In Appalachia’s coal country, researchers envision turning toxic waste into treasure. The pollution left behind by abandoned mines is an untapped source of rare earth elements.
Rare earths are a valuable set of 17 elements needed to make everything from smartphones and electric vehicles to fluorescent bulbs and lasers. With global demand skyrocketing and China having a near-monopoly on rare earth production — the United States has only one active mine — there’s a lot of interest in finding alternative sources, such as ramping up recycling. Pulling rare earths from coal waste offers a two-for-one deal: By retrieving the metals, you also help clean up the pollution.
Long after a coal mine closes, it can leave a dirty legacy. When some of the rock left over from mining is exposed to air and water, sulfuric acid forms and pulls heavy metals from the rock. This acidic soup can pollute waterways and harm wildlife.
Recovering rare earths from what’s called acid mine drainage won’t single-handedly satisfy rising demand for the metals, acknowledges Paul Ziemkiewicz, director of the West Virginia Water Research Institute in Morgantown. But he points to several benefits.
Unlike ore dug from typical rare earth mines, the drainage is rich with the most-needed rare earth elements. Plus, extraction from acid mine drainage also doesn’t generate the radioactive waste that’s typically a by-product of rare earth mines, which often contain uranium and thorium alongside the rare earths. And from a practical standpoint, existing facilities to treat acid mine drainage could be used to collect the rare earths for processing. “Theoretically, you could start producing tomorrow,” Ziemkiewicz says.
From a few hundred sites already treating acid mine drainage, nearly 600 metric tons of rare earth elements and cobalt — another in-demand metal — could be produced annually, Ziemkiewicz and colleagues estimate.
Currently, a pilot project in West Virginia is taking material recovered from an acid mine drainage treatment site and extracting and concentrating the rare earths.
If such a scheme proves feasible, Ziemkiewicz envisions a future in which cleanup sites send their rare earth hauls to a central facility to be processed, and the elements separated. Economic analyses suggest this wouldn’t be a get-rich scheme. But, he says, it could be enough to cover the costs of treating the acid mine drainage.
More than a century ago, scientists proved that carbon dioxide in Earth’s atmosphere could act like a thermostat — adding more CO2 would turn up the heat, removing it would chill the planet. But back then, most scientists thought that Earth’s climate system was far too large and stable to change quickly, that any fluctuations would happen over such a long timescale that it wouldn’t matter much to everyday life (SN: 3/12/22, p. 16).
Now all it takes is a look at the Weather Channel to know how wrong scientists were. Things are changing fast. Last year alone, Europe, South Asia, China, Japan and the American West endured deadly, record-breaking heat waves (SN: 12/17/22 & 12/31/22, p. 38). As I write this, torrential rains are bringing death and destruction to California. And with levels of climate-warming gases continuing to increase in the atmosphere, extreme weather events will become even more frequent. Given the vastness of this threat, it’s tempting to think that any efforts that we make against it will be futile. But that’s not true. Around the world, scientists and engineers; entrepreneurs and large corporations; state, national and local governments; and international coalitions are acting to put the brakes on climate change. Last year, the United States signed into law a $369 billion investment in renewable energy technologies and other responses (SN: 12/17/22 & 12/31/22, p. 28). And the World Bank invested $31.7 billion to assist other countries.
In this issue, contributing correspondent Alexandra Witze details the paths forward: which responses will help the most, and which remain challenging. Shifting to renewable energy sources like wind and solar should be the easiest. We already have the technology, and costs have plunged over the last decade. Other approaches that are feasible but not as far along include making industrial processes more energy efficient, trapping greenhouse gases and developing clean fuels. Ultimately, the goal is to reinvent the global energy infrastructure. Societies have been retooling energy infrastructures for centuries, from water and steam power to petroleum and natural gas to nuclear power and now renewables. This next transformation will be the biggest yet. But we have the scientific understanding and technological savvy to make it happen.
This cover story kicks off a new series for Science News, The Climate Fix. In future issues, we will focus on covering solutions to the climate crisis, including the science behind innovations, the people making them happen, and the social and environmental impacts. You’ll also see expanded climate coverage for our younger readers, ages 9 and up, at Science News Explores online and in print.
