Links for Keyword: Sexual Behavior

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By Karl Gruber Birds, fish, and even humans have shattered barriers when it comes to mating rituals, from which partner initiates the courting to which one picks up the check at a fancy restaurant. But things are a bit simpler for frogs, as males and females stick to clearly defined roles: Males serenade the females, and females pick their favorite males to mate. Now, a new study suggests that the smooth guardian frog of Borneo (Limnonectes palavanensis) is an exception to that rule. During the mating season, the female frogs sing to the males in an attempt to win them over—a reversal of the normal process. In fact, if you see a single frog surrounded by a bunch of serenading croakers, called a “lek,” it’s most likely a lucky male being courted by a chorus of females. Males occasionally belt out “advertisement calls” to let females know that they are available. After mating, it’s the males who stay behind to care for the eggs, even taking tadpoles to small ponds after they hatch. This is the first known example of role reversal in singing frogs, scientists write in a recent issue of Behavioral Ecology and Sociobiology. It may even represent the first case of full-blown sex role reversal, which would also require that males do the mate choosing. Researchers are working on that now, but they say that—judging by the high rate of female serenading—males may be the picky ones. © 2017 American Association for the Advancement of Science.

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 23755 - Posted: 06.21.2017

Laurel Hamers When things get hot, embryonic bearded dragon lizards turn female — and now scientists might know why. New analyses, reported online June 14 in Science Advances, reveal that temperature-induced changes in RNA’s protein-making instructions might set off this sex switch. The findings might also apply to other reptile species whose sex is influenced by temperature. Unlike most mammals, many species of reptiles and fish don’t have sex chromosomes. Instead, they develop into males at certain temperatures and females at others. Bearded dragon lizards are an unusual case because chromosome combinations and temperature are known to influence sex determination, says ecologist Clare Holleley of the Commonwealth Scientific and Industrial Research Organisation in Canberra, Australia (SN: 7/25/15, p.7). When eggs are incubated below 32° Celsius, embryonic bearded dragons with two Z chromosomes develop as male, while dragons with a Z and a W chromosome develop as female. But as temperatures creep above 32°, chromosomally male ZZ dragons will reverse course and develop as females instead. “They have two sex chromosomes, but they also have this temperature override,” Holleley says. By comparing bearded dragons that are female because of their chromosomes and those that are female because of environmental influences, Holleley and her colleagues hoped to sort out genetic differences that might point to how the lizards make the switch. The team collected RNA from the brain, reproductive organs and other tissues of normal female, normal male and sex-reversed female Australian central bearded dragons (Pogona vitticeps). Then, the researchers compared that RNA, looking for differences in the ways the lizards were turning on genes. |© Society for Science & the Public 2000 - 2017.

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 23745 - Posted: 06.15.2017

Hannah Devlin Science correspondent “Love looks not with the eyes, but with the mind. And therefore is winged Cupid painted blind,” Shakespeare wrote. Now scientists have pinpointed the specific patterns of brain activity that accompany romance, offering a new explanation for why love sends our judgement haywire. As a relationship takes root, the study found, the brain’s reward circuit goes into overdrive, rapidly increasing the value placed on spending time with one’s love interest. This, at least, was the case in the prairie vole, scientists’ animal model of choice for studying the neuroscience of love. Elizabeth Amadei, who co-led the work at Emory University in Atlanta, said: “As humans, we know the feelings we get when we view images of our romantic partners, but, until now, we haven’t known how the brain’s reward system works to lead to those feelings.” In order to get more direct access to what is happening in the brain, Amadei and colleagues turned to the North American voles, which as a species have almost perfected monogamy. They mate for life, share nest-building duties and have an equal role in raising their young – although, like humans, voles have the occasional “extramarital” fling. Using electrical probes, the scientists recorded directly from the brains of female voles as they encountered a potential partner, mated for the first time and began to show signs of having formed a lifelong bond, indicated by “huddling” behaviour.

