Chapter 12. Sex: Evolutionary, Hormonal, and Neural Bases
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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
By Sabrina Imbler To our knowledge, there’s no correlation between a man’s singing ability and his care and attentiveness as a father. But any Pavarotti among the nightingales will serenade his mate while she sits on her eggs. And after they hatch he will visit the nest about 16 times each hour to feed their offspring. Because, among nightingales at least, the best singers also make the best fathers. So finds a study in the journal BMC Evolutionary Biology. [Conny Bartsch, Michael Weiss and Silke Kipper, Multiple song features are related to paternal effort in common nightingales] Some 80 percent of birds practice biparental care, meaning both the male and female rear their offspring together. So it’s crucial for a female bird to pick as a mate the most promising father—both genetically and behaviorally. Female birds look for signs of fitness that range from the flamboyant plumage of the peacock to the bizarre dances of birds of paradise. And for nightingales, it’s the most elaborate song that apparently wins the day. The average male has some 180 tunes in his repertoire. These avian Sinatras vocalize highly variable song types including buzzes, whistles and trills. And such virtuoso singing seems to signal the female that this is a guy she can count on. That is, when it’s time to help raise the kids, he’s not a flight risk. © 2015 Scientific American
Taunya English What do we know about the power of food to rev up sex drive? Not much. "Really, science has not figured out what determines sexual motivation and sexual attraction. If we knew the answer to that, we'd probably be richer than Pfizer after they invented Viagra," says Dolores Lamb, director of the Center for Reproductive Medicine at Baylor College of Medicine. She hasn't seen any compelling evidence that any particular food can intensify desire. Lamb is a men's health researcher and knows a lot about the intricacies of male plumbing, but she says desire is largely psychological. Even medicines that treat erectile dysfunction can't create enthusiasm. "So the trigger still has to be up in the brain," Lamb says. Still, the idea persists that ginger stirs up lust, or that hot peppers make you hot. "Probably for some folks they do, and it's certainly fun to try," Lamb says. Some legendary aphrodisiacs do have a chemical here or a nutrient there that might support sexual health, but not enough of it to make an immediate difference in the bedroom. Red, juicy watermelon, for example, contains the amino acid citrulline, and that plant nutrient is healthy for erectile tissue in both men and women. But most of the amino acid is found in the rind of the fruit. Consider chili peppers. Capsaicin, which is what provides the heat in a jalapeno, also raises your metabolism and releases feel-good endorphins. "You get kind of a chill down the back of your neck and kind of a tingly, good sensation," Lamb says. "Gets blood flowing better." © 2015 NPR
Keyword: Sexual Behavior
Link ID: 21134 - Posted: 07.06.2015
by Michael Le Page It's good to be mixed-up. People whose parents are distantly related are, on average, taller, smarter and better educated than those whose parents are close relatives. Based on what we know about plants and animals, biologists have long suspected that people of mixed parentage have a genetic advantage. Now an extensive study may have confirmed the hunch. "It does imply that people who come from very different ancestry would be a bit taller and a bit more cognitively able," says team member Jim Wilson of the University of Edinburgh, UK. It has long been known that children are more likely to suffer from genetic diseases if their parents are close relatives, because they may inherit the same harmful gene variants from their mother and father. To probe the wider implications, Wilson and his colleagues analysed genome and life history data from 110 genome studies involving 350,000 people from Africa, Asia, Europe and North America. They were surprised to find no evidence of a link between having closely related parents and most of the traits they looked at, such as cholesterol levels, blood pressure and rates of diabetes. © Copyright Reed Business Information Ltd
by Lisa Grossman Marriage for all, no gay gene required. For same-sex couples in the US, 26 June was a landmark date: the Supreme Court legalised marriage between two men or two women in all 50 states. "[Same-sex couples] ask for equal dignity in the eyes of the law," wrote Associate Justice Anthony Kennedy in the decision. "The Constitution grants them that right." But one thing the decision didn't do was declare sexual orientation a "suspect class" under the law, which would have given it the same protection as race. One of the criteria for this classification is that the trait must be immutable – an argument that the gay rights movement has internalised under the banner of "we're born this way". But although there is some evidence that sexual orientation has a genetic component, most scientists agree that it's not that simple. "There's significant consensus in the scientific community that there's enough different interacting causes for sexual orientation that two different individuals can be gay for different combinations of reasons," says sexuality researcher Lisa Diamond at the University of Utah. "I think all the evidence suggests that we're born with an underlying capacity and then that capacity interacts with a whole bunch of other influences," she says – whether they be prenatal, genetic or environmental. © Copyright Reed Business Information Ltd
