Chapter 12. Sex: Evolutionary, Hormonal, and Neural Bases

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Eleven years on, I still remember the evening I decided to kill my baby daughter. It's not something you're supposed to feel as a new parent with a warm, tiny bundle in your arms. But this is how postnatal depression can twist your logic. At the time it made perfect sense. Catherine was screaming, in pain. She had colic, there was nothing I could do about it. If an animal were in this much pain you'd put it out of its misery, so why not a human? Postnatal depression can have this kind of effect even on the most reasonable woman, yet you won't find much about it in baby books. We're expected to love our kids the moment they pop out, even while the memory of the labour pains is still raw. I knew a baby would be hard work, of course, but I expected motherhood to be fulfilling. As it happened I had a wonderful pregnancy, followed by a quick and easy birth. But the problems started soon after. Catherine wouldn’t feed, her blood sugar levels tumbled and I ended up bottle-feeding her, in tears, in a hospital room filled with posters promoting the breast. I was a Bad Mother within 48 hours. Things were no better after the first month. This was meant to be a joyous time, but all I seemed to feel was rage and resentment. In pregnancy all the attention had been on me, and suddenly I was a sideshow to this wailing thing in a crib. I was tired, tetchy and resentful. My daughter had rapidly become a ball and chain. My freedom was over. I kept hoping this was just the “baby blues” and that it would soon pass, but things only got worse. When colic set in, for around five hours each evening Catherine would scream, her face a mix of red and purple rage. No amount of pacing, tummy-rubbing or soothing words could stop this tiny demanding creature. So one night, alone with her in her room, I decided it would be best to put her out of her misery. © 2014 Guardian News and Media Limited

Keyword: Depression; Aggression
Link ID: 19626 - Posted: 05.16.2014

By RONI CARYN RABIN For decades, scientists have embarked on the long journey toward a medical breakthrough by first experimenting on laboratory animals. Mice or rats, pigs or dogs, they were usually male: Researchers avoided using female animals for fear that their reproductive cycles and hormone fluctuations would confound the results of delicately calibrated experiments. That laboratory tradition has had enormous consequences for women. Name a new drug or treatment, and odds are researchers know far more about its effect on men than on women. From sleeping pills to statins, women have been blindsided by side effects and dosage miscalculations that were not discovered until after the product hit the market. Now the National Institutes of Health says that this routine gender bias in basic research must end. In a commentary published on Wednesday in the journal Nature, Dr. Francis Collins, director of the N.I.H., and Dr. Janine A. Clayton, director of the institutes’ Office of Research on Women’s Health, warned scientists that they must begin testing their theories in female lab animals and in female tissues and cells. The N.I.H. has already taken researchers to task for their failure to include adequate numbers of women in clinical trials. The new announcement is an acknowledgment that this gender disparity begins much earlier in the research process. “Most scientists want to do the most powerful experiment to get the most durable, powerful answers,” Dr. Collins said in an interview. “For most, this has not been on the radar screen as an important issue. What we’re trying to do here is raise consciousness.” Women now make up more than half the participants in clinical research funded by the institutes, but it has taken years to get to this point, and women still are often underrepresented in clinical trials carried out by drug companies and medical device manufacturers. © 2014 The New York Times Company

Keyword: Sexual Behavior; Aggression
Link ID: 19619 - Posted: 05.15.2014

Ewen Callaway In the silk business, sex is money. Male silkworms weave cocoons with more silk of a higher quality than females do, and the multibillion dollar sericulture industry has long sought an easy way to breed only males. That might now be a realistic goal, as researchers have identified the process that determines sex in the silkworm Bombyx mori1. The sex factor is found to be a small RNA molecule — the first time that anything other than a protein has been implicated in a sex-detemination process. In nearly all Lepidoptera — the order that includes moths and butterflies — sex is determined in silkworms by a WZ chromosome system, in contrast to the XY system used in mammals. Female silkworms carry W and Z sex chromosomes, whereas males boast a pair of Z chromosomes. Last year, researchers showed how to genetically modify silkworms so that the females would express a deadly protein (see 'Genetic kill switch eradicates female silkworms for a better crop'). But efforts to identify the genes on the W chromosome that make silkworms female have come up short: the W does not seem to have any protein-making genes, and is instead almost completely filled with parasitic, mobile genetic elements called transposons. In 2011, a team led by entomologist Susumu Katsuma at the University of Tokyo reported that the W chromosome produces short RNA molecules that keep transposons at bay in newly formed egg cells2. Katsuma and his team report in Nature today1 that one such molecule, which the authors called Fem, is specific to female silkworms, suggesting that it has a role in sex determination. The Fem RNA breaks down a corresponding molecule made by a gene known as Masculinizer, which is found on the Z chromosome. When the researchers silenced Masculinizer, embryos execute a genetic programme that makes female tissue. © 2014 Nature Publishing Group

