The Aedes aegypti mosquito, which can carry devastating diseases, was recently engineered by a biotech company to have a genetic "kill switch" intended to crash the local population in the Florida Keys.
Decades of efforts to eradicate the disease-carrying Aedes aegypti mosquito from the Keys and other tropical locales have had limited impact. Since the advent of pesticides, homes and neighborhoods have been drenched with them, but after each spraying, the mosquito population quickly bounces back, and the pesticides have to be sprayed over and over. But thanks to genetic engineering, new approaches are underway that could possibly prove safer, cheaper and more effective than any pesticide.
One of those approaches involves, ironically, releasing more mosquitoes in the Florida Keys.
The kill-switch will ensure that the female offspring die before they reach maturity and thus, be unable to reproduce.
British biotech company Oxitec has engineered male mosquitoes to have a genetic "kill-switch" that could potentially crash the local population of Aedes aegypti, at least in the short-term. The modified males that are being released are intended to mate with wild females.
Males don't bite; it's the female that's deadly, always seeking out blood to gorge on to help mature her eggs. After settling her filament-thin legs on her prey, she sinks a needlelike proboscis into the skin and sucks the blood until her translucent belly is bloated and glowing red.
The kill-switch will ensure that the female offspring die before they reach maturity and thus, be unable to reproduce. In some experiments using genetically modified mosquitoes, the small number of females that survived were rendered unable to bite. The modification prevented the proboscis, the sickle-like needle that pierces the skin, from forming properly. But this isn't the case with Oxitec's mosquitoes; in the Oxitec release, the females simply die off before they can mate.
The modified mosquitoes are the second genetically engineered insect to be released in the U.S. by Oxitec. The first was a modified diamondback moth, an agricultural pest that doesn't bite humans. But with the mosquitoes, there are many questions about the long-term effects on wild ecosystems, other species in the food chain, and human health. With the Keys initiative, there has been vociferous opposition from environmental groups and some local residents, but some scientists and public health experts say that genetically modified insects pose less of a risk than the diseases they carry and the powerful, indiscriminant pesticides used to combat them.
Oxitec spent a decade developing the technology and engaging in a massive public education campaign before beginning the field test in April. Eventually, the company will release 750,000 of the insects from six locations on three islands of the Florida Keys. Although the release has been approved by the Environmental Protection Agency, the Florida Department of Agriculture and Consumer Services, and the Florida Keys Mosquito Control District, the company was never able to obtain unanimous approval among local residents, some of whom worry that the experiment could cause irreversible damage to the ecosystem.
The company has already begun distributing multiple blue and white boxes containing the eggs of thousands of the mosquitoes which, when water is added, will hatch legions of modified males.
There are a number of techniques available to genetically engineer animals and plants to minimize disease and maximize crop yields. According to Kevin Gorman, chief development officer for Oxitec, the company's mosquitoes were altered by injecting genetic material into the eggs, testing them, then re-injecting them if not enough of the new genes were incorporated into the developing embryos. "We insert genes, but take nothing away," he says.
Gorman points out that the Oxitec mosquitoes will only pass the kill-switch genes on to some of their offspring, and that they will die out fairly quickly. They should temporarily lessen diseases by reducing the local population of Aedes aegypti, but to have a long-term effect, repeated introductions of the altered mosquitoes would have to take place.
Critics say the Oxitec experiment is a precursor to a far more consequential, and more troubling development: the introduction of gene drives in modified species that aggressively tilt inheritance factors in a decided direction.
Gene Drives
Gene drives coupled with the recent development of the gene-editing technique, CRISPR-Cas9, promise to be far more targeted and powerful than previous gene altering efforts. Gene drives override the normal laws of inheritance by harnessing natural processes involved in reproduction. The technique targets small sections of the animal's DNA and replaces it with an altered allele, or trait-determining snippet. Normally, when two members of a species mate, the offspring have a 50 percent chance of receiving an allele because they will receive one from each parent. But in a gene drive, each offspring ends up getting two copies of a desired allele from a single parent—the modified parent. The method "drives" the modified DNA into up to 100 percent of the animals' offspring.
