By Mitch Leslie If papers published in the past 6 months are right, a single number is enough to show whether people are likely to suffer a premature heart attack, land first authorship on published papers, become dependent on alcohol, or put on fat around the middle. That magic number is the ratio between the lengths of the second and fourth fingers, known as the 2D:4D ratio. It tends to be lower in men—meaning their fourth fingers tend to be longer than their second—than in women. Researchers who believe in its predictive power say it reflects a fetus's exposure to testosterone and other hormones that guide development, including that of the brain. The idea that the lengths of human fingers reveal so much stems from the work of evolutionary biologist John Manning, now at Swansea University in the United Kingdom. But the field he inspired has ballooned beyond what he could have imagined. More than 1400 papers in just over 20 years have linked the finger ratio to attributes such as personality, cognitive abilities, and sexual orientation as well as to risk of illnesses such as cardiovascular disease, cancer, and amyotrophic lateral sclerosis. Researchers have even tried to use ratios gleaned from stenciled handprints on cave walls to determine whether the artists behind ancient paintings were men or women. But the notion has also riled plenty of critics, who argue that researchers who rely on the 2D:4D comparison have been seduced by a simplistic, faulty measure. Some doubters contend that the difference in ratios between the sexes is an illusion resulting from men's larger hands or that the measure itself is statistically problematic. "I'm skeptical about every single finding involving that ratio," says physiologist and biostatistician Douglas Curran-Everett of National Jewish Health in Denver. © 2019 American Association for the Advancement of Science

Related chapters from BN8e: 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: 26311 - Posted: 06.07.2019

By Marisa Iati A bill in Alabama awaiting the governor’s signature would require people convicted of certain sex offenses to undergo “chemical castration” as a condition of parole — a requirement meant to keep perpetrators from committing similar crimes. The proposed law, passed by the state legislature, says a judge must order anyone convicted of a sex offense involving a child under the age of 13 to start receiving testosterone-inhibiting medication a month before their release from prison. Most offenders would have to pay for their treatment, which would be administered by the Department of Public Health, until a judge decides the medication is no longer necessary. Under the proposed law, a judge — and not a doctor — would tell the offender about the effects of the treatment. An offender could choose to stop getting the medication and return to prison to serve the remainder of their term. Anyone who stopped receiving the castration treatment without approval would be considered guilty of a Class C felony, punishable under Alabama law by up to 10 years in prison and a fine of up to $15,000. “Chemical castration” is a misnomer, as the process leaves the testes intact, can be reversed and does not prevent a man from reproducing. It does not guarantee a man’s sexual urge will be eliminated. (There’s no consensus on whether chemical castration would be effective for women.) © 1996-2019 The Washington Post

Related chapters from BN8e: 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: 26304 - Posted: 06.06.2019

By JoAnna Klein Say you are prescribed medication for depression, anxiety or even just to sleep. Would you want to take it if you knew that the drug had only been tested on men and male animals? Rebecca Shansky, a neuroscientist at Northeastern University in Boston, thinks you might not. When she tells nonscientific audiences that researchers “for the most part don’t study female animals, people are blown away,” she said. She added: “It seems like such an obvious thing to a normal person. But when you come up in the academic and science world, it’s like, ‘Oh no, females are so complicated, so we just don’t study them.’” In 2016, the National Institutes of Health and its Canadian counterpart mandated that all preclinical research they fund must include female subjects. Now, Dr. Shansky and other scientists wonder if that requirement will do enough to improve how research is conducted. In an essay published Thursday in Science, Dr. Shansky questions whether simply adding female organisms to experiments or looking for sex differences misses the point. She warns that this is a public health problem — with implications beyond neuroscience — and says scientists should design experiments better suited to both biological sexes. If scientists don’t stop looking through a male lens, outdated gender stereotypes will continue to foster dangerous assumptions about the brain and behavior, resulting in clinical studies and eventual treatments that don’t work equally for all people on the gender spectrum. Basic research is the foundation for clinical studies and practice, and that often begins with animals, which offer controlled settings for research of human diseases. © 2019 The New York Times Company

Related chapters from BN8e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 26284 - Posted: 05.31.2019

