Thousands of years ago, it didn’t just rain on the Sahara Desert. It poured.

Grasslands, trees, lakes and rivers once covered North Africa’s now arid, unforgiving landscape. From about 11,000 to 5,000 years ago, much higher rainfall rates than previously estimated created that “Green Sahara,” say geologist Jessica Tierney of the University of Arizona in Tucson and her colleagues. Extensive ground cover, combined with reductions of airborne dust, intensified water evaporation into the atmosphere, leading to monsoonlike conditions, the scientists report January 18 in Science Advances.
Tierney’s team reconstructed western Saharan rainfall patterns over the last 25,000 years. Estimates relied on measurements of forms of carbon and hydrogen in leaf wax recovered from ocean sediment cores collected off the Sahara’s west coast. Concentrations of these substances reflected ancient rainfall rates.

Rainfall ranged from 250 to 1,670 millimeters annually during Green Sahara times, the researchers say. Previous estimates — based on studies of ancient pollen that did not account for dust declines — reached no higher than about 900 millimeters. Saharan rainfall rates currently range from 35 to 100 millimeters annually.

Leaf-wax evidence indicates that the Green Sahara dried out from about 8,000 to at least 7,000 years ago before rebounding. That’s consistent with other ancient climate simulations and with excavations suggesting that humans temporarily left the area around 8,000 years ago. Hunter-gatherers departed for friendlier locales, leaving cattle herders to spread across North Africa once the Green Sahara returned (SN Online: 6/20/12), the investigators propose.

Hunter-gatherers and farming villagers who live in worlds without lightbulbs or thermostats sleep slightly less at night than smartphone-toting city slickers, researchers say.

“Contrary to conventional wisdom, people in societies without electricity do not sleep more than those in industrial societies like ours,” says UCLA psychiatrist and sleep researcher Jerome Siegel, who was not involved in the new research.

Different patterns of slumber and wakefulness in each of these groups highlight the flexibility of human sleep — and also point to potential health dangers in how members of Western societies sleep, conclude evolutionary biologist David Samson of Duke University and colleagues. Compared with other primates, human evolution featured a shift toward sleeping more deeply over shorter time periods, providing more time for learning new skills and knowledge as cultures expanded, the researchers propose. Humans also evolved an ability to revise sleep schedules based on daily work schedules and environmental factors such as temperature.
Samson’s team describes sleep patterns in 33 East African Hadza hunter-gatherers over a total of 393 days in a paper published online January 7 in the American Journal of Physical Anthropology. The team’s separate report on slumber among 21 rural farmers in Madagascar over 292 days will appear later this year in the American Journal of Human Biology.

Sleep patterns in these groups were tracked with wrist devices that measure a person’s activity levels. Both Hadza and Malagasy volunteers slept an average of about 6.5 hours nightly, less than the about seven-hour average for most U.S. adults. Foragers and villagers, who slept in areas with various family and group members, awoke more frequently during the night than has been reported among Westerners. Scalp electrodes worn at night by nine villagers during nine nights revealed biological signs of relatively light sleep compared with Westerners, including shorter periods of slow-wave and rapid eye movement sleep.
But Hadza and Malagasy individuals often supplemented nighttime sleep with one or two daytime naps. Shut-eye breaks averaged 47.5 minutes for the Hadza and about 55 minutes for villagers. Critically, Samson says, foragers and villagers displayed more consistent daily cycles of sleep and wakefulness than are characteristic of Westerners. Hadza adults tended to hit the sack — or, more commonly, the mat — shortly after midnight and nap in the early afternoon. Malagasy villagers napped once or twice during the day’s hottest hours, usually starting around noon, and retired in the early evening. At night, they slept in two phases, awakening for around an hour shortly after midnight. Historical accounts describe a similar sleep pattern among Western Europeans between 500 and 200 years ago — two sleep segments, divided by a period of activity or reflection (SN: 9/25/99, p. 205).
Nighttime sleep in both populations became deeper and less fragmented as tropical humidity dipped.