In the case of gene drive mosquitoes, the modified males will mate with wild females. Upon fertilization of the egg, the offspring will start off with one copy of the targeted allele from each parent. But an enzyme, called Cas9, is introduced and acts as a kind of molecular scissors to cut, or damage, the "wild" allele. Then the developing embryo's genetic repair mechanisms kick in and, to repair the damage, copy the undamaged allele from the modified parent. In this way, the offspring ends up with two copies of the modified allele, and it will pass the modification on to virtually all of its progeny.
There is some debate among researchers and others about what constitutes a gene drive, but leaders in the nascent field, such as Andrea Crisanti, generally agree that the defining factor is the heritability of a change introduced into a species. A gene drive is not a particular gene or suite of genes, but a program that proliferates in a species because it is inherited by virtually all offspring.
An illustration of how gene drives spread an altered gene through a population.
Mariuswalter, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Of the experts who spoke with Leaps.org for this article, there was disagreement on whether the Oxitec mosquitoes carry a gene drive, but Gorman says they don't because they carry no inheritance advantage. The mosquitoes have baked-in limitations on their potential impact on the tropical ecosystem because the kill-switch should only temporarily affect the local population of Aedes aegypti. The modified mosquitoes will die pretty quickly. But modified organisms that do carry gene drives have the potential to spread widely and persist for an unknown period of time.
Since it has such a reproductive advantage, animals modified by CRISPR and carrying gene drives can quickly replace wild species that compete with them. On the other hand, if the gene drive carries a kill-switch, it can theoretically cause a whole species to collapse.
This makes many people uneasy in an age of mass extinctions, when animals and ecosystems are already under extreme stress due to climate change and the ceaseless destruction of their habitats. Ecosystems are intricate, delicately balanced mosaics where one animal's competitor is another animal's food. The interconnectedness of nature is only partially understood and still contains many mysteries as to what effects human intervention could eventually cause.
But there's a compelling case to be made for the use of gene drives in general. Economies throughout the world are often based on the ecosystem and its animals, which rely on a natural food chain that was evolved over billions of years. But diseases carried by mosquitoes and other animals cause massive damage, both economically and in terms of human suffering.
Malaria alone is a case in point. In 2019, the World Health Organization reported 229 million cases of malaria, which led to 449,000 deaths worldwide. Over 70 percent of those deaths were in children under the age of 12. Efforts to combat malaria-carrying mosquitoes rely on fogging the home with chemical pesticides and sleeping under pesticide-soaked nets, and while this has reduced the occurrence of malaria in recent years, the result is nowhere near as effective as eradicating the Anopheles gambiae mosquito that carries the disease.
Pesticides, a known carcinogen for animals and humans, are a blunt instrument, says Anthony Shelton, a biologist and entomologist at Cornell University. "There are no pesticides so specific that they just get the animal you want to target. They get pollinators. They get predators and parasites. They negatively affect the ecosystem, and they get into our bodies." And it's not uncommon for insects to develop resistance to pesticides, necessitating the continuous development of new, more powerful chemicals to control them.
"The harm of insecticides is not debatable," says Shelton. With gene drives, the potential harm is less clear.
Shelton also points out that although genetic modification sounds radical, people have been altering the genes of animals since before recorded history, through the selective breeding of farm and domesticated animals. While critics of genetic modification decry the possibility of changing the trajectory of evolution in animals, "We've been doing it for centuries," says Shelton. "Gene drives are just a much faster way to do what we've been doing all along."
Still, one might argue that farms are closed experiments, because animals enclosed within farms don't mate with wild animals. This limits the impact of human changes on the larger ecosystem. And getting new genes to work their way through multiple generations in longer-lived animals through breeding can take centuries, which imposes the element of time to ascertain the relative benefits of any introduced change. Gene drives fast-forward change in ways that have never been harnessed before.
