’re still here. And the animals are fighting the same way. It might be hard,” he says, “but if we can’t adapt, then what are we going to be?”

One weekday morning, I reach Pungowiyi while he’s making pancakes for his grandson. He’s tired. “It won’t get any better for our children. Those are the ones I hurt for the most.” In the background, his grandson calls to him. “I wish I could tell those giant [fossil fuel] companies, all the wealth they accumulated will become useless, and their children and grandchildren will suffer. For god’s sake — what are you going to leave behind for them?”

We sit for a moment, and then he says he was “thinking about the environmental lady who wrote about the birds that sang, and are no longer there.” I tell him she also loved the sea. “It’s really on the verge of collapsing. We can’t stop it,” he says. “But it needs to be documented. The world needs to know it is unfolding.”

Anyone who has stood on a shore and watched a bird dive to where they can’t follow knows its dip and disappearance, like a trick of the eye. Seabirds live in the in-between, plunging from the sky into the deep, slipping back and forth between laws of motion. Their future might be liminal, too. “If you cannot save the physical birds, you probably can save a memory of the birds in culture,” Krupnik says. Small salvage, knowing that even as the island’s colonies dwindle, our very longing might preserve a time when the sky here drummed to life with wings.

“Where is everybody?” he mused.

He and a few other physicists had been discussing technological extraterrestrials, and Fermi appeared to be making the innocuous argument that since no aliens had landed on Earth, interstellar travel must be a tall order.

Seventy years later, his question has morphed into something else — a case against the very existence of extraterrestrial civilizations and an implication that astronomers are wasting their time looking — the infamous “Fermi Paradox.” Its continued occupation of the popular consciousness tends to make the researchers doing this work salty.

“There is no Fermi Paradox,” says Sofia Sheikh, a postdoctoral researcher at the Berkeley SETI Research Center . “You can’t say something about why there isn’t something there if you haven’t searched for it.” (Others point out that the academic argument does not actually belong to Fermi, and is not a paradox.)

Despite decades of talk, the Search for Extraterrestrial Intelligence (SETI) has been a field of comparatively little action — largely starved of federal funding due in part to Fermi Paradox-influenced thinking. SETI pioneer Frank Drake spent four months in 1960 scanning two stars for radio signals. More than a half century later, SETI researchers have made only modest progress. The privately funded Breakthrough Listen project is currently conducting one of the most exhaustive searches to date, listening to nearby stars for roughly fifteen minutes each. Preliminary results suggest that of our closest couple hundred neighbors, no star system harbors a civilization that broadcasts a powerful radio signal in our direction all the time. That leaves a couple hundred billion stars in the galaxy yet to be searched.

In 2012, Jill Tartar, a foundational SETI astronomer and inspiration for Carl Sagan’s novel Contact, likened the search for signals that could arrive from any direction at any time to hunting for marine creatures in a volume as vast as the Earth’s oceans. She estimated that SETI efforts had, collectively, sampled roughly one glass of water. An academic calculation suggested that, as of last year, SETI astronomers were up to perhaps “a large hot tub” of water.

To speed the cosmic trawl, researchers are increasingly leaning on a concept first articulated in — of all places — economics. Due to the current limits of technology, the modern SETI enterprise is mainly a search for potential civilizations that want to be found. Extraterrestrial intelligences would, by definition, be rational agents, and might intentionally beam out signals indicating their presence, shouting “We are here!” into the void. If so, astronomers could turn our common intelligence to their advantage, working out how to cooperate even without communicating. All they need to do is think like aliens.

“This is clearly the way we should think about how to design things,” says James Davenport, an astronomer at the University of Washington. “It’s a natural framework to think about how you might communicate with an unknown actor.”

A galactic game of seek and don’t hide

Stripped of its science-fiction trappings, the challenge of making contact looks like a special kind of game in economic theory: two players share one goal, but they can’t communicate as they attempt to achieve it.

While such an exercise might initially seem futile, Thomas Schelling, an iconoclastic and Nobel prize winning economist who popularized the Cold War concept of Mutual Assured Destruction, realized that games where players can’t communicate are still games. They may lack sure-fire paths to victory, but some strategies beat others. In Schelling’s 1960 book The Strategy of Conflict, he described how to identify such “focal” or “Schelling” points; focus on what you suppose your counterpart might know and what your counterpart supposes you might know.

A classic example is two strangers tasked with finding each other in Manhattan. An organized, but rather hopeless plan might be to walk the streets in a grid from Battery Park to Inwood, from the Hudson to the East River. Rather, Schelling reasoned, canny players might consider unique places and times that jump out to both parties as special, such as Grand Central Terminal at noon. Schelling’s theory has been born out in real demonstrations. In 2006, ABC staged just such a game, dropping off six pairs of people at random spots in the city. Within hours, the teams converged on two spots: Time Square and the observation deck of the Empire State Building. All six groups independently choose noon as their meeting time.

