Chapter 12. Sex: Evolutionary, Hormonal, and Neural Bases
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Susan Milius The Nyctibatrachus humayuni frogs live only in India’s Western Ghats, a region of still-unexplored biodiversity. Video now shows that the mating male of the species positions himself loosely on a female’s back, with his hands on the ground or leaves. From this position, called a dorsal straddle, the male then releases sperm directly onto the female’s back. Then, in an unusual move, he retreats before she lays the eggs. Sperm trickling down the female’s back and legs fertilize the eggs, an international research team reports June 14 in PeerJ. It’s the first time biologists have documented this loose straddling position. More typically, male frogs, which don’t deliver sperm into a female reproductive tract, hold tight and contact freshly deposited eggs to fertilize them. Bombay night frogs do on occasion crawl over their eggs, but researchers found the eggs are already fertilized. Biologists studying the challenges of external fertilization have previously cataloged six basic forms of male frog mating grasp, or amplexus. Four take some kind of back-hug approach or a head straddle. Other species position themselves rump-to-rump or, in what’s called glued amplexus, with the male dangling from a behemoth female. Position is hardly the only unexpected feature of courting Bombay night frogs. Females give courtship croaks, one of only a few dozen female-vocal species among the 6,500-plus known kinds of frogs. © Society for Science & the Public 2000 - 2016
Keyword: Sexual Behavior
Link ID: 22326 - Posted: 06.16.2016
by Laura Sanders Any parent trying to hustle a school-bound kid out the door in the morning knows that her child’s skull possesses a strange and powerful form of black magic: It can repel parents’ voices. Important messages like “find your shoes” bounce off the impenetrable fortress and drift unheeded to the floor. But when this perplexing force field is off, it turns out that mothers’ voices actually have profound effects on kids. Children’s brains practically buzz when they hear their moms’ voices, scientists report in the May 31 Proceedings of the National Academy of Sciences. (Fun and not surprising side note: Babies’ voices get into moms’ brains, too.) The parts of kids’ brains that handle emotions, face recognition and reward were prodded into action by mothers’ voices, brain scans of 24 children ages 7 to 12 revealed. And words were not required to get this big reaction. In the study, children listened to nonsense words said by either their mother or one of two unfamiliar women. Even when the words were fake, mothers’ voices still prompted lots of neural action. The study was done in older kids, but children are known to tune into their mothers’ voices early. Really early, in fact. One study found that fetuses’ heart rates change when they hear their moms read a story. For a fetus crammed into a dark, muffled cabin, voices may take on outsized importance. |© Society for Science & the Public 2000 - 2016.
By Linda Marsa| Helen Epstein felt deeply isolated and alone. Haunted by her parents’ harrowing experiences in Nazi concentration camps in World War II, she was troubled as a child by images of piles of skeletons and barbed wire, and, in her words, “a floating sense of danger and incipient harm.” But her Czech-born parents’ defense against the horrific memories was to detach. “Their survival strategy in the war was denial and dissociation, and that carried into their behavior afterward,” recalls Epstein, who was born shortly after the war and grew up in Manhattan. “They believed in action over reflection. Introspection was not encouraged, but a full schedule of activities was.” It was only when she was a student at Israel’s Hebrew University in the late 1960s that she realized she was part of a community that shared a cultural and historical legacy that included both pain and fear. “I met dozens of kids of survivors,” she says, “one after the other who shared certain characteristics: preoccupation with a family past and Israel, and who spoke several middle European languages — just like me.” Epstein’s 1979 book about her observations, Children of the Holocaust, gave voice to that sense of alienation and free-floating anxiety. In the years since, mental health professionals have largely attributed the second generation’s moodiness, hypervigilance and depression to learned behavior. It is only now, more than three decades later, that science has the tools to see that this legacy of trauma becomes etched in our DNA — a process known as epigenetics, in which environmental factors trigger genetic changes that may be passed on, just as surely as blue eyes and crooked smiles.