With this issue, we also welcome our new publisher, Michael Gordon Voss. He comes to us with deep knowledge of the media industry, experience in both for-profit and nonprofit publishing and a love of science. Before joining Science News Media Group, Voss was publisher of Stanford Social Innovation Review, and vice president and associate publisher at Scientific American. With his arrival, publisher Maya Ajmera takes on her new role as executive publisher. Under her leadership, we have seen unprecedented growth. We’re fortunate to have these two visionaries directing our business strategy amid a rapidly changing media environment.
In full swing The swaying feeling in jazz music that compels feet to tap may arise from near-imperceptible delays in musicians’ timing, Nikk Ogasa reported in “Jazz gets its swing from small, subtle delays” (SN: 11/19/22, p. 5).
Reader Oda Lisa, a self-described intermediate saxophonist, has noticed these subtle delays while playing.“I recorded my ‘jazzy’ version of a beloved Christmas carol, which I sent to a friend of mine,” Lisa wrote. “She praised my effort overall, but she suggested that I get a metronome because the timing wasn’t consistent. My response was that I’m a slave to the rhythm that I hear in my head. I think now I know why.” On the same page Murky definitions and measurements impede social science research, Sujata Gupta reported in “Fuzzy definitions mar social science” (SN: 11/19/22, p. 10).
Reader Linda Ferrazzara found the story thought-provoking. “If there’s no consensus on the terms people use … then there can be no productive discussion or conversation. People end up talking and working at cross-purposes with no mutual understanding or progress,” Ferrazzara wrote.
Fly me to the moon Space agencies are preparing to send the next generation of astronauts to the moon and beyond. Those crews will be more diverse in background and expertise than the crews of the Apollo missions, Lisa Grossman reported in “Who gets to go to space?” (SN: 12/3/22, p. 20).
“It is great to see a broader recognition of the work being done to make spaceflight open to more people,” reader John Allen wrote. “Future space travel will and must accommodate a population that represents humanity. It won’t be easy, but it will be done.”
The story also reminded Allen of the Gallaudet Eleven, a group of deaf adults who participated in research done by NASA and the U.S. Navy in the 1950s and ’60s. Experiments tested how the volunteers responded (or didn’t) to a range of scenarios that would typically induce motion sickness, such as a ferry ride on choppy seas. Studying how the body’s sensory systems work without the usual gravitational cues from the inner ear allowed scientists to better understand motion sickness and the human body’s adaptation to spaceflight.
Sweet dreams are made of this A memory-enhancing method that uses sound cues may boost an established treatment for debilitating nightmares, Jackie Rocheleau reported in “Learning trick puts nightmares to bed” (SN: 12/3/22, p. 11).
Reader Helen Leaver shared her trick to a good night’s sleep: “I learned that I was having strong unpleasant adventures while sleeping, and I would awaken hot and sweaty. By eliminating the amount of heat from bedding and an electrically heated mattress pad, I now sleep well without those nightmares.” Pest perspectives In “Why do we hate pests?” (SN: 12/3/22, p. 26), Deborah Balthazar interviewed former Science News Explores staff writer Bethany Brookshire about her new book, Pests. The book argues that humans — influenced by culture, class, colonization and much more — create animal villains.
The article prompted reader Doug Clapp to reflect on what he considers pests or weeds. “A weed is a plant in the wrong place, and a pest is an animal in the wrong place,” Clapp wrote. But what’s considered “wrong” depends on the humans who have power over the place, he noted. “Grass in a lawn can be a fine thing. Grass in a garden choking the vegetables I’m trying to grow becomes a weed. Mice in the wild don’t bother me. Field mice migrating into my house when the weather cools become a pest, especially when they eat into my food and leave feces behind,” Clapp wrote.
The article encouraged Clapp to look at pests through a societal lens: “I had never thought of pests in terms of high-class or low-class. Likewise, the residual implications of [colonization]. Thanks for provoking me to consider some of these issues in a broader context.”
Patricia Hidalgo-Gonzalez saw the future of energy on a broiling-hot day last September.
An email alert hit her inbox from the San Diego Gas & Electric Company. “Extreme heat straining the grid,” read the message, which was also pinged as a text to 27 million people. “Save energy to help avoid power interruptions.”