By Susan Rudnick I was a month shy of turning 16 when a red-faced man in a white coat told me I had been born without a uterus. With a huge dark desk between us, he told me I would never menstruate, and would need plastic surgery to correct the anomaly of my vaginal opening that was a mere dimple, so that one day I would to be able to have sexual intercourse. I have M.R.K.H. These four letters stand for Mayer, Rokitansky, Küster and Hauser, the names of the four doctors who discovered the syndrome over a hundred years ago. This anatomical condition occurs during the first trimester of pregnancy, when the duct that normally forms the uterus, cervix and vaginal canal fails to develop. Ovaries do develop, but there is no menstruation. Although the condition is rare, impacting just one in every 4,500 women, for over 40 years I thought I was like nobody else. At the time of the diagnosis, he described my symptoms but neglected to tell that the condition had a name. Without a name for my syndrome, I couldn’t connect with others like me. I was left to navigate my life feeling defective, marginalized and alone. I carried my difference as a secret shame, acting as if I were just like other people. In high school I learned to pretend I had my period. I even talked about having period cramps, which I never had. Even though swimming and water ballet club were my favorite activities, I didn’t go swimming a few times so that it would seem as if I had my period, like all the other girls. There was nothing I wouldn’t do to be like everybody else. One day in college I was lying in my dorm room bed with a gaggle of women, when the conversation turned to diaphragms, something I would never need, but which seemed a rite of passage. Birth control was way beyond my knowledge base. This was in the early 60s, when abortions were still illegal, but you could go to Planned Parenthood and get fitted for a diaphragm. While my girlfriends laughed about looking at condoms in the drugstore, I spaced out. I felt like such an outsider carrying the pain of my secret. © 2019 The New York Times Company

Related chapters from BN8e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 26268 - Posted: 05.28.2019

By Megan Schmidt “The women’s winter is here. The freeze is upon us,” warns a Game of Thrones parody about men and women’s office temperature preferences. If you have a Y chromosome, you probably haven’t experienced “women’s winter.” As the video explains, women’s winter is “when spring turns to summer and there’s blossom on the trees, the office air doth turns to ice and all the women freeze.” Although the skit is now a few years old, it perfectly captures women’s daily struggle with overly air-conditioned workplaces. To some people, thermostat complaints might seem trivial. But a new study has found that cold offices do more than make women shiver. Thermostat settings geared for men’s comfort — typically cooler temperatures — may actually disadvantage women by lowering their ability to perform some tasks. The study, published in PLOS One, found that women are better at math and word tests when room temperatures are warmer. The women in the study answered more questions correctly and submitted more answers overall during the timed tests. Men, on the other hand, performed marginally better on the same tests at cooler room temperatures, the researchers found. Temperature didn’t influence performance on the logic test for either gender. Study author Agne Kajackaite, a behavioral economics researcher at the WZB Berlin Social Science Center, said the research illustrates that “the battle for the thermostat is not just a complaint about comfort levels.” When it comes to women succeeding in the classroom or in the workplace, room temperatures may make a big difference.

Related chapters from BN8e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases; Chapter 13: Homeostasis: Active Regulation of the Internal Environment
Related chapters from MM:Chapter 8: Hormones and Sex; Chapter 9: Homeostasis: Active Regulation of the Internal Environment
Link ID: 26266 - Posted: 05.24.2019

Ian Sample Science editor Male bonobos living with their mothers are three times more likely to father offspring, research suggests. Their mothers are so keen for them to father children that they usher them in front of promising partners, shield them from violent competitors and dash the chances of other males by charging them while they are at it. For a bonobo mother, it is all part of the parenting day, and analysis finds the hard work pays off. Males of the species that live with their mothers are three times more likely to father offspring than those whose mothers are absent. Martin Surbeck, a primatologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, said: “We wanted to see if the mothers’ behaviour changes the odds of their sons’ success, and it does. The mothers have a strong influence on the number of grandchildren they get.” Bonobo mothers seize every opportunity to give their sons a leg-up. In bonobo society, the lower ranks tend to be gender balanced, but females dominate the top ranks. Many mothers have social clout and chaperone their sons to huddles with fertile females, ensuring them better chances to mate. “The mothers tend to be a social passport for their sons,” said Surbeck. © 2019 Guardian News & Media Limited

Related chapters from BN8e: 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: 26256 - Posted: 05.21.2019