By Virginia Morell Sex is never simple—even among lizards. Unlike mammals, the sex of central bearded dragons, large lizards found in eastern Australia, is determined by their chromosomes and the environment. If the eggs are incubated in high temperatures, male embryos turn into females. Such sex-reversed lizards still retain the chromosomal makeup of a male, but they develop into functional superfemales, whose output of eggs exceeds that of the regular females. Now, a new study predicts that—in some cases—these superfemales may be able to drive regular ones to extinction. That’s because superfemales not only produce more eggs, but they’re also exceptionally bold. Looking at the shape, physiology, and behavior of 20 sex-reversed females, 55 males, and 40 regular females, scientists found that the sex-reversed dragons were physically similar to regular males: They had a male dragon’s long tail and high body temperature. They were also behaviorally similar, acting like bold, active males—even as they produced viable eggs. Indeed, the scientists report in the current issue of the Proceedings of the Royal Society B that these sex-reversed females were behaviorally more malelike than the genetic males. Because of these advantages, this third sex could reproductively outcompete normal females, the scientists say, possibly causing some populations to lose the female sex chromosome. (Females are the heterogametic sex, like human males.) In such a population, the dragons’ sex would then be determined solely by temperature instead of genetics—something that’s occurred in the lab within a single generation. Could it happen in the wild? The scientists are still investigating. © 2016 American Association for the Advancement of Science
By Perri Klass, M.D. When girls come in for their physical exams, one of the questions I routinely ask is “Do you get your period?” I try to ask before I expect the answer to be yes, so that if a girl doesn’t seem to know about the changes of puberty that lie ahead, I can encourage her to talk about them with her mother, and offer to help answer questions. And I often point out that even those who have not yet embarked on puberty themselves are likely to have classmates who are going through these changes, so, again, it’s important to let kids know that their questions are welcome, and will be answered accurately. But like everybody else who deals with girls, I’m aware that this means bringing up the topic when girls are pretty young. Puberty is now coming earlier for many girls, with bodies changing in the third and fourth grade, and there is a complicated discussion about the reasons, from obesity and family stress to chemicals in the environment that may disrupt the normal effects of hormones. I’m not going to try to delineate that discussion here — though it’s an important one — because I want to concentrate on the effect, rather than the cause, of reaching puberty early. A large study published in May in the journal Pediatrics looked at a group of 8,327 children born in Hong Kong in April and May of 1997, for whom a great deal of health data has been collected. The researchers had access to the children’s health records, showing how their doctors had documented their physical maturity, according to what are known as the Tanner stages, for the standardized pediatric index of sexual maturation. Before children enter puberty, we call it Tanner I; for girls, Tanner II is the beginning of breast development, while for boys, it’s the enlargement of the scrotum and testes and the reddening and changing of the scrotum skin. Boys and girls then progress through the intermediate changes to stage V, full physical maturity. © 2016 The New York Times Company
By Ann Lukits Teens who baby-sit may not only gain confidence in caring for young children, they may also alter their brain chemistry in a way that could make them better parents, suggests an animal study in Developmental Psychobiology. Young female rats housed with various groups of unrelated rat pups had fully developed mothering skills as adults, compared with control rats without caregiving, or alloparenting, experience. The early caregivers had significantly higher concentrations of tryptophan hydroxylase-2 (TPH2) in the brain, an enzyme associated with increased production of serotonin, a chemical involved in mood and social behavior. Previous research has associated baby-sitting experience in humans with greater confidence in new mothers, researchers said. Experiments at Michigan State University involved two groups of juvenile or adolescent female rats from 16 litters. In one group, 24 rats were housed in separate cages with a different group of week-old pups each day. A second group of 24 controls were given pink pup-size pencil erasers. The experiments continued for 14 days. Eight mature rats from both groups were subsequently exposed to new groups of pups. Six rats with alloparenting experience acted maternally toward the pups, whereas none of the control rats exhibited maternal behavior. Rats with alloparenting experience also displayed less anxiety during behavioral testing. The animals were euthanized after testing and TPH2 levels measured in a section of the brain called the dorsal raphe nucleus. ©2016 Dow Jones & Company, Inc