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases; Chapter 5: Hormones and the Brain
Related chapters from MM:Chapter 8: Hormones and Sex; Chapter 8: Hormones and Sex
Link ID: 23692 - Posted: 06.01.2017

By STEPH YIN A female and male get together. One thing leads to another, and they have sex. His sperm fuses with her egg, half of his DNA combining with half of her DNA to form an embryo. As humans, this is how we tend to think of reproduction. But there are many other bizarre ways reproduction can take place. For instance, scientists have discovered a fish carrying genes only from its father in the nucleus of its cells. Found in a type of fish called Squalius alburnoides, which normally inhabits rivers in Portugal or Spain, this is the first documented instance in vertebrates of a father producing a near clone of itself through sexual reproduction — a rare phenomenon called androgenesis — the researchers reported in the journal Royal Society Open Science on Wednesday. The possibility of androgenesis is just one of many mysteries about Squalius alburnoides. It’s not a species in the usual sense, but rather something called a hybrid complex, a group of organisms with multiple parental combinations that can mate with one another. The group is thought to have arisen from hybridization between females of one species, Squalius pyrenaicus, and males of another species, now extinct, that belonged to a group of fish called Anaecypris. To sustain its population, Squalius alburnoides mates with several other closely related species belonging to the Squalius lineage. That it can reproduce at all is unusual enough. Most hybrids, like mules, are sterile because the chromosomes from their parents of different species have trouble combining, swapping DNA and dividing — steps required for egg or sperm production. Squalius alburnoides males circumvent this problem by producing sperm cells that do not divide, and therefore contain more than one chromosome set. This is important because most animals, Squalius alburnoides included, need at least two chromosome sets to survive. © 2017 The New York Times Company

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 23669 - Posted: 05.27.2017

Tonight, our economics correspondent, Paul Solman, explores another potential connection: whether there’s a link between risk-taking in leadership, testosterone and the perceptions around gender. It’s part of his ongoing weekly series, Making Sense, which airs every Thursday. MAN: Welcome, everybody, to this CNBC discussion on the future of banking at the World Economic Forum. PAUL SOLMAN: Financial CEOs at Davos this year. ANDREW LIVERIS, CEO, Dow Chemical: Good morning. Mr. President. Andrew Liveris, Dow Chemical. PAUL SOLMAN: Manufacturing CEOs at the White House. MARK FIELDS, CEO, Ford Motor Company: CEO of Ford. DOUGLAS OBERHELMAN, CEO, Caterpillar: Chairman of Caterpillar. PRESIDENT DONALD TRUMP: Some of the great people in the world of business. PAUL SOLMAN: CEOs now being mentioned as the next president. But, in 2017, the vast majority of CEOs, 96 percent of the Fortune 500, are still men. JENNIFER LERNER, Harvard University: I think that this is socially constructed. The differences between males and females on a wide variety of things are smaller than the differences within males and within females. PAUL SOLMAN: Psychologist Jennifer Lerner studies gender and leadership at Harvard. We will hear more from her in a bit. But, first, let’s check in with economist Andy Kim, who has made a career out of studying CEOs in intriguingly quirky ways. Now, a few of you might remember Andy Kim teaching me two years ago the equestrian dance move in the hyper-viral video sensation “Gangnam Style,” part of his offbeat research showing that CEOs who become visible, for whatever reason, can see their stock price rise irrationally. Well, he presented his brand-new research, not yet published, at this year’s annual Economics Convention. His latest hypothesis is as offbeat as ever. ANDY KIM: There is a strong linkage between your facial masculinity and your risk-taking behavior. PAUL SOLMAN: Kim is now exploring a possible link between CEO risk-taking and the hormone testosterone, which, starting with mid-19th century experiments on roosters, has been linked to male dominance and aggression throughout the animal kingdom. But how do you measure testosterone in CEOs with little time and probably even less inclination to give Korean assistant finance professors blood or saliva samples? One possible way, thought Kim, would be to study their facial bone structure. © 1996 - 2017 NewsHour Productions LLC.

