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2016 year in review.

At first glance, the stories taking the top two spots in Science News' review of 2016 have little In common. Scientists began searching decades ago for gravitational waves. Discussions of these subtle signals from dramatic and distant phenomena appear dozens of times in the SN archive starting as early as the 1950s. Their long-awaited discovery, our No. 1 story of the year, touched off celebration of a new era In astronomy. Less expected, and far from subtle, was the sudden rise in Brazil of microcephaly cases, linked this year to Zika virus infections--our No. 2 story. Little was known about Zika before the outbreak, which delivered devastation and fear across the Americas. In fact, only a single previous mention of Zika exists in the SN archive, in a book review from the 1990s.

But the stories have at least one thing in common: Both highlight the power of scientific discoveries to trigger our deepest human emotions. Pure elation as well as overwhelming dread can accompany research advances. 2016 brought many more sentiments, too. There was enthusiasm for the discovery of the exoplanet Proxima b, concern for the prospects of three-parent babies and feelings of potential but also impending peril in the openings of Arctic passageways.

The editors and writers at Science News also recognize that some of the best and most moving stories are those that are still unfolding. So, in addition to the discoveries of 2016, we review milestones, setbacks and other tales of unsteady progress. Sonia Shah writes about a new wave of infectious diseases; Tom Siegfried explores convergent failures in the field of particle physics; and Laurel Hamers covers key challenges for self-driving cars. Then, Science News writers share what science news they're most excited about in the year to come.

Caption: The first gravitational wave signal detected by LIGO came from the merger of two black holes spiraling inward, as depicted in this numerical simulation.

Gravitational waves offer new view of dynamic cosmos

By Emily Conover

1 The secrets gleaned from the universe's most mysterious giants are incongruously subtle when witnessed at Earth: Detectors budge by a tiny fraction of a proton's breadth, outputting a feeble, birdlike chirp.

For centuries, astronomers have peered out into the universe almost exclusively by observing its light. But 2016's announcement of the first detection of gravitational waves, produced 1.3 billion years ago in the collision of two monstrous black holes, has given scientists a whole new way of observing the heavens.

The waves tore through the cosmos at the speed of light and arrived at Earth just in time for the start-up of the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, which measured the minute stretching and squeezing of space. With a second detection already recorded and more expected in 2017, scientists hope to uncover new details about elusive black holes and their pairings. Soon, as more detectors come online, scientists will even be able to pinpoint where gravitational waves originate and inspect the sky for the aftermath of the cataclysms that caused them.

"This is a great success story of science," says astrophysicist Avi Loeb of Harvard University, who was not involved in the detection. It's the kind of major discovery that comes along only once in a few decades, he says.

On February 11, LIGO scientists announced the discovery at a news conference in Washington, D.C., and in a paper published in Physical Review Letters. Since publication, the paper has garnered around 100 citations a month, evidence of a newly intensified focus on the waves. Some physicists had dedicated entire careers to finding the spacetime tremors, which will be a boon for researchers for decades if not centuries to come.

The patterns of ripples appeared nearly simultaneously in LIGO's two enormous L-shaped detectors--in Hanford, Wash., and Livingston, La.,--on September 14, 2015. The signal closely matched that expected from a pair of black holes that spiral around one another, getting closer and closer before merging into one. At the early stages of their do-si-do, the two black holes were about 35 and 30 times the mass of the sun. The behemoths melded together into a black hole 62 times the sun's mass, releasing three suns' masses worth of energy (SN: 3/5/16, p. 6; SN: 7/9/16, p. 8). When scientists converted the gravitational waves into sound waves, the waves produced something like the everyday chirp of a bird, quickly rising in pitch and volume before cutting off. The sound felt like a plaintive question, as if the universe was asking, "Hello? Is anyone there?" This time, the answer was yes.

Taken on its own, the discovery was a blockbuster--confirming Einstein's prediction that spacetime can ripple, providing an intimate new glimpse of black holes and verifying astrophysicists' calculations for how two black holes can fuse into one. But the detection's landmark status is largely because of its future promise. LIGO is expected to usher in a new era of astronomy, in which gravitational wave detections could become commonplace. Black holes, previously dark to humankind, will regularly communicate their coalescences to Earth.

In pursuit of this new type of astronomy, scientists have been chasing gravitational waves for decades. After such a long search, it was "incredibly gratifying," says David Shoemaker, leader of LIGO's efforts at MIT, "to wake up in the morning and know in my bones" that gravitational waves had finally been detected.

Almost as soon as LIGO's updated detectors were turned on, the gravitational waves rippled by, slightly altering the length of LIGO's ultrasensitive detectors. "We flipped the switch and said, 'OK, we're going to start running,' and boom," says LIGO laboratory executive director David Reitze of Caltech. That quick detection raised hopes among astrophysicists who daydream of datasets with tens or hundreds of such events.

With each new coalescence, scientists will learn more about how common black hole pairs are, as well as the properties of black holes and the dying stars that collapsed into oblivion to create them. "What we're really learning about when we study these black holes is the stars that were their progenitors," says LIGO member Daniel Holz of the University of Chicago. "From the stars, we then are learning about the early universe."

Scientists hope to reconstruct how pairs of black holes find one another in the lonely universe. There are two main competing theories: Two stars could be born together like twins, with each later collapsing into a black hole, or the black holes could meet up later in life, in dense systems where many black holes and stars interact (SN Online: 6/19/16).

Proving that the detection was no fluke, LIGO scientists reported June 15 that they had spotted the quivers of a smaller pair of merging black holes (SN: 7/9/16, p. 8). LIGO shut down for upgrades following the two detections, but restarted again in November. Further improvements to the LIGO detectors will boost their sensitivity, allowing them to catch even fainter ripples. When those upgrades are complete--perhaps by 2019--scientists could glimpse black hole mergers as frequently as once a day.

With the first detections, physicists used LIGO's data to confirm Einstein's general theory of relativity in a more extreme environment than ever before. "That's a triumph," says Loeb. But future detections will add even more precision to tests of general relativity. Any deviation from expectations could signal some way in which Einstein's theory breaks down. The equations of general relativity also suggest that black holes have no "hair," or distinguishing characteristics aside from mass, electric charge and angular momentum. But this leads to a conundrum about what happens to information swallowed up by the black hole (SN: 10/3/15, p. 10). In the future, scientists could use gravitational waves to test whether the no-hair theorem is true.

