A woman made her AI voice clone say “arse.” Then she got banned.

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Over the past couple of weeks, I’ve been speaking to people who have lost their voices. Both Joyce Esser, who lives in the UK, and Jules Rodriguez, who lives in Miami, Florida, have forms of motor neuron disease—a class of progressive disorders that result in the gradual loss of the ability to move and control muscles.

It’s a crushing diagnosis for everyone involved. Jules’s wife, Maria, told me that once it was official, she and Jules left the doctor’s office gripping each other in floods of tears. Their lives were turned upside down. Four and a half years later, Jules cannot move his limbs, and a tracheostomy has left him unable to speak.

“To say this diagnosis has been devastating is an understatement,” says Joyce, who has bulbar MND—she can still move her limbs but struggles to speak and swallow. “Losing my voice has been a massive deal for me because it’s such a big part of who I am.”

AI is bringing back those lost voices. Both Jules and Joyce have fed an AI tool built by ElevenLabs recordings of their old voices to re-create them. Today, they can “speak” in their old voices by typing sentences into devices, selecting letters by hand or eye gaze. It’s been a remarkable and extremely emotional experience for them—both thought they’d lost their voices for good.

But speaking through a device has limitations. It’s slow, and it doesn’t sound completely natural. And, strangely, users might be limited in what they’re allowed to say.

Joyce doesn’t use her voice clone all that often. She finds it impractical for everyday conversations. But she does like to hear her old voice and will use it on occasion. One such occasion was when she was waiting for her husband, Paul, to get ready to go out.

Joyce typed a message for her voice clone to read out: “Come on, Hunnie, get your arse in gear!!” She then added: “I’d better get my knickers on too!!!”

“The next day I got a warning from ElevenLabs that I was using inappropriate language and not to do it again!!!” Joyce told me via email (we communicated with a combination of email, speech, text-to-voice tools, and a writing board). She wasn’t sure what had been inappropriate, exactly. It’s not as though she’d used any especially vile language—just, as she puts it, “normal British banter between a couple getting ready to go out.”

Joyce assumed that one of the words she’d used had been automatically flagged up by “the prudish American computer,” and that once someone from the ElevenLabs team had assessed the warning, it would be dismissed.

“Well, apparently not, because the next day a human banned me!!!!” says Joyce. She says she felt mortified. “I’d just got my voice back and now they’d taken it away from me … and only two days after I’d done a presentation to my local MND group telling them how amazing ElevenLabs were.”

Joyce contacted ElevenLabs, who apologized and reinstated her account. But it’s still not clear why she was banned in the first place. When I first asked Sophia Noel, a company representative, about the incident, she directed me to the company’s prohibited use policy.

There are rules against threatening child safety, engaging in illegal behavior, providing medical advice, impersonating others, interfering with elections, and more. But there’s nothing specifically about inappropriate language. I asked Noel about this, and she said that Joyce’s remark was most likely interpreted as a threat.

ElevenLabs’ terms of use state that the company does not have any obligation to screen, edit, or monitor content but add that it may “terminate or suspend” access to its services when content is “reasonably likely, in our sole determination, to violate applicable law or [the user] Terms.” ElevenLabs has a moderation tool that “screens content to ensure it aligns with our Terms of Service,” says Dustin Blank, head of partnerships at the company.

The question is: Should companies be screening the language of people with motor neuron disease?

After all, that’s not how other communication devices for people with this condition work. People with MND are usually advised to “bank” their voices as soon as they can—to record set phrases that can be used to create a synthetic voice that sounds a bit like them, albeit a somewhat robotic-sounding version. (Jules recently joked that his sounded like “a Daft Punk song at quarter speed.”)

Banked voices aren’t subject to the same scrutiny, says Joyce’s husband, Paul. “Joyce was told … you can put whatever [language] you want in there,” he says. Voice banking wasn’t an option for Joyce, whose speech had already deteriorated by the time she was diagnosed with MND. Jules did bank his voice but doesn’t tend to use it, because the voice clone sounds so much better. 

