Chapter 9. Hearing, Vestibular Perception, Taste, and Smell
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Bats can understand the emotional state of other bats from the intonations of their calls, a new study suggests. In the lab, researchers observed greater false vampire bats (Megaderma lyra, pictured) that had been trained to wait for food on a perch. In some tests, they played “aggression calls” over a speaker, typically made by a bat defending its place on a perch from an approaching bat. In other trials, the researchers played “appeasement calls” often made by a bat approaching one already ensconced on a perch and thus seeking to share its space. (Bats were tested individually, and the use of recorded calls ensured that the bats were responding to the content of the call and not visual cues from another bat.) In all tests, the scientists played a call once every 20 seconds until the bats began to ignore the call (by not turning toward the speaker), and then they played a slightly different version of the same call—one that was either more urgent (with shorter, more closely spaced syllables) or less urgent. The novel aggression calls always caused a bat to turn toward the speaker, but the novel appeasement calls only drew a response when they became more urgent, the researchers report online today in Frontiers of Zoology. The failure of a bat to react to weakening appeasement calls suggests that the bats can interpret the emotional content of the calls—a sign that such perception might exist more widely in mammals than previously thought. © 2013 American Association for the Advancement of Science.
Associated Press The U.S. Navy plans to increase sonar testing over the next five years, even as research it funded reveals worrying signs that the loud underwater noise could disturb whales and dolphins. Reported mass strandings of whale species have increased worldwide since the military started using sonar half a century ago. Scientists think the sounds scare animals into shallow waters where they can become disoriented and wash ashore, but technology capable of close monitoring has emerged only in the past decade. Aside from strandings, biologists are concerned marine mammals could suffer prolonged stress from changes in diving, feeding and communication. Two studies off the Southern California coast found certain endangered blue whales and beaked whales stopped feeding and fled from recordings of sounds similar to military sonar. Beaked whales are highly sensitive to sound and account for the majority of beachings near military exercises. Scientists, however, were surprised by the reaction of blue whales - the world's largest animal - long thought to be immune to the high-pitched sounds. It's unclear how the change in behavior would affect the overall population, estimated at between 5,000 and 12,000 animals. The studies involved only a small group of tagged whales, and noise levels were less intense than what's used by the Navy. Shy species - such as the Cuvier's beaked whale, which can dive 3,000 feet below the surface - have taken years to find and monitor. "This is a warning flag and deserves more research," said Stanford University biologist Jeremy Goldbogen, who led the blue whale study published this summer in the journal Proceedings of the Royal Society B. © 2013 Hearst Communications, Inc.
Brian Owens Fruitflies know exactly how much alcohol will be good for their young. Larvae living on a food source with the right concentration of ethanol will grow into heavy, healthy adults and will be protected against parasites — which explains why the insects are attracted to rotting fruit or the crate of empty beer bottles in your kitchen but not to the vodka or gin. Now researchers have uncovered the neural mechanism that allows the fruitfly Drosophila melanogaster to choose the best place to lay its eggs. The work is published today in Proceedings of the National Academy of Sciences1. A team led by Ulrike Heberlein, a molecular biologist at the Howard Hughes Medical Institute’s Janelia Farm Research Campus in Ashburn, Virginia, found that clusters of neurons, working in opposition to each other, help the flies to choose the place with the most beneficial concentration of ethanol in which to lay their eggs. The neurons all release the neurotransmitter dopamine, a key player in the brain's reward circuitry. Neurons of the PAM and PPM3 clusters encourage the flies to seek out ethanol, whereas PPL1 neurons apply the brakes, preventing the flies from laying their eggs on food containing high levels of ethanol that could harm the larvae. “They can discriminate among ethanol concentrations that are very similar — 3% versus 5% — so the system evolved to have great sensitivity,” says Heberlein. Their favourite booze strength is 5%, similar to that of a typical beer. Heberlein's team also traced the neurons involved in ethanol preference to specific brain regions. Both the pro-ethanol PAM and anti-ethanol PPL1 neurons were active in the mushroom body, whereas the pro-ethanol PPM3 ones were active in the ellipsoid body. Both of these brain structures are involved in decision-making and memory, and mushroom body neurons also play a part in ethanol-reward memory. © 2013 Nature Publishing Group,
Keyword: Chemical Senses (Smell & Taste)
Link ID: 19013 - Posted: 12.10.2013
