Chapter 12. Sex: Evolutionary, Hormonal, and Neural Bases
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Nell Greenfieldboyce Picking a mate can be one of life's most important decisions. But sometimes people make a choice that seems to make no sense at all. And humans aren't the only ones — scientists have now seen apparently irrational romantic decisions in frogs. Little tungara frogs live in Central America, and they're found everywhere from forests to ditches to parking lot puddles. These frogs are only about 2 centimeters long, but they are loud. The males make calls to woo the females. Amanda Lea, a biologist in the laboratory of Mike Ryan at the University of Texas, Austin, says past studies have given scientists a pretty good idea of what the females find appealing. "They tend to like longer calls. They also like lower-frequency calls," says Lea. "Then, the other thing that's a really big one for these gals is the 'call rate.' They love faster call rates. The faster a male can call, the better." But in real life, love is complicated. Female frogs face countless suitors. So Lea and Ryan wondered: Would a female really always pick the male that scored highest on the froggy love-call meter? To find out, they put female frogs in a room with some loudspeakers. From one speaker the scientists played a recording of frog call that had a really fast rate. But other features in this voice were less attractive. Then the researchers played a second, different call for the female frogs. This voice was more attractive, but it was slower. The ladies had to make a choice. "They have two traits to evaluate," Lea explains. "They have the call rate and they have the attractiveness of the call." © 2015 NPR
Christopher Joyce Male treehoppers make their abdomens thrum like tuning forks to transmit very particular vibrating signals that travel down their legs and along leaf stems to other bugs — male and female. Male treehoppers make their abdomens thrum like tuning forks to transmit very particular vibrating signals that travel down their legs and along leaf stems to other bugs — male and female. Courtesy of Robert Oelman Animals, including humans, feel sound as well as hear it, and some of the most meaningful audio communication happens at frequencies that people can't hear. Elephants, for example, use these low-frequency rumbles to, among other things, find family or a mate across long distances. Whales do it, too. But you don't have to weigh a ton to rumble. In fact, you don't have to be bigger than a pea. Consider, for example, the treehopper, a curious little sap-sucking insect that lives on the stems of leaves. Or the tree cricket, which communicates by rubbing together tooth-like structures on its wings, the way you might draw your thumb across the teeth of a comb. University of Missouri biologist Rex Cocroft has spent much of his career listening closely to treehoppers. In 1999, a team from NPR's Radio Expeditions program rendezvoused with Cocroft at a locust tree in a backyard in Virginia. Soft-spoken and bespectacled, he was pressing a phonograph needle up against the stem of a leaf. © 2015 NPR
By Melinda Wenner Moyer As many as four out of every five pregnant women say that they suffer from “pregnancy brain”—deficits in memory and cognitive ability that arise during pregnancy, making women more forgetful and slow-witted. Yet studies on the phenomenon have generally not supported these claims: although some have found evidence of problems on certain types of tasks, others, including a recent paper published by researchers in Utah, have found no signs of cognitive problems at all. Some experts believe that pregnancy brain and its postnatal cousin, “baby brain,” could largely be a product of confirmation bias: pregnant women and new moms expect to experience brain fog and therefore believe they are actually affected. Others argue that the mental symptoms might simply be too difficult to confirm in a laboratory setting. In the most recent study, researchers at Brigham Young University gave cognitive and neuropsychological tests to 21 women in their third trimester of pregnancy and then tested them again six months after they gave birth. They administered the same tests at similar intervals to 21 women who had never been pregnant. They found no differences between the groups no matter when they were tested, including before and after giving birth. These findings mesh with those from a 2003 study, which found that pregnant women did not score differently from nonpregnant women on tests of verbal memory, divided attention and focused attention. “There is variety in the results, but overall most studies suggest there are few to no memory impairments associated with pregnancy,” says Michael Larson, a psychologist at Brigham Young and a co-author of the recent paper. He thinks the reason the myth persists may be that women selectively look for evidence that supports the cultural expectation. © 2015 Scientific American
