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Las células errantes: La increíble biología del microquimerismo
Microchimérisme : mélange de cellules génétiquement distinctes dans le même corps.
Une femme qui accouche d’enfants qui sont génétiquement parlant ses neveux, des cellules d’origine foetale qui battent dans le coeur d’une mère et des cellules de grand-mères retrouvées dans le sang de nouveau-nés : autant d’exemples de folles histoires liées au microchimérisme, ce phénomène biologique que nous commençons tout juste à explorer.
Il y a une vingtaine d’années, la découverte du microbiote nous révélait que nous
étions à moitié constitués de micro-organismes. Nous réalisons aujourd’hui que même nos cellules humaines ne partagent pas toutes le même ADN.
Une femme qui accouche d’enfants qui sont génétiquement parlant ses neveux, des cellules d’origine foetale qui battent dans le coeur d’une mère et des cellules de grand-mères retrouvées dans le sang de nouveau-nés : autant d’exemples de folles histoires liées au microchimérisme, ce phénomène biologique que nous commençons tout juste à explorer.
Il y a une vingtaine d’années, la découverte du microbiote nous révélait que nous
étions à moitié constitués de micro-organismes. Nous réalisons aujourd’hui que même nos cellules humaines ne partagent pas toutes le même ADN.
160 pages, Paperback
Published May 15, 2025
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Displaying 1 - 30 of 54 reviews
December 28, 2025
A very short, broad, but well written and fascinating, overview of the astonishing phenomenon of microchimerism: the presence of a small number of cells from one individual living within another genetically distinct person. These migrating cells most commonly occur between mother and fetus during pregnancy, where fetal cells enter the mother and maternal cells enter the fetus. The migrating cells may also persist for years, and can even become specialized, acting like native cells in tissues and organs. These "foreign" cells are currently being studied for potential links to autoimmune diseases and tissue repair. Migrating cells may also be exchanged through organ transplants, in-utero twin-to-twin transfer (or reabsorbed twin) and blood transfusion, and possibly even through sex (this is a bit surprising - humans are not fruit flies!). The discovery of this phenomenon leaves questions, and raises implications, about everything we know so far about the immune system, lineage, and identity. However, the exact roles of these migrating cells, whether beneficial or detrimental, are still largely unknown and will require more research into this emerging field of medical science. An interesting book that I really wish had been longer and included more details.
September 5, 2026
Lise Barnéoud is a French science journalist. I read the English version translated by Bronwyn Haslam. Published in 2025, Hidden Guests explores the fascinating world of microchimerism: the presence of cells from one individual in another genetically distinct individual.
Microchimerism is a brand new topic to me. I find this book utterly eye-opening. This is what I’ve learned:
– Pregnancy is the main cause of natural microchimerism through transplacental bi-directional cell trafficking between mother and fetus. You carry a tiny population of your mother, grandmother, even your older siblings' cells, and your mother carries you and your siblings’ cells.
– Scientists hypothesize that microchimerism is one mechanism that makes a mother’s immune system accept the fetus. Microchimerism during pregnancy often is mutually beneficial, especially for the fetus, even after the baby was born. However, sometimes the cell exchange can be detrimental to the mother.
– Microchimerism could partially explain why women have a higher chance of developing autoimmune diseases
– Fetuses that failed to develop in the first trimester and then re-obsorbed by the mother’s body, a.k.a vanished twins, are not as rare as one might think. DNA tests should be put into context because of this phenomenon. In the case of Lydia Fairchild, whose children were “not hers” based on DNA tests, it is because Fairchild’s gametes came from a vanished twin sister.
– Bone marrow transplant, organ transplant and blood transfusion, could also cause microchimerism
– Using the intruder metaphor to describe chimerical cells may not always be accurate. They can be useful “migrants” or assimilated “citizens”. It could also cause cancer, depending on the type and location of the chimerical cells. Among different types of microchimerism, it seems the cancer risk is higher in a recipient of an organ donation from an unrelated donor.
