When small lies snowball into blizzards of deception, the brain becomes numb to dishonesty. As people tell more and bigger lies, certain brain areas respond less to the whoppers, scientists report online October 24 in Nature Neuroscience. The results might help explain how small transgressions can ultimately set pants aflame.
The findings “have big implications for how lying can develop,” says developmental psychologist Victoria Talwar of McGill University in Montreal, who studies how dishonest behavior develops in children. “It starts to give us some idea about how lying escalates from small lies to bigger ones.” During the experiment, researchers from University College London and Duke University showed 80 participants a crisp, big picture of a glass jar of pennies. They were told that they needed to send an estimate of how much money was in the jar to an unseen partner who saw a smaller picture of the same jar. Each participant was serving as a “well-informed financial adviser tasked with advising a client who is less informed about what investments to make,” study coauthor Neil Garrett of University College London said October 20 during a news briefing. Researchers gave people varying incentives to lie. In some cases, for instance, intentionally overestimating the jar’s contents was rewarded with a bigger cut of the money.
As the experiment wore on, the fibs started flying. People lied the most when the lie would benefit both themselves and their unseen partner. But these “financial advisers” still told self-serving lies even when it would hurt their partner.
Twenty-five participants underwent fMRI scans while lying. When a person had previously lied, brain activity lessened in certain areas of the brain, most notably in the amygdala. A pair of almond-shaped brain structures nestled deep in the brain, the amygdalae are tightly linked to emotions. This diminished amygdala activity could even predict whether a person would lie on the next trial, results that suggest that the reduced brain activity is actually influencing the decision to lie.
The study design gets around a problem that confounds other lying experiments, says neuroscientist Bernd Weber of the University of Bonn in Germany. Many experiments are based on lies that people have been instructed to say, a situation that “hardly resembles real-world behavior,” he says. Here, the participants were self-motivated liars.
Without any negative consequences from their lies, participants weren’t afraid of being caught. That impunity might affect activity in the amygdala, Weber says. Further experiments are needed to reveal the effects of such fear. From Ponzi schemes to current politics, case studies abound of small lies spiraling into much bigger deceits, study coauthor Tali Sharot of the University College London said in the news briefing. “There are many reasons why this might happen, societal reasons, but we suspected that there might be a basic biological principle of how our brain works that contributes to this phenomenon,” she said.
The principle she had in mind is called emotional adaptation — the same phenomenon that explains why the scent of strong perfume becomes less noticeable over time. The first time you cheat on your taxes, you’d probably feel quite bad about it, Sharot said. That bad feeling is good, because it curbs your dishonesty. “The next time you cheat, you have already adapted,” she said. “There’s less negative reaction to hold you back so you might be lying more.”
DNA in cancerous tissues of tobacco smokers shows mutation patterns that differ from those in cancerous tissues of nonsmokers, a new analysis finds. The new study, in the Nov. 4 Science, reveals how smoking contributes to different cancers, enhancing several kinds of DNA damage.
“We are doing a sort of molecular archaeology,” says cancer geneticist Ludmil Alexandrov of Los Alamos National Laboratory in New Mexico, who led the analysis. While smoking’s link to cancer has been known for decades, “it’s always been a bit of a mystery why smoking increases the risk of cancers like bladder or kidney — tissues that aren’t exposed to smoke.” Mutations in DNA arise naturally in a person’s lifetime, but some genetic changes — such as those spurred by smoking — increase the risk of certain cancers. Scientists have identified several patterns of DNA mutations that consistently show up in tissues of some cancers. These patterns, which may appear over and over again in a stretch of tumor DNA, can serve as a signature of the underlying mechanism that led to the mutations, offering clues to how different cancers strike.
“When someone has a cancer, we only see what is now — we don’t know what happened 20 years ago when that cancer was only one cell,” says cancer biologist Gerd Pfeifer of the Van Andel Research Institute in Grand Rapids, Mich.
“These signatures give us a really good clue of what might have happened,” says Pfeifer, who was not involved with the study.