Researchers also noted that hunter-gatherers and villagers got plenty of direct sunlight, unlike many Westerners. Several studies have linked inconsistent sleep-wake cycles and lack of sun exposure to health problems, including inflammation and heart problems, Samson says. “People in modern societies can take lessons from this research by attempting to get lots of light exposure during the day while reducing blue-wave light exposure after dark and dropping inside temperatures by a few degrees at night.” Smartphones and other digital devices emit blue-wave light, which can suppress melatonin production and delay sleep.

Effects of wayward sleep patterns or too little sleep on health vary across cultures and regions, says biomedical anthropologist Kristen Knutson of Northwestern University Feinberg School of Medicine in Chicago. For instance, sleeping less than six hours per night may increase appetite, as some studies suggest, but a sleep-deprived office worker surrounded by fast-food joints is more likely to become obese than a physically active hunter-gatherer faced with a limited food supply.

Samson’s research aligns with previous evidence, conducted by Knutson, that rural Haitians living without electricity sleep an average of about seven hours nightly. In addition, Siegel’s team recently reported that nightly sleep averages 5.7 to 7.1 hours in three hunter-gatherer societies, including the Hadza (SN: 11/14/15, p. 10).

Until recently, researchers thought cannibalism took place only among a few species in the animal kingdom and only under extraordinary circumstances. But as zoologist Bill Schutt chronicles in Cannibalism, plenty of creatures inhabit their own version of a dog-eat-dog world.

Over the last few decades, scientists have observed cannibalism — defined by Schutt as eating all or part of another individual of the same species — among all major groups of vertebrates. The practice seems to be even more prevalent, and less discriminating, among invertebrates such as mollusks, insects and spiders, whose eggs, larvae and young are often produced in profusion and are therefore readily available, not to mention nutritious.
Cannibalism, Schutt contends, makes perfect evolutionary sense, and not merely as a feeding strategy. When food supplies are low or living conditions are crowded, some mammals and birds may eat some or all of their offspring to terminate an expenditure of effort with poor chances of paying off. For birds, eating a dead or dying hatchling also is a way to get rid of a carcass that could spread infection or whose scent could attract flies or predators to the nest.

Switching to a historical and cultural perspective, Schutt tackles the various forms of human cannibalism, where, he admits, “the ick factor is high.” That includes medicinal cannibalism, from 17th and 18th century Europeans’ consumption of powdered mummies to modern moms’ ingestion of their newborns’ placentas to purportedly restore nutrients lost during childbirth. The author also explores survival cannibalism (think famine victims, people under siege, plane-crash survivors and the ill-fated Donner Party) and briefly addresses our natural shock and seemingly unnatural fascination with criminal cannibalism (à la Jeffrey Dahmer).

As Schutt explains, ritual cannibalism — the consumption of a foe or loved one to acquire the decedent’s strength, courage or wisdom — is a practice that has apparently taken place in different cultures throughout history. In an interesting aside, Schutt ponders whether people who consume wafers and wine during Communion, especially those who firmly believe these items are literally converted into the body and blood of Christ, are engaging in a form of ritual cannibalism.

Cannibalism is a wide-ranging, engaging and thoroughly fun read. The author’s numerous field trips and lab visits with scientists who study the phenomenon heartily enrich this captivating book.

Human gene editing to prevent genetic diseases from being passed to future generations may be permissible under certain conditions, a panel of experts says.

Altering DNA in germline cells — embryos, eggs, and sperm, or cells that give rise to them — may be used to cure genetic diseases for future generations, provided it is done only to correct disease or disability, not to enhance people’s health or abilities, a report issued February 14 by the National Academies of Sciences and Medicine recommends. The decision contradicts earlier recommendations by organizers of a global summit on human gene editing, who concluded that gene editing with molecular scissors such as CRISPR/Cas9 should not be used to produce babies (SN: 12/26/15, p. 12).
Heritable gene editing is not yet ready to be done in people, says Alta Charo, a bioethicist at the University of Wisconsin‒Madison Law School who cochaired the panel. “We are not trying to greenlight heritable germline editing. We’re trying to find that limited set of circumstances where its use is justified by a compelling need and its application is limited to that compelling need,” says Charo. “We’re giving it a yellow light.”