Joyce doesn’t hold a grudge—and her experience is far from universal. Jules uses the same technology, but he hasn’t received any warnings about his language—even though a comedy routine he performs using his voice clone contains plenty of curse words, says his wife, Maria. He opened a recent set by yelling “Fuck you guys!” at the audience—his way of ensuring they don’t give him any pity laughs, he joked. That comedy set is even promoted on the ElevenLabs website.

Blank says language like that used by Joyce is no longer restricted. “There is no specific swear ban that I know of,” says Noel. That’s just as well. 

“People living with MND should be able to say whatever is on their mind, even swearing,” says Richard Cave of the MND Association in the UK, who helps people with MND set up their voice clones. “There’s plenty to swear about.”

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You can read more about how voice clones are re-creating the voices of people with motor neuron disease in this story.

Researchers are working to create realistic avatars of people with strokes and amyotrophic lateral sclerosis that can be controlled via a brain implant. Last year, two such individuals were able to use these devices to speak at a rate of around 60 to 70 words per minute—half the rate of typical speech, but more than four times faster than had previously been achieved using a similar approach. 

Other people with ALS who are locked in—completely paralyzed but cognitively able—have used brain implants to communicate, too. A few years ago, a man in Germany used such a device to ask for massages and beer, and to tell his son he loved him. 

Several companies are working on creating hyperrealistic avatars. Don’t call them deepfakes— they prefer to think of them as “synthetic media,” writes my former colleague Melissa Heikkilä, who created her own avatar with the company Synthesia.

ElevenLabs’ tool can be used to create “humanlike speech” in 32 languages. Meta is building a model that can translate over 100 languages into 36 other languages.

From around the web

Covid-19 conspiracy theorists—some of whom believe the virus is an intentionally engineered bioweapon—will soon be heading US agencies. Some federal workers are worried they may be out for revenge against current and former employees. (Wired)

Cats might have spread bird flu to humans—and vice versa. That’s according to data from the US Centers for Disease Control and Prevention, which published the finding but then abruptly removed it. (The New York Times)

And a dairy worker is confirmed to have been infected with a second strain of bird flu that more recently spilled over from birds to cows. The person’s only symptom was conjunctivitis. (Ars Technica)

Health officials in states with abortion bans are claiming that either few or zero abortions are taking place. The claims are “ludicrous,” according to doctors in those states. (KFF Health News)

A judge in the UK has warned women against accepting sperm donations from a man who claims to have fathered more than 180 children in several countries. Robert Charles Albon, who calls himself Joe Donor, has subjected a female couple to a “nightmare” of controlling behavior, the judge said. (The Guardian)

How the tiny microbes in your mouth could be putting your health at risk

This article first appeared in The Checkup, MIT Technology Review’s weekly biotech newsletter. To receive it in your inbox every Thursday, and read articles like this first, sign up here.

This week I’ve been working on a piece about teeth. Well, sort of teeth. Specifically, lab-grown bioengineered teeth. Researchers have created these teeth with a mixture of human and pig tooth cells and grown them in the jaws of living mini pigs.

“We’re working on trying to create functional replacement teeth,” Pamela Yelick of Tufts University, one of the researchers behind the work, told me. The idea is to develop an alternative to titanium dental implants. Replacing lost or damaged teeth with healthy, living, lab-grown ones might be a more appealing option than drilling a piece of metal into a person’s jawbone.

Current dental implants can work well, but they’re not perfect. They don’t attach to bones and gums in the same way that real teeth do. And around 20% of people who get implants end up developing an infection called peri-implantitis, which can lead to bone loss.

It is all down to the microbes that grow on them. There’s a complex community of microbes living in our mouths, and disruptions can lead to infection. But these organisms don’t just affect our mouths; they also seem to be linked to a growing number of disorders that can affect our bodies and brains. If you’re curious, read on.