The discovery "injected a lot of momentum in the field," says Emanuele Berti, an astrophysicist at the University of Mississippi in Oxford.

Another gravitational wave detector, Virgo, in Italy, is undergoing upgrades and should be switched on in 2017 (SN: 3/5/16, p. 24). The trio of detectors--Virgo, plus LIGO's two--will give scientists the ability to locate the sources of gravitational waves on the sky. The government of India is also taking steps toward creating a gravitational wave observatory. And related projects are garnering more attention: Results announced in June from the European Space Agency's LISA Pathfinder satellite demonstrated the technological capabilities needed to search for gravitational waves not from the ground but from space (SN Online: 6/7/16).

If researchers can triangulate the source of the waves, they can point telescopes in that direction to spot any luminous aftermath. Such a signal would be unexpected for shadowy black holes, but they aren't the only source. Scientists expect to find undulations from smashups of neutron stars, which might produce detectable light. If luck is on LIGO's side and a star explodes within the Milky Way, LIGO maybe able to spot its gravitational fallout, too.

Combining gravitational waves with other messengers from space, including various wavelengths of light and particles such as neutrinos, will create a diverse toolkit for observing the cosmos. Scientists may even find unforeseen sources of gravitational waves, says Loeb. "There is a chance that our imagination is limited."

Public health checkup

Drug use continued to threaten the health and safety of the American public in 2016, while a hidden menace in drinking water remained a major worry for the people of Flint, Mich.

Teen vaping

Vaping has surpassed cigarette smoking among U.S. high school students, according to a report released in 2016 from the National Youth Tobacco Survey. Estimates suggest that some 2.39 million U.S. high school kids vaped in 2015, compared with an estimated 1.37 million who smoked cigarettes (SN: 5/28/16, p. 4). The popularity of e-cigarettes has increased recently despite a lack of evidence showing that they are safer than conventional tobacco products, according to the U.S. Food and Drug Administration, which in May extended its regulatory authority to e-cigarettes. Studies reported in 2016 show a host of potential health risks, including effects on the brain, immune system and fertility (SN: 3/5/16, p. 16).

Opioid epidemic

Against a backdrop of rising prescription opioid addiction, deaths related to opioid use have become an issue of national importance. A surge in fentanyl-spiked drugs emerged as a primary concern in 2016 (SN: 9/3/16, p. 14). U.S. deaths from synthetic opioids rose from 3,105 in 2013 to 5,544 in 2014, a change that could not be explained by fentanyl prescription rates, according to a report released in August by the Centers for Disease Control and Prevention. Drug enforcement seizures involving fentanyl more than doubled from 2014 to 2015.

Fallout in Flint

After lead in the drinking water in Flint, Mich., launched a public health crisis (SN: 3/19/16, p. 8), a federal state of emergency remained in effect into August. The most recent tests conducted by the U.S. Environmental Protection Agency show that levels of lead, which is toxic to the brain, are below those considered dangerous and that filtered tap water is safe to drink. Many residents are still relying on bottled water, however. There's also growing concern that lead contamination and testing is not being taken seriously elsewhere in the United States.--Cassie Martin

2 Zika virus devastates Brazil, spreads fear across Americas

By Meghan Rosen

A Brazilian mother cradles her baby girl under a bruised purple sky. The baby's face is scrunched up, mouth open wide--like any other crying child. But her head is smaller than normal, as if her skull has collapsed above her eyebrows.

A week earlier, not far away, a doctor wrapped a measuring tape around the forehead of a 1-month-old boy, held in the arms of his grandmother. This baby too has a shrunken head, a birth defect whose name--microcephaly--has now become seared into the public consciousness.

These images and many more told a harrowing story that case reports alone couldn't convey: A little-known mosquito-borne virus called Zika appeared to be taking a terrible toll on women and babies, and their families. The world got a gut-wrenching view of microcephaly in 2016, along with a mountain of evidence convincing scientists that Zika bears much of the blame for the dramatic increase in cases.

"Once you've seen those pictures from Brazil, you realize what a huge impact this kind of outbreak can have," says Sonja Rasmussen, a pediatrician at the U.S. Centers for Disease Control and Prevention in Atlanta. Brazil logged its first cases of Zika in 2015, but infections there peaked this spring with perhaps up to 8,000 new infections per week. The virus crept northward and infiltrated many more countries including Panama, Haiti and Mexico. Now, the threat has come to the United States: Cases have been reported in every state except Alaska. They stem mostly from travelers infected abroad, but the virus has staked out new territory in Puerto Rico, the U.S. Virgin Islands, American Samoa and Florida.

As of December 1, Puerto Rico had reported more than 34,000 people with Zika infections. More than 2,700 are pregnant women. And elsewhere in the United States, the CDC has reported well over 4,000 laboratory-confirmed cases of Zika. In these places and others, the images from Brazil have filled expectant mothers (and anyone considering having kids) with uncertainty and fear. "It's really scary to be pregnant right now," Rasmussen says. "We don't know what to tell women." The threat to unborn babies wasn't clear when Zika first hit Brazil, or in earlier, smaller outbreaks on Yap Island in the western Pacific and in French Polynesia. In fact, before 2016, not much was known about the virus at all. The majority of people infected don't show any symptoms. But in the last year, scientists have thrown themselves at Zika, publishing more than 1,500 papers on different facets of the virus, from what species of mosquito it hides in to what cells it invades.

"We're learning something new every day," says obstetrician/gynecologist Catherine Spong, deputy director of the National Institute of Child Health and Human Development in Bethesda, Md.

The studies have scrubbed away some of Zika's mystery--in particular, what the virus does in the womb. Scientists have found traces of Zika in the brains of human fetuses and confirmed that the virus can infect and kill brain cells in the lab. "This is the year that people became convinced that this mosquito-borne virus could cause birth defects," Rasmussen says.

Though there was no smoking gun--no single piece of evidence that clinched Zika as the culprit--little clues began adding up, beginning with the conspicuous timing of Brazil's microcephaly upsurge (SN: 4/2/16, p. 26). In January the CDC first issued a warning to pregnant women to postpone travel to Zika-affected regions. On April 13, a day that may be forever etched into Rasmussen's memory, she and colleagues reported "a causal relationship" between Zika and microcephaly, along with other birth defects, in a study published online in the New England Journal of Medicine. Since then, Rasmussen says, "The data have become absolutely overwhelming."