Keyword: Sexual Behavior
Link ID: 21117 - Posted: 07.01.2015
by Colin Barras Men often lose their sex drive with age – and so, it seems do male Drosophila. Tsai-Feng Fu at the National Chi Nan University in Taiwan and his colleagues suspected that low levels of dopamine in the flies were to blame. Almost 300 neurones in the fruit-fly brain use dopamine. Comparing those linked to sexual function in elderly 40-day-old male flies and sprightly 10-day-old flies, Fu found the older neurones carried 10 times less dopamine. Boosting levels lengthened the time the older flies spent trying to mate. There are obviously big differences between a man's brain and that of a male Drosophila, but Fu says that the new results could provide a useful starting point for in-depth studies that may have clinical implications. For instance, that research might eventually identify ways to fine-tune dopamine levels in humans, perhaps to reverse age-related declines in sexual drive, or even to suppress an overactive libido. We already have therapies for treating male sexual dysfunction – notably the drug viagra. But probing the link between dopamine and sexual dysfunction is still important. For instance, dopamine-replacement therapy is one of the most effective treatments for Parkinson's disease – but the therapy can lead to harmful compulsive sexual behaviour. But Wendi Neckameyer at the Saint Louis University School of Medicine in Missouri isn't sure we should talk about potential implications for men just yet – it's enough to say that the researchers "have begun to tease out an incredibly complex neural circuit", she says. © Copyright Reed Business Information Ltd
Keyword: Sexual Behavior
Link ID: 21115 - Posted: 07.01.2015
Moheb Costandi Different immune cells regulate pain sensitization in male and female mice, according to research published on 29 June in Nature Neuroscience1. The surprising biological divide may explain why some clinical trials of pain drugs have failed, and highlights shortcomings in the way that many researchers design their experiments. The immune system has important roles in chronic pain, with cells called microglia being key players. Microglia express a protein called brain-derived neurotrophic factor (BDNF) to signal to spinal-cord neurons. When injury or inflammation occurs, this signal sensitizes the body to pain, so that even light touch hurts. Robert Sorge, a psychologist at the University of Alabama in Birmingham, and his colleagues induced persistent pain and inflammation in healthy male and female mice by severing two of the three sciatic nerve branches in their hind paws. Seven days later, they injected the animals with one of three drugs that inhibit microglial function. They found that all three drugs reversed pain sensitization in the male animals, as had been previously reported. But the treatments had no effect on the females, even though the animals had displayed equivalent levels of pain. The researchers also genetically engineered mice in which the BDNF gene could be deleted in microglia at any time during the animals' lives. At first, these animals exhibited normal responses to a nerve injury. Killing the microglia one week later extinguished that hypersensitivity in the male animals, but not in the females. This confirmed that in males, hypersensitivity to pain depends on BDNF signals from microglia, but that in females it is mediated by some other mechanism. © 2015 Nature Publishing Group,
By Christopher Intagliata Two decades ago, Swiss researchers had women smell the tee shirts that various men had slept in for two nights. Turned out that if women liked the aroma of a particular shirt, the guy who’d worn it was likely to have genetically coded immunity that was unlike the woman’s. Well the effect isn't just limited to sweaty shirts. Turns out we all smell things a little differently—you pick up a note of cloves, say, where I smell something more soapy—and that too gives clues to our degree of genetic similarity. Researchers tried that test with 89 people—having them sniff a couple dozen samples, and label each one using terms like lemony, coconut, fishy and floral. And each volunteer classified the scents differently enough that the researchers could single them out in subsequent tests, based on what they called each subject’s "olfactory fingerprint." Researchers then repeated that sniff test on another 130 subjects. But this time they did a blood test, too, to figure out each person's HLA type—an immune factor that determines whether you'll reject someone's organ, for example. They found that people who perceived smells similarly also had similar HLA types. Study author Lavi Secundo, a neuroscientist at the Weizmann Institute of Science in Israel, says the smell test could have real-world applications. "For organ donation you can think of this method as a quick, maybe a quick and dirty, method to sift between the best and the rest." He and his colleagues say it might even eliminate the need for 30 percent of the HLA tests done today. The work appears in the Proceedings of the National Academy of Sciences. [Lavi Secundo et al, Individual olfactory perception reveals meaningful nonolfactory genetic information] © 2015 Scientific American