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases; Chapter 15: Emotions, Aggression, and Stress
Related chapters from MM:Chapter 8: Hormones and Sex; Chapter 11: Emotions, Aggression, and Stress
Link ID: 23663 - Posted: 05.26.2017

Susan Milius The supermoms of the mammal world are big, shy redheads. Studying growth layers in orangutan teeth shows that mothers can nurse their youngsters for eight-plus years, a record for wild mammals. Teeth from a museum specimen of a young Bornean orangutan (Pongo pygmaeus) don’t show signs of weaning until 8.1 years of age. And a Sumatran orangutan (P. abelii) was still nursing during the few months before it was killed at 8.8 years, researchers report May 17 in Science Advances. Tests also show that youngsters periodically start to taper off their dependence on their mother’s milk and then, perhaps if solid food grows scarce, go back to what looks like an all-mom diet. Such on-again, off-again nursing cycles aren’t known in other wild mammals, says study coauthor Tanya Smith, an evolutionary anthropologist at Griffith University in Nathan, Australia. Marks of milk drinking Two images of a cross section of a first molar from a 4.5-year-old Bornean orangutan are shown. At left, numbers indicate days from birth (dotted line, starting with 0) when particular spots formed. At right, colors indicate concentrations of barium, which increase (shading toward red) when the youngster depended more on mother’s milk. A greenish swath at the top indicates nursing as an infant that gave way to blue as solid food became part of the diet. Yellow and red streaks indicate repeated times when the youngster again depended mostly on milk for nutrition. oragutan molar |© Society for Science & the Public 2000 - 2017.

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases; Chapter 7: Life-Span Development of the Brain and Behavior
Related chapters from MM:Chapter 8: Hormones and Sex; Chapter 13: Memory, Learning, and Development
Link ID: 23632 - Posted: 05.18.2017

By STEPH YIN In most mammals, us included, biological sex is determined by a lottery between two letters: X and Y, the sex chromosomes. Inherit one X each from mom and dad, and develop ovaries, a womb and a vagina. Inherit an X from mom and a Y from dad, and develop testes and a penis. But there are rare, mysterious exceptions. A small number of rodents have no Y chromosomes, yet are born as either females or males, not hermaphrodites. Now, scientists may be one step closer to figuring out how sex determination works in one of these rodents. In a study published in Science Advances on Friday, Japanese scientists suggested that cells of the endangered Amami spiny rat, from Japan, are sexually flexible and capable of adapting to either ovaries or testes. When the researchers injected stem cells derived from a female rat into male embryos of laboratory mice, the cells developed into and survived as sperm precursors in adult males. The result was surprising since scientists have never been able to generate mature sperm from female stem cells, largely because sperm production normally requires the Y chromosome. Found only in the subtropical forests of an island in Japan called Amami Oshima, Amami spiny rats are threatened by habitat destruction, competition with black rats not native to the island and predation by mongooses and feral cats and dogs. Their range has been reduced to less than 300 square miles, an area smaller than New York City. Both female and male Amami spiny rats have only one X chromosome, an arrangement only known to occur in a handful of rodents among mammals. Arata Honda, associate professor at the University of Miyazaki and the lead author of the paper, said in an email that he was partly motivated to study Amami spiny rats in the hope that learning about them might reduce their risk of extinction. © 2017 The New York Times Company