Alexandrov and an international team of researchers found several differences in the number of altered DNA signatures in tumors of smokers compared with those from nonsmokers with the same type of cancer. The research adds dismal specifics to what’s already known about smoking: It is really bad for you.
“Tobacco smoking leaves permanent mutations — it erodes the genetic material of most cells in your body,” says Alexandrov. “Even if you are a just a social smoker who occasionally has one or two or five cigarettes, there is still a cumulative effect.” Alexandrov and colleagues compiled data on DNA extracted from more than 5,000 human samples representing 17 cancers for which smoking is a known risk factor. About half of the samples were from smokers. The team then searched the DNA for various patterns of damage, or “mutational signatures.”
One suite of mutations, called signature 4, was consistently found in tissues exposed to tobacco smoke. While this signature also appeared in nonsmokers’ tumors, it occurred far less often. Smokers with lung squamous cancer, lung adenocarcinoma and larynx cancers had an especially high number of signature 4 mutations. Signature 4 signals damage to guanine (the structural component of DNA known as “G”). This signature also appears in the DNA of cells in a lab dish that are exposed to a chemical found in burnt products, including polluted air and the tar in cigarette smoke.
Signature 4 mutations also showed up in cancers of the oral cavity, pharynx and esophagus, but much less often. The researchers aren’t sure why these tissues, which are also directly exposed to smoke, don’t have as heavy a mutational load. Those tissues may metabolize smoke differently, the researchers speculate.
DNA damage in smokers also differed from that in nonsmokers for another suite of mutations, known as signature 5. This signature typically shows up in all cancers and across all tissue types. The cause of signature 5 remains unknown, but scientists do know that the number of signature 5 mutations is “clocklike” — it increases with age. The new analysis revealed that the signature 5 “clock” ticks faster in smokers. Depending how heavily a person smoked, the more signature 5 mutations were found.
In patients with lung adenocarcinoma, far more mutations associated with two other signatures, 2 and 13, had accumulated in smokers than in nonsmokers. There are hints that these mutations result from overactive DNA editing machinery. But because these signatures are found in many kinds of cancer, it isn’t clear why smoking ups the mutations load. Inflammation from smoke might be activating the cellular machinery that underlies the mutations.
When the researchers took into account the quantity smoked, they discovered that the number of mutations for some cancers was linked to the “pack years” smoked (a pack of cigarettes a day for one year). Breaking these data down into cancer types allowed the team to calculate the mutations caused by smoking for a particular tissue type: A pack a day for one year leads to 150 mutations in a lung cell, 97 in a larynx cell, 39 in the pharynx, 23 in the oral cavity, 18 in the bladder and six in a liver cell.
Narwhals use highly targeted beams of sound to scan their environment for threats and food. In fact, the so-called unicorns of the sea (for their iconic head tusks) may produce the most refined sonar of any living animal.
A team of researchers set up 16 underwater microphones to eavesdrop on narwhal click vocalizations at 11 ice pack sites in Greenland’s Baffin Bay in 2013. The recordings show that narwhal clicks are extremely intense and directional — meaning they can widen and narrow the beam of sound to find prey over long and short distances. It’s the most directional sonar signal measured in a living species, the researchers report November 9 in PLOS ONE.
The sound beams are also asymmetrically narrow on top. That minimizes clutter from echoes bouncing off the sea surface or ice pack. Finally, narwhals scan vertically as they dive, which could help them find patches of open water where they can surface and breathe amid sea ice cover. All this means that narwhals employ pretty sophisticated sonar.
The audio data could help researchers tell the difference between narwhal vocalizations and those of neighboring beluga whales. It also provides a baseline for assessing the potential impact of noise pollution from increases in shipping traffic made possible by sea ice loss.
SAN DIEGO — Over the course of months, clumps of a protein implicated in Parkinson’s disease can travel from the gut into the brains of mice, scientists have found.