Helen Shen In April 2011, Robert Froemke and his team were reprogramming the brains of virgin mice with a single hormone injection. Before the treatment, the female mice were largely indifferent to the cries of a distressed baby, and were even known to trample over them. But after an injection of oxytocin, the mice started to respond more like mothers, picking up the mewling pup in their mouths. Froemke, a neuroscientist at New York University's Langone Medical Center in New York City, was monitoring the animals' brains to find out why that happened. At first, the mice showed an irregular smattering of neural impulses when they heard the baby's cries. Then, as the oxytocin kicked in, the signal evolved into a more orderly pattern typical of a maternal brain. The study showed in unusual detail how the hormone changed the behaviour of neurons1. “Oxytocin is helping to transform the brain, to make it respond to those pup calls,” Froemke says. Oxytocin has been of keen interest to neuroscientists since the 1970s, when studies started to show that it could drive maternal behaviour and social attachment in various species. Its involvement in a range of social behaviours2, including monogamy in voles, mother–infant bonding in sheep, and even trust between humans, has earned it a reputation as the 'hug hormone'. “People just concluded it was a bonding molecule, a cuddling hormone, and that's the pervasive view in the popular press,” says Larry Young, a neuroscientist at Emory University in Atlanta, Georgia, who has been studying the molecule since the 1990s. “What we need to start thinking about is the more fundamental role that oxytocin has in the brain.” © 2015 Nature Publishing Group,
by Curtis Abraham A step forward for equal LGBT rights in Africa. Last week, the influential Academy of Science of South Africa (ASSAf) published a study on the science of human sexual diversity. A comprehensive review of recent scientific papers on the subject, it concluded that sexual behaviour is naturally varied, and discrimination unjustified. It stated that there is no evidence that orientation can be altered by therapy or that being gay is contagious. The report also sets straight the idea that homosexuality is a Western malaise: "There is no basis for the view that homosexuality is 'un-African' either in the sense of it being a 'colonial import', or on the basis that prevalence of people with same-sex or bisexual orientations is any different in African countries compared to countries on any other continent." Going further, the report asserted not only that tolerance of sexual diversity benefits communities but it positively affects public health, civil society and long-term economic growth. Zero tolerance Launched at the Seventh South African AIDS Conference in Durban, the study comes a year after the Ugandan government passed a law imposing a life sentence on anyone who has sexual relations with someone of the same sex. Other countries, including Burundi, Cameroon and Nigeria, then passed similar anti-gay laws. © Copyright Reed Business Information Ltd.
Keyword: Sexual Behavior
Link ID: 21071 - Posted: 06.18.2015
Tom Bawden The mystery behind the nightingale’s beautiful song has been revealed, with scientists finding that male birds sing complex notes to prove to females that they would be a good father to their children. Nightingales use their songs to advertise their family values, according to new research which discovers that the better the singer, the more support they are likely to offer their young family by feeding and defending them from predators. But while the beauty comes from the complexity of the song, the effect it has on the females is based on something far more mundane – the amount of effort the singer has put into his performance. Researchers at the Freie Universitat Berlin found that complicated choral arrangements are much harder to sing, especially when they include frequent appearances of long buzzing sounds and require the bird to be in good physical condition. “We don’t think the female is concerned with the beauty of the song but rather the information encoded in the song that tells her about the singer’s characteristics – his age, where he was raised, the strength of his immune system and how motivated he is to contribute to bringing up the young,” Professor Silke Kipper, one of the report’s authors, told The Independent. “The songs can also be a good indication of the bird’s ability to learn, which is another important characteristic of a good parent.” © independent.co.uk
by Michael Sean Pepper and Beverley Kramer People who are attracted to others of the same sex develop their orientation before they are born. This is not a choice. And scientific evidence shows their parents cannot be blamed. Research proving that there is biological evidence for sexual orientation has been available since the 1980s. The links have been emphasised by new scientific research. In 2014, researchers confirmed the association between same-sex orientation in men and a specific chromosomal region. This is similar to findings originally published in the 1990s, which, at that time, gave rise to the idea that a “gay gene” must exist. But this argument has never been substantiated, despite the fact that studies have shown that homosexuality is a heritable trait. Evidence points towards the existence of a complex interaction between genes and environment, which are responsible for the heritable nature of sexual orientation. These findings are part of a report released by the Academy of Science South Africa. The report is the outcome of work conducted by a panel put together in 2014 to evaluate all research on the subject of sexual orientation done over the last 50 years. It did this against the backdrop of a growing number of new laws in Africa which discriminate against people attracted to others of the same sex. The work was conducted in conjunction with the Ugandan Academy of Science.
