Chapter 12. Sex: Evolutionary, Hormonal, and Neural Bases
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By Nicholas Weiler The grizzled wolf stalks from her rival’s den, her mouth caked with blood of the pups she has just killed. It’s a brutal form of birth control, but only the pack leader is allowed to keep her young. For her, this is a selfish strategy—only her pups will carry on the future of the pack. But it may also help the group keep its own numbers in check and avoid outstripping its resources. A new survey of mammalian carnivores worldwide proposes that many large predators have the ability to limit their own numbers. The results, though preliminary, could help explain how top predators keep the food chains beneath them in balance. Researchers often assume that predator numbers grow and shrink based on their food supply, says evolutionary biologist Blaire Van Valkenburgh of the University of California, Los Angeles, who was not involved in the new study. But several recent examples, including an analysis of the resurgent wolves of Yellowstone National Park, revealed that some large predators keep their own numbers in check. The new paper is the first to bring all the evidence together, Van Valkenburgh says, and presents a “convincing correlation.” Hunting and habitat loss are killing off big carnivores around the world, just as ecologists are discovering how important they are for keeping ecosystems in balance. Mountain lions sustain woodlands by hunting deer that would otherwise graze the landscape bare. Coyotes protect scrub-dwelling birds by keeping raccoons and foxes in line. Where top carnivores disappear, these smaller predators often explode in numbers, with potentially disastrous consequences for small birds and mammals. © 2015 American Association for the Advancement of Science
// by Jennifer Viegas It’s long been suspected that males of many species, including humans, can sniff out whether a female is pregnant, and now new research suggests that some — if not all — female primates release a natural “pregnancy perfume” that males can probably detect. What’s more, such scents appear to broadcast whether the mom-to-be is carrying a boy or a girl. The study, published in the journal Biology Letters, focused on lemurs as a model for primates. It presents the first direct evidence in any animal species that a pregnant mother’s scent differs depending on the sex of her baby. The scent signatures “may help guide social interactions, potentially promoting mother–infant recognition, reducing intragroup conflict” or sort out paternity, wrote authors Jeremy Crawford and Christine Drea. The latter presents a loaded scenario, as it could be that males can sense — even before the birth — whether they fathered the baby. The researchers additionally suspect that odors advertising fetal sex may help dads and moms prepare for what’s to come. Crawford, from the University of California, Berkeley, and Drea, from Duke University, used cotton swabs to collect scent secretions from the genital regions of 12 female ringtailed lemurs at the Duke Lemur Center in Durham, N.C., before and during pregnancy. The scientists next used chemical analysis to identify the hundreds of ingredients that make up each female’s scent change during pregnancy. A surprising finding from this is that expectant lemur moms give off simpler scents that contain fewer odor compounds compared with their pre-pregnancy bouquet. The change is more pronounced when the moms are carrying boys, Drea said. © 2015 Discovery Communications, LLC.
By Emily Underwood Infants born prematurely are more than twice as likely to have difficulty hearing and processing words than those carried to full-term, likely because brain regions that process sounds aren’t sufficiently developed at the time of delivery. Now, an unusual study with 40 preemies suggests that recreating a womblike environment with recordings of a mother's heartbeat and voice could potentially correct these deficits. "This is the kind of study where you think ‘Yes, I can believe these results,’ " because they fit well with what scientists know about fetal brain development, says cognitive scientist Karin Stromswold of Rutgers University, New Brunswick, in New Jersey. A fetus starts to hear at about 24 weeks of gestation, as neurons migrate to—and form connections in—the auditory cortex, a brain region that processes sound, Stromswold explains. Once the auditory cortex starts to function, a fetus normally hears mostly low-frequency sounds—its mother’s heartbeat, for example, and the melody and rhythm of her voice. Higher frequency tones made outside of the mother's body, such as consonants, are largely drowned out. Researchers believe that this introduction to the melody and rhythm of speech, prior to hearing individual words, may be a key part of early language acquisition that gets disrupted when a baby is born too soon. In addition to being bombarded with the bright lights, chemical smells, and shrill sounds of a hospital’s intensive care unit, preemies are largely deprived of the sensations they'd get in the womb, such as their mother's heartbeat and voice, says Amir Lahav, a neuroscientist at Harvard Medical School in Boston. Although mothers are sometimes allowed to hold premature newborns for short periods of time, the infants are often considered too fragile to leave their temperature- and humidity-controlled incubators, he says. Preemies often have their eyes covered to block out light, and previous studies have shown that reducing overall levels of high-frequency noise in a neonatal intensive care unit—by lowering the number of incubators in a unit, for example, or giving preemies earplugs—can improve premature babies' outcomes. Few studies have actively simulated a womblike environment, however, he says. © 2015 American Association for the Advancement of Science.