It worked. People cut their energy use. Demand plunged, blackouts were avoided and California successfully weathered a crisis exacerbated by climate change. “It was very exciting to see,” says Hidalgo-Gonzalez, an electrical engineer at the University of California, San Diego who studies renewable energy and the power grid. This kind of collective societal response, in which we reshape how we interact with the systems that provide us energy, will be crucial as we figure out how to live on a changing planet.
Earth has warmed at least 1.1 degrees Celsius since the 19th century, when the burning of coal, oil and other fossil fuels began belching heat-trapping gases such as carbon dioxide into the atmosphere. Scientists agree that only drastic action to cut emissions can keep the planet from blasting past 1.5 degrees of warming — a threshold beyond which the consequences become even more catastrophic than the rising sea levels, extreme weather and other impacts the world is already experiencing.
The goal is to achieve what’s known as net-zero emissions, where any greenhouse gases still entering the atmosphere are balanced by those being removed — and to do it as soon as we can.
Scientists say it is possible to swiftly transform the ways we produce and consume energy. To show the way forward, researchers have set out paths toward a world where human activities generate little to no carbon dioxide and other greenhouse gases — a decarbonized economy.
The key to a decarbonized future lies in producing vast amounts of new electricity from sources that emit little to none of the gases, such as wind, solar and hydropower, and then transforming as much of our lives and our industries as possible to run off those sources. Clean electricity needs to power not only the planet’s current energy use but also the increased demands of a growing global population.
Once humankind has switched nearly entirely to clean electricity, we will also have to counterbalance the carbon dioxide we still emit — yes, we will still emit some — by pulling an equivalent amount of carbon dioxide out of the atmosphere and storing it somewhere permanently.
Achieving net-zero emissions won’t be easy. Getting to effective and meaningful action on climate change requires overcoming decades of inertia and denial about the scope and magnitude of the problem. Nations are falling well short of existing pledges to reduce emissions, and global warming remains on track to charge past 1.5 degrees perhaps even by the end of this decade.
Yet there is hope. The rate of growth in CO2 emissions is slowing globally — down from 3 percent annual growth in the 2000s to half a percent annual growth in the last decade, according to the Global Carbon Project, which quantifies greenhouse gas emissions.
There are signs annual emissions could start shrinking. And over the last two years, the United States, by far the biggest cumulative contributor to global warming, has passed several pieces of federal legislation that include financial incentives to accelerate the transition to clean energy. “We’ve never seen anything at this scale,” says Erin Mayfield, an energy researcher at Dartmouth College.
Though the energy transition will require many new technologies, such as innovative ways to permanently remove carbon from the atmosphere, many of the solutions, such as wind and solar power, are in hand — “stuff we already have,” Mayfield says. The current state of carbon dioxide emissions Of all the emissions that need to be slashed, the most important is carbon dioxide, which comes from many sources such as cars and trucks and coal-burning power plants. The gas accounted for 79 percent of U.S. greenhouse gas emissions in 2020. The next most significant greenhouse gas, at 11 percent of emissions in the United States, is methane, which comes from oil and gas operations as well as livestock, landfills and other land uses.
The amount of methane may seem small, but it is mighty — over the short term, methane is more than 80 times as efficient at trapping heat as carbon dioxide is, and methane’s atmospheric levels have nearly tripled in the last two centuries. Other greenhouse gases include nitrous oxides, which come from sources such as applying fertilizer to crops or burning fuels and account for 7 percent of U.S. emissions, and human-made fluorinated gases such as hydrofluorocarbons that account for 3 percent.
Globally, emissions are dominated by large nations that produce lots of energy. The United States alone emits around 5 billion metric tons of carbon dioxide each year. It is responsible for most of the greenhouse gas emissions throughout history and ceded the spot for top annual emitter to China only in the mid-2000s. India ranks third.
Because of the United States’ role in producing most of the carbon pollution to date, many researchers and advocates argue that it has the moral responsibility to take the global lead on cutting emissions. And the United States has the most ambitious goals of the major emitters, at least on paper. President Joe Biden has said the country is aiming to reach net-zero emissions by 2050. Leaders in China and India have set net-zero goals of 2060 and 2070, respectively.