Keyword: Sexual Behavior
Link ID: 21049 - Posted: 06.15.2015
By Brian Handwerk When it comes to mating, female mice must follow their noses. For the first time, scientists have shown that hormones in mice hijack smell receptors in the nose to drive behavior, while leaving the brain completely out of the loop. According to the study, appearing this week in Cell, female mice can smell attractant male pheromones during their reproductive periods. But during periods of diestrus, when the animals are unable to reproduce, the hormone progesterone prompts nasal sensory cells to block male pheromone signals so that they don't reach a female's brain. During this time, female mice display indifference or even hostility toward males. The same sensors functioned normally with regard to other smells, like cat urine, showing they are selective for male pheromones. When ovulation begins, progesterone levels drop, enabling the females to once more smell male pheromones. In short, the system "blinds" female mice to potential mates when the animals are not in estrus. The finding that the olfactory system usurped the brain's role shocked the research team, says lead author Lisa Stowers of the Scripps Research Institute. “The sensory systems are just supposed to sort of suck up everything they can in the environment and pass it all on to the brain. The result just seems wacky to us,” Stowers says. “Imagine this occurring in your visual system," she adds. "If you just ate a big hamburger and then saw a buffet, you might see things like the table and some people and maybe some fruit—but you simply wouldn't see the hamburgers anymore. That's kind of what happens here. Based on this female's internal-state change, she's missing an entire subset of the cues being passed on to her brain.”
by Clare Wilson The first drug for treating low sexual desire in women looks set to go on sale in the US next year Flibanserin, sometimes called the female Viagra, was approved by 18 votes to 6 by a US Food and Drug Administration advisory panel yesterday, although some of the committee members had doubts about the drug's risks and benefits. They required that certain "risk-management options" be put in place, on top of the usual list of side effects listed in the medicine's patient information leaflet. We have yet to hear what this means, but options include doctors having to verbally warn women not to drink alcohol or use various other medicines when taking the drug. The FDA's final say is due by August, but it usually follows the decision of its advisory panel. Assuming it gets the go-ahead, manufacturer Sprout Pharmaceuticals of Raleigh, North Carolina, plans to give the drug the brand-name Addyi, and has promised not to advertise the product directly to patients – which is normally allowed in the US – for the first 18 months it goes on sale. Addyi is no Viagra though – women would have to take it every day, whether or not they want sex. And, while the famous little blue pill works by increasing blood flow to the genitals, this new drug instead alters brain chemistry, affecting receptors for various signalling chemicals including serotonin and dopamine. © Copyright Reed Business Information Ltd.
Keyword: Sexual Behavior
Link ID: 21020 - Posted: 06.06.2015
By Elahe Izadi Researchers classified two new species of Dusky Antechinus, mouse-like creatures that engage in suicidal reproduction, and published their findings last week in the peer-reviewed journal Memoirs of the Queensland Museum -- Nature. The Mainland Dusky Antechinus, found in southeastern Australia, has been elevated from sub-species to a distinct species. And the newly discovered Tasman Peninsula Dusky Antechinus, found in southeastern Tasmania, already faces the threat of extinction due in part to loss of habitat and feral pests, researchers said. Their proclivity for ferocious, suicidal sex frenzies aren't helping them any. "The breeding period is basically two to three weeks of speed-mating, with testosterone-fueled males coupling with as many females as possible, for up to 14 hours at a time," lead author Andrew Baker of the Queensland University of Technology said in a release. All of that testosterone "triggers a malfunction in the stress hormone shut-off switch" for the males, Baker said. The males then get so stressed out that their immune systems fail, and they die before the females actually give birth. Suicidal reproduction -- or semelparity-- is rare in mammals, and has so far just been documented in these kinds of marsupials.