In May, a mouse study offered the first direct proof in animals that in utero Zika infection can lead to microcephaly (SN Online: 5/11/16). In September, researchers reported that a pregnant pigtailed macaque infected with Zika in the third trimester then gave birth to a baby whose brain had stopped growing. In human babies, the range of disorders linked to Zika has ballooned to include problems with the eyes, ears and joints, as well as seizures and extreme irritability (SN: 10/29/16, p. 14). At a workshop in North Bethesda, Md., this fall, a room crowded with doctors and scientists watched videos of inconsolable infants jerking erratically, arms and legs unnaturally stiff. "Heartbreaking," Rasmussen says.

Zika isn't the first virus to harm babies in the womb. Cytomegalovirus can also cause microcephaly, for example, and rubella, known as "German measles," can leave babies with hearing, vision and heart problems. Even among these viruses, though, Zika stands out. "It's such a precedent-setting thing," Rasmussen says. "Never before has there been a mosquito-borne virus known to cause birth defects."

Despite what scientists have learned in 2016, there's little consolation for families already affected by microcephaly. And huge questions remain for expectant mothers. In particular, says Spong, it's not clear just how risky Zika infection during pregnancy really is. One study published in the New England Journal of Medicine in July estimated that the risk of bearing a child with microcephaly increases to somewhere between 1 and 13 percent for women infected in their first trimester.

Spong hopes that a new study will clarify things. It's called the Zika in Infants and Pregnancy Cohort Study, or ZIP, and the plan is to enroll 10,000 women in their first trimester. They'll come from Puerto Rico, as well as Brazil and other countries, Spong says, and include both infected and uninfected women.

Tracking these women through pregnancy, birth and their baby's first year of life could fill in some answers, like whether an infected pregnant woman who doesn't have symptoms is better off than one who does. It's also possible that some type of cofactor, like environmental toxins or other infections, is working with Zika to cause birth defects. Such a cofactor might explain why there have been fewer babies born with microcephaly in Colombia than expected. It's also possible that greater awareness has led to more terminated pregnancies.

"You're supposed to avoid stress when you're pregnant," Rasmussen says. "How do you avoid stress when you're thinking that your baby could have these problems related to Zika?"

In the best-case scenario, a Zika vaccine could still be a few years away. And though infection rates may be winding down in some places, in areas with seasonally high temperatures and rainfall, such as Puerto Rico, Zika could become a local fixture. Still, any scrap of new information might help. Results from ZIP and other studies won't erase the damage, but they could offer a pinprick of light following a year darkened by disease.

1-13 percent

Estimated risk of bearing a baby with microcephaly for a pregnant woman infected with Zika in the first trimester

Caption: A young woman holds her daughter, born with microcephaly, outside their home in Recife, Brazil. Researchers this year linked the upsurge in microcephaly cases in Brazil to the mosquito-borne Zika virus.

3 Closest known exoplanet 'just' 4.24 light-years away

By Christopher Crockett

Worlds in the Alpha Centauri system--the trio of stars closest to our sun--have been a staple of science fiction for decades. From Star Trek to Avatar, writers have dreamed up exotic landscapes (and inhabitants) for interstellar explorers to encounter. Now a planet around one of those stars is no longer fiction.

In August, breathless headlines heralded the discovery of a small, potentially habitable planet orbiting Proxima Centauri, a dim red dwarf star just 4.24 light-years away (SN: 9/17/16, p. 6). The planet, Proxima b, isn't the first roughly Earthmass planet discovered. It's not the first seen in a star's habitable zone, the region where temperatures are just right for liquid water. Nor is it the first found around a red dwarf, the most common type of star in the galaxy.

Proxima b got special attention for one reason: It's the closest known exoplanet to us. "This is a game changer in exoplanetary science," says Rory Barnes, an astronomer at the University of Washington in Seattle. "The fact that it's so close means we have the opportunity to follow up on it better than any other planet discovered so far."

When it comes to interstellar distances, "so close" is still incomprehensibly far. Proxima Centauri is a roughly 40 trillion kilometer jaunt (SN Online: 8/25/16). The fastest spacecraft to leave Earth--the New Horizons probe that zipped past Pluto in 2015 (the mission took the top spot in Science News' 2015 Year in Review)--would need nearly 80,000 years to get there, traveling at its launch speed of roughly 58,000 kilometers per hour. But if Earthlings ever do venture beyond the solar system, Proxima Centauri is likely to be the first stop.

Astronomers found Proxima b by looking for a tiny wobble in the speed of its parent star, the sign of a gravitational tug from an orbiting planet. Observations from telescopes in Chile confirmed its existence. But not much is known about the planet. Researchers have determined, based on that tiny wobble, that the planet is at least 1.3 times as massive as Earth and it travels along an 11.2-day orbit. Its habitability is speculative. The planet basks in enough light to sustain liquid water, but other factors might foil the possibility of life. The planet's climate depends strongly on the characteristics of its atmosphere--if it even has one. No one knows if Proxima b has a solid surface where water could pool and critters could crawl. No one knows the planet's size. Even its mass is just a minimum estimate.

With a near-term voyage to Proxima b unlikely, the best chance to learn more about the planet might come from a transit, when a planet periodically slips between us and its sun. If the planet transits, it would block a smidgen of starlight from reaching Earth, subtly dimming Proxima Centauri. Astronomers could then estimate the size of Proxima b by measuring how much light the planet intercepts. A transit could also pin down the true mass by removing some ambiguity in the details of the planet's orbit. By considering the size of the planet and its mass, researchers could calculate the planet's density, revealing whether Proxima b is really a rocky world like Earth (as a lot of the initial news coverage jumped to proclaim) or a gassy one.

During a transit, a sliver of light would also have to pass through Proxima b's atmosphere. Molecules in the atmosphere would block specific wavelengths of starlight, allowing astronomers to deduce the chemical makeup of the atmosphere and hunt for any by-products of living organisms.

The odds of a transit are slim--there's just a 1.5 percent chance the orbit's orientation is right--and one early investigation is not promising. The Canadian Microvariability and Oscillations of Stars satellite, MOST for short, monitored Proxima Centauri for hints of a transiting planet in May 2014 and May 2015 for about 44 days and turned up nothing, astronomer David Kipping of Columbia University and colleagues reported online at in September.