The unique thing about gene drives, Shelton says, is that they only affect the targeted species, because those animals will only breed with their own species. Although the Oxitec mosquitoes are modified but not imbued with a gene drive, they illustrate the point. Aedes aegypti will only mate with its own species, and not with any of the other 3,000 varieties of mosquito. According to Shelton, "If they were to disappear, it would have no effect on the fish, bats and birds that feed on them." But should gene drives become widely used, this won't always be true of animals that play a larger part in the food chain. This will be especially true if gene drives are used in mammals.
One factor, cited by both proponents of gene drives and those who want a complete moratorium on them, is that once a gene drive is released into the wild, animals tend to evolve strategies to resist them. In a 2017 article in Nature, Philip Messer, a population geneticist at Cornell, says that gene drives create "the ideal conditions for resistant organisms to flourish."
Sometimes, when CRISPR is used and the Cas9 enzyme cuts an allele soon after egg fertilization, the animal's repair mechanism, rather than creating a straight copy of the desired allele, inserts random DNA letters. The gene drive won't recognize the new sequence, and the change will slip through. In this way, nature has a way of overriding gene drives.
In caged experiments using CRISPR-modified mosquitoes, while the gene drive initially worked, resistance has developed fairly rapidly. Scientists working for Target Malaria, the massive anti-malaria enterprise funded by the Bill and Melinda Gates Foundation, are now working on developing a new version of a gene drive that is not so vulnerable to genetic resistance. But cage conditions are not representative of complex natural ecosystems, and to figure out how a modified species is going to affect the big picture, ultimately they will have to be tested in the wild.
Because there are so many unknowns, such testing is just too dangerous to undertake, according to environmentalists such as Dana Perls of the Friends of the Earth, an international consortium of environmental organizations headquartered in Amsterdam. "There's no safe way to experiment in the wild," she says. "Extinction is permanent, and to drive any species to extinction could have major environmental problems. At a time when we're seeing species disappearing at a high rate, we need to focus on safe processes and a slow approach rather than assume there's a silver bullet."
She cites a number of possible harmful outcomes from genetic modification, including the possible creation of dangerous hybrids that could be more effective at spreading disease and more resistant to pesticides. She points to a 2019 paper in Scientific Reports in which Yale researchers suggested there's evidence that genetically modified species can interbreed with organisms outside their own species. The researchers claimed that when Oxitec tested its modified Aedes aegypti mosquitoes in Brazil, the release resulted in a dangerous hybrid due to the altered animals breeding with two other varieties of mosquito. They suggested that the hybrid mosquito was more robust than the original gene drive mosquitoes.
The paper contributed to breathless headlines in the media and made a big splash with the anti-GMO community. However, it turned out that when other scientists reviewed the data, they found it didn't support the authors' claims. In a short time, the editors of Nature ran an Editorial Expression of Concern for the article, noting that of the insects examined by the researchers, none of them contained the transgenes of the released mosquitoes. Among multiple concerns, Nature found that the researchers didn't follow the released population for more than a short time, and that previous work from the same authors had shown that after a short time, transgenes would have faded from the population.
Of course, unintended consequences are always a concern any time we interfere with nature, says Michael Montague, a senior scholar at Johns Hopkins University's Center for Health Security. "Unpredictability is part of living in the world," he says. Still, he's relatively comfortable with the limited Florida Keys release.
"Even if one type of mosquito was eliminated in the Keys, the ecosystem wouldn't notice," he says. This is because of the thousands of other species of mosquito. He says that while the Keys initiative is ultimately a test, "Oxitec has done their due diligence."
Montague addressed another concern voiced by Perls. The Oxitec mosquitoes were developed so that the female larvae will only hatch in water containing the antibiotic tetracycline. Perls and others caution that, because of the widespread use of antibiotics, the drug inevitably makes its way into the water system, and could be present in the standing pools of water that mosquitoes mate and lay their eggs in.
It's highly unlikely that tetracycline would exist in concentrations high enough to make any difference, says Montague. "But even if it did happen, and the modified females hatched out and mated with wild males, many of their offspring would inherit the modification and only be able to hatch in tetracycline-laced water. The worst-case scenario would be that the pest control didn't work. Net effect: Zero," he says.