National Academies reports carry no legislative weight, but do often influence policy decisions in the United States and abroad. It will be up to Congress, regulatory agencies such as the U.S. Food and Drug Administration, and state and local governments to implement the recommendations.

Supporters of new genetic engineering technologies hailed the decision.

“It looks like the possibility of eliminating some genetic diseases is now more than a theoretical option,” says Sean Tipton, a spokesman for the American Society for Reproductive Medicine in Washington, D.C. “That’s what this sets up.” Diseases such as cystic fibrosis and Huntington’s, which are caused by mutations in single genes, could someday be corrected by gene editing. More complex diseases or disorders caused by changes in multiple genes, such as autism or schizophrenia, probably would not be the focus of genome editing.

Others worry that allowing any tinkering with the germline will inevitably lead to “designer babies” and other social ills. It raises fears of stigmatization of people with disabilities, exacerbation of inequalities between people who can afford such therapies and those who can’t, and even a new kind of eugenics, critics say.
“Once you approve any form of human germline modification you really open the door to all forms,” says Marcy Darnovsky, executive director of the Center for Genetics and Society in Berkeley, Calif.

Panelist Jeffrey Kahn, a bioethicist at Johns Hopkins University, says the door to heritable gene therapy remains closed until stringent requirements can be met. “It’s frankly more of a knock on the door,” he said at the public presentation of the report.

The report also changes the debate from whether to allow germline editing to instead focus on the line between therapy and enhancement, Darnovsky says. “I’m feeling very unsettled and disappointed by what they are recommending.”

Several clinical trials in the United States, China and other countries are already under way to do gene editing in people who have cancer or other diseases. But those therapies do not involve altering germline cells; instead they fix defects or make alterations to DNA in other body, or “somatic,” cells. The panel recommended that such somatic cell therapies should also be restricted to treating diseases, not allowing enhancements.

Researchers in the United Kingdom, Sweden and China have already done gene editing on early human embryos in the lab. Recent clinical trials in Mexico and Ukraine to produce “three-parent babies” are also seen as altering the germline because such children carry a small amount of DNA from an egg donor (SN Online: 10/18/16). But those children don’t have modifications of their nuclear DNA, where the genetic instructions that determine traits are stored.

Currently, researchers in the United States are effectively banned from conducting clinical trials that would produce heritable changes in the human genome, either by gene editing or making three-parent babies. The new recommendations could pave the way to allow such experiments.

But the panel lays out a number of hurdles that must be cleared before germline editing could move forward, ones that may be impossible to overcome, says Nita Farahany, a bioethicist at Duke Law School in Durham, N.C. “Some people could read into the stringency of the requirements to think that the benefits could never outweigh the risks,” she says.

One hurdle is a requirement to follow multiple generations of children who have gotten gene editing to determine whether the therapy has consequences for future generations. Researchers would never be able to guarantee that they could conduct such long-term studies, Farahany says. “You can’t bind your children and grandchildren to agree to be tracked by such studies.”

Distinctions between therapies and enhancements are also vague. Researchers may not be able to convincingly draw lines between them, says George Church, a Harvard University geneticist who has developed CRISPR/Cas9 for a variety of purposes. Virtually everything medicine has accomplished could be considered as enhancing human life, he says. “Vaccines are advancements over our ancestors. If you could tell our ancestors they could walk into a smallpox ward and not even worry about it, that would be a superpower.”

But the new technology may make it harder to enhance humans than drugs do, says Charo. Gene-editing technologies are so precise and specific that someone who does not carry a disease-causing mutation would probably not benefit from the technology, she says.

