Links for Keyword: Sexual Behavior

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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

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: 29924 - Posted: 09.10.2025

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

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: 29890 - Posted: 08.16.2025

‘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

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: 29785 - Posted: 05.14.2025

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.

Mating and Monogamy: The Tricky Sex Lives of Birds

By Nathan H. Lents For generations, anthropologists have argued whether humans are evolved for monogamy or some other mating system, such as polygyny, polyandry, or promiscuity. But any exploration of monogamy must begin with a bifurcation of the concept into two completely different phenomena: social monogamy and sexual monogamy. WHAT I LEFT OUT is a recurring feature in which book authors are invited to share anecdotes and narratives that, for whatever reason, did not make it into their final manuscripts. In this installment, author Nathan H. Lents, professor of biology at John Jay College, shares a story that didn’t make it into his recent book “The Sexual Evolution: How 500 Million Years of Sex, Gender, and Mating Shape Modern Relationships” (Mariner Books). Sexual monogamy is just what it sounds like: The restriction of sexual intercourse to within a bonded pair. Social monogamy, also known as economic monogamy, describes the bonding itself, a strong, neurohormone-driven attachment between two adults that facilitates food and territory sharing, to the exclusion of others, for at least one breeding season, and generally purposed towards raising offspring. Because these two aspects of monogamy are so often enjoined among humans, they are considered two sides of the same coin. But, as it turns out, they are entirely separable among animals. In fact, social monogamy is extremely common in birds and somewhat common in mammals, while sexual monogamy is vanishingly rare among any species. Because of the unique way their embryos develop — externally but with constant warmth required — birds are the real stars of monogamy and have thus borne the brunt of its misconceptions. The marriage (if you’ll pardon the pun) of two very different behaviors into one concept is — and always was — unsupported by evidence from the natural world. Monogamy, as it is commonly understood, was the invention of anthropomorphic bias. Naturalists in the 19th and 20th centuries documented how pairs of various bird species dutifully toiled together building a nest, protecting the eggs, mutually feeding each other and their offspring, before eventually flying off into the sunset together. These prim and proper Victorians didn’t have to squint very hard to see a perfect model in nature of what they valued most in human society — lifelong and sexually exclusive marriage.

Why women’s brains are more resilient: it could be their ‘silent’ X chromosome

By Katherine Bourzac Women tend to live longer than men and are often more resilient to cognitive decline as they age. Now researchers might have uncovered a source for this resilience: the second X chromosome in female cells that was previously considered ‘silent’. In work published today in the journal Science Advances1, a team reports that, at least in female mice, ageing activates expression of genes on what is usually the ‘silent’, or inactivated, X chromosome in cells in the hippocampus, a brain region crucial to learning and memory. And when the researchers gave mature mice of both sexes a type of gene therapy to boost expression of one of those genes, it improved their cognition, as measured by how well they explored a maze. Assuming these results can be confirmed in humans, the team suggests it could mean that women’s brains are being protected by their second X chromosome as they age — and that the finding could translate into future therapies boosting cognition for everyone. “The X chromosome is powerful,” says Rachel Buckley, a neurologist who studies sex differences in Alzheimer’s disease at Massachusetts General Hospital in Charlestown, and who was not involved in the research. This kind of work, she says, is helping researchers to understand “where female resilience lies and how to harness it”. (This article uses ‘women’ and ‘female’ to describe people with two X chromosomes and no Y chromosome, reflecting the language of the study. Nature recognizes that not all people who identify as women have this chromosomal make-up.) Double dose Female cells typically have two X chromosomes, one from each parent; male cells usually have one X and one Y. Early in development, one of the two X chromosomes in female cells is inactivated — coated in various proteins and RNA molecules that prevent its genes from being expressed. Which one is ‘silenced’ — meaning which parent it comes from — is random, and the tissues in the body are a mosaic of both types. © 2025 Springer Nature Limited

