Chapter 8. Hormones and Sex
Follow us on Facebook and Twitter, or subscribe to our mailing list, to receive news updates. Learn more.
By Debra W. Soh What should parents do if their little boy professes an intense desire to be a girl? Or if their daughter comes home from kindergarten and says she wants to be a boy? In recent years the dominant thinking has changed dramatically regarding children’s gender dysphoria. Previously, parents might hope that it would be a passing phase, as it usually is. But now they are under pressure from gender-identity politics, which asserts that children as young as 5 should be supported in wanting to live as the opposite sex. Any attempts to challenge this approach are deemed intolerant and oppressive. I myself was a gender-dysphoric child who preferred trucks and Meccano sets to Easy-Bake Ovens. I detested being female and all of its trappings. Yet when I was growing up in the 1980s, the concept of helping children transition to another sex was completely unheard of. My parents allowed me to wear boys’ clothing and shave my head, to live as a girl who otherwise looked and behaved like a boy. I outgrew my dysphoria by my late teens. Looking back, I am grateful for my parents’ support, which helped me work things out. Since then, research has established best-treatment practices for adolescents and adults with gender dysphoria: full transitioning, which includes treatment with hormones to suppress puberty and help the individual develop breasts or facial hair, as well as gender-reassignment surgery. But prepubescent children who identify with the opposite sex are another matter entirely. How best to deal with them has become so politicized that sexologists, who presumably would be able to determine the healthiest approach, are extremely reluctant to get involved. They have seen what happens when they deviate from orthodoxy. ©2016 Dow Jones & Company, Inc
By Darryl Fears For male smallmouth bass, sex change is increasingly not an option. In the chemical-laced Chesapeake Bay watershed and in rivers up through New England, it comes with the territory. Based on the latest U.S. Geological Survey on intersex fish, 85 percent of male smallmouth bass in waters in and around national wildlife refuges in the Northeast have developed "characteristics of the opposite sex." That's in addition to 90 percent of the species in some West Virginia waters and 50 percent to 100 percent in the southern stretch of the Potomac River. All of the affected fish had eggs where their testes should be, according to previous studies. Why this is happening remains a mystery, says the lead author of a new study, despite the problem being detected more than a decade ago. “It is not clear what the specific cause of intersex is in these fish,” said Luke Iwanowicz, a USGS research biologist. “This study was designed to identify locations that may warrant further investigation." The strongest suspicion focuses on what is poured down the drains of homes, businesses and farms every day. Scientists are worried that prescription drugs such as birth control and mood-control pharmaceuticals, flushed down toilets, and chemical pesticides such as atrazine, washed off farms by rain, have turned creeks, streams and rivers into chemical soups that disrupt the endocrines of marine life.
By Roni Caryn Rabin Melatonin has been shown to be effective in randomized clinical trials — the kind considered the gold standard in medicine — but it may work better for some sleep problems than others. “There is pretty strong evidence it’s effective for jet lag,” said D. Craig Hopp, a program director at the National Center for Complementary and Integrative Health, part of the National Institutes of Health. But “the evidence is more equivocal for chronic things like insomnia.” A 2002 Cochrane review that analyzed 10 randomized trials, most of them comparing oral melatonin to placebo, concluded that melatonin is “remarkably effective in preventing or reducing jet lag.” It not only helped people fall asleep faster and sleep more soundly, but also led to less daytime fatigue and improved general well-being. Eight of the 10 trials found that taking melatonin for several days after arriving at a destination reduced jet lag from flights crossing at least five time zones. In many of the trials, people also took melatonin on the day of the flight or for several days before the trip, usually in the late afternoon or early evening. Once at the destination, melatonin should be taken close to bedtime, aiming for the local hours between 10 p.m. and midnight. Doses of 0.5 milligrams and 5 milligrams were both effective, though people fell asleep faster and slept better with the larger dose. For others with insomnia, melatonin has more modest benefits. A 2013 analysis that looked at 19 randomized controlled trials involving 1,683 subjects determined that on average, melatonin reduced the amount of time it took to fall asleep by seven minutes when compared with placebo and increased total sleep time by eight minutes. © 2015 The New York Times Company
Love a sugar hit? Your sweet tooth may hail from an unlikely source: your liver. A hormone made by the organ appears to control how much carbohydrate and sugar we want to eat, and helps slow us down when we are overindulging. The hormone, called FGF21, has already been found to help obese mice lose weight and regain their sensitivity to insulin. A modified form is currently in clinical trials to test whether it has the same effect in people with diabetes. Our bodies break down carbohydrates into sugars such as sucrose, glucose and fructose. Recent genetic studies have suggested that people with altered levels of FGF21 consume more carbohydrates. To find out more, a team co-led by Matthew Potthoff at the University of Iowa observed the eating habits of mice with either abnormally high or low levels of the hormone. They found that mice genetically modified to lack the hormone chose to drink much higher levels of sugar-sweetened drinks than normal mice. Those given an extra dose of the hormone, on the other hand, reduced their sugar intake. The team also showed that the hormone is produced in response to high carbohydrate levels; it then enters the bloodstream, where it sends a signal to the brain to suppress our sugar intake. In people, blood levels of FGF21 triple 24 hours after a spike in blood sugar levels. When monkeys were given the synthetic version of the hormone being tested in clinical trials, they also opted for a diet low in sugar, according to a separate study by Steven Kliewer at the University of Texas Southwestern Medical Center at Dallas and colleagues. The team also found that these monkeys consumed less alcohol than those that weren’t given the compound. © Copyright Reed Business Information Ltd.