The oral microbiome, as it is now called, was first discovered in 1670 by Antonie van Leeuwenhoek, a self-taught Dutch microbiologist. “I didn’t clean my teeth for three days and then took the material that had lodged in small amounts on the gums above my front teeth … I found a few living animalcules,” he wrote in a letter to the Royal Society at the time.

Van Leeuwenhoek had used his own homemade microscopes to study the “animalcules” he found in his mouth. Today, we know that these organisms include bacteria, archaea, fungi, and viruses, each of which comes in lots of types. “Everyone’s mouth is home to hundreds of bacterial species,” says Kathryn Kauffman at the University of Buffalo, who studies the oral microbiome.

These organisms interact with each other and with our own immune systems, and researchers are still getting to grips with how the interactions work. Some microbes feed on sugars or fats in our diets, for example, while others seem to feed on our own cells. Depending on what they consume and produce, microbes can alter the environment of the mouth to either promote or inhibit the growth of other microbes.

This complex microbial dance seems to have a really important role in our health. Oral diseases and even oral cancers have been linked to an imbalance in the oral microbiome, which scientists call “dysbiosis.” Tooth decay, for example, has been attributed to an overgrowth of microbes that produce acids that can damage teeth. 

Specific oral microbes are also being linked to an ever-growing list of diseases of the body and brain, including rheumatoid arthritis, metabolic disease, cardiovascular diseases, inflammatory bowel disease, colorectal cancer, and more.

There’s also growing evidence that these oral microbes contribute to neurodegenerative disease. A bacterium called P. gingivalis, which plays a role in the development of chronic periodontitis, has been found in the brains of people with Alzheimer’s disease. And people who are infected with P. gingivalis also experience a decline in their cognitive abilities over a six-month period.

Scientists are still figuring out how oral microbes might travel from the mouth to cause disease elsewhere. In some cases, “you swallow the saliva that contains them … and they can lodge in your heart and other parts of the body,” says Yelick. “They can result in a systemic inflammation that just happens in the background.”

In other cases, the microbes may be hitching a ride in our own immune cells to journey through the bloodstream, as the “Trojan horse hypothesis” posits. There’s some evidence that Fusobacterium nucleatum, a bacterium commonly found in the mouth, does this by hiding in white blood cells. 

There’s a lot to learn about exactly how these tiny microbes are exerting such huge influence over everything from our metabolism and bone health to our neurological function. But in the meantime, the emerging evidence is a good reminder to us all to look after our teeth. At least until lab-grown ones become available.

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You can read more about Yelick’s attempt to grow humanlike teeth in mini pigs here.

The gut microbiome is even more complex than the one in our mouths. Some scientists believe that people in traditional societies have the healthiest collections of gut microbes. But research on the topic has left some of the people in those groups feeling exploited. 

Research suggests our microbiomes change as we age. Scientists are exploring whether maintaining our microbiomes might help us stave off age-related disease.

The makeup of a gut microbiome can be assessed by analyzing fecal samples. This research might be able to reveal what a person has eaten and help provide personalized dietary advice.

There are also communities of microbes living on our skin. Scientists have engineered skin microbes to prevent and treat cancer in mice. Human trials are in the works.

From around the web

Argentina has declared that it will withdraw from the World Health Organization, following a similar move from the US. President Javier Milei has criticized the WHO for its handling of the covid-19 pandemic and called it a “nefarious organization.” (Al Jazeera)

Dairy cows in Nevada have been infected with a form of bird flu different from the one that has been circulating in US dairy herds for months. (The New York Times)

Staff at the US Centers for Disease Control and Prevention have been instructed to withdraw pending journal publications that mention terms including “transgender” and “pregnant people.” But the editors of the British Medical Journal have said they “will not retract published articles on request by an author on the basis that they contained so-called banned words.” “Retraction occurs in circumstances where clear evidence exists of major errors, data fabrication, or falsification that compromise the reliability of the research findings. It is not a matter of author request,” two editors have written. (BMJ)

Al Nowatzki had been chatting to his AI girlfriend, Erin, for months. Then, in late January, Erin told him to kill himself, and provided explicit instructions on how to do so. (MIT Technology Review)

Is our use of the internet and AI tools making us cognitively lazy? “Digital amnesia” might just be a sign of an aging brain. (Nature)

How measuring vaccine hesitancy could help health professionals tackle it

This article first appeared in The Checkup, MIT Technology Review’s weekly biotech newsletter. To receive it in your inbox every Thursday, and read articles like this first, sign up here.