Keyword: Sexual Behavior
Link ID: 19611 - Posted: 05.15.2014

|By Jason G. Goldman When a male fallow deer wants to mate, he isn't shy about letting everyone around him know. The males, also called fallow bucks, can produce their mating calls as many as 3,000 times each hour during the mating season. Those calls serve two functions: to attract females and to deter rival males. Yet there is more hidden in the groans of fallow bucks than first meets the ear, according to a new study in Behavioral Ecology. Every October around 25 bucks gather in Petworth Park in England's county of West Sussex, where each stakes out a territory, hoping to entice a female at a feral conclave of romance, combat and deer calling, an event known as a lek. “Leks are really rare in mammals, and they're really rare in ungulates. Fallow deer are the only species of deer that we know that lek,” says Alan McElligott of Queen Mary, University of London, who oversaw the study. Mating calls reveal information about the caller, such as body size or dominance rank, which is useful both to interested females and to rival males—and every conceivable type of fallow deer utterance turns up at the lek. In one study, McElligott found that the quality of groans decreased over time. “The mature bucks stop eating for a couple of weeks,” over the course of the lek, McElligott explains, so “they are really worn out.” That fatigue is reflected in their calls, but do other males notice? Because the lek is such a spectacle, the deer in Petworth Park are accustomed to human interlopers, which allowed Queen Mary postdoctoral scholar Benjamin J. Pitcher to cart a sound system around without interrupting the festivities. © 2014 Scientific American

Keyword: Sexual Behavior; Aggression
Link ID: 19599 - Posted: 05.12.2014

By Pippa Stephens Health reporter, BBC News A key difference in the brains of male and female MS patients may explain why more women than men get the disease, a study suggests. Scientists at Washington University School of Medicine in the US found higher levels of protein S1PR2 in tests on the brains of female mice and dead women with MS than in male equivalents. Four times more women than men are currently diagnosed with MS. Experts said the finding was "really interesting". MS affects the nerves in the brain and spinal cord, which causes problems with muscle movement, balance and vision. It is a major cause of disability, and affects about 100,000 people in the UK. Abnormal immune cells attack nerve cells in the central nervous system in MS patients. There is currently no cure, although there are treatments that can help in the early stages of the disease. Researchers in Missouri looked at relapsing remitting MS, where people have distinct attacks of symptoms that then fade away either partially or completely. About 85% of people with MS are diagnosed with this type. Scientists studied the blood vessels and brains of healthy mice, mice with MS, and mice without the gene for S1PR2, a blood vessel receptor protein, to see how it affected MS severity. They also looked at the brain tissue samples of 20 people after they had died. They found high levels of S1PR2 in the areas of the brain typically damaged by MS in both mice and people. The activity of the gene coding for S1PR2 was positively correlated with the severity of the disease in mice, the study said. Scientists said S1PR2 could work by helping to make the blood-brain barrier, in charge of stopping potentially harmful substances from entering the brain and spinal fluid, more permeable. BBC © 2014

