Links for Keyword: Sexual Behavior

Follow us on Facebook or subscribe to our mailing list, to receive news updates. Learn more.

Links 1 - 20 of 1730

Gene activity in human cortex shows striking sex differences

By Lauren Schenkman More than 3,000 genes are differently expressed in the cerebral cortex of people with XX versus XY sex chromosomes, according to a single-cell transcriptomics study published last month in Science. The differences could help explain why certain neurodegenerative and neurodevelopmental conditions affect one group more than the other, or vice versa. The results present “a pretty dramatic shift in how we’re thinking about sex differences,” says Tomasz Nowakowski, associate professor of neurological surgery, anatomy and psychiatry, and of behavioral sciences, at the University of California, San Francisco. He was not involved in the new work but uncovered gene expression differences in prenatal developing brains last year. Previous research traced sex differences to subcortical structures, where sex hormone receptors are expressed, but “the cortex is not the part of the brain that you typically think of when you think about sex differences,” he says. “I think it’s a landmark.” Of the thousands of genes flagged in the new study, 133 showed consistent sex differences across all brain cell types in six cortical regions sampled from postmortem brains, donated by 15 men (who all had XY sex chromosomes) and 15 women (who all had XX sex chromosomes), aged 26 to 78 years. Two of these regions—the fusiform gyrus and the inferior lateral temporo-occipital cortex—have more gray-matter volume in men, previous MRI studies suggest; two others, the caudal insula and intraparietal sulcus, have more gray matter in women; and the final two regions, the angular gyrus and the retrosplenial cortex, show no sex bias in gray-matter volume. Intriguingly, 119 of the 133 genes are autosomal, meaning men and women should have, at least in theory, an equal dose. That makes them “ground zero for molecular sex differences in the brain,” says study investigator Armin Raznahan, chief of the Section on Developmental Neurogenomics at the U.S. National Institute of Mental Health. © 2026 Simons Foundation

Related chapters from BN: 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 and Learning
Link ID: 30235 - Posted: 05.06.2026

Revealed: how male and female brain cells differ in gene activity

Miryam Naddaf By analysing more than a million brain cells, researchers have uncovered widespread differences in patterns of gene activity between male and female brains. The work, which defined sex on the basis of a person’s combination of sex chromosomes, could help to explain why the risk of developing some brain conditions — such as schizophrenia and Alzheimer’s disease — differs between males and females. Although the differences were subtle, the team identified more than 100 genes that showed consistent variation in their expression between males and females across several brain regions. The work was published on 16 April in Science1. “Having these gene-expression signatures provides a molecular handle to understanding the biology of how the brains of men and women might be functioning slightly differently in the context of the different hormonal environments that their bodies produce,” says Jessica Tollkuhn, a neuroscientist and molecular biologist at Cold Spring Harbor Laboratory in New York. She adds that “understanding sex differences in disease susceptibility could lead to better treatments to benefit everyone”. Subtle differences Previous studies2,3 have documented sex differences when it comes to a person’s risk of developing various neurological conditions. For example, schizophrenia, attention deficit hyperactivity disorder (ADHD) and Parkinson’s disease are more common in biological males — who typically have XY sex chromosomes. By contrast, Alzheimer’s disease and mood disorders such as depression and anxiety tend to be more common in females, whose sex chromosomes are usually XX. © 2026 Springer Nature Limited