– Unprotected sexual intercourse could cause male cells (not just sperms) to get into the female partner’s body
Microchimerism challenges our definition of an individual and how our immune system functions. Some scientists think it has philosophical implications, although I don’t think much about it: I am not the sum of my cells; besides, my body already hosts trillions of bacteria, what’s the harm of adding a few mostly beneficial human cells?
Microchimerism is a brand new topic to me. I find this book utterly eye-opening. This is what I’ve learned:
– Pregnancy is the main cause of natural microchimerism through transplacental bi-directional cell trafficking between mother and fetus. You carry a tiny population of your mother, grandmother, even your older siblings' cells, and your mother carries you and your siblings’ cells.
– Scientists hypothesize that microchimerism is one mechanism that makes a mother’s immune system accept the fetus. Microchimerism during pregnancy often is mutually beneficial, especially for the fetus, even after the baby was born. However, sometimes the cell exchange can be detrimental to the mother.
– Microchimerism could partially explain why women have a higher chance of developing autoimmune diseases
– Fetuses that failed to develop in the first trimester and then re-obsorbed by the mother’s body, a.k.a vanished twins, are not as rare as one might think. DNA tests should be put into context because of this phenomenon. In the case of Lydia Fairchild, whose children were “not hers” based on DNA tests, it is because Fairchild’s gametes came from a vanished twin sister.
– Bone marrow transplant, organ transplant and blood transfusion, could also cause microchimerism
– Using the intruder metaphor to describe chimerical cells may not always be accurate. They can be useful “migrants” or assimilated “citizens”. It could also cause cancer, depending on the type and location of the chimerical cells. Among different types of microchimerism, it seems the cancer risk is higher in a recipient of an organ donation from an unrelated donor.
– Unprotected sexual intercourse could cause male cells (not just sperms) to get into the female partner’s body
Microchimerism challenges our definition of an individual and how our immune system functions. Some scientists think it has philosophical implications, although I don’t think much about it: I am not the sum of my cells; besides, my body already hosts trillions of bacteria, what’s the harm of adding a few mostly beneficial human cells?
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September 15, 2026genetics is so fckn cool, dude. and women are magical
February 8, 2026
Lise Barneoud is a French science journalist; her 2025 book Hidden Guests (which I listened to in its English translation from its original French language publication) is an exploration of the current state of microchimerism. This is a topic I remember being previously discussed in some depth in Carl Zimmer's 2018 book She Has Her Mother's Laugh: The Powers, Perversions, and Potential of Heredity, though Hidden Guests provides a more up-to-date appraisal.
I think this is a good introduction to this topic for a lay audience, though I wish there was more contextualization of how this area fits into the broader study of human biology. I work in the genetics space and routinely deal with issues of chimerism (particularly, looking for the presence or absence of genetic variants from donors and recipients of transplants), and important distinction to make is the scale of chimerism in proportion to the total number of cells present and its ability or inability to be detected by current qualitative and quantitative tests. For instance, most sequencing technologies routinely used in clinical testing today can detect chimerism at a level of around 5%, with allogen testing being even more sensitive. But, these are orders of magnitudes higher than many of the research studies Barneoud cites that depend on single cell imaging. So it's difficult for us to be able to draw conclusions of the physiologic and disease impact of 0.0001% of chimeric cells in a population.
So while I find the conclusions of the book needing to be taken with a big grain of salt, this is definitely an area of research to watch going forward.
My statistics:
Book 33 for 2026
Book 2339 cumulatively
I think this is a good introduction to this topic for a lay audience, though I wish there was more contextualization of how this area fits into the broader study of human biology. I work in the genetics space and routinely deal with issues of chimerism (particularly, looking for the presence or absence of genetic variants from donors and recipients of transplants), and important distinction to make is the scale of chimerism in proportion to the total number of cells present and its ability or inability to be detected by current qualitative and quantitative tests. For instance, most sequencing technologies routinely used in clinical testing today can detect chimerism at a level of around 5%, with allogen testing being even more sensitive. But, these are orders of magnitudes higher than many of the research studies Barneoud cites that depend on single cell imaging. So it's difficult for us to be able to draw conclusions of the physiologic and disease impact of 0.0001% of chimeric cells in a population.