By Esther Landhuis The birth of a child leaves its mark on the brain. Most investigations of these changes have focused on mothers, but scientists have recently begun looking more closely at fathers. Neural circuits that support parental behaviors appear more robust in moms a few weeks after the baby is born, whereas in dads the growth can take several months. A study in Social Neuroscience analyzed 16 dads several weeks after their baby's birth and again a few months later. At each check, the researchers administered a multiple-choice test to check for signs of depression and used MRI to image the brain. Compared with the earlier scans, MRI at three to four months postpartum showed growth in the hypothalamus, amygdala and other regions that regulate emotion, motivation and decision making. Furthermore, dads with more growth in these brain areas were less likely to show depressive symptoms, says first author Pilyoung Kim, who directs the Family and Child Neuroscience Lab at the University of Denver. Although some physiological brain changes are similar in new moms and dads, other changes seem different and could relate to the roles of each parent, says senior author James Swain, a psychiatrist at the University of Michigan (brain diagrams below). A 2014 behavioral study of expectant fathers showed that midpregnancy ultrasound imaging was a “magic moment” in the dads' emerging connection with their baby. Yet the emotional bond was different than it is in expectant moms. Instead of thinking about cuddling or feeding the baby, dads-to-be focused on the future: they imagined saving money for a college fund or walking down the aisle at their daughter's wedding. © 2015 Scientific American
By Hanae Armitage The libido enhancement drug flibanserin (trade name Addyi) took center stage last week after winning long-sought approval from the U.S. Food and Drug Administration (FDA). The coverage from advocates and nonbelievers has run the gamut—advice, caution, and criticism likely to confuse undecided—but curious—onlookers. But exactly how Addyi drums up sex drive is still murky. The drug has a long backstory. It was originally investigated in 1995 by pharmacologist Franco Borsini and a team of researchers at Boehringer Ingelheim Italia in Milan as an antidepressant because of its ability to regulate neurotransmitters—the brain’s chemical-signaling molecules. In particular, the team suspected that the drug regulated three key neurotransmitters thought to influence mood: serotonin, dopamine, and norepinephrine. A clinical trial found it did little to alleviate depression, but did seem to have an effect on mood. It just wasn’t the mood the researchers were expecting. These early trials tipped clinicians to flibanserin’s more prominent role in sexual health, as female subjects had higher scores on the Arizona Sexual Experience Scale, a survey that asks participants to rate their satisfaction on a variety of sexual health topics, like how often participants felt sexual desire and how intense that desire was. A separate group of researchers, also at Boehringer Ingelheim, completed their first clinical trials to explore flibanserin as a libido-enhancer in 2008. They measured levels of desire through a journal-based evaluation in which subjects recorded their levels of sexual drive on a daily basis. But FDA twice concluded that the resulting increases in libido were not statistically significant, and regulators were wary of potentially dangerous side effects like dizziness, sleepiness, nausea, and fainting. © 2015 American Association for the Advancement of Science
Keyword: Sexual Behavior
Link ID: 21332 - Posted: 08.25.2015
Richard A. Friedman THANKS to Caitlyn Jenner, and the military’s changing policies, transgender people are gaining acceptance — and living in a bigger, more understanding spotlight than at any previous time. We’re learning to be more accepting of transgender individuals. And we’re learning more about gender identity, too. The prevailing narrative seems to be that gender is a social construct and that people can move between genders to arrive at their true identity. But if gender were nothing more than a social convention, why was it necessary for Caitlyn Jenner to undergo facial surgeries, take hormones and remove her body hair? The fact that some transgender individuals use hormone treatment and surgery to switch gender speaks to the inescapable biology at the heart of gender identity. This is not to suggest that gender identity is simply binary — male or female — or that gender identity is inflexible for everyone. Nor does it mean that conventional gender roles always feel right; the sheer number of people who experience varying degrees of mismatch between their preferred gender and their body makes this very clear. In fact, recent neuroscience research suggests that gender identity may exist on a spectrum and that gender dysphoria fits well within the range of human biological variation. For example, Georg S. Kranz at the Medical University of Vienna and colleagues elsewhere reported in a 2014 study in The Journal of Neuroscience that individuals who identified as transsexuals — those who wanted sex reassignment — had structural differences in their brains that were between their desired gender and their genetic sex. © 2015 The New York Times Company