Keyword: Multiple Sclerosis; Aggression
Link ID: 19595 - Posted: 05.10.2014

By Diana Kwon Would you rather have $50 now or $100 two weeks from now? Even though the $100 is obviously the better choice, many people will opt for the $50. Both humans and animals show this tendency to place lower value on later rewards, a behavior known as temporal discounting. High rates of temporal discounting can lead to impulsive behavior, and at its worst, too much of this “now bias” is associated with pathological gambling, attention deficit hyperactivity disorder and drug addiction. What determines if you’ll be an impulsive decision-maker? New evidence suggests that for women, estrogen levels might be a factor. In a recent study published in the Journal of Neuroscience, Charlotte Boettiger and her team at the University of North Carolina revealed that greater increases in estrogen levels across the menstrual cycle led to less impulsive decision making. The researchers tested the “now bias” in 87 women between the ages of 18 and 40 at two different points in their menstrual cycle – in the menstrual phase when estrogen levels are low and the follicular phase when estrogen levels are high. Participants were given a delay-discounting task where they had to choose between two options: a certain sum of money at a later date or a discounted amount immediately (e.g. $100 in one week or $70 today). Subjects showed a greater bias toward the immediate choice during the menstrual phase of the cycle, when estrogen levels were low. Estrogen levels vary between women and can change with factors like stress and age. When the researchers measured amounts of estradiol (the dominant form of estrogen) from the saliva in a subset of the participants at the two points in their menstrual cycles, they found that not all of them showed a detectable increase. Only those with a measureable rise in estradiol showed a significant change in impulsive decision-making. © 2014 Scientific American

Keyword: Attention; Aggression
Link ID: 19589 - Posted: 05.08.2014

The gene that most likely determines the sex of the platypus and echidna has been identified by Australian and Swiss researchers. The study also shows that the Y chromosome, contrary to previous assumptions, carries genes that are important to the basic viability of male mammals, says geneticist Dr Paul Waters from the University of New South Wales. Although the Y chromosome is known to be important in sex determination, little is known about the function and evolution of its genes, says Waters. He says this is because it has so many repetitive and palindromic sequences, which make it hard to reconstruct the true sequences of its genes from fragments of sequenced DNA. Monotremes (the platypus and the echidna), whose males have 5 X chromosomes and 5 Y chromosomes, are especially challenging. "No one had really characterised any Y chromosomes in platypus before because they've got quite a complex sex chromosome system," says Waters. Waters and colleagues from the University of Adelaide and the University of Lausanne now report on their new analysis of male and female DNA from 15 representative mammals, including human, elephants, marsupials and monotremes. The study, reported recently in the journal Nature, is the largest of its kind, and relied on a rapid new sequencing technique. © 2014 Discovery Communications, LLC.

Keyword: Sexual Behavior
Link ID: 19582 - Posted: 05.07.2014

by Bethany Brookshire When I was a lab scientist working with mice, I spent hours controlling variables. I stood on precarious chairs to tape tarps over lights to get the light level perfectly right. I made one undergraduate who wore perfume to the lab for animal training wear the same perfume for a whole semester. I was so worried about the mice “recognizing” me over long, overlapping experiments that I did not change the scents of any of my personal care products for nine years. Many of these variables got reported in the methods sections of my papers. “All experiments conducted between 5:00 and 7:00 a.m. Maze dimensions: 4 inches wide, with walls 6 inches tall. Lighting held constant at 10 lux.” All of these variables are reported to allow other people to repeat my experiments, and hopefully get the same result. Now, a new study suggests that maybe I should have included another element in my methods section: “All mice exposed to the scent of a woman.” Jeffrey Mogil’s lab at McGill University in Montreal, Canada, reports April 28 in Nature Methods that mice respond differently to men and women, and that men in fact are a stressful influence. The results show that there’s yet another variable to control when doing sensitive mouse behavioral studies, a variable that could impact fields from pain to depression and beyond. Every department that does animal research has stories about particular experimenters. I recall hearing a story of a lab technician who could get results no one else could, because mice just loved her strawberry-scented hair conditioner. Another colleague told of one experimenter who was so good at handling rats that no one believed her anxiety results. Her rats were just so relaxed. And Mogil’s lab had its own story. In their lab, the presence of human experimenters seemed to stop mice from showing pain. © Society for Science & the Public 2000 - 2013