Under the auspices of a 2015 international climate change treaty known as the Paris agreement, 193 nations plus the European Union have pledged to reduce their emissions. The agreement aims to keep global warming well below 2 degrees, and ideally to 1.5 degrees, above preindustrial levels. But it is insufficient. Even if all countries cut their emissions as much as they have promised under the Paris agreement, the world would likely blow past 2 degrees of warming before the end of this century.
Every nation continues to find its own path forward. “At the end of the day, all the solutions are going to be country-specific,” says Sha Yu, an earth scientist at the Pacific Northwest National Laboratory and University of Maryland’s Joint Global Change Research Institute in College Park, Md. “There’s not a universal fix.”
But there are some common themes for how to accomplish this energy transition — ways to focus our efforts on the things that will matter most. These are efforts that go beyond individual consumer choices such as whether to fly less or eat less meat. They instead penetrate every aspect of how society produces and consumes energy.
Such massive changes will need to overcome a lot of resistance, including from companies that make money off old forms of energy as well as politicians and lobbyists. But if society can make these changes, it will rank as one of humanity’s greatest accomplishments. We will have tackled a problem of our own making and conquered it.
Here’s a look at what we’ll need to do.
Make as much clean electricity as possible To meet the need for energy without putting carbon dioxide into the atmosphere, countries would need to dramatically scale up the amount of clean energy they produce. Fortunately, most of that energy would be generated by technologies we already have — renewable sources of energy including wind and solar power.
“Renewables, far and wide, are the key pillar in any net-zero scenario,” says Mayfield, who worked on an influential 2021 report from Princeton University’s Net-Zero America project, which focused on the U.S. economy.
The Princeton report envisions wind and solar power production roughly quadrupling by 2030 to get the United States to net-zero emissions by 2050. That would mean building many new solar and wind farms, so many that in the most ambitious scenario, wind turbines would cover an area the size of Arkansas, Iowa, Kansas, Missouri, Nebraska and Oklahoma combined. Such a scale-up is only possible because prices to produce renewable energy have plunged. The cost of wind power has dropped nearly 70 percent, and solar power nearly 90 percent, over the last decade in the United States. “That was a game changer that I don’t know if some people were expecting,” Hidalgo-Gonzalez says.
Globally the price drop in renewables has allowed growth to surge; China, for instance, installed a record 55 gigawatts of solar power capacity in 2021, for a total of 306 gigawatts or nearly 13 percent of the nation’s installed capacity to generate electricity. China is almost certain to have had another record year for solar power installations in 2022.
Challenges include figuring out ways to store and transmit all that extra electricity, and finding locations to build wind and solar power installations that are acceptable to local communities. Other types of low-carbon power, such as hydropower and nuclear power, which comes with its own public resistance, will also likely play a role going forward. Get efficient and go electric The drive toward net-zero emissions also requires boosting energy efficiency across industries and electrifying as many aspects of modern life as possible, such as transportation and home heating.
Some industries are already shifting to more efficient methods of production, such as steelmaking in China that incorporates hydrogen-based furnaces that are much cleaner than coal-fired ones, Yu says. In India, simply closing down the most inefficient coal-burning power plants provides the most bang for the buck, says Shayak Sengupta, an energy and policy expert at the Observer Research Foundation America think tank in Washington, D.C. “The list has been made up,” he says, of the plants that should close first, “and that’s been happening.”
To achieve net-zero, the United States would need to increase its share of electric heat pumps, which heat houses much more cleanly than gas- or oil-fired appliances, from around 10 percent in 2020 to as much as 80 percent by 2050, according to the Princeton report. Federal subsidies for these sorts of appliances are rolling out in 2023 as part of the new Inflation Reduction Act, legislation that contains a number of climate-related provisions.
Shifting cars and other vehicles away from burning gasoline to running off of electricity would also lead to significant emissions cuts. In a major 2021 report, the National Academies of Sciences, Engineering and Medicine said that one of the most important moves in decarbonizing the U.S. economy would be having electric vehicles account for half of all new vehicle sales by 2030. That’s not impossible; electric car sales accounted for nearly 6 percent of new sales in the United States in 2022, which is still a low number but nearly double the previous year.