A new book finds parenting inspiration in the animal kingdom

By Erin Garcia de Jesús My early days of nursing a newborn felt like I’d transformed into a 24-hour diner. A demanding yet adorable customer flagged me down with piercing cries to demand milk around the clock. Unfortunately, I was also on clean-up duty, wiping spit-ups and poopy butts. Breastfeeding is hard work. But after reading science journalist Elizabeth Preston’s book The Creatures’ Guide to Caring, I’m glad I’m not a burying beetle. The critters use mouth and anal secretions to knead small dead animals into slick balls of meat. Parent beetles then bury the smothered carcasses and lay their eggs nearby. Some species even feed their brood regurgitated bits of carcass, helping the young beetles grow to 200 times their original size in just six days. “A newborn human growing at that rate would be the size of a beluga whale in less than a week,” Preston writes. Suddenly my own kid doesn’t seem so heavy. The Creatures’ Guide to Caring was born out of Preston’s growing fascination with the biology of parenting after having her first child. “If so many people have done it before you, and are doing it right now — if so many animals are doing it without books or apps or advice to heed — why is it the hardest thing you’ve ever done?” she writes. Perhaps by finding kinship in the animal world, Preston could learn something about her new role as a parent. Each chapter dissects the benefits and drawbacks of parenting, piecing together how it evolved in humans and other creatures. © Society for Science & the Public 2000–2026

Related chapters from BN: 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: 30191 - Posted: 04.08.2026

Hormone linked to morning sickness may help reduce alcohol intake

By Catherine Offord For most people, Oktoberfest means guzzling liters of beer inside a giant tent. But for one research group in Denmark, it’s a chance to study how our bodies know when we’ve had enough. In a preprint posted on bioRxiv last week, researchers combined a small study of people at Germany’s fall beer festival with mouse experiments, genetic analyses, and blood tests from drunk medical students as well as people with alcohol dependence. Their findings, though preliminary, hint that a hormone commonly associated with morning sickness might also have a role in limiting humans’ alcohol consumption. “I found it fascinating,” says Marlena Fejzo, a women’s health scientist at the University of Southern California who has studied GDF15, the hormone involved. Though the study relies mostly on associations and can’t prove cause and effect, it “lends support” to the idea that GDF15 stops us from overconsuming harmful substances, she adds. GDF15 rises sharply during early pregnancy and is thought to contribute to vomiting and feelings of sickness. Some researchers think it evolved as a protective mechanism: Nausea may help an expectant parent avoid unfamiliar or spoiled food that could harm the fetus. But GDF15 is also present in people who aren’t pregnant and has been linked to appetite suppression. It has even attracted interest from the pharmaceutical industry as a potential antiobesity drug. Matthew Gillum, an endocrinologist at the University of Copenhagen, began to wonder about the hormone’s effect on alcohol intake after collaborating on a study of revelers at the Roskilde music festival. That research measured blood hormone levels in young men who’d spent a week binge drinking and eating junk food and found multiple changes—including a rise in GDF15. © 2026 American Association for the Advancement of Science.

Related chapters from BN: Chapter 5: Hormones and the Brain; Chapter 4: The Chemistry of Behavior: Neurotransmitters and Neuropharmacology
Related chapters from MM:Chapter 8: Hormones and Sex; Chapter 4: Development of the Brain
Link ID: 30168 - Posted: 03.21.2026

Why African striped mice can be the best of dads — or the worst

By Viviane Callier The difference between a doting dad and a deadbeat one may come down to a molecular switch in the brain — at least in African striped mice. Boosting activity of a particular gene in part of the brain known for regulating maternal care turned nurturing males into standoffish ones and even, in some cases, into mouse pup killers, researchers report February 18 in Nature. The findings reveal how social context can alter gene activity in the brain and thereby shape male caregiving. Male caregiving is prevalent in fish and amphibians, suggesting that it is a very ancient behavior in vertebrates. Among mammals, however, fewer than 5 percent of species have fathers that stick around to raise their young. Male African striped mice (Rhabdomys pumilio) are one of the exceptions to the rule, though they vary a lot in their nurturing tendencies, making them an ideal species in which to study the factors that influence this behavior. Some look after the young and groom them; others ignore the pups or even attack them. The same male could become aggressive or doting. To understand that behavior, comparative neurobiologist Forrest Rogers and his colleagues observed the mice’s social environment. In laboratory settings, group-housed males tended to be aggressive toward mouse pups when introduced to them. But surprisingly, when these males were moved to be housed alone, they became very paternal. “I thought clearly something must be wrong, because all the work we know of in mice and rats is that if you socially isolate them, they become very anxious and often not the most caring of individuals,” says Rogers, of Princeton University. But the lone African striped male mice didn’t seem anxious at all. © Society for Science & the Public 2000–2026.