Keyword: Stress; Aggression
Link ID: 19567 - Posted: 05.04.2014

Humans stink, and it’s wonderful. A few whiffs of a pillow in the morning can revive memories of a lover. The sweaty stench of a gym puts us in the mood to exercise. Odors define us, yet the scientific zeitgeist is that we don’t communicate through pheromones—scents that influence behavior. A new study challenges that thinking, finding that scent can change whether we think someone is masculine or feminine. Humans carry more secretion and sweat glands in their skin than any other primate. Yet 70% of people lack a vomeronasal organ, a crescent-shaped bundle of neurons at the base of each nostril that allows a variety of species—from reptiles to nonprimate mammals—to pick up on pheromones. (If you’ve ever seen your cat huff something, he’s using this organ.) Still, scientists have continued to hunt for examples of pheromones that humans might sense. Two strong candidates are androstadienone (andro) and estratetraenol (estra). Men secrete andro in their sweat and semen, while estra is primarily found in female urine. Researchers have found hints that both trigger arousal—by improving moods and switching on the brain’s “urge” center, the hypothalamus—in the opposite sex. Yet to be true pheromones, these chemicals must shape how people view different genders. That’s exactly what they do, researchers from the Chinese Academy of Sciences in Beijing report online today in Current Biology. The team split men and women into groups of 24 and then had them watch virtual simulations of a human figure walking (see video). The head, pelvis, and major joints in each figure were replaced with moving dots. Subjects in prior studies had ranked the videos as being feminine or masculine. For instance, watch the figure on the far left, which was gauged as having a quintessential female strut. Notice a distinctive swagger in the “hip” dots and how they contrast with the flat gait of the “male” prototype all the way to the right. © 2014 American Association for the Advancement of Science

Keyword: Chemical Senses (Smell & Taste); Aggression
Link ID: 19565 - Posted: 05.03.2014

A UBC neuroscientist says motherhood permanently alters the brain, exposing moms to different health risks than women without children. Liisa Galea, a professor in the university's psychology department, says some changes are temporary while others are permanent. The most obvious example is size. According to Galea, a mother's brain shrinks by up to eight per cent during pregnancy. While it bounces back about six months after birth, she notes the reaction could have repercussions. “Our research shows that, as a result of these transformations, mothers experience different cognitive abilities and health risks than women without children,” said Galea. And she warns that women who’ve borne children may even react to medication differently. “If mothers’ brains are different than other women’s brains, as our research finds, it means we must embrace greater personalization of medical care – not only for men versus women, but even among women with different life experiences,” she said. But that’s a challenge that may be insurmountable given that medical research studies at the animal model level have relied predominantly on the use of male rats. “Why would we assume that what works in a male rat automatically works in a female patient before testing it on a female rat?” questioned Galea. She claims one of the big failures of translational studies is that most fail to acknowledge how subjects’ gender, or other unique characteristics, like motherhood, plays a role. © CBC 2014

Keyword: Sexual Behavior; Aggression
Link ID: 19561 - Posted: 05.03.2014

By Helen Briggs BBC News A mother's diet around the time of conception can permanently influence her baby's DNA, research suggests. Animal experiments show diet in pregnancy can switch genes on or off, but this is the first human evidence. The research followed women in rural Gambia, where seasonal climate leads to big differences in diet between rainy and dry periods. It emphasises the need for a well-balanced diet before conception and in pregnancy, says a UK/US team. Scientists followed 84 pregnant women who conceived at the peak of the rainy season, and about the same number who conceived at the peak of the dry season. Nutrient levels were measured in blood samples taken from the women; while the DNA of their babies was analysed two to eight months after birth. Lead scientist Dr Branwen Hennig, from the London School of Hygiene & Tropical Medicine, said it was the first demonstration in humans that a mother's nutrition at the time of conception can change how her child's genes will be interpreted for life. She told BBC News: "Our results have shown that maternal nutrition pre-conception and in early pregnancy is important and may have implications for health outcomes of the next generation. "Women should have a well-balanced food diet prior to conception and during pregnancy." BBC © 2014

Keyword: Epigenetics; Aggression
Link ID: 19556 - Posted: 04.30.2014

Guys, do you prefer more feminine faces? If so, chances are you grew up in a relatively healthy place. New research suggests that men raised in countries with higher average lifespans and lower child mortality more strongly prefer women with softer features than do men raised in less healthy nations. The finding bolsters the idea that years of human evolution have made men attracted to faces that could help them survive. Previous studies have found that women living in harsher conditions—such as communities with high homicide rates and low income—are more inclined to find more masculine men attractive. Urszula Marcinkowska, a biologist at the University of Turku in Finland, and her colleagues wanted to know whether culture also influenced males’ preferences for females, or whether men judged females in a more universal way. Using an online survey conducted in 16 different languages, the researchers presented 1972 heterosexual males between the ages of 18 and 24 from 28 different countries with 20 pairs of Caucasian female faces. Each pair contained one face with more feminine traits—such as larger eyes, fuller lips, and a less angular jaw—as well as a more androgynous face, with thinner lips and a wider chin. Participants were asked to select which face in each pair they found more sexually attractive. While men across all cultures generally preferred a more feminine face, the strength of that preference varied between countries. The difference couldn’t be explained by the ratio of men to women in a country, its gross national income, or the race of the participants, but it did correlate with the national health index of the men’s countries—a measure of overall well-being. Those from countries like Japan, with high national health index scores, chose the more feminine face more than three-quarters of the time, the authors report online today in Biology Letters. Men from countries such as Nepal, which has a lower health rating, selected the more feminine face in only slightly more than half of the cases, on average. © 2014 American Association for the Advancement of Science

