Chapter 15. Emotions, Aggression, and Stress
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By Karl Gruber Five lionesses in Botswana have grown a mane and are showing male-like behaviours. One is even roaring and mounting other females. Male lions are distinguished by their mane, which they use to attract females, and they roar to protect their territory or call upon members of their pride. Females lack a mane and are not as vocal. . New Scientist Live: Book tickets to our festival of ideas and discovery – 22 to 25 September in London But sometimes lionesses grow a mane and even behave a bit like males. However, until now, reports of such maned lionesses have been extremely rare and largely anecdotal. We knew they existed, but little about how they behave. Now, Geoffrey D. Gilfillan at the University of Sussex in Falmer, UK, and colleagues have reported five lionesses sporting a mane at the Moremi Game Reserve in Botswana’s Okavango delta. Gilfillan started studying these lionesses back in March 2014, and for the next two years he focused on recording the behaviour of one of them, called SaF05. She had an underdeveloped mane and was larger than most females. “While SaF05 is mostly female in her behaviour – staying with the pride, mating males – she also has some male behaviours, such as increased scent-marking and roaring, as well as mounting other females,” says Gilfillan. © Copyright Reed Business Information Ltd.
Nicola Davis Tyrannosaur, Breaking the Waves and Schindler’s List might make you reach for the tissues, but psychologists say they have found a reason why traumatic films are so appealing. Researchers at Oxford University say that watching traumatic films boosts feelings of group bonding, as well as increasing pain tolerance by upping levels of feel-good, pain-killing chemicals produced in the brain. “The argument here is that actually, maybe the emotional wringing you get from tragedy triggers the endorphin system,” said Robin Dunbar, a co-author of the study and professor of evolutionary psychology at the University of Oxford. Previous research has found that laughing together, dancing together and working in a team can increase social bonding and heighten pain tolerance through an endorphin boost. “All of those things, including singing and dancing and jogging and laughter, all produce an endorphin kick for the same reason - they are putting the musculature of the body under stress,” said Dunbar. Being harrowed, he adds, could have a similar effect. “It has turned out that the same areas in the brain that deal with physical pain also handle psychological pain,” said Dunbar. Writing in the journal Royal Society Open Science, Dunbar and colleagues describe how they set out to unpick whether our love of storytelling, a device used to share knowledge and cultivate a sense of identity within a group, is underpinned by an endorphin-related bonding mechanism. © 2016 Guardian News and Media Limited
Richard J. McNally The welcoming letter to the class of 2020 in which Jay Ellison, a dean at the University of Chicago, told incoming students not to expect trigger warnings on campus struck a nerve in a highly polarized debate that is embroiling academia. Trigger warnings are countertherapeutic because they encourage avoidance of reminders of trauma, and avoidance maintains P.T.S.D. Trigger warnings, critics claim, imperil academic freedom and further infantilize a cohort of young people accustomed to coddling by their helicopter parents. Proponents of trigger warnings point out that many students have suffered trauma, exemplified by alarming rates of sexual assault on campus. Accordingly, they urge professors to warn students about potentially upsetting course materials and to exempt distressed students from classes covering topics likely to trigger post-traumatic stress disorder, or P.T.S.D., symptoms, such as flashbacks, nightmares and intrusive thoughts about one’s personal trauma. Proponents of trigger warnings are deeply concerned about the emotional well-being of students, especially those with trauma histories. Yet lost in the debate are two key points: Trauma is common, but P.T.S.D. is rare. Epidemiological studies show that many people are exposed to trauma in their lives, and most have had transient stress symptoms. But only a minority fails to recover, thereby developing P.T.S.D. Students with P.T.S.D. are those most likely to have adverse emotional reactions to curricular material, not those with trauma histories whose acute stress responses have dissipated. However, trigger warnings are countertherapeutic because they encourage avoidance of reminders of trauma, and avoidance maintains P.T.S.D. Severe emotional reactions triggered by course material are a signal that students need to prioritize their mental health and obtain evidence-based, cognitive-behavioral therapies that will help them overcome P.T.S.D. These therapies involve gradual, systematic exposure to traumatic memories until their capacity to trigger distress diminishes. © 2015 The New York Times Company
