Chapter 8. Hormones and Sex
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By SINDYA N. BHANOO Tiny nematode worms called Caenorhabditis elegans have a peculiar reproductive story: Most females are hermaphrodites that make sperm, self-fertilize and produce more hermaphrodites. Males are few, and are known to mate with each other. Now, a new study reports that a variation in a single gene results in male worms with excretory pores that attract the sexual attentions of other males. “Other males copulate with this excretory pore, located on the neck,” said Matthew Rockman, a biologist at New York University. He and his colleagues reported their findings in the journal Current Biology. Although male worms are rare in the wild, they are easily bred in the laboratory. Researchers report that the gene variant, known as plep-1, may somehow be altering the chemical profile of the excretions in a way that makes them more attractive to other males. Copulation often does not work out well for the male that is approached, Dr. Rockman said. Males that mate with the excretory pore of another male usually leave behind a plug that weakens the worm and reduces life expectancy. Hermaphrodites with the variation of the same gene also have a lower life expectancy and do not reproduce as well. Next, the researchers want to learn what it is about a mutation in the plep-1 gene that makes males attractive to other males. © 2015 The New York Times Company
Ed Yong This week, a team from the University of California, Los Angeles claimed to have found several epigenetic marks—chemical modifications of DNA that don’t change the underlying sequence—that are associated with homosexuality in men. Postdoc Tuck Ngun presented the results yesterday at the American Society of Human Genetics 2015 conference. Nature News were among the first to break the story based on a press release issued by the conference organisers. Others quickly followed suit. “Have They Found The Gay Gene?” said the front page of Metro, a London paper, on Friday morning. Meanwhile, the mood at the conference has been decidedly less complimentary, with several geneticists criticizing the methods presented in the talk, the validity of the results, and the coverage in the press. Ngun’s study was based on 37 pairs of identical male twins who were discordant—that is, one twin in each pair was gay, while the other was straight—and 10 pairs who were both gay. He analysed 140,000 regions in the genomes of the twins and looked for methylation marks—chemical Post-It notes that dictate when and where genes are activated. He whittled these down to around 6,000 regions of interest, and then built a computer model that would use data from these regions to classify people based on their sexual orientation. The best model used just five of the methylation marks, and correctly classified the twins 67 percent of the time. “To our knowledge, this is the first example of a biomarker-based predictive model for sexual orientation,” Ngun wrote in his abstract. The problems begin with the size of the study, which is tiny. The field of epigenetics is littered with the corpses of statistically underpowered studies like these, which simply lack the numbers to produce reliable, reproducible results.
By Kat Long In the delivery room, the (slight) odds are that a newborn is a baby boy, not a girl. Males make up 51.3 percent of live births in the U.S., a rate that has remained about constant for the past seven decades. Experts assumed that this male-skewed sex ratio began at conception, but a new analysis of fetal records shows that the chances overall of finding a boy or a girl start out at 50–50 and change over the course of pregnancy—leaning female, then male, then female again as nine months pass. In the most comprehensive study of its kind to date, biologist Steven Hecht Orzack of the Fresh Pond Research Institute in Massachusetts and his collaborators analyzed roughly 36 million fertility treatment records, prenatal tests, induced abortions and U.S. Census data points. They discovered several nodes at which the sex ratio wavered from 50–50. Those vacillations most likely arise because of genetic and chromosomal abnormalities that cause natural abortions at various stages of gestation, write the study's authors in the Proceedings of the National Academy of Sciences USA. “This is basic knowledge about human pregnancy that we didn't have before,” Orzack says. “Demographers, developmental biologists, and many more can all get something out of this study.” © 2015 Scientific American
Keyword: Sexual Behavior
Link ID: 21500 - Posted: 10.12.2015