Keyword: Sexual Behavior
Link ID: 21329 - Posted: 08.24.2015
By Kazi Stastna The U.S. approval of a pill to treat low libido in women has whipped up a whirlwind of debate and raised questions about whether the so-called female Viagra addresses the real reasons for lack of sexual desire. The U.S. Food and Drug Administration last week approved flibanserin, to be sold under the name Addyi starting in October, for the treatment of hypoactive sexual desire disorder (HSDD) among premenopausal women — some two decades after Viagra was approved for the treatment of male erectile dysfunction. Sprout Pharmaceuticals pitched flibanserin as a drug that would finally give women with sexual dysfunction similar treatment options to men and bused dozens of women to FDA hearings in Maryland to attest to its benefits and plead for its approval in what some saw as a heavy-handed and misleading public relations campaign. The FDA gave flibanserin the OK after twice rejecting it and despite concerns about its risks and modest efficacy because it said women suffering distress from low libido have an "unmet medical need." Days after it did, Canadian pharmaceutical company Valeant offered to buy Sprout for $1 billion US and said it will apply to get flibanserin approved in Canada and other countries. Although often likened to Viagra, flibanserin was created as an antidepressant and works on the brain while erectile dysfunction medications stimulate blood flow to the penis. Critics argue it's an ineffectual pharmacological solution for a problem better treated with relationship counselling, sex therapy and behavioural changes. "Their suffering is real, but the women who testified had a lot of different stories, and some of those stories were very good reasons for having low libido, including having six children, having a one-year-old, having had breast cancer treatment …," says Adriane Fugh-Berman, associate professor of pharmacology and physiology at Georgetown University in Washington, D.C., and director of PharmedOut, a pharmaceutical marketing watchdog group. ©2015 CBC/Radio-Canada.
Keyword: Sexual Behavior
Link ID: 21328 - Posted: 08.24.2015
By ANDREW POLLACK The first prescription drug to enhance women’s sexual drive won regulatory approval on Tuesday, clinching a victory for a lobbying campaign that had accused the Food and Drug Administration of gender bias for ignoring the sexual needs of women. The drug — Addyi from Sprout Pharmaceuticals — is actually the first drug approved to treat a flagging or absent libido for either sex. Viagra and other drugs available for men are approved to help achieve erections, or to treat certain deficiencies of the hormone testosterone, not to increase desire. Advocates who pressed for approval of Addyi, many of them part of a coalition called Even the Score, said that a drug to improve women’s sex lives was long overdue, given the many options available to men. “This is the biggest breakthrough for women’s sexual health since the pill,” said Sally Greenberg, executive director of the National Consumers League. But critics said the campaign behind Addyi had made a mockery of the system that regulates pharmaceuticals and had co-opted the women’s movement to pressure the F.D.A. into approving a drug that was at best minimally effective and could cause side effects like low blood pressure, fainting, nausea, dizziness and sleepiness. In announcing the approval, Dr. Janet Woodcock, a senior F.D.A. official, said the agency was “committed to supporting the development of safe and effective treatments for female sexual dysfunction.” The F.D.A. decision on Tuesday was not a surprise since an advisory committee of outside experts had recommended by a vote of 18 to 6 in June that the drug be approved, albeit with precautions required to try to limit the risks and ensure that it was not overused. © 2015 The New York Times Company
Keyword: Sexual Behavior
Link ID: 21311 - Posted: 08.19.2015