The results, reported November 14 at the annual meeting of the Society for Neuroscience, suggest that in some cases, Parkinson’s may get its start in the gut. That’s an intriguing concept, says neuroscientist John Cryan of the University College Cork in Ireland. The new study “shows how important gut health can be for brain health and behavior.” Collin Challis of Caltech and colleagues injected clumps of synthetic alpha-synuclein, a protein known to accumulate in the brains of people with Parkinson’s, into mice’s stomachs and intestines. The researchers then tracked alpha-synuclein with a technique called CLARITY, which makes parts of the mice’s bodies transparent.
Seven days after the injections, researchers saw alpha-synuclein clumps in the gut. Levels there peaked 21 days after the injections. These weren’t the same alpha-synuclein aggregates that were injected, though. These were new clumps, formed from naturally occurring alpha-synuclein, that researchers believe were coaxed into forming by the synthetic versions in their midst.
Also 21 days after the injections, alpha-synuclein clumps seemed to have spread to a part of the brain stem containing nerve cells that make up the vagus nerve, a neural highway that connects the gut to the brain. Sixty days after the injections, alpha-synuclein had accumulated in the midbrain, a region packed with nerve cells that make the chemical messenger dopamine. These are the nerve cells that die in people with Parkinson’s, a progressive brain disorder that affects movement.
After reaching the brain, alpha-synuclein spreads thanks in part to brain cells called astrocytes, a second study suggests. Experiments with cells in dishes showed that astrocytes can store up and spread alpha-synuclein among cells. That work was presented by Jinar Rostami of Uppsala University in Sweden at a news briefing on November 14.
The gradual accumulation and spread of alpha-synuclein caused trouble in the mice. As alpha-synuclein clumps slowly crept brainward, the mice began exhibiting gut and movement problems. Seven days after the injections, the mice’s stool was more plentiful than usual. Sixty and 90 days after the injections — after clumps of alpha-synuclein had reached the brain — the mice performed worse on some physical tests, including getting a sticker off their face and flipping around to shimmy down a pole headfirst. In many ways, the mice resembled other mice that have mutations that cause Parkinson’s-like symptoms, Challis says. An earlier study turned up evidence that clumps of alpha-synuclein can move from the gut to the brain stem in rats, but those experiments looked at shorter time scales, Challis says. And previous work monitored the movements of the injected alpha-synuclein, as opposed to the alpha-synuclein clumps that the mice produced themselves.
The idea that alpha-synuclein can spread from the gut to the brain is very new, says Alice Chen-Plotkin, a clinician and Parkinson’s researcher at the Hospital of the University of Pennsylvania. These new results and others have prompted scientists to start looking outside of the brain for the beginning stages of the disease, she says. “Increasingly, people are wondering if it starts earlier.”
Some evidence suggests that the gut is a good place to look. People with Parkinson’s disease often suffer from gut problems such as constipation. And in 2015, scientists reported that a group of Danish people who had their vagus nerves severed were less likely to develop Parkinson’s disease. Cut alpha-synuclein’s transit route from the gut to the brain, and the disease is less likely to take hold, that study hints.
It’s not clear why alpha-synuclein accumulates in the gut in the first place. “There are a lot of theories out there,” Challis says. Bacteria may produce compounds called curli that prompt alpha-synuclein to aggregate, a recent study suggests. Pesticides, acid reflux and inflammation are other possible culprits that could somehow increase alpha-synuclein clumps in the gut, Challis says.
Not all galaxies sparkle with stars. Galaxies as wide as the Milky Way but bereft of starlight are scattered throughout our cosmic neighborhood. Unlike Andromeda and other well-known galaxies, these dark beasts have no grand spirals of stars and gas wrapped around a glowing core, nor are they radiant balls of densely packed stars. Instead, researchers find just a wisp of starlight from a tenuous blob.