As technology improves and bigger astronomical data sets become available, SETI astronomers are rolling out a wide variety of novel searches based on the same principle. But it’s  easier said than done. What, if anything, can SETI researchers hope to have in common with alien civilizations? What do we know extraterrestrials know, and what do they know we know?

“We’ve got to pick some signal strategy or signal reception strategy that will match with what someone else comes up with,” Sheikh says. “Otherwise, the task is hopeless.”

Special frequencies

Human astronomy remains, for the time being, firmly attached to Earth. Presumably, other civilizations have a home base from which they broadcast too. In SETI, the question of “where to meet” often becomes a question of “what frequency to chat on.” After all, even just here on Earth humans reach each other on a dizzying array of radio channels, microwaves, and with beams of visible and infrared light.

In a foundational SETI publication appearing in Nature in 1959, physicists Giuseppe Cocconi and Philip Morrison proposed that 1420 MHz or thereabouts would be a good place to start the conversation. Hydrogen gas buzzes at precisely this radio frequency, and since hydrogen is the most common element in the galaxy (and the universe), this channel might be of particular interest. Schelling himself called out the frequency as an example of a Schelling point the next year in The Strategy of Conflict, writing in a footnote, “In the most favored radio region there lies a unique, objective standard of frequency, which must be known to every observer in the universe.”

The “hydrogen line” has since fallen out of favor in SETI, partially because all that hydrogen makes the channel rather noisy, and partially because astronomers no longer need to spend months turning the radio dial by hand as Drake did. “In the first SETI searches you’d look at a channel at a time,” Sheikh says. “Now we're doing billions of times that with a single observation with a single instrument.”

Yet researchers continue to think about special frequencies. When analyzing a billion signals at once, there are a billion chances for the algorithm to mistakenly flag one channel as artificial. Identifying the most promising candidates ahead of time could lend confidence to future detections.

Jason Wright, a Penn State astrophysicist, described a novel set of Schelling point frequencies last year in the International Journal of Astrobiology. Using base ten numbers and the units of Hertz to measure radio frequencies are merely conventions of human culture, so Wright sought culture-independent frequencies in fundamental physics. He found inspiration in research from the pioneer quantum physicist, Max Planck, who in 1900 wrote about physical quantities that “remain meaningful for all times, and also for extraterrestrial and non-human cultures, and therefore can be understood as ‘natural units.’”

These fundamental constants of nature describe the speed of light, the strength of gravity, and the relationship between a photon’s energy and its frequency. Any civilization capable of building a radio beacon would likely be able to measure these numbers as humans have, and by mixing them together could find a particular frequency — a universal frequency specified by fundamental physics. “If you know those three things, you say huh, something funny happens at that frequency,” Wright says.

Electromagnetic radiation with the fundamental frequency would be impossible to detect, so Wright added the fundamental charge of atomic particles to the mix and used the four constants to construct a base — like we use the number 10 as a base — to formulate a list of more reasonable frequencies in both radio waves and visible light, a frequency “comb,” that SETI researchers could use to sift through the haystack of radio channels.

Special times

As some SETI researchers ponder how aliens might reach out, others wonder when. Transmitting beacons take energy, and civilizations may not transmit all the time. (We certainly don’t. Our highest profile message lasted for three minutes in 1974, a powerful blast from the recently ruined Arecibo radio dish in Puerto Rico.)

To get picked up during Breakthrough Listen’s 15-minute scans, for instance, our nearest neighbors would need to be beaming out an all-directional signal using around a trillion watts of power, according to Wright, or about five percent of humanity’s total energy consumption. That’s an expensive porch light to leave on all the time. To hear from cultures on a budget, researchers may need to work out the cosmic equivalent of noon — a universal hailing time.

Sheikh reasons that any civilizations engaged in sending interstellar messages are likely to be at least as good at astronomy as we are. In recent decades, astronomers have spotted thousands of exoplanets, often by looking for stars that regularly dim as planets pass in front of them. Any aliens doing the same could already know Earth is here.

That knowledge could focus their efforts to make contact by specifying a unique time to say hello — the moment when Earth eclipses the sun, dimming our star and revealing our presence. Sheikh is moving to the SETI Institute in California in January, and for her first project there she plans to use the institute’s Allen Telescope Array to sweep the night sky directly overhead when the sun is positioned “behind” the Earth from the perspective of any inhabitants of star systems in view.

She estimates that the survey will be sensitive to radio broadcasts from an extraterrestrial dish analogous to Arecibo transmitting within about 220 light years. Weaker signals, or signals coming from deeper in the galaxy — which spans 100,000 light years — would go unnoticed.