By Bill Berkrot (Reuters) - U.S. researchers on Thursday said they had found a way to predict male sexual orientation based on molecular markers that control DNA function, but genetics experts warned that the research has important limitations and will not provide definitive answers to a potential biological basis for sexual preference. Findings from the study, which has yet to be published or reviewed in detail by other scientists, were presented at a meeting of the American Society of Human Genetics in Baltimore. It followed 37 pairs of identical male twins in which one was homosexual and one heterosexual, and 10 sets of twins in which both males were homosexual. The study found that the presence of specific epigenetic marks in nine areas of the human genome could predict homosexual preference with up to 70% accuracy. The epigenome is sometimes described as molecular "switches" that can turn on or silence individual genes in DNA. Scientists believe epigenetic differences can be influenced by environmental and lifestyle factors, from exposure to chemicals to parental nurturing. "To our knowledge, this is the first example of a predictive model for sexual orientation based on molecular markers," Tuck Ngun, lead researcher on the study from the David Geffen School of Medicine of the University of California, Los Angeles, said in a statement. Genetics experts who critiqued the findings said it was premature to draw any conclusions on the predictive powers of epigenetic markers. © 2015 Scientific American
Gay or straight? A saliva test can predict the answer, and get it right 67 per cent of the time – for male identical twins at least. The test, which uses clues from tiny modifications to a person’s genome, is the first that claims to detect sexual orientation. Many scientists have expressed caution over the results, while concerns over potential misuse of the test have led the study’s lead researcher to quit the project entirely. “The scientific benefit to understanding [why people vary in sexual orientation] is obvious to anyone with an iota of curiosity,” says Michael Bailey at Northwestern University in Evanston, Illinois. “The predictive test needs replication on larger samples in order to know how good it is, but in theory it’s quite interesting.” Over the last two decades, several studies have suggested that sexual orientation is, in part, down to our genes. Perhaps the biggest splash was made in 1993 by Dean Hamer’s team at the National Cancer Institute in Bethesda, Maryland, when they found that gay brothers tended to share a sequence of five genetic markers in a region of the X chromosome. The same region has been implicated in other studies of sexual orientation since, although researchers haven’t been able to single out “gay genes”. Other observations also suggest a genetic basis for sexual orientation, such as the mysterious fraternal birth order effect. For every male pregnancy a woman has, a subsequent son has a 33 per cent higher chance of being homosexual, although no one knows why. The overall chance is still low, however, rising from around 2 per cent to just 6 per cent for a third son. © Copyright Reed Business Information Ltd.
By Somer Bishop Subtle, significant. In a nutshell, these two words capture the symptoms of many girls with autism. Like many in my field, I’ve seen this subtlety firsthand. One 6-year-old girl I met several years ago seemed, at first, to have good social skills. She responded appropriately when I introduced myself, complimented my outfit, and politely answered all of my questions. It was only when I saw her again a few days later that I understood her family’s concerns: She made nearly identical overtures, as if our interaction were part of a play she had rehearsed. I also met a teenage girl with autism who was highly intelligent. Because she could not relate to the other girls at her high school, she began interacting exclusively with boys, whose social behaviors she found easier to imitate. She even went through a period of wanting to become a boy, reasoning that she might have more success navigating the social world as a male. The past several years have seen an explosion of studies aimed at backing up these one-off observations about how autism presents differently in girls than in boys. This is a welcome development, as understanding the unique presentation of autism in girls will help us to better identify and treat the disorder. Consistently recognizing autism in girls can be challenging, however. This is not only because girls with autism are as diverse as any other group of individuals with the disorder but also because most autism screening and diagnostic tools were developed based primarily on observations of behaviors in boys. © 2015 The Slate Group LLC.