As for comparing GMO mosquitoes with insecticides, Montague says, "We 100 percent know insecticides have a harmful effect on human health, whereas modified [male] mosquitoes don't bite humans. They're essentially a chemical-free insecticide, and if there were to be some harmful effect on human health, it would have to be some complicated, convoluted effect" that no one has predicted.
It's not clear, though, given the transitory nature of self-limiting genetically modified insects, whether any effects on the ecosystem would be long-lasting. Certainly in the case of the Oxitec mosquitoes, any effect on the environment would likely be subtle. However, there are other species that are far more important to the food chain, and humans have been greatly impacting them for centuries, sometimes with disastrous effects.
The world's oceans are particularly vulnerable to the effects of human actions. "Codfish used to dominate the North Atlantic ecosystem," says Montague, but due to overfishing, there were huge changes to that ecosystem, including the expansion of their prey—lobsters, crabs and shrimp. The whole system got out of balance." The fish illustrate the international nature of the issues related to gene drives, because wild species have few boundaries and a change in one region can easily spread far and wide.
On the other hand, gene drives can be used for beneficial purposes beyond eliminating disease-carrying species. They could also be used to combat invasive species, fight crop-destroying insects, promote biodiversity, and give a leg up to endangered species that would otherwise die out.
Today nearly 90 percent of the world's islands have been invaded by disease-carrying rodents that have over-multiplied and are driving other island species to extinction. Common rodents such as rats and mice normally encounter a large number of predators in mainland territories, and this controls their numbers. Once they are introduced into island ecosystems, however, they have few predators and often become invasive. Because of this, they are a prevalent cause of the extinction of both animals and plants globally. The primary way to combat them has been to spread powerful toxicants that, when ingested, cause death. Not only has this inhumane practice had limited impact, the toxicants can be eaten by untargeted species and are toxic to humans.
The Genetic Biocontrol of Invasive Rodents program (GBIRd), an international consortium of scientists, ethicists, regulatory experts, sociologists, conservationists and others, is exploring the possible development of a genetically modified mouse that could be introduced to islands where rodents are invasive. Similar to the Oxitec mosquitoes, the mice would carry a modification that results in the appearance of only one sex, and they would also carry a gene drive. Theoretically, once they mate with the wild mice, all of the surviving offspring would be either male or female, and the species would disappear from the islands, giving other, threatened species an opportunity to revive.
GBIRd is moving slowly by design and is currently focused on asking if a genetically engineered mouse should be developed. The program is a potential model for how gene drives can be ethically developed with maximum foresight and the least impact on complex ecosystems. By first releasing a genetically engineered mouse on an island — likely years from now — the impact would naturally be contained within a limited locale.
Regulating GM Insects
While multiple agencies in the U.S. were involved in approving the release of the Oxitec mosquitoes, most experts agree that there is not a straightforward path to regulating genetically modified organisms released into the environment. Clearly, international regulation is needed as genetically modified organisms are released into open environments like the air and the ocean.
The United Nations' Convention on Biological Diversity, which oversees environmental issues at an international level, recently met to continue a process of hammering out voluntary protocols concerning gene drives. Multiple nations have already signed on to already-established protocols, but the United States has not and, according to Montague, is not expected to. "The U.S. will never be signatory to CBD agreements because agricultural companies are huge businesses" that may not see them as in their best interests, he says. Bans or limitations on the release of genetically modified organisms could limit crop yields, for example, thereby limiting profits.
Even if every nation signed on to international regulations of gene drives, cooperation is voluntary. The regulations wouldn't prevent bad actors from using the technology in nefarious ways, such as developing gene drives that can be used as weapons, according to Perls. An example would be unleashing a genetically modified invasive insect to destroy the crops of enemy nations. Or the releasing of a swarm of disease-carrying insects. But in this scenario, it would be very hard to limit the genetically modified species to a specific environment, and the bad actors could be unleashing disaster on themselves.