Make clean fuels Some industries such as manufacturing and transportation can’t be fully electrified using current technologies — battery powered airplanes, for instance, will probably never be feasible for long-duration flights. Technologies that still require liquid fuels will need to switch from gas, oil and other fossil fuels to low-carbon or zero-carbon fuels.
One major player will be fuels extracted from plants and other biomass, which take up carbon dioxide as they grow and emit it when they die, making them essentially carbon neutral over their lifetime. To create biofuels, farmers grow crops, and others process the harvest in conversion facilities into fuels such as hydrogen. Hydrogen, in turn, can be substituted for more carbon-intensive substances in various industrial processes such as making plastics and fertilizers — and maybe even as fuel for airplanes someday.
In one of the Princeton team’s scenarios, the U.S. Midwest and Southeast would become peppered with biomass conversion plants by 2050, so that fuels can be processed close to where crops are grown. Many of the biomass feedstocks could potentially grow alongside food crops or replace other, nonfood crops. Cut methane and other non-CO2 emissions Greenhouse gas emissions other than carbon dioxide will also need to be slashed. In the United States, the majority of methane emissions come from livestock, landfills and other agricultural sources, as well as scattered sources such as forest fires and wetlands. But about one-third of U.S. methane emissions come from oil, gas and coal operations. These may be some of the first places that regulators can target for cleanup, especially “super emitters” that can be pinpointed using satellites and other types of remote sensing.
In 2021, the United States and the European Union unveiled what became a global methane pledge endorsed by 150 countries to reduce emissions. There is, however, no enforcement of it yet. And China, the world’s largest methane emitter, has not signed on.
Nitrous oxides could be reduced by improving soil management techniques, and fluorinated gases by finding alternatives and improving production and recycling efforts.
Sop up as much CO2 as possible Once emissions have been cut as much as possible, reaching net-zero will mean removing and storing an equivalent amount of carbon to what society still emits.
One solution already in use is to capture carbon dioxide produced at power plants and other industrial facilities and store it permanently somewhere, such as deep underground. Globally there are around 35 such operations, which collectively draw down around 45 million tons of carbon dioxide annually. About 200 new plants are on the drawing board to be operating by the end of this decade, according to the International Energy Agency.
The Princeton report envisions carbon capture being added to almost every kind of U.S. industrial plant, from cement production to biomass conversion. Much of the carbon dioxide would be liquefied and piped along more than 100,000 kilometers of new pipelines to deep geologic storage, primarily along the Texas Gulf Coast, where underground reservoirs can be used to trap it permanently. This would be a massive infrastructure effort. Building this pipeline network could cost up to $230 billion, including $13 billion for early buy-in from local communities and permitting alone.
Another way to sop up carbon is to get forests and soils to take up more. That could be accomplished by converting crops that are relatively carbon-intensive, such as corn to be used in ethanol, to energy-rich grasses that can be used for more efficient biofuels, or by turning some cropland or pastures back into forest. It’s even possible to sprinkle crushed rock onto croplands, which accelerates natural weathering processes that suck carbon dioxide out of the atmosphere.
Another way to increase the amount of carbon stored in the land is to reduce the amount of the Amazon rainforest that is cut down each year. “For a few countries like Brazil, preventing deforestation will be the first thing you can do,” Yu says.
When it comes to climate change, there’s no time to waste The Princeton team estimates that the United States would need to invest at least an additional $2.5 trillion over the next 10 years for the country to have a shot at achieving net-zero emissions by 2050. Congress has begun ramping up funding with two large pieces of federal legislation it passed in 2021 and 2022. Those steer more than $1 trillion toward modernizing major parts of the nation’s economy over a decade — including investing in the energy transition to help fight climate change.
Between now and 2030, solar and wind power, plus increasing energy efficiency, can deliver about half of the emissions reductions needed for this decade, the International Energy Agency estimates. After that, the primary drivers would need to be increasing electrification, carbon capture and storage, and clean fuels such as hydrogen. The trick is to do all of this without making people’s lives worse. Developing nations need to be able to supply energy for their economies to develop. Communities whose jobs relied on fossil fuels need to have new economic opportunities.
