Chapter 12. Sex: Evolutionary, Hormonal, and Neural Bases
Follow us on Facebook and Twitter, or subscribe to our mailing list, to receive news updates. Learn more.
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.
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
Claire Cain Miller Boys are falling behind. They graduate from high school and attend college at lower rates than girls and are more likely to get in trouble, which can hurt them when they enter the job market. This gender gap exists across the United States, but it is far bigger for poor people and for black people. As society becomes more unequal, it seems, it hurts boys more. New research from social scientists offers one explanation: Boys are more sensitive than girls to disadvantage. Any disadvantage, like growing up in poverty, in a bad neighborhood or without a father, takes more of a toll on boys than on their sisters. That realization could be a starting point for educators, parents and policy makers who are trying to figure out how to help boys — particularly those from black, Latino and immigrant families. “It’s something about family disadvantage itself,” said David Figlio, a Northwestern University economist and co-author of a new paper, presented publicly for the first time on Thursday. “Black people in America are more disadvantaged than white people in America, and if we were to reduce the disadvantage, we may see a reduction in the relative gender gap as well.” Marianne Bertrand, an economist at University of Chicago who with Jessica Pan has studied the gender gap, also found that boys fare worse than girls in disadvantaged homes, and are more responsive than girls to parental time and resources. “Their findings were very consistent: Families that invest more in children are protective for boys,” she said. The reasons that boys react more negatively to disadvantage are varied and hard to pinpoint. Even in utero, boys are more sensitive to extreme stress than girls, and tend to have more unruly temperaments. Society discourages boys from showing vulnerability. Low-income families are often led by single mothers, which has been found to affect boys differently than girls. © 2015 The New York Times Company
By Bob Grant Scientists delving into the neurological underpinnings of traumatic brain injuries (TBI) are finding that there may be crucial differences in the long-term effects of the events that depend not only on the insult, but also on the victim. “No two brain injuries are identical,” University of Pennsylvania neuroscientist Akiva Cohen said during a press conference held at the Society for Neuroscience (SfN) annual meeting in Chicago on Monday (October 19). “Brain injury, like many pathologies these days, constitutes a spectrum.” In addition to a severity spectrum that spans mild to severe, brain injuries may differ in terms of how male and female animals respond to them, according to Ramesh Raghupathi, a neurobiologist at Drexel University. Raghupathi and his colleagues have found that young male mice suffer more depressive behaviors than female mice at both four and eight weeks after mild TBI, and females display more headache-like symptoms after similar insults, which can include concussion. “All of these animals at these times after injury are cognitively normal,” Raghupathi told reporters. “And they do not have any movement problems.” Raghupathi and his colleagues also found molecular differences that may underlie the sex differences in TBI response that they observed. “In the male mice,” he said, “there is a dramatic difference in dopamine transmission” compared to the uninjured mice.” Researchers have previously linked impaired dopamine signaling to depression. Raghupathi’s team tested for the lingering effects of TBI in mice by subjecting the animals to certain swimming tests—which are accepted as proxies for depression—and by using a thin filament to touch the faces of the rodents and recording their sensitivity as a measure of headache-like behaviors.
By JAMES GORMAN No offense to tenors, but outside of opera, a high male voice is seldom, if ever, considered seductive. Scientific research has shown that women find deep male voices attractive, and the same is true in other species, like howler monkeys. Stories from Our Advertisers But evolution is often stingy in its gifts, and researchers investigating male competition to reproduce have discovered an intriguing trade-off in some species of howler monkeys: the deeper the call, the smaller the testicles. Jacob Dunn of Cambridge University, one of the leaders of the research, said that species evolved either to make lower-frequency sounds, or have larger testicles, but none had both a very low sound and very large testicles. “It’s a great study,” said Stuart Semple, an evolutionary anthropologist at the University of Roehampton in London who was not involved in the research. “It shows this really clear trade-off.” Dr. Dunn and other researchers, including W. Tecumseh Fitch, of the University of Vienna, and Leslie A. Knapp, of the University of Utah, studied the size of a bone in the vocal apparatus, which is directly related to how deep the calls are, and the size of testicles, to come up for averages in nine species of howlers. They had been intrigued by great variations in both the size of the howlers’ hyoid bones in museum collections and in the size of the monkeys’ testicles as seen in the field. Dr. Knapp said that some of them are large enough that they are quite obvious “when you look up into the trees.” They used the museum samples of the bone and living monkeys in zoos for testicle measurements, and reported their findings Thursday in the journal Current Biology. © 2015 The New York Times Company
By Hanae Armitage CHICAGO, ILLINOIS—When prairie voles choose a mate, there’s no turning back—the “love chemical” oxytocin increases in their brains and they devote themselves to only each other. Although scientists have observed the behavioral and chemical side of prairie vole love, the neural networks behind commitment are still a mystery. Now, a group of scientists are working toward clearing up the neuronal backdrop of long-term love, and yesterday, presented their findings here at the annual meeting of the Society for Neuroscience. Studies have long suggested the nucleus accumbens, a part of the brain involved in reward processing, plays a crucial role in this type of devotion. To get a better look at the neuronal activity of this region, the scientists mounted a small-scale microscope that monitors calcium flux on top of a male prairie vole’s head (the more calcium into the neuron, the more neuronal activity). They saw that when male prairie voles interacted with their special lady vole, neuronal activity in the nucleus accumbens jumped 20% compared with when they interacted with a random female. Upon closer inspection, scientists saw that specific neurons that fired when the voles interacted with their mates stayed silent when they interacting with a different female. The result, though preliminary, indicates that mates stimulate the brain’s reward center in ways that nonmates cannot. © 2015 American Association for the Advancement of Science.