Allie Wilkinson For many species, reproduction is a duet between male and female. Now, for the first time, scientists report evidence of 'virgin birth' in a wild vertebrate, the smalltooth sawfish. The fish (Pristis pectinata) normally reproduces sexually, requiring contributions from both sexes. But the latest analysis estimates that nearly 4% of sawfish in a Florida estuary were born without any genetic contribution from a male, in a phenomenon known as parthenogenesis. This asexual reproduction is rare in vertebrates, and had previously been observed only in a handful of species in captivity, including snakes collected from the wild1 and Komodo dragons2. The latest findings appear in the 1 June issue of Current Biology3. Smalltooth sawfish are one of five large ray species that have chainsaw-like appendages protruding from their faces, and are in the same subclass as sharks. The smalltooth sawfish was once abundant along the US eastern and southern coastlines from North Carolina to Texas, but overfishing and coastal development have drastically reduced its numbers. The critically endangered fish are now found only off the coast of southwest Florida. Researchers discovered evidence of 'virgin births' among the sawfish while conducting a routine genetic analysis to determine whether they were inbreeding. Some of the 190 sawfish sampled in a Florida estuary showed unusually high levels of relatedness to other fish in the same population. © 2015 Nature Publishing Group
By ANDREW SOLOMON At the beginning of spring in 2013, Mary Guest, a lively, accomplished 37-year-old woman, fell in love, became pregnant and married after a short courtship. At the time, Mary taught children with behavioral problems in Portland, Ore., where she grew up. Her supervisor said that he had rarely seen a teacher with Mary’s gift for intuiting students’ needs. “Mary was a powerful person,” he wrote to her mother, Kristin. “Around Mary, one felt compassion, drive, calmness and support.” Mary had struggled with depression for much of her life. Starting in her 20s, she would sometimes say to Kristin that she just wanted to die. “She would always follow up by saying, ‘But you don’t need to worry, Mama,’ ” Kristin told me. “ ‘I don’t have a plan, and I don’t intend to do anything.’ ” In recent years, Mary and her mother went for a walk once a week, and Mary would describe the difficulties she was having. She was helped somewhat by therapy and by antidepressant and antianxiety medications, which blunted her symptoms. Mary’s friends appreciated her wacky sense of humor and her engaging wit. Colleagues said that her moods never impinged on her work; in fact, few of them knew what she was dealing with. Yet for years Mary worried that she would never be in a stable relationship and experience love or a family of her own. She said plaintively to Kristin, “I think I would be a really good mother.” So when she discovered that she was pregnant, she was delighted, and she expected the experience to be blissful. She decided to discontinue her antidepressants, having read about their potential danger for a growing fetus. Given her history of severe depression, she was monitored closely by a psychiatric nurse practitioner, who told her that she could call anytime for an immediate prescription. But Mary elected to stay off medication.
By ANDREW POLLACK Is sexual desire a human right? And are women entitled to a little pink pill to help them feel it? Those questions are being raised in a campaign that is pressing the Food and Drug Administration to approve a pill aimed at restoring lost libido in women. The campaign, backed by the drug’s developer and some women’s groups, accuses the F.D.A. of gender bias for approving Viagra and 25 other drugs to help men have sex, but none for women. “Women have waited long enough,” the effort, known as Even the Score, says in an online petition that has gathered more than 40,000 signatures. “In 2015, gender equality should be the standard when it comes to access to treatments for sexual dysfunction.” The drug, flibanserin, has been rejected twice by the F.D.A. on the grounds that its very modest effectiveness was outweighed by side effects like sleepiness, dizziness and nausea. The first rejection, in 2010, followed a decision by a committee of outside advisers to the agency who unanimously opposed approval. On Thursday, F.D.A. advisers will once again consider whether flibanserin should be approved. Sprout Pharmaceuticals, which now owns the drug, has submitted new data, including a study to demonstrate that the pill does not impair driving. Still, approval might hinge on whether the F.D.A. agrees to interpret the old data in a new way and whether the politics of such drugs has changed. © 2015 The New York Times Company
Keyword: Sexual Behavior
Link ID: 21002 - Posted: 06.01.2015