Chapter 12. Sex: Evolutionary, Hormonal, and Neural Bases
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Scientists haven’t pinpointed a definitive cause for Alzheimer’s disease—a fatal brain disorder that robs people of their memory and cognitive abilities. But now researchers have uncovered an intriguing clue about why more women than men develop the condition. A particular gene variant, found in a quarter of the population and long known to raise people’s risk for the disease, seems less menacing in men, new research shows. The findings could have implications for potential gender-specific treatments, some Alzheimer’s investigators suggest. Though a small percentage of Alzheimer’s cases arise from genetic mutations that cause obvious disease before the age of 65, the vast majority of people who develop the condition do so later in life from undefined triggers, some thought to be genetic. In 1993, scientists found that people who inherit a gene variant called apolipoprotein E4 (APOE4) are more prone to the common form of Alzheimer’s that strikes in late life. There’s also a “risk-neutral” variant (APOE3) and a much rarer version of the gene (APOE2) that decreases a person’s risk for Alzheimer’s. Shortly thereafter, other research groups replicated the finding and some data hinted that APOE4 raises Alzheimer’s risk more in women than in men. Indeed, when scientists combed through a massive data set containing 5930 Alzheimer’s patients and 8607 dementia-free elderly from 40 independent studies, they reported in 1997 that females with the APOE4 variant were four times more likely to have Alzheimer’s compared with people with the more common, neutral form of the gene. However, in men, APOE4 seemed virtually harmless. “It was a pretty big effect,” says Michael Greicius, a neurologist at Stanford University Medical Center in California, of the analysis. Yet the findings didn’t create much of a stir at the time. © 2014 American Association for the Advancement of Science
by Agata Blaszczak-Boxe, LiveScience.com Unlike many humans, some monkeys are genuinely faithful to their mates. A species known as Azara's owl monkeys tends to be monogamous, according to a new study of these primates. The research also found that the monkeys' inclination to be faithful was related to the male monkeys' tendency to care for their offspring. "They [Azara's owl monkeys] live in pairs, so, in a group, we have only one adult male and one adult female, and both of them are faithful," study author Maren Huck, a professor at the University of Derby in England, told Live Science. "We found a link between... parental care and having few instances of cheating," Huck said. Researchers had known before this study that members of the Azara's species were socially monogamous, which means that males and females live in pairs. But in animals, including humans, social monogamy is not always equivalent to what researchers call genetic monogamy, where females and males only reproduce with their mates. One way researchers can check for genetic monogamy is to analyze the DNA of mating pairs, and check the paternity of the offspring. In the study, the researchers analyzed field observations of the monkeys' behavior, along with genetic samples from a total of 128 monkeys, including some that lived in groups, and others that were solitary "floaters." The material used by the research team included samples from 35 offspring that were born to 17 reproducing pairs. © 2014 Discovery Communications, LLC
By KATRINA KARKAZIS and REBECCA JORDAN-YOUNG In 2009, the South African middle-distance runner Caster Semenya was barred from competition and obliged to undergo intrusive and humiliating “sex testing” after fellow athletes at the Berlin World Championships questioned her sex. Ms. Semenya was eventually allowed to compete again, but the incident opened the world’s eyes to the process of sex testing and the distress it could bring to an athlete who had lived her whole life as a girl. When an endocrinologist, a gynecologist and a psychologist were brought in to determine whether the teenager was really a woman, she simply asserted, “I know who I am.” From 2011, major sports governing bodies, including the International Olympic Committee, the Fédération Internationale de Football Association and the International Association of Athletics Federations, instituted new eligibility rules that were intended to quell the outrage over the handling of the Semenya case. Instead, as recent cases attest, they may have made things worse. Rather than trying to decide whether an athlete is “really” female, as decades of mandatory sex tests did, the current policy targets women whose bodies produce more testosterone than is typical. If a female athlete’s T level is deemed too high, a medical team selected by the sport’s governing bodies develops a “therapeutic proposal.” This involves either surgery or drugs to lower the hormone level. If doctors can lower the athlete’s testosterone to what the governing bodies consider an appropriate level, she may return to competition. If she refuses to cooperate with the investigation or the medical procedures, she is placed under a permanent ban from elite women’s sports. © 2014 The New York Times Company