Mitchel Daniel If you’re looking for love, it pays to stand out from the crowd. Or at least that’s how it works in some parts of the animal kingdom. Scientists have found that in several species – green swordtail fish, Trinidadian guppies, fruit flies, Poecilia parae fish – ladies overwhelmingly go for the guy that looks different from the rest. But the reason for this attraction to novelty has remained a mystery. So my colleagues and I used the Trinidadian guppy to investigate the psychology behind why many females have an affinity for the unusual. Male features that attract females The guppy has long been a workhorse for biologists like me who are interested in understanding the mating decisions that animals make and the evolutionary forces behind those decisions. Male guppies attempt to woo females using courtship dances that show off the elaborate color patterns adorning their bodies. The females of the species are color pattern connoisseurs, carefully choosing among their suitors based, in large part, on their visual appeal. This tendency has made the guppy an excellent model for studying mate choice. Male guppies showcase their colors during their courtship dances. Many types of animals exhibit what evolutionary biologists call directional preferences, an attraction to more of a certain thing – think bigger antlers, a longer tail or brighter color spots. And there are evolutionary theories that help make sense of these preferences. If a male can grow more extreme features, that can be a sign that he is in good physical condition, has good genes, or would make a good parent. What’s less clear, though, is why females should value unusualness in a mate. © 2010–2019,

Related chapters from BN8e: 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: 26233 - Posted: 05.15.2019

By Gina Kolata The Court of Arbitration for Sport in Zurich has ruled that women with very high testosterone levels — far above the normal range — cannot compete against other women in races from 400 meters to one mile unless they take drugs to suppress production of the hormone. The ruling prevents Caster Semenya, 28, an elite runner and Olympic champion from South Africa, from competing in those races because her testosterone levels are naturally very high. She had challenged attempts to disqualify her from racing as a woman. The science underpinning that decision is complicated, raising difficult questions about biology, fairness and gender identity. What is testosterone? Where does it come from in women? It’s a hormone, an androgen, that has a variety of effects on the body. Women and men produce testosterone, but women don’t make nearly as much In men, high levels of testosterone are made by the testes. Much lower levels are produced in the adrenal glands, which rest above the kidneys. Women also make testosterone in their adrenal glands, and in their ovaries. But testes produce much more: Testosterone levels in men are 295 to 1,150 nanograms per deciliter of blood, while the levels in the women are 12 to 61 nanograms per deciliter of blood. Testosterone “builds muscle,” said Dr. Benjamin D. Levine, who studies sex differences in athletic performance at the University of Texas Southwestern Medical Center. “It builds skeletal muscle, it builds cardiac muscle. It increases the number of red blood cells.” The effects are seen whether the hormone is naturally present or introduced with drugs. In one of the most infamous examples, women who represented East Germany at the Olympic Games in the ’70s and ’80s achieved astounding success after they were unknowingly doped with anabolic steroids including testosterone. “The science is quite clear,” said Dr. Aaron Baggish of Massachusetts General Hospital, who is an expert on testosterone’s effects. “An androgenized body has a performance advantage.” © 2019 The New York Times Company

Related chapters from BN8e: 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: 26196 - Posted: 05.02.2019

By Emily Oster In 1980, 8.6 percent of first births were to women over 30; by 2015 this was 31 percent. This is more than an interesting demographic fact. It means that many of us are having children much later than our parents did. By the time a baby arrives, many of us have been through school, spent time in the working world, developed friendships, hobbies. And through all of these activities, we have probably grown used to the idea that if we work harder — at our jobs, at school, at banking that personal record in the half marathon — we can achieve more. Babies, however, often do not respond to a diligent work ethic. Take, as an example, crying. When my daughter, Penelope, was an infant, she was typically inconsolable between 5 and 8 p.m. I’d walk her up and down the hall, sometimes just crying (me crying, that is — obviously she was crying). I once did this in a hotel — up and down, up and down, Penelope screaming at the top of her lungs. I hope no one else was staying there. I tried everything — bouncing her more, bouncing her less, bouncing with swinging, bouncing with nursing (difficult). Nothing worked; she would eventually just exhaust herself. I wondered whether this was normal. I’m an economist, someone who works with data. I wrote a book on using data to make better choices during pregnancy; it was natural for me to turn to the data again once the baby arrived. And here, faced with crying, I found that the data was helpful. We often say babies are “colicky,” but researchers have an actual definition of colic (three hours of crying, more than three days a week, for more than three weeks) and some estimates of what share of babies fit this description (about 2 percent). But the same data can also tell us that many babies cry just a bit less than that, and almost 20 percent of parents report their baby “cries a lot.” So I was not alone. The data also told me the crying would get better, which it eventually did. © 2019 The New York Times Company