Claire Ainsworth As a clinical geneticist, Paul James is accustomed to discussing some of the most delicate issues with his patients. But in early 2010, he found himself having a particularly awkward conversation about sex. A 46-year-old pregnant woman had visited his clinic at the Royal Melbourne Hospital in Australia to hear the results of an amniocentesis test to screen her baby's chromosomes for abnormalities. The baby was fine — but follow-up tests had revealed something astonishing about the mother. Her body was built of cells from two individuals, probably from twin embryos that had merged in her own mother's womb. And there was more. One set of cells carried two X chromosomes, the complement that typically makes a person female; the other had an X and a Y. Halfway through her fifth decade and pregnant with her third child, the woman learned for the first time that a large part of her body was chromosomally male1. “That's kind of science-fiction material for someone who just came in for an amniocentesis,” says James. Sex can be much more complicated than it at first seems. According to the simple scenario, the presence or absence of a Y chromosome is what counts: with it, you are male, and without it, you are female. But doctors have long known that some people straddle the boundary — their sex chromosomes say one thing, but their gonads (ovaries or testes) or sexual anatomy say another. Parents of children with these kinds of conditions — known as intersex conditions, or differences or disorders of sex development (DSDs) — often face difficult decisions about whether to bring up their child as a boy or a girl. Some researchers now say that as many as 1 person in 100 has some form of DSD2. © 2015 Nature Publishing Group
Keyword: Sexual Behavior
Link ID: 20589 - Posted: 02.18.2015
Berit Brogaard On popular websites, we read headlines such as “Scientists are finding that love really is a chemical addiction between people.” Love, of course, is not literally a chemical addiction. It’s a drive perhaps, or a feeling or an emotion, but not a chemical addiction or even a chemical state. Nonetheless, romantic love, no doubt, often has a distinct physiological, bodily, and chemical profile. When you fall in love, your body chemicals go haywire. The exciting, scary, almost paranormal and unpredictable elements of love stem, in part, from hyper-stimulation of the limbic brain’s fear center known as the amygdala. It’s a tiny, almond-shaped brain region in the temporal lobe on the side of your head. In terms of evolutionary history, this brain region is old. It developed millions of years before the neocortex, the part of the brain responsible for logical thought and reasoning. While it has numerous biological functions, the prime role of the amagdala is to process negative emotional stimuli. Significant changes to normal amygdala activation are associated with serious psychological disorders. For example, human schizophrenics have significantly less activation in the amygdala and the memory system (the hippocampus), which is due to a substantial reduction in the size of these areas. People with depression, anxiety, and attachment insecurity, on the other hand, have significantly increased blood flow in the amygdala and memory system. Neuroscientist Justin Feinstein and his colleagues (2010) studied a woman whose amygdala was destroyed after a rare brain condition. They exposed her to pictures of spiders and snakes, took her on a tour of the world’s scariest haunted house, and had her take notes about her emotional state when she heard a beep from a random beeper that had been attached to her. After three months of investigation, the researchers concluded that the woman could not experience fear. This is very good evidence for the idea that the amygdala is the main center for fear processing. (The chief competing hypothesis is that fear is processed in a brain region that receives its main information from the amygdala.) © 2015 Salon Media Group, Inc.