But researchers aren't giving up yet. Several groups are keeping an eye on Proxima Centauri in the hopes of catching the telltale dip from a transit. "We should know whether there is a transit or not before the end of the year," says Guillem Anglada-Escude, the astronomer at Queen Mary University of London who led the Proxima b discovery team. Seeing the planet directly could also reveal new details, though that is probably beyond the capability of any current or planned telescopes.

Even if astronomers can't learn anything more about Proxima b, there will be plenty of other nearby worlds to study. Late in 2017, NASA plans to launch the Transiting Exoplanet Survey Satellite, or TESS, a telescope on a two-year mission to monitor about 200,000 stars for transiting exoplanets. Many of these stars are among the sun's closest neighbors.

Astronomers estimate that TESS will turn up about 1,700 worlds in addition to the more than 3,500 already discovered. That haul could include more than 500 planets less than twice the size of Earth, roughly 50 of which might lie within the habitable zone of their stars, Peter Sullivan, now an engineer at NASA's Jet Propulsion Laboratory in Pasadena, Calif., and colleagues reported in 2015 in the Astrophysical Journal. And because TESS will add only transiting planets, many will be ripe for follow-up investigations by future observatories such as the James Webb Space Telescope, which will view the cosmos in the infrared and is scheduled to launch in 2018 (SN: 4/30/16, p. 32).

More planets means more chances of finding life beyond the solar system. But finding aliens isn't the only goal. Astronomers want "to understand how our solar system--and how Earth--fits into the universe," Barnes says. "What's special and what's not special about our solar system?"

And interstellar travel will continue to capture imaginations. In the 1935 short story Proxima Centauri, published just 18 years after astronomers measured the distance to the star, Murray Leinster wrote of Earth's first interstellar spaceship closing in on an imagined planet orbiting our stellar neighbor. In Leinster's story, an alien race of mobile carnivorous plants ends up devouring most of the crew. Hopefully our first ambassadors to an exoplanet, whether Proxima b or elsewhere, will fare better.

Caption: Proxima b, depicted with its star in this illustration, is at least 1.3 times as massive as Earth--but that is just a minimum estimate.

Caption: Astronomers are monitoring Proxima Centauri (shown in a Hubble Space Telescope image) hoping to catch a transit of Proxima b. The chance that the planet's orbit is oriented for a transit is just 1.5 percent.

4 Birth of 'three-parent baby' prompts hope and concern

By Tina Hesman Saey

A "three-parent baby" was born in April, the world's first reported birth from a controversial technique designed to prevent mitochondrial diseases from passing from mother to child.

"As far as we can tell, the baby is normal and free of disease," says Andrew R. La Barbera, chief scientific officer of the American Society for Reproductive Medicine. "This demonstrates that, in point of fact, the procedure works."

The baby boy carries DNA not only from his mother and father but also from an egg donor, raising both safety and ethical concerns. In particular, people worry that alterations of the genetic makeup of future generations won't stop with preventing diseases but could lead to genetically enhanced "designer babies."

Opponents, such as Marcy Darnovsky, executive director of the Center for Genetics and Society in Berkeley, Calif., are also worried that the technique hasn't been fully tested. "We wish the baby and family well, and hope the baby stays healthy," Darnovsky says. "But I have a lot of concerns about this child and about future efforts to use these techniques before they've been shown to be safe."

About one in 4,000 children are born with dysfunctional mitochondria. These energy-generating organelles are inherited from the mother and have their own DNA. Mutations in some of the 37 mitochondrial genes can lead to fatal diseases, often affecting energy-hungry organs such as the brain and muscles. Because there is no cure or effective treatment for many mitochondrial diseases, the recent birth has been heralded as a sign of new hope for affected families.

Even if women don't have mitochondrial diseases themselves, they can pass the diseases to their children if their egg cells contain large numbers of defective mitochondria. The mother of the recent three-parent baby had previously had two children who died of Leigh syndrome, a mitochondrial disease that affects the nervous system and eventually prevents a person from breathing.

Fertility doctor John Zhang of the New Hope Fertility Center in New York City and colleagues performed what's called a spindle transfer to put all the chromosomes from the mother's egg into a donor egg that contained healthy mitochondria but had been emptied of its chromosomes (SN Online: 10/18/16). The egg was then fertilized with sperm and implanted in the mother.

"It's very important that they follow up," to monitor the child's long-term health, says Shoukhrat Mitalipov, a mitochondrial biologist at Oregon Health & Science University in Portland. Mitalipov pioneered the spindle transfer technique in monkeys (SN: 9/26/09, p. 8). Even a small number of defective mitochondria carried over from the mother's egg may replicate and cause problems later on, he and other scientists have found (SN: 6/25/16, p. 8; SN Online: 11/30/16).

Zhang reported that just 1.6 percent of the baby boy's mitochondrial DNA came from his mother (SN Online: 10/19/16). Mitalipov notes, however, that doctors can't know from sampling a few types of tissue whether other tissues have different levels of mitochondrial carryover. What's more, levels of mutant mitochondria may change as the child grows.

Mitalipov supports research on the technique but says it should be done in carefully controlled clinical trials. Results of a mouse study published in July suggest that mismatches between the parents' nuclear DNA and the donor mitochondrial DNA could affect metabolism and aging (SN: 8/6/16, p. 8). Those effects could show up years or decades after birth.

The baby boy born in April is technically not the first three-parent baby. At least two children born in the late 1990s carry mitochondrial DNA from a donor. Those two and 15 other children were born to mothers who had a small amount of cytoplasm--the gelatinous fluid that fills cells and holds mitochondria --from a donor egg injected into their own eggs in an effort to improve results of in vitro fertilization. No major health problems have been reported, but the studies were abandoned because of ethical concerns, lack of funding and the difficulties in obtaining newly required permits.

La Barbera disputes the term "three-parent baby" entirely. "A person's essence as a human being comes from their nuclear genetic material, not their mitochondrial genetic material,"

La Barbera says. Children who are born after mitochondrial transfer procedures have only two parents, he contends.