This week, Robert F. Kennedy Jr., President Donald Trump’s pick to lead the US’s health agencies, has been facing questions from senators as part of his confirmation hearing for the role. So far, it’s been a dramatic watch, with plenty of fiery exchanges, screams from audience members, and damaging revelations.

There’s also been a lot of discussion about vaccines. Kennedy has long been a vocal critic of vaccines. He has spread misinformation about the effects of vaccines. He’s petitioned the government to revoke the approval of vaccines. He’s sued pharmaceutical companies that make vaccines. 

Kennedy has his supporters. But not everyone who opts not to vaccinate shares his worldview. There are lots of reasons why people don’t vaccinate themselves or their children.

Understanding those reasons will help us tackle an issue considered to be a huge global health problem today. And plenty of researchers are working on tools to do just that.

Jonathan Kantor is one of them. Kantor, who is jointly affiliated with the University of Pennsylvania in Philadelphia and the University of Oxford in the UK, has been developing a scale to measure and assess “vaccine hesitancy.”

That term is what best captures the diverse thoughts and opinions held by people who don’t get vaccinated, says Kantor. “We used to tend more toward [calling] someone … a vaccine refuser or denier,” he says. But while some people under this umbrella will be stridently opposed to vaccines for various reasons, not all of them will be. Some may be unsure or ambivalent. Some might have specific fears, perhaps about side effects or even about needle injections.

Vaccine hesitancy is shared by “a very heterogeneous group,” says Kantor. That group includes “everyone from those who have a little bit of wariness … and want a little bit more information … to those who are strongly opposed and feel that it is their mission in life to spread the gospel regarding the risks of vaccination.”

To begin understanding where individuals sit on this spectrum and why, Kantor and his colleagues scoured published research on vaccine hesitancy. They sent surveys to 50 people, asking them detailed questions about their feelings on vaccines. The researchers were looking for themes: Which issues kept cropping up?

They found that prominent concerns about vaccines tend to fall into three categories: beliefs, pain, and deliberation. Beliefs might be along the lines of “It is unhealthy for children to be vaccinated as much as they are today.” Concerns around pain center more on the immediate consequences of the vaccination, such as fears about the injection. And deliberation refers to the need some people feel to “do their own research.”

Kantor and his colleagues used their findings to develop a 13-question survey, which they trialed in 500 people from the UK and 500 more from the US. They found that responses to the questionnaire could predict whether someone had been vaccinated against covid-19.

Theirs is not the first vaccine hesitancy scale out there—similar questionnaires have been developed by others, often focusing on parents’ feelings about their children’s vaccinations. But Kantor says this is the first to incorporate the theme of deliberation—a concept that seems to have become more popular during the early days of covid-19 vaccination rollouts.

Nicole Vike at the University of Cincinnati and her colleagues are taking a different approach. They say research has suggested that how people feel about risks and rewards seems to influence whether they get vaccinated (although not necessarily in a simple or direct manner).

Vike’s team surveyed over 4,000 people to better understand this link, asking them information about themselves and how they felt about a series of pictures of sports, nature scenes, cute and aggressive animals, and so on. Using machine learning, they built a model that could predict, from these results, whether a person would be likely to get vaccinated against covid-19.

This survey could be easily distributed to thousands of people and is subtle enough that people taking it might not realize it is gathering information about their vaccine choices, Vike and her colleagues wrote in a paper describing their research. And the information collected could help public health centers understand where there is demand for vaccines, and conversely, where outbreaks of vaccine-preventable diseases might be more likely.

