Latest news with #StarreVartan
Yahoo
6 days ago
- Science
- Yahoo
The choice of sperm is 'entirely up to the egg' — so why does the myth of 'racing sperm' persist?
When you buy through links on our articles, Future and its syndication partners may earn a commission. It's a commonly held belief: Sperm cells are like runners in an epic race, competing against each other for access to the coveted egg at the finish line. The egg, in turn, waits patiently for the winning sperm to pierce its outer membrane, triggering fertilization. This narrative of racing sperm and waiting eggs has persisted through time — and yet, it simply isn't accurate. Scientific research has debunked this idea time and time again. In her new book "The Stronger Sex: What Science Tells Us about the Power of the Female Body" (Seal Press/Hachette, 2025), science writer Starre Vartan addresses this and other pervasive myths about the female body, highlighting what science actually tells us about differences in biology between the sexes and where gaps in knowledge still exist, in part, due to a historic lack of research focused on females. Making all your eggs at once, stress-testing and dumping most of them, and having one available at a time for fertilization is a mammalian adaptation. It represents a shift in reproductive strategy, according to Professor Lynnette Sievert, a biological anthropologist at the University of Massachusetts, Amherst. That shift is away from an earlier, or more ancient method of reproduction, which fish, amphibians, and most reptiles still employ today to great success. They both make both eggs and sperm continually, in great quantities, and throughout their lifetimes until they die. Female fish and frogs expel their masses of eggs into the water, and the males shoot, deposit, or generally aim their sperm in the eggs' direction. The eggs that get fertilized then develop — or don't, due to environmental conditions, or get eaten by predators. Sea turtles have sex, but still lay hundreds of fertilized eggs at a time and do so until they are elderly, as do oviparous snakes (viviparous snakes give birth to live young). For all these animals, reproduction is a numbers game. Lots of eggs, lots of sperm, plenty of fertilized eggs and hatchlings, with just a few young surviving to adulthood. In many cases the newly hatched turtles, tadpoles and wee snake-babies are an important food source for other animals who live in their ecosystem, like a biological offering to the greater community. This more-reproductive-stuff-is-better design is still employed by male humans, but not females. Related: Do sperm really race to the egg? "Human males still follow the fish pattern. They're still putting out a million sperm. They're not cleaning the sperm, they're not putting out the best sperm, they're just putting out all the sperm just like a fish," Sievert says. She wonders why then, female mammals made a significant shift away from that model. "Why was there never a selection on male sperm and mammals to be like eggs? Something shifted, that separated the sexes," she says. It's an unanswered biological question, but there is one obvious possible answer: Control. Female mammals house the mechanisms over which eggs (and sperm) are used for reproduction inside their bodies, while amphibians, reptiles, and fish let outside ecological conditions like temperature, predators, salinity and pollutants decide who lives and dies. Both strategies are clearly effective, but why would mammals have shifted away from a successful model? It could be that longer-lived mammals are able to store epigenetic information about local conditions as they grow, which could influence when and which eggs and sperm are chosen. The choices about who lives and who doesn't are made before or during conception, instead of after, resulting in offspring that are best suited to current conditions. Why all this trouble to "turn your body into an eggshell," as Cat Bohannon puts it in her book "Eve: How the Female Body Drove 200 Million Years of Evolution" — when the eggshell, or other reproductive strategies work so well? It could be explained by a combination of energetics and fine-tuning. By bringing fertilization and growing their young inside the female body, mammals can then use their lived experience (not just conditions at the moment of conception) to affect which traits are selected for. They can do this by controlling both which egg and which sperm are preferred. All this energy being used at or before the stage of conception means there are fewer fertilized eggs, and fewer babies. When you only have a baby or two at a time, instead of hundreds, it then becomes logical to invest in ensuring it has the best chances of survival — so an egg battle and a female body that's choosy about sperm makes total sense. As do the years of parenting that follow. That eggs choose sperm