By Helen Briggs BBC News Young men with an eating disorder are not getting the help and support they need because of a perceptions about a "women's illness", say researchers. Men are underdiagnosed and undertreated for anorexia and other eating disorders, despite making up about a quarter of cases, a UK study suggests. Frontline health workers have a key role in identifying eating disorders in young men, they report in BMJ Open. Men are under pressure to have the "ideal" body image, says a charity. Researchers from the University of Oxford and University of Glasgow interviewed 39 young people aged 16 to 25, including 10 men, about their experiences of diagnosis, treatment and support for eating disorders. They say young men with eating disorders were "underdiagnosed, undertreated and underresearched". This is partly because the men themselves were unaware of the symptoms, despite purging, not eating for days or obsessive calorie counting, they said. "Our findings suggest that men may experience particular problems in recognising that they may have an eating disorder as a result of the continuing cultural construction of eating disorders as uniquely or predominantly a female problem," said Dr Ulla Raisanen and Dr Kate Hunt. One man said he thought eating disorders only affected "fragile teenage girls"; another said he thought eating disorders were "something girls got"; while one was told by his doctor to "man up". Others said they often had to wait a long time for specialist referral and had sometimes been misdiagnosed. GPs and other professionals such as teachers have a key role in improving the outlook for men with eating disorders by challenging misconceptions, the researchers said. BBC © 2014
Julia Baird SYDNEY, Australia — PRETTY much the No. 1 question you are asked when you’re pregnant is: “Girl or boy?” If you choose not to find out, but to be deliciously surprised at birth, as I did, then you will be asked to guess: “What do you feel it is?” I used to scrunch up my eyes and try hard to draw on what people told me was an age-old female intuition: Which genitals were sprouting in my round belly? I could never tell, though. It is as though the entire world is trying to guess what, or who, is inside you. One oft-told tale is that girls steal your looks and make you fat, while boys just make your belly stick out straight. When I stood wearily bulging at one friend’s baby shower in Manhattan, a stylist confided that she thought our mutual friend was having a boy, because she looked so pretty. Then she looked me up and down: “I think you’re having a girl.” (I placed her in the same category as the neighbor who yelled, “Morning, Fatty!” over the side fence each day.) Why is whether a baby wears blue or pink the most pressing matter for adult acquaintances of a soon-to-be-born? Green is just fine, or white. But a 2007 Gallup poll found that most young Americans, and women under 50, would like to find out the sex of their baby before it is born. In some American fertility clinics, staff experts check the embryo’s sex before they implant it in the womb. So what will it do to our collective minds when forced to grasp that some people are neither gender? Not male, or female, but something else either encompassing, or rejecting, or just adapting from both? Last week, Australia had to grapple with just that after the High Court, in a historic decision, ruled that a person called Norrie May-Welby could register as “nonspecific” on official certificates. Now 52, Norrie was identified, physically, as male when she was born, in Scotland, but was drawn to the world of girls, playing with dolls at age 4 and tying her school tie around her head at night to create the illusion of long hair. She escaped into the library monitors’ group at school and made up adventures where she played six characters, five of whom were female: “I didn’t think there was any problem with this,” she says. “After all, just because I wasn’t really from Krypton, didn’t mean I couldn’t imagine being Supergirl.” © 2014 The New York Times Company