By Rachel Ehrenberg SAN JOSE, Calif. — New moms suffering from postpartum depression change their activity on Facebook, suggesting that the social media site could help detect the onset of the baby blues. Many new parents share pictures and videos of their babies on Facebook and use the site to interact with friends they might be too busy to see in person. But compared with most typical new moms, those suffering from postpartum depression are less active on the social media site, Munmun De Choudhury of Georgia Tech reported February 14 at the annual meeting of the American Association for the Advancement of Science. She and her colleagues at Microsoft Research in Redmond, Wash., conducted an elaborate study that included a depression screening questionnaire, interviews and an analysis of Facebook activity and interactions of 165 mothers both before and after they had their babies. These women also tend to keep a stiff upper lip on the site, refraining from reporting on their emotional well-being and instead posting objective content geared toward getting feedback or advice on a specific matter, De Choudhury and her colleagues discovered. The scientists also found they could train a computer program to identify which moms had the blues. Such research might help with designing interventions, whereby moms could be warned that they might be sinking into depression and encouraged to reach out for social support or medical attention. M. De Choudhury. Online Social Dynamics and Emotional Wellbeing. American Association for the Advancement of Science Annual Meeting, San Jose, Calif., February 14, 2015. © Society for Science & the Public 2000 - 2015
By Anne Harding NEW YORK (Reuters Health) - Reduced sexual activity could cause a dip in testosterone levels in older men, new findings suggest. Among men 70 and older, those who reported a decline in sexual activity and desire over a two-year period also showed small declines in serum testosterone, Dr. David Handelsman of the ANZAC Research Institute at the University of Sydney and Concord Hospital in New South Wales, Australia, and colleagues found. They report their findings in the Journal of Clinical Endocrinology and Metabolism, online January 28. "Decline in serum testosterone is more likely to be the result rather than the cause of sexual dysfunction among older men who don't have reproductive disorders," Dr. Handelsman told Reuters Health by email. "The widely prevalent misinterpretation of this (as if the mild lowering of serum testosterone needs or might benefit from testosterone treatment) is one of the main drivers of the massive over-use of testosterone prescriptions in North America over the last decade." While declines in androgens and sexual function are both thought to be aging-related, Dr. Handelsman and his colleagues note in their report, the relationship between androgen levels and sexual function is not clear. To better understand the temporal and predictive relationship between androgen levels and sexual function, the researchers looked at 1,226 men participating in the Concord Health and Ageing in Men Project (CHAMP), measuring their levels of testosterone, dihydrotestosterone, estradiol, and estrone with liquid chromatography-tandem mass spectrometry. Men also reported on their sexual function using standardized questions, at baseline and two years later. © 2015 Scientific American
By Nicholas Weiler When you spend your days battling giant squid, it’s good to have friends you can rely on. New research from the Caribbean suggests that female sperm whales (Physeter macrocephalus, pictured) swim with favored companions and form long-term family allegiances. Sperm whales raise their young in communal family groups of about a dozen related females, but mapping out the giant animals' social lives in much detail has been a challenge for scientists. The whales spend 60% of their lives hunting squid hundreds of meters below the waves, and researchers can watch them interact for only a few minutes at a time when they surface to breathe. But a new multiyear study has created the most detailed map yet of sperm whales’ social networks. Between 2005 and 2010, scientists followed nine whale families along the west coast of the Caribbean island of Dominica and mapped their social relationships by counting which females spent the most time together at the surface between dives. As expected, whales mostly preferred to relax with family members, but within families they played favorites, frequently swimming with the same sister, auntie, or aged granny, the researchers report online this week in Animal Behaviour. The network diagram also revealed three pairs of families that mingled frequently over the years to socialize and share babysitting duty. One of these pairs has been fraternizing since 1995, according to data from other researchers, suggesting that such allegiances can last more than a decade. These observations suggest sperm whale families may be similar to the matriarchal clans of elephants, which also form long-lasting family bonds, the researchers say. Further research may determine whether allied families are actually distant cousins and investigate whether whales use signature songs to find their best friends. © 2015 American Association for the Advancement of Science