If your young child is facing ear tubes, an MRI or even extensive dental work, you’ve probably got a lot of concerns. One of them may be about whether the drugs used to render your child briefly unconscious can permanently harm his brain. Here’s the frustrating answer: No one knows.

“It’s a tough conundrum for parents of kids who need procedures,” says pediatric anesthesiologist Mary Ellen McCann, a pediatric anesthesiologist at Boston Children’s Hospital. “Everything has risks and benefits,” but in this case, the decision to go ahead with surgery is made more difficult by an incomplete understanding of anesthesia’s risks for babies and young children. Some studies suggest that single, short exposures to anesthesia aren’t dangerous. Still, scientists and doctors say that we desperately need more data before we really understand what anesthesia does to developing brains.

It helps to know this nonanswer comes with a lot of baggage, a sign that a lot of very smart and committed people are trying to answer the question. In December, the FDA issued a drug safety communication about anesthetics that sounded alarming, beginning with a warning that “repeated or lengthy use of general anesthetic and sedation drugs during surgeries or procedures in children younger than 3 years or in pregnant women during their third trimester may affect the development of children’s brains.” FDA recommended more conversations between parents and doctors, in the hopes of delaying surgeries that can safely wait, and the amount of anesthesia exposure in this potentially vulnerable population.

The trouble with that statement, though, is that it raises concerns without answering them, says pediatric anesthesiologist Dean Andropoulos of Texas Children’s Hospital in Houston. And that concern might lead to worse outcomes for their youngest patients. “Until reassuring new information from well-designed clinical trials is available, we are concerned that the FDA warning will cause delays for necessary surgical and diagnostic procedures that require anesthesia, resulting in adverse outcomes for patients,” Andropoulos and a colleague wrote February 8 in a New England Journal of Medicine perspective article.

By and large, the surgeries done in young children have good reasons. Surgery for serious heart disease and other life-threatening conditions can’t wait. Ear tubes need to be put in so that a child can hear and get auditory input that’s required early in life for normal language skills. Likewise, certain kinds of eye surgery and cleft palate repairs all lead to better developmental outcomes if done early.

That doesn’t leave many surgeries that can be put off. “The things that can be delayed are few and far between,” Andropoulos says. That’s why the FDA’s recent drug safety communication might cause extra parental worry about surgeries that ought to be done.

Scientists have lots of data showing that anesthetic drugs can cause long-lasting damage in a variety of species, from roundworms to rats to nonhuman primates. Anesthetics are “like any toxin,” says Andrew Davidson, an anesthesiologist at the Murdoch Childrens Research Center in Melbourne, Australia. “The more you have, the worse it is.”
Yet Davidson and others have uncovered some reassuring news for parents. Quick, single exposures to anesthesia, about an hour or less, don’t seem dangerous.

Davidson, McCann and colleagues recently compared children who, as babies, had undergone hernia repair surgery. Of these babies, 359 had brief general anesthesia and 363 instead received local anesthesia. At age 2, the children showed no differences in mental abilities, the researchers reported last year in The Lancet. That trial, called the GAS study, was particularly well-done because unlike many other studies of this question, babies were randomly assigned to receive either general or local anesthesia. And the experiment isn’t over yet. Scientists will test the children again at age 5, when it will be easier to test more complex forms of thinking.

More encouraging news came from the PANDA study, which tracked over 100 children who had received a short dose of anesthesia (the median was 80 minutes) when they were younger than 3. When those same kids were 8 to 15 years old, their IQs and most other thinking skills were similar to their healthy siblings who had not received anesthesia when they were young.

Along with the GAS results, the PANDA study, published June 7 in the Journal of the American Medical Association, offers some reassurance to parents whose child might need surgery. “If it’s a short procedure, you don’t have to worry about it,” Davidson says.