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 23611 - Posted: 05.13.2017

By Alice Klein It is pest control without poison. A new type of bait that stops rats from having babies is helping to tackle infestations in several US cities. The bait – known as ContraPest – was approved by the US Environmental Protection Agency last August. It makes rats infertile by triggering early menopause in females and impairing sperm production in males. There are no side effects and the rats eventually die of natural causes. The technique is considered more benign than other control strategies being investigated, such as gene drive, which can be used to spread infertility genes through pest populations. A recent report by the US National Academies of Sciences warned that gene drive could have unforeseen consequences. The first field trial of ContraPest, conducted in the New York City Subway in 2013, halved the resident rat population in three months. Two more trials have now been completed in the US – one at a large-scale farm and one in an urban area – both in East Coast cities. Rat numbers at the farm fell by one-third over three months. In the urban area, population growth was suppressed during the peak breeding season so that the population expanded at only one-third the expected rate. “You’ll never wipe out rats completely – they’re too smart,” says Brandy Pyzyna from SenesTech, the biotechnology company in Arizona that developed the bait. © Copyright Reed Business Information Ltd.

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases; Chapter 5: Hormones and the Brain
Related chapters from MM:Chapter 8: Hormones and Sex; Chapter 8: Hormones and Sex
Link ID: 23583 - Posted: 05.06.2017

By Jef Akst Drawing on data on organ-, tissue-, and individual-specific gene expression from the Genotype-Tissue Expression (GTex) Portal, Shmuel Pietrokovski and Moran Gershoni of the Weizmann Institute of Science in Israel developed a comprehensive map of genes that are differentially expressed in men and women. The study was inspired by work the duo conducted several years ago, in which they found that mutations accumulated in genes for sperm formation likely because they were expressed only in men, not in women. As a result, even harmful mutations would only cause problems to half the population; unaffected women would continue to pass on the defective gene without any hit to their fitness. To explore whether other genes expressed differentially between the sexes might be similarly subject to mutation accumulation, Pietrokovski and Gershoni examined some 20,000 protein-coding genes, of which around 6,500 were expressed more in one sex than the other somewhere in the body. And sure enough, selection was effectively weaker in these genes, leading to the pile up of deleterious mutations. “The more a gene was specific to one sex, the less selection we saw on the gene,” Gershoni told the institute’s news publication, Weizmann Wonder Wander, this week (May 3). “The basic genome is nearly the same in all of us, but it is utilized differently across the body and among individuals,” he continued. “Thus, when it comes to the differences between the sexes, we see that evolution often works on the level of gene expression.” © 1986-2017 The Scientist

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 23581 - Posted: 05.06.2017

By RICHARD O. PRUM In a mossy forest in the western Andes of Ecuador, a small, cocoa-brown bird with a red crown sings from a slim perch. Bip-Bip-WANNGG! It sounds like feedback from an elfin electric guitar. Three rival birds call back in rapid response. These male club-winged manakins are showing off to attract female mates. Their strange songs are associated with an even stranger movement. Instead of opening their beaks, they flick their wings open at their sides to make the Bips, and then snap their wings up over their backs to produce the extraordinary WANNGG. They are singing with their wings, and their potential mates seem to find the sound very alluring. This is an evolutionary innovation — a whole new way to sing. But the evolutionary mechanism behind this novelty is not adaptation by natural selection, in which only those who survive pass on their genes, allowing the species to become better adapted to its environment over time. Rather, it is sexual selection by mate choice, in which individuals pass on their genes only if they’re chosen as mates. From the peacock’s tail to the haunting melodies of the wood thrush, mate choice is responsible for much of the beauty in the natural world. Most biologists believe that these mechanisms always work in concert — that sex appeal is the sign of an objectively better mate, one with better genes or in better condition. But the wing songs of the club-winged manakin provide new insights that contradict this conventional wisdom. Instead of ensuring that organisms are on an inexorable path to self-improvement, mate choice can drive a species into what I call maladaptive decadence — a decline in survival and fecundity of the entire species. It may even lead to extinction. © 2017 The New York Times Company