By Gary Stix A lingering question asked by neuroscientists has to do with what, if anything, makes the male and female brain distinctive, whether in mice or (wo)men. There is still no concise answer. The best evidence from the most recent research suggests that both males and females share the same neural circuitry, but use it differently. Catherine Dulac, a professor of molecular and cellular biology at Harvard, and investigator at the Howard Hughes medical Institute, is a pioneer in exploring these questions. I talked to her briefly about her research, which also extends far beyond just the neurobiology of gender. Can you tell me in broad overview about what you study? I'm interested in understanding how the brain engages in instinctive social behaviors. There are a lot of instinctive behaviors such as eating and sleeping that are essential in animals and humans, but social behavior is a very distinctive and particularly interesting set of instinctive behaviors that we would like to understand at the neuronal level. What we would like to understand in mechanistic terms is how does an individual recognize other animals of its own species, for example how does an animal identifies a male, a female, or an infant, how does the brain processes these signals in order to trigger appropriate social behaviors such as mating, aggression or parenting. Can you tell me a little bit about your work of the last few years that relates to gender identification? © 2015 Scientific American
By Katrina Schwartz It has become a cultural cliché that raising adolescents is the most difficult part of parenting. It’s common to joke that when kids are in their teens they are sullen, uncommunicative, more interested in their phones than in their parents and generally hard to take. But this negative trope about adolescents misses the incredible opportunity to positively shape a kid’s brain and future life course during this period of development. “[Adolescence is] a stage of life when we can really thrive, but we need to take advantage of the opportunity,” said Temple University neuroscientist Laurence Steinberg at a Learning and the Brain conference in Boston. Steinberg has spent his career studying how the adolescent brain develops and believes there is a fundamental disconnect between the popular characterizations of adolescents and what’s really going on in their brains. Because the brain is still developing during adolescence, it has incredible plasticity. It’s akin to the first five years of life, when a child’s brain is growing and developing new pathways all the time in response to experiences. Adult brains are somewhat plastic as well — otherwise they wouldn’t be able to learn new things — but “brain plasticity in adulthood involves minor changes to existing circuits, not the wholesale development of new ones or elimination of others,” Steinberg said. Adolescence is the last time in a person’s life that the brain can be so dramatically overhauled. © 2015 KQED Inc.