Keyword: Sexual Behavior; Aggression
Link ID: 19555 - Posted: 04.30.2014

THAT health and beauty are linked is not in doubt. But it comes as something of a surprise that who is perceived as beautiful depends not only on the health of the person in question but also on the average level of health in the place where she lives. This, though, is the conclusion of a study just published in Biology Letters by Urszula Marcinkowska of the University of Turku, in Finland, and her colleagues—for Ms Marcinkowska has found that men in healthy countries think women with the most feminine faces are the prettiest whilst those in unhealthy places prefer more masculine-looking ones. Ms Marcinkowska came to this conclusion by showing nearly 2,000 men from 28 countries various versions of the same female faces, modified to look less or more feminine, and thus reflect the effects of different levels of oestrogen and testosterone. Oestrogen promotes features, such as large eyes and full lips, that are characteristically feminine. Testosterone promotes masculine features, such as wide faces and strong chins. As the chart shows, the correlation is remarkable—and statistical analysis shows it is unconnected with a country’s wealth or its ratio of men to women and thus the amount of choice available to men. The cause, though, is unclear. Previous studies have shown that women with feminine features are more fertile. A man’s preference for them is thus likely to enhance his reproductive success. Ms Marcinkowska speculates that testosterone-induced behavioural characteristics like dominance, which might be expected to correlate with masculine-looking faces even in women (they certainly do in men), help in the competition for resources needed to sustain children once they are born. But why that should be particularly important in an unhealthy country is unclear.

Keyword: Sexual Behavior; Aggression
Link ID: 19554 - Posted: 04.30.2014

Jeffrey Mogil’s students suspected there was something fishy going on with their experiments. They were injecting an irritant into the feet of mice to test their pain response, but the rodents didn’t seem to feel anything. “We thought there was something wrong with the injection,” says Mogil, a neuroscientist at McGill University in Montreal, Canada. The real culprit was far more surprising: The mice that didn’t feel pain had been handled by male students. Mogil’s group discovered that this gender distinction alone was enough to throw off their whole experiment—and likely influences the work of other researchers as well. “This is very important work with wide-ranging implications,” says M. Catherine Bushnell, a neuroscientist and the scientific director of the Division of Intramural Research at the National Center for Complementary and Alternative Medicine (NCCAM) in Bethesda, Maryland, who was not involved in the study. “Many people doing research have never thought of this.” Mogil has studied pain for 25 years. He’s long suspected that lab animals respond differently to the sensation when researchers are present. In 2007, his lab observed that mice spend less time licking a painful injection—a sign that they’re hurting—when a person is nearby, even if that “person” is a cardboard cutout of Paris Hilton. Other scientists began to wonder if their own data were biased by the same effect. “There were whisperings at meetings that this was confounding research results,” Mogil says. So he decided to take a closer look. In the new study, Mogil told the researchers in his lab to inject an inflammatory agent into the foot of a rat or mouse and then take a seat nearby and read a book. A video camera trained on the rodent’s face assessed the animal’s pain level, based on a 0- to 2-point “grimace scale” developed by the team. The results were mixed. Sometimes the animals showed pain when an experimenter was present, and sometimes they seemed just fine. So, on a hunch, Mogil and colleagues recrunched the data, this time controlling for whether a male or a female experimenter was present. “We were stunned by the results,” he says. © 2014 American Association for the Advancement of Science.