Keyword: Sexual Behavior
Link ID: 19462 - Posted: 04.09.2014
By: Larry Cahill, Ph.D. Early in 2013, the Food and Drug Administration (FDA) ordered the makers of the well-known sleep aid Ambien (zolpidem) to cut their recommended dose in half-but only for women. In essence, the FDA was acknowledging that despite extensive testing prior to the drug's release on the market, millions of women had been overdosing on Ambien for 20 years. On February 9, 2014, CBS's 60 Minutes highlighted this fact-and sex differences in general-by powerfully asking two questions: Why did this happen, and are men and women treated equally in research and medicine?1 The answer to the first question is that the biomedical community has long operated on what is increasingly being viewed as a false assumption: that biological sex matters little, if at all, in most areas of medicine. The answer to the second question is no, today's biomedical research establishment is not treating men and women equally. What are some of the key reasons for the biomedical community's false assumption, and why is this situation now finally changing? What are some of the seemingly endless controversies about sex differences in the brain generated by "anti-sex difference" investigators? And what lies at the root of the resistance to sex differences research in the human brain? For a long time, for most aspects of brain function, sex influences hardly mattered to the neuroscience mainstream. The only sex differences that concerned most neuroscientists involved brain regions (primarily a deep-brain structure called the hypothalamus) that regulate both sex hormones and sexual behaviors.2 Neuroscientists almost completely ignored possible sex influences on other areas of the brain, assuming that the sexes shared anything that was fundamental when it came to brain function. Conversely, the neuroscience mainstream viewed any apparent sex differences in the brain as not fundamental- something to be understood after they grasped the fundamental facts. By this logic, it was not a problem to study males almost exclusively, since doing so supposedly allowed researchers to understand all that was fundamental in females without having to consider the complicating aspects of female hormones. To this day, neuroscientists overwhelmingly study only male animals.3 © 2014 The Dana Foundation
Keyword: Sexual Behavior
Link ID: 19461 - Posted: 04.09.2014
By Paul D. Thacker When the FDA denied Sprout Pharmaceutical’s bid last October to begin marketing flibanserin, a drug aimed at treating low sexual desire in women, women’s groups responded in anger. In January, representatives from eight different women’s groups, including the National Organization of Women, met with Janet Woodcock, the FDA’s head of pharmaceuticals, to protest the decision. Congress also got in on the act, with Reps. Debbie Wasserman Schultz, Chellie Pingree, Nita Lowey, and Louise Slaughter sending a letter to FDA Commissioner Margaret Hamburg to implore that, when evaluating drugs for female dysfunction (in medical terms Hypoactive Sexual Desire Disorder, or HSDD), Dr. Hamburg apply "the same standards of consideration given to the approved drugs for men in your risk/benefit evaluation." “We’ve now got 24 drugs for men for either testosterone replacement or erectile dysfunction,” Cindy Whitehead, Sprout’s chief operating officer told the Associated Press. “Yet there are zero drugs for the most common form of sexual dysfunction in women.” Anita H. Clayton, the interim chair of the department of psychiatry and neurobehavioral sciences at the University of Virginia School of Medicine, was more explicit, writing in a blistering column for the Huffington Post: “For the millions of women with HSDD, the FDA must overcome the problem of institutionalized sexism—unconscious and perhaps unintended, but damaging nonetheless.” The chorus was loud and clear: The FDA is sexist. The federal agency charged with approving drugs to protect and improve our health is now standing in the way of a woman’s right to have a satisfying sex life. This framing played out in numerous stories, with similar charges appearing in the American Prospect (“the FDA’s kinda sexist”), and the Washington Post (“Some critics say the agency—consciously or not—may be succumbing to society’s squeamishness about women’s sexual desires compared with those of men”). Not to be outdone with mere institutional sexism, a writer for the Wire mused whether “blatant, medieval sexism is also at play.” © 2014 The Slate Group LLC.