For now, doctors are making good efforts to talk through these complex questions with parents as they make medical decisions. “We face this issue essentially every day,” Andropoulos says, and at his institute, the FDA guidelines prompted even more conversations. Parents are largely appreciative of having these talks, he says. And hopefully scientists will soon have something more to tell parents about what Andropoulos calls “the most important problem we face in pediatric anesthesia.”

Mosquitoes are more than an itchy nuisance. They can carry serious diseases, including Zika, West Nile, yellow fever and chikungunya. Now after testing 11 types of mosquito repellents, researchers say they’ve identified the products most effective at warding off the bloodsuckers.

Spray-on repellents with DEET or a refined tree extract called oil of lemon eucalyptus are most likely to keep you bite-free, the scientists report online February 16 in the Journal of Insect Science. The OFF! Clip-On repellent, which puffs out a vapor of the chemical metofluthrin, killed every mosquito in the cage. But Hansen says the mosquitoes couldn’t escape, so they probably got a higher dose than they would in a natural setting.
Other tested repellents such as a citronella candle simply don’t work, says study coauthor Immo Hansen, an insect physiologist at New Mexico State University in Las Cruces.

“There are a whole lot of different products out on the market that are sold as mosquito repellents, and most of them haven’t ever been tested in a scientific setting,” Hansen says.

To evaluate the repellents, the researchers used a person, safely protected from bites, as “bait.” The volunteer sat in a wind tunnel as her alluring scent — and repelling chemicals — were pulled toward a cage of Aedes aegypti mosquitoes.
The three-compartment cage allowed the mosquitoes to move toward or away from the volunteer. After 15 minutes, the researchers determined the portion of mosquitoes that had moved into the compartment closest to the volunteer.
Three deterrents did little to dissuade the insects: bracelets with geraniol oil, a sound machine that buzzes like a dragonfly and a citronella candle (which appeared to slightly attract the mosquitoes). Burning a candle releases carbon dioxide, which might have drawn the mosquitoes, which home in on a human meal by sensing exhaled CO2 (SN: 3/18/17, p. 10).

Repellents face-off
Researchers measured attraction rates of A. aegypti mosquitoes to a person one meter or three meters away who was wearing or seated next to the repellent. Attraction rates are the percentage of total mosquitoes, averaged over four tests, that flew toward the person.
These repellents were not significantly different from the no-repellent control: bracelets (Mosquito-NO!, Invisaband, Mosquitavert), Cutter Citro Guard candle and Personal Sonic Mosquito Repeller.

WASHINGTON — A second cancer later in life is common for childhood cancer survivors, and scientists now have a sense of the role genes play when this happens. A project that mined the genetic data of a group of survivors finds that 11.5 percent carry mutations that increase the risk of a subsequent cancer.

“We’ve always known that among survivors, a certain population will experience adverse outcomes directly related to therapy,” says epidemiologist and team member Leslie Robison of St. Jude Children’s Research Hospital in Memphis. The project sought “to find out what contribution genetics may play.” The team presented their work at the American Association of Cancer Research meeting April 3.
“This is a nice first step,” says David Malkin, a pediatric oncologist at the University of Toronto. “The results validate the thoughts of those of us who believe there is a genetic risk that increases the risk of second malignancies.”

Five-year survival rates for kids with cancer have grown to more than 80 percent. But “there are long-term consequences for having been diagnosed and treated for cancer as a child,” notes Robison. Some survivors develop a later, second cancer due to the radiation or chemotherapy that treated the first cancer (SN: 3/10/07, p. 157).

The researchers examined 3,007 survivors of pediatric cancer who routinely undergo medical evaluation at St. Jude. About a third had leukemia as children. By age 45, 29 percent of this group had developed new tumors, often in the skin, breast or thyroid.