This Backyard Bird Has a Lot to Teach Us about Sex Variability

By Donna L. Maney It’s springtime in your backyard. You watch a pair of little brown songbirds flit about, their white throats flashing in the sun. One of the birds has striking black and white stripes on its crown and occasionally belts out its song, “Old Sam Peabody, Peabody, Peabody.” Its partner is more drab, with tan and gray stripes on its head and brown streaks through its white throat. Knowing the conventional wisdom about songbirds—that the males are flashy show-offs and the females more camouflaged and quiet—you decide to name the singer with bright plumage Romeo and the subtler one Juliet. But later that day you notice Juliet teed up on the fence, belting out a song. Juliet’s song is even louder and showier than Romeo’s. You wonder, Do female birds sing? Then you see Romeo bringing a twig to the pair’s nest, hidden under a shrub. Your field guide says that in this species the female builds the nest by herself. What is going on? Turns out, when you named Romeo and Juliet, you made the same mistake 19th-century artist and naturalist John Audubon did when, in his watercolor of this species, he labeled the bright member of the pair “male” and the drab one “female.” Romeo might look male, even to a bird expert such as Audubon, but will build a nest and lay eggs in it. Juliet, who might look female, has testes and will defend the pair’s territory by singing both alone and alongside Romeo, who also sings. Juliet and Romeo are White-throated Sparrows (Zonotrichia albicollis). At first glance, members of this species of songbird might look rather ordinary. For example, like many other songbirds, one member of each breeding pair of these sparrows has more striking plumage—that is, its appearance is what we would traditionally consider malelike for songbirds. The other bird in the pair is more femalelike, with drabber plumage. © 2024 SCIENTIFIC AMERICAN

Birds of Paradise Glow on Mating Parade

By Jason Bittel Elaborate poses, tufts of feathers, flamboyant shuffles along an immaculate forest floor — male birds-of-paradise have many ways to woo a potential mate. But now, by examining prepared specimens at the American Museum of Natural History in New York, scientists have discovered what could be yet another tool in the kit of the tropical birds — a visual effect known as photoluminescence. Sometimes called biofluorescence in living things, this phenomenon occurs when an object absorbs high-energy wavelengths of light and re-emits them as lower energy wavelengths. Biofluorescence has already been found in various species of fishes, amphibians and even mammals, from bats to wombats. Interestingly, birds remain woefully understudied when it comes to the optical extras. Until now, no one had looked for the glowing property in birds-of-paradise, which are native to Australia, Indonesia and New Guinea and are famous for their elaborate mating displays. In a study published on Tuesday in the journal Royal Society Open Science, researchers examined prepared specimens housed at the American Museum of Natural History and found evidence of biofluorescence in 37 of 45 birds-of-paradise species. “What they’re doing is taking this UV color, which they can’t see, and re-emitting it at a wavelength that is actually visible to their eyes,” said Rene Martin, the lead author of the study and a biologist at the University of Nebraska-Lincoln. “In their case, it’s kind of a bright green and green-yellow color.” In short, biofluorescence supercharges a bright color to make it even brighter. © 2025 The New York Times Company