Keyword: Sexual Behavior
Link ID: 19458 - Posted: 04.08.2014
By SINDYA N. BHANOO Monogamy is rare in animals. Even among species that pair off, there is often philandering. But a new genetic analysis adds to the evidence that the South American primates called Azara’s owl monkeys are remarkably faithful to their partners. The study confirms what one of its authors, Eduardo Fernandez-Duque, an evolutionary anthropologist at the University of Pennsylvania who leads the Owl Monkey Project, had long suspected. For 18 years, he and other Penn researchers have been observing the Azara’s owl monkey in the Chaco region of Argentina. Not only have they never witnessed a philanderer, but they have also found that infant owl monkeys get an unusual amount of care from their fathers. “The male plays with the infant and the male shares food with the infant even more than the mother,” Dr. Fernandez-Duque said. “The males care because these are their offspring, and this has a direct benefit in terms of reproductive success.” In the new study, published in the Proceedings of the Royal Society B, the researchers performed genetic analysis on 35 offspring born to 17 owl monkey pairs and confirmed that the parents were monogamous for the mating season. The monkey is the first primate and only the fifth mammal for which monogamy has been verified through genetics. Because paternal care is also seen in other species of owl monkeys, the scientists suspect that they, too, are serially monogamous. © 2014 The New York Times Company
by Clare Wilson It's a vicious circle of the cruellest kind. Stress might be causing infertility in women, according to new research. This could explain some cases in which couples are diagnosed as infertile with no apparent cause. Taking longer than usual to conceive can lead to stress, so the problem could become self-perpetuating. A link between everyday life stresses and infertility has long been suspected, but there has been little hard evidence connecting the two. Women receiving fertility treatment are generally advised to avoid stress, but not so the average person trying to conceive. An estimated one in seven couples in the UK have fertility problems and, in about a quarter of those, there is no known medical explanation, and they are given a diagnosis of "unexplained infertility". To explore the role of stress, Courtney Lynch at Ohio State University in Columbus and her colleagues collected saliva samples from 373 women in the US who had just started trying to conceive naturally and measured levels of an enzyme called alpha-amylase, a marker of stress. After one year of regular unprotected sex, about 13 per cent of the couples had failed to get pregnant, the standard definition of infertility. The third of women who had the highest alpha-amylase levels were twice as likely to be in the infertile group as the third with the lowest levels. In a previous study, Lynch's team found that those with higher levels of the stress enzyme were slightly less likely to conceive in their first month of trying. But this is the first time that alpha-amylase has been linked to clinical infertility. © Copyright Reed Business Information Ltd.
By BENOIT DENIZET-LEWISy The traffic was bad, even by the warped standards of a Southern California commute. We were headed south from Los Angeles to San Diego on an overcast morning last spring, but we hadn’t moved in 10 minutes. I was sandwiched in the back seat of the car between John Sylla and Denise Penn, two board members of the Los Angeles-based American Institute of Bisexuality (A.I.B.), a deep-pocketed group partly responsible for a surge of academic and scientific research across the country about bisexuality. We were on our way to an A.I.B. board meeting, where members would decide which studies to fund and also brainstorm ways to increase bisexual visibility “in a world that still isn’t convinced that bisexuality — particularly male bisexuality — exists,” as Allen Rosenthal, a sex researcher at Northwestern University, told me. When someone suggested that we try another route, Sylla, A.I.B.’s friendly and unassuming 55-year-old president, opened the maps app on his iPhone. I met Sylla the previous day at A.I.B. headquarters, a modest two-room office on the first floor of a quiet courtyard in West Hollywood that’s also home to film-production companies and a therapist’s office. Tall and pale, with an easy smile, Sylla offered me books from A.I.B.’s bisexual-themed bookshelf and marveled at the unlikelihood of his bisexual activism. “For the longest time, I didn’t even realize I was bi,” Sylla said. “When I did, I assumed I’d probably just live a supposedly straight life in the suburbs somewhere.” In the back seat, Sylla lifted his eyes from his phone and suggested an alternate course. Then he shrugged his shoulders. “We could go either way, really,” he told us. He smiled at me. “Get it? Either way?” © 2014 The New York Times Company