“If you took the Milky Way but threw away about 99 percent of the stars, that’s what you’d get,” says Roberto Abraham, an astrophysicist at the University of Toronto. How these dark galaxies form is unclear. They could be a whole new type of galaxy that challenges ideas about the birth of galaxies. Or they might be outliers of already familiar galaxies, black sheep shaped by their environment. Wherever they come from, dark galaxies appear to be ubiquitous. Once astronomers reported the first batch in early 2015 — which told them what to look for — they started picking out dark denizens in many nearby clusters of galaxies. “We’ve gone from none to suddenly over a thousand,” Abraham says. “It’s been remarkable.” This haul of ghostly galaxies is puzzling on many fronts. Any galaxy the size of the Milky Way should have no trouble creating lots of stars. But it’s still unclear how heavy the dark galaxies are. Perhaps these shadowy entities are failed galaxies, as massive as our own but mysteriously prevented from giving birth to a vast stellar family. Or despite being as wide as the Milky Way, they could be relative lightweights stretched thin by internal or external forces. Either way, with so few stars, dark galaxies must have enormous deposits of unseen matter to resist being pulled apart by the gravity of other galaxies.
Astronomers can’t resist a good cosmic mystery. With detections of these galactic oddballs piling up, there is a push to figure out just how many of these things are out there and where they’re hiding. “There are more questions than answers,” says Remco van der Burg, an astrophysicist at CEA Saclay in France. Cracking the code of dark galaxies could provide insight into how all galaxies, including the Milky Way, form and evolve. Compound eye on the sky Telescopes designed to detect faint objects have revealed the presence of many sizable but near-empty galaxies — officially known as “ultradiffuse galaxies.” The deluge of discoveries started in New Mexico, with a telescope that looks more like a honeycomb than a traditional observatory. Sitting in a park about 110 kilometers southwest of Roswell (a city that has turned extraterrestrials into a tourism industry), the Dragonfly telescope consists of 48 telephoto lenses; it started with three in 2013 and continues to grow. The lenses are divided evenly among two steerable racks, and each lens is hooked up to its own camera. Partly inspired by the compound eye found in dragonflies and other insects, this relatively small scope has revealed dim galaxies missed by other observatories.
The general rule for telescopes is that bigger is better. A large mirror or lens can collect more light and therefore see fainter objects. But even the biggest telescopes have a limitation: unwanted light. Every surface in a telescope is an opportunity for light coming in from any direction to reflect onto the image. The scattered light shows up as dim blobs, or “ghosts,” that can wash out faint detail in pictures of space or even mimic very faint galaxies.
Large dark galaxies look a lot like these ghosts, and so went unnoticed. But Dragonfly was designed to keep these splashes of light in check. Unlike most conventional professional telescopes, it has no mirrors. Precision antireflection coatings on the lenses keep scattered light to a minimum. And having multiple cameras pointed at the same part of the sky helps distinguish blobs of light bouncing around in the telescope from blobs that actually sit in deep space. If the same blob shows up in every camera, it’s probably real.
“It’s a very clever idea, very brilliant,” says astronomer Jin Koda of Stony Brook University in New York. “Dragonfly made us realize that there is a chance to find a new population of galaxies beyond the boundary of what we know so far.”
In spring 2014, researchers pointed Dragonfly at the well-studied Coma cluster, a conglomeration of thousands of galaxies. At a distance of about 340 million light-years, Coma is a close, densely packed collection of galaxies and a rich hunting ground for astronomers. A team led by Abraham and astronomer Pieter van Dokkum of Yale University was looking at the edges of galaxies for far-flung stars and stellar streams, evidence of the carnage left behind after small galaxies collided to build larger ones. They were not expecting to find dozens of galaxies hiding in plain sight. “People have been studying Coma for 80 years,” Abraham says. “How could we find anything new there?” And yet, scattered throughout the cluster appeared 47 dark galaxies, many of them comparable in size to the Milky Way — tens of thousands to hundreds of thousands of light-years across (SN: 12/13/14, p. 9). This was perplexing. A galaxy that big should have no problem forming lots of stars, van Dokkum and colleagues noted in September in Astrophysical Journal Letters.