Keyword: Stress; Aggression
Link ID: 19550 - Posted: 04.29.2014

The hormone oxytocin appears to increase social behaviors in newborn rhesus monkeys, according to a study by researchers at the National Institutes of Health, the University of Parma in Italy, and the University of Massachusetts, Amherst. The findings indicate that oxytocin is a promising candidate for new treatments for developmental disorders affecting social skills and bonding. Oxytocin, a hormone produced by the pituitary gland, is involved in labor and birth and in the production of breast milk. Studies have shown that oxytocin also plays a role in parental bonding, mating, and in social dynamics. Because of its possible involvement in social encounters, many researchers have suggested that oxytocin might be useful as a treatment for conditions affecting social behaviors, such as autism spectrum disorders. Although oxytocin has been shown to increase certain social behaviors in adults, before the current study it had not been shown to do so in primate infants of any species. Working with infant rhesus monkeys, the NIH researchers found that oxytocin increased two facial gestures associated with social interactions— one used by the monkeys themselves in certain social situations, the other in imitation of their human caregivers. “It was important to test whether oxytocin would promote social behaviors in infants in the same respects as it appears to promote social interaction among adults,” said the study’s first author, Elizabeth A. Simpson, Ph.D., postdoctoral fellow of the University of Parma, conducting research in the Comparative Behavioral Genetics Section of the NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development. “Our results indicate that oxytocin is a candidate for further studies on treating developmental disorders of social functioning.” The study was published online in Proceedings of the National Academy of Sciences.

Keyword: Hormones & Behavior; Aggression
Link ID: 19547 - Posted: 04.29.2014

Epigenetics is one of the hottest fields in the life sciences. It’s a phenomenon with wide-ranging, powerful effects on many aspects of biology, and enormous potential in human medicine. As such, its ability to fill in some of the gaps in our scientific knowledge is mentioned everywhere from academic journals to the mainstream media to some of the less scientifically rigorous corners of the Internet. Epigenetics is essentially additional information layered on top of the sequence of letters (strings of molecules called A, C, G, and T) that makes up DNA. If you consider a DNA sequence as the text of an instruction manual that explains how to make a human body, epigenetics is as if someone's taken a pack of highlighters and used different colours to mark up different parts of the text in different ways. For example, someone might use a pink highlighter to mark parts of the text that need to be read the most carefully, and a blue highlighter to mark parts that aren't as important. There are different types of epigenetic marks, and each one tells the proteins in the cell to process those parts of the DNA in certain ways. For example, DNA can be tagged with tiny molecules called methyl groups that stick to some of its C letters. Other tags can be added to proteins called histones that are closely associated with DNA. There are proteins that specifically seek out and bind to these methylated areas, and shut it down so that the genes in that region are inactivated in that cell. So methylation is like a blue highlighter telling the cell "you don't need to know about this section right now." Methyl groups and other small molecular tags can attach to different locations on the histone proteins, each one having a different effect. Some tags in some locations loosen the attachment between the DNA and the histone, making the DNA more accessible to the proteins that are responsible for activating the genes in that region; this is like a pink highlighter telling the cell "hey, this part's important". © 2014 Guardian News and Media Limited

Keyword: Genes & Behavior; Aggression
Link ID: 19541 - Posted: 04.28.2014

by Laura Sanders When a baby cries at night, exhausted parents scramble to figure out why. He’s hungry. Wet. Cold. Lonely. But now, a Harvard scientist offers more sinister explanation: The baby who demands to be breastfed in the middle of the night is preventing his mom from getting pregnant again. This devious intention makes perfect sense, says evolutionary biologist David Haig, who describes his idea in Evolution, Medicine and Public Health. Another baby means having to share mom and dad, so babies are programmed to do all they can to thwart the meeting of sperm and egg, the theory goes. Since babies can’t force birth control pills on their mothers, they work with what they’ve got: Nighttime nursing liaisons keep women from other sorts of liaisons that might lead to another child. And beyond libido-killing interruptions and extreme fatigue, frequent night nursing also delays fertility in nursing women. Infant suckling can lead to hormone changes that put the kibosh on ovulation (though not reliably enough to be a fail-safe birth control method, as many gynecologists caution). Of course, babies don’t have the wherewithal to be interrupting their mothers’ fertility intentionally. It’s just that in our past, babies who cried to be nursed at night had a survival edge, Haig proposes. The timing of night crying seems particularly damning, Haig says. Breastfed babies seem to ramp up their nighttime demands around 6 months of age and then slowly improve — precisely the time when a baby would want to double down on its birth control efforts. © Society for Science & the Public 2000 - 2013