by Barbara J. King Why do little boys tend to behave differently from little girls? Why do boys and girls play differently, for instance, choosing different toys as their favorites? Ask these questions and you invite a firestorm — of more questions. Is the premise behind these queries even accurate? Aren't our sons and daughters really more similar than different, after all? And when behavioral sex differences do occur, aren't parents who inflict sex-stereotypical expectations on their children largely responsible? Seven experts on chimpanzee behavior, led by of Franklin and Marshall College and including the world-famous primatologist , have in Animal Behaviour that speaks, they say, to these issues. Their data on wild chimpanzees from , Tanzania, indicate that human sex differences in childhood are primarily the result of biological, evolutionary mechanisms. The scientists analyzed data on the behavior of 12 male and eight female chimpanzee youngsters, ages 30-36 months. At that age, chimpanzees, who develop quite slowly compared with many other mammals, are still considered infants. As a rule, chimpanzees spend most of their day in close proximity to their mothers clear through their ninth year of life. In the Gombe study, male infants were found to be more gregarious than female chimpanzees; they interacted with significantly more individuals outside the immediate family, including more adult males, than did females. This result held even when the number of the mothers' social partners was controlled. ©2014 NPR
by Ashley Yeager Owl monkeys don't sleep around, genetic tests show. That could be a result of the amount of care males provide for their young, a new study suggests. Infidelity appears to be common in mammals that live in pairs. But new genetic tests suggest that Azara's owl monkeys are unusually faithful. Scientists studied 35 infants born to 17 owl monkey pairs and found that in all cases the youngsters were being raised by their biological parents. Data from the owl monkeys and 14 other species showed that the more involved the males were in raising an infant, the more likely the males were to be faithful, the team reports March 18 in Proceedings of the Royal Society B. Owl monkeys are the only primates and one of five mammal species, including coyotes and California mice, that don’t seem to cheat, according to genetic studies. The evolution of animals’ sexual fidelity is probably linked to the intensity of male care, the researchers suggest. © Society for Science & the Public 2000 - 2013.
Keyword: Sexual Behavior
Link ID: 19386 - Posted: 03.20.2014
By Maggie Fox and Erika Edwards Women are carrying the bigger burden of Alzheimer’s disease in the U.S., according to a new report — making up not only most of the cases, but paying more of the cost of caring for the growing population of people with the mind-destroying illness. The new report from the Alzheimer’s Association paints Alzheimer’s as a disease that disproportionately affects women, both as patients and as caregivers. It points out that women in their 60s are about twice as likely to develop Alzheimer’s over the rest of their lives as they are to develop breast cancer. “So women are at the epicenter of Alzheimer's disease today, not only by being most likely to be diagnosed with Alzheimer's, but also by being the caregiver most of the time,” said Maria Carrillo, vice president of the advocacy group. Alzheimer’s affects more than 5 million Americans, a number projected to soar to 13 million over the next 35 years. A study published earlier this year suggested it’s a big killer, taking down more than 500,000 Americans every year. Three out of five of those living with Alzheimer’s are women, the report finds. “The surprising statistic we pulled out of this report actually is that women over 65 have a one in six chance of developing Alzheimer's disease, in comparison to one out of 11 in men,” Carrillo said. And that compares to a one in eight lifetime risk for developing breast cancer.
By Ella Davies Reporter, BBC Nature The whales are known for their tusks which can reach 2.6m (9ft) in length, earning them comparisons with mythological unicorns. The tusk is an exaggerated front tooth and scientists have discovered that it helps the animals sense changes in their environment. Dr Martin Nweeia from the Harvard School of Dental Medicine, US, undertook the study alongside an international team of colleagues. Through the years, many theories have tried to explain the function of the narwhal's impressive tusk. "People have said it's everything from an ice pick to an acoustic probe, but this is the first time that someone has discovered sensory function and has the science to show it," said Dr Nweeia. More recently, experts have agreed that the tusk is a sexual characteristic because it is more often exhibited by males and they appear to use them during fights to assert their social hierarchy. But because the animals are rarely seen, the exact function of the tusk has remained a mystery. Previous studies have revealed that the animals have no enamel on their tusk - the external layer of the tooth that provides a barrier in most mammal teeth. Dr Nweeia and the team's analysis revealed that the outer cementum layer of the tusk is porous and the inner dentin layer has microscopic tubes that channel in towards the centre. In the middle of the tusk lies the pulp, where nerve endings which connect to the narwhal's brain are found. BBC © 2014