Geoff Brumfiel Learning to make sounds by listening to others is a skill that helps make us human. But research now suggests a species of monkey may have evolved similar abilities. Marmosets have the capacity to learn calls from their parents, according to research published Thursday in the journal Science. The results mean that studying marmosets might provide insights into developmental disorders found in humans. It also suggests that vocal learning may be more widespread than many researchers thought. Many animals can link sounds with meaning. Dogs respond to simple calls; chimpanzees can even communicate with people using sign language. But the ability to hear a sound and mimic it is possessed by only a small number of species: primarily song birds and humans. "We didn't think that mammals and primates in particular — besides us — had any type of vocal learning," says Asif Ghazanfar, a neuroscientist at Princeton University who led the new study. Enter the small, adorable common marmoset. These fuzzy South American primates look more like squirrels than a monkey. "They're cute, and they smell. They wash themselves in their own urine," Ghazanfar says. "I'm not sure why they do that." But once you get over the stink, these little guys are interesting. Marmoset mommies always give birth to twins and they need help rearing them. So, unlike many mammal species, fathers lend a hand, along with siblings and other community members. Ghazanfar thinks all that child care is what gives marmosets another special trait: They're super talkative. "They're chattering nonstop," he says. "That is also very different from our close relatives the chimpanzees." © 2015 NPR
By C. CLAIBORNE RAY Q. Are men more likely to be claustrophobic than women? A. The opposite seems to be true, as is the case in almost all anxiety disorders, large epidemiological studies have found. The reasons for such a gender difference are not clear, and claustrophobia, the feeling of extreme panic when faced with being in a confined or enclosed space, is not as well studied as some other phobias. One situation that has been comparatively well researched is what happens when people need magnetic resonance imaging, which often involves a prolonged period of confinement in a small enclosure, the perfect storm of claustrophobia triggers. A recent study found that certain factors seem to correlate with an increase in claustrophobic reactions, including being female, going into the scanner head first and having a previous negative experience with the test. Another large study involving scanners with a shorter chamber and noise reduction found a significant reduction in claustrophobic reactions, but being female and middle-aged were still associated with a higher rate of claustrophobia. It has often been assumed that claustrophobia develops as a response to a traumatic experience, like being trapped in a closet as a child, but newer research suggests a genetic component. In one study in mice, a single defective gene was associated with claustrophobia. firstname.lastname@example.org © 2015 The New York Times Company
Victoria E Brings & Mark J Zylka A study finds that pain hypersensitivity in male and female mice is differentially dependent on microglia and T cells, and describes a sex-specific response to microglia-targeted pain treatments. This sex difference will be important to consider when developing treatments for pain and other neurological disorders involving microglia and immune cells. Animal studies1, 2 have spawned great interest in using microglial inhibitors such as minocycline to treat pain in humans. However, these studies were conducted largely on male rodents. Now, Sorge et al.3 have evaluated several microglial inhibitors in nerve-injured mice of both sexes. The study—led by Jeffrey Mogil, who has championed the testing of males and females in pain studies4—found that microglial inhibitors did reduce allodynia, a form of pain hypersensitivity to touch, in males. Surprisingly, however, these inhibitors were ineffective in female mice, despite a robust activation of spinal microglia (Fig. 1). The authors instead found that cells of the adaptive immune system promote pain hypersensitivity in females. Although focused on pain, these findings could have implications for other neurological disorders that disproportionately affect one sex, such as autism and neurodegeneration, and in which microglia and immune cells are implicated5, 6. Figure 1: Pain mechanisms differ in male and female mice. Pain mechanisms differ in male and female mice. Nerve injury activates microglial cells in the spinal cord of male and female mice, but microglial inhibitors only block allodynia in males. P2RX4 is upregulated in males only. Female mice have about twice as many T cells as males. Testosterone increases PPARα and decreases PPARγ gene expression in T cells. Compounds that activate PPARα inhibit mechanical pain hypersensitivity (allodynia) in males, whereas those that activate PPARγ inhibit allodynia in females. © 2015 Macmillan Publishers Limited