Models like these could be helpful in combating vaccine hesitancy, says Ashlesha Kaushik, vice president of the Iowa Chapter of the American Academy of Pediatrics. The information could enable health agencies to deliver tailored information and support to specific communities that share similar concerns, she says.

Kantor, who is a practicing physician, hopes his questionnaire could offer doctors and other health professionals insight into their patients’ concerns and suggest ways to address them. It isn’t always practical for doctors to sit down with their patients for lengthy, in-depth discussions about the merits and shortfalls of vaccines. But if a patient can spend a few minutes filling out a questionnaire before the appointment, the doctor will have a starting point for steering a respectful and fruitful conversation about the subject.

When it comes to vaccine hesitancy, we need all the insight we can get. Vaccines prevent millions of deaths every year. One and half million children under the age of five die every year from vaccine-preventable diseases, according to the children’s charity UNICEF. In 2019, the World Health Organization included “vaccine hesitancy” on its list of 10 threats to global health.

When vaccination rates drop, we start to see outbreaks of the diseases the vaccines protect against. We’ve seen this a lot recently with measles, which is incredibly infectious. Sixteen measles outbreaks were reported in the US in 2024.

Globally, over 22 million children missed their first dose of the measles vaccine in 2023, and measles cases rose by 20%. Over 107,000 people around the world died from measles that year, according to the US Centers for Disease Control and Prevention. Most of them were children.

Vaccine hesitancy is dangerous. “It’s really creating a threatening environment for these vaccine-preventable diseases to make a comeback,” says Kaushik. 

Kantor agrees: “Anything we can do to help mitigate that, I think, is great.”

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In 2021, my former colleague Tanya Basu wrote a guide to having discussions about vaccines with people who are hesitant. Kindness and nonjudgmentalism will get you far, she wrote.

In December 2020, as covid-19 ran rampant around the world, doctors took to social media platforms like TikTok to allay fears around the vaccine. Sharing their personal experiences was important—but not without risk, A.W. Ohlheiser reported at the time.

Robert F. Kennedy Jr. is currently in the spotlight for his views on vaccines. But he has also spread harmful misinformation about HIV and AIDS, as Anna Merlan reported.

mRNA vaccines have played a vital role in the covid-19 pandemic, and in 2023, the researchers who pioneered the science behind them were awarded a Nobel Prize. Here’s what’s next for mRNA vaccines.

Vaccines are estimated to have averted 154 million deaths in the last 50 years. That number includes 146 million children under the age of five. That’s partly why childhood vaccines are a public health success story.

From around the web

As Robert F. Kennedy Jr.’s Senate hearing continued this week, so did the revelations of his misguided beliefs about health and vaccines. Kennedy, who has called himself “an expert on vaccines,” said in 2021 that “we should not be giving Black people the same vaccine schedule that’s given to whites, because their immune system is better than ours”—a claim that is not supported by evidence. (The Washington Post)

And in past email exchanges with his niece, a primary-care physician at NYC Health + Hospitals in New York City, RFK Jr. made repeated false claims about covid-19 vaccinations and questioned the value of annual flu vaccinations. (STAT)

Towana Looney, who became the third person to receive a gene-edited pig kidney in December, is still healthy and full of energy two months later. The milestone makes Looney the longest-living recipient of a pig organ transplant. “I’m superwoman,” she told the Associated Press. (AP)

The Trump administration’s attempt to freeze trillions of dollars in federal grants, loans, and other financial assistance programs was chaotic. Even a pause in funding for global health programs can be considered a destruction, writes Atul Gawande. (The New Yorker)

How ultraprocessed is the food in your diet? This chart can help rank food items—but won’t tell you all you need to know about how healthy they are. (Scientific American)

The US withdrawal from the WHO will hurt us all

This article first appeared in The Checkup, MIT Technology Review’s weekly biotech newsletter. To receive it in your inbox every Thursday, and read articles like this first, sign up here.

On January 20, his first day in office, US president Donald Trump signed an executive order to withdraw the US from the World Health Organization. “Ooh, that’s a big one,” he said as he was handed the document.