By Jessica Schmerler Many studies trumpet the positive effects of oxytocin. The hormone facilitates bonding, increases trust and promotes altruism. Such findings earned oxytocin its famous nickname, the “love hormone.” But more recent research has shown oxytocin has a darker side, too: it can increase aggression, risk taking and prejudice. A new analysis of this large body of work reveals that oxytocin's effects on our brain and behavior actually look a lot like another substance that can cut both ways: alcohol. As such, the hormone might point to new treatments for addiction. Researchers led by Ian Mitchell, a psychologist at the University of Birmingham in England, conducted the meta-analysis, which reveals that both oxytocin and alcohol reduce fear, anxiety and stress while increasing trust, generosity and altruism. Yet both also increase aggression, risk taking and “in-group” bias—favoring people similar to ourselves at the expense of others, according to the paper published in August in Neuroscience and Biobehavioral Reviews. The scientists posit that these similarities probably exist because oxytocin and alcohol act at different points in the same chemical pathway in the brain. Oxytocin stimulates release of the neurotransmitter GABA, which tends to reduce neural activity. Alcohol binds to GABA receptors and ramps up GABA activity. Oxytocin and alcohol therefore both have the general effect of tamping down brain activity—perhaps explaining why they both lower inhibitions. © 2015 Scientific American
Susan Milius Bachelor prairie voles can’t tell females of their species apart. Yet the clueless fellows can change, forming pair-bonds for life with the opposite sex and even distinguishing between two female strangers. Bachelors aren’t blind or stupid; they recognize individual males among their fellow short-tailed Microtus ochrogaster rodents scurrying through old fields in the center of North America. And males are certainly interested in the interchangeable females. In lab tests, bachelors claw and bite at cage dividers between the sexes, says Alexander Ophir of Cornell University. Conquering the divide and mating with a female after just six hours of her company can form a lifelong pair-bond between voles. Only about 5 percent of mammal species live this socially monogamous lifestyle, and the voles have played starring roles in studies of the neurobiology of bonding. (Social monogamists, including both voles and some Homo sapiens, don’t entirely forgo extra-pair encounters.) A pair-bonded couple can crowd three litters of young into their roughly six to nine months of life in the wild, Ophir says. One aid to speeding through family life: Females can get pregnant as soon as they give birth. “You sometimes see pups being delivered as males are trying to copulate with the female,” he says. Pair-bonding requires recognizing at least one female. “It’s all well and good to fall in love, but if you don’t know who you fell in love with, it’s worthless,” Ophir says. And paired-up voles can go further. Tests show they notice the difference between two females they have never mated with, Ophir and former student Tomica Blocker report in the October Animal Behaviour. © Society for Science & the Public 2000 - 2015
By Margaret M. McCarthy “We have raised our children in a gender-neutral household since the day they were born, and we never allowed any sort of weapons, not even a water pistol,” a young mother told me emphatically from the microphone in the lecture hall where I’d just given a talk on the differences between male and female brains. “But the other day my seven-year-old son bit his peanut butter and jelly sandwich into the shape of a gun and started shooting his little sister with it!” The audience laughed appreciatively; everyone had a similar story. “What did we do wrong?” she pleaded. This story is a common refrain I hear when discussing my research on sex differences in the brain. There is no single correct answer when it comes to human behavior. Some researchers would insist that there is nothing parents can do to suppress the innate tendencies of boys to gravitate to guns and trucks while girls prefer dolls and tea sets. Others would disagree, arguing that there is no inherent biological difference between the brains of boys and girls. Rather, it is the parents’ own implicit biases and those of society at large that influence their children to behave in gender-typical ways. In the end, my response is that sex differences in the brain are more than some would like and less than others believe. Just how large those differences are, however, is the crux of an ongoing debate in science. And how much a brain’s function can be attributed to biology versus cultural expectations is a challenging question to answer. Confounding the issue is the concept of gender, a purely human construct that can itself influence brain development. Gender refers to both personal and societal perceptions of one’s sex, and embodies all the complexities of cultural expectations, inherent biases, and predetermined norms of behavior, each of which differs for boys and girls and can affect the young brain. © 1986-2015 The Scientist
Keyword: Sexual Behavior
Link ID: 21472 - Posted: 10.03.2015
By Kelli Whitlock Burton They say beauty is in the eye of the beholder. But whether the beholder’s opinion is a product of one's genes or one's environment has long been a question for scientists. Although some research suggests that a preference for certain physical traits, such as height or muscular build, may be encoded in our genes, a new study finds it’s our individual life experiences that lead us to find one face more attractive than another. To get some closure on the nature versus nurture debate in human aesthetics, researchers asked 547 pairs of identical twins and 214 pairs of same-gender fraternal twins to view 200 faces and rate them on a scale of one to seven, with one being the least attractive and seven the most attractive. A group of 660 nontwins then completed the same survey. If genes were more involved in facial preference, identical twins would have had similar ratings; if the influence of a familial environment carried more weight, fraternal twins would have also answered similarly. However, most twins’ scores were quite different from one another, suggesting that something else was at play. The researchers suspect that it’s an individual’s life experiences that guide our opinions of attractiveness. The findings, reported today in Current Biology, build on earlier work by the same team that shows the ability to recognize faces is largely a genetic trait. The research is ongoing, and you can participate, too. Just complete the facial preference survey through the researchers’ website at: www.TestMyBrain.org. © 2015 American Association for the Advancement of Science.