Related chapters from BN: 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: 30159 - Posted: 03.14.2026

A genetic trick helps this all-female fish species escape evolutionary doom

By Phie Jacobs Talk about an odd couple. At least 100,000 years ago, a female Atlantic molly (Poecilia mexicana) living in the fresh waters near what is now Tampico, Mexico, mated with a male sailfin molly (Poecilia latipinna). The offspring of this cross-species coupling ought to have been sterile, like a mule. But this particular hybrid went on to birth a brood of daughters—all of which were genetic clones of their mother. Scientists have long assumed this reproductive strategy of birthing clones to be an evolutionary dead end among vertebrate animals, with offspring inevitably succumbing to genomic degradation over time. But the Amazon molly (Poecilia formosa), named for the fierce female warriors of Greek mythology, has kept on defying the odds. According to research published today in Nature, it all comes down to a quirk of genetics that helps reverse harmful mutations. “This is a very cool story,” says University of Oklahoma biologist Ingo Schlupp, who provided the study authors with samples but otherwise wasn’t involved in the new work. Researchers who study asexual animals, he explains, have been “scratching our heads” trying to figure out how some species manage to avoid what evolutionary theory predicts to be certain doom. Although asexual reproduction is common in bacteria and plants, it only rarely occurs in vertebrate animals. Often, these “virgin births” involve a process called parthenogenesis, in which an embryo develops from an unfertilized egg cell—no contribution from the other sex required. The Amazon molly, however, is far from celibate. These fish still mate with males from closely related species because they need sperm to kick-start the development of their embryos. But none of the male’s genetic material gets passed on to the next generation. © 2026 American Association for the Advancement of Science.

Related chapters from BN: Chapter 6: Evolution of the Brain and Behavior; Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 30158 - Posted: 03.14.2026

Female caribou grow antlers as a built-in postbirthing snack

By Emma Gometz Caribou, large deer that are native to the northernmost parts of the world (and sometimes called reindeer), are the only deer whose females grow antlers. In a study published today, researchers observed behavior that might explain why: female caribou appear to gnaw on shed antlers as a kind of postbirthing supplement. Caribou migrate huge distances every year between the places where they graze during the winter and the grounds where they calve in the spring. They can walk thousands of miles per year and likely have the longest terrestrial migration of any animal. Caribou mothers complete these extremely long migrations with antlers on their head and a calf in their womb. The period is very nutritionally demanding for them but culminates with a reserve stock of supplements when they need it the most. The researchers behind the new study figured this out when they observed bite marks in more than 80 percent of the 1,500 caribou antlers that littered the part of the Arctic National Wildlife Refuge in northeastern Alaska where the deer give birth. “[Caribou] are just really going after the antlers. They are highly selective,” says study co-author Joshua Miller, a paleoecologist at the University of Cincinnati. Female caribou shed their antlers just days before giving birth. Miller and co-author Madison Gaetano, a conservation paleobiologist, say that the findings suggest that female caribou are essentially banking nutrients in the form of antlers before they give birth and then gnawing on their freshly shed antlers to get a boost of protein, calcium and phosphorus they need to make up for having less time to graze as they nurse their calves. © 2025 SCIENTIFIC AMERICAN,

Related chapters from BN: 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: 30136 - Posted: 02.25.2026