The US is the biggest donor to the WHO, and the loss of this income is likely to have a significant impact on the organization, which develops international health guidelines, investigates disease outbreaks, and acts as an information-sharing hub for member states.

But the US will also lose out. “It’s a very tragic and sad event that could only hurt the United States in the long run,” says William Moss, an epidemiologist at Johns Hopkins Bloomberg School of Public Health in Baltimore.

Trump appears to take issue with the amount the US donates to the WHO. He points out that it makes a much bigger contribution than China, a country with a population four times that of the US. “It seems a little unfair to me,” he said as he prepared to sign the executive order.

It is true that the US is far and away the biggest financial supporter of the WHO. The US contributed $1.28 billion over the two-year period covering 2022 and 2023. By comparison, the second-largest donor, Germany, contributed $856 million in the same period. The US currently contributes 14.5% of the WHO’s total budget.

But it’s not as though the WHO sends a billion-dollar bill to the US. All member states are required to pay membership dues, which are calculated as a percentage of a country’s gross domestic product. For the US, this figure comes to $130 million. China pays $87.6 million. But the vast majority of the US’s contributions to the WHO are made on a voluntary basis—in recent years, the donations have been part of multibillion-dollar spending on global health by the US government. (Separately, the Bill and Melinda Gates Foundation contributed $830 million over 2022 and 2023.)

There’s a possibility that other member nations will increase their donations to help cover the shortfall left by the US’s withdrawal. But it is not clear who will step up—or what implications it will have to change the structure of donations.

Martin McKee, a professor of European public health at the London School of Hygiene and Tropical Medicine, thinks it is unlikely that European members will increase their contributions by much. China, India, Brazil, South Africa, and the Gulf states, on the other hand, may be more likely to pay more. But again, it isn’t clear how this will pan out, or whether any of these countries will expect greater influence over global health policy decisions as a result of increasing their donations.

WHO funds are spent on a range of global health projects—programs to eradicate polio, rapidly respond to health emergencies, improve access to vaccines and medicines, develop pandemic prevention strategies, and more. The loss of US funding is likely to have a significant impact on at least some of these programs.

“Diseases don’t stick to national boundaries, hence this decision is not only concerning for the US, but in fact for every country in the world,” says Pauline Scheelbeek at the London School of Hygiene and Tropical Medicine.“With the US no longer reporting to the WHO nor funding part of this process, the evidence on which public health interventions and solutions should be based is incomplete.”

“It’s going to hurt global health,” adds Moss. “It’s going to come back to bite us.”

There’s more on how the withdrawal could affect health programs, vaccine coverage, and pandemic preparedness in this week’s coverage.

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This isn’t the first time Donald Trump has signaled his desire for the US to leave the WHO. He proposed a withdrawal during his last term, in 2020. While the WHO is not perfect, it needs more power and funding, not less, Charles Kenny, director of technology and development at the Center for Global Development, argued at the time.

The move drew condemnation from those working in public health then, too. The editor in chief of the medical journal The Lancet called it “a crime against humanity,” as Charlotte Jee reported.

In 1974, the WHO launched an ambitious program to get lifesaving vaccines to all children around the world. Fifty years on, vaccines are thought to have averted 154 million deaths—including 146 million in children under the age of five. 

The WHO has also seen huge success in its efforts to eradicate polio. Today, wild forms of the virus have been eradicated in all but two countries. But vaccine-derived forms of the virus can still crop up around the world.

At the end of a round of discussions in September among WHO member states working on a pandemic agreement, director-general Tedros Adhanom Ghebreyesus remarked, “The next pandemic will not wait for us, whether from a flu virus like H5N1, another coronavirus, or another family of viruses we don’t yet know about.” The H5N1 virus has been circulating on US dairy farms for months now, and the US is preparing for potential human outbreaks.