By BENEDICT CAREY Dr. Robert L. Spitzer, who gave psychiatry its first set of rigorous standards to describe mental disorders, providing a framework for diagnosis, research and legal judgments, as well as a lingua franca for the endless social debate over where to draw the line between normal and abnormal behavior, died on Friday. He was 83. From Our Advertisers Dr. Spitzer died from complications of heart disease at the assisted living facility where he lived in Seattle, his wife, Janet Williams, said. The couple had moved to Seattle from Princeton, N.J., this year. Dr. Spitzer’s remaking of psychiatry began with an early interest in one of the least glamorous and, historically, most ignored corners of the field: measurement. In the early 1960s, the field was fighting to sustain its credibility, in large part because diagnoses varied widely from doctor to doctor. For instance, a patient told he was depressed by one doctor might be called anxious or neurotic by another. The field’s diagnostic manual, at the time a pamphlet-like document rooted in Freudian ideas, left wide latitude for the therapist’s judgment. Dr. Spitzer, a rising star at Columbia University, was himself looking for direction, increasingly frustrated with Freudian analysis. A chance meeting with a colleague working on a new edition of the manual — the Diagnostic and Statistical Manual of Mental Disorders, or the D.S.M. for short — led to a job taking notes for the committee debating revisions. There, he became fascinated with reliable means for measuring symptoms and behavior — i.e., assessment. “At the time, there was zero interest in assessment,” said Dr. Michael First, a professor of clinical psychiatry at Columbia. “He saw how important it was, and his whole career led to assessment being taken seriously.” © 2015 The New York Times Company
By Francine Russo Some children insist, from the moment they can speak, that they are not the gender indicated by their biological sex. So where does this knowledge reside? And is it possible to discern a genetic or anatomical basis for transgender identity? Exploration of these questions is relatively new, but there is a bit of evidence for a genetic basis. Identical twins are somewhat more likely than fraternal twins to both be trans. Male and female brains are, on average, slightly different in structure, although there is tremendous individual variability. Several studies have looked for signs that transgender people have brains more similar to their experienced gender. Spanish investigators—led by psychobiologist Antonio Guillamon of the National Distance Education University in Madrid and neuropsychologist Carme Junqué Plaja of the University of Barcelona—used MRI to examine the brains of 24 female-to-males and 18 male-to-females—both before and after treatment with cross-sex hormones. Their results, published in 2013, showed that even before treatment the brain structures of the trans people were more similar in some respects to the brains of their experienced gender than those of their natal gender. For example, the female-to-male subjects had relatively thin subcortical areas (these areas tend to be thinner in men than in women). Male-to-female subjects tended to have thinner cortical regions in the right hemisphere, which is characteristic of a female brain. (Such differences became more pronounced after treatment.) “Trans people have brains that are different from males and females, a unique kind of brain,” Guillamon says. “It is simplistic to say that a female-to-male transgender person is a female trapped in a male body. It's not because they have a male brain but a transsexual brain.” Of course, behavior and experience shape brain anatomy, so it is impossible to say if these subtle differences are inborn. © 2015 Scientific American
By David Shultz As the Rolling Stones, Revlon, and Angelina Jolie can attest, not many body parts are more sexualized than the lips. A new study published online today in Royal Society Open Science, suggests that we’re not the only primates that feel this way. Black-and-white snub-nosed monkeys (Rhinopithecus bieti, pictured) have a strict social hierarchy in which a few, older males mate with multiple females, while the younger males form bachelor groups and bide their time. The males’ lips naturally redden with age, but the story seems a little more complicated than that: A series of photographs taken over multiple months shows that mating males’ lips redden during the mating season, whereas the bachelor males’ become paler. Scientists still aren’t sure why the animals’ lips seem to correspond with their social rank, but one idea is that females prefer the redder shades when choosing a mate, similar to how a female peacock chooses the male with the most elaborate tail. Another explanation could be that the males are using lip color as a preemptive indicator of their status in order to minimize conflict: Paler lips could make bachelors appear less threatening, allowing the mating males to focus their aggression on other red-lipped competitors. Both mechanisms could also be acting simultaneously, the authors say. © 2015 American Association for the Advancement of Science.