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 23580 - Posted: 05.06.2017

Jon Brooks Max, age 13, is agender — neither male nor female. When referring to Max, you don't use "he" or "she;" you use "they." Once strictly a pronoun of the plural variety, "they" is now doing double duty as singular, too — referring to individuals, like Max, who do not see gender as an either/or option. (NPR agreed not to use Max's last name, because the family feared the sort of online threats that have been made to other transgender families.) If the whole he/she pronoun thing feels awkward to you, Max is sympathetic — and patient. 'We are seeing more and more kids saying, 'You know what? What's with this either-or business? What's with this boy-girl and you have to fit in one box or the other?' " Diane Ehrensaft, psychologist, Child and Adolescent Gender Center, UCSF Benioff Children's Hospital "I can't expect anyone to use the right pronouns for me because it's not a thing that people know," Max tells me. "It's been great being myself, but it's also been really hard for people to get it, and for even family to get pronouns and stuff." We're talking in Max's room at home, where posters on the wall showcase the teen's love of theater: Peter Pan, Tarzan, The Pirates of Penzance. Max is old enough now to enjoy using make-up — blush, foundation, lipstick — but still young enough to enjoy going with their mom to see "Willy Wonka & The Chocolate Factory." (The review from Max: Gene Wilder's great!) From these surroundings, you wouldn't think the room's occupant is someone who has already poked and prodded at the most fundamental sense of who they are. Really, this is just a kid's room. © 2017 npr

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 23562 - Posted: 05.02.2017

By Debra W. Soh The reasons behind why people are gay, straight, or bisexual have long been a source of public fascination. Indeed, research on the topic of sexual orientation offers a powerful window into understanding human sexuality. The Archives of Sexual Behavior recently published a special edition devoted to research in this area, titled “The Puzzle of Sexual Orientation.” One study, conducted by scientists at the University of Lethbridge in Alberta, Canada, offers compelling, cross-cultural evidence that common genetic factors underlie same-sex, sexual preference in men. In southern Mexico, individuals who are biologically male and sexually attracted to men are known as muxes. They are recognized as a third gender: Muxe nguiiu tend to be masculine in their appearance and behavior, while muxe gunaa are feminine. In Western cultures, they would be considered gay men and transgender women, respectively. Several correlates of male androphilia — biological males who are sexually attracted to men — have been shown across different cultures, which is suggestive of a common biological foundation among them. For example, the fraternal birth order effect—the phenomenon whereby male androphilia is predicted by having a higher number of biological older brothers—is evident in both Western and Samoan cultures. Interestingly, in Western society, homosexual men, compared with heterosexual men, tend to recall higher levels of separation anxiety — the distress resulting from being separated from major attachment figures, like one’s primary caregiver or close family members. Research in Samoa has similarly demonstrated that third-gender fa’afafine—individuals who are feminine in appearance, biologically male, and attracted to men—also recall greater childhood separation anxiety when compared with heterosexual Samoan men. Thus, if a similar pattern regarding separation anxiety were to be found in a third, disparate culture—in the case, the Istmo region of Oaxaca, Mexico—it would add to the evidence that male androphilia has biological underpinnings. © 2017 Scientific American

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases; Chapter 7: Life-Span Development of the Brain and Behavior
Related chapters from MM:Chapter 8: Hormones and Sex; Chapter 13: Memory, Learning, and Development
Link ID: 23540 - Posted: 04.26.2017