Because of the risks of misuse, scientists disagree on whether to openly share their gene drive research with others. But Montague believes that there should be a universal registry of gene drives, because "one gene drive can mess up another one. Two groups using the same species should know about each other," he says.
Ultimately, the decision of whether and when to release gene drives into nature rests with not one group, but with society as a whole. This includes not only diverse experts and regulatory bodies, but the general public, a group Oxitec spent considerable time and resources interacting with for their Florida Keys project. In the end, they gained approval for the initiative by a majority of Keys residents, but never gained a total consensus.
There's no escaping the fact that the use of gene drives is a nascent field, and even geneticists and regulators are still grapping with the best ways to develop, oversee, regulate, and control them. Much more data is needed to fully ascertain its risks and benefits.
Experts agree that the Oxitec venture isn't likely to have a noticeable effect on the larger ecosystem unless something truly catastrophic goes wrong. But following the GMO mosquitoes over time will give scientists more real-world data about the long-term effects of genetically altered species. If the release doesn't work, nothing about the ecosystem will change and Aedes aegypti will continue to be a menace to human health. But if something goes horribly wrong, it could hinder the field for years, if not forever.
On the other hand, if the Oxitec mosquitoes and other early initiatives achieve their goals of reducing disease, increasing crop yields, and protecting biodiversity, in the words of Anthony Shelton, "Maybe, 25 to 50 years from now, people will wonder what all the fuss was about."
Correction: The original version of this article mistakenly stated that the modified Oxitec mosquitoes would not be able to form a proper proboscis to bite humans. That is true for some modified mosquitoes but not the Oxitec ones, whose female offspring die off before they reach maturity. Additionally, the Oxitec release was not approved by the FDA and CDC, as originally stated. The FDA and CDC withdrew their role and passed the oversight to other regulatory entities.
Some researchers argue that active, playful engagement with a "robot nanny" for a few hours a day is better than several hours in front of a TV or with an iPad.
A 2017 study led by Google executive James Manyika suggested that skills like creativity, emotional intelligence, and communication will always be needed in the classroom and that robots aren’t likely to provide them at the same level that humans naturally do. But robot teachers do bring advantages, such as a depth of subject knowledge that teachers can’t match, and they’re great for student engagement.
The teacher and robot can complement each other in new ways, with the teacher facilitating interactions between robots and students. So far, this is the case with teaching “assistants” being adopted now in China, Japan, the U.S., and Europe. In this scenario, the robot (usually the SoftBank child-size robot NAO) is a tool for teaching mainly science, technology, engineering, and math (the STEM subjects), but the teacher is very involved in planning, overseeing, and evaluating progress. The students get an entertaining and enriched learning experience, and some of the teaching load is taken off the teacher. At least, that’s what researchers have been able to observe so far.
To be sure, there are some powerful arguments for having robots in the classroom. A not-to-be-underestimated one is that robots “speak the language” of today’s children, who have been steeped in technology since birth. These children are adept at navigating a media-rich environment that is highly visual and interactive. They are plugged into the Internet 24-7. They consume music, games, and huge numbers of videos on a weekly basis. They expect to be dazzled because they are used to being dazzled by more and more spectacular displays of digital artistry. Education has to compete with social media and the entertainment vehicles of students’ everyday lives.
Another compelling argument for teaching robots is that they help prepare students for the technological realities they will encounter in the real world when robots will be ubiquitous. From childhood on, they will be interacting and collaborating with robots in every sphere of their lives from the jobs they do to dealing with retail robots and helper robots in the home. Including robots in the classroom is one way of making sure that children of all socioeconomic backgrounds will be better prepared for a highly automated age, when successfully using robots will be as essential as reading and writing. We’ve already crossed this threshold with computers and smartphones.
Students need multimedia entertainment with their teaching. This is something robots can provide through their ability to connect to the Internet and act as a centralized host to videos, music, and games. Children also need interaction, something robots can deliver up to a point, but which humans can surpass. The education of a child is not just intended to make them technologically functional in a wired world, it’s to help them grow in intellectual, creative, social, and emotional ways. When considered through this perspective, it opens the door to questions concerning just how far robots should go. Robots don’t just teach and engage children; they’re designed to tug at their heartstrings.