Zhang drew fire for going to Mexico to perform the procedure. Congress currently bars the U.S. Food and Drug Administration from reviewing applications to make heritable changes in human embryos, which includes the spindle transfer technique. A panel of experts said in February that it is ethical to make three-parent baby boys (SN Online: 2/3/16), a provision that would prevent future generations from inheriting the donor mitochondria. Because mothers pass mitochondria on to their babies but fathers usually do not, technically baby boys born through this technique don't carry an inheritable modification in their DNA.

Clinics in the United Kingdom can legally perform the procedures, but none have been reported yet. A panel of experts there recommended November 30 that clinical studies could move ahead, so more babies maybe born in 2017.

Caption: Cell swap A baby boy born in April has DNA from three people. To produce the embryo, researchers transferred the chromosomes from the mother's egg into a donor egg with healthy mitochondria. The technique is called "spindle transfer" for the cellular structure that segregates the chromosomes.

5 Opening Arctic passageways will shake up ecosystems

By Susan Milius

In a better world, it would be the big news of the year just to report that Arctic sea ice shrank to 4.14 million square kilometers this summer, well below the 1981-2010 average of 6.22 million square kilometers (SN Online: 9/19/16). But in this world of changing climate, extreme summer ice loss has become almost expected. More novel in 2016 were glimpses of the complex biological consequences of melting at the poles and the opening of Arctic passageways, talked about for at least a decade and now well under way.

With top-of-the-world trade and tourist shortcuts opening, less ice means more travel. Europe-to-Asia shipping routes will typically shorten by about 10 days by midcentury, a report in Geophysical Research Letters predicted. Hopes for Northwest Passage routes obsessed (and killed) explorers in previous centuries, but in 2016, the thousand-passenger cruise ship Crystal Serenity offered the first megascale tourist trip from Alaska to New York with fine dining, casino gambling and an escort icebreaker vessel.

Biologists are delving into consequences for organisms other than human tourists--or the much-discussed polar bear. "There's been a marked shift in the research community," says climate change ecologist Eric Post of the University of California, Davis. There's new interest in considering more than just species that dwell on sea ice, with researchers looking for the less direct effects of declining ice (see Page 15).

In the February Global Change Biology, eight scientists issued a call for observations of what could be early signs of faunal exchange: the mingling of Atlantic and Pacific species. One possible indicator is the sighting of gray whales off the

coast of Namibia and also off Israel, even though that species went extinct in the Atlantic two centuries ago. These whales feed by snouting around in soft ocean bottoms, adding another predator to the system but also creating new habitat opportunities for some creatures (SN: 1/23/16, p. 14).

Since the call was published, biodiversity scientist Seabird McKeon of Colby College in Waterville, Maine, has heard new reports, such as a sighting of an ancient murrelet off the coast of Maine. It's not the first wrong-coast report for the bird, which typically resides in the northern Pacific, but repeat sightings could be important, too. "What I think we're seeing is not just new species coming across, but also perhaps an increased chance of survival and reproduction if more come over," McKeon says. He is hoping to get new data from the online Encyclopedia of Life's upcoming Fresh Data system, which connects scientists to people reporting nature observations.

For terrestrial northerners, melting ice often means loss of mobility. Peary caribou on the 36,000 or more islands of Canada's northern archipelago occasionally use ice bridges to travel to new territories and mix genes with other populations. to find traveling paths, researchers reported in September in Biology Letters (SN: 10/29/16, p. 8).

Even some plants such as dwarf birch probably travel by ice, scientists also reported in September in Biology Letters. Reconstructing long-ago sea ice extent and plant colonization dates suggests that seeds hitchhiked on slowly creeping frozen conveyors around northern Europe to colonize new territory at the end of the Ice Age. Losing ice roads could lead to tattered, disconnected populations as recolonization becomes less likely. Yet, there are pluses and minuses, says Post, who is helping to develop a package of scientific articles for Biology Letters on the biological effects of sea ice loss. Reseeding populations after a wipeout could be more difficult with tattered ice, but for the highly specialized and vulnerable plants very far north, the loss of sea ice could slow the arrival of invasive species that threaten the natives.

The minimum summer sea ice extent since 1979 has declined by about 87,000 square kilometers per year, equivalent to an area more than three times the size of New Jersey disappearing annually, as Post has put it. The September 2016 sea ice minimum didn't break a record, as some had expected it might. It tied for second worst, behind the 2012 minimum, and roughly equaled the 2007 minimum. 2016 did set a new record low for winter Arctic ice extent (SN Online: 3/28/16).

Sea ice changes reverberate through the ecosystem. Ice melting cues the springtime phytoplankton blooms that feed copepods and other tiny marine grazers. The grazers feed their predators and, in turn, the predators of those predators. In years when spring warming brings an early ice retreat, the phytoplankton bloom is not a huge, rich burst. It favors smaller grazing zooplankton that don't fuel as much of a boom in their predators, marine ecologist Martin Renner of Homer, Alaska, and colleagues reported in a paper for the Biology Letters special collection.

Tracing the effects of shrinking ice through these grazers to fish to seabirds revealed a tangled web of ups and downs and shifting foraging grounds. In the end, Renner and colleagues predict "a very different eastern Bering Sea ecosystem and fishery than we know today." And that may be far from the only sea change in the far north.

Big if true

These findings would have rocked the scientific world, if only the evidence had been more convincing.

New Planet 9 clues

A giant planet lurking at the outskirts of the solar system could explain the odd orbits of far-flung hunks of icy debris (SN: 2/20/16, p. 6). If the planet (illustrated above) exists, its average distance from the sun would be between 500 and 600 times Earth's distance (SN: 7/23/16, p. 7).

Signs of ancient life

Mounds of minerals discovered in Greenland appear to have been deposited by clusters of microbes 3.7 billion years ago. If so, these stromatolites represent the oldest fossilized evidence of life on Earth (SN: 10/1/16, p. 7).

Lucy's big fall

A controversial study claims that Lucy, the most famous fossil in the study of human evolution, died after falling from high up in a tree (SN: 9/17/16, p. 16). The autopsy supports the hypothesis that Australopithecus afarensis split its time between the ground and the trees.