by Bethany Brookshire Spring will be here soon. And with daffodils, crocuses and other signs of spring comes a burst of birdsong as males duke it out to get female attention. While the males trill loud songs, the females sit quietly, choosing who will be the lucky male. Vocal male and quiet female songbirds are common in temperate zones, and have given rise to a common assumption. The best male songs get picked for reproduction, and this sexual selection results in complex song; females just listen and choose, so female song should be rare. After all, females don’t need to sing to attract mates. But it turns out this commonly held assumption is not true. A new study shows that the majority of females of songbird species do sing, and it’s likely that the ancestor of modern songbirds was also a vocal diva. The results challenge the old wisdom about female songbirds, and suggest that when it comes to female song, it’s not all about sex. Karan Odom, a behavioral ecologist at the University of Maryland, Baltimore County, has always been interested in birdsong. “As I began to study it in depth,” she says, “I realized there was a lot that’s unknown, and one area was the extent to which females were singing and the role that song plays in males and females.” Odom and her colleagues did a survey of 44 songbird families, going through bird handbooks and other sources to find records of whether males, females or both were singers. In results published March 4 in Nature Communications, they showed that female melodies are not rare at all. In fact, 71 percent of the species surveyed have singing ladies. So much for that quiet, retiring female bird. © Society for Science & the Public 2000 - 2013.
By Ella Davies Reporter, BBC Nature Peacocks make fake sex sounds to attract females' attention, scientists say. The birds are known for shaking their tail feathers but Canadian researchers have revealed a further sexual tactic. Peacocks have a wide vocabulary of calls, and during mating they make a distinctive hoot. Biologists also recorded males making this sound when out of sight of females and suggest such deception could prove rewarding for the birds. Peacocks are one of the most obvious examples of advertising sexual fitness in the animal kingdom with their eye-catching plumage and strutting courtship displays. The mating behaviour takes place in open areas of land referred to as a "lek". When a male has successfully attracted a female, or peahen, it rushes at her making a distinctive hooting call before attempting to mate. These calls are loud enough to be heard from a distance, prompting scientists to investigate what benefit this has. "It's much louder than it needs to be to communicate with just the female that the male is trying to mate with," explained Dr Roslyn Dakin from the University of British Columbia, Canada, who co-authored the study. BBC © 2014
Keyword: Sexual Behavior
Link ID: 19352 - Posted: 03.12.2014
by Colin Barras Treat them mean, keep them keen? Female preying mantis and black widow spiders are notorious for their tendency to kill and eat males before, during or after sex. The behaviour is clearly risky, though – not least because the scent of a dead rival hardly encourages other males to try their luck. Or so we thought. For male Pennsylvania grass spiders, the whiff of dead male seems to be exactly what they look for in a mate. They are far more likely to approach a female if she has recently killed and eaten a male. Grass spiders are found across North America. With a body length – not including legs – of 17 millimetres, the Pennsylvania grass spider is among the largest. It's harmless to humans, though, spending most of its time hiding away in a tunnel at the corner of its flat, sheet-like web. Unlike many arachnids, grass spiders don't produce sticky webs. But they can move surprisingly quickly, dashing out of their tunnel to grab any insect that ventures too near. It's not just insects that have reason to fear female Pennsylvania grass spiders. Males of the species can find themselves on the wrong end of a female's voracious appetite when the two meet to breed. As mating strategies go, it seems a pretty foolhardy one: studies suggest females in urban settings are typically approached by no more than three – and as few as zero – males during their 3-week-long breeding season. Cannibalism seems to leave the females at risk of self-inflicted celibacy. © Copyright Reed Business Information Ltd
Keyword: Sexual Behavior
Link ID: 19351 - Posted: 03.12.2014
Think women can’t do math? You’re wrong—but new research shows you might not change your mind, even if you get evidence to the contrary. A study of how both men and women perceive each other's mathematical ability finds that an unconscious bias against women could be skewing hiring decisions, widening the gender gap in mathematical professions like engineering. The inspiration for the experiment was a 2008 study published in Science that analyzed the results of a standardized test of math and verbal abilities taken by 15-year-olds around the world. The results challenged the pernicious stereotype that females are biologically inferior at mathematics. Although the female test-takers lagged behind males on the math portion of the test, the size of the gap closely tracked the degree of gender inequality in their countries, shrinking to nearly zero in emancipated countries like Sweden and Norway. That suggests that cultural biases rather than biology may be the better explanation for the math gender gap. To tease out the mechanism of discrimination, two of the authors of the 2008 study, Paola Sapienza and Luigi Zingales, economic researchers at Northwestern University’s Kellogg School of Management in Evanston, Illinois, and the University of Chicago Booth School of Business in Illinois, respectively, teamed up with Ernesto Reuben, an experimental psychologist at Columbia Business School in New York City, to design an experiment to test people's gender bias when it comes to judging mathematical ability. Study participants of both genders were divided into two groups: employers and job candidates. The job was simple: As accurately and quickly as possible, add up sets of two-digit numbers in a 4-minute math sprint. (The researchers did not tell the subjects, but it is already known that men and women perform equally well on this task.) © 2014 American Association for the Advancement of Science.