Related chapters from BN8e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 26162 - Posted: 04.22.2019

Nicola Davis Philandering men have unfaithfulness written all over their faces, according to research that suggests men and women are able to spot cheating chaps just by looking at them. Experts found men with more “masculine” faces were more likely to be thought to be unfaithful, and such men also self-reported more cheating or “poaching” of other men’s partners. However, they stressed the results were modest, and said people should be wary of deciding whether someone is a love rat based on impressions of facial features alone. The team said being suspicious of men with masculine features – such as a strong browridge, strong jaw and thinner lips – might have offered an evolutionary advantage, allowing heterosexual women to spot a flaky partner and men to recognise a potential rival who might seduce their partner or leave them raising someone else’s child. Previous research has suggested women are able to spot unfaithful men from their mugshot, with the masculinity of the man’s face a key factor in the judgment, while weaker effects have been found for men weighing up images of women. However, it was unclear whether people could also spot a philanderer of the same sex. Writing in the journal Royal Society Open Science, researchers described how they asked heterosexual white participants to judge the facial features of 189 white adults who had been photographed and taken part in previous research. Overall, 293 men and 472 women rated pictures of women, while 299 men and 452 women judged images of men, rating on a scale of one to 10 how likely they thought each person was to be unfaithful. © 2019 Guardian News & Media Limited

Related chapters from BN8e: 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: 26147 - Posted: 04.17.2019

Robert J King Ph.D. Saying that people deserve to be treated decently is not a factual claim. You can’t look it up in a textbook, and no amount of brain-scanning is going to reveal why it’s true. People have been either succeeding (or more often failing) to treat each other kindly, fairly, and honorably, since before there was science, since before there were people really. And—they will continue to try (and often fail) far into the future, whatever science reveals about our natures. If I am trying to help a child understand why stealing from another child was wrong, or that they should share the sandpit, or apologize to that other annoying (and now crying) kid…yes…I know he took your dolly, but you still can’t hit him with that Lego dinosaur… Well, I don’t get out my copy of Eric Kandel's Principles of Neural Science, and start pointing meaningfully to the diagram of Brodmann area 11 in the prefrontal cortex. This seems blindingly obvious. However, the corollary: That you don’t need neurological backup to argue that you should treat people fairly, seems lost on writers like Cordelia Fine and Gina Rippon. Both are trying to argue that humans are neurological hermaphrodites, as if somehow admitting any sex differences in brains would mandate the unfair treatment of women. Gina Rippon is back to “debunk” neuroscience with her latest, The Gendered Brain: The New Neuroscience That Shatters The Myth Of The Female Brain. It is tempting to rebunk these debunkings but, if I am right in my guess about what is going on here, no amount of factual piling on is going to help. In fact—it may make things worse, because it’s going to convince writers like Fine and Rippon that some hideous conspiracy is occurring and, like some horrible feminist version of Alex Jones, that the whole of brain science is fake news. Let’s stop things before they get out of hand. © 2019 Sussex Publishers, LLC

Related chapters from BN8e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 26135 - Posted: 04.13.2019