Keyword: Sexual Behavior
Link ID: 22273 - Posted: 06.01.2016
Susan Milius Forget it, peacocks. Nice try, elk. Sure, sexy feathers and antlers are showy, but the sperm of a fruit fly could be the most over-the-top, exaggerated male ornamentation of all. In certain fruit fly species, such as Drosophila bifurca, males measuring just a few millimeters produce sperm with a tail as long as 5.8-centimeters, researchers report May 25 in Nature. Adjusted for body size, the disproportionately supersized sperm outdoes such exuberant body parts as pheasant display feathers, deer antlers, scarab beetle horns and the forward-grasping forceps of earwigs. Fruit flies’ giant sperm have been challenging to explain, says study coauthor Scott Pitnick of Syracuse University in New York. Now he and his colleagues propose that a complex interplay of male and female benefits has accelerated sperm length in a runaway-train scenario. Males with longer sperm deliver fewer sperm, bucking a more-is-better trend. Yet, they still manage to transfer a few dozen to a few hundred per mating. And as newly arrived sperm compete to displace those already waiting in a female’s storage organ, longer is better. Fewer sperm per mating means females tend to mate more often, intensifying the sperm-vs.-sperm competition. Females that have the longest storage organs, which favor the longest sperm, benefit too: Males producing megasperm, the researchers found, tend to be the ones with good genes likely to produce robust offspring. “Sex,” says Pitnick, “is a powerful force.” © Society for Science & the Public 2000 - 2016
By Christie Aschwanden When concussions make the news, it’s usually about football. But head injuries happen in other sports too, and not just to men. During a congressional hearing on concussions in youth sports on Friday, Dawn Comstock, an epidemiologist who studies sports injuries, told a House Energy and Commerce subcommittee that in sports like soccer and basketball in which girls and boys play by the same rules, with the same equipment and the same facilities, “girls have higher concussion rates than boys.” Comstock, a researcher at the Colorado School of Public Health, is the first author of a 2015 study published in JAMA Pediatrics that quantified concussions in high school soccer and found that they were about one and a half times more common in girls than in boys. When U.S. Rep. Diana DeGette, D-Colo., asked whether more data was needed to show that girls have higher concussion rates, Comstock replied, “We already have the data that’s consistently shown this gender difference.” What we don’t have, she said, is a proven explanation for the discrepancy. Some researchers have wondered whether women and girls are simply more likely to report their symptoms than men and boys are. “It’s a sexist way to say that they’re not as tough,” said Katherine Price Snedaker, executive director of Pink Concussions,1 an organization that is seeking answers to how concussions affect women and girls. The group recently held a summit on female concussion and traumatic brain injuries at Georgetown University, and one of the speakers was Shannon Bauman, a sports physician who presented data from 207 athletes — both male and female — who’d been evaluated at her specialty concussion clinic in Barrie, Ontario, between September 2014 and January 2016.
By Simon Oxenham The “cuddle chemical”. The “moral molecule”. Oxytocin has quite a reputation – but much of what we thought about the so-called “love hormone” may be wrong. Oxytocin is made by the hypothalamus and acts on the brain, playing a role in bonding, sex and pregnancy. But findings that a sniff of the hormone is enough to make people trust each other more are being called into question after a string of studies failed to replicate classic experiments. Paul Zak at the Centre for Neuroeconomic Studies in Claremont, California, made his moral molecule hypothesis famous in 2011 when he memorably squirted a syringe of the hormone into the air while delivering a TED talk. When people sniff oxytocin before playing a money-lending game, it increases how much they trust each other, he explained. But several teams have been unable to replicate his finding. Last November, Gideon Nave at the California Institute of Technology in Pasadena and his colleagues reviewed studies of oxytocin, and concluded that the effect of nasal squirts of the hormone on trust are not reliably different from zero. Nave’s team aren’t the only ones calling the moral molecule hypothesis into question. In 2012, Moïra Mikolajczak at the Catholic University of Louvain (UCL) in Belgium and her colleagues published their own seminal findings backing a link between trust and oxytocin. They found that when people filled out an anonymous questionnaire about their sex lives and fantasies, they were less likely to seal the envelopes they returned them in if given a nasal dose of oxytocin beforehand. © Copyright Reed Business Information Ltd.