So while I find the conclusions of the book needing to be taken with a big grain of salt, this is definitely an area of research to watch going forward.
My statistics:
Book 33 for 2026
Book 2339 cumulatively
October 22, 2025
Michrochimerism (a phenomenon where cells from one individual can be found in another’s body) isn’t just about cells that push the boundary of self vs nonself but emphasize that we are nothing without the collective, ie the extremely Individualistic greedy American society. We are who we surround ourselves with, we are what we eat (not in the diet fad way but in the way we nourish our gut biota). We are as healthy as our earth is healthy (gulp). It begs the question what makes you you when you have cells present in your body from other individuals like immigrants, people a with different sex assigned at birth, different race?
June 10, 2026
A short and very well researched book about microchimerism. The seemingly science-fiction like idea of having cells from others (mothers, Children, siblings, siblings who don't exist and even organ donors and previous partners) in your body and it having wide scale implications for health is quite eye opening. It has major repercussions for law enforcement, social ideas around relations and more uniquely the philosophy of what makes us an individual. The subdiscipline is quite young - so lots of cool discoveries are bound to change our views about genetic inheritance, immune diseases among other things.
Loved this book! Definitely recommend!
Loved this book! Definitely recommend!
July 17, 2026
RIP, Targaryen family. You would have loved this information.
September 21, 2026
Read for work but really enjoyed this!! Really cool science but also a very good discussion on how science and society interact and shape each other
Nice and short also
Nice and short also
June 8, 2025
Book Review: Hidden Guests: Migrating Cells and How the New Science of Microchimerism Is Redefining Human Identity by Lise Barnéoud - A Public Health Practitioner’s Perspective
Lise Barnéoud’s Hidden Guests is a revelatory exploration of microchimerism that fundamentally challenges our understanding of human biology and its implications for public health. As a practitioner, I found myself oscillating between wonder at the science of cellular migration and discomfort at how this paradigm shift exposes gaps in our current medical frameworks. The book’s central premise—that we are walking ecosystems harboring genetically distinct cells from pregnancy, organ transplants, and even deceased twins—left me questioning the very definition of individual health.
Emotional Resonance: Between Awe and Existential Dread
Reading about fetal cells persisting in mothers’ brains decades after pregnancy, or a transplant recipient’s bloodline becoming genetically hybrid, triggered a profound professional reckoning. Barnéoud’s vivid descriptions of these “hidden guests” made me reflect on how public health has traditionally treated bodies as closed systems—vaccinating, screening, and treating individuals without considering these cellular legacies. The chapter linking microchimerism to autoimmune diseases stirred both excitement (could this explain sex disparities in lupus?) and frustration (why isn’t this taught in medical schools?). Most haunting was the realization that these microscopic migrants may influence everything from cancer risk to psychiatric disorders—variables we’ve never adequately accounted for in population health studies.
Key Public Health Insights
-The Myth of Biological Autonomy: Barnéoud dismantles the fiction of bodily independence, revealing how microchimerism blurs the lines between self and other—a paradigm shift with radical implications for maternal health, transplantation ethics, and even vaccine response.
-Microchimerism as Social Determinant: The book suggests that socioeconomic factors (e.g., access to reproductive care) may shape microchimerism patterns, creating yet another invisible health disparity.
-Rethinking Immunity: By framing the immune system as a “negotiation tool” between host and migrant cells (rather than purely defensive), the book challenges public health’s war metaphors (“fighting” pathogens) in favor of ecological models.
Constructive Criticism
-From Bench to Policy: While Barnéoud excels at explaining the science, public health practitioners need more guidance on translating microchimerism research into interventions (e.g., should prenatal care include microchimerism monitoring?).
-Global Health Equity: The book’s focus on high-income country research risks obscuring how microchimerism might interact with endemic infections or malnutrition in low-resource settings.
Final Thoughts
Hidden Guests is a seismic intervention in public health thinking. It left me convinced that until we integrate microchimerism into our frameworks—whether studying intergenerational trauma or designing precision medicine—we’re practicing with blinders on. Barnéoud’s work demands we redefine health not as individual purity, but as skillful coexistence.