By Susan Chenelle and Audrey Fisch “Lord of the Flies” has been a classroom staple for decades, perhaps because the issues of bullying and male aggression remain central concerns in the lives of adolescents, even if they aren’t stranded on a desert island. “To Study Aggression, a Fight Club for Flies” zeros in on the issue of male aggression, but in fruit flies, rather than humans. The connections, beyond the titular, are tantalizing. James Gorman, the science reporter, is focused on research about the neuropeptide tachykinin, produced in the brains of male fruit flies only. When researchers manipulated the neurons, they could decrease aggression in the flies. What does this suggest about the neuroscience of aggression? And what is the relationship between aggression and gender? Below, we match Mr. Gorman’s article with a passage from Chapter 8 of “Lord of the Flies” in which Jack leads his peers in the hunt of a sow. At this point in the novel, Jack has overthrown Ralph and Piggy’s attempts to establish order and civility among the boys. Jack has won over a majority of the boys, and in this scene the group engages in a collective hunt for food that transforms itself into a kind of orgy of male violence. The gender politics of the scene are striking: The attack on the mother pig calls out for careful analysis. The boys are, for example, “wedded to her in lust” and climactically “heavy and fulfilled upon her” at the moment of her killing. What point is William Golding trying to make, here and elsewhere in the novel, about the nature of these young men and the ways in which they turn to and relish in aggression and violence? Key Question: What is the relationship between aggression and gender? © 2015 The New York Times Company
Helen Fisher, a biological anthropologist at Rutgers University responds: Several years ago I embarked on a project to see if the seven-year itch really exists. I began by studying worldwide data on marriage and divorce and noticed that although the median duration of marriage was seven years, of the couples who divorced, most did so around their fourth year together (the “mode”). I also found that divorce occurred most frequently among couples at the height of their reproductive and parenting years—for men, ages 25 to 29, and for women, ages 20 to 24 and 25 to 29—and among those with one dependent child. To try to explain these findings, I began looking at patterns of pair bonding in birds and mammals. Although only about 3 percent of mammals form a monogamous bond to rear their young, about 90 percent of avian species team up. The reason: the individual that sits on the eggs until they hatch will starve unless fed by a mate. A few mammals are in the same predicament. Take the female fox: the vixen produces very thin milk and must feed her young almost constantly, so she relies on her partner to bring her food while she stays in the den to nurse. But here's the key: although some species of birds and mammals bond for life, more often they stay together only long enough to rear their young through infancy and early toddlerhood. When juvenile robins fly away from the nest or maturing foxes leave the den for the last time, their parents part ways as well. Humans retain traces of this natural reproductive pattern. In more contemporary hunter-gatherer societies, women tend to bear their children about four years apart. Moreover, in these societies after a child is weaned at around age four, the child often joins a playgroup and is cared for by older siblings and relatives. This care structure allows unhappy couples to break up and find a more suitable partner with whom to have more young. © 2015 Scientific American