By Jessica Hamzelou After experiencing post-traumatic stress disorder after being raped, Karestan Koenen made it her career to study the condition. Now at Harvard University, Koenen is leading the largest ever genetic study of PTSD, by sifting through the genomes of tens of thousands of people (see Why women are more at risk of PTSD – and how to prevent it”). She tells New Scientist how her experiences shaped her career What was your idea of PTSD before you experienced it yourself? I would have associated it with men who served in the military – the stereotype of a Vietnam veteran who has experienced really horrible combat, and comes back and has nightmares about it. Do you think that is how PTSD is perceived by the public generally? Yes. People know that PTSD is related to trauma, and that people can have flashbacks and nightmares. But they tend to think it is associated with combat. A lot of popular images of PTSD come from war movies, and people tend to associate being a soldier with being a man. They are less aware that most PTSD is related to things that happen to civilians – things like rape, sexual assault and violence, which can affect women more than men. Is this misperception of PTSD problematic? It’s a problem in the sense that women or men who have PTSD from non-combat experiences might not recognise what they have as PTSD, and because of that, may not end up getting help. And if you saw it in a loved one, you may not understand what was going on with them. © Copyright Reed Business Information Ltd.
By NATALIE ANGIER The female bonobo apes of the Wamba forest in the Democratic Republic of Congo had just finished breakfast and were preparing for a brief nap in the treetops, bending and crisscrossing leafy branches into comfortable day beds. But one of the females was in estrus, her rump exceptionally pink and swollen, and four males in the group were too excited to sleep. They took turns wildly swinging and jumping around the fertile female and her bunkmates, shaking the branches, appearing to display their erections and perforating the air with high-pitched screams and hoots. Suddenly, three older, high-ranking female bonobos bolted up from below, a furious blur of black fur and swinging limbs and, together with the female in estrus, flew straight for the offending males. The males scattered. The females pursued them. Tree boughs bounced and cracked. Screams on all sides grew deafening. Three of the males escaped, but the females cornered and grabbed the fourth one — the resident alpha male. He was healthy, muscular and about 18 pounds heavier than any of his captors. But no matter. The females bit into him as he howled and struggled to pull free. Finally, “he dropped from the tree and ran away, and he didn’t appear again for about three weeks,” said Nahoko Tokuyama, of the Primate Research Institute at Kyoto University in Japan, who witnessed the encounter. When the male returned, he kept to himself. Dr. Tokuyama noticed that the tip of one of his toes was gone. “Being hated by females,” she said in an email interview, “is a big matter for male bonobos.” The toe-trimming incident was extreme but not unique. Describing results from their long-term field work in the September issue of Animal Behaviour, Dr. Tokuyama and her colleague Takeshi Furuichi reported that the female bonobos of Wamba often banded together to fend off male aggression, and in patterns that defied the standard primate rule book. © 2016 The New York Times Company
By Daniel Engber In the spring of 2013, a 63-year-old social psychologist in Wurzburg, Germany, made a bold suggestion in a private email chain. For months, several dozen of his colleagues had been squabbling over how to double-check the scientific literature on “social priming,” the idea that even very subtle cues—the height of a chair, the temperature of a cup of coffee, the color of a printed word—can influence someone’s behavior or judgment. Now the skeptics in the group wanted volunteers: Who among the priming experts and believers would help them with a large-scale replication effort, in which a major finding would be tested in many different labs at once? Who—if anyone—would agree to put his research to this daunting test? The experts were reluctant to step forward. In recent months their field had fallen into scandal and uncertainty: An influential scholar had been outed as a fraud; certain bedrock studies—even so-called “instant classics”—had seemed to shrivel under scrutiny. But the rigidity of the replication process felt a bit like bullying. After all, their work on social priming was delicate by definition: It relied on lab manipulations that had been precisely calibrated to elicit tiny changes in behavior. Even slight adjustments to their setups, or small mistakes made by those with less experience, could set the data all askew. So let’s say another lab—or several other labs—tried and failed to copy their experiments. What would that really prove? Would it lead anyone to change their minds about the science?