The team cataloged each survivor’s DNA, and looked closely at 156 genes known as cancer predisposition genes. Of the survivors, 11.5 percent carried a problematic mutation in one of the 156 genes. Some genes on the list convey a higher risk than others, so the team looked further at a subset of 60 genes in which only one mutated copy in each cell is enough to cause disease. These 60 genes also have high penetrance, meaning that a mutated copy is highly likely to lead to a cancer. Nearly 6 percent of the survivors had a problematic mutation in one of these 60 genes.

The research team also separated the survivors based on whether or not they had received radiation therapy as children. Close to 17 percent of survivors not exposed to radiation therapy had a problematic mutation in the subset of 60 genes. These survivors had an increased risk for any second cancer. Those with both a mutation in one of the 60 genes and radiation in their treatment history had a higher risk for specific kinds of second cancers: breast, thyroid or sarcomas, tumors in connective tissues.
Based on the new estimates of genetic risk, the team suggests that survivors not given radiation therapy undergo genetic counseling if a second cancer develops. Counseling is also recommended “for survivors who develop a secondary breast cancer, thyroid cancer or sarcoma in a site that received prior radiation therapy,” says St. Jude epidemiologist and project team member Carmen Wilson. Counseling can provide guidance on health practices going forward, reproductive choices and the implications for immediate family members who may have inherited the mutation, notes Robison.

The extensive amount of medical and genomic information collected for the survivors could help with cancer prevention efforts in the future, Robison says. The team would like to create prediction models that consider treatment, genetics and other clinical information, in order to place survivors into different risk groups. “It’s eventually going to have clear implications for how these patients are clinically managed, and how we either prevent or ameliorate the adverse effects,” Robison says.

Malkin notes that not only “what you got for treatment, but when you got it” is another factor influencing a survivor’s risk profile for second cancers, as treatments and doses have changed over time. He also thinks the percentage of survivors at risk reported by Robison’s team is lower than expected. “Expanding the pool of genes to look at will be very informative,” he says.

A new device the size of a coffee mug can generate drinkable water from desert air using nothing but sunlight.

With this kind of device, “you can harvest the equivalent of a Coke can’s worth of water in an hour,” says cocreator Omar Yaghi, a chemist at the University of California, Berkeley. “That’s about how much water a person needs to survive in the desert.”

Though that may not sound like much, its designers say the current device is just a prototype. But the technology could be scaled up to supply fresh water to some of the most parched and remote regions of the globe, such as the Middle East and North Africa, they say.
Previous attempts at low-energy water collection struggled to function below 50 percent relative humidity (roughly the average afternoon humidity of Augusta, Ga.). Thanks to a special material, the new device pulled water from air with as low as 20 percent relative humidity, Yaghi and colleagues report online April 13 in Science. That’s like conjuring water in Las Vegas, where the average afternoon relative humidity is 21 percent.

Drinking water supplies can’t keep up with the rising demands of a growing human population, and shifts in rainfall caused by climate change are expected to exacerbate the problem. Already, two-thirds of the world’s population is experiencing water shortages (SN: 8/20/16, p. 22). One largely untapped water source is the atmosphere, which contains more than 5 billion Olympic-sized pools’ worth of moisture in the form of vapor and droplets.

Getting that moisture out is easy when the air is saturated with water. But humid regions aren’t where the water-shortage problem is, and drawing water from the drier air in parched areas is a greater challenge. Spongy materials such as silica gels can extract moisture from the air even at low relative humidity. Those materials, however, either amass water too slowly or require lots of energy to extract the collected water from the material.

The new device uses a material that avoids both problems. MIT mechanical engineer Evelyn Wang, Yaghi and colleagues repurposed an existing material composed of electrically charged metal atoms linked by organic molecules. This metal-organic framework, christened MOF-801, creates a network of microscopic, spongelike pores that can trap such gases as water vapor. At room temperature, water vapor collects in the pores. As temperatures rise, the water escapes.