By Julia Calderone As we sat in my car outside a silent movie theater in Los Angeles, my friend anxiously opened a plastic bag containing a white T-shirt she’d slept in for the past three nights. “Does it smell like me?” she asked nervously, gesturing the open end toward my face. I stuck my nose into the bag and inhaled. We were about to attend a pheromone-based speed dating party with the following rules: 1. Find a clean white T-shirt. 2. Sleep in only that shirt for three consecutive nights. 3. Bring the shirt to the party sealed in a bag. As we walked into the theater, coordinators assigned each of our bags a unique color-coded sticker (pink for female, blue for male), and tossed them into a pile. A pack of hipsters nursing PBRs sat in the wooden theater seats, slightly amused by the bizarre 70s Egyptian-themed silent porn projected onto the screen. In the courtyard, 20-somethings mingled by the outdoor bar. Did they think alcohol would make us okay with sniffing strangers’ dirty laundry? Mounds of bags sat on two long tables – beckoning our nostrils. We were instructed to sniff as many T-shirts of the sex we were attracted to, and select shirts that innately smelled the sexiest. I came across bag number 166, which shockingly smelled exactly like my grandmother’s house – a delightful mix of Christmas and chicken parmesan. The point was to trust our instincts, right? I went with it. © 2013 Scientific American
By NICHOLAS BAKALAR A high body mass and a large waist are both associated with self-reported hearing loss, a new study has found. Researchers used data from a 20-year prospective study of 68,421 women who were25 to 42 years old at the start. After controlling for age, smoking, diabetes, hypertension and other factors, they found that the higher the body mass index, the greater the risk for hearing loss. Compared with women with a B.M.I. under 25, those with an index of 25 to 29 had an 8 percent increased risk. The numbers kept going up in tandem: 11 percent for 30 to 34, 16 percent for 35 to 39 and 19 percent for those above 40. The increasing risk associated with larger waist circumference followed a similar pattern. The study, published in the December issue of The American Journal of Medicine, found that moderate physical activity — as little as four hours of walking a week — also reduced the risk for hearing loss. Researchers found no further advantage in more vigorous exercise. The lead author, Dr. Sharon G. Curhan, a clinical researcher at Brigham and Women’s Hospital in Boston, suggested that obesity might compromise blood flow to the inner ear, and that exercise might improve it, which could explain the associations. “Hearing loss may not be an inevitable part of growing older,” she said. “There may be things we can do to prevent it.” Copyright 2013 The New York Times Company
By JOYCE COHEN Earlier this fall, Seattle Seahawks fans at CenturyLink Field broke the world record for loudest stadium crowd with a skull-splitting 136.6 decibels. That volume, as the Seahawks’ website boasts, hits the scale somewhere between “serious hearing damage” and “eardrum rupture.” Just weeks later, Kansas City Chiefs fans at Arrowhead Stadium topped that number with 137.5 screaming decibels of their own. The measuring method used for the Guinness World Record has an edge of gimmickry. That A-weighted peak measurement, reached for a split second near the measuring device, displays the highest possible readout. For a vulnerable ear, however, game-day noise isn’t just harmless fun. With peaks and troughs, the decibel level of noise reaching a typical spectator averages in the mid-90s, but for a longer time. Such noise is enough to cause permanent damage and to increase the likelihood of future damage. “The extent to which hearing-related issues get so little attention is amazing and troubling,” said M. Charles Liberman, a professor of otology at Harvard Medical School and director of a hearing research lab at the Massachusetts Eye and Ear Infirmary. “Many people are damaging their ears with repeated noise exposure such that their hearing abilities will significantly diminish as they age, much more so than if they were more careful,” he said. Ears are deceptive. Even if they seem to recover from the muffling, ringing and fullness after a rousing game, they don’t really recover. It’s not just the tiny sensory cells in the cochlea that are damaged by noise, Dr. Liberman said, but also the nerve fibers between the ears and the brain that degrade over time. Copyright 2013 The New York Times Company
Link ID: 18950 - Posted: 11.21.2013
Female mice that compete in promiscuous environments have sexier smelling sons, research has found. Scientists in Utah, US, studied the pheromones produced in the urine of male mice. They found that those whose mothers competed for mates were more sexually attractive to females. But this success was short-lived: their life spans were shorter than mice with monogamous parents. Adam Nelson from the University of Utah completed the study alongside senior author Prof Wayne Potts. It is published in the journal Proceedings of the National Academy of Sciences. "Only recently have we started to understand that environmental conditions experienced by parents can influence the characteristics of their offspring. This study is one of the first to show this kind of 'epigenetic' process working in a way that increases the mating success of sons," said Prof Potts. Epigenetics is the study of how differences in a parent's environment can influence how its offspring's genes are expressed. The researchers studied domestic mice which are usually paired in a cage and therefore breed with only one partner. To reintroduce the social competition wild mice experience, lab mice were kept in "mouse barns" which were large enclosures divided by mesh to create territories. The mice were able to climb over the mesh to access nest boxes, feeding stations and drinking water. BBC © 2013