Link ID: 22609 - Posted: 08.29.2016
James Hamblin Like The Atlantic? Subscribe to the Daily, our free weekday email newsletter. Elite tennis players have an uncanny ability to clear their heads after making errors. They constantly move on and start fresh for the next point. They can’t afford to dwell on mistakes. Peter Strick is not a professional tennis player. He’s a distinguished professor and chair of the department of neurobiology at the University of Pittsburgh Brain Institute. He’s the sort of person to dwell on mistakes, however small. “My kids would tell me, dad, you ought to take up pilates. Do some yoga,” he said. “But I’d say, as far as I’m concerned, there's no scientific evidence that this is going to help me.” Still, the meticulous skeptic espoused more of a tennis approach to dealing with stressful situations: Just teach yourself to move on. Of course there is evidence that ties practicing yoga to good health, but not the sort that convinced Strick. Studies show correlations between the two, but he needed a physiological mechanism to explain the relationship. Vague conjecture that yoga “decreases stress” wasn’t sufficient. How? Simply by distracting the mind? The stress response in humans is facilitated by the adrenal glands, which sit on top of our kidneys and spit adrenaline into our blood whenever we’re in need of fight or flight. That stress response is crucial in dire circumstances. But little of modern life truly requires it (especially among academic scientists). Most of the time, our stress responses are operating as a sort of background hum, keeping us on edge. Turn that off, and we relax. © 2016 by The Atlantic Monthly Group
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Are you a giver or a taker? Brain scans have identified a region of the cerebral cortex responsible for generosity – and some of us are kinder than others. The area was identified using a computer game that linked different symbols to cash prizes that either went to the player, or one of the study’s other participants. The volunteers readily learned to score prizes that helped other people, but they tended to learn how to benefit themselves more quickly. Read more: The kindness paradox: Why be generous? MRI scanning revealed that one particular brain area – the subgenual anterior cingulate cortex – seemed to be active when participants chose to be generous, prioritising benefits for someone else over getting rewards for themselves. But Patricia Lockwood, at the University of Oxford, and her team found that this brain area was not equally active in every volunteer. People who rated themselves as having higher levels of empathy learned to benefit others faster, and these people had more activity in this particular brain area, says Lockwood. This finding may lead to new ways to identify and understand anti-social and psychopathic behavior. Journal reference: PNAS, DOI: 10.1073/pnas.1603198113 © Copyright Reed Business Information Ltd.
In a global study of myasthenia gravis, an autoimmune disease that causes muscle weakness and fatigue, researchers found that surgical removal of an organ called the thymus reduced patients’ weakness, and their need for immunosuppressive drugs. The study, published in the New England Journal of Medicine, was partially funded by the National Institutes of Health. “Our results support the idea that thymectomy is a valid treatment option for a major form of myasthenia gravis,” said Gil Wolfe, M.D., Professor and Irvin and Rosemary Smith Chair of Neurology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, New York, and a leader of the study. The Thymectomy Trial in Non-Thymomatous Myasthenia Gravis Patients Receiving Prednisone (MGTX) was a randomized, controlled study conducted on 126 patients aged 18-65 between 2006 and 2012. The researchers compared the combination of surgery and immunosuppression with the drug prednisone with prednisone treatment alone. They performed extended transternal thymectomies on 57 patients. This major surgical procedure aims to remove most of the thymus, which requires opening of a patient’s chest. On average the researchers found that the combination of surgery and prednisone treatment reduced overall muscle weakness more than prednisone treatment alone. After 36 months of prednisone treatment, both groups of patients had better QMG scores, a measure of muscle strength. Scores for the patients who had thymectomies and prednisone were 2.84 points better than patients who were on prednisone alone.