Hidden strength Even more surprising, says Abraham, is that those galaxies survive in Coma, a cluster crowded with galactic bullies. A galaxy’s own gravity holds it together, but gravity from neighboring galaxies can pull hard enough to tear apart a smaller one. To create sufficient gravity to survive, a galaxy needs mass in the form of stars, gas and other cosmic matter. In a place like Coma, a galaxy needs to be fairly massive or compact. But with so few stars (and presumably so little mass) spread over a relatively large space, dark galaxies should have been shredded long ago. They are either recent arrivals to Coma or a lot stronger than they appear.
From what researchers have learned so far, dark galaxies seem to have been lurking for many billions of years. They are located throughout their home clusters, suggesting that they’ve had a long time to spread out among the other galaxies. And the meager stars they have are mostly red, indicating that they are very old. With this kind of longterm survival, dark galaxies probably have a hidden strength, most likely due to dark matter.
All galaxies are loaded with dark matter, a mysterious substance that reveals itself only via gravitational interactions with luminous gas and stars. Much of that dark matter sits in an extended blob (known as the halo) that reaches well beyond the visible edge of a galaxy. On average, dark matter accounts for about 85 percent of all the matter in the universe. Within the central regions of the dark galaxies in Coma, dark matter must make up about 98 percent of the mass for there to be enough gravity to keep the galaxy intact, van Dokkum and colleagues say. Dark galaxies appear to have similar fractions of dark matter focused near their cores as the Milky Way does throughout its broader halo.
Astronomers had never seen such a strong preference for dark matter in galaxies so large. The initial cache of galactic enigmas lured a slew of researchers to the hunt. They pored over existing images of Coma and other clusters, looking for more dark galaxies. These galaxies are so faint that they could easily blend in with a cluster’s background light or be mistaken for reflections within a telescope. But once the galaxy hunters knew what to look for, they were not disappointed — those first 47 were just the tip of the iceberg.
Looking at old images of Coma taken by the Subaru telescope in Hawaii, Koda and colleagues easily confirmed that those 47 were really there. But that wasn’t all. They found a total of 854 dark galaxies, 332 of which appeared to be roughly the size of the Milky Way (SN: 7/25/15, p. 11). They calculated that Coma could harbor more than 1,000 dark galaxies of all sizes — comparable to its number of known galaxies. Astronomer Christopher Mihos of Case Western Reserve University in Cleveland and colleagues, reporting in 2015 in Astrophysical Journal Letters, found three more in the Virgo cluster, a more sparsely populated but closer gathering of galaxies that’s a mere 54 million light-years away.
In June, van der Burg and collaborators reported another windfall in Astronomy & Astrophysics. Using the Canada-France-Hawaii Telescope atop Mauna Kea in Hawaii, they measured the masses of several galaxy clusters. Taking a closer look at eight clusters, all less than about 1 billion light-years away, the group found roughly 800 more ultradiffuse galaxies.
“As we go to bigger telescopes, we find more and more,” says Michael Beasley, an astrophysicist at Instituto de Astrofísica de Canarias in Santa Cruz de Tenerife, Spain. “We don’t know how many there are, but we know there are a lot of them.” There could even be more dark galaxies than bright ones.
Nature vs. nurture What dark galaxies are and how they formed is still a mystery. There are many proposals, but with so little data, few conclusions. For the vast majority of dark galaxies, researchers know only how big and how bright each one is. Three so far have had their masses measured. Of those, two appear to have more in common masswise with some of the small galaxies that orbit the Milky Way, while the third is as massive as our galaxy itself — roughly 1 trillion times as massive as the sun.
A dark galaxy in the Virgo cluster, VCC 1287, and another in Coma, Dragonfly 17, each have a total mass of about 70 billion to 90 billion suns. But only about one one-thousandth of that or less is in stars. The rest is dark matter. That puts the total masses of these two galaxies on par with the Large Magellanic Cloud, the largest of the satellite galaxies that orbit the Milky Way. But focus on just the mass of the stars, and the Large Magellanic Cloud is about 35 times as large as Dragonfly 17 and roughly 100 times as large as VCC 1287.