Revisiting sex and gender in the brain

By Marija Kundakovic The role of sex and gender in the brain is a popular but controversial research topic. Neuroscience has a reputation for being male-centric and focused on studying male brains, although researchers have recently embraced the idea that it is critical to study female brains as well. Generally speaking, human female and male brains are morphologically similar, but that does not suggest they don’t differ in their activity and function, or in their underlying molecular and cellular mechanisms. In fact, sex and gender bias in neuropsychiatric conditions is the rule rather than the exception. Men are three to five times as likely as women to have autism or attention-deficit/hyperactivity disorder, for example, and women are twice as likely as men to have anxiety or depression disorders. Understanding the biological factors and mechanisms that underlie gender- and sex-related bias in brain function and psychiatric conditions is essential to improve our fundamental knowledge of the brain and to open a path to develop novel, sex-informed treatments. But simply including females in research studies is insufficient to resolve the role of sex and gender in neuroscience. “Sex” and “gender” are both complex and evolving concepts, extending beyond a simple binary. In practice, people are assigned female or male at birth based on external genitalia, although up to 2 percent do not belong to either category because of differences in sex development. Though gender has traditionally been co-assigned with sex—females/women and males/men—the binary nature of sex does not suffice to account for today’s expanding gender landscape. Gender exists on a spectrum, including nonbinary, gender-fluid and agender people. In transgender people, gender identity differs from gender or sex assigned at birth. Some researchers would say that this complexity cannot (and perhaps should not) be tackled by science, and that we should stick to scientifically discernible female-male comparisons, particularly in animal research. But science should not exist in a vacuum; when detached from society, it does not serve its purpose. Indeed, in the case of gender, biology can be falsely used to fuel discriminatory laws and practices against gender-diverse and gender-non-conforming people, supposedly based on a scientific understanding of “biological sex.” © 2025 Simons Foundation

Related chapters from BN: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 29651 - Posted: 02.01.2025

Brain gene expression syncs between bonded prairie voles

By Shaena Montanari Just as romantic partners exhibit more similar brain waves than do strangers when, say, drawing on an Etch A Sketch toy together, animal pairs also show neural synchrony during social interactions and cooperation tasks. “Neural synchrony is something that happens in these minute-to-minute engagements that you have with another individual,” says Zoe Donaldson, associate professor of behavioral neuroscience at the University of Colorado Boulder. But over time, too, pairs in a relationship learn to infer what their partner is going to do, she adds. In prairie voles, at least, that learning process may unfold at the molecular level in the form of “transcriptional synchrony,” according to a preprint Donaldson and her colleagues posted on bioRxiv in November. Prairie voles are socially monogamous, and after two of them bond, gene-expression patterns in their nucleus accumbens—a forebrain region linked to reward and social interaction—start to align. It remains unclear whether this transcriptional synchrony causes pair bonding or only correlates with it, she adds, but in the meantime, it offers researchers a new place to hunt for the basis of these strong social ties. This new study “pushes the limits of what’s possible” technically, says Robert Froemke, professor in New York University’s Neuroscience Institute and otolaryngology department, who was not involved in the study. Though the existence of neural synchrony logically suggests that there may also be shared patterns of gene expression, “it’s still remarkable to actually have it documented,” he says. The new preprint offers the first evidence of transcriptional synchrony in prairie voles, Donaldson says, but a 2020 study revealed that fighting pairs of Betta splendens fish show a strong correlation of gene expression after 60 minutes of fighting, and only a weak correlation after 20 minutes. © 2025 Simons Foundation

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: 29630 - Posted: 01.15.2025

She ain’t scary, she’s my mother

By Tim Vernimmen Few people are fond of earwigs, with their menacing abdominal pincers — whether they’re skittering across your floor, getting comfy in the folds of your camping tent or minding their own business. Scientists, too, have given them short shrift, compared with the seemingly endless attention they have lavished on social insects like ants and bees. Yet there are a handful of exceptions. Some researchers have made conscious career decisions to dig into the hidden, underground world where earwigs reside, and have found the creatures to be surprisingly interesting and social, if still not exactly endearing. Work in the 1990s and early 2000s focused on earwig courtship. These often-intricate performances of attraction and repulsion — in which pincers and antennae play prominent roles — can last hours, and the mating itself as long as 20 hours, at least in one Papua New Guinea species, Tagalina papua. The females usually decide when they’ve had enough, though males of some species use their pincers to restrain the object of their desire. Males of the bone-house earwig Marava arachidis (often found in bone meal plants and slaughterhouses) are particularly coercive, says entomologist Yoshitaka Kamimura of Keio University in Japan, who has studied earwig mating for 25 years. “They bite the female’s antennae and use a little hook on their genitalia to lock them inside her reproductive tract.” Size matters

Related chapters from BN: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 29559 - Posted: 11.16.2024

Did the human kiss begin as an ape grooming ritual?