By Effy Redman “There is no one who has not smiled at least once,” writes Marianne LaFrance, a Yale University psychology professor, in her 2011 book “Lip Service: Smiles in Life, Death, Trust, Lies, Work, Memory, Sex and Politics.” Her book explores how smiling unifies us. Like breath, the smile is universal. We smile to connect, to forgive, to love. A smile is beauty, human. But I have never smiled. Not once. I was born with Moebius syndrome — a rare form of facial paralysis that results from damage in the womb to the sixth and seventh cranial nerves, which control the muscles of the face. I was born in Britain, on the same day in 1982 the country’s first test-tube twins were born. But while science has created medical miracles like test-tube babies, there’s little that doctors can do for someone with Moebius syndrome. Decades later, I still cannot smile. Or frown. Or do any of the infinite subtle and not-so-subtle things with my face that I see others in the world around me doing every day. Doctors describe people with Moebius as having a “mask-like expression.” And that is what strangers must see. A frozen face, eyes unblinking. My mouth always open, motionless, the left corner of my lips slightly lower than the right. Walking down the street, I can feel the touch of casual observers’ eyes. A child’s very first “social smile” usually occurs six to eight weeks after birth, eagerly awaited by new parents. Because, as an infant, my face remained so expressionless, when I began laughing it took my mother a while to realize that the sound I was making was laughter. At what point, I wonder, did I begin to compensate for the absence of my smile. © 2016 The New York Times Company
Link ID: 22542 - Posted: 08.11.2016
By TATIANA SCHLOSSBERG Need a laugh? Get online and take a look at videos of baby Japanese macaques smiling as they sleep. Their faces twitch, usually just on one side and for less than a second. A lip curls, a nose wrinkles — as if they were hairy, wry elves. Newborn Japanese macaques -- like humans and chimpanzees -- were found to make facial expressions called "spontaneous smiles." Watch the full video. Credit Kyoto University Primate Research Institute Maybe you don’t laugh, maybe you just smile back — O.K., fine. But you may owe that smile to the human version of this infant’s facial spasm. Some scientists suspect spontaneous smiles in these monkeys echo the development of our own expressions. Scientists from the Primate Research Institute at Kyoto University in Japan have observed these spontaneous smiles in Japanese macaques for the first time, according to a new study published in the journal Primates. Spontaneous smiles have previously been observed in infant humans and chimpanzees, but this is the first time they have been seen in another primate species. The scientists watched seven macaque monkeys for an average of 44 minutes, during which the monkeys happened to fall asleep. During REM sleep, each of the monkeys spontaneously smiled at least once, for a little less than a second on average. All told, the seven monkeys smiled 58 times, mostly on the left side of their faces. Human and macaque infants alike primarily smile on one side of their faces. But after two months, human babies begin to smile bilaterally. Around the same time, they also begin to offer up “social smiles,” indicating to others a feeling of happiness. According to the study, scientists think that the earliest spontaneous smiles are key to the development of the zygomaticus major muscle, which is responsible for moving your lips up or to the side, allowing you to smile, among other things. Spontaneous smiles in these monkeys echo the development of our own expressions. Watch the full video.