is a basic biological fact that has been "discovered" quite a few times over the years. The stubbornness of the "active sperm and waiting egg" story despite the facts highlights how hard it is for humans to accept biological narratives that run counter to our cultural ideas. As Emily Martin detailed in her memorable paper, we know that it was once the narrative that the sperm was the active party in fertilization, with all the speedy, tough sperm out swimming each other and trying to be the first one to attack the egg's outer membrane to gain entry and deposit their DNA packages. Way back in the mid-1980s, it was first discovered that the egg was actually the active decider in fertilization. The egg does this by using its zona pellucida (a thick protein coat that protects the egg cell) to chemically grab onto sperm, test it, and then reject or admit its DNA into the egg. The sperm, wiggling back-and-forth, can't break even a single chemical bond, but the egg can. Research in the 1990s went on to support the idea, and it's widely accepted. Yet, over the last 20 years, scientists continue to "discover" this fact. In 2017, Quanta magazine published an article about a researcher whose work was "challenging this dogma" that "the egg is not the submissive, docile cell that scientists long thought it was" and in 2019, a University of Virginia magazine article stated: "The old notion of the egg as a passive partner for sperm entry is out. Instead, the researchers found, there are molecular players on the surface of the egg that bind with a corresponding substance on the sperm to facilitate the fusion of the two." The writer called this an "unexpected discovery." This "rediscovery" of already known scientific information about the egg and sperm's interaction was covered by a Ms. Magazine article in 2024 about Evelyn Fox Keller, a pioneer in the field of feminist philosophy of science. The passive egg/active sperm idea just wouldn't go away, even in the same journals that published the research that it wasn't true. "One of Fox Keller's key findings was that seemingly neutral assumptions in biology can in fact be gendered. Keller's informed social analysis of the sciences paved the way to approach science as a cultural phenomenon." That researchers and the science press are repeating the same "discoveries" for decades shows just how gendered ideas stick to the culture, and can hold science back. The newest evidence shows that not only does an egg decide which sperm it wants to admit, the egg may be attracting or repelling different sperm even before they make it to the egg. In 2020, scientists at Stockholm University collaborating with colleagues at the University of Manchester found that eggs release a chemical that can attract sperm as it makes its journey. They also found that different eggs attract different varieties of sperm — not all eggs attracted the same sperm. The eggs sometimes attracted sperm that was not their partner's. They figured this out by obtaining reproductive material from couples who gave them permission to at an IVF clinic in Manchester, U.K. "Each experimental block comprised the follicular fluid and sperm samples from a unique set of two couples, exposing sperm from each male to follicular fluid from their partner and a non-partner," the researchers wrote of their methods. RELATED STORIES —1st 'atlas' of human ovaries could lead to fertility breakthrough, scientists say —Sperm don't swim anything like we thought they did, new study finds —Watch 1st-ever video of ovulation occurring in real time Chemosensory communication between eggs and sperm allows "female choice and bias fertilizations toward specific males," the researchers wrote. What are the egg's criteria? It's unknown at this point. It could be selecting higher-quality sperm or sperm that's more genetically compatible in some way. "This shows that interactions between human eggs and sperm depend on the specific identity of the women and men involved," one of the researchers told Labroots. He went on to say that the choice of sperm was entirely up to the egg. The science shows that contrary to some cultural stories, the menstrual cycle is highly sensitive to conserve energy; eggs go to war each month so that only the strongest survive; that winner egg sends out come-hither signals to sperm it likes; and then it chooses which sperm to unite with to make a possible new human being. So much for the inherent weakness of women's bodies and the passive female reproductive system. In interviews with dozens of researchers from biology, anthropology, physiology, and sports science, plus in-depth conversations with runners, swimmers, wrestlers, woodchoppers, thru-hikers, firefighters, and more, "The Stronger Sex" squashes outdated ideas about women's bodies. It's a celebration of female strength that doesn't argue "down with men" but "up with us all."