Nucleus with no charge

Researchers have spotted signs of a "tetraneutron," an atomic nucleus with four neutrons but no protons (SN: 3/5/16, p. 10). If confirmed, this first-of-its-kind nucleus might be explained by a new, interneutron force.--Cassie Martin

Caption: Polar melting Arctic sea ice hit its annual low on September 10, extending just 4.14 million square kilometers (shown). Though it didn't break a record, this minimum is more than 2 million square kilometers less than the average minimum from 1981 to 2010 (outlined in yellow). Yet ice losses since 1979 have made it some 15 percent harder

Caption: The melting of Arctic ice could affect seed dispersal among plants, such as the dwarf birch (shown here in Greenland).

6 Genetics alone won't explain how humans left Africa

By Bruce Bower

No paper or digital trails document ancient humans' journey out of Africa to points around the globe. Fortunately, those intrepid travelers left a DNA trail. Genetic studies released in 2016 put a new molecular spin on humans' long-ago migrations. These investigations also underscore the long trek ahead for scientists trying to reconstruct Stone Age road trips.

"I'm beginning to suspect that the ancient out-of-Africa process was complex, involving several migrations and subsequent extinctions," says evolutionary geneticist Carles Lalueza-Fox of the Institute of Evolutionary Biology in Barcelona.

Untangling those comings, goings and dead ends increasingly looks like a collaborative job for related lines of evolutionary research--comparisons of DNA differences across populations of present-day people, DNA samples retrieved from the bones of ancient hominids, archaeological evidence, fossil finds and studies of ancient climates. It's still hard to say when the clouds will part and a clear picture of humankind's journey out of Africa will appear. Consider four papers published in October that featured intriguing and sometimes contradictory results.

Three new studies expanded the list of present-day populations whose DNA has been analyzed. The results suggest that most non-Africans have inherited genes from people who left Africa in a single pulse between about 75,000 and 50,000 years ago (SN: 10/15/16, p. 6). One team, studying DNA from 142 distinct human populations, proposed that African migrants interbred with Neandertals in the Middle East before splitting into groups that headed into Europe or Asia. Other scientists whose dataset included 148 populations concluded that a big move out of Africa during that time period erased most genetic traces of a smaller exodus around 120,000 years ago. A third paper found that aboriginal Australians and New Guinea's native Papuans descend from a distinctive mix of Eurasian populations that, like ancestors of other living non-Africans, trace back to Africans who left their homeland around 72,000 years ago.

The timing of those migrations maybe off, however. A fourth study, based on climate and sea level data, identified the period from 72,000 to 60,000 years ago as a time when deserts largely blocked travel out of Africa. Computer models suggested several favorable periods for intercontinental travel, including one starting around 59,000 years ago. But archaeological finds suggest that humans had already spread across Asia by that time.

Clashing estimates of when ancient people left Africa should come as no surprise. To gauge the timing of these migrations, scientists have to choose a rate at which changes in DNA accumulate over time. Evolutionary geneticist Swapan Mallick of Harvard Medical School and the other authors of one of the new genetics papers say that the actual mutation rate could be 30 percent higher or lower than the mutation rate they used. Undetermined levels of interbreeding with now-extinct hominid species other than Neandertals may also complicate efforts to retrace humankind's genetic history (SN: 10/15/16, p. 22), as would mating between Africans and populations that made return trips.

"This can be clarified, to some extent, with genetic data from ancient people involved in out-of-Africa migrations," says Lalueza-Fox. So far, though, no such data exist.

The uncertainty highlights the need for more archaeological evidence. Though sites exist in Africa and Europe dating from more than 100,000 years ago to 10,000 years ago, little is known about human excursions into the Arabian Peninsula and the rest of Asia. Uncovering more bones, tools and cultural objects will help fill in the picture of how humans traveled, and what key evolutionary transitions occurred along the way.

Mallick's team has suggested, for example, that symbolic and ritual behavior mushroomed around 50,000 years ago, in the later part of the Stone Age, due to cultural changes rather than genetic changes. Some archaeologists have proposed that genetic changes must have enabled the flourishing of personal ornaments and artifacts that might have been used in rituals. But comparisons of present-day human DNA to that of Neandertals and extinct Asian hominids called Denisovans don't support that idea. Instead, another camp argues, humans may have been capable of these behaviors some 200,000 years ago.

Nicholas Conard, an archaeologist at the University of Tubingen in Germany, approaches the findings cautiously. "I do not assume that interpretations of the genetic data are right," he says. Such reconstructions have been revised and corrected many times over the last couple of decades, which is how "a healthy scientific field moves forward," Conard adds. Collaborations connecting DNA findings to archaeological discoveries are most likely to produce unexpected insights into where we come from and who we are.

Caption: Recent genetic analyses suggest that natives of Papua New Guinea, shown here during a traditional Enga cultural show in 2015, descend from people who left their African homeland some 72,000 years ago.

7 Synthetic cell may reveal what is necessary for life

By Rachel Ehrenberg

One of biology's biggest achievements of 2016 was intentionally as small as possible: building a bacterium with only 473 genes. That pint-size genetic blueprint, the smallest for any known free-living cell, is a milestone in a decades-long effort to create an organism containingjust the bare essentials necessary to exist and reproduce. Such "minimal genome" cells might eventually serve as templates for lab-made organisms that pump out medicines, make innovative chemicals for industry and agriculture, or churn out other molecules not yet imagined. The project also identified genes crucial for the microbe's survival yet largely unfamiliar to science, highlighting major gaps in researchers' grasp of life's playbook.

The newly engineered bacterium was praised as a technical triumph. In 2010, researchers at the J. Craig Venter Institute in La Jolla, Calif., had stitched together a copy of the entire genome of the bacterium Mycoplasma mycoides and popped it into the cell of another bacterium whose genome had been removed. But that "synthetic cell," dubbed JCVI-synl.0, contained a full copy of an existing genome. With more than 1 million chemical building blocks of DNA, including 901 genes, it was far from minimal.

The latest version, JCVI-syn3.0, reported in March in Science (SN: 4/16/16, p. 6), has roughly half that much DNA. It's also the first cell built using human design principles: One segment of the genome has genes for various processes, such as DNA repair, grouped together rather than scattered willy-nilly. Abandoning the untidiness of evolution for a logic-driven blueprint enables a "plug and play" approach, says Daniel Gibson, a member of the JCVI team. To tinker with a metabolic process such as glycolysis, for example, "Rather than changing one gene, then another, then another, you could pop out a whole module and then pop in a new one."