Rhonda Voskuhl & Sabra Klein We are concerned that Lise Eliot’s review of Gina Rippon’s book The Gendered Brain (Nature 566, 453–454; 2019) undermines the premise that sex is a biological variable with respect to many medical conditions and drug responses (see J. A. Clayton and F. S. Collins Nature 509, 282–283; 2014). As president-elect and president, respectively, of the Organization for the Study of Sex Differences, we disagree with Eliot’s claim that the brain is “no more gendered than the liver or kidneys or heart”. We also disagree that sex differences in behaviour are due to cultural effects on newborns, not to biological effects. In our view, these are not mutually exclusive. Sex disparities occur in animal models that are not subject to cultural bias. The brain, like many organs, shows differences attributable to sex, both during health (see, for example, E. Luders et al. J. Neurosci. 29, 14265–14270; 2009) and during disease. Two-thirds of people with Alzheimer’s disease are women; twice as many men as women have Parkinson’s disease (see, for example, L. J. Young and D. W. Pfaff Front. Neuroendocrinol. 35, 253–254; 2014). And multiple sclerosis affects three times more women than men, although men with the condition develop neurological disability more quickly (see, for example, R. R. Voskuhl and S. M. Gold Nature Rev. Neurol. 8, 255–263; 2012). Sex is a modifier of disease risk and progression. © 2019 Springer Nature Publishing AG

Related chapters from BN8e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 26130 - Posted: 04.12.2019

By Sarah Mervosh He is called the “father of the American cavalry,” a Polish-born Revolutionary War hero who fought for American independence under George Washington and whose legend inspired the dedication of parades, schools, roads and bridges. But for more than 200 years, a mystery persisted about his final resting place. Historical accounts suggested the cavalryman, Casimir Pulaski, had been buried at sea, but others maintained he was buried in an unmarked grave in Savannah, Ga. Researchers believe they have found the answer — after coming to another significant discovery: The famed general was most likely intersex. New evidence suggests that although Pulaski identified and lived as a man, biologically, he did not fit into the binary definitions of male and female, a twist that helps explain why scientists could not previously identify his remains. The revelatory findings are detailed in a new documentary, “The General Was Female?,” which is showing on the Smithsonian Channel on Monday. The discovery offers historical representation to people who are intersex, a group that has often been stigmatized and overlooked throughout history. About one in 2,000 people is born with ambiguous genitalia, which can lead doctors to perform what advocates say are unnecessary and harmful surgeries, according to the Intersex Society of North America. But intersex includes a variety of conditions, and many more people have subtler variations in sex anatomy, which may manifest later in life — or not at all. Some estimates suggest that about 1.7 percent of the population has intersex traits, making such characteristics about as common as having red hair. Though Pulaski’s role in history has long been embraced in areas with strong Polish and Catholic ties — his birthday is an Illinois state holiday and he is celebrated with an annual Polish pride parade in New York City — the new findings now also place him alongside the few historical figures who are known to have had intersex traits. © 2019 The New York Times Company

Related chapters from BN8e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 26120 - Posted: 04.08.2019

“What we didn’t know before was some individuals seem to be able to choose whether they lay eggs or give birth to live babies,” Whittington said on Wednesday. “That was pretty staggering. We had no idea that could be the case. So I think it just makes this lizard even weirder.” Previous research has shown that if a Sydney skink was taken north it would still lay eggs, while live bearers transferred south would also continue to reproduce as they previously did. “I’m curious to know what happens if you breed an egg layer with a live bearer – what do their sons and daughters do?” Whittington said. Another skink in South Australia has also been shown to be bimodal. Bougainville’s skinks give birth to babies on Kangaroo Island, while on the mainland they lay eggs. Only a handful of species in the world do this. The University of Sydney study into the three-toed skink will be published in Biology Letters this week. Whittington hopes to map where they lay eggs and where they give birth in further research. The three-toed skink, which looks like a baby snake with tiny legs, is widespread along Australia’s east coast and is often seen in gardens or compost heaps. © 2019 Guardian News & Media Limited

Related chapters from BN8e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 26106 - Posted: 04.03.2019

By Michael C. Reichert Early in my first go at being a father, I was hijacked by ancient impulses. Our family lived in a rowhouse neighborhood in Philadelphia, and right down the street was a small playground where gangs of boys gathered for games of stickball and basketball. My son loved playing sports. But he was unprepared for what developed as his friends grew older. After years together laughing and riding their tricycles and then bikes up and down the block, several of the boys grew angry and mean. Ultimately, they turned on my son, taunting him, leaving him out of their games. He began to trudge home, tail between his legs. And I felt called to action. At first, I tried to bolster his confidence so he would give the playground another go. But one Saturday morning I met him at the front steps and told him he could not come into the house. “You have to figure this out,” I said. “I’ll stay with you as long as you need, but I cannot let you just give up.” He tried to push past me, his humiliation becoming frantic. He melted down, screaming and crying. I kept saying: “You can do it. You don’t have to give up.” A neighbor poked her head out, concerned about what must have sounded like child abuse. Did I do the right thing? Even now I’m not sure. He did go back to the playground, and eventually managed some kind of truce with the other kids. He grew up into a fine man, a teacher, and understands I was trying to help, in my clumsy way. But while teaching him to stand up for himself, was I also passing along the prejudice that a boy should override his pain and never back down from a fight? What happened in my son’s peer group was perfectly predictable. Boyhood immerses boys in violence and the bullying that leads to it. High school boys are more likely than girls to have been in a physical fight in the past year and male children are more likely to have been victims of violence. Three types of male violence — violence against women, violence against other men and violence against themselves — are deeply interwoven. © 2019 The New York Times Company