Qazi Rahman In a recent Guardian article , Simon Copland argued that it is very unlikely people are born gay (or presumably any other sexual orientation). Scientific evidence says otherwise. It points strongly to a biological origin for our sexualities. Finding evidence for a biological basis should not scare us or undermine gay, lesbian and bisexual (LGB) rights (the studies I refer to do not include transgendered individuals, so I’ll confine my comments to lesbian, gay and bisexual people). I would argue that understanding our fundamental biological nature should make us more vigorous in promoting LGB rights. Let’s get some facts and perspective on the issue. Evidence from independent research groups who studied twins shows that genetic factors explain about 25-30% of the differences between people in sexual orientation (heterosexual, gay, lesbian, and bisexual). Twin studies are a first look into the genetics of a trait and tell us that there are such things as “genes for sexual orientation” (I hate the phrase “gay gene”). Three gene finding studies showed that gay brothers share genetic markers on the X chromosome; the most recent study also found shared markers on chromosome 8. This latest research overcomes the problems of three prior studies which did not find the same results. Gene finding efforts have issues, as Copland argues, but these are technical and not catastrophic errors in the science. For example, complex psychological traits have many causal genes (not simply “a gay gene”). But each of these genes has a small effect on the trait so do not reach traditional levels of statistical significance. In other words, lots of genes which do influence sexual orientation may fall under the radar. But scientific techniques will eventually catch up. In fact there are more pressing problems that I would like to see addressed, such as the inadequate research on female sexuality. Perhaps this is due to the stereotype that female sexuality is “too complex” or that lesbians are rarer than gay men. © 2015 Guardian News and Media Limited
By Sarah Schwartz Researchers have developed a chemical that transforms into a powerful hormone once inside a rat — but only in the brain, not the body. A protein in rats’ brains turns a chemical nicknamed DHED into the hormone estrogen, scientists report July 22 in Science Translational Medicine. This targeted treatment could provide estrogen to the brain and avoid potentially dangerous side effects in the body, the researchers say. “This is an interesting breakthrough,” says neuroendocrinologist Bruce McEwen of the Rockefeller University in New York City. The idea of treatments that affect the brain but not the body, or the body but not the brain, could be useful in treating a number of conditions, including cancer, he says. But the implications of this study for hormone replacement therapy in women is up for debate, a number of researchers say. In menopausal women or those who have had their ovaries surgically removed, lack of estrogen in the brain can cause symptoms such as hot flashes and sleep disturbances. Taking estrogen can relieve those symptoms but can cause side effects in the rest of the body, including an increased risk of certain cancers. The chemical DHED is nearly identical to natural human estrogen, but it has an extra oxygen atom. A specialized protein found in rodents’ brains recognizes the chemical and chops off the oxygen, turning DHED into estrogen. The body’s other organs lack this protein, so they can’t turn DHED into estrogen, says study author Laszlo Prokai, a chemical biologist at the University of North Texas Health Science Center in Fort Worth. © Society for Science & the Public 2000 - 2015.
THERE’S more to semen than sperm. In many animals, seminal fluid alters both the bodies and sometimes even the behaviour of females. Human semen, too, triggers changes in the uterus, and might have wider effects on women, aimed at just one goal. “It’s all about maximising the chances of the male reproducing,” says Sarah Robertson of the University of Adelaide in Australia. The effects are most striking in fruit flies: seminal fluid can make the females eat more, lay more eggs and be less receptive to other males. Now a team led by Tracey Chapman at the University of East Anglia in Norwich, UK, has found that male fruit flies selectively alter the chemical make-up of their seminal fluid. In the presence of rivals, the males produce more seminal proteins. “It came as a real surprise,” says Chapman. “It’s a sophisticated response to the social and sexual situation.” Some of their findings were presented at the Society for Molecular Biology and Evolution conference in Vienna, Austria, last week, including their discovery that one of these proteins is a “master regulator” of genes. Females exposed to it show a wide range of changes in gene expression. Chapman thinks this kind of seminal signalling is widespread in the animal world. The semen of people, pigs and mice affects the female reproductive tract, and the question is whether it can also produce behavioural responses in female mammals similar to those seen in fruit flies. © Copyright Reed Business Information Ltd.