Laura Glynn, Pregnancy brain typically refers to lapses in attention and memory. About 80 percent of new mothers report difficulties remembering things that once came naturally, and although not all studies support this, the weight of the evidence shows that during pregnancy, women exhibit measurable declines in important cognitive skills. But it's not all bad news. The maternal brain also features important enhancements. Mother rats score higher in tests of attention, foraging and planning than peers who have never given birth. These gains most likely render them better able to defend and provide for their pups. The benefits for human moms are less clear, but data are emerging that suggest human pregnancies initiate neural restructuring. A 2010 study found that in the first few months after giving birth, human females show changes in several key brain regions. Specifically, they often exhibit increased volume in the hypothalamus, striatum and amygdala—areas essential for emotional regulation and parental motivation—as well as in regions governing decision making and protective instincts. We can glean further evidence from behavioral changes during pregnancy. Many women exhibit blunted physiological and psychological responses to stress, which may afford mother and fetus protection from the potentially adverse effects of taxing situations. And in the postpartum period, the hormones that sustain breast-feeding maintain these dampened stress responses. © 2016 Scientific American
Sara Reardon As a medical student in Paris in the 1980s, Eric Vilain found himself pondering the differences between men and women. What causes them to develop differently, and what happens when the process goes awry? At the time, he was encountering babies that defied simple classification as a boy or girl. Born with disorders of sex development (DSDs), many had intermediate genitalia — an overlarge clitoris, an undersized penis or features of both sexes. Then, as now, the usual practice was to operate. And the decision of whether a child would be left with male or female genitalia was often made not on scientific evidence, says Vilain, but on practicality: an oft-repeated, if insensitive, line has it that “it's easier to dig a hole than build a pole”. Vilain found the approach disturbing. “I was fascinated and shocked by how the medical team was making decisions.” Vilain has spent the better part of his career studying the ambiguities of sex. Now a paediatrician and geneticist at the University of California, Los Angeles (UCLA), he is one of the world's foremost experts on the genetic determinants of DSDs. He has worked closely with intersex advocacy groups that campaign for recognition and better medical treatment — a movement that has recently gained momentum. And in 2011, he established a major longitudinal study to track the psychological and medical well-being of hundreds of children with DSDs. © 2016 Nature Publishing Group
By David Shultz Did you sleep well? The answer may depend on your age, location and gender. A survey of 5000 sleepers from across the world has revealed that women get the most sleep, particularly those under the age of 25. Daniel Forger at the University of Michigan in Ann Arbor and his team were able to get their huge dataset thanks to Entrain, a smartphone app that people use to track their sleep. With their consent, Forger’s team accessed users’ data on their wake time, bed time, time zone and how much light they were exposed to during the day. Analysing this information, they found that middle-aged men sleep the least, while women under the age of 25 sleep the most. As a whole, women appear to sleep on average for 30 minutes longer than men, thanks to going to bed slightly earlier and waking up slightly later. For an individual, the time they woke up had the strongest link to how much sleep they got, suggesting that having a job that starts early every day can mean that you get less sleep than someone who starts work at a later hour. There were also differences between countries. People in Singapore, for example, sleep for an average of 7.5 hours a night, while Australians get 8.1 hours. Late bedtimes seem to be to blame – people in Singapore tended to stay up until after 11.45 pm each night, while people in Australia were likely to hit the hay closer to 10.45 pm. The team found that, in general, national wake-up times were linked more to daylight hours than bedtimes. This could be because bedtimes are more affected by social factors. © Copyright Reed Business Information Ltd.
By Virginia Morell After defeating other males in boxing matches and winning a territorial roost—and a bevy of females—a male Seba’s short-tailed bat (Carollia perspicillata, pictured) might think his battles for reproductive rights are over. But the defeated males of this neotropical species have a trick up their sleeve: clandestine matings with willing females. The tactic works, and now researchers know why. Scientists studied bats in a captive colony in Switzerland, removing alpha males from their harems for 3 days, and examining their sperm—as well as that of their rivals. A previous study showed that the sneaky males have faster, longer lived sperm, which gives them a leg-up on the alpha male. Researchers had suspected this was because the sneakers produced this supersperm to compete. But the new study finds that after the 3 days of abstinence, the alpha male’s sperm is as agile and vigorous as that of his rivals. Thus, the team reports today in the Journal of Experimental Biology, the sneaky males aren’t generating special sperm—they just mate less, so their sperm is in better shape when it comes time to race to the egg. © 2016 American Association for the Advancement of Science.