by Erika Engelhaupt When I was in graduate school, I once gassed out my lab with the smell of death. I was studying the products of plant decomposition, and I had placed copious quantities of duckweed into large tubs and let the mix decompose for a few weeks. Duckweed is a small floating aquatic plant; it looks harmless enough. But when I dragged my tubs into the lab and set up a pump and filtration system, all hell broke loose. The filter clogged, the back pressure threw the hose off the pump, and a spray of decomposed mess flew all over a poor professor who had come in to help. For the rest of the day, he smelled like a pile of dead raccoons. That day, I learned about cadaverine and putrescine. These two molecules are produced during the decomposition of proteins, when the amino acids lysine and ornithine break down, and they are largely responsible for the smell of rotting flesh. My mistake in the lab was to think that rotting plants are more innocuous than rotting animals. Duckweed, it turns out, has such high protein levels that it’s used as animal feed, and those proteins, like any proteins, can create a deathly stench. The smells of cadaverine and putrescine tend to provoke a strong reaction (as I learned once the duckweed stench subsided and my labmates were able to return to the lab). But not every animal finds the odors disgusting. Carrion flies, rats and other animals that eat or lay eggs in dead things are attracted to the molecules. So researchers have started to look for exactly how animals tune in to these smells. Pinning down animals' odor detectors gives researchers a way to study aversion or attraction to certain objects. And understanding how these behavioral responses work will, I believe, help researchers clarify why humans feel the distinct emotion known as disgust. © Society for Science & the Public 2000 - 2013.
by Colin Barras IT'S musical mind-reading. Your patterns of brain activity can show what song you are listening to. In the area of the brain that processes sound – the auditory cortex – different neurons become active in response to different sound frequencies. So it should be possible to work out which musical note someone is listening to just by looking at this activity, says Geoff Boynton at the University of Washington in Seattle. To find out, Boynton and his colleague Jessica Thomas had four volunteers listen to various notes, while they used fMRI to record the resulting neural activity. "Then the game is to play a song and use the neural activity to guess what was played," he says. They were able to identify melodies like Twinkle, Twinkle, Little Star from neural activity alone, Boynton told the Society for Neuroscience annual meeting in San Diego, California, this week. The results could help probe the neural roots of people who are tone deaf. This can be a problem for people with cochlear implants, says Rebecca Schaefer, who researches neuroscience and music at the University of California in Santa Barbara. Another study into the music of the mind, also presented this week in San Diego, suggests that the brain is highly attuned to rhythm and this might explain why we talk at certain speeds. David Poeppel at New York University and his colleagues monitored brain activity in 12 volunteers while they listened to three piano sonatas. One sonata had a quick tempo, with around eight notes per second, one had five per second, and the slowest had one note every 2 seconds. © Copyright Reed Business Information Ltd.
by Jennifer Viegas Music skills evolved at least 30 million years ago in the common ancestor of humans and monkeys, according to a new study that could help explain why chimpanzees drum on tree roots and monkey calls sound like singing. The study, published in the latest issue of Biology Letters, also suggests an answer to this chicken-and-egg question: Which came first, language or music? The answer appears to be music. "Musical behaviors would constitute a first step towards phonological patterning, and therefore language," lead author Andrea Ravignani told Discovery News. For the study, Ravignani, a doctoral candidate at the University of Vienna's Department of Cognitive Biology, and his colleagues focused on an ability known as "dependency detection." This has to do with recognizing relationships between syllables, words and musical notes. For example, once we hear a certain pattern like Do-Re-Mi, we listen for it again. Hearing something like Do-Re-Fa sounds wrong because it violates the expected pattern. Normally monkeys don't respond the same way, but this research grabbed their attention since it used sounds within their frequency ranges. In the study, squirrel monkeys sat in a sound booth and listened to a set of three novel patterns. (The researchers fed the monkeys insects between playbacks, so the monkeys quickly got to like this activity.) Whenever a pattern changed, similar to our hearing Do-Re-Fa, the monkeys stared longer, as if to say, "Huh?" © 2013 Discovery Communications, LLC.