A galaxy dubbed Dragonfly 44, however, is another story. It’s a dark beast, weighing about as much as the entire Milky Way and made almost entirely of dark matter, van Dokkum and colleagues report in September in Astrophysical Journal Letters. “It’s a bit of a puzzle,” Beasley says. “If you look at simulations of galaxy formation, you expect to have many more stars.” For some reason, this galaxy came up short. The environment may be to blame. A cluster like Coma grows over time by drawing in galaxies from the space around it. As galaxies fall into the cluster, they feel a headwind as they plow through the hot ionized gas that permeates the cluster. The headwind can strip gas from an incoming galaxy. But galaxies need gas to form stars, which are created when self-gravity crushes a blob of dust and gas until it turns into a thermonuclear furnace. If a galaxy falls into the cluster just as it is starting to make stars, this headwind might remove enough gas to prevent many stars from forming, leaving the galaxy sparsely populated.
Or maybe there’s something intrinsic to a galaxy that turns it dark. A volley of supernovas or a prolific burst of star formation might drive gas out of the galaxy. Nicola Amorisco of the Max Planck Institute for Astrophysics in Garching, Germany, and Abraham Loeb of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., suggest that ultradiffuse galaxies start off as small galaxies that spun rapidly as they formed. All galaxies rotate, but perhaps dark galaxies are a subset that twirl so fast that their stars and gas have spread out, turning them into diffuse blobs rather than star-building machines.
To test these and other ideas, astronomers are focused on two key pieces of information: the masses of these galaxies and their locations in the universe. Mass can help researchers distinguish between formation scenarios, such as whether or not dark galaxies are failed Milky Way–like behemoths. A survey of other locales would indicate whether dark galaxies are unique to big clusters such as Coma, suggesting that the environment plays a role in their creation. But if they turn up outside of clusters, isolated or with small groups of galaxies, then perhaps they’re just born that way.
There’s already a hint that dark galaxies depend more on nature than nurture. Yale astronomer Allison Merritt and colleagues reported in October online at arXiv.org that four ultradiffuse galaxies lurk in a small galactic gathering about 88 million light-years away, indicating that clusters aren’t the only place dark galaxies can be found. And van der Burg, in his survey of eight clusters, found that dark galaxies make up the same fraction of all galaxies in a cluster regardless of cluster mass — at least, for clusters weighing between 100 trillion and 1 quadrillion times the mass of the sun. About 0.2 percent of the mass of the stars is tied up in the dark galaxies. Since all eight clusters host roughly the same relative number of dark galaxies, that suggests that there is something intrinsic about a galaxy that makes it dark, van der Burg says.
What this all means for understanding how galaxies form is hard to say. These cosmic specters might be an entirely new entity that will require new ideas about galaxy formation. Or they could be one page from the galaxy recipe book. Timing, location and luck might send some of our heavenly neighbors toward a bright future and force others to fade into the background. Perhaps dark galaxies are a mixed bag, the end result of many different processes going on in a variety of environments.
“I see no reason why the universe couldn’t make these things in many ways,” Abraham says. “Part of the fun over the next few years will be to figure out which is in play in any particular galaxy and what sort of objects the universe has chosen to make.”
What is clear is that as astronomers push to new limits — fainter, farther, smaller — the universe turns up endless surprises. Even in Coma, a locale that has been intensively studied for decades, there are still things to discover. “There’s just a ton of stuff out there that we’re going to find,” Abraham says. “But what that is, I don’t know.”
In crested penguin families, moms heavily favor offspring No. 2 from the start, and a new analysis proposes why. The six or seven species of crested (Eudyptes) penguins practice the most extreme egg favoritism known among birds, says Glenn Crossin of Dalhousie University in Halifax, Canada.