Seth Stephens-Davidowitz Feeling worried? These days, much of America is. Over the past eight years, Google search rates for anxiety have more than doubled. They are higher this year than they have been in any year since Google searches were first tracked in 2004. So far, 2016 has been tops for searches for driving anxiety, travel anxiety, separation anxiety, anxiety at work, anxiety at school and anxiety at home. Americans have also become increasingly terrified of the morning. Searches for “anxiety in the morning” have risen threefold over the past decade. But this is nothing compared with the fear of night. Searches for “anxiety at night” have risen ninefold. For years, I have confidently pontificated on topics that I think are important but that I have little experience of — child abuse, racism, sexism, sex. Now I am ready to tackle a topic I actually know something about. Over the past few weeks, I’ve taken a break from worrying about my own anxiety to studying our country’s. While I am not sure I totally nailed down why anxiety seems to have risen so much during the Obama era, I did learn a lot. The places where anxiety is highest are not where I would have expected. When I was growing up, if you had asked me which people were the most anxious, I would have said New York Jews. And a decade of interacting with our country’s urban intelligentsia, Jewish and otherwise, has confirmed that pretty much all of us are a neurotic mess. © 2016 The New York Times Company
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By PHYLLIS KORKKI Ever experienced a bout of anxiety at work? I just did. One day last week I had several assignments to finish in quick succession. I could feel thoughts pinging around in my brain as I tried and failed to decide what to focus on first. Once I was able to get the pandemonium under control, my brain felt like mush. So what did I do? I breathed deeply from the middle of my body. I imagined the top of my head, and pictured arrows coming out the sides of my shoulders. I stood up for a while and then walked around the newsroom. And went back to work. These simple solutions to anxiety are not so easy to practice in an era of multitasking, multiple screens and mindless distractions. I learned them only after signing a contract to write a book — and becoming so anxious about it that I developed back and stomach pains. Unable to score a prescription for Klonopin (it’s addictive, my doctor said), I was reduced to seeking out natural methods to relieve my anxiety. The methods I learned helped me write the book. But they also made me realize that workers of all stripes could use them to reduce stress, and to think more clearly and creatively. My first stop was Belisa Vranich, a clinical psychologist who teaches — or rather reteaches — people how to breathe. Dimly I sensed that the way I was inhaling and exhaling was out of whack, and she confirmed it by giving me some tests. First off, like most people, I was a “vertical” breather, meaning my shoulders moved upward when I inhaled. Second, I was breathing from my upper chest, where the lungs don’t have much presence. © 2016 The New York Times Company
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By JoAnna Klein I expected a bumpy ride on a whitewater trip, so when I fell off my raft and coughed up the water I’d inhaled, I wasn’t afraid. But at the time I didn’t know I was swimming with a deadly parasite. I’d been at a bachelorette party at the U.S. National Whitewater Center in Charlotte, N.C., but after returning home I learned that I had shared the churning rapids with Naegleria fowleri, a single-celled amoeba found mostly in soil and warm freshwater lakes, rivers and hot springs. An Ohio teenager had contracted the amoeba infection after visiting the center around the same time I did, and some of the waters and sediment at and around the center had tested positive for the bug. News that my friends and I had all been at risk of exposure triggered a few days of worry. The illness is rare and, if infected, symptoms show up between one and 10 days after exposure. Chances were that we were fine (we were), but the experience prompted me to learn more about the parasite. Naegleria fowleri lives in fresh water, but not in salt water. If forced up the nose, it can enter the brain and feed on its tissue, resulting in an infection known as primary amebic meningoencephalitis. Death occurs in nearly all of those infected with the parasite, usually within five days after infection. The 18-year-old Ohio woman who died most likely contracted the parasite when she sucked water through her nose after falling from a raft during a church trip. Samples from a channel at the rafting center, collected by the Centers for Disease Control and Prevention, tested positive for the bug. The center’s channels are man-made, and it gets its water from the Charlotte-Mecklenburg Utilities Department and two wells on its property. The center has announced that it disinfects all water with ultraviolet radiation and chlorine, and it added more after the water tests. © 2016 The New York Times Company