Time of India
08-07-2025
- Health
- Time of India
From larger chromosomes to bigger intenstines, the reasons why women outlive men
Social media is full of memes showing men doing reckless stunts with captions like, 'This is why women live longer than men.' While entertaining, these memes barely scratch the surface of the real reasons behind the gender longevity gap. According to a new book - 'The Stronger Sex: What Science Tells Us About the Power of the Female Body' of Starre Vartan - the truth is far more scientific—and fascinating. In an article on CNN, Starre citing numerous studies said that women tend to outlive men, even under extreme conditions like famines, epidemics, and slavery. As per Starre, this trend persists across history and geography, suggesting deep-rooted biological advantages. Genetics, hormones, and even the structure of the female body all contribute to this survival edge. by Taboola by Taboola Sponsored Links Sponsored Links Promoted Links Promoted Links You May Like 모발이식 46만원 할인 받는 방법! 500모~1000모 진행가능 지원할인 모발이식 더 알아보기 Undo She cited a 2018 study published in PNAS, which examined data from seven historical populations affected by crises like the Irish Potato Famine, Icelandic measles outbreaks, and slavery in Trinidad. The study found that women consistently lived longer than men—sometimes even as newborns—under brutal conditions. So, what gives women this edge? Live Events The Genetic and Hormonal Advantage A key factor lies in the XX chromosome pairing. Unlike males, who inherit one X and one Y chromosome, females have two Xs. The X chromosome is much larger and carries nearly 10 times more genes, many of which play critical roles in immune function. This genetic surplus provides women with a stronger and more adaptable immune system. Dr. Sharon Moalem, neurogeneticist and author of The Better Half, notes that this double-X setup allows women to 'out-mutate' men immunologically, giving them an edge in the fight against constantly evolving viruses and bacteria. Estrogen, a hormone found in higher levels in women, also plays a role in enhancing immune responses. Stronger Immune Responses Female bodies generally exhibit stronger immune responses—both in the innate system (the first line of defense) and the adaptive system (which targets specific pathogens). Women have higher levels of neutrophils (infection-fighting white blood cells) and more robust B cell activity, allowing them to produce more targeted antibodies and retain immunological memory longer. This makes them better equipped to handle repeat infections and vaccinations. However, this powerful immunity comes at a cost: women are more prone to autoimmune diseases and are more likely to live with chronic illnesses after surviving conditions that could be fatal to men. Testosterone: A Risky Trade-Off On the other hand, testosterone—present in higher levels in males—appears to weaken immune function. Animal studies show that removing testosterone improves immunity, while adding it suppresses it. Evolutionarily, this might be a trade-off: testosterone may boost competitiveness and reproductive success, but it also increases the risk of infections and disease. Lifestyle Factors Also Matter Men, on average, are more likely to engage in high-risk behaviors—smoking, heavy drinking, and dangerous activities—and hold more physically hazardous jobs. However, even in populations where men and women live similar lifestyles, women still tend to outlive men, suggesting biology plays the dominant role. Anatomy Plays a Part, Too Recent research led by microbial ecologist Erin McKenney and anthropologist Amanda Hale at North Carolina State University uncovered another surprising difference: women's small intestines are significantly longer than men's. Published in PeerJ in 2023, the study found this anatomical trait allows women to extract more nutrients from food—a possible evolutionary adaptation to support pregnancy and breastfeeding.
Yahoo
07-07-2025
- Health
- Yahoo
The hidden physical powers that help women outlive men
EDITOR'S NOTE: Starre Vartan is the author of 'The Stronger Sex: What Science Tells Us About the Power of the Female Body,' which will be published on July 15. People who lived through the Irish Potato Famine, enslavement in Trinidad and Icelandic measles epidemics all have something in common: Women outlive men in dire circumstances. That's because the female body is built for resilience and longevity, as I found while researching for my new book, 'The Stronger Sex.' Despite having more complex reproductive organs and the burdensome, sometimes fatal, functions that come with them — menstruation, pregnancy, childbirth and breastfeeding — female bodies tend to outlast male bodies. And that's the case even though girls in many parts of the world have access to fewer resources, such as food and medical care, than boys do. That female toughness holds true in extreme circumstances, as Virginia Zarulli, now an associate professor of demography at Italy's University of Padua, found when she analyzed survival data across seven historical populations experiencing famines, epidemics and enslavement. Under these brutal conditions, women outlived men across almost all ages and locations, including among the 'high-mortality' populations who confronted famine in Ukraine, Ireland and Sweden; enslavement in Trinidad; and measles epidemics in Iceland, according to her 2018 study, published in the journal PNAS. Even newborn girls in these environments had a higher survival rate than newborn boys — a hint that the female survival advantage is rooted in biology. Essential female strength also shows up today in