Making such fundamental changes to the genome while still getting a functioning cell is noteworthy, says genome scientist George Church of Harvard University. "They could have found that, no matter what they did putting it together, it broke," Church says.

The potential of synthetic cells is enormous, says Claudia Vickers, a biotechnologist at the Australian Institute for Bioengineering and Nanotechnology in Brisbane. Scientists have succeeded in engineering existing organisms such as yeast to help make, for example, malaria drugs. Now little cellular factories designed to be highly efficient and tailored to specific tasks are within sight, Vickers says.

The techniques used to build JCVI-syn3.0, especially when considered alongside other engineering tools such as the recently developed CRISPR/Cas9 system (SN: 9/3/16, p. 22), are a meaningful step toward the once-distant goal of self-replicating minimachines. "It's important for the future it allows us to imagine," Vickers says.

Since announcing JCVI-syn3.0, the team has used the same engineering techniques to turn the fast-growing bacterium Vibrio natriegens into a laboratory workhorse. The engineered Vibrio--dubbed Vmax--cuts the time it takes to do particular lab experiments in half compared with the original, Gibson says.

The minimal genome effort also aims at a larger philosophical question: What is life? In a lecture in 1984, origin-of-life expert Harold Morowitz discussed how studying the small and simple Mycoplasma genome might invigorate basic biology in much the way that studying the hydrogen atom sharpened questions for physics and chemistry. (Morowitz died in March, two days before the JCVI-syn3.0 work was published online.)

Many scientists, for example, were stunned to learn that JCVI-syn3.0 had 65 genes with no known function that were nevertheless required for survival. "This is one of our best studied organisms, and we haven't the foggiest idea what those genes are doing," says evolutionary genomics expert Laurence Hurst of the University of Bath in England. "It's a brilliant result."

Caption: Dubbed syn3.0, engineered bacteria developed at the J. Craig Venter Institute can survive and function with just 473 genes.

8 Promising Alzheimer's drug will test amyloid hypothesis

By Laura Sanders

A quarter century after scientists proposed an idea that profoundly influenced the arc of Alzheimer's research, they might finally find out whether they are correct. A new antibody drug called aducanumab appears to sweep the brain clean of sticky amyloid-beta protein. The drug may or may not become a breakthrough Alzheimer's treatment--it's too soon to say--but either way it will probably answer a key question: Have researchers been aiming at the right target?

According to the proposal, called the amyloid hypothesis, Alzheimer's disease, estimated to affect more than 5 million people in the United States alone, is caused by abnormal buildup of A-beta protein in the brain. The buildup chokes vital brain areas and destroys nerve cells. Despite amassing much support in recent decades, the proposal hasn't managed to shake off its detractors. Aducanumab offers a seemingly reliable and safe way to lower A-beta levels and thus test the amyloid hypothesis.

Over the course of a year, aducanumab entered the brains of people with early Alzheimer's disease and cleared out the A-beta, scientists reported in September in Nature (SN: 10/1/16, p. 6). The trial was small--only 165 people. Yet in these people's brains, amyloid-beta clearly declined. The higher the dose, the more A-beta cleanup.

There were hints that people on higher doses of the drug had cognitive improvements, too. If confirmed in larger studies, those cognitive benefits "would be a game changer for the field," says Alzheimer's researcher Eric Reiman of the Banner Alzheimer's Institute in Phoenix. But those results "need to be treated agnostically for now," at least until the larger studies currently under way are completed, he cautions.

There is already strong evidence that A-beta is a disease culprit: Rare genetic mutations in genes related to A-beta almost always come with Alzheimer's, an observation that has been confirmed in mice. A-beta is toxic to nerve cells in dishes, damaging their communication abilities before eventually killing the cells outright. "All the basic science work and natural history work supports it," says neuroscientist John Hardy of University College London, who is among those who proposed the amyloid hypothesis.

Yet contradictions exist. Cognitively healthy people have been found with A-beta accumulation in their brain (SN: 12/10/16, p. 13). And so far, scientists have found only a weak correlation between A-beta plaques and cognition, results that have led some scientists to look elsewhere--to inflammation, overzealous pruning of brain cell connections called synapses and changes to the protein tau, which is known to accumulate inside nerve cells in people with Alzheimer's. Each of these cellular processes has also been implicated as a driver of the disease.

Identifying the true cause of Alzheimer's is difficult because all of these processes are closely related and occur simultaneously, making it nearly impossible to study their effects in isolation. What's more, many of the key changes might happen years, or even decades, before symptoms begin to appear. Hardy concedes that in the years since he and others introduced the amyloid hypothesis, scientists have struggled to put together a full picture of Alzheimer's. "It is tougher than we all thought it would be," he says.

There won't be clear answers for several years yet. In August of 2015, larger clinical trials of aducanumab began enrolling patients around the world with the goal of finishing by 2022. As more people with Alzheimer's are tested, researchers hope to see obvious signs of mental improvement that track reductions in brain A-beta. It's possible that aducanumab will lower A-beta in the brain yet fail to bring meaningful improvements in symptoms. Such a result might appear to be a strike against the amyloid hypothesis, a contradiction that could prod some researchers to explore other ideas more deeply. Either way, people with Alzheimer's and their loved ones are waiting anxiously.

Caption: Plaques begone in a small trial of the experimental Alzheimer's drug aducanumab, brain scans of people receiving the drug showed reductions in amyloid-beta plaques (red). Larger trials are now testing the drug in over 2,000 participants to look for signs of mental improvement.

9 Antarctic ozone hole officially on the mend

By Alexandra Witze

In a rare bright spot for global environmental news, atmospheric scientists reported in 2016 that the ozone hole that forms annually over Antarctica is beginning to heal. Their data nail the case that the Montreal Protocol, the international treaty drawn up in 1987 to limit the use of ozone-destroying chemicals, is working.

The Antarctic ozone hole forms every Southern Hemisphere spring, when chemical reactions involving chlorine and bromine break apart the oxygen atoms that make up ozone molecules. Less protective ozone means that more ultraviolet radiation reaches Earth, where it can damage DNA and lead to higher rates of skin cancer, among other threats.

The Montreal Protocol cut back drastically on the manufacture of ozone-destroying compounds such as chlorofluorocarbons, or CFCs, which had been used in air conditioners, refrigerators and other products. It went into force in 1989 and phased out CFCs by 2010.