Single gene sways caregiving circuits, behavior in male mice

By Natalia Mesa Most male mammals do not dote on their young and may even attack them, but some African striped mice actively feed, groom and nuzzle their own and even others’ pups. These profound behavioral differences come down to a single gene: agouti. This gene controls pigment production in the hair or skin of many animals. But in African striped mice, it also acts as a volume knob to silence caregiving circuits in the brain, according to a study published today in Nature. “It’s remarkable that this one gene is able to lead to a dramatic change in behavior,” says Robert Froemke, professor of genetics, neuroscience and otolaryngology at New York University, who was not involved in the work. Male African striped mice that live in isolation for roughly 2 months after weaning tend to nurture pups later in life, even those that are not their own, whereas their peers that live with other mice tend to be indifferent fathers or even infanticidal, the study found. The fatherly mice express lower levels of agouti in the brain compared with their more aggressive counterparts, the study shows. “Agouti, we think, is a molecular integrator of environmental experience,” says study author Ricardo Mallarino, associate professor of molecular biology at Princeton University. Despite the fact that only about 5 percent of mammalian species show fatherly behavior, parental care may be the default mode in striped mice, the research suggests. Both males and females use the same brain circuitry to care for their young, but enhanced agouti expression in the brain suppresses these instincts in the former. © 2026 Simons Foundation

Brain differences between sexes get more pronounced from puberty

By Chris Simms Some sex differences in brain-connectivity patterns become more pronounced with age, according to new research. Researchers studying brain-imaging data from people aged between 8 and 100 found that sex differences in the brain’s connections are minimal in early life, but then increase drastically at puberty; some of these differences continue to grow throughout adult life. The study was published as a preprint on bioRxiv1, and has not yet been peer reviewed. The work could help us to understand why men and women have different likelihoods of developing some mental-health disorders — and perhaps give insight into treating them, say the researchers. For example, women are about twice as likely as men to develop anxiety or depression2, and boys are about four times more likely to be diagnosed with autism spectrum disorder than girls3. “We are very excited about this study, which to our knowledge is the first one to compare how sex differences in brain networks evolve over the lifespan,” says Amy Kuceyeski, a computational neuroimager at Weill Cornell Medicine in Ithaca, New York. However, some neuroscientists who spoke to Nature aren’t convinced that the differences found between male and female brains are due to sex, and say the study does not address differences in gender roles, which are known to be important factors when researching brain mechanisms of health and disease. Human brains do not belong in distinct ‘female’ and ‘male’ categories, says Daphna Joel, a neuroscientist at the University of Tel Aviv in Israel, referring to a 2015 study she co-authored, which suggests that each human brain is a mosaic of features, some of which are more common in men, others in women4. © 2026 Springer Nature Limited

Related chapters from BN: 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: 30128 - Posted: 02.18.2026

Primates’ same-sex sexual behaviour ‘may reinforce bonds amid environmental stress’

Nicola Davis Science correspondent Same-sex sexual behaviour among non-human primates may arise as a way to reinforce bonds and keep societies together in the face of environmental or social challenges, researchers have suggested. Prof Vincent Savolainen, a co-author of the paper from Imperial College London, added that while the work focused on our living evolutionary cousins, early human species probably experienced similar challenges, raising the likelihood they, too, showed such behaviour. “There were many different species that unfortunately [are] all gone, that must have done this same thing as we see in apes, for example,” he said. Writing in the journal Nature Ecology & Evolution, Savolainen and colleagues reported how they analysed accounts of same-sex sexual behaviour in non-human primates, finding it to be widespread in most major groups, with reports in 59 species including chimpanzees, Barbary macaques and mountain gorillas. That, they added, either suggested an evolutionary origin far back in the primate family tree, or the independent evolution of the behaviour multiple times. While some studies have previously highlighted the possibility such behaviour could help reduce tensions in groups or aid bonding, the new study looked across different species to explore its possible drivers. The results reveal it to be more likely in species living in drier environments, where resources are scarce, and where there is greater risk from predators. “Previous research has shown there is a heritable element to [same-sex sexual behaviour], however, there is also environmental influence which is often overlooked,” said Chloe Coxshall, the first author of the study. © 2026 Guardian News & Media Limited