By Sarah Kaplan The ancient Greeks spoke of a mythological society composed entirely of warrior women. The medieval traveler John Mandeville wrote of a place whose female rulers "never would suffer man to dwell amongst them." "Paradise Island," home of Wonder Woman, was a feminist utopia where no one with a Y chromosome was allowed. Sadly, those places only exist in fiction. But something like them does exist in the real world. It's in a wetland in rural Ohio. And it's full of salamanders. "They’re pretty incredible," said Robert Denton, a biologist at Ohio State who studies an unusual group of salamander species that literally don't need men. These creatures – all female – reproduce by cloning themselves. To keep their gene pool diverse, they sometimes "steal" sperm left behind on trees and leaves by male salamanders of other species and incorporate that DNA into their offspring. Most sexually reproducing organisms have two sets of chromosomes to make up their genome – one from each parent. But one of these strange salamanders can have between two and five times that much genetic material lying in wait within her cells. It's as if they have multiple genomes to fall back on, and that's made them incredibly successful. "Polyploid" salamanders have been around some 6 million years, Denton said — far longer than most other animal species that reproduce asexually. Since a lack of diversity means having a smaller arsenal of genetic variation to fall back on when living conditions change, these groups usually go extinct relatively quickly. © 1996-2016 The Washington Post
by Susan Milius There’s nothing like a guy doing all the child care to win female favor, even among giant water bugs. Thumbnail-sized Appasus water bugs have become an exemplar species for studying paternal care. After mating, females lay eggs on a male’s back and leave him to swim around for weeks tending his glued-on load. For an A. major water bug, lab tests show an egg burden can have the sweet side of attracting more females, researchers in Japan report May 4 in Royal Society Open Science. Given a choice of two males, females strongly favored, and laid more eggs on, the one already hauling around 10 eggs rather than the male that researchers had scraped eggless. Females still favored a well-egged male even when researchers offered two males that a female had already considered, but with their egg-carrying roles switched from the previous encounter. That formerly spurned suitor this time triumphed. A similar preference, though not as clear-cut, showed up in the slightly smaller and lighter A. japonicus giant water bug. “We conclude that sexual selection plays an important role in the maintenance of elaborate paternal care,” says study coauthor Shin-ya Ohba of Nagasaki University. © Society for Science & the Public 2000 - 2016
Nicola Davis Benedict Cumberbatch’s deep and booming voice might have made him a hit among women, but a low pitch is more likely to have evolved to intimidate other men, new research suggests. When both heterosexual men and women were played recordings of male voices, the deeper tones were hailed by men as sounding more dominant. While the deeper voices were judged to be more attractive by female listeners, the effect was weaker, the researchers report. “If you look at what men’s traits look like they are designed for, they look much better designed for intimidating other males than for attracting females,” said David Puts of Pennsylvania State University, who led the study. Published in Proceedings of the Royal Society B: Biological Sciences, the three-part study by an international team of scientists explored the links between voice pitch and mating systems, attractiveness and, for males only, perceived dominance. A formula for the perfect voice? Read more In the first leg of the research, the scientists turned their attention to primates encompassing Old and New World monkeys, as well as humans and other apes, to explore differences in “fundamental frequency” between males and females of each species - the aspect of the voice that is perceived as pitch. After selecting 1721 recordings, they found large differences were more common in polygynous species - where males mate with more than one female - than monogamous ones. That, they say, could be because in polygynous species, competition between males is greater - hence a male with a lower-pitched voice deemed to be intimidating could have the edge in securing a mate. Intriguingly, the researchers found that among the apes humans showed the greatest difference in pitch between the sexes, suggesting our ancestors were not searching for “the one” but were polygynous - a situation Puts still believes to be the case. © 2016 Guardian News and Media Limited
By Leonard Sax, M.D., Ph.D Why is it that girls tend to be more anxious than boys? It may start with how they feel about how they look. Some research has shown that in adolescence, girls tend to become more dissatisfied with their bodies, whereas boys tend to become more satisfied with their bodies. Another factor has to do with differences in how girls and boys use social media. A girl is much more likely than a boy to post a photo of herself wearing a swimsuit, while the boy is more likely to post a photo where the emphasis is on something he has done rather than on how he looks. If you don’t like Jake’s selfie showing off his big trophy, he may not care. But if you don’t like Sonya’s photo of herself wearing her bikini, she’s more likely to take it personally. Imagine another girl sitting in her bedroom, alone. She’s scrolling through other girls’ Instagram and Snapchat feeds. She sees Sonya showing off