Link ID: 22514 - Posted: 08.04.2016
By Colby Itkowitz On any given day people face any number of minor annoyances such as being stuck in traffic or spilling coffee on their shirts or forgetting their keys. Then there’s the persistent stressors that come from work, relationships and finances. And there’s the uncontrollable anxieties of global terrorism, mass shootings and Zika-carrying mosquitoes. But why are some people able to deal with it all so calmly, while others freak out? A team of researchers at Yale University may have found the answer in the brain. The scientists studied the brains of 30 adult volunteers with no history of mental or physical health issues as they watched a slideshow of gruesome and terrifying images for six minutes. To compare brain activity, they then showed the participants benign images that would evoke little emotion, such as a photo of a chair. They located three areas of the brain that responded to the stress of seeing photos of people mutilated or at gunpoint or in other harrowing scenarios. But what the researchers found most interesting was how the ventromedial prefrontal cortex (vmPFC), which processes risk and emotional response, adapted while viewing the photos. In everyone, activity in that region decreased initially in response to the images, as though their guard was down, but then in some people, it became hyperactive, as if working overtime to control the emotional response, or in other words, to cope. “We have not had a way of breaking that apart to see what the brain is doing,” said Rajita Sinha, director of the Yale Stress Center and lead author of the study. “How do we cope in the moment? Here, we said, in the moment under acute threat how does the brain cope and regain control?” © 1996-2016 The Washington Post
Link ID: 22506 - Posted: 08.03.2016
By Tanya Lewis The tangled buildup of tau protein in brain cells is a hallmark of the cognitive decline linked with Alzheimer’s disease. Antibodies have been shown to block tau’s spread, but some scientists worry it could also fuel inflammation. Now, researchers from Genentech in San Francisco and colleagues have found that an antibody’s ability to recruit immune cells—known as its effector function—is not necessary for stopping tau’s spread, the team reported today (July 28) in Cell Reports. “Our results suggest that, given that effector function is not required for efficacy [in treating tau accumulation], going without it could offer a safer approach for immunotherapy,” study coauthor Gai Ayalon of Genentech told The Scientist. Alzheimer’s disease causes a characteristic constellation of pathologies: accumulation of amyloid-β plaques outside neurons, neurofibrillary tangles of tau inside brain cells, and chronic inflammation. Clinical research has mostly focused on targeting amyloid-β with antibody therapies, and several treatments based on this approach are currently in clinical trials. But recent efforts have zeroed in on tau as a new potential target. Antibodies are known to spur the brain’s defense system, microglia, to absorb and degrade tau, but their recruitment of immune cells may also worsen inflammation. Ayalon and colleagues wondered whether effector function was necessary for stopping tau’s spread. © 1986-2016 The Scientist
Research supported by the National Institutes of Health has identified brain patterns in humans that appear to underlie “resilient coping,” the healthy emotional and behavioral responses to stress that help some people handle stressful situations better than others. People encounter stressful situations and stimuli everywhere, every day, and studies have shown that long-term stress can contribute to a broad array of health problems. However, some people cope with stress better than others, and scientists have long wondered why. The new study, by a team of researchers at Yale University, New Haven, Connecticut, is now online in the Proceedings of the National Academy of Sciences. “This important finding points to specific brain adaptations that predict resilient responses to stress,” said George F. Koob, Ph.D., director of the National Institute on Alcohol Abuse and Alcoholism (NIAAA), part of NIH and a supporter of the study. “The findings also indicate that we might be able to predict maladaptive stress responses that contribute to excessive drinking, anger, and other unhealthy reactions to stress.” In a study of human volunteers, scientists led by Rajita Sinha, Ph.D., and Dongju Seo, Ph.D., used a brain scanning technique called functional magnetic resonance imaging (fMRI) to measure localized changes in brain activation during stress. Study participants were given fMRI scans while exposed to highly threatening, violent and stressful images followed by neutral, non-stressful images for six minutes each. While conducting the scans, researchers also measured non-brain indicators of stress among study participants, such as heart rate, and levels of cortisol, a stress hormone, in blood. The brain scans revealed a sequence of three distinct patterns of response to stress, compared to non-stress exposure.