What It’s Like When Your Wife Goes on Testosterone

By Susan Dominus After years of a marriage that had little sex in it, Greg Carter had largely accepted that his wife no longer had any interest. The last thing he expected was that right around the time that they both were nearing 50, his wife would have a complete change of heart. “She was pouncing on me,” he said. His wife had recently started taking testosterone to manage her menopausal symptoms — at a dose so high that it brought her testosterone levels higher than is typical even for women in their 20s. The difference in her desire was almost immediate. “I had the experience of feeling like a teenage boy,” she told me. The shift vastly improved Greg’s own happiness, so much so that he sometimes felt pangs of regret about the years they spent together without a sex life. “I realized, later in life, all that we had missed out on,” he says. Earlier this year, I published an article on how women are increasingly — with widely varying results — seeking out testosterone to help them with energy or their sex lives. Some women who take testosterone at relatively low doses approved by major medical societies feel little change in their bodies, while others see an increase in their desire. Women who take high doses — doses that exceed levels approved by major medical societies — often report sharp upticks in their interest in sex. Franny’s doctor prescribed her testosterone (along with estrogen and progesterone) in what’s known as a pellet, a small medical product the size of a grain of rice that is inserted beneath the skin. Often those pellets, which release hormones over the course of several months, provide doses of testosterone that bring their levels much higher than those that women would have naturally — which was true in Franny’s case. “I feel like I want it sometimes more than my husband,” Franny told me when I was reporting my original article. There was a hint of nervousness in her tone of voice — that dynamic was a shift from their norm and one that made me realize it wasn’t just Franny’s life that had changed, but also Greg’s. And that made me wonder what it would be like to be the partner of someone who was undergoing such a radical shift. © 2025 The New York Times Company

Kissing Has Existed for at Least 16 Million Years, Scientists Say

By Ali Watkins The act has been called many things: Centrifugal motion. Perpetual bliss. The thrill of the moment. Unstoppable. In technical terms, it is “non-agonistic interaction involving directed, intraspecific, oral-oral contact with some movement of the lips/mouthparts and no food transfer.” Or, as her majesty Faith Hill might say, “This kiss.” And, it turns out, it’s also really old. British scientists say they’ve traced the age of the kiss, to anywhere from 16 million to 21 million years ago, and have found that it was far more common among other species than previously understood. Ants? They smooch. Fish? Kissers. Neanderthals? Yep, they puckered up, too — sometimes even with us. But kissing, the researchers said, has always been something of a so-called evolutionary mystery. It doesn’t present much benefit for survival, it has minimal reproductive benefits, and it’s mostly symbolic. “Kissing is a really interesting behavior,” said Matilda Brindle, an evolutionary biologist at Oxford University who led the study. Dozens of societies and cultures use it, it’s common, and it has weighted symbolism. But, she said, “we’ve not really tested it from an evolutionary perspective.” In prehistoric kissing, it seems, could be the primitive origins of our search for intimate connection. The act inherently requires vulnerability, and trust. It’s not always sexual and is often used among and between genders simply to show affection, and often between parents and offspring. Though researchers found evidence of kissing in several species, they narrowed the focus of the study mostly to the behavior of large apes, like gorillas, orangutans and baboons. © 2025 The New York Times Company

Oxytocin shapes both mouse mom and pup behavior

By Claudia López Lloreda Mouse pups, like other infants across the animal kingdom, cry to get their mother’s attention. The oxytocin system drives this communication and shapes how baby mice interact when reunited with their mothers, according to a study out today in Science. Oxytocin, known colloquially as the “love” or “cuddle” hormone, stimulates milk release during nursing and promotes maternal care behaviors. But most oxytocin research thus far has focused solely on the mother, overlooking the neuropeptide’s potential effects on an infant’s brain and behavior. This new study shows “the other half of the equation to what we already knew,” says Zoe Donaldson, associate professor of behavioral neuroscience at the University of Colorado Boulder, who was not involved with the study. Oxytocin is “this social signal that ultimately reinforces relationships,” she says. The work employed a novel optogenetic tool that enabled the team to turn off neurons deep in the hypothalamus of mouse pups. After being separated from their mothers for three hours, the pups vocalized more using distinct patterns when reunited with their mothers than did pups that had not been separated, a process controlled by oxytocin neurons in the pups’ hypothalamus, the team found. “It would make sense if oxytocin is on both sides of this: making moms want to take care of their pups that are calling, and making pups call in a manner that makes mom want to take care of them,” Donaldson says. “Then we have this sort of convergence where oxytocin is once again doing everything.” © 2025 Simons Foundation