By DOUGLAS QUENQUA A sparrow’s song may sound simple, consisting of little more than whistles and trills. But to the sparrows, those few noises can take on vastly different meanings depending on small variations in context and repetition, researchers have found. In humans, the ability to extract nearly endless meanings from a finite number of sounds, known as partial phonemic overlapping, was key to the development of language. To see whether sparrows shared this ability, researchers at Duke University recorded and analyzed the songs of more than 200 Pennsylvania swamp sparrows. They found that the sparrows’ whistles could be divided into three lengths: short, intermediate and long. The researchers then played the sparrows two versions of the songs — the original and a slightly altered one. They found that replacing a single short whistle with an intermediate one, for example, could significantly alter a bird’s reaction, but only if it came at the right moment in the song. “Identical sounds seemed to belong to a different category depending on the context,” said Robert F. Lachlan, a biologist now with Queen Mary University of London and the lead author of the study. The findings, which were published in Proceedings of the National Academy of Sciences, are part of a larger effort to better understand how human language evolved. If even birds rely on phonemic overlapping to communicate, Dr. Lachlan said, it could indicate that such features “developed independently of higher aspects of language.” © 2015 The New York Times Company
ByDavid Malakoff This bird might look like a holiday ornament, but it is actually a rare half-female, half-male northern cardinal (Cardinalis cardinalis, pictured with female plumage on the left and male plumage on the right) spotted a few years ago in Rock Island, Illinois. Researchers have long known such split-sex “gynandromorphs” exist in insects, crustaceans, and birds. But scientists rarely get to extensively study a gynandromorph in the wild; most published observations cover just a day or so. Observers got to follow this bird, however, for more than 40 days between December 2008 and March 2010. They documented how it interacted with other birds and even how it responded to recorded calls. The results suggest being half-and-half carries consequences: The cardinal didn’t appear to have a mate, and observers never heard it sing, the researchers report this month in The Wilson Journal of Ornithology. On the other hand, it wasn’t “subjected to any unusual agonistic behaviors from other cardinals,” according to the paper. Intriguingly, another gynandromorph cardinal sighted briefly in 1969 had the opposite plumage, they note: the male’s bright red plumes on the right, the drabber female feathers on the left. © 2014 American Association for the Advancement of Science
Keyword: Sexual Behavior
Link ID: 20442 - Posted: 12.27.2014
By Sandhya Sekar A well-fed female mantis is irresistible to a male. She’s chock-full of eggs and draws him in by producing high levels of pheromones. Now, a new study reveals that starving females can deceive males by enticing them to their doom. Researchers have found that female false garden mantises (Pseudomantis albofimbriata, pictured) that were fed just a quarter of what others got actually produced more pheromones than well-fed females—and attracted almost twice the number of males. This is despite the fact that the number of eggs in the starved females was less than 10, compared with more than 60 eggs in well-fed females. The finding, reported online today in the Proceedings of the Royal Society B, is the first experimental demonstration of sexual deception using false chemical signals in any animal. The starving females seem to be treating the males as easy prey to gain nutritional benefits and potentially produce more eggs. © 2014 American Association for the Advancement of Science
Katie Langin In the first couple of years after birth, sea lion sons seem to be more reliant on their mothers—consuming more milk and sticking closer to home—than sea lion daughters are, according to a study on Galápagos sea lions published in the December issue of the journal Animal Behaviour. The young males venture out to sea on occasion, but their female counterparts dive for their own food much more often. The curious thing is, it's not like the young males aren't capable of diving. As one-year-olds, males can dive to the same depth as females (33 feet, or 10 meters, on a typical dive). It's also not like their mother's milk is always on hand. Sea lion moms frequently leave their growing offspring for days at a time to find food at sea. (Watch a video of a Galápagos sea lion giving birth.) And yet, despite all this, for some reason sons are far less likely than daughters to take to the sea and seek out their own food. "We always saw the [young] males around the colony surfing in tide pools, pulling the tails of marine iguanas, resting, sleeping," said Paolo Piedrahita, a Ph.D. student at Bielefeld University in Germany and the lead author of the study. "It's amazing. You can see an animal—40 kilograms [88 pounds]—just resting, waiting for mom." © 1996-2014 National Geographic Society.