By Nicholas Bakalar Sleep apnea may be even more dangerous for women than for men, a new study suggests. Epidemiological studies have linked sleep apnea to heart disease in men, but the differences in risk between men and women have been largely unexplored. For the current study, researchers measured sleep quality electronically in 737 men and 879 women, average age 63, who were free of cardiovascular disease at the start of the study. They also tested all of them for troponin T, a protein that can be released into the bloodstream if the heart is damaged, and whose presence in otherwise healthy people indicates an increased risk for heart disease. They tracked the participants for 14 years, recording incidents of coronary artery disease, heart failure and death from cardiovascular disease or other causes. The study was published in Circulation. Obstructive sleep apnea was independently associated with increased troponin T, heart failure and death in women, but not in men. And in women, but not men, sleep apnea was associated with an enlarged heart, another risk factor for cardiovascular disease. “Most people who have sleep apnea have a lot of other risks for heart disease,” said the lead author, Dr. Amil M. Shah, an assistant professor of medicine at Harvard. “But in women, the relationship between sleep apnea and heart disease persisted even after accounting for the other risks.” “Even among women with sleep apnea who don’t get heart failure,” he continued, “it’s associated with changes in the heart that lead to worse outcomes.” © 2015 The New York Times Company
Sara Reardon Naked mole rats are among the ugliest creatures in the animal kingdom, and they engage in acts that seem repulsive — such as eating one another’s, and their own, faeces. Now researchers have found one biological motivation for this behaviour. When a queen mole rat’s subordinates feed on her hormone-filled faeces, the resulting oestrogen boost causes the beta rats to take care of the queen’s pups, according to results presented on 18 October at the Society for Neuroscience meeting in Chicago, Illinois. Like bees, naked mole rats live in eusocial colonies, with only one queen rat and a few males that can reproduce. The rest of the colony consists of dozens of infertile subordinates that help with tasks such as foraging and defending the nest. The subordinate rats also take care of the queen’s pups as though the babies were their own: they build the nests, lick the pups and keep them warm with their body heat. Because they have no mature sex organs, subordinate rats cannot produce the hormones that would usually drive parenting behaviour. To look at what generates the rats’ caring ways, animal biologist Akiyuki Watarai and behavioural scientist Takefumi Kikusui at Azabu University in Japan played recordings of crying mole-rat pups to subordinate rats. Animals whose queens had just given birth paid more attention to the crying than those from other groups, suggesting that the pregnancy itself triggered subordinates’ maternal instincts. © 2015 Nature Publishing Group
By Brook Borel and Spectrum In a lab in Sacramento, California, a wall of plastic boxes lined with corncob bedding holds around 800 mice. Even in this clean and bright room, the smell of so many mice concentrated in one place is overpowering — pungent, and familiar to anyone who has spent time with a pet hamster or gerbil. Most of the boxes hold four adult mice, which flit about, noses twitching as they stare out at the humans staring in. But in one of the boxes, a sleek white mouse is tucked in a corner suckling her litter of half a dozen or so squirmy, dark-furred pups. In most research labs, the fate of these pups would be determined by their sex. The males would spend their lives as test subjects. The females would either be kept for breeding or simply euthanized because they’re not ideal for experiments: They’re supposedly more difficult to work with and generate less consistent data than males do, and it costs too much to maintain both males and females, which must be housed separately. Or so the rationale has gone. But these little female pups are different. The lab where they live is run by Jill Silverman and Mu Yang, researchers at the University of California, Davis (UC Davis) MIND Institute. The two scientists study the behavior of about 15 autism mouse models, and they have always included both males and females in their work. When the pups get older, they will learn to paddle through water mazes or bury black marbles in their bedding, giving researchers insight into how their memory and behavior compare with that of typical mice. Finding the best animal behavioral models of autism is essential because behavior is at the heart of the disorder. In people, autism is diagnosed based on behavioral criteria: abnormal social interactions, difficulties with communication and repetitive actions. © 2015 Scientific American
Kerri Smith Scientists have discovered two extra neurons in a worm species that — they thought — already had its entire nervous system mapped. “It is a bit of a shock,” says Richard Poole, a developmental biologist at University College London (UCL), and one of the team that found the neurons by accident. The researchers call them mystery cells of the male, or MCMs, because they are found only in male nematode worms. The neurons help the worms learn when to prioritize mating over eating, revealing how a seemingly simple brain can be capable of a complex learned behaviour — and one that differs between the sexes. Caenorhabditis elegans worms are the model animal of choice for many neuroscientists, because their neural circuits are so simple that they can be mapped in full. They have two sexes: hermaphrodite and male. Hermaphrodites, the best studied, have just 302 neurons, but males have more — the MCMs raise their total to 385 neurons1. The two ‘mystery’ cells were discovered when Poole’s colleague at UCL, Arantza Barrios, was looking at the distribution of a peptide often found in neurons, called pdf-1. She saw cells light up where she thought they should not — near the worm’s nose. The neurons develop when male worms reach maturity, the researchers worked out. Their report is published in Nature1. Sex or food? © 2015 Nature Publishing Group,
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.