Keyword: Sexual Behavior
Link ID: 21703 - Posted: 12.16.2015
By SINDYA N. BHANOO Prairie voles are small Midwestern rodents known for monogamous behavior. But some males are also known to stray and seek out other females. A new study reports that mating preferences in the voles are linked to genetic differences, and that both monogamous and nonmonogamous males are readily found in nature. The study appears in the journal Science. Generally, animal neuroscientists believe that natural selection minimizes genetic variation. In this case, however, one mating strategy does not seem to be more successful than the other. Monogamous males stay near their nests, which ensures that female mates remain faithful. Promiscuous males have more partners, but they also lose sight of their own mates. “When you roam, your own female is free to mate with whoever she wants,” said Steven M. Phelps, a neurobiologist at the University of Texas at Austin and one of the study’s authors. The genetic differences between nonmonogramous and monogamous males affect a part of the brain important for spatial memory. Good memory may help a male keep track of his mate or keep him from returning to a hostile male’s territory. “We’ve shown for the first time that not only can brains be variable, but natural selection can keep that variability around,” Dr. Phelps said. © 2015 The New York Times Company
By Andrea Anderson Mom's ovaries could hold clues to some autism cases, new research suggests—and this time it's not because of genetic vulnerabilities carried in her eggs. A new, large-scale study out of Sweden suggests that women with polycystic ovarian syndrome (PCOS)—an endocrine disorder that affects 5 to 10 percent of women of childbearing age—have an increased risk of giving birth to children with autism spectrum disorder (ASD). The Karolinska Institute's Renee Gardner, along with colleagues from Sweden and the U.S., tapped into a Swedish national population health database to look at potential ties between PCOS and ASD. As they reported online December 8 in Molecular Psychiatry, the team looked at 23,748 individuals with ASD and nearly 209,000 unaffected individuals, all born in Sweden between 1984 and 2007. Although identifying information about the individuals was removed, the researchers had access to information about their relationships to others in the database as well as documented diagnoses and use of health care services. The group found that ASD was 59 percent more prevalent in children born to women with PCOS—a relationship that was independent of PCOS complications such as increased neonatal distress or C-section delivery. This risk level is roughly comparable with that of having a father over age 50 (estimated to be 66 percent) but lower than it is in those with certain rare genetic syndromes or mutations. The authors of the analysis believe PCOS increases ASD risk in offspring to a greater extent than maternal infection, one of many factors previously implicated in autism. © 2015 Scientific American
By Ariana Eunjung Cha Attention-deficit/hyperactivity disorder is often thought of a boy thing. In explaining the jump in cases in recent years, numerous researchers, educators and parents have theorized that perhaps boys are hardwired to be more impulsive, wiggly and less able to stay on task in the early years than their female counterparts. That may be a myth. A study published in The Journal of Clinical Psychiatry on Tuesday shows a surprising 55 percent increase in prevalence of diagnoses among girls — from 4.7 percent to 7.3 percent from 2003 to 2011. The rise in cases in girls mirrors a similar but less-sharp rise in cases in boys from a prevalence of 11.8 to 16.5 percent. During the same period, the researchers found an increase in cases across all races and ethnicities but especially in Hispanic children. In all children, the prevalence increased from 8.4 percent to 12 percent. The analysis, conducted by George Washington University biostatistician Sean D. Cleary and his co-author Kevin P. Collins of Mathematica Policy Research, was based on data from the National Survey of Children's Health in which parents were asked whether they had been told by a doctor or other health care provider that their child has ADHD.
Laura Sanders Taking a pregnancy hormone staves off multiple sclerosis relapses, a small clinical trial suggests. The results hint at a potential therapy for women who suffer from MS, a debilitating disease in which the body’s immune system attacks the insulation that wraps around nerve cell fibers. A curious observation kicked off this line of research: Pregnancy offers a temporary reprieve for women with MS. Since that discovery, in the 1990s, scientists have been testing whether certain pregnancy hormones might combat MS in women who aren’t pregnant. In addition to a standard MS drug, 164 women with MS received either a placebo or estriol, an estrogen made by the placenta that peaks toward the end of pregnancy. After two years, women who received estriol had an average of 0.25 relapses a year, while women who received the placebo had 0.37 relapses a year, UCLA neurologist Rhonda Voskuhl and colleagues write online November 24 in Lancet Neurology. Researchers don’t know whether estriol would have similar effects in men with MS. The results warrant a larger clinical trial, the authors say. An accompanying commentary in the same issue of Lancet Neurology questions the results, though. MS specialist Annette Langer-Gould of Kaiser Permanente in Pasadena, Calif., raises methodological issues and writes that pregnancy comes with a host of changes that could be responsible for protection from MS. © Society for Science & the Public 2000 - 2015.
You may have read that having a male brain will earn you more money. Or maybe that female brains are better at multitasking. But there is no such thing as a female or male brain, according to the first search for sex differences across the entire human brain. It reveals that most people have a mix of male and female brain features. And it also supports the idea that gender is non-binary, and that gender classifications in many situations are meaningless. “This evidence that human brains cannot be categorised into two distinct classes is new, convincing, and somehow radical,” says Anelis Kaiser at the University of Bern, Switzerland. The idea that people have either a “female” or “male” brain is an old one, says Daphna Joel at Tel Aviv University in Israel. “The theory goes that once a fetus develops testicles, they secrete testosterone which masculinises the brain,” she says. “If that were true, there would be two types of brain.” To test the theory, Joel and her colleagues looked for differences in brain scans taken from 1400 people aged between 13 and 85. The team looked for variations in the size of brain regions as well as the connections between them. In total, the group identified 29 brain regions that generally seem to be different sizes in self-identified males and females. These include the hippocampus, which is involved in memory, and the inferior frontal gyrus, which is thought to play a role in risk aversion. When the group looked at each individual brain scan, however, they found that very few people had all of the brain features they might be expected to have, based on their sex. Across the sample, between 0 and 8 per cent of people had “all-male” or “all-female” brains, depending on the definition. “Most people are in the middle,” says Joel. © Copyright Reed Business Information Ltd.