Related chapters from BN8e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases; Chapter 4: The Chemistry of Behavior: Neurotransmitters and Neuropharmacology
Related chapters from MM:Chapter 8: Hormones and Sex; Chapter 4: The Chemistry of Behavior: Neurotransmitters and Neuropharmacology
Link ID: 26098 - Posted: 04.01.2019

New rules to reduce naturally high testosterone levels in female athletes have been branded "unscientific". Last year, athletics chiefs ruled women with levels of five nanomoles per litre or more must have hormone treatment before being allowed to compete. But experts, reporting in the British Medical Journal, say there is a lack of evidence about testosterone's effects and the cut-off figure is arbitrary. A decision on the legality of the rules is expected later this month. The International Association of Athletics Federations (IAAF) delayed implementing its regulations after South African runner Caster Semenya contested the legality of the new rules. She was banned from international competitions for nearly a year for having testosterone levels above the athletics body's limit for female athletes. World athletics bosses have previously said they want to protect the sanctity of fair and open competition. Writing in an editorial in the BMJ, Dr Sheree Bekker, from the University of Bath, and Prof Cara Tannenbaum, from the University of Montreal, say the IAAF's regulations risked "setting an unscientific precedent for other cases of genetic advantage". "The medical profession does not define biological sex or physical function by serum testosterone levels alone," they say. And they warned that the proposed rules could have "far reaching implications" on individuals and societies. Dr Bekker and Prof Tannenbaum argue that testosterone levels vary naturally in men and women, with higher averages among elite athletes. But there is also a big crossover between men and women, with 16% of men classified as having low testosterone and 14% of women having high, according to some definitions. They say testosterone is just one indicator of sports performance and many other factors also play a role. "If more science is needed... then call for health research organisations to deliver on this mandate," they say. © 2019 BBC

Related chapters from BN8e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 26057 - Posted: 03.21.2019

By Michael Price Female twins who shared a womb with a brother tend to get less education, earn less money, and have fewer children than girls who shared a womb with another girl, according to an analysis of hundreds of thousands of births over more than a decade. Researchers suspect the cause is testosterone exposure during fetal development, though the exact mechanism remains a mystery. “I think it’s a really interesting look at how this really complicated system might impact females,” says Talia Melber, a biological anthropologist at the University of Illinois in Urbana who wasn’t involved in the study. Still, she cautions, a lot more work needs to be done to establish a causal link. Fraternal twins, in which each of two eggs is fertilized by a different sperm cell, occur in about four of every 1000 births. About half of those result in male-female twin pairs. Typically, about 8 to 9 weeks into gestation, a male fetus begins to produce massive amounts of testosterone, which helps jump-start the development of male reproductive organs and brain architecture; female fetuses receive only modest amounts of the sex hormone. In male-female twins, though, small amounts of the male fetus’s testosterone can seep into the female twin’s separate amniotic sac. Scientists have known about this phenomenon for decades, and have been arguing for just as long over what effects, if any, it has on women later in life. © 2019 American Association for the Advancement of Science

Related chapters from BN8e: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 26051 - Posted: 03.19.2019