her new bikini; Sonya looks awesome. She sees Madison at a party, having a blast. She sees Vanessa with her adorable new puppy. And she thinks: I’m just sitting here in my bedroom, not doing anything. My life sucks. Boys are at lower risk for the toxic effects of social media than girls are, for at least three reasons. First, boys are less likely to be heavily invested in what you think of their selfies. “Does this swimsuit make me look fat?” is a question asked by girls more often than by boys. Second, boys tend to overestimate how interesting their own life is. Third, the average boy is likely to spend more time playing video games than Photoshopping his selfie for Instagram. And in video games, unlike social media, everybody truly can be a winner, eventually. If you play Grand Theft Auto or Call of Duty long enough, you will, sooner or later, complete all the missions, if you just keep at it. © 2016 The New York Times Company
By Patrick Monahan You might have seen a video from David Attenborough’s The Life of Birds series where a male superb lyrebird (Menura novaehollandiae) attempts to lure a mate by imitating a smorgasbord of bird calls and even chainsaws. As nature’s show-offs, male animals tend to have more elaborate colors and courtship behaviors than their female counterparts, so it’s typical that the male would get the public’s attention. The same is true in science: Plenty of female birds sing songs, but researchers have in the past often dismissed them as simply being evolutionary tag-alongs of the males’ “come hither” calls. Now, by recording the calls of female superb lyrebirds, researchers have found that they can keep up with the boys just fine. According to a study published this week in Frontiers in Ecology and Evolution, the females collectively imitated 19 other species of birds, and also sang lyrebird-specific songs. And they changed their songs depending on context, using more lyrebird-specific “whistle” calls when out foraging and vying for territory, but more mimicking calls when defending their nests (as in the audio file below). The fact that the females change their type of call depending on the context makes it likely that these songs evolved in their own right—and the males’ calls aren’t so special after all. Plus, that part about the chainsaw? It probably doesn’t even happen in the wild. © 2016 American Association for the Advancement of Science
Medical research and new drugs to treat human illness usually start with studies on mice and rats. But that type of research has been traditionally sexist — using far more male than female rodents. Scientists warn that has already led to drugs and treatments that are potentially dangerous for women and say the approach slows down the development of treatments and drugs that are safe and effective for everyone. Cara Tannenbaum, scientific director of the Institute of Gender and Health at the Canadian Institutes of Health Research, cited a couple of examples on CBC's The Current of cases where drug side-effects turned out to be far more harmful in women: A stomach drug called cisapride that was sold in the 1990s under the name Prepulsid was withdrawn by Health Canada in 2000 because it sometimes caused irregular heartbeat and sudden death "in women only," Tannenbaum said. Among the victims was the 15-year-old daughter of former Ontario MP Terence Young. "It's not clear that the drug was ever tested in female animals or minors," Tannenbaum added. Health Canada has issued a warning about sleeping pills containing the drug zolpiclone, also known as Ambien, Tannenbaum said. Women are recommended to take half the dose that is prescribed to men. "It was recently discovered that the level of the drug was 45 per cent higher in women the next day, which can lead to car accidents," Tannenbaum said. Jeffrey Mogil, a neuroscientist and pain specialist at McGill University, said there are lots of reasons to suspect men and women respond differently to many different kinds of drugs, but very little actual data. "We actually don't know the scope of the problem," he told The Current. ©2016 CBC/Radio-Canada.
Ian Sample Science editor The subtle impact of genetics on the age at which people lose their virginity has been teased apart by scientists and shown to have an effect on how well people fare at school. Though mostly driven by upbringing and peer behaviour, a person’s age when they first have sex is also shaped by biological factors where genes have a role to play. Researchers found that differences in DNA could account for a quarter of the variation in the age at which people lost their virginity, with other factors, among them religious beliefs, family background and peer pressure, making up the rest. Genes influence academic ability across all subjects, latest study shows Read more “We were able to calculate for the first time that there is a heritable component to age at first sex, and the heritability is about 25%, so one quarter nature, three quarters nurture,” said John Perry, an expert in reproductive ageing and related health conditions at Cambridge University. Among 38 sections of DNA found to affect the age at which people first had sex were genes that drive reproductive biology, such as the release of sex hormones and the age of puberty. Still others were found that appear to affect behaviour, personality and appearance. A variant of one of the genes, named CADM2, linked an early start to one’s sex life with risk-taking behaviour and having a large number of children. A version of another gene, MSRA, found in people who lost their virginity later than average, was linked to irritability. © 2016 Guardian News and Media Limited