By Nicholas Bakalar Breast-feeding has many benefits, but a new study suggests that it has no effect on a child’s IQ from toddlerhood through adolescence. The idea that breast-feeding might have an effect on cognition is plausible, since long-chain polyunsaturated fatty acids, which are important in neurological development, are more plentiful in breast-fed babies. British researchers studied 11,582 children born between 1994 and 1996. About two-thirds were breast-fed, for an average of four months. They followed them through age 16 and administered nine intelligence tests at regular intervals over the years. The study is in PLOS One. After controlling for parental education, maternal age, socioeconomic status and other variables, they found that girls who had been breast-fed had a weak but statistically insignificant advantage in early life over those who had not been, but the effect was not apparent in boys. Breast-feeding was not associated with gains in IQ through adolescence for either girls or boys. The lead author, Sophie von Stumm, a senior lecturer in psychology at Goldsmiths University of London, said that mothers who do not breast-feed are sometimes criticized. “It’s almost an accusation these days,” she said, “that you’re purposely harming your child. That’s not the case, and it’s not helpful for new mothers. Kids do lots of things that have an influence on IQ. Breast-feeding has no effect that can be distinguished from family background or socioeconomic status.” © 2015 The New York Times Company
By Puneet Kollipara The list of health problems that scientists can confidently link to exposure to hormone-disrupting chemicals has grown to include diabetes, cardiovascular disease, and obesity, a new scientific statement suggests. The statement, released today by the Endocrine Society, also adds support to the somewhat controversial idea that even minute doses of these chemicals can interfere with the activity of natural hormones, which play a major role in regulating physiology and behavior. But the report—which updates a similar statement released in 2009—is drawing sharp criticism from the chemical industry. An executive summary of the new statement, which synthesizes 1300 studies on endocrine disrupters, posits that scientists are more confident than ever before in linking these substances to a host of known health issues, including reproductive and developmental problems, thyroid impairment, certain reproductive cancers, and neurodevelopmental problems such as decreased IQ. But studies suggest those links can now be extended to heart and weight problems, and diabetes, says the executive summary's first author, Andrea C. Gore, a professor of pharmacology and toxicology at the University of Texas, Austin. Six years ago, scientists couldn’t make such a strong case for those links, Gore says, because there weren’t enough good studies. “But this has really been an emerging field where there is much stronger evidence now,” Gore told reporters today on a conference call. Still, some toxicologists and industry groups have long disputed the assertion that endocrine disrupters can trigger effects at minimal doses; this idea can be tough to test in lab animals, which are usually exposed to high doses in toxicology studies. © 2015 American Association for the Advancement of Science
By Martin Enserink AMSTERDAM—Is being a woman a disadvantage when you're applying for grant money in the Netherlands? Yes, say the authors of a paper published by the Proceedings of the National Academy of Sciences (PNAS) this week. The study showed that women have a lower chance than men of winning early career grants from the Netherlands Organization for Scientific Research (NWO), the country's main grant agency. NWO, which commissioned the study, accepted the results and announced several changes on Monday to rectify the problem. "NWO will devote more explicit attention to the gender awareness of reviewers in its methods and procedures," a statement said. But several Dutch scientists who have taken a close look at the data say they see no evidence of sexism. The PNAS paper, written by Romy van der Lee and Naomi Ellemers of Leiden University's Institute of Psychology, is an example of a classic statistical trap, says statistician Casper Albers of the University of Groningen, who tore the paper apart in a blog post yesterday. (In Dutch; a shortened translation in English is here.) Albers says he plans to send the piece as a commentary to PNAS as well. Van der Lee and Ellemers analyzed 2823 applications for NWO's Veni grants for young researchers in the years 2010, 2011, and 2012. Overall, women had a success rate of 14.9%, compared with 17.7% for men, they wrote, and that difference was statistically significant. But Albers says the difference evaporates if you look more closely at sex ratios and success rates in NWO's nine scientific disciplines. Those data, which Van der Lee and Ellemers provided in a supplement to their paper, show that women simply apply more often in fields where the chance of success is low. © 2015 American Association for the Advancement of Science
By Virginia Morell Standing 2 meters tall and weighing as much as 1000 kilograms, European bison (Bison bonasus) are impressive animals. These cousins of the American bison—nearly driven to extinction in the last century—are being reintroduced in small herds across Europe, leading some farmers and forest managers to worry that the large herbivores will destroy their habitat. To better understand how the bison decide when and where to move, scientists studied a herd of 43 individuals in the Reserve Biologique des Monts-d’Azur in the Alpes-Maritimes region of France. They recorded the animals’ movements for 4 hours daily, identifying leaders, what type of action led others to follow, and where the herd moved. The herd wasn’t guided by a single leader, the scientists report in the November issue of Animal Behaviour. Instead, any individual regardless of sex or age could prompt the group to move, although most decisions were made by adult females—as is the case with most ungulates. A bison shows that it plans to change its location by taking at least 20 steps without stopping or lowering its head to graze. A potential leader was most likely to be followed if it walked in the direction that most of the others were facing—suggesting that bison vote with their feet. The researchers suspect that most leaders are adult females because they require higher quality food when lactating or pregnant. Wildlife managers can use this research to reduce human-bison conflicts, the scientists say. They need only identify a herd’s leaders, fit them with GPS collars, and install a virtual fence of alarms and electrical shocks. It should then be possible to control the leaders’ movements—and, thus, those of the entire herd.