places where women experience fewer extreme physical stresses overall: 'When we analyze the empirical data, for modern people it shows that death rates for men are higher than for women, pretty much at every age,' Zarulli said. Recognizing and building on these sex-based differences can help transform how we approach health care, including treatments for cancer and vaccine protocols — making medicine more precise, personalized and effective, especially for women. People assigned female at birth have two X chromosomes, a fundamental advantage over XY, the chromosomes males have at birth. That's because the X chromosome is much larger, containing roughly 10 times more genes. Female bodies therefore have access to a wider range of immune genes, making their defense system remarkably strong and diverse. As neurogeneticist and evolutionary biologist Dr. Sharon Moalem wrote in 'The Better Half: On the Genetic Superiority of Women,' his book about the XX chromosome advantage, 'Women have immunologically evolved to out-mutate men.' Since viruses and bacteria are always mutating, an immune system that can quickly adapt is more resilient. Estrogen, generally higher in female bodies, also confers a variety of immune advantages. As a result, female mammals — including humans — have better-equipped immune systems, in both their innate, generalized responses and their adaptive, specialized responses. Female bodies also have higher counts of active neutrophils, the most common type of white blood cell that fights infections. Scientists have also found that female bodies have more robust B cell activity — the action of white blood cells that adapt to fight off viruses or bacteria. This advantage may also be due in part to estrogen, and researchers are trying to tease apart what is mediated by hormones, what is affected by genes and what might be attributable to other causes. Women produce more targeted antibodies to fight infections and also retain immunological memory longer, making their bodies more adept at responding to future infections, according to researchers. This all leads to 'the very well-known phenomenon that males tend to be more susceptible to a lot of diseases than females — though not in every disease or every individual, of course,' said Marlene Zuk, a Regents Professor and evolutionary biologist at the University of Minnesota in St. Paul. Since female bodies mount stronger immune defenses, they generally have a stronger vaccine and virus response, a greater ability to fight off sepsis and a decreased risk of some cancers. The downside of this powerful system, however, is that women get more autoimmune diseases than men do. Women are also more likely to live with chronic illness after surviving diseases that would have killed male bodies. Testosterone also seems to be an immune disadvantage, and males have more of that hormone than females do. Zuk said that in early experiments scientists found they could 'neuter male animals and their immunity would get better or inject female animals with testosterone and their immunity would get worse.' Why? It may be that the testosterone enables male animals toward greater reproductive success by 'living hard and dying young,' Zuk said. Some of the female immune advantage may be male immune disadvantage, and while it's accepted that hormones affect immunity, determining to what degree is an ongoing research question. Some scientists argue that lifestyle and culture lead to a significant part of the male longevity disadvantage. As a population, men tend to smoke more, drink more alcohol and engage in riskier activities than women, and men tend to exclude most women from more physically dangerous jobs. Studies focused on what happens when women adopt some of the unhealthy habits traditionally more likely among male populations, such as smoking, still show that women live longer than men, Zarulli said. 'In populations where men and women had the same lifestyle, there was still a difference in mortality — women had a higher life expectancy than men.' The female advantage is likely due to more than genetic and hormonal factors, according to new research: It's also found in the very structure of women's bodies. At North Carolina State University, a team led by microbial ecologist Erin McKenney and forensic anthropologist Amanda Hale conducted a landmark study measuring the lengths of the small intestines in cadavers for the first time since 1885. The team discovered that women's small intestines were significantly longer than men's — an advantage that allows women to extract more nutrition from the same quantity of food. This finding, published in the journal PeerJ in a 2023 paper, might be explained by the extra demands on female bodies throughout human history: 'The vast majority of the nutrients you need to replenish your system — especially during reproduction and nursing, like protein and fat — that's what's being absorbed by your small intestine,' Hale said. This could be a key piece of the 'Female Buffering Hypothesis' — the idea that female biology evolved to withstand environmental and physiological stress better — according to Hale. Traditional medical research has long ignored the complexities of the female body. As these genomic and physiological functions are better studied and understood, the drivers behind the strength and resilience of the female body will come into focus. This knowledge will inform more targeted treatments for infection and immunity—for all bodies. Get inspired by a weekly roundup on living well, made simple. Sign up for CNN's Life, But Better newsletter for information and tools designed to improve your well-being.