Keyword: Sexual Behavior
Link ID: 21670 - Posted: 12.01.2015
Helen Thompson Just after dawn, barbershop quartets of male howler monkeys echo over the canopy of Mexico’s forests. Jake Dunn remembers them well from his early fieldwork in Veracruz. “Most people who don’t know what they’re listening to assume it’s a jaguar,” says Dunn, a primatologist at the University of Cambridge. The calls serve as a warning to male competitors and an alluring pickup line for females. While studying primates in Mexico, Dunn heard drastic differences between resident howler monkeys. He and his colleagues decided to pin down the origin and evolution of this well-known variation among species. After reading a 1949 paper that classified howlers based on a vocal tract bone called the hyoid, Dunn paired up with Lauren Halenar of the American Museum of Natural History in New York City, who was studying the hyoid’s role in howler biology. Scouring collections at museums and zoos in the United States and Europe, the team used laser scanners to create 3-D models of hyoids from nine howler species. The work required a lot of digging through cupboards for skeletons. “Some of these specimens are hundreds of years old,” says Dunn, who recalls imagining “the early naturalists hunting these animals and bringing back the collections.” Real pay dirt came from the National Museums of Scotland, which had preserved the remains of two howlers that had died of natural causes in zoos. CT and MRI scans of the two specimens provided a rare peek at the howler vocal system’s layout. © Society for Science & the Public 2000 - 2015.
Ian Sample Science editor Humans buy flowers. Capuchins throw stones. Giant tortoises bellow. But the blue-capped cordon bleu, a small finch found in Africa, really knows how to win over a mate. The three-inch-high omnivores perform energetic cabaret acts to woo their partners, rattling through routines that feature head-bobbing, singing and tap dance, and often all three at once. The birds were known to sing and nod their heads to impress the opposite sex, but high speed video footage has now revealed that they spice up their displays with nifty footwork that adds percussion to their repertoire and sends vibrations racing down their perches. Scientists at Hokkaido University filmed the birds as they tried their luck with cagemates, and found that both males and females turned to tap to seduce their targets. The steps have not been seen before because they are too fast for the naked eye to spot. “Like humans, males and females of cordon-bleus are mutually choosy and both sexes need to show off,” said Masayo Soma who lead the research. “They show tap dancing throughout the courtship display, and they sometimes add songs to tap dancing.” Whether the steps and songs are coordinated is the focus of ongoing research. Footage of the birds in cabaret mode showed that an entire routine could include more than 200 steps in bursts of anything from five seconds to more than a minute. Both males and females danced more vigorously when their mate was on the same perch. Males danced more often and tapped their feet faster, but apart from that, the sexes had similar moves. © 2015 Guardian News and Media Limited
Ewen Callaway A long stretch of DNA called a supergene explains the variety of bizarre tactics that a wading bird species deploys to win mates, a pair of genome-sequencing studies concludes1, 2. Common to marshes and wet meadows in northern Europe and Asia, ruffs (Philomachus pugnux) are named after the decorative collars popular in Renaissance Europe. But the birds’ poufy plumage is not the only baroque aspect of their biology. Males gather at mass breeding grounds where they juke, jump and lunge toward other males, in hopes of winning females. Male ruffs belong to one of three different forms, each with a unique approach to mating. 'Independent' males, with hodgepodge of brown and black neck feathers, are territorial and defend their bit of the breeding ground. White-feathered 'satellite' males, by contrast, invade the turf of independents to steal nearby females. A third, rarer form, called 'faeders' (Old English for father), take advantage of their resemblance to female ruffs to interrupt coital encounters. “They dash in and jump on the female before the territorial males does,” says Terry Burke, an evolutionary biologist at University of Sheffield, UK. “My colleague describes this as the 'sandwich'. You end up with the territorial male jumping on the back of the mimic.” Burke was part of a team that, in 1995, found that the different approaches of male ruffs were caused by a single inherited factor3. But it seemed improbable that one gene could trigger such wide-ranging differences in behaviour and appearance. © 2015 Nature Publishing Group