By Phie Jacobs Whether it’s two newlyweds going in for a smooch after saying “I do” or a parent soothing their child’s scraped knee, kissing is one of humanity’s most recognizable symbols of affection. Clay tablets from ancient Mesopotamia dating to 2500 B.C.E. provide the earliest archaeological evidence of romantic kissing. But the behavior may be older than civilization itself, with some studies suggesting Neanderthals swapped spit with modern humans—and shared each other’s oral microbes—more than 100,000 years ago. Some researchers have suggested kissing evolved from behaviors such as sniffing, nursing babies, or even parents passing chewed-up food to their offspring. But in an article published this month in Evolutionary Anthropology, evolutionary psychologist Adriano Lameira of the University of Warwick offers another hypothesis. Drawing on his knowledge of great ape behavior, Lameira suggests kissing got its start as a fur grooming ritual still observed in modern-day chimpanzees and other great apes. Science sat down with Lameira to learn more about his work. This interview has been edited for length and clarity. Q: What made you want to study kissing? A: It’s a behavior that is charged with so much meaning and symbolism, perhaps the most iconic way of how we show affection on an individual and societal level. I was surprised to find that we know so little about its evolution and nature. In our lab, we’re mostly intrigued by the evolution of language, dance, and imagination. But in the largest sense we’re interested in behaviors and rituals that are evolutionary heirlooms from our apelike ancestors—things our ancestors did that set us on course towards who we are today. Q: Do other animals kiss, or is the behavior unique to humans? © 2024 American Association for the Advancement of Science.

Are you my baby? The clever ways that brood parasites trick other birds

By Sofia Quaglia Parenting can be lots of work for a bird: all that flying back and forth transporting grubs and insects to a nest of demanding young. But some birds manage to forgo caring for their chicks — while still ensuring they’re well looked after. These birds lay their eggs in the nests of other birds that unknowingly adopt the hatchlings, nourishing and protecting them as their own. Only about 1 percent of all bird species resort to this sneaky family planning method, called obligate brood parasitism, but it has evolved at least seven separate times in the history of birds and is a way of life for at least 100 species. Since some brood parasites rely on several different bird species as foster parents, more than a sixth of all species in the avian world care for chicks that aren’t their own at some point. Throughout the millennia, these trespassers have evolved ingenious ways to fool the hosts, and the hosts have developed equally clever ways to protect themselves and their own. At each stage of the nesting cycle, it’s a game of subterfuge that plays out in color, sound and behavior. “There’s always something new — it’s like, ‘Oh, man, this group of birds went down a slightly different pathway,’” says behavioral ecologist Bruce Lyon of the University of California, Santa Cruz, who studies the black-headed duck (Heteronetta atricapilla), the sole obligate parasitic duck species. While many mysteries remain, new research is constantly unearthing just how intense this evolutionary tug-of-war can get.

Pregnancy overhauls the brain. Here’s what that looks like

By Laura Sanders Pregnancy overhauls a woman’s body. The brain is no exception. A detailed study of a woman’s brain before, during and after pregnancy revealed sweeping neural changes, some of which stuck around months after her baby was born. The dataset, published September 16 in Nature Neuroscience, is the first comprehensive view of the neural changes that accompany gestation — a sort of “what to expect when you’re expecting” for the brain. “The results of this case study are astonishing,” says neuroscientist Clare McCormack of New York University Langone Health. “Here we see, for the first time in humans, the extent of brain changes that are under way throughout pregnancy.” This research joins a small number of other studies aimed at understanding the female brain at various stages of life (SN: 9/29/22). Collectively, the work suggests that the process of becoming a mother, called matrescence, is another stage of development, like the brain overhaul that happens in adolescence (SN: 2/27/23). Earlier experiments mostly compared brains of women before and after their pregnancies and inferred what happens in between (SN: 12/19/16). “There was a missing piece,” McCormack says. “The nine months of pregnancy was a black box, and we could only guess what that trajectory looks like.” With four MRI scans before pregnancy, 15 scans during pregnancy and seven scans in the two years after the baby was born, the new study follows the entire arc for one mother. © Society for Science & the Public 2000–2024.