Rating: ★★★★☆ (4.5/5) – A groundbreaking but occasionally esoteric masterpiece.
Gratitude: Thank you to the publisher and Edelweiss for the review copy. In a field obsessed with measurable outcomes, this book reminds us that some of health’s most powerful determinants are invisible.
Lise Barnéoud’s Hidden Guests is a revelatory exploration of microchimerism that fundamentally challenges our understanding of human biology and its implications for public health. As a practitioner, I found myself oscillating between wonder at the science of cellular migration and discomfort at how this paradigm shift exposes gaps in our current medical frameworks. The book’s central premise—that we are walking ecosystems harboring genetically distinct cells from pregnancy, organ transplants, and even deceased twins—left me questioning the very definition of individual health.
Emotional Resonance: Between Awe and Existential Dread
Reading about fetal cells persisting in mothers’ brains decades after pregnancy, or a transplant recipient’s bloodline becoming genetically hybrid, triggered a profound professional reckoning. Barnéoud’s vivid descriptions of these “hidden guests” made me reflect on how public health has traditionally treated bodies as closed systems—vaccinating, screening, and treating individuals without considering these cellular legacies. The chapter linking microchimerism to autoimmune diseases stirred both excitement (could this explain sex disparities in lupus?) and frustration (why isn’t this taught in medical schools?). Most haunting was the realization that these microscopic migrants may influence everything from cancer risk to psychiatric disorders—variables we’ve never adequately accounted for in population health studies.
Key Public Health Insights
-The Myth of Biological Autonomy: Barnéoud dismantles the fiction of bodily independence, revealing how microchimerism blurs the lines between self and other—a paradigm shift with radical implications for maternal health, transplantation ethics, and even vaccine response.
-Microchimerism as Social Determinant: The book suggests that socioeconomic factors (e.g., access to reproductive care) may shape microchimerism patterns, creating yet another invisible health disparity.
-Rethinking Immunity: By framing the immune system as a “negotiation tool” between host and migrant cells (rather than purely defensive), the book challenges public health’s war metaphors (“fighting” pathogens) in favor of ecological models.
Constructive Criticism
-From Bench to Policy: While Barnéoud excels at explaining the science, public health practitioners need more guidance on translating microchimerism research into interventions (e.g., should prenatal care include microchimerism monitoring?).
-Global Health Equity: The book’s focus on high-income country research risks obscuring how microchimerism might interact with endemic infections or malnutrition in low-resource settings.
Final Thoughts
Hidden Guests is a seismic intervention in public health thinking. It left me convinced that until we integrate microchimerism into our frameworks—whether studying intergenerational trauma or designing precision medicine—we’re practicing with blinders on. Barnéoud’s work demands we redefine health not as individual purity, but as skillful coexistence.
Rating: ★★★★☆ (4.5/5) – A groundbreaking but occasionally esoteric masterpiece.
Gratitude: Thank you to the publisher and Edelweiss for the review copy. In a field obsessed with measurable outcomes, this book reminds us that some of health’s most powerful determinants are invisible.
June 19, 2026
4.5 rounded up
Absolutely fascinating. My mind was spinning rethinking how microchimerism may play a part in so many medical fields and in ways we never imagined. As someone with complex autoimmune and autonomic issues, I will only be delving further and further down this rabbit hole. I needed to reread some parts to be sure I understood the science but overall, I think this is a fairly accessible book that packs a huge punch and satisfying payoff. Highly recommend!
Absolutely fascinating. My mind was spinning rethinking how microchimerism may play a part in so many medical fields and in ways we never imagined. As someone with complex autoimmune and autonomic issues, I will only be delving further and further down this rabbit hole. I needed to reread some parts to be sure I understood the science but overall, I think this is a fairly accessible book that packs a huge punch and satisfying payoff. Highly recommend!
May 17, 2026
Chimerism was one of the topics I most enjoyed studying about way back when, even though I didn't end up in any field remotely close to it. Anyways, this was a great reminder of that. Definitely some more speculative parts, but the author does a good job of clarifying which portions are in the realm of hypothesis or imagination.