By CATHERINE SAINT LOUIS In her 30s, Sophie Marat, now 42, used to record herself reading poetry aloud, then play it back to hear if she sounded like a woman. Ms. Marat, who is transgender, had spent years trying to remake her voice in private by speaking in a higher pitch but ultimately felt that her efforts were hopeless. “I was feeling like changing my voice to match my gender identity was almost impossible,” she said. “It was terrible.” Ms. Marat’s transition from male to female has been a gradual evolution. She had come out to friends and family back home in Mexico, then began to wear skirts to work as a software engineer in Manhattan. Still, her confidence would falter with everyday tasks like ordering takeout. “It was really painful to speak on the phone,” she said, “because they would reply, ‘O.K., sir.’” That was before she started her weekly sessions with a voice therapist at New York University’s speech-language-hearing clinic, one of a growing number of programs that cater to transgender clients seeking to retrain their voices. Just as some transgender women and men choose to take hormones or have surgery, or choose neither, some seek to feminize or masculinize their voices. Many say they want a voice that matches their appearance or that the change allows them to escape unwanted attention. There’s also a growing recognition among health professionals who have transgender patients that altering one’s voice can improve quality of life and reduce distress. After eight months, she had raised her pitch, worked on moving her resonance forward and finishing phrases with an open ending, rather than bluntly. “This isn’t just a sidebar,” said Sandy Hirsch, a Seattle-based speech language pathologist who was a co-author of the pioneering textbook on transgender voice and communication therapy. “It’s an integral part of care for transgender people as they transition.” © 2017 The New York Times Company

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases; Chapter 19: Language and Hemispheric Asymmetry
Related chapters from MM:Chapter 8: Hormones and Sex; Chapter 15: Brain Asymmetry, Spatial Cognition, and Language
Link ID: 23539 - Posted: 04.26.2017

Carl Zimmer The oldfield mouse doesn’t seem extraordinary. With soulful black eyes and tiny teacup ears, the rodent lives a humdrum life scurrying about meadows and beaches in the Southeast. But field biologists have long known that when it comes to sex and family life, this mouse is remarkable: Peromyscus polionotus is monogamous — an exception among mammals — and a solicitous parent. Fathers and mothers will dig burrows together and build elaborate nests when pups are on the way; after they’re born, the father will help tend to the pups, retrieving them when they fall out of the nest, licking them, and huddling to keep them warm. In a pioneering study published on Wednesday in the journal Nature, researchers at Harvard University identified a genetic basis for this distinctive behavior. It is the first time that scientists have linked DNA to variations in parenting habits among mammals. Dieter Lukas, an evolutionary biologist at the University of Cambridge who was not involved in the research, hailed the study as a sophisticated tour de force, saying that uncovering these links “is like designing a tool to follow individual threads through a large colorful tapestry.” The findings may one day help scientists make sense of how human couples bond and care for their children. Mammals share many of the genes governing the production of hormones and neurotransmitters in the brain. Variations in how they function may explain why most species are promiscuous, why a few are monogamous — and why some, like humans, are somewhere in between. “We can go from the bottom up and build our knowledge base, and then ask questions about human biology,” said Gene E. Robinson, a biologist at the University of Illinois who was not involved in the new work. © 2017 The New York Times Company

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases; Chapter 5: Hormones and the Brain
Related chapters from MM:Chapter 8: Hormones and Sex; Chapter 8: Hormones and Sex
Link ID: 23516 - Posted: 04.20.2017

by Claire Lehmann and Debra W Soh “Neurosexism,” “populist science,” “neurotrash,” the problem with using terms like these to describe scientific investigations of sex differences is that their use may be interpreted as hostile. “Not fair!” claim the espousers of these terms, who argue that they only ever use such terms for pseudoscience and media distortions, not robust and replicable studies. In a recent op-ed for The Guardian, Cordelia Fine—the author who coined the term “neurosexism”—together with Rebecca Jordan-Young, argue that they have never been prima facie opposed to sex differences research. Their only concern is that of scientific rigour. In 2005, the British philosopher Nicholas Shackel proposed the term “Motte and Bailey Doctrine” for this type of argumentative style. Taking the name of the castle fortification, the “motte” is strong and is built high on an elevated patch of land and is easy to defend. By contrast, the “bailey” is built on lower, more exposed ground, and is much more difficult to defend from attacks. Shackel used this metaphor to describe a common rhetorical trap used by postmodern academics, where a controversial proposition is put forward (a “bailey”) but is then switched for an uncontroversial one (a “motte”) when faced with criticism. In this case, the controversial position that has been proposed by authors such as Fine and Jordan-Young is that the scientific investigation of sex differences reinforce and legitimize harmful and sexist stereotypes about women. The uncontroversial proposition is that their concern is simply one of “[ensuring] the [maximum possible contribution] of neuroimaging research.” © 2017 Quillette