The team’s prototype includes a layer of MOF-801 mixed with copper foam. Left in the shade, this layer collects water vapor from the air. When moved into direct sunlight, the layer heats up and the water vapor escapes into an underlying chamber. A condenser in the chamber cools the vapor, converting it into a potable liquid. This entire process takes around two hours.
Laboratory tests of the device harvested 2.8 liters of water per day for every kilogram of MOF-801 used. As it is now, the device could be used as a personal water source in dry regions without water-producing infrastructure, Yaghi says, or the system could be scaled up to produce enough water for a whole community.

The device’s ability to produce water at low relative humidity is a breakthrough, says Krista Walton, a chemical engineer at Georgia Tech in Atlanta. “No one else is using MOFs like this today,” she says.

As for the cost of scaling up, the ingredients used in the device’s metal-organic framework “aren’t exotic,” Walton says. Producing large amounts of the material “would definitely be possible if the demand were there.”

A recent upsurge in planet-warming methane may not be caused by increasing emissions, as previously thought, but by methane lingering longer in the atmosphere.

That’s the conclusion of two independent studies that indirectly tracked concentrations of hydroxyl, a highly reactive chemical that rips methane molecules apart. Hydroxyl levels in the atmosphere decreased roughly 7 or 8 percent starting in the early 2000s, the studies estimate.

The two teams propose that the hydroxyl decline slowed the breakdown of atmospheric methane, boosting levels of the greenhouse gas. Concentrations in the atmosphere have crept up since 2007, but during the same period, methane emissions from human activities and natural sources have remained stable or even fallen slightly, both studies suggest. The research groups report their findings online April 17 in Proceedings of the National Academy of Sciences.
“If hydroxyl were to decline long-term, then it would be bad news,” says Matt Rigby, an atmospheric scientist at the University of Bristol in England who coauthored one of the studies. Less methane would be removed from the atmosphere, he says, so the gas would hang around longer and cause more warming.

The stability of methane emissions might also vindicate previous studies that found no rise in emissions. The Environmental Protection Agency, for instance, has reported that U.S. emissions remained largely unchanged from 2004 to 2014 (SN Online: 4/14/16).

Methane enters the atmosphere from a range of sources, from decomposing biological material in wetlands to leaks in natural gas pipelines. Ton for ton, that methane causes 28 to 36 times as much warming as carbon dioxide over a century.

Since the start of the Industrial Revolution, atmospheric methane concentrations have more than doubled. By the early 2000s, though, levels of the greenhouse gas inexplicably flatlined. In 2007, methane levels just as mysteriously began rising again. The lull and subsequent upswing puzzled scientists, with explanations ranging from the abundance of methane-producing microbes to the collapse of the Soviet Union.

Those proposals didn’t account for what happens once methane enters the atmosphere. Most methane molecules in the air last around a decade before being broken apart during chemical reactions with hydroxyl. Monitoring methane-destroying hydroxyl is tricky, though, because the molecules are so reactive that they survive for less than a second after formation before undergoing a chemical reaction.
Neither study can show conclusively that hydroxyl levels changed, notes Stefan Schwietzke, an atmospheric scientist at the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory in Boulder, Colo. The papers nevertheless add a new twist in explaining the mysterious methane rise, he says. “Basically these studies are opening a new can of worms, and there was no shortage of worms.”

Despite being conducted by two separate teams — one headed by Rigby and the other by atmospheric scientist Alex Turner of Harvard University — the new studies used the same roundabout approach to tracking hydroxyl concentrations over time.

Both teams followed methyl chloroform, an ozone-depleting substance used as a solvent before being banned by the Montreal Protocol. Like methane, methyl chloroform also breaks apart in reactions with hydroxyl. Unlike methane, though, emission rates of methyl chloroform are fairly easy to track because the chemical is entirely human-made.

Examining methyl chloroform measurements gathered since the 1980s revealed that hydroxyl concentrations have probably wobbled over time, contributing to the odd pause and rise in atmospheric methane concentrations. But to know for sure whether hydroxyl levels varied or remained steady, scientists will need to take a more detailed look at regional emissions of methane and methyl chloroform, Rigby says.