Brian Owens The hordes of microbes that inhabit every nook and cranny of every animal are not just passive hitchhikers: they actively shape their hosts’ well-being and even behaviour. Now, researchers have found evidence that bacteria living in the scent glands of hyenas help to produce the smells that the animals use to identify group members and tell when females are ready to mate. Kevin Theis, a microbial ecologist at Michigan State University in East Lansing, had been studying hyena scent communication for several years when, after he gave a talk on the subject, someone asked him what part the bacteria might play. “I just said, ‘I don’t know’,” he says. He started investigating. He found that for 40 years, scientists had wondered whether smelly bacteria were involved in animals' chemical communication. But experiments to determine which bacteria were present had been inconclusive, because the microbes had to be grown in culture, which is not possible with all bacteria. However, next-generation genetic sequencing would enable Theis to identify the microbes in a sample without having to grow them in a dish. Using this technique, Theis and his colleagues last year published a study1 that identified more types of bacterium living in the hyenas’ scent glands than the 15 previous studies of mammal scent glands combined. In both spotted hyenas (Crocuta crocuta) and striped hyenas (Hyaena hyaena), most of the bacteria were of a kind that ferments nutrients exuded by the skin and produces odours. “The diversity of the bacteria is enough to potentially explain the origin of these signals,” says Theis. Now, they have found that the structure of the bacterial communities varied depending on the scent profiles of the sour, musky-smelling 'pastes' that the animals left on grass stalks to communicate with members of their clan. In addition, in the spotted hyenas, both the bacterial and scent profiles varied between males and females, and with the reproductive state of females — all attributes that hyenas are known to be able to infer from scent pastes. The work is published this week in Proceedings of the National Academy of Sciences. © 2013 Nature Publishing Group
By PAULA SPAN Jim Cooke blames his hearing loss on the constant roar of C-119 aircraft engines he experienced in the Air Force. He didn’t wear protective gear because, like most 20-year-olds, “you think you’re indestructible,” he said. By the time he was 45, he needed hearing aids for both ears. Still, he had a long career as a telephone company executive while he and his wife, Jean, raised two children in Broadview Heights, Ohio. Only after retirement, he told me in an interview, did he start having trouble communicating. Jean and Jim Cooke Jean and Jim Cooke Mr. Cooke had to relinquish a couple of part-time jobs he enjoyed because “I felt insecure about dealing with people on the phone,” he said. He withdrew from a church organization he led because he couldn’t grasp what members were saying at meetings. “He didn’t want to be in social situations,” Mrs. Cooke said. “It gave him a feeling of inadequacy, and anger at times.” Two years ago, when their grandchildren began saying that Granddad needed to replace his hearing aid batteries — although the batteries were fine — the Cookes went to the Cleveland Clinic, where an audiologist there, Dr. Sarah Sydlowski, told Jim that at 76, he might consider a cochlear implant. Perhaps the heart-tugging YouTube videos of deaf toddlers suddenly hearing sounds have led us to think of cochlear implants as primarily for children. Or perhaps, said Dr. Frank R. Lin, a Johns Hopkins University epidemiologist, we consider late-life hearing loss normal (which it is), “an unfortunate but inconsequential aspect of aging,” and don’t explore treatment beyond hearing aids. In any case, the idea of older adults having a complex electronic device surgically implanted has been slow to catch on, even though by far the greatest number of people with severe hearing loss are seniors. © 2013 The New York Times Company
by Laura Sanders Neonatal intensive care units are crammed full of life-saving equipment and people. The technology that fills these bustling hubs is responsible for saving the lives of fragile young babies. That technology is also responsible for quite a bit of noise. In the NICU, monitors beep, incubators whir and nurses, doctors and family members talk. This racket isn’t just annoying: NICU noise often exceeds acceptable levels set by the American Academy of Pediatrics, a 2009 analysis found. To dampen the din, many hospitals are shifting away from open wards to private rooms for preemies. Sounds like a no-brainer, right? Fragile babies get their own sanctuaries where they can recover and grow in peace. But in a surprising twist, a new study finds that this peace and quiet may actually be bad for some babies. Well aware of the noise problem in the NICU ward, Roberta Pineda of Washington University School of Medicine in St. Louis and colleagues went into their study of 136 preterm babies expecting to see benefits in babies who stayed in private rooms. Instead, the researchers found the exact opposite. By the time they left the hospital, babies who stayed in private rooms had less mature brains than those who stayed in an open ward. And two years later, babies who had stayed in private rooms performed worse on language tests. The results were not what the team expected. “It was extremely surprising,” Pineda told me. The researchers believe that the noise abatement effort made things too quiet for these babies. As distressing data from Romanian orphanages highlights, babies need stimulation to thrive. Children who grew up essentially staring at white walls with little contact from caregivers develop serious brain and behavioral problems, heartbreaking results from the Bucharest Early Intervention Project show. Hearing language early in life, even before birth, might be a crucial step in learning to talk later. And babies tucked away in private rooms might be missing out on some good stimulation. © Society for Science & the Public 2000 - 2013