Keyword: Sexual Behavior; Aggression
Link ID: 19539 - Posted: 04.26.2014

Here to stay. The Y chromosome is small compared with the X, but is required to keep levels of some genes high enough for mammals to survive. The small, stumpy Y chromosome—possessed by male mammals but not females, and often shrugged off as doing little more than determining the sex of a developing fetus—may impact human biology in a big way. Two independent studies have concluded that the sex chromosome, which shrank millions of years ago, retains the handful of genes that it does not by chance, but because they are key to our survival. The findings may also explain differences in disease susceptibility between men and women. “The old textbook description says that once maleness is determined by a few Y chromosome genes and you have gonads, all other sex differences stem from there,” says geneticist Andrew Clark of Cornell University, who was not involved in either study. “These papers open up the door to a much richer and more complex way to think about the Y chromosome.” The sex chromosomes of mammals have evolved over millions of years, originating from two identical chromosomes. Now, males possess one X and one Y chromosome and females have two Xs. The presence or absence of the Y chromosome is what determines sex—the Y chromosome contains several genes key to testes formation. But while the X chromosome has remained large throughout evolution, with about 2000 genes, the Y chromosome lost most of its genetic material early in its evolution; it now retains less than 100 of those original genes. That’s led some scientists to hypothesize that the chromosome is largely indispensable and could shrink away entirely. © 2014 American Association for the Advancement of Science.

Keyword: Sexual Behavior
Link ID: 19531 - Posted: 04.24.2014

It takes a lot to deter a male from wanting sex. A new study has found that male mice keep trying to copulate even when they are in pain, whereas females engage in less sex. But when given drugs that target pleasure centers in the human brain, the females again became interested. The findings could shed light on the nature of libido across various animal species. To assess how pain influences sexual desire, researchers first identified pairs of mice that wanted to have sex. “What we found early on was not all mice will mate with each other,” says clinical psychologist Melissa Farmer, who led the study while earning her Ph.D. at McGill University in Montreal, Canada. The team set up the rodents on a series of “dates,” during which a male and female were paired together for 30 minutes. Couples that copulated for most of the session were deemed compatible and moved into a cage with separate rooms. A small doorway allowed a female mouse to freely cross over from her chamber, but the male—which is larger—could not. The scientists then induced pain in males or females by applying a small dose of inflammatory compounds to the cheek, tail, foot, or genitals. The sensation would primarily be soreness, like a bad sunburn, says Farmer, who now works at Northwestern University’s Feinberg School of Medicine in Chicago, Illinois. Female mice that were in pain, whether genital or nongenital, spent 50% less time with their male partners, implying a decrease in sexual motivation. Even when they did visit their paramours, females wouldn’t allow males to mount them with the same frequency, the team reports online today in The Journal of Neuroscience. © 2014 American Association for the Advancement of Science.

Keyword: Sexual Behavior; Aggression
Link ID: 19526 - Posted: 04.23.2014

|By Daisy Yuhas Strange as it may sound, some scientists suspect that the humble armpit could be sending all kinds of signals from casual flirtation to sounding the alarm. That’s because the body’s secretions, some stinky and others below the threshold your nose can detect, may be rife with chemical messages called pheromones. Yet despite half a century of research into these subtle cues, we have yet to find direct evidence of their existence in humans. Humans and other animals have an olfactory system designed to detect and discriminate between thousands of chemical compounds. For more than 50 years, scientists have been aware of the fact that certain insects and animals can release chemical compounds—often as oils or sweat—and that other creatures can detect and respond to these compounds, which allows for a form of silent, purely chemical communication. Although the exact definition has been debated and redefined several times, pheromones are generally recognized as single or small sets of compounds that transmit signals between organisms of the same species. They are typically just one part of the larger potpourri of odorants emitted from an insect or animal, and some pheromones do not have a discernable scent. Since pheromones were first defined in 1959, scientists have found many examples of pheromonal communication. The most striking of these signals elicits an immediate behavioral response. For example, the female silk moth releases a trail of the molecule bombykol, which unerringly draws males from the moment they encounter it. Slower-acting pheromones can affect the recipient’s reproductive physiology, as when the alpha-farnesene molecule in male mouse urine accelerates puberty in young female mice. © 2014 Scientific American

Keyword: Chemical Senses (Smell & Taste); Aggression
Link ID: 19500 - Posted: 04.17.2014