Why hydroxyl levels might have fallen also remains unclear. Turner and colleagues note that the ban on ozone-depleting substances like methyl chloroform might be the cause. The now-recovering ozone layer (SN: 12/24/16, p. 28) blocks some ultraviolet light, an important ingredient in the formation of hydroxyl. Identifying the cause of the hydroxyl changes could help climate scientists better predict how methane levels will behave in the future.

NEW ORLEANS — A relatively small brain can pack a big evolutionary punch. Consider Homo naledi, a famously puzzling fossil species in the human genus. Despite having a brain only slightly larger than a chimpanzee’s, H. naledi displays key humanlike neural features, two anthropologists reported April 20 at the annual meeting of the American Association of Physical Anthropologists.

Those brain characteristics include a region corresponding to Broca’s area, which spans parts of the right and left sides of the brain in present-day people. The left side is typically involved in speech and language.
“It looks like Homo naledi’s brain evolved a huge amount of shape change that supported social emotions and advanced communication of some type,” said Shawn Hurst of Indiana University Bloomington, who presented the new findings. “We can’t say for sure whether that included language.” Frontal brain locations near Broca’s area contribute to social emotions such as empathy, pride and shame. As interactions within groups became more complex in ancient Homo species, neural capacities for experiencing social emotions and communicating verbally blossomed, Hurst suspects.

Scientists don’t know how long ago H. naledi inhabited Africa’s southern tip. If H. naledi lived 2 million or even 900,000 years ago, as some researchers have suggested (SN: 8/6/16, p. 12), humanlike brains with a language-related area would be shocking. A capacity for language is thought to have emerged in Homo over the last few hundred thousand years at most.

Discoverers of H. naledi, led by anthropologist Lee Berger of the University of the Witwatersrand in Johannesburg, will announce an estimated age for the species and describe new fossil finds within the next few weeks, Hurst said.

Hurst and Ralph Holloway of Columbia University led a team that laser scanned the inside surfaces of several partial H. naledi skulls to create virtual casts, or endocasts, of brain surfaces. An endocast reproduces the shape and, with varying success, details of the surface of the brain that were imprinted on the walls of the braincase while an individual was alive. Such brain impressions are not always clear, which has sparked debate over how to interpret them.

Two grooves identified on an endocast from a partial H. naledi skull frame the language-related section of Broca’s area in humans today, Hurst said. H. naledi’s brain also possessed folds of tissue that largely covered a surface section where the grooves converged. Similar folds of tissue typically cover the surface of Broca’s area in modern human brains.
The general shape of that part of the frontal brain in humans differs greatly from that of living apes and fossil hominids dating to at least 700,000 to 1 million years years ago, Hurst added.

H. naledi also displays a humanlike pattern of surface features at the back of the brain, although to a lesser extent than at the brain’s front, Holloway said. Endocasts for this analysis came from two other partial H. naledi skulls.

Specific protrusions and other features at the back of H. naledi’s brain are more pronounced on the left side, Holloway said. In people today, the same left-sided bias in brain organization is associated with right-handedness.

In the past, Holloway and anthropologist Dean Falk of Florida State University in Tallahassee have sharply disagreed over how to identify neural features on fossil endocasts, including a key groove in tissue at the back of the brain. After hearing Hurst and Holloway’s presentations, Falk expressed doubt that H. naledi’s brain was as humanlike as they concluded.

Shortly after the presentations, Hurst and Falk hashed out their differences head-to-head as they jointly studied a solid cast of the partial H. naledi brain surface displaying proposed signs of Broca’s area. They agreed on much about the fossil species’ neural setup, with one major exception. “I’m skeptical that two frontal [grooves] frame an area that corresponds to Broca’s area,” Falk said. If she’s right, then H. naledi communicated much less like present-day people than proposed by Hurst. Falk plans to study the new endocasts more closely and compare them with endocasts of other fossil hominids.