Julia Haggerty, a geographer at Montana State University in Bozeman who studies communities that are dependent on natural resources, says that those who have money and other resources to support the transition will weather the change better than those who are under-resourced now. “At the landscape of states and regions, it just remains incredibly uneven,” she says.
The ongoing energy transition also faces unanticipated shocks such as Russia’s invasion of Ukraine, which sent energy prices soaring in Europe, and the COVID-19 pandemic, which initially slashed global emissions but later saw them rebound.
But the technologies exist for us to wean our lives off fossil fuels. And we have the inventiveness to develop more as needed. Transforming how we produce and use energy, as rapidly as possible, is a tremendous challenge — but one that we can meet head-on. For Mayfield, getting to net-zero by 2050 is a realistic goal for the United States. “I think it’s possible,” she says. “But it doesn’t mean there’s not a lot more work to be done.”
As far back as roughly 25,000 years ago, Ice Age hunter-gatherers may have jotted down markings to communicate information about the behavior of their prey, a new study finds.
These markings include dots, lines and the symbol “Y,” and often accompany images of animals. Over the last 150 years, the mysterious depictions, some dating back nearly 40,000 years, have been found in hundreds of caves across Europe.
Some archaeologists have speculated that the markings might relate to keeping track of time, but the specific purpose has remained elusive (SN: 7/9/19). Now, a statistical analysis, published January 5 in Cambridge Archeological Journal, presents evidence that past people may have been recording the mating and birthing schedule of local fauna. By comparing the marks to the animals’ life cycles, researchers showed that the number of dots or lines in a given image strongly correlates to the month of mating across all the analyzed examples, which included aurochs (an extinct species of wild cattle), bison, horses, mammoth and fish. What’s more, the position of the symbol “Y” in a sequence was predictive of birth month, suggesting that “Y” signifies “to give birth.”
The finding is one of the earliest records of a coherent notational system, the researchers say. It indicates that people at the time were able to interpret the meaning of an item’s position in a sequence and plan ahead for the distant future using a calendar of sorts — reinforcing the suggestion that they were capable of complex cognition. “This is a really big deal cognitively,” says Ben Bacon, an independent researcher based in London. “We’re dealing with a system that has intense organization, intense logic to it.”
A furniture conservator by day, Bacon spent years poring through scientific articles to compile over 800 instances of these cave markings. From his research and reading the literature, he reasoned that the dots corresponded to the 13 lunar cycles in a year. But he thought that the hunter-gatherers would’ve been more concerned with seasonal changes than the moon.
In the new paper, he and colleagues argue that rather than pinning a calendar to astronomical events like the equinox, the hunter-gatherers started their calendar year with the snowmelt in the spring. Not only would the snowmelt be a clear point of origin, but the meteorological calendar would also account for differences in timing across locations. For example, though snowmelt would start on different dates in different latitudes, bison would always mate approximately four lunar cycles — or months — after that region’s snowmelt, as indicated by four dots or lines.
“This is why it’s such a clever system, because it’s based on the universal,” Bacon says. “Which means if you migrate from the Pyrenees to Belgium, you can just use the same calendar.”
He needed data to prove his idea. After compiling the markings, he worked with academic researchers to identify the timing of migration, mating and birth for common Ice Age animals targeted by hunter-gatherers by using archaeological data or comparing with similar modern animals. Next, the researchers determined if the marks aligned significantly with important life events based on this calendar. When the team ran the statistical analysis, the results strongly supported Bacon’s theory.
When explaining the markings, “we’ve argued for notational systems before, but it’s always been fairly speculative as to what the people were counting and why they were counting,” says Brian Hayden, an archaeologist at Simon Fraser University in Burnaby, British Columbia, who peer-reviewed the paper. “This adds a lot more depth and specificity to why people were keeping calendars and how they were using them.”
Linguistic experts argue that, given the lack of conventional syntax and grammar, the marks wouldn’t be considered writing. But that doesn’t make the finding inherently less exciting, says paleoanthropologist Genevieve von Petzinger of the Polytechnic Institute of Tomar in Portugal, who wasn’t involved in the study. Writing systems are often mistakenly considered a pinnacle of achievement, when in fact writing would be developed only in cultural contexts where it’s useful, she says. Instead, it’s significant that the marks provide a way to keep records outside of the mind.