Earlier studies had hinted that the ozone hole was on the mend. The new work, reported in Science in June, is the most definitive yet (SN: 7/23/16, p. 6). A team led by Susan Solomon, an atmospheric chemist at MIT, looked not only at the month of October, when Antarctic ozone loss typically peaks, but also at September, when the hole is growing. The healing trend was most obvious in September. Satellite measurements showed that from 2000 to 2015, the average extent of the September ozone hole shrank by about 4.5 million square kilometers, to approximately 18 million square kilometers. Soundings taken by weather balloons over Antarctica confirmed the findings.

CFC concentrations peaked above Antarctica in the late 1990s and early 2000s and have been dropping ever since, says Birgit Hassler, an atmospheric chemist at Bodeker Scientific in Alexandra, New Zealand. Each passing year allows scientists to gather more convincing data. The new study, Hassler says, "makes the whole development of the Antarctic ozone hole healing very transparent and understandable."

It is a fitting capstone to Solomon's career. In the 1980s she led a team that proposed that chlorine compounds were to blame for Antarctic ozone loss. She then traveled to the frozen continent to conduct pioneering experiments that measured the accumulating chemicals there. "It's very humbling now to be 30 years later and be able to say we have a clear fingerprint that the ozone hole is starting to get better," she says.

Solomon says that public engagement was key to solving the ozone problem, with people coming together to identify an issue that threatened society and develop new technologies to fix it. In that respect, the most successful environmental treaty in history holds lessons for dealing with a much bigger threat, she says--climate change.

To fix the ozone layer, industry stopped using CFCs and similar compounds and replaced them with hydrofluorocarbons. Those chemicals, however, turned out to be powerful greenhouse gases that accelerated global warming. In October, the nations that ratified the Montreal Protocol agreed to expand it to cover hydrofluorocarbons as well (SN: 11/26/16, p. 13).

Caption: Ozone restored a study of satellite measurements over Antarctica from 2000 to 2015 found the ozone healing trend was most obvious In September. Average total ozone for Septembers, Including 2016, are shown. Blue and purple Indicate areas with the least ozone.

10 Computer defeats master at ancient Chinese game

By Thomas Sumner

In a hotel ballroom in Seoul, South Korea, early in 2016, a centuries-old strategy game offered a glimpse into the fantastic future of computing.

The computer program AlphaGo bested a world champion player at the Chinese board game Go, four games to one (SN Online: 3/15/16). The victory shocked Go players and computer gurus alike. "It happened much faster than people expected," says Stuart Russell, a computer scientist at the University of California, Berkeley. "A year before the match, people were saying that it would take another 10 years for us to reach this point."

The match was a powerful demonstration of the potential of computers that can learn from experience. Elements of artificial intelligence are already a reality, from medical diagnostics to self-driving cars (see Page 34), and computer programs can even find the fastest routes through the London Underground (SN Online: 10/14/16). "We don't know what the limits are," Russell says. "I'd say there's at least a decade of work just finding out the things we can do with this technology."

AlphaGo's design mimics the way human brains tackle problems and allows the program to fine-tune itself based on new experiences. The system was trained using 30 million positions from 160,000 games of Go played by human experts. AlphaGo's creators at Google DeepMind honed the software even further by having it play games against slightly altered versions of itself, a sort of digital "survival of the fittest."

These learning experiences allowed AlphaGo to more efficiently sweat over its next move. Programs aimed at simpler games play out every single hypothetical game that could result from each available choice in a branching pattern--a brute-force approach to computing. But this technique becomes impractical for more complex games such as chess, so many chess-playing programs sample only a smaller subset of possible outcomes. That was true of Deep Blue, the computer that beat chess master Garry Kasparov in 1997.

But Go offers players many more choices than chess does. A full-sized Go board includes 361 playing spaces (compared with chess' 64), often has various "battles" taking place across the board simultaneously and can last for more moves.

AlphaGo overcomes Go's sheer complexity by drawing on its own developing knowledge to choose which moves to evaluate. This intelligent selection led to the program's surprising triumph, says computer scientist Jonathan Schaeffer of the University of Alberta in Canada. "A lot of people have put enormous effort into making small, incremental progress," says Schaeffer, who led the development of the first computer program to achieve perfect play of checkers. "Then the AlphaGo team came along and, incremental progress be damned, made this giant leap forward."

Real-world problems have complexities far exceeding those of chess or Go, but the winning strategies demonstrated in 2016 could be game changers.

Life list

Scientists filled in the details of some famous evolutionary tales in 2016--and discovered a few surprises about creatures large and small.

Venom repertoire

By studying a gene family important for toxin production, researchers found that modern rattlesnakes (one above) have pared down their venom arsenal over time (SN: 10/15/16, p. 9). Rattlers now have a smaller repertoire of toxins, perhaps more specialized to their prey.

Stepping forward

Small tweaks to a gene that makes a protein important for skeletal development may have led to the big toe and helped shape the human foot for bipedalism (SN: 2/6/16, p. 15).

Surprise absence

A gut microbe collected from chinchilla droppings appears to have no mitochondria, making it the first known complex life without the supposedly universal organelle (SN: 6/11/16, p. 14).

Turtle power

Studies of prototurtle fossils suggest that, instead of serving as natural armor, turtle shells might have got their start by aiding in burrowing (SN: 8/6/16, p. 15). The idea could help explain how turtle ancestors survived a mass extinction 252 million years ago.

Color change

Scientists pinned down the genetic changes that, in a famous example of natural selection, made peppered moths soot-colored (SN: 6/25/16, p. 6).

Tall beginnings

Giraffes should thank genes that regulate embryonic development for their long necks and strong hearts (SN: 6/11/16, p. 9).

Evolution at speed

A study of Darwin's finches found that medium ground finches with smaller beaks survived better than big-beaked counterparts during a drought. The advantage was linked to a key gene, offering insight into the birds' speedy evolution (SN: 5/28/16, p. 7).

Age record

Scientists have crowned a Greenland shark as the vertebrate with the longest known life span. Their analysis suggests the predator lived to an age of 392 years (SN: 9/17/16, p. 13).

Caption: AlphaGo won four games to Lee Sedol's one in their Go matchup. Sedol, a South Korean professional player, studies the board after his third loss.


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Author:Quill, Elizabeth
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Date:Dec 24, 2016
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