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 23507 - Posted: 04.19.2017

By Michael Price Do the anatomical differences between men and women—sex organs, facial hair, and the like—extend to our brains? The question has been as difficult to answer as it has been controversial. Now, the largest brain-imaging study of its kind indeed finds some sex-specific patterns, but overall more similarities than differences. The work raises new questions about how brain differences between the sexes may influence intelligence and behavior. For decades, brain scientists have noticed that on average, male brains tend to have slightly higher total brain volume than female ones, even when corrected for males’ larger average body size. But it has proved notoriously tricky to pin down exactly which substructures within the brain are more or less voluminous. Most studies have looked at relatively small sample sizes—typically fewer than 100 brains—making large-scale conclusions impossible. In the new study, a team of researchers led by psychologist Stuart Ritchie, a postdoctoral fellow at the University of Edinburgh, turned to data from UK Biobank, an ongoing, long-term biomedical study of people living in the United Kingdom with 500,000 enrollees. A subset of those enrolled in the study underwent brain scans using MRI. In 2750 women and 2466 men aged 44–77, Ritchie and his colleagues examined the volumes of 68 regions within the brain, as well as the thickness of the cerebral cortex, the brain’s wrinkly outer layer thought to be important in consciousness, language, memory, perception, and other functions. © 2017 American Association for the Advancement of Science

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases; Chapter 2: Functional Neuroanatomy: The Nervous System and Behavior
Related chapters from MM:Chapter 8: Hormones and Sex; Chapter 2: Cells and Structures: The Anatomy of the Nervous System
Link ID: 23478 - Posted: 04.11.2017

By Andy Coghlan “PRENATAL exposure to progesterone affects sexual orientation in humans”. A bold and unequivocal-sounding title for a scientific paper. And certainly important if true. But is it? The study claimed to show that women given extra progesterone during pregnancy, routinely prescribed to prevent miscarriage, bleeding or premature delivery, have children who are “29 per cent more likely” to later identify as bisexual. It would be a landmark finding, allowing us to also ground in biology the established social science contention that sexuality has more dimensions than straight and gay. We suspected that exposing a fetus to strong hormones can shape sexual orientation. But there are no animal models of sexual orientation, and doing this kind of experiment in humans would be deeply unethical. The next best thing would be a retrospective analysis looking at a birth cohort exposed to a specific hormone “in the wild”. And that’s what this study did. June Reinisch of the Kinsey Institute in Indiana and her colleagues trawled a public database containing records of more than 9000 pregnancies in Denmark between 1959 and 1961. They identified women who were given a progesterone-mimicking hormone by the trade name lutocyclin to prevent miscarriage. Lutocyclin did seem to have mild effects on sexual orientation: later in life, exposed individuals were five times more likely to self-identify as non-heterosexual, and were more likely to report relationships with the same sex, than unexposed controls. © Copyright Reed Business Information Ltd.

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 23477 - Posted: 04.11.2017

Cordelia Fine and Rebecca Jordan-Young At a time when both science and feminism are under attack, there are welcome signs that neuroscience is showing new openness to critiques of research into sex differences. Mainstream journals increasingly publish studies that reveal how misleading assumptions about the sexes bias the framing of hypotheses, research design and interpretation of findings – and these critiques increasingly come with constructive recommendations, discussions and debates. For example, we, together with other colleagues, made recommendations in the peer-reviewed journal Frontiers in Human Neuroscience on best practice in sex/gender neuroscience. Some of the errors and traps we identified included human neuroimaging studies with small sample sizes, and the common “snapshot” approach, which interprets neural associations with sex as a matter of timeless and universal male and female essences, without taking seriously the fact that biological associations might as easily be the effect of social differences as the cause of them. For example, a study reporting female-male differences in spatial processing should take into account that women and men have different life experiences, on average, that can build such skills – such as practice with aiming at targets that comes from certain kinds of sports and video games. We also expressed concern about studies that draw on and reinforce stereotypes, even as they slip and slide regarding specific predictions about sex differences in the brain, and what findings might mean for how women and men think, feel, and behave.