It’s no coincidence that many toy makers and manufacturers are designing cute robots that look and behave like real children or animals, says Turkle. “When they make eye contact and gesture toward us, they predispose us to view them as thinking and caring,” she has written in The Washington Post. “They are designed to be cute, to provide a nurturing response” from the child. As mentioned previously, this nurturing experience is a powerful vehicle for drawing children in and promoting strong attachment. But should children really love their robots?
ROBOTS AND THE PEOPLE WHO LOVE THEM: Holding on to Our Humanity in an Age of Social Robots by Eve Herold (January 9, 2024).
St. Martin’s Publishing Group
The problem, once again, is that a child can be lulled into thinking that she’s in an actual relationship, when a robot can’t possibly love her back. If adults have these vulnerabilities, what might such asymmetrical relationships do to the emotional development of a small child? Turkle notes that while we tend to ascribe a mind and emotions to a socially interactive robot, “simulated thinking may be thinking, but simulated feeling is never feeling, and simulated love is never love.”
Always a consideration is the fact that in the first few years of life, a child’s brain is undergoing rapid growth and development that will form the foundation of their lifelong emotional health. These formative experiences are literally shaping the child’s brain, their expectations, and their view of the world and their place in it. In Alone Together, Turkle asks: What are we saying to children about their importance to us when we’re willing to outsource their care to a robot? A child might be superficially entertained by the robot while his self-esteem is systematically undermined.
Research has emerged showing that there are clear downsides to child-robot relationships.
Still, in the case of robot nannies in the home, is active, playful engagement with a robot for a few hours a day any more harmful than several hours in front of a TV or with an iPad? Some, like Xiong, regard interacting with a robot as better than mere passive entertainment. iPal’s manufacturers say that their robot can’t replace parents or teachers and is best used by three- to eight-year-olds after school, while they wait for their parents to get off work. But as robots become ever-more sophisticated, they’re expected to perform more of the tasks of day-to-day care and to be much more emotionally advanced. There is no question children will form deep attachments to some of them. And research has emerged showing that there are clear downsides to child-robot relationships.
Some studies, performed by Turkle and fellow MIT colleague Cynthia Breazeal, have revealed a darker side to the child-robot bond. Turkle has reported extensively on these studies in The Washington Post and in her book Alone Together. Most children love robots, but some act out their inner bully on the hapless machines, hitting and kicking them and otherwise trying to hurt them. The trouble is that the robot can’t fight back, teaching children that they can bully and abuse without consequences. As in any other robot relationship, such harmful behavior could carry over into the child’s human relationships.
And, ironically, it turns out that communicative machines don’t actually teach kids good communication skills. It’s well known that parent-child communication in the first three years of life sets the stage for a very young child’s intellectual and academic success. Verbal back-and-forth with parents and care-givers is like fuel for a child’s growing brain. One article that examined several types of play and their effect on children’s communication skills, published in JAMA Pediatrics in 2015, showed that babies who played with electronic toys—like the popular robot dog Aibo—show a decrease in both the quantity and quality of their language skills.
Anna V. Sosa of the Child Speech and Language Lab at Northern Arizona University studied twenty-six ten- to sixteen- month-old infants to compare the growth of their language skills after they played with three types of toys: electronic toys like a baby laptop and talking farm; traditional toys like wooden puzzles and building blocks; and books read aloud by their parents. The play that produced the most growth in verbal ability was having books read to them by a caregiver, followed by play with traditional toys. Language gains after playing with electronic toys came dead last. This form of play involved the least use of adult words, the least conversational turntaking, and the least verbalizations from the children. While the study sample was small, it’s not hard to extrapolate that no electronic toy or even more abled robot could supply the intimate responsiveness of a parent reading stories to a child, explaining new words, answering the child’s questions, and modeling the kind of back- and-forth interaction that promotes empathy and reciprocity in relationships.