By Diana Kwon Few things feel worse than not knowing when your next paycheck is coming. Economic insecurity has been shown to have a whole host of negative effects, including low self-esteem and impaired cognitive functioning. It turns out financial stress can also physically hurt, according to a paper published in February in Psychological Science. Eileen Chou, a public policy professor at the University of Virginia, and her collaborators began by analyzing a data set of 33,720 U.S. households and found that those with higher levels of unemployment were more likely to purchase over-the-counter painkillers. Then, using a series of experiments, the team discovered that simply thinking about the prospect of financial insecurity was enough to increase pain. For example, people reported feeling almost double the amount of physical pain in their body after recalling a financially unstable time in their life as compared with those who thought about a secure period. In another experiment, university students who were primed to feel anxious about future employment prospects removed their hand from an ice bucket more quickly (showing less pain tolerance) than those who were not. The researchers also found that economic insecurity reduced people's sense of control, which, in turn, increased feelings of pain. Chou and her colleagues suggest that because of this link between financial insecurity and decreased pain tolerance, the recent recession may have been a factor in fueling the prescription painkiller epidemic. Other experts are cautious about taking the findings that far. “I think the hypothesis [that financial stress causes pain] has a lot of merit, but it would be helpful to see additional rigorous evidence in a real-world environment,” says Heather Schofield, an economist at the University of Pennsylvania who was not involved in the study. © 2016 Scientific American,
Ramin Skibba Is Justin Bieber a musical genius or a talentless hack? What you 'belieb' depends on your cultural experiences. Some people like to listen to the Beatles, while others prefer Gregorian chants. When it comes to music, scientists find that nurture can trump nature. Musical preferences seem to be mainly shaped by a person’s cultural upbringing and experiences rather than biological factors, according to a study published on 13 July in Nature1. “Our results show that there is a profound cultural difference” in the way people respond to consonant and dissonant sounds, says Josh McDermott, a cognitive scientist at the Massachusetts Institute of Technology in Cambridge and lead author of the paper. This suggests that other cultures hear the world differently, he adds. The study is one of the first to put an age-old argument to the test. Some scientists believe that the way people respond to music has a biological basis, because pitches that people often like have particular interval ratios. They argue that this would trump any cultural shaping of musical preferences, effectively making them a universal phenomenon. Ethnomusicologists and music composers, by contrast, think that such preferences are more a product of one’s culture. If a person’s upbringing shapes their preferences, then they are not a universal phenomenon. © 2016 Macmillan Publishers Limited
By Virginia Morell Infanticide—the killing of offspring—is generally rare among birds. And when it happens, it’s usually because of outsiders that want the nesting site or territory. But what happens among birds, such as the greater ani (Crotophaga major, pictured), which have a more socialist approach to nesting? Two to four pairs of the Central and South American cuckoos (which are usually unrelated) build a single nest, and then work together to raise their chicks, which generally hatch at the same time. Intriguingly, the adults cannot recognize either their own eggs or chicks, so they care for all of them. To find out why—and if the simultaneous hatching protects the chicks from infanticide—a scientist analyzed data on nestling mortality gathered at 104 communal greater ani nests from 2006 to 2015. Of the 741 nestlings, 321 (43%) fledged and 420 (57%) died. Most of the deaths (78.5%) were due to predation. But another 13.8%, or 58 nestlings, died from infanticide, the scientist reports online today in Evolution. The remaining 32 (7.7%) died from starvation. At most of the nests, the chicks hatched within 1 day of each other. Those that first emerged from their eggs were the most likely to be dispatched by one of the nest founders, not an outsider. Chicks that hatched last were also unlucky; weaker than their older and larger nest-mates, they weren’t able to compete for food and starved. Those two pressures—infanticide and food competition—end up favoring the chicks in the middle and those that hatch on the same day, the researcher reports. © 2016 American Association for the Advancement of Science