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 23465 - Posted: 04.08.2017

Erin Ross The sex of a sea lamprey may be determined by how fast it grows as a larva. Sex is determined by chromosomes in mammals and by temperature in many reptiles. But for sea lampreys — eel-like creatures that dine on blood — the growth rate of their larvae seems to control whether they are male or female. They are the first creatures known to undergo sex determination in this way. Researchers know next to nothing about sex determination in sea lampreys (Petromyzon marinus) and have long been puzzled by the observation that some adult populations are mostly male, and others female. The fish begin their lives as larvae with undifferentiated sexual organs. After a year or so, they develop gonads, and after a few more years — the timing can vary — they metamorphose into adult sucker-mouthed parasites. A team led by biologist Nick Johnson, at the US Geological Survey in Millersburg, Michigan, identified lamprey habitats in and near streams leading to the Great Lakes. Some areas were productive, with lots of food, whereas others were unproductive sites with little food. After taking measures to ensure no wild lamprey were present, they released between 1,500 and 3,000 wire-tagged larval lamprey into each of the study sites. The researchers recaptured the tagged lamprey and checked their sex after the larvae had metamorphosed into adults and migrated upstream. They found that lamprey in productive streams with lots of food were larger, reached maturity earlier and were more likely to be female. But in unproductive sites, smaller, male lamprey dominated, Johnson’s team reports in a paper published on 29 March in Proceedings of the Royal Society B1. © 2017 Macmillan Publishers Limited

Related chapters from BP7e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 23427 - Posted: 03.30.2017

By Kate Yandell In a 1971 paper published in Science, biologist Roger Payne, then at Rockefeller University, and Scott McVay, then an administrator at Princeton University, described the “surprisingly beautiful sounds” made by humpback whales (Megaptera novaeangliae; Science, 173:585-97). Analyzing underwater recordings made by a Navy engineer, the duo found that these whale sounds were intricately repetitive. “Because one of the characteristics of bird songs is that they are fixed patterns of sounds that are repeated, we call the fixed patterns of humpback sounds ‘songs,’” they wrote. OCEAN SONGS: Humpback whales make diverse, broadband sounds that travel miles through the ocean. Their function, however, remains somewhat murky.PLOS ONE, dx.doi.org/10.1371/journal.pone.0079422, 2013 It’s now clear that, in addition to simpler calls, several baleen whale species—including blue, fin, and bowhead—make series of sounds known as song. Humpback song is the most complex and by far the best studied. Units of humpback songs form phrases, series of similar phrases form themes, and multiple themes form songs. All the males in a given population sing the same song, which evolves over time. When whale groups come into contact, songs can spread. But why do whales sing? “The short answer is, we don’t know,” says Alison Stimpert, a bioacoustician at Moss Landing Marine Laboratories in California. Humpback songs are only performed by males and are often heard on breeding grounds, so the dominant hypothesis is that these songs are a form of courtship. The quality of a male’s performance could be a sign of his fitness, for example. But female whales do not tend to approach singing males. Alternatively, whale researchers have proposed that the male whales sing to demarcate territory or to form alliances with other males during mating season. © 1986-2017 The Scientist

Related chapters from BP7e: Chapter 9: Hearing, Vestibular Perception, Taste, and Smell; Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell; Chapter 8: Hormones and Sex
Link ID: 23419 - Posted: 03.29.2017