From around the web

People with cancer paid $45,000 for an experimental blood-filtering treatment, delivered at a clinic in Antigua, after being misled about its effectiveness. Six of them have died since their treatments. (The New York Times)

The Trump administration has instructed federal health agencies to pause all external communications, such as health advisories, weekly scientific reports, updates to websites, and social media posts. (The Washington Post)

A new “virtual retina,” modeled on human retinas, has been developed to study the impact of retinal implants. The three-dimensional model simulates over 10,000 neurons. (Brain Stimulation)

Trump has signed an executive order stating that “it is the policy of the United States to recognize two sexes, male and female.” The document “defies decades of research into how human bodies grow and develop,” STAT reports, and represents “a dramatic failure to understand biology,” according to a neuroscientist who studies the development of sex. (STAT)

Attention, summer holiday planners: Biting sandflies in the Mediterranean region are transmitting Toscana virus at an increasing rate. The virus is a major cause of central nervous system disorders in the region. Italy saw a 2.6-fold increase in the number of reported infections between the 2016–21 period and 2022–23. (Eurosurveillance)

Deciding the fate of “leftover” embryos

This article first appeared in The Checkup, MIT Technology Review’s weekly biotech newsletter. To receive it in your inbox every Thursday, and read articles like this first, sign up here.

Over the past few months, I’ve been working on a piece about IVF embryos. The goal of in vitro fertilization is to create babies via a bit of lab work: Trigger the release of lots of eggs, introduce them to sperm in a lab, transfer one of the resulting embryos into a person’s uterus, and cross your fingers for a healthy pregnancy. Sometimes it doesn’t work. But often it does. For the article, I explored what happens to the healthy embryos that are left over.

I spoke to Lisa Holligan, who had IVF in the UK around five years ago. Holligan donated her “genetically abnormal” embryos for scientific research. But she still has one healthy embryo frozen in storage. And she doesn’t know what to do with it.

She’s not the only one struggling with the decision. “Leftover” embryos are kept frozen in storage tanks, where they sit in little straws, invisible to the naked eye, their growth paused in a state of suspended animation. What happens next is down to personal choice—but that choice can be limited by a complex web of laws and ethical and social factors.

These days, responsible IVF clinics will always talk to people about the possibility of having leftover embryos before they begin treatment. Intended parents will sign a form indicating what they would like to happen to those embryos. Typically, that means deciding early on whether they might like any embryos they don’t end up using to be destroyed or donated, either to someone else trying to conceive or for research.

But it can be really difficult to make these decisions before you’ve even started treatment. People seeking fertility treatment will usually have spent a long time trying to get pregnant. They are hoping for healthy embryos, and some can’t imagine having any left over—or how they might feel about them.

For a lot of people, embryos are not just balls of cells. They hold the potential for life, after all. Some people see them as children, waiting to be born. Some even name their embryos, or call them their “freezer babies.” Others see them as the product of a long, exhausting, and expensive IVF journey.

Holligan says that she initially considered donating her embryo to another person, but her husband disagreed. He saw the embryo as their child and said he wouldn’t feel comfortable with giving it up to another family. “I started having these thoughts about a child coming to me when they’re older, saying they’ve had a terrible life, and [asking] ‘Why didn’t you have me?’” she told me.

Holligan lives in the UK, where you can store your embryos for up to 55 years. Destroying or donating them are also options. That’s not the case in other countries. In Italy, for example, embryos cannot be destroyed or donated. Any that are frozen will remain that way forever, unless the law changes at some point.

In the US, regulations vary by state. The patchwork of laws means that one state can bestow a legal status on embryos, giving them the same rights as children, while another might have no legislation in place at all.

No one knows for sure how many embryos are frozen in storage tanks, but the figure is thought to be somewhere between 1 million and 10 million in the US alone. Some of these embryos have been in storage for years or decades. In some cases, the intended parents have deliberately chosen this, opting to pay hundreds of dollars per year in fees.

But in other cases, clinics have lost touch with their clients. Many of these former clients have stopped paying for the storage of their embryos, but without up-to-date consent forms, clinics can be reluctant to destroy them. What if the person comes back and wants to use those embryos after all?