Related chapters from BN: Chapter 5: Hormones and the Brain; Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex; Chapter 8: Hormones and Sex
Link ID: 29928 - Posted: 09.13.2025

Babies’ cries can make humans physically hotter

Ian Sample Science editor The cry of a distressed baby triggers a rapid emotional response in both men and women that is enough to make them physically hotter, researchers say. Thermal imaging revealed that people experienced a rush of blood to the face that raised the temperature of their skin when they were played recordings of babies wailing. The effect was stronger and more synchronised when babies were more distressed, leading them to produce more chaotic and disharmonious cries. The work suggests that humans respond automatically to specific features in cries that ramp up when babies are in pain. “The emotional response to cries depends on their ‘acoustic roughness’,” said Prof Nicolas Mathevon at the University of Saint-Etienne in France. “We are emotionally sensitive to the acoustic parameters that encode the level of pain in a baby’s cry.” Evolution equipped baby humans with a hard-to-ignore wail to boost their odds of getting the care they need. But not all infant cries are the same. When a baby is in real distress, they forcefully contract their rib cage, producing higher pressure air that causes chaotic vibrations in the vocal cords. This produces “acoustic roughness”, or more technically, disharmonious sounds called nonlinear phenomena (NLP). To see how men and women responded to infants’ cries, scientists played recordings to volunteers with little or no experience with babies. While listening, the participants were filmed with a thermal camera that captured subtle changes in their facial temperature. © 2025 Guardian News & Media Limited

A single protein makes lovesick flies spill their guts

By Sofia Caetano Avritzer Vomiting up a droplet of sugar might not seem like the most romantic gesture from a potential suitor. But for one fly species, males that spill their guts are quite a catch. Drosophila subobscura flies’ peculiar “romantic” barfing might have evolved by repurposing brain cells that usually control digestion for more romantic pursuits, researchers report August 14 in Science. Most male fruit flies court by following the females around and vibrating their wings to serenade them with a species-specific love song, says Adriane Otopalik. But some fly species, like D. subobscura, spice things up a little. The males will vomit a bit of their last meal and offer it to females they are interested in, says Otopalik, a neuroscientist at Howard Hughes Medical Institute’s Janelia Research Campus in Ashburn, Va. Nuptial gifts like these are common in some animals, like male spiders attempting to win over their mates without getting their heads bitten off. Scientists think female flies, which can be “very choosy,” might use this romantic barf to pick suitable suitors, says Otopalik, who was not involved in the study. The thousands of neurons that control most of male fruit flies’ courtship produce a male-specific version of a protein called fruitless. Artificially activating these neurons can make D. subobscura males go through the motions of their seduction dance — even when there aren’t any females around, says Daisuke Yamamoto, an evolutionary biologist at National Institute of Information and Communications Technology in Kobe, Japan. Yamamoto and his collaborators wondered if somewhere in these courtship brain cells was the key to understanding how nuptial gift giving evolved. © Society for Science & the Public 2000–2025