Keyword: Sexual Behavior
Link ID: 21432 - Posted: 09.23.2015
Nancy Shute There have been suggestions that low levels of vitamin D might be a factor in cognitive decline and Alzheimer's disease, but there's no proof that the lack of D is actually causing the problems. A study published Monday doesn't prove that link, but it does find that people with low levels of vitamin D lost key thinking skills more quickly than people with enough. The study is notable because of the diversity of the participants: 62 percent were women, 30 percent were African-American, 25 percent Hispanic and 41 percent white. Most earlier studies looking at cognitive decline and vitamin D were in white people. The participants lived in California's Sacramento Valley and were mostly in their 70s when they entered the study. The researchers followed up with them for about five years, having them take annual neurological exams and neuropsychological testing at the University of California, Davis, Alzheimer's Disease Center. Most of the 382 people in the study were low on vitamin D, tested by measuring 25-hydroxyvitamin D in the blood. One-quarter of the participants were deficient in vitamin D, and 35 percent had levels deemed insufficient. That's not a surprise — most older people are below the "adequate" level of 20 to less than 50 ng/ml, often because they're not outside much. And most of the people in the study weren't getting the recommended three servings of dairy foods daily that could help. © 2015 NPR
By Emily DeMarco When it comes to finding a mate in the animal kingdom, females tend to gravitate toward males who appear strong and healthy. But a new study in zebra finches reveals that the small, gray-striped birds prefer mates with similar interests, such as a penchant for exploring the world. The drive for this compatibility is so strong that when scientists forced the females to mate up with males not of their choosing, the birds were more likely to cheat and shirk their parental duties, leading to more deaths among their chicks. The research “suggests that having a mate you’re behaviorally compatible with is very important from an evolutionary perspective for zebra finches,” says behavioral ecologist Sasha Dall of the University of Exeter, Cornwall, in the United Kingdom, who wasn’t involved in the study. Scientists have long been puzzled by female zebra finches. As opposed to females of other bird species, which tend to prefer males with brighter plumage or longer tails (traits that suggest that the males have good, healthy genes), female zebra finches seem to choose mates for some mysterious reason known only to each lady bird. Sometimes one will go for the guy with the bright red beak, sometimes the male with the thrilling song, sometimes neither. So what’s really driving this mate choice? In the past, scientists have speculated that a desire for compatibility might be the answer. But they have disagreed over whether the birds are on the lookout for males with the right genes (genetic compatibility between the partners might help lower the high rates of embryonic mortality seen in the species) or the right behaviors. © 2015 American Association for the Advancement of Science
Keyword: Sexual Behavior
Link ID: 21412 - Posted: 09.15.2015
By Elizabeth Landau Ask a physician what the hormone vasopressin is good for, and she will explain that it regulates the volume of water in your body and also affects blood pressure. But since the 1990s, vasopressin has been a hot topic in a very different field: social behavior. And recently it has emerged as a possible target for treating autism spectrum disorders (ASD), which are characterized by social, behavioral and communication impairments. The research is still in early stages, however, and has yielded more questions than answers. Given that one out of 68 children in the U.S. has an autism spectrum disorder, researchers are scrambling to figure out what in the brain might be related to the symptoms, and how they might design an effective treatment. Vasopressin may be a key player in the disorder. But scientists do not yet know whether too much or too little of the hormone—or perhaps some combination of both—is tied to autism. New clinical trials may yield insights. “I think that the work is exciting and important” says Suma Jacob, who leads an autism research laboratory at the University of Minnesota. “I also think we still have a lot more work to do in this field as a whole.” Previous research has shown that vasopressin, like the hormone oxytocin, is associated with parenting behavior and social bonding, including falling in love. In fact, the two hormones are structurally very similar, and there are receptors in the brain that interact with both of them. But high levels of vasopressin are also associated with anxiety and aggression. Intriguingly, some animal studies have found that higher levels of vasopressin increased aggression specifically in males. © 2015 Scientific American