Females that lay two eggs produce a runty first egg weighing 18 to 57 percent less than the second, with some of the greatest mismatches among erect-crested and macaroni penguins. Some Eudyptes species don’t even incubate the first egg; royal penguins occasionally push it out of the nest entirely. Biologists have proposed benefits for the unusual behavior: A sacrificial first egg might mark a claim to a nesting spot or improve chances of one chick surviving predators. But those ideas haven’t held up, Crossin says. He and Tony Williams of Simon Fraser University in Burnaby, Canada, propose in the Oct. 12 Proceedings of the Royal Society B that egg favoritism is just a downside of an open-water, migratory lifestyle. Among the 16 penguin species that lay two eggs, only the Eudyptes species evolved what’s called a pelagic life, spending their nonbreeding season mostly at sea and migrating, in some cases considerable distances, to breeding sites.
Female crested penguins tend to lay their first eggs soon after arriving at a breeding site, meaning that the egg must have started its roughly 16-day development while mom was migrating. The biology of long swims, now encoded genetically, interferes with producing a full-sized egg. A puny first egg might just be a sign that mom is trying to do two things at once, Crossin says.
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 may be 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 Tübingen 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.
You may have read the news this week that pregnancy shrinks a mother’s brain. As a mom-to-be’s midsection balloons, areas of her cerebral cortex wither, scientists reported online December 19 in Nature Neuroscience.
Yes, that sounds bad. But don’t fret. As I learned in reporting that story, a smaller brain can be more efficient and specialized. In fact, post-pregnancy brains could be considered evolutionary works of art, perfectly sculpted to better respond to their babies. The researchers found that the brain regions most changed during pregnancy are the ones that fire up when mothers see pictures of their babies. Pregnancy (and possibly childbirth) may make these neural networks sleeker and stronger, helping moms to tune in to their infants.
As someone whose brain has shriveled at least one time, maybe twice (scientists don’t know if the brain keeps getting smaller with subsequent pregnancies), I find it fascinating to think about this remodeling. The lingering question, however, is whether those brain changes relate to a mother’s smarts. The world abounds with anecdotal attacks of baby brain and placenta dementia (a name that both entertains and offends me), but are the conditions real? Do pregnant women and new moms really turn into forgetful, bumbling idiots?
Study coauthor Elseline Hoekzema, a neuroscientist at Leiden University in the Netherlands, says that the data on this are fuzzy. “It is not well-established whether there are objective changes in memory as a result of pregnancy,” she says. Some studies find effects, while others find none. Research round-ups indicate that certain kinds of memory may be affected, leaving others unscathed. In their study of 25 first-time mothers, Hoekzema and her colleagues didn’t find any memory changes from pre-pregnancy to the months after they gave birth. This study didn’t test the women while they were pregnant, though.
But there are signs of memory slips during pregnancy and the immediate aftermath in both people and animals, says neuroscientist Liisa Galea of the University of British Columbia in Vancouver. Those results vary depending on trimester, fetal sex and other factors, she says. My first thought on hearing those results was, “of course.” Anyone forced to sleep in two-hour increments for months at a time will have trouble remembering things. But Galea says that extreme exhaustion can’t account for the deficits.
Lest mothers despair, Galea pointed me to some different research by her and others that indicates after this early rough spell, motherhood may actually make the brain stronger. In a maze test, first-time rat mothers that were no longer nursing their babies actually outperformed rats that had never given birth. And rats that had been pregnant multiple times outperformed non-mother rats on a different memory test, Galea says.
What’s more, motherhood may help keep the brain young. When tested at the ripe old age of 24 months, rats that had given birth earlier in life performed better on tests of learning and memory than rats that had not given birth. Those results suggest that something about motherhood — perhaps the stew of hormones and the brain changes that follow — may actually protect the brain as it ages.
Despite the spotty scientific literature on these sorts of changes in women, Galea thinks the evidence suggests that there’s a temporary dip in memory during pregnancy and the early postpartum period, followed by not just a recovery, but an actual improvement. “Pregnancy and motherhood are dramatic life-changing events that can have long-lasting repercussions in the brain,” she says. And it’s quite likely that some of those repercussions might be good.
GRAPEVINE, TEXAS — Green was all the rage a couple of billion years after the Big Bang.