By BENEDICT CAREY Women who develop slight but detectable deficits in memory and mental acuity late in life tend to decline faster than men with mild impairment, researchers reported on Tuesday. Some two-thirds of the five million Americans with Alzheimer’s disease are women, in part because women live longer. Researchers have searched in vain for decades to determine other reasons for the disparity. The authors of the new study, who presented their work at the Alzheimer’s Association International Conference in Washington, said their findings indicated nothing about possible causes of gender differences and had no immediate implications for treatment. “All we can say at this point is that there appears to be a faster trajectory for women than men” toward dementia, said Dr. P. Murali Doraiswamy, a professor of psychiatry at the Duke Institute for Brain Sciences and the study’s senior author. Katherine Amy Lin, a student of Dr. Doraiswamy’s and a co-author, presented the study. Previous research had found a steeper decline in women with mild deficits over a period of about a year. The new study extends that finding to up to eight years. “It’s a very interesting finding, but it’s also still early, so we’re limited in what conclusions we can draw,” said Dr. Edward D. Huey, a geriatric psychiatrist at Columbia University, who was not involved in the study. “I think of this as an excellent hypothesis generator. It’s something we need to investigate more deeply.” In the study, the Duke researchers analyzed scores on standard cognitive tests taken by 398 men and women, most in their 70s, being followed as part of a large, continuing Alzheimer’s trial. The participants have been taking the cognitive tests — as well as other tests, like PET scans — on average for four years, and as long as eight years. Controlling for factors that influence memory and mental acuity, like age, education and genetic predisposition, the research team found that women’s scores slipped by an average of about two points a year, compared with one point for men. The team also looked at a standard measure of life quality, rating how well people functioned socially: at home, at work and with family. That, too, slipped faster for women than for men, at about the same rate. © 2015 The New York Times Company
by Stephen Buchmann Flowers, bugs and bees: Stephen Buchmann wanted to study them all when he was a kid. "I never grew out of my bug-and-dinosaur phase," he tells NPR's Arun Rath. "You know, since about the third grade, I decided I wanted to chase insects, especially bees." These days, he's living that dream. As a pollination ecologist, he's now taking a particular interest in how flowers attract insects. In his new book, The Reason for Flowers, he looks at more than just the biology of flowers — he dives into the ways they've laid down roots in human history and culture, too. On the real 'reason for flowers' The reason for flowers is actually one word: sex. So, flowers are literally living scented billboards that are advertising for sexual favors, whether those are from bees, flies, beetles, butterflies or us, because quite frankly most of the flowers in the world have gotten us to do their bidding. But that's only the first stage because flowers, if they're lucky, turn into fruits, and those fruits and seeds feed the world. On the raucous secret lives of beetles One of my favorite memories is roaming the Napa foothills as a UC Davis grad student. And I would go to the wineries, of course, and in between I would find western spice bush, which is this marvelous flower that kind of smells like a blend between a cabernet and rotten fruit. And when you find those flowers and open them up, you discover literally dozens of beetles in there, mating, defecating, pollinating — having a grand time. © 2015 NPR
By THE EDITORIAL BOARD Scientific research has a gender gap, and not just among humans. In many disciplines, the animals used to study diseases and drugs are overwhelmingly male, which may significantly reduce the reliability of research and lead to drugs that won’t work in half the population. A new study published in the journal Nature Neuroscience suggests that research done on male animals may not hold up for women. Its authors reported that hypersensitivity to pain works differently in male and female mice. For males, immune cells called microglia appear to be required for pain hypersensitivity, and inhibiting their function also relieves the pain. But in female mice, different cells are involved, and targeting the microglia has no effect. If these differences occur in mice, they may occur in humans too. This means a pain drug targeting microglia might appear to work in male mice, but wouldn’t work on women. Failure to consider gender in research is very much the norm. According to one analysis of scientific studies that were published in 2009, male animals outnumbered females 5.5 to 1 in neuroscience, 5 to 1 in pharmacology, and 3.7 to 1 in physiology. Only 45 percent of animal studies involving depression or anxiety and only 38 percent involving strokes used females, even though these conditions are more common in women. In 1994, the National Institutes of Health confronted gender imbalance in clinical drug trials and began requiring that women and minorities be included in clinical studies; women now make up around half of clinical trial participants. In June, the N.I.H. announced that it would begin requiring researchers to take gender into account in preclinical research on animals as well. © 2015 The New York Times Company