By Virginia Morell You and your partner are hungry, but your favorite pizza parlor will only let your mate in to dine. What do you do? If you’re a great tit (Parus major), a songbird found from Europe to Northern Asia, you wait by yourself, even though theoretically you would be better off looking for food elsewhere, scientists have discovered. To find out whether the small birds, pictured above, prefer food or hanging out with their mates, the researchers conducted a series of experiments with a long-studied population of wild great tits in the United Kingdom. They set up 12 feeding stations that would only open to great tits wearing particular radio frequency identification (RFID) tags. Half of the stations unlocked only to birds with even-numbered RFID tags; the others opened to great tits wearing odd-numbered tags. The scientists randomly outfitted 10 mated pairs of the birds with identical tags so that they could enter the stations and feed together; and seven pairs with incompatible tags, so that one was locked out. They followed the birds for 90 days, recording 66,184 visits to the feeders. The pairs with the incompatible tags spent almost four times longer at the prohibited feeders than did the compatible pairs—even though one bird was stuck outside, the scientists report today in Current Biology. Other studies have shown that birds may forage in flocks, despite having less to eat, because there are other benefits, such as having others to help watch for or defend against predators. But this is the first experimental study to show that wild birds will choose their mate over food—a decision that also determines where they travel and what other individuals they associate with, which could affect their social rank, the scientists say. Many of the locked-out birds learned a new trick, too. After a great tit with the correct RFID code entered a feeder, the door didn’t slam shut for 2 seconds—just enough time for one of the incompatible birds to slip in and join his sweetie. © 2015 American Association for the Advancement of Science.
Keyword: Sexual Behavior
Link ID: 21630 - Posted: 11.14.2015
Lauren Morello When Fiona Ingleby took to Twitter last April to vent about a journal’s peer-review process, she didn’t expect much of a response. With only around 100 followers on the social-media network, Ingleby — an evolutionary geneticist at the University of Sussex near Brighton, UK — guessed that she might receive a few messages of support or commiseration from close colleagues. What she got was an overwhelming wave of reaction. In four pointed tweets, Ingleby detailed her frustration with a PLoS ONE reviewer who tried to explain away her findings on gender disparities in the transition from PhD to postdoc. He suggested that men had “marginally better health and stamina”, and that adding “one or two male biologists” as co-authors would improve the analysis. The response was a full-fledged ‘Twitterstorm’ that spawned more than 5,000 retweets, a popular hashtag — #addmaleauthorgate — and a public apology from the journal. “Things went really mental,” Ingleby says. “I had to turn off the Twitter notifications on my e-mail.” Yet her experience is not as unusual as it may seem. Social media has enabled an increasingly public discussion about the persistent problem of sexism in science. When a male scientist with the European Space Agency (ESA) wore a shirt patterned with half-naked women to a major media event in November 2014, Twitter blazed with criticism. The site was where the first reports surfaced in June of Nobel Prizewinning biologist Tim Hunt’s self-confessed “trouble with girls” in laboratories. And in mid-October, many astronomers took to Twitter to register their anger and disappointment when the news broke that Geoffrey Marcy, an exoplanet hunter at the University of California, Berkeley, was found to have sexually harassed female subordinates for at least a decade. © 2015 Nature Publishing Group
Keyword: Sexual Behavior
Link ID: 21627 - Posted: 11.12.2015
Natasha Gilbert The eye-catching plumage of some male songbirds has long been explained as a result of sexual selection: brighter males compete more successfully for mates, so evolution favours their spread. Females, by contrast, remain drab. A new study turns this explanation on its head. Sexual-selection pressures drive females to evolve dull feathers more strongly than they drive males to become colourful, argues James Dale, an evolutionary ecologist at Massey University in Auckland, New Zealand. That surprising conclusion is based on a data set of plumage colour in nearly 6,000 songbirds, which Dale and his colleagues built. They used their data to ask how various potential evolutionary factors drive male and female plumage colour. If a particular songbird species was polygynous (that is, the males had more than one mate), displayed a large difference in size between males and females, and left care of the young mainly up to the females, then the researchers judged that sexual selection was likely to be an important factor in that species' evolution. The study, published in Nature1, found that sexual selection does play an important role in creating colour differences between male and female plumage. But the contrast is largely driven by females evolving to become drab. “Females are the chief architect of the difference,” says Dale. © 2015 Nature Publishing Group