CNN
07-07-2025
- Health
- CNN
The hidden physical powers that help women outlive men
EDITOR'S NOTE: Starre Vartan is the author of 'The Stronger Sex: What Science Tells Us About the Power of the Female Body,' which will be published on July 15. People who lived through the Irish Potato Famine, enslavement in Trinidad and Icelandic measles epidemics all have something in common: Women outlive men in dire circumstances. That's because the female body is built for resilience and longevity, as I found while researching for my new book, 'The Stronger Sex.' Despite having more complex reproductive organs and the burdensome, sometimes fatal, functions that come with them — menstruation, pregnancy, childbirth and breastfeeding — female bodies tend to outlast male bodies. And that's the case even though girls in many parts of the world have access to fewer resources, such as food and medical care, than boys do. That female toughness holds true in extreme circumstances, as Virginia Zarulli, now an associate professor of demography at Italy's University of Padua, found when she analyzed survival data across seven historical populations experiencing famines, epidemics and enslavement. Under these brutal conditions, women outlived men across almost all ages and locations, including among the 'high-mortality' populations who confronted famine in Ukraine, Ireland and Sweden; enslavement in Trinidad; and measles epidemics in Iceland, according to her 2018 study, published in the journal PNAS. Even newborn girls in these environments had a higher survival rate than newborn boys — a hint that the female survival advantage is rooted in biology. Essential female strength also shows up today in places where women experience fewer extreme physical stresses overall: 'When we analyze the empirical data, for modern people it shows that death rates for men are higher than for women, pretty much at every age,' Zarulli said. Recognizing and building on these sex-based differences can help transform how we approach health care, including treatments for cancer and vaccine protocols — making medicine more precise, personalized and effective, especially for women. People assigned female at birth have two X chromosomes, a fundamental advantage over XY, the chromosomes males have at birth. That's because the X chromosome is much larger, containing roughly 10 times more genes. Female bodies therefore have access to a wider range of immune genes, making their defense system remarkably strong and diverse. As neurogeneticist and evolutionary biologist Dr. Sharon Moalem wrote in 'The Better Half: On the Genetic Superiority of Women,' his book about the XX chromosome advantage, 'Women have immunologically evolved to out-mutate men.' Since viruses and bacteria are always mutating, an immune system that can quickly adapt is more resilient. Estrogen, generally higher in female bodies, also confers a variety of immune advantages. As a result, female mammals — including humans — have better-equipped immune systems, in both their innate, generalized responses and their adaptive, specialized responses. Female bodies also have higher counts of active neutrophils, the most common type of white blood cell that fights infections. Scientists have also found that female bodies have more robust B cell activity — the action of white blood cells that adapt to fight off viruses or bacteria. This advantage may also be due in part to estrogen, and researchers are trying to tease apart what is mediated by hormones, what is affected by genes and what might be attributable to other causes. Women produce more targeted antibodies to fight infections and also retain immunological memory longer, making their bodies more adept at responding to future infections, according to researchers. This all leads to 'the very well-known phenomenon that males tend to be more susceptible to a lot of diseases than females — though not in every disease or every individual, of course,' said Marlene Zuk, a Regents Professor and evolutionary biologist at the University of Minnesota in St. Paul. Since female bodies mount stronger immune defenses, they generally have a stronger vaccine and virus response, a greater ability to fight off sepsis and a decreased risk of some cancers. The downside of this powerful system, however, is that women get more autoimmune diseases than men do. Women are also more likely to live with chronic illness after surviving diseases that would have killed male bodies. Testosterone also seems to be an immune disadvantage, and males have more of that hormone than females do. Zuk said that in early experiments scientists found they could 'neuter male animals and their immunity would get better or inject female animals with testosterone and their immunity would get worse.' Why? It may be that the testosterone enables male animals toward greater reproductive success by 'living hard and dying young,' Zuk said. Some of the female immune advantage may be male immune disadvantage, and while it's accepted that hormones affect immunity, determining to what degree is an ongoing research question. Some scientists argue that lifestyle and culture lead to a significant part of the male longevity disadvantage. As a population, men tend to smoke more, drink more alcohol and engage in riskier activities than women, and men tend to exclude most women from more physically dangerous jobs. Studies focused on what happens when women adopt some of the unhealthy habits traditionally more likely among male populations, such as smoking, still show that women live longer than men, Zarulli said. 'In populations where men and women had the same lifestyle, there was still a difference in mortality — women had a higher life expectancy than men.' The female advantage is likely due to more than genetic and hormonal factors, according to new research: It's also found in the very structure of women's bodies. At North Carolina State University, a team led by microbial ecologist Erin McKenney and forensic anthropologist Amanda Hale conducted a landmark study measuring the lengths of the small intestines in cadavers for the first time since 1885. The team discovered that women's small intestines were significantly longer than men's — an advantage that allows women to extract more nutrition from the same quantity of food. This finding, published in the journal PeerJ in a 2023 paper, might be explained by the extra demands on female bodies throughout human history: 'The vast majority of the nutrients you need to replenish your system — especially during reproduction and nursing, like protein and fat — that's what's being absorbed by your small intestine,' Hale said. This could be a key piece of the 'Female Buffering Hypothesis' — the idea that female biology evolved to withstand environmental and physiological stress better — according to Hale. Traditional medical research has long ignored the complexities of the female body. As these genomic and physiological functions are better studied and understood, the drivers behind the strength and resilience of the female body will come into focus. This knowledge will inform more targeted treatments for infection and immunity—for all bodies. Get inspired by a weekly roundup on living well, made simple. Sign up for CNN's Life, But Better newsletter for information and tools designed to improve your well-being.