By Pippa Stephens Health reporter, BBC News Women are more likely than men to display symptoms of depression when in a position of authority at work, according to US scientists. In men, authority, such as the ability to hire and fire people, decreases depressive symptoms, the study said. The study, published in the Journal of Health and Social Behaviour, looked at 2,800 middle-aged men and women. One expert said the study showed the need for more women in authority and more varied female role models. Scientists at the University of Texas at Austin interviewed 1,300 male and 1,500 female graduates from Wisconsin high schools over the phone in 1993 and 2004, when they were aged about 54 and 64. Researchers asked participants about job authority and about the number of days in the past week they felt depressive symptoms, such as feeling sad and thinking one's life is a failure. When the job included hiring, firing and influencing pay, women were predicted to have a 9% increased rate of depressive symptoms than women without authority. Meanwhile, men had a 10% decreased rate of depressive symptoms. The study said it controlled for other factors that could cause depression, such as hours worked per week, whether people had flexible hours and how often workers were checked by a supervisor. Scientists also said men were more likely to decide when to start and finish work than women and were less frequently monitored by their advisers. Lead researcher Tetyana Pudrovska said: "These women have more education, higher incomes, more prestigious occupations, and higher levels of job satisfaction and autonomy than women without job authority. Yet they have worse mental health than lower status women." BBC © 2014
By Elahe Izadi Putting very little babies through numerous medical procedures is especially challenging for physicians, in part because reducing the pain they experience is so difficult. Typically for patients, "the preferred method of reducing pain is opiates. Obviously you don't want to give opiates to babies," says neurologist Regina Sullivan of NYU Langone Medical Center. "Also, it's difficult to know when a baby is in pain and not in pain." In recent years, research has shown environmental factors, like a mother or caregiver having contact with a baby during a painful procedure, appears to reduce the amount of pain felt by the baby, at least as indicated by the child's behavior, Sullivan said. But she and Gordon Barr of the University of Pennsylvania, an expert in pain, were interested in whether a mother's presence actually changed the brain functioning of a baby in pain. So Sullivan and Barr turned to rats. Specifically mama and baby rats who were in pain. And they found that hundreds of genes in baby rats' brains were more or less active, depending on whether the mothers were present. Sullivan and Barr presented their committee peer-reviewed research before the Society for Neuroscience annual meeting Tuesday. They gave mild electric shocks to infant rats, some of which had their mothers around and others who didn't. The researchers analyzed a specific portion of the infants' brains, the amygdala region of neurons, which is where emotions like fear are processed.
By Kelly Servick Dean Hamer finally feels vindicated. More than 20 years ago, in a study that triggered both scientific and cultural controversy, the molecular biologist offered the first direct evidence of a “gay gene,” by identifying a stretch on the X chromosome likely associated with homosexuality. But several subsequent studies called his finding into question. Now the largest independent replication effort so far, looking at 409 pairs of gay brothers, fingers the same region on the X. “When you first find something out of the entire genome, you’re always wondering if it was just by chance,” says Hamer, who asserts that new research “clarifies the matter absolutely.” But not everyone finds the results convincing. And the kind of DNA analysis used, known as a genetic linkage study, has largely been superseded by other techniques. Due to the limitations of this approach, the new work also fails to provide what behavioral geneticists really crave: specific genes that might underlie homosexuality. Few scientists have ventured into this line of research. When the genetics of being gay comes up at scientific meetings, “sometimes even behavioral geneticists kind of wrinkle up their noses,” says Kenneth Kendler, a psychiatric geneticist at Virginia Commonwealth University in Richmond. That’s partially because the science itself is so complex. Studies comparing identical and fraternal twins suggest there is some heritable component to homosexuality, but no one believes that a single gene or genes can make a person gay. Any genetic predispositions probably interact with environmental factors that influence development of a sexual orientation. © 2014 American Association for the Advancement of Science.