By Jessica Wright and SFARI.org It takes more mutations to trigger autism in women than in men, which may explain why men are four times more likely to have the disorder, according to a study published 26 February in the American Journal of Human Genetics. The study found that women with autism or developmental delay tend to have more large disruptions in their genomes than do men with the disorder. Inherited mutations are also more likely to be passed down from unaffected mothers than from fathers. Together, the results suggest that women are resistant to mutations that contribute to autism. “This strongly argues that females are protected from autism and developmental delay and require more mutational load, or more mutational hits that are severe, in order to push them over the threshold,” says lead researcher Evan Eichler, professor of genome sciences at the University of Washington in Seattle. “Males on the other hand are kind of the canary in the mineshaft, so to speak, and they are much less robust.” The findings bolster those from previous studies, but don't explain what confers protection against autism in women. The fact that autism is difficult to diagnose in girls may mean that studies enroll only those girls who are severely affected and who may therefore have the most mutations, researchers note. “The authors are geneticists, and the genetics is terrific,” says David Skuse, professor of behavioral and brain sciences at University College London, who was not involved in the study. “But the questions about ascertainment are not addressed adequately.” © 2014 Scientific American
Why do some humans have lighter skin than others? Researchers have longed chalked up the difference to tens of thousands of years of evolution, with darker skin protecting those who live nearer to the equator from the sun’s intense radiation. But a new study of ancient DNA concludes that European skin color has continued to change over the past 5000 years, suggesting that additional factors, including diet and sexual attraction, may also be at play. Our species, Homo sapiens, first arose in Africa about 200,000 years ago, and researchers assume that its first members were as dark-skinned as Africans are today, because dark skin is advantageous in Africa. Dark skin stems from higher levels of the pigment melanin, which blocks UV light and protects against its dangers, such as DNA damage—which can lead to skin cancer—and the breakdown of vitamin B. On the other hand, skin cells need exposure to a certain amount of UV light in order to produce vitamin D. These competing pressures mean that as early humans moved away from the equator, it makes sense that their skin lightened. Recent research, however, has suggested that the picture is not so simple. For one thing, a number of genes control the synthesis of melanin (which itself comes in two different forms in humans), and each gene appears to have a different evolutionary history. Moreover, humans apparently did not begin to lighten up immediately after they migrated from Africa to Europe beginning about 40,000 years ago. In 2012, for example, a team led by Jorge Rocha, a geneticist at the University of Porto in Portugal, looked at variants of four pigmentation genes in modern Portuguese and African populations and calculated that at least three of them had only been strongly favored by evolution tens of thousands of years after humans left Africa. In January, another team, led by geneticist Carles Lalueza-Fox of the University of Barcelona in Spain, sequenced the genome of an 8000-year-old male hunter-gatherer skeleton from the site of La Braña-Arintero in Spain and found that he was dark rather than light-skinned—again suggesting that natural selection for light skin acted relatively late in prehistory. © 2014 American Association for the Advancement of Science