Galaxies in the early universe blasted out a specific wavelength of green light, researchers reported January 7 at a meeting of the American Astronomical Society. It takes stars much hotter than most stars found in the modern universe to make that light. The finding offers a clue to what the earliest generation of stars might have been like (SN: 10/1/16, p. 25). Some nearby galaxies and nebulas produce a little bit of this hue today. But these early galaxies, seen as they were roughly 11 billion years ago, produce an overwhelming amount. “Everybody was doing it,” said Matthew Malkan, an astrophysicist at UCLA. “It seems like all galaxies started this way.”
Malkan and colleagues used the United Kingdom Infrared Telescope in Hawaii and the Spitzer Space Telescope to collect the light from over 5,000 galaxies. They found that, in all of these galaxies, one wavelength of green light — now stretched to infrared by the expansion of the universe — was twice as bright compared with light from the typical mix of stars and gas seen in galaxies today.
The green light comes from oxygen atoms that have lost two of their electrons. To knock off two electrons requires harsh ultraviolet radiation, possibly from lots of extremely hot stars — each roughly 50,000° Celsius. The sun, by comparison, is about a paltry 5,500° C at its surface.
“Stars must have been much hotter than most energetic stars familiar to us today,” said Malkan. How they got so hot — perhaps via exotic chemical abundances or just piling on lots of mass — is unsettled.
Legend has it that hundreds of years ago, a rich, powerful city stood in the jungle of what is now eastern Honduras. Then, suddenly, all of the residents vanished, and the abandoned city became a cursed place — anyone who entered risked death.
In a captivating real-life adventure tale, journalist and novelist Douglas Preston argues that the legend is not complete fiction. The Lost City of the Monkey God is his firsthand account of the expedition that uncovered the sites of at least two large cities, along with other settlements, that may form the basis of the “White City” myth. Even the curse might be rooted in reality. Stories of the White City, so named because it was supposedly built of white stone, trace back to the Spanish conquistadores of the 16th century, Preston explains. These stories enthralled filmmaker Steve Elkins, who set out in the mid-1990s to uncover the truth. Finding the ruins of an ancient culture in one of the most remote parts of Central America would require a combination of high-tech remote sensing, old-fashioned excavation and persistence.
Elkins enlisted the help of experts who used satellite images and lidar to find potential targets to explore. Lidar involves shooting laser pulses from above to sketch out the contours of a surface, even a thickly vegetated one. The resulting maps revealed outlines of human-made structures in several locations. Preston deftly explains the science behind this work and makes it exciting (being crammed into a small, rickety plane for hours on end requires its own kind of bravery). By 2015, archaeologists, accompanied by a film crew and Preston, hit the ground to investigate. They weren’t disappointed. The team uncovered an earthen pyramid, other large mounds, a plaza, terraces, canals, hundreds of ornate sculptures and vessels, and more. These discoveries are providing clues to the identity of the people who lived there and what happened to them. What’s clear is that they belonged to a culture distinct from their Maya neighbors. This culture probably prospered for several hundred years, perhaps longer, before vanishing around 1500. Drawing on historical evidence, Preston argues that disease brought by Europeans was the culture’s downfall. A series of epidemics, perhaps smallpox, may have prompted people to desert the area, inspiring the myth’s curse. The expedition did not escape this curse. Preston and others brought back a parasitic infection known as leishmaniasis. Preston devotes the last quarter of the book to detailing his and others’ struggle to deal with this potentially fatal disease.
The Lost City of the Monkey God is at its best when Preston recounts his time in the field. He presents an unglorified look at doing fieldwork in a rainforest, contending with poisonous snakes, hordes of biting pests and relentless rain and mud. He also offers a window into the politics of science, offering a frank appraisal of the criticism and skepticism this unconventional expedition (paid for by a filmmaker) faced.
Much of the book is a thrill to read, but by the end, it takes a more somber tone. The “White City” faces threats of looting and logging. And researchers who go there risk contracting disease. Some readers may wonder whether the discovery was worth it. Perhaps some mysteries are better left unsolved.