February 16, 2026
Fascinating!
July 14, 2026
Very interesting if u like science otherwise u won’t gaf
December 6, 2025
I knew chimerism could be a thing in a few humans, but I did not know that micro-chimerism was a thing in all of us.
Do the human cells in our bodies that did not come from the single fertilised egg that most of our cells come from help or hinder, heal, protect or attack? Are they essential for a properly functioning immune system or the cause of autoimmune diseases? The answers are varied and nuanced and some of them are still speculative.
A short, but fascinating book with right up to date information on the state of research into this phenomenon.
Do the human cells in our bodies that did not come from the single fertilised egg that most of our cells come from help or hinder, heal, protect or attack? Are they essential for a properly functioning immune system or the cause of autoimmune diseases? The answers are varied and nuanced and some of them are still speculative.
A short, but fascinating book with right up to date information on the state of research into this phenomenon.
June 16, 2026
Took me a while to read because I stopped and started this book but the topic was so interesting and very well written!!
December 13, 2023
J'ai tout simplement adoré. Le sujet est passionnant et il est rendu accessible par l'autrice qui nous entraîne dans une questionnement quasiment philosophie.
March 12, 2026
This is how you write a science communication book for the public: clearly, engagingly, concisely. Lise Barneoud manages to bring the reader up to speed about the most recent science in microchimerism in just over 150 pages using short clear descriptions of science, and clear and creative metaphors. Her choices turn what could have been a dry book of facts into a philosophical meditation on the self and immigration. Because what are chimeric cells if not shadow immigrants.
Some of the examples offered in this book where known to me, but most were completely new. I was familiar with chimerism caused by an absorbed twin, and that caused by fetal cells passing from the fetus to their mother. I wasn't aware how bi-directional that highway truly is, or that cells from three generations (grandmother, mother and latest offspring) can sometimes be found in the same person. Microchimerism caused by sexual intercourse that doesn't result in fertilization was something I'd heard of but had thought it was all wacky--it looks like it's a real phenomenon, but how long this lingers is yet unclear. The book goes beyond merely describing how cells from different individuals can end up in other bodies: whether through sexual intercourse, pregnancy, or transplant, the effects may be similar and equally diverse. Sometimes the migrating cells become established productive members of the cellular body, regenerating, pruning synapses and boosting immunity or triggering life-saving tolerance. Other times the cells may boost inflammation and cancer. This part brought to mind "The Master Builder: How the New Science of the Cell Is Rewriting the Story of Life" by Alfonso Martinez Arias. In his thesis, that cells rather than genes are the engines of life, Arias emphasizes how context (i.e. cellular environment and intra and inter-cellular communication) is the most important thing deciding a cell's fate.
The metaphors did occasionally jump way ahead of current knowledge, especially in the final chapters. There was a lot of speculation about how many generations can be trapped in an individuals, without any discussion on how migrant cells can break the Hayflick limit--the hard stop for future cell divisions caused by an exhaustion of telomeres that protect the ends of chromosomes. The author gives an example of migrant cells that were able to traverse bodies across 10 generations of mice, but mouse cells can immortalize themselves spontaneously in culture--something human cells have never been able to do. Some of that poetic license was a bit disorienting after multiple chapters in which science and poetry had blended seamlessly. Take for example the case of marmoset fathers who the author presumes may be providing more care to offspring who are macro-chimeric because their skin-to-skin contact 'recognizes' more of their HLA genes; this is completely absurd, given that skin cells on the upper levels are dead and don't establish any connections with other dead skin cells on another individual--they cannot given they're just empty shells. I was surprised how at times the language was also quite gender inclusive, until I found out that was an artifact of the translation and not part of the original French writing.
Despite small confusions and unnecessary speculations, I think the book did an excellent job of introducing the public to the latest science of microchimerism, and highlighted both its promises and challenges laying ahead. The most important part of this book was the reminder of how limited and artificial our biological 'rules' truly are. Micro and macro-chimeric individuals and their migrating cells do not break the laws of nature; rather they break the rules we imposed on nature in order to understand it. As usual, when we probe deeper into an area, we find more exceptions and more options that we previously thought. How we react to this uncertainty tells us more about ourselves, than about the multitudes hiding inside us.