Learning a musical instrument as a child gives the brain a boost that lasts long into adult life, say scientists. Adults who used to play an instrument, even if they have not done so in decades, have a faster brain response to speech sounds, research suggests. The more years of practice during childhood, the faster the brain response was, the small study found. The Journal of Neuroscience work looked at 44 people in their 50s, 60s and 70s. The volunteers listened to a synthesised speech syllable, "da", while researchers measured electrical activity in the region of the brain that processes sound information - the auditory brainstem. Despite none of the study participants having played an instrument in nearly 40 years, those who completed between four and 14 years of music training early in life had a faster response to the speech sound than those who had never been taught music. Lifelong skill Researcher Michael Kilgard, of Northwestern University, said: "Being a millisecond faster may not seem like much, but the brain is very sensitive to timing and a millisecond compounded over millions of neurons can make a real difference in the lives of older adults." As people grow older, they often experience changes in the brain that compromise hearing. For instance, the brains of older adults show a slower response to fast-changing sounds, which is important for interpreting speech. Musical training may help offset this, according to Dr Kilgard's study. BBC © 2013
On Easter Sunday in 2008, the phantom noises in Robert De Mong’s head dropped in volume -- for about 15 minutes. For the first time in months, he experienced relief, enough at least to remember what silence was like. And then they returned, fierce as ever. It was six months earlier that the 66-year-old electrical engineer first awoke to a dissonant clamor in his head. There was a howling sound, a fingernails-on-a-chalkboard sound, “brain zaps” that hurt like a headache and a high frequency "tinkle" noise, like musicians hitting triangles in an orchestra. Many have since disappeared, but two especially stubborn noises remain. One he describes as monkeys banging on symbols. Another resembles frying eggs and the hissing of high voltage power lines. He hears those sounds every moment of every day. De Mong was diagnosed in 2007 with tinnitus, a condition that causes a phantom ringing, buzzing or roaring in the ears, perceived as external noise. When the sounds first appeared, they did so as if from a void, he said. No loud noise trauma had preceded the tinnitus, as it does for some sufferers -- it was suddenly just there. And the noises haunted him, robbed him of sleep and fueled a deep depression. He lost interest in his favorite hobby: tinkering with his ‘78 Trans Am and his two Corvettes. He stopped going into work. That month, De Mong visited an ear doctor, who told him he had high frequency hearing loss in both ears. Another doctor at the Stanford Ear, Nose and Throat clinic confirmed it, and suggested hearing aids as a possibility. They helped the hearing, but did nothing for the ringing. © 1996-2013 MacNeil/Lehrer Productions.
Link ID: 18885 - Posted: 11.07.2013
by Sarah Zielinski In the United States, you’re rarely far from a road. And as you get closer to one, or other bits of human infrastructure, bird populations decline. But are the birds avoiding our cars or the noises produced by them? Noise might be a big factor, scientists have reasoned, because they’ve seen declines in bird populations near noisy natural gas compressor sites. It turns out that the sound of cars driving down a road is enough to deter many bird species from an area. Researchers from Boise State University in Idaho created a “phantom road” at a site in the Boise Foothills that is a stopover for migratory birds in the fall. They put up 15 speakers in Douglas fir trees and played recorded sounds of a road at intervals of four days — four days on, four days off. They then counted birds at three locations along their phantom road and three locations nearby where the road noises couldn’t be heard. The scientists spotted lots of birds during their study — more than 8,000 detections and 59 species. The birds they saw changed as the fall progressed, which was natural because the various species of migrating birds hit the stopover point at different times. But all that variation was good for the experiment, the researchers say, because it helped even out any fluctuations they might have seen from site to site and from noise-on to noise-off intervals, letting the researchers tease out the effects of the road noise. © Society for Science & the Public 2000 - 2013.