“In a way, that was the huge cognitive leap,” she says. “Suddenly, we have the ability to preserve [information] beyond the moment. We have the ability to transmit it across space and time. Everything starts to change.”
The debate over these marks’ meanings continues. Archaeologist April Nowell doesn’t buy many of the team’s assumptions. “It boggles my mind why one would need a calendar … to predict that animals were going to have offspring in the spring,” says Nowell, of the University of Victoria in British Columbia. “The amount of information that this calendar is providing, if it really is a calendar, is quite minimal.”
Hayden adds that, while the basic pattern would still hold, some of the cave marks had “wiggle room for interpretation.” The next step, he says, will be to review and verify the interpretations of the marks.
Prairie voles have long been heralded as models of monogamy. Now, a study suggests that the “love hormone” once thought essential for their bonding — oxytocin — might not be so necessary after all.
Interest in the romantic lives of prairie voles (Microtus ochrogaster) was first sparked more than 40 years ago, says Devanand Manoli, a biologist at the University of California, San Francisco. Biologists trying to capture voles to study would frequently catch two at a time, because “what they were finding were these male-female pairs,” he says. Unlike many other rodents with their myriad partners, prairie voles, it turned out, mate for life (SN: 10/5/15). Pair-bonded prairie voles prefer each other’s company over a stranger’s and like to huddle together both in the wild and the lab. Because other vole species don’t have social behaviors as complex as prairie voles do, they have been a popular animal system for studying how social behavior evolves.
Research over the last few decades has implicated a few hormones in the brain as vital for proper vole manners, most notably oxytocin, which is also important for social behavior in humans and other animals.
Manoli and colleagues thought the oxytocin receptor, the protein that detects and reacts to oxytocin, would be the perfect test target for a new genetic engineering method based on CRISPR technology, which uses molecules from bacteria to selectively turn off genes. The researchers used the technique on vole embryos to create animals born without functioning oxytocin receptors. The team figured that the rodents wouldn’t be able to form pair-bonds — just like voles in past experiments whose oxytocin activity was blocked with drugs.
Instead, Manoli says, the researchers got “a big surprise.” The voles could form pair-bonds even without oxytocin, the team reports in the March 15 Neuron.
“I was very surprised by their results,” says Larry Young, a biologist at Emory University in Atlanta, who was not involved with the study but has studied oxytocin in prairie voles for decades.
A key difference between the new study and past studies that used drugs to block oxytocin is the timing of exactly when the hormone’s activity is turned off. With drugs, the voles are adults and have had exposure to oxytocin in their brains before the shutoff. With CRISPR, “these animals are born never experiencing oxytocin signaling in the brain,” says Young, whose research group has recently replicated Manoli’s experiment and found the same result.
It may be, Young says, that pair-bonding is controlled by a brain circuit that typically becomes dependent on oxytocin through exposure to it during development, like a symphony trained by a conductor. Suddenly remove that conductor and the symphony will sound discordant, whereas a jazz band that’s never practiced with a conductor fares just fine without one. Manoli agrees that the technique’s timing matters. A secondary reason for the disparity, he says, could be that drugs often have off-target effects, such that the chemicals meant to block oxytocin could have been doing other things in the voles’ brains to affect pair-bonding. But Young disagrees. “I don’t believe that,” he says. “The [drug] that people use is very selective,” not even binding to the receptor of oxytocin’s closest molecular relative, vasopressin.
Does this result mean that decades of past work on pair-bonding has been upended? Not quite.
“It shows us that this is a much more complicated question,” Manoli says. “The pharmacologic manipulations … suggested that [oxytocin] plays a critical role. The question is, what is that role?”
The new seemingly startling result makes sense if you look at the big picture, Manoli says. The ability for voles to pair-bond is “so critical for the survival of the species,” he says. “From a genetics perspective, it may make sense that there isn’t a single point of failure.”
The group now hopes to look at how other hormones, like vasopressin, influence pair-bonding using this relatively new genetic technique. They are also looking more closely at the voles’ behavior to be sure that the CRISPR gene editing didn’t alter it in a way they haven’t noticed yet.
In the game of vole “love,” it looks like we’re still trying to understand all the players.