***
Most experts acknowledge that robots can be valuable educational tools. But they can’t make a child feel truly loved, validated, and valued. That’s the job of parents, and when parents abdicate this responsibility, it’s not only the child who misses out on one of life’s most profound experiences.
We really don’t know how the tech-savvy children of today will ultimately process their attachments to robots and whether they will be excessively predisposed to choosing robot companionship over that of humans. It’s possible their techno literacy will draw for them a bold line between real life and a quasi-imaginary history with a robot. But it will be decades before we see long-term studies culminating in sufficient data to help scientists, and the rest of us, to parse out the effects of a lifetime spent with robots.
This is an excerpt from ROBOTS AND THE PEOPLE WHO LOVE THEM: Holding on to Our Humanity in an Age of Social Robots by Eve Herold. The book will be published on January 9, 2024.
Stem cells from a fetus can travel to the heart and regenerate the muscle, essentially saving a mother’s life.
If there is a silver lining to peripartum cardiomyopathy, it’s that it is perhaps the most survivable form of heart failure. A remarkable 50% of women recover spontaneously. And there’s an even more remarkable explanation for that glowing statistic: The fetus‘ stem cells migrate to the heart and regenerate the beleaguered muscle. In essence, the developing or recently born child saves its mother’s life.
Saving mama
While this process has not been observed directly in humans, it has been witnessed in mice. In a 2015 study, researchers tracked stem cells from fetal mice as they traveled to mothers’ damaged cardiac cells and integrated themselves into hearts.
Evolutionarily, this function makes sense: It is in the fetus’ best interest that its mother remains healthy.
Scientists also have spotted cells from the fetus within the hearts of human mothers, as well as countless other places inside the body, including the skin, spleen, liver, brain, lung, kidney, thyroid, lymph nodes, salivary glands, gallbladder, and intestine. These cells essentially get everywhere. While most are eliminated by the immune system during pregnancy, some can persist for an incredibly long time — up to three decades after childbirth.
This integration of the fetus’ cells into the mother’s body has been given a name: fetal microchimerism. The process appears to start between the fourth and sixth week of gestation in humans. Scientists are actively trying to suss out its purpose. Fetal stem cells, which can differentiate into all sorts of specialized cells, appear to target areas of injury. So their role in healing seems apparent. Evolutionarily, this function makes sense: It is in the fetus’ best interest that its mother remains healthy.
Sending cells into the mother’s body may also prime her immune system to grow more tolerant of the developing fetus. Successful pregnancy requires that the immune system not see the fetus as an interloper and thus dispatch cells to attack it.
Fetal microchimerism
But fetal microchimerism might not be entirely beneficial. Greater concentrations of the cells have been associated with various autoimmune diseases such as lupus, Sjogren’s syndrome, and even multiple sclerosis. After all, they are foreign cells living in the mother’s body, so it’s possible that they might trigger subtle, yet constant inflammation. Fetal cells also have been linked to cancer, although it isn’t clear whether they abet or hinder the disease.
A team of Spanish scientists summarized the apparent give and take of fetal microchimerism in a 2022 review article. “On the one hand, fetal microchimerism could be a source of progenitor cells with a beneficial effect on the mother’s health by intervening in tissue repair, angiogenesis, or neurogenesis. On the other hand, fetal microchimerism might have a detrimental function by activating the immune response and contributing to autoimmune diseases,” they wrote.
Regardless of a fetus’ cells net effect, their existence alone is intriguing. In a paper published earlier this year, University of London biologist Francisco Úbeda and University of Western Ontario mathematical biologist Geoff Wild noted that these cells might very well persist within mothers for life.
“Therefore, throughout their reproductive lives, mothers accumulate fetal cells from each of their past pregnancies including those resulting in miscarriages. Furthermore, mothers inherit, from their own mothers, a pool of cells contributed by all fetuses carried by their mothers, often referred to as grandmaternal microchimerism.”
So every mother may carry within her literal pieces of her ancestors.