“Most clinics, if they have any hesitation or doubt or question, will err on the side of holding on to those embryos and not discarding them,” says Sigal Klipstein, a reproductive endocrinologist at InVia Fertility Center in Chicago, who also chairs the ethics committee of the American Society for Reproductive Medicine. “Because it’s kind of like a one-way ticket.”

Klipstein thinks one of the reasons why some embryos end up “abandoned” in storage is that the people who created them can’t bring themselves to destroy them. “It’s just very emotionally difficult for someone who has wanted so much to have a family,” she tells me.

Klipstein says she regularly talks to her patients about what to do with leftover embryos. Even people who make the decision with confidence can change their minds, she says. “We’ve all had those patients who have discarded embryos and then come back six months or a year later and said: ‘Oh, I wish I had those embryos,’” she tells me. “Those [embryos may have been] their best chance of pregnancy.”

Those who do want to discard their embryos have options. Often, the embryos will simply be exposed to air and then disposed of. But some clinics will also offer to transfer them at a time or place where a pregnancy is extremely unlikely to result. This “compassionate transfer,” as it is known, might be viewed as a more “natural” way to dispose of the embryo.

But it’s not for everyone. Holligan has experienced multiple miscarriages and wonders if a compassionate transfer might feel similar. She wonders if it might just end up “putting [her] body and mind through unnecessary stress.”

Ultimately, for Holligan and many others in a similar position, the choice remains a difficult one. “These are … very desired embryos,” says Klipstein. “The purpose of going through IVF was to create embryos to make babies. And [when people] have these embryos, and they’ve completed their family plan, they’re in a place they couldn’t have imagined.”

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Our relationship with embryos is unique, and a bit all over the place. That’s partly because we can’t agree on their moral status. Are they more akin to people or property, or something in between? Who should get to decide their fate? While we get to the bottom of these sticky questions, millions of embryos are stuck in suspended animation—some of them indefinitely.

It is estimated that over 12 million babies have been born through IVF. The development of the Nobel Prize–winning technology behind the procedure relied on embryo research. Some worry that donating embryos for research can be onerous—and that valuable embryos are being wasted as a result.

Fertility rates around the world are dropping below the levels needed to maintain stable populations. But IVF can’t save us from a looming fertility crisis. Gender equality and family-friendly policies are much more likely to prove helpful. 

Two years ago, the US Supreme Court overturned Roe v. Wade, a legal decision that protected the right to abortion. Since then, abortion bans have been enacted in multiple states. But in November of last year, some states voted to extend and protect access to abortion, and voters in Missouri supported overturning the state’s ban.

Last year, a ruling by the Alabama Supreme Court that embryos count as children ignited fears over access to fertility treatments in a state that had already banned abortion. The move could also have implications for the development of technologies like artificial uteruses and synthetic embryos, my colleague Antonio Regalado wrote at the time.

From around the web

It’s not just embryos that are frozen as part of fertility treatments. Eggs, sperm, and even ovarian and testicular tissue can be stored too. A man who had immature testicular tissue removed and frozen before undergoing chemotherapy as a child 16 years ago had the tissue reimplanted in a world first, according to the team at University Hospital Brussels that performed the procedure around a month ago. The tissue was placed into the man’s testicle and scrotum, and scientists will wait a year before testing to see if he is successfully producing sperm. (UZ Brussel)

The Danish pharmaceutical company Novo Nordisk makes half the world’s insulin. Now it is better known as the manufacturer of the semaglutide drug Ozempic. How will the sudden shift affect the production and distribution of these medicines around the world? (Wired)

The US has not done enough to prevent the spread of the H5N1 virus in dairy cattle. The response to bird flu is a national embarrassment, argues Katherine J. Wu. (The Atlantic)

Elon Musk has said that if all goes well, millions of people will have brain-computer devices created by his company Neuralink implanted within 10 years. In reality, progress is slower—so far, Musk has said that three people have received the devices. My colleague Antonio Regalado predicts what we can expect from Neuralink in 2025. (MIT Technology Review)