By Susan Milius The larger Pacific striped octopus hunts shrimp using a strategy worthy of a schoolyard prank. And that’s not the only oddity about the species. It’s only the second octopus known with females that prolong motherhood, instead of dying after weeks of all-out coddling a single brood. But what everyone wants to talk about, researchers who study the species have found, is beak-to-beak mating. Before writhing, wrestling videos of the larger Pacific striped octopus (nicknamed LPSO), biologists knew of two forms of eight-armed sex. Some species mate at a distance, says Roy Caldwell of the University of California, Berkeley. The male extends one arm, always the same one, toward the female and up under her mantle. A travel-ready package of sperm emerges onto his skin and settles into a specialized groove on his mating arm. Waves of arm flexing resembling mammal intestinal motions nudge the packet toward one of two openings to her reproductive tracts. “It’s a messy way of reproducing,” Caldwell says. A lot of sperm packets “are wasted and go floating off.” Distance mating has other challenges. In an Indonesian octopus species, Caldwell’s former student Christine Huffard of the Monterey Bay Aquarium Research Institute discovered males hunkered in their dens sending an arm across the seafloor into the den of the female next door. On occasion, such females leave their dens on some octopus errand, dragging the male along by his mating arm. © Society for Science & the Public 2000 - 2015.
Keyword: Sexual Behavior
Link ID: 21389 - Posted: 09.09.2015
By Amy Ellis Nutt There may finally be an explanation for why men are often less verbally adept than women at expressing themselves. It's the testosterone. Scientists have long known that language development is different between boys and girls. But in scanning the brains of 18 individuals before and after undergoing hormone treatment for female-to-male sex reassignment, Austrian and Dutch researchers found evidence of specific brain structure differences. In particular, they found two areas in the left hemispheres of the transgender men that lost gray matter volume during high-testosterone treatment over a period of four weeks: Broca's area, which is involved in the production of language, and Wernicke's area, which processes language. All of which suggests, according to the study, which was presented this week at the European College of Neuropsychopharmacology Congress, why verbal abilities are often stronger in women than men. "In more general terms, these findings may suggest that a genuine difference between the brains of women and men is substantially attributable to the effects of circulating hormones," said one of the researchers at the conference, Rupert Lanzenberger from Vienna. "Moreover, the hormonal influence on human brain structure goes beyond the early developmental phase and is still present in adulthood." Previous research has shown that higher testosterone is linked to smaller vocabulary in children and also that verbal fluency skills seemed to decrease after female-to-male sex reassignment testosterone treatment.
Shankar Vedantam Girls often outperform boys in science and math at an early age but are less likely to choose tough courses in high school. An Israeli experiment demonstrates how biases of teachers affect students. RENEE MONTAGNE, HOST: At early ages, girls often outperform boys in math and science classes. Later, something changes. By the time they get into high school, girls are less likely than boys to take difficult math courses and less likely, again, to go into careers in science, technology, engineering or medicine. To learn more about this, David Greene spoke with NPR social science correspondent Shankar Vedantam. SHANKAR VEDANTAM, BYLINE: Well, the new study suggests, David, that some of these outcomes might be driven by the unconscious biases of elementary school teachers. What's remarkable about the new work is it doesn't just theorize about the gender gap, it actually has very hard evidence. Edith Sand at Tel Aviv University and her colleague, Victor Lavy, analyzed the math test scores of about 3,000 students in Tel Aviv. When the students were in sixth grade, the researchers got two sets of math test scores. One set of scores were given by the classroom teachers, who obviously knew the children whom they were grading. The second set of scores were from external teachers who did not know if the children they were grading were either boys or girls. So the external teachers were blind to the gender of the children. © 2015 NPR