Keyword: Sexual Behavior
Link ID: 21188 - Posted: 07.20.2015
Don’t do drugs, kids. Especially if you’re female. Women dependent on stimulants like cocaine and methamphetamine appear to have less grey matter, even after they stop using them. Weirdly, men’s brains don’t show this difference. The brain regions most affected are those involved in reward, emotion and learning – although it isn’t clear yet whether the smaller than average size of these brain areas could be a cause or effect of addiction. Jody Tanabe, at the University of Colorado Hospital in Aurora, hopes these results will help lead to a better understanding of sex differences in substance abuse, and better, more distinct treatments for women. Tanabe’s team used MRI scans to measure the brain volumes of 59 people previously dependent on stimulants and compared them with people who have never been dependent on these kinds of drugs. On average, the 28 women who had formerly been dependent on a stimulant drug had a smaller volume of grey matter in their prefrontal cortices, temporal lobes, insulae and other regions. This effect was not seen in men. Shrinking brains The women who had been addicted also differed in their personalities – on average, they were more impulsive and more reward-driven. We already know that women respond differently to stimulants: they start taking the drugs earlier, use larger quantities and may have more difficulty quitting. It’s possible that this pattern of female addiction could be linked to the brain size difference. However, it’s unclear whether less grey matter causes female addictive behaviours, or if addiction might shrink these brain regions. “The question of causality is complex. There is evidence for both pre-existing and post-drug changes in brain structure and function,” says Tanabe.
Simon Copland Over the past decade the idea that we are “born this way” — or that our sexuality is genetic — has become increasingly important. The mantra has become a political strategy, in particular for gay and lesbian communities, who see it as a way to protect themselves from discrimination. The movement has spawned blogs where people show pictures of their childhood to highlight the innate nature of their sexuality, and attacks on those who have questioned the theory. But do the politics match the science? People have been searching for biological explanations for sexual desires for centuries — primarily as a way to try and find a “cure” for “perverted desires”. In the most horrible of examples, the Nazi regime in Germany invested significant resources in attempts to find the reasons for homosexuality in attempt to cure it. In recent decades the search for a “gay gene” has intensified. In 1991, for example, Simon LeVay released a study that suggested small differences in the size of certain cells in the brain could influence sexual orientation in men. In 1993 this research turned to genetics, when Dean Hamer claimed that markers on the X chromosome could influence the development of same-sex orientation in men. The issue hit the headlines again last year after the release of a study from Dr. Alan Sanders. Sanders studied the genes on 409 pairs of gay brothers, finding they may share genetic markers on the X chromosome and chromosome 8. © 2015 Guardian News and Media Limited
By David Shultz Like many arthropods, spiders don’t have penises. Instead they rely on a set of modified appendages—termed pedipalps—to transfer sperm during reproduction. Previous studies had concluded that the pedipalps, which are basically modified arms emanating from the arachnid’s head, were lacking any sort of neurons that might convey a sense of touch. But new research, published online today in Biology Letters, suggests that the spider’s sex life isn’t an entirely numb deal. Using a combination of histological and computer-based techniques, scientists have identified neurons in the pedipalps of the Tasmanian cave spider (Hickmania troglodytes, seen above). Two main groups of nervous tissue were present: a nerve running to the tip of the sex organ, and two clusters of neurons in the palpal bulb—the region of the pedipalps used for transferring sperm. Though further research is needed to confirm the hypothesis, the team suspects that the sense of touch may enable the males to stimulate the females and even provide feedback about the quality of their mate. The latter hypothesis is especially intriguing because the analyses also revealed that one of the glands in the spider’s sex organ was directly innervated. The team believes this might mean the spiders can control the quality and volume of their ejaculate—reserving the best secretions for the choicest mates. © 2015 American Association for the Advancement of Science
Keyword: Sexual Behavior
Link ID: 21145 - Posted: 07.08.2015