How pregnancy transforms the brain to prepare it for parenthood

By Liam Drew In November 2008, neuroscientist Susana Carmona — then a postdoc studying attention deficit hyperactivity disorder — was driving two colleagues to a party when one of them revealed that she was thinking about having a child. The trio became so engulfed in conversation about how pregnancy might change her brain that they diverted from the party and headed to their laboratory to search the literature. They found numerous studies in rodents, but in humans, “there was basically nothing at all”, says Carmona. Shocked by this gap in research, Carmona and her colleagues convinced their mentor at the Autonomous University of Barcelona, Spain, Oscar Vilarroya, to let them run a study using magnetic resonance imaging (MRI) to measure the neuroanatomy of women before they became pregnant, and then again after they gave birth. Squeezed in alongside their main projects, the investigation took eight years and included dozens of participants. The results, published in 2016, were revelatory1. Two to three months after giving birth, multiple regions of the cerebral cortex were, on average, 2% smaller than before conception. And most of them remained smaller two years later. Although shrinkage might evoke the idea of a deficit, the team showed that the degree of cortical reduction predicted the strength of a mother’s attachment to her infant, and proposed that pregnancy prepares the brain for parenthood. Today, Carmona, now at the Gregorio Marañón Health Research Institute in Madrid, is one of several scientists uncovering how pregnancy and parenthood transform the brain. Elseline Hoekzema, one of Carmona’s passengers that evening in 2008, is another. In 2022, Hoekzema, who is now at the Amsterdam University Medical Centre in the Netherlands, confirmed that the cortical regions that shrink during pregnancy also function differently for at least a year after giving birth2. These studies and others, say researchers, highlight a transformational life event that has long been neglected by neuroscience — one that around 140 million women experience annually.

Related chapters from BN: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases; Chapter 17: Learning and Memory
Related chapters from MM:Chapter 8: Hormones and Sex; Chapter 13: Memory and Learning
Link ID: 29418 - Posted: 08.02.2024

These brain cells help days-old mice to bond with mum

By Miryam Naddaf Researchers have identified neurons in the brains of baby mice that enable them to form a unique, strong bond with their mother in the first few days of life. Stimulating these neurons in mouse pups that had been separated from their mother could mimic the soothing effect of their mother’s presence, and reduced behaviours associated with stress. The findings, published today in Science1, offer fresh clues about the formation of the mother–infant bond in mammals, and could help researchers to better understand how brain development influences behaviour. “We know very little about how the brains of infants make sense of their social world,” says study co-author Marcelo Dietrich, a neurobiologist at Yale University in New Haven, Connecticut. “When I started my lab ten years ago, and I wanted to study this kind of stuff, people said it was delusional. It will fail. It’s too difficult.” Now, “we show that it’s possible: one can do rigorous science and try to understand these mechanisms that are potentially very important for development and health”. “I see these neurons as the ‘I feel good with mommy’ neurons,” says Catharine Dulac, a neuroscientist at the University of Harvard in Cambridge, Massachusetts. “The features that [they] discovered provide some framework to think about humans.” Bonding in the brain Dietrich and his team studied nursing mouse pups that were between 16 and 18 days old. They used live imaging techniques to record activity in the zona incerta (ZI), a thin layer of grey matter located below the thalamus, while the animals interacted with their mother. © 2024 Springer Nature Limited

Related chapters from BN: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 29409 - Posted: 07.27.2024

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