‘Sex reversal’ is surprisingly common in birds, new study suggests

By Phie Jacobs When it comes to telling males and females apart, many bird species reject subtlety altogether. Roosters stand out thanks to their big, bright comb and ear-splitting “cock-a-doodle-doo.” Bachelor birds-of-paradise flaunt their vibrant plumage to attract more subdued females. And the male peacock’s feathered train is so ostentatious it famously threw even Charles Darwin for a loop. But that’s not the case for all bird species. When males and females look pretty much the same, scientists must try harder—often using DNA testing—to separate the sexes. According to a new study of wild Australian birds, these methods may be leading to misidentification in cases where an individual’s gonads and outward appearance don’t align with the genetic sex determined by its chromosomes. As scientists report today in Biology Letters, this phenomenon—known as sex reversal—may be more common than anyone expected. The discovery is likely to “raise some eyebrows” (or is it ruffle some feathers?), says Blanche Capel, a biologist at Duke University who wasn’t involved in the new work. Although sex determination is often viewed as a straightforward process, she explains, the reality is much more complicated. In humans, individuals with XX chromosomes typically develop as female, whereas those with XY chromosomes are usually male. But Judith Mank, a zoologist at the University of British Columbia, notes it’s the genes carried on those chromosomes—not the chromosomes—that are the main players. The SRY gene on the Y chromosome, for example, kick-starts male development in mammals. Anyone missing this key gene will end up developing as female, even if they have XY chromosomes. “We think of sex chromosomes as being sex determining,” says Mank, who also wasn’t involved in the new research. “That’s not true.” What’s more, it can matter how these genes are expressed on a cell-by-cell basis. In some species such as fruit flies, zebrafish, and chickens, individual cells have their own sexual identity based on the genes they happen to contain or express, rather than being influenced by the body’s overall hormone levels. When different cells contain different sets of chromosomes, this process can give rise to individuals called gynandromorphs, which exhibit both male and female characteristics. © 2025 American Association for the Advancement of Science.

Starlings form ‘friendships’ to help each other with breeding

Nicola Davis Science correspondent Birds of a feather flock together, so the saying goes. But scientists studying the behaviour of starlings have found their ability to give and take makes their relationships closer to human friendships than previously thought. About 10% of bird species and 5% of mammal species breed “cooperatively”, meaning some individuals refrain from breeding to help others care for their offspring. Some species even help those they are unrelated to. Now researchers studying superb starlings have found the support cuts both ways, with birds that received help in feeding or guarding their chicks returning the favour when the “helper” bird has offspring of its own. Prof Dustin Rubenstein, a co-author of the study from the University of Colombia, said such behaviour was probably necessary for superb starlings as they live in a harsh environment where drought is common and food is limited. “Two birds probably can’t feed their offspring on their own, so they need these helpers to help them,” he said, adding that as each breeding pair produces few offspring, birds must be recruited from outside the family group to help the young survive. “What happens is the non-relatives come into the group, and they breed pretty quickly, usually in the first year, maybe the second year, and then they take some time off and some of the other birds breed – and we never understood why,” said Rubenstein. “But they’re forming these pairwise reciprocal relationships, in the sense that I might help you this year, and then you’ll help me in the future.” The results chime with previous work from Rubenstein and colleagues that found superb starlings living in larger groups have a greater chance of survival and of producing offspring, with the new work suggesting the give-and-take approach helps to stabilise these groups. © 2025 Guardian News & Media Limited

Frog ribbits erupt via an extravagant variety of vocal sacs

By Susan Milius Here’s a great case of real life turning out to be stranger than fiction. From baby’s first storybook to sly adult graphic novels, the story we’re told is the same: Male frogs croak with the bottom of their mouths ballooning out in one fat, rounded bubble. Yet “that’s actually only half the species of frogs,” says herpetologist Agustín Elías-Costa of the Bernardino Rivadavia Natural Science Museum in Buenos Aires. The diversity of body parts for ribbitting is astounding. Some males serenade with a pair of separate puff-out disks like padded headphones that slipped down the frog’s neck, throbbing in brilliant blue. Some have sacs that look like balloon Mickey Mouse ears in khaki. Others ribbit with a single upright like a fat horn stub on some inflatable swimming pool toy rhino. All together, 20 basic forms for vocal sacs have evolved among frogs and toads, Elías-Costa and herpetologist Julián Faivovich report in March in the Bulletin of the American Museum of Natural History. Still, about 18 percent of the 4,358 species examined didn’t have vocal sacs at all. The team studied 777 specimens over 10 years of visiting museums around the world, including the Smithsonian’s National Museum of Natural History in Washington, D.C. “Libraries of nature,” Faivovich calls them. Just drawing a picture of something doesn’t authenticate details the way a preserved specimen does. These collections for biodiversity studies are “what makes them a science,” he says. The survey showed that vocal sacs disappeared between 146 and 196 times across the very twiggy evolutionary branchings of the frog and toad family tree. That’s “an astounding number considering their biological importance,” Elías-Costa says. Even without sacs, the animals still emit sounds because, like human speech, frog and toad ribbits originate from the larynx. Vocal sacs amplify the sound and could convey nuances of male quality and sexiness, but can also tip off eavesdropping predators. Females in a few species vocalize too, but it’s mostly a male endeavor. © Society for Science & the Public 2000–2025.