Carl Zimmer In the early 1970s, Sarah Blaffer Hrdy, then a graduate student at Harvard, traveled to India to study Hanuman langurs, monkeys that live in troops, each made up of several females and a male. From time to time, Dr. Hrdy observed a male invade a troop, driving off the patriarch. And sometimes the new male performed a particularly disturbing act of violence. He attacked the troop’s infants. There had been earlier reports of infanticide by adult male mammals, but scientists mostly dismissed the behavior as an unimportant pathology. But in 1974, Dr. Hrdy made a provocative counter proposal: infanticide, she said, is the product of mammalian evolution. By killing off babies of other fathers, a male improves his chances of having more of his own offspring. Dr. Hrdy went on to become a professor at the University of California, Davis, and over the years she broadened her analysis, arguing that infanticide might well be a common feature of mammalian life. She spurred generations of scientists to document the behavior in hundreds of species. “She’s the goddess of all this stuff,” said Kit Opie, a primatologist at University College London. Forty years after Dr. Hrdy’s initial proposal, two evolutionary biologists at the University of Cambridge have surveyed the evolution of infanticide across all mammals. In a paper published Thursday in Science, the scientists concluded that only certain conditions favor the evolution of infanticide — the conditions that Dr. Hrdy had originally proposed. “My main comment is, ‘Well done,'” said Dr. Hrdy. She said the study was particularly noteworthy for its scope, ranging from opossum to lions. The authors of the new study, Dieter Lukas and Elise Huchard, started by plowing through the scientific literature, looking for evidence of infanticide in a variety of mammalian species. The researchers ended up with data on 260 species, and in 119 of them — over 45 percent — males had been observed killing unrelated young animals. © 2014 The New York Times Company
Carl Zimmer Milk is not just food. The more closely scientists examine it, the more complexity they find. Along with nutrients like protein and calcium, milk contains immune factors that protect infants from disease. It hosts a menagerie of microbes, too, some of which may colonize the guts of babies and help them digest food. Milk even contains a special sugar that can fertilize that microbial garden. Now, it turns out, milk also contains messages. A new study of monkeys, published in the journal Behavioral Ecology, demonstrates that a hormone present in milk, cortisol, can have profound effects on how babies develop. Infant monkeys rely on cortisol to detect the condition of their mothers, the authors suggest, then adjust their growth and even shift their temperaments. Jeffrey French, a neuroendocrinologist at the University of Nebraska at Omaha who was not involved in the study, praised its “remarkable sophistication” and said that it helped to change how we think about breast milk. “Milk serves almost like a pheromone, a chemical signal sent from one individual to another,” he said. Katie Hinde, a behavioral biologist at Harvard and lead author on the new study, and her colleagues studied 108 rhesus macaque mothers nursing infants at the California National Primate Research Center. The researchers collected samples of milk, measuring how much energy each provided and the cortisol it contained. Dr. Hinde and her colleagues also measured how much weight each nursing monkey gained and tracked its behavior. Cortisol serves many functions in mammals, but it is best known as a stress hormone. When cortisol courses through our bodies, it prepares us to handle alarming or fearful situations, increasing the brain’s consumption of glucose and suppressing the digestive system. © 2014 The New York Times Company
by Catherine Brahic Once described as the finest sound in nature, the song of the North American hermit thrush has long captivated the human ear. For centuries, birdwatchers have compared it to human music – and it turns out they were on to something. The bird's song is beautifully described by the same maths that underlies human harmonies. To our ears, two notes usually sound harmonious together if they follow a set mathematical relationship. An octave is a doubling of frequencies. Tripling the frequency of sound produces a perfect fifth, quadrupling is yet another octave, and quintupling produces a perfect third. These relationships define the most common major chords – the ones that, across human cultures, we tend to find most pleasant to listen to. Early studies sought to determine whether these mathematical relationships also governed the notes in bird song. Studies in the white-throated sparrow and the northern nightingale-wren failed to find the same musical intervals as those used in human music, and deemed birdsong to be something different entirely. Making tweet music The song of the hermit thrush challenges that conclusion. Tecumseh Fitch of the University of Vienna in Austria and colleagues analysed recordings taken in the wild of 70 full songs from this species. They isolated the frequencies corresponding to each note, and calculated the relationships between pitches appearing in each song. Lo and behold, the vast majority of songs used notes that fitted the same simple mathematical ratios as human harmony. What's more, Fitch says the thrush can produce other notes - meaning it must choose to use these harmonic chords. © Copyright Reed Business Information Ltd.