By Elizabeth Pennisi Cowbirds are the quintessential deadbeat parents. They, and about 90 other bird species, abandon their eggs in other birds’ nests, leaving the burden of chick care to others. An arms race is the result: Cuckolded foster parents keep evolving ways to fight back, and deadbeats evolve countermeasures. Now, researchers have discovered how spots on an egg play a crucial role in a parent’s decision to keep an egg—or boot it from the nest. One of the shiny cowbird’s (Molothrus bonariensis) most common victims is the chalk-browed mockingbird (Mimus saturninus). The mockingbird’s eggs are blue-green and spotted, whereas the cowbird’s eggs vary from pure white to brown and spotted. Researchers had assumed mockingbirds reject cowbird eggs that don't look like their own, in pattern and color. But the new study finds it’s not that simple. To get a better sense of how mockingbirds decide which eggs to boot, evolutionary ecologist Daniel Hanley at Long Island University in Brookville, New York, and colleagues painted 70 3D-printed eggs a range of colors and put spots on half of them. They distributed these eggs among 85 mockingbird nests and checked several days later to see which eggs were still there. Spots tended to make the mockingbirds hedge their bets and keep an egg, even if the color wasn’t “right,” Hanley and his colleagues report in the April issue of the Philosophical Transactions of the Royal Society B. For example, the mockingbirds removed unspotted brown eggs—a “wrong” color and pattern—90% of the time. But the birds were less sure when the egg had spots. They removed brown eggs with spots just 60% of the time, for example. In general, mockingbirds were more accepting of very blue eggs, even those that were much bluer than their own eggs. And when these blue eggs had spots, parents kept them more than 90% of the time. © 2019 American Association for the Advancement of Science

Related chapters from BN8e: 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: 26014 - Posted: 03.07.2019

Nicola Davis A pair of twins have stunned researchers after it emerged that they are neither identical nor fraternal – but something in between. The team say the boy and girl, now four years old, are the second case of semi-identical twins ever recorded, and the first to be spotted while the mother was pregnant. The situation was a surprise to the researchers. An ultrasound of the 28-year old mother at six weeks suggested the twins were identical – with signs including a shared placenta. But it soon became clear all was not as it seemed. “What happened was the mother came back for her routine ultrasound some months later, and we saw one [twin] to be a boy and one to be a girl,” said Dr Michael Gabbett, first author of the report from Queensland University of Technology in Australia. “At that point we started the genetic studies and worked it out from there.” Twins are normally either identical or fraternal. In the case of identical, one egg is fertilised by one sperm, but the resulting ball of cells splits in two, giving rise to two offspring with identical genetic material. In the case of fraternal, or non-identical, twins, two eggs are fertilised, each by a different sperm. The resulting siblings arise from the same pregnancy, but are no more genetically similar than siblings from the same parents born at a different time. Faced with a puzzling scenario, Gabbett and colleagues report in the New England Journal of Medicine that they took samples from the two amniotic sacs, allowing them to investigate the genomes of the twins during the pregnancy. © 2019 Guardian News & Media Limited

Related chapters from BN8e: 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: 25997 - Posted: 03.01.2019

Susan Milius Cheating pays, sort of. But for a glossy blue-black bird with a bright yellow eye, cheating doesn’t outdo regular honest parenting. The greater ani, a type of cuckoo found from Panama to the Amazon Basin, usually starts out as a dutiful parent. Two or three male-female pairs typically build and fill a communal nest “like a big basket of eggs,” says behavioral ecologist Christina Riehl of Princeton University. But if a snake or some other disaster kills the young, a bereft female sometimes gets sneaky. She slips into neighboring ani nests and leaves an egg here and there that she won’t care for, but the rightful nest owners might. Not all females from trashed nests do that. Some just wait for the next breeding season, when all the birds get a fresh start building another nest. Greater anis’ sporadic cheating offers a rare chance to compare the success of egg-sneaks with honest mothers in the same species. Over 11 breeding seasons, Riehl and colleagues determined the parentage of more than 1,700 eggs and found 65 eggs in foster nests. Mothers that parasitize other nests in this way seem to lay more eggs a year, on average, Riehl says. “It’s actually kind of hard to be a parasite,” she says. But the average number of chicks that survived to flutter out of the nest on their own frantic wing power was about the same for all females, Riehl and Princeton colleague Meghan Strong report online February 27 in Nature. The mothers that always cooperated averaged about one fledgling a year, and so did the females that laid stealth eggs. |© Society for Science & the Public 2000 - 2019

Related chapters from BN8e: 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: 25991 - Posted: 02.28.2019