Related chapters from BN: Chapter 9: Hearing, Balance, 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: 29774 - Posted: 05.07.2025

What birds can teach us about the ‘biological truth’ of sex

By Nicole M. Baran One of the biggest misconceptions among students in introductory biology courses is that our characteristics are determined at conception by our genes. They believe—incorrectly—that our traits are “immutable.” The much more beautiful, complicated reality is that we are in fact a product of our genes, our environment and their interaction as we grow and change throughout our lives. Nowhere is this truer than in the developmental process of sexual differentiation. Early in development when we are still in the womb, very little about us is “determined.” Indeed, the structures that become our reproductive system start out as multi-potential, capable of taking on many possible forms. A neutral structure called the germinal ridge, for example, can develop into ovaries or testes—the structures that produce reproductive cells and sex hormones—or sometimes into something in between, depending on the molecular signals it receives. Our genes influence this process, of course. But so do interactions among cells, molecules in our body, including hormones, and influences from the outside world. All of these can nudge development in one direction or another. Understanding the well-studied science underlying this process is especially important now, given widespread misinformation about—and the politicization of—sex and gender. I am a neuroendocrinologist, which means that I study and teach about hormones and the brain. In my neuroendocrinology classroom, students learn about the complex, messy process of sexual differentiation in both humans and in birds. Because sexual differentiation in birds is both similar to and subtly different from that in humans, studying how it unfolds in eggs can encourage students to look deeper at how this process works and to question their assumptions. So how does sexual differentiation work in birds? Like us, our feathered friends have sex chromosomes. But their sex chromosomes evolved independently of the X and Y chromosomes of mammals. In birds, a gene called DMRT1 initiates sexual differentiation. (DMRT1 is also important in sexual differentiation in mammals and many other vertebrate animals.) Males inherit two copies of DMRT1 and females inherit only one copy. Reduced dosage of the gene in females leads to the production of the sex hormone estradiol, a potent estrogen, in the developing embryo. © 2025 Simons Foundation

Does testosterone make men?

is a psychologist, writer and professor in the history and philosophy of science programme at the University of Melbourne. She is the author of Delusions of Gender: How Our Minds, Society, and Neurosexism Create Difference (2010), Testosterone Rex: Myths of Sex, Science, and Society (2017) and Patriarchy Inc.: What We Get Wrong About Gender Equality – and Why Men Still Win at Work (2025). She lives in Melbourne, Australia. Carole Hooven is a human evolutionary biologist with a focus on behavioural endocrinology. She is a nonresident senior fellow at the American Enterprise Institute, an associate in Harvard’s Department of Psychology, and the author of T: The Story of Testosterone, the Hormone That Dominates and Divides Us (2021). She lives in Cambridge, Massachusetts. Does biology determine destiny, or is society the dominant cause of masculine and feminine traits? In this spirited exchange, the psychologist Cordelia Fine and the evolutionary biologist Carole Hooven unpack the complex relationship between testosterone and human behaviour. Fine emphasises variability, flexibility and context – seeing gender as shaped by social forces as much as it is by hormones. By contrast, Hooven stresses consistent patterns; while acknowledging the influence of culture and the differences between individuals, she maintains that biology explains why certain sex-linked behaviours persist across cultures. © Aeon Media Group Ltd. 2012-2025.

Links By Chapter:

Links for Keyword: Sexual Behavior