By Cheryl G. Murphy Is it possible that our vision can affect our taste perception? Let’s review some examples of studies that claim to have demonstrated that sometimes what we see can override what we think we taste. From wine to cheese to soft drinks and more it seems that by playing with the color palette of food one can trick our palates into thinking we taste things that aren’t necessarily there. © 2013 Scientific American
Brian Owens Bats that nest inside curled-up leaves may be getting an extra benefit from their homes: the tubular roosts act as acoustic horns, amplifying the social calls that the mammals use to keep their close-knit family groups together. South American Spix’s disc-winged bats (Thyroptera tricolor) roost in groups of five or six inside unfurling Heliconia and Calathea leaves. The leaves remain curled up for only about 24 hours, so the bats have to find new homes almost every day, and have highly specialized social calls to help groups stay together. When out flying, they emit a simple inquiry call. Bats inside leaves answer with a more complex response call to let group members know where the roost is. Gloriana Chaverri, a biologist at the University of Costa Rica in Golfito, took curled leaves into the lab and played recorded bat calls through them, to see how the acoustics were changed by the tapered tubular shape of the leaves. “The call emitted by flying bats got really amplified,” she says, “while the calls from inside the leaves were not amplified as much.” Sound system The inquiry calls from outside the roost were boosted by as much as 10 decibels as the sound waves were compressed while moving down the narrowing tube — the same thing that happens in an amplifying ear trumpet. Most response calls from inside the leaf were boosted by only 1–2 decibels, but the megaphone shape of the leaf made them highly directional. The results are published today in Proceedings of the Royal Society B1. © 2013 Nature Publishing Group
By Cat Bohannon Halos, auras, flashes of light, pins and needles running down your arms, the sudden scent of sulfur—many symptoms of a migraine have vaguely mystical qualities, and experts remain puzzled by the debilitating headaches' cause. Researchers at Harvard University, however, have come at least one step closer to figuring out why women are twice as likely to suffer from chronic migraines as men. The brain of a female migraineur looks so unlike the brain of a male migraineur, asserts Harvard scientist Nasim Maleki, that we should think of migraines in men and women as “different diseases altogether.” Maleki is known for looking at pain and motor regions in the brain, which are known to be unusually excitable in migraine sufferers. In one notable study published in the journal Brain last year, she and her colleagues exposed male and female migraineurs to painful heat on the backs of their hands while imaging their brains with functional MRI. She found that the women had a greater response in areas of the brain associated with emotional processing, such as the amygdala, than did the men. Furthermore, she found that in these women, the posterior insula and the precuneus—areas of the brain responsible for motor processing, pain perception and visuospatial imagery—were significantly thicker and more connected to each other than in male migraineurs or in those without migraines. In Maleki's most recent work, presented in June at the International Headache Congress, her team imaged the brains of migraineurs and healthy people between the ages of 20 and 65, and it made a discovery that she characterizes as “very, very weird.” In women with chronic migraines, the posterior insula does not seem to thin with age, as it does for everyone else, including male migraineurs and people who do not have migraines. The region starts thick and stays thick. © 2013 Scientific American
Alice Roberts It's the rutting season. From Richmond Park to the Isle of Rum, red deer hinds will be gathering, and the stags that have spent the past 10 months minding their own business in bachelor groups are back in town, with one thing on their minds. A mature male that has netted himself a harem is very dedicated. He practically stops eating, focusing instead on keeping his hinds near and his competitors at bay. If you're a red deer stag, one of the ways you make sure that your adversaries know you mean business – and that you're big – is roaring. And you don't let up. You can keep roaring all day, and through the night too, twice a minute, if necessary. While female red deer prefer the deeper roars of larger stags, roaring also appears to be part of how stags size one another up, before deciding whether or not to get engaged in a full-on physical fight. Most confrontations are settled without locking antlers. In male red and fallow deer, the voicebox or larynx is very low in the throat – and gets even lower when they roar. Strap-like muscles that attach to the larynx contract to drag it down towards the breastbone – lengthening the vocal tract and deepening the stag's roar. Deepening the voice exaggerates body size. Over generations, stags with deeper roars presumably had more reproductive success, so the position of the larynx moved lower and lower in the neck. When a red deer stag roars his larynx is pulled down so far that it contacts the front of his breastbone – it couldn't get any lower. In human evolution, much is made of the low position of the larynx in the neck. So much, in fact, that it has been considered to be a uniquely human trait, and intrinsically linked to that other uniquely human trait: spoken language. But if red and fallow deer also have low larynges, that means, first, that we're not as unusual as we like to think we are, and second, that there could be other reasons – that are nothing to do with speaking – for having a descended larynx. © 2013 Guardian News and Media Limited