Sheikh admits that her plan might seem like a long shot, but argues that it beats scanning the sky from one side to the other — the celestial equivalent of wandering Manhattan south to north. “You have to start somewhere,” she says. “Why not start somewhere you think is more likely?”

Another Schelling-inspired lesson is to test out as many Schelling points as possible. If your counterpart doesn’t show up at Grand Central at noon, try Times Square at midnight. In that spirit, Sheikh is collaborating with Davenport, at the  University of Washington to study another temporal landmark.

Nearly 35 years ago, astronomers witnessed a star just outside the Milky Way explode like a bomb. “SN 1987a” quickly became the subject of more academic papers than any other supernova.  “It’s the only supernova that’s gone off in our neighborhood in the last 100 years,” Davenport says. “It’s kind of a big event. It’s rare, visible, and outshone the entire galaxy.

If any civilizations were poised, waiting for a special galactic moment to announce their presence, SN 1987a would have been a great opportunity, suggested Argentinian astrophysicist Guillermo Lemarchand in 1994. Now Sheikh and Davenport, together with undergraduate physics and astronomy student Bárbara Cabrales at Smith College, are working out the math to look for signals that would just be reaching Earth now, had they been sent in response to SN 1987a.

As light from the supernova reaches new stars, and potential signals from those stars ripple out through space, the zone of the sky to search changes. Using data from NASA’s Transiting Exoplanet Survey Satellite (TESS), which watches for stars being eclipsed by exoplanets, the group is developing an algorithm to look for stars that dim or flash at precisely the right moment. They don’t expect to find a smoking gun with TESS, which keeps tabs on hundreds of thousands of stars. Their main goal is to get the software tools ready for the upcoming Vera Rubin Telescope, which will monitor 10 to 20 billion stars on a weekly basis.

Further down the line, other SETI researchers could tweak the software to search for radio signals, rather than looking only for civilizations with the technology to make their star flicker. “We’re looking at signals now in [visible light] because that’s where the data is,” Davenport says. “We’re scavengers. We’re taking what is already available to us. Astronomers have to be crafty.”

Shy Civilizations

The central conceit of seeking Schelling points in modern SETI is the assumption that both sides are playing the same game. But with more powerful instruments, researchers might be able to start looking for more bashful  civilizations. In that case too, crafty astronomers are already thinking about what common behaviors might give an inhabited planet away, even if it’s not actively broadcasting.

Humanity, for instance, has benefited from putting television, radio, and weather satellites in high enough orbits that they continuously face the same part of the Earth. These spacecraft in “geosynchronous” orbits form an artificial ring around our planet roughly 22,000 miles above the ground. If another planet sported a thick enough artificial ring, it might block the light from its star in a peculiar way that astronomers could spot.

Our ring is sparse today but gets slightly denser every year. In 200 years, the satellite belt would become notable enough to be seen by extraterrestrial astronomers at a distance of ten light years using current telescopes, astrophysicist Hector Socas-Navarro calculated in 2018.

Another proposal assumes that civilizations have a vested interest in their long-term survival and may develop the technology to watch out for catastrophic asteroid collisions. As Carl Sagan reportedly quipped, “If the dinosaurs had had a space program, they would not be extinct."

Some of the loudest radio pulses humanity has sent out into space have been for exactly this purpose, with much of the responsibility of monitoring the trajectories of asteroids falling to Arecibo’s 2.5-million-watt radar beam, before its destruction. Most of that radio signal bounced back to Earth carrying vital information about its target, but some would spill past the asteroid into the galaxy. Similar signals from another world would come sporadically. But since the orbits of asteroids and planets form a flat disk, any radar signals originating from a planet and directed toward an asteroid would always spill outward from the plane of the disk. Future eavesdropping attempts could use this fact to prioritize systems that are oriented “edge on” to Earth, rather than “top down.”

Some researchers recoil from efforts to get into the heads of extraterrestrial beings, considering them too outlandish, and Sheikh understands the instinct to avoid assumptions. Nevertheless, since coming to view SETI through a Schelling-tinted lens, she has realized that every project assumes some shared attributes between humanity and whomever else could be out there. Even the fact that many SETI searches target stars betrays a presumption that other lifeforms, like us, are more likely to live on planets than in deep space.

“Everything is a Schelling point, Sheikh says. “You can't get away from it.”

Seeking universality

The more Schelling-inclined researchers can intuit commonalities between terrestrials and hypothetical extraterrestrials, the better their odds of success. And the only commonalities likely to span light years are going to be potential universalities, like knowing how fast sunbeams travel, or not wanting to be taken out by an asteroid. In the interest of ferreting out such universalities, some researchers point out that Earth might hold more than just one example to learn from.

Human cultures have risen and fallen for millennia,and have a long history of misinterpreting each others’ legacies. Spanish conquistadors, for instance, mistook the Great Pyramid of Cholula (the world’s largest pyramid by volume) for a hill and built a church on it. “Looking at the full sweep of human behaviors, anthropology-style, is useful for shaking us out of our own cultural biases,”  Kathryn Denning, an anthropologist at York University in Toronto.

She goes even farther, suggesting that observing how dolphins, whales, birds, and other social animals interact while sharing or dividing up territory would be a “good way to broaden our thinking beyond the human.”

Penn State’s Wright conceives of Schelling points in a similar way. The goal isn’t to get into an alien’s head per se, but rather to decipher the essential behaviors of all intelligent beings, starting with animals here on Earth. “They have to use energy. They have to move around. At some point they have to interact with each other. They have to eat. And so, we hope that there are similar fundamental things the alien species out there might be doing,” he says.

Perhaps in another 70 years, equipped with more sensitive instruments and smarter searching algorithms, SETI astronomers will have checked enough galactic Schelling points to start to answer Fermi’s question. If we show up at enough interesting landmarks at enough unique times and fail to connect, we’ll have to conclude that no one else is trying to meet up. Or, if they are, they’re going about it in a way that’s truly alien.

We usually think of mutations as harmful, but they often have no consequence and don’t change the meaning of our genetic code. There are two main categories of mutations — germline mutations and somatic mutations. Germline mutations found in our sperm or egg cells, can be passed on to our children. Somatic mutations in other cells of our body — such as in the brain, liver, or lungs, are never passed on to our children. Although somatic mutations cannot be inherited, they can still be important for human health. For example, somatic mutations in a subset of brain cells can cause seizures within a brain region either with or without visible changes to brain structure.

Over many years, the Walsh lab at Harvard University has contributed to our understanding of somatic mutations in the human brain. The group has studied how somatic mutations in brain cells may contribute to seizures, developmental disorders, or psychiatric and neurological conditions including autism spectrum disorders. They, and others, have investigated how often changes in a single letter of the DNA genetic code — called “single-nucleotide variants (SNVs)”— can be detected in typical and atypical brain cells.

Interestingly, by finding which somatic mutations are present in which cells, we can build a “family tree” of cells in the body and trace back the path of cell divisions that produced our trillions of cells from the single original cell. This “family tree” would be a treasure trove for understanding how our bodies develop. The Brain Somatic Mosaic Network is a group of researchers who study this problem specifically in the area of human brain development. Since we cannot watch the cells dividing inside a human embryo and cannot “see” the mutations within cells in tissue samples, these types of studies are quite technically challenging.

The Walsh group recently applied several ingenious methods to trace the developmental path of single cells in the human brain. How complex would this task be? The genome is like a book with six billion letters. Our cells are like trillions of copies of this book in a gigantic library – our body. Trying to find somatic SNVs is like trying to find single letter typos present in some of the copies of the book but not all of them. It is a mammoth task. So how would you find these typos? You could read the entire book multiple times or focus on a section you suspect has a typo and read that section multiple times. The first approach would be akin to “whole genome sequencing” while the second would be equivalent to “targeted amplicon sequencing”, and the researchers used both approaches in their study.

They also compared somatic SNVs in different organs, including the brain, liver, spleen, and heart, among others. Different body organs grow from different parts of the embryo and start out as distinct groups of cells. The authors were able to see these patterns of “branches” in the cell family tree. The fraction of cells in each organ with a specific somatic SNV varied depending on the organ’s origin within the embryo. Even within the brain, a single organ, the fraction of cells with specific sSNVs varied from the forebrain to the hindbrain, showing that they develop from different groups of cells in the embryo.

Measuring the frequency of specific somatic SNVs, the authors also estimated that around 50-100 cells within the embryo probably contributed to forming the brain. The estimate is not exact, because there are many unknowns. The methods used cannot detect all the somatic SNVs in the samples. Even with very deep genome sequencing (“reading the book” many times) somatic mutations present only in a small number of cells can still be missed. Moreover, the estimate was based on measurements mostly in one individual donor, highlighting another limitation of these approaches. Such studies are technically challenging and expensive, so they mostly include only a few individuals and a few organs from those individuals.

Nevertheless, the study brings us closer to understanding the complex, awe-inspiring process of human development from a single cell. It demonstrates that we can track how individual cells in a human embryo give rise to the organs of an adult human, and how even within the same organ, groups of cells have unique “barcodes” made of somatic SNVs recording the history of their “ancestor” embryo cells.

Malosree Maitra studies

Neuroscience