4.5 stars rounded up
Some of the examples offered in this book where known to me, but most were completely new. I was familiar with chimerism caused by an absorbed twin, and that caused by fetal cells passing from the fetus to their mother. I wasn't aware how bi-directional that highway truly is, or that cells from three generations (grandmother, mother and latest offspring) can sometimes be found in the same person. Microchimerism caused by sexual intercourse that doesn't result in fertilization was something I'd heard of but had thought it was all wacky--it looks like it's a real phenomenon, but how long this lingers is yet unclear. The book goes beyond merely describing how cells from different individuals can end up in other bodies: whether through sexual intercourse, pregnancy, or transplant, the effects may be similar and equally diverse. Sometimes the migrating cells become established productive members of the cellular body, regenerating, pruning synapses and boosting immunity or triggering life-saving tolerance. Other times the cells may boost inflammation and cancer. This part brought to mind "The Master Builder: How the New Science of the Cell Is Rewriting the Story of Life" by Alfonso Martinez Arias. In his thesis, that cells rather than genes are the engines of life, Arias emphasizes how context (i.e. cellular environment and intra and inter-cellular communication) is the most important thing deciding a cell's fate.
The metaphors did occasionally jump way ahead of current knowledge, especially in the final chapters. There was a lot of speculation about how many generations can be trapped in an individuals, without any discussion on how migrant cells can break the Hayflick limit--the hard stop for future cell divisions caused by an exhaustion of telomeres that protect the ends of chromosomes. The author gives an example of migrant cells that were able to traverse bodies across 10 generations of mice, but mouse cells can immortalize themselves spontaneously in culture--something human cells have never been able to do. Some of that poetic license was a bit disorienting after multiple chapters in which science and poetry had blended seamlessly. Take for example the case of marmoset fathers who the author presumes may be providing more care to offspring who are macro-chimeric because their skin-to-skin contact 'recognizes' more of their HLA genes; this is completely absurd, given that skin cells on the upper levels are dead and don't establish any connections with other dead skin cells on another individual--they cannot given they're just empty shells. I was surprised how at times the language was also quite gender inclusive, until I found out that was an artifact of the translation and not part of the original French writing.
Despite small confusions and unnecessary speculations, I think the book did an excellent job of introducing the public to the latest science of microchimerism, and highlighted both its promises and challenges laying ahead. The most important part of this book was the reminder of how limited and artificial our biological 'rules' truly are. Micro and macro-chimeric individuals and their migrating cells do not break the laws of nature; rather they break the rules we imposed on nature in order to understand it. As usual, when we probe deeper into an area, we find more exceptions and more options that we previously thought. How we react to this uncertainty tells us more about ourselves, than about the multitudes hiding inside us.
4.5 stars rounded up
April 3, 2026
I began this book with a robust interest in microchimerism and all of its many implications for life, love, and our pursuits of everything in between as creatures of this world. "Who are we really?" is the question I ask as we learn more about the microbiota of our bodies, and the epigenetics and environments that shape our minds and bodies even before we are born from our mother's womb. Who are we really, as individuals, if we are instead a literal amalgamation of all we've seen, touched, and experienced, even from our earliest existence as "fetal cells"? The book is captivating in how it summarizes developments in science and research on the topic, and it is simple enough for the average layperson to understand. The metaphors and similes about immigration are notably a bit heavy-handed in parts, but not so bothersome that they become a distraction.
No, the one specific part that caught me off guard and made me wince, if not recoil in disgust, was near the front of the book, where the author recalls a secretive conversation with Lee Nelson. Barneoud writes of the conversation:
"'An abortion in the early stages of pregnancy might be expected to lead to a greater proportion of stem cells of fetal origin than a full-term birth. They may even have a greater potential for regeneration.'"
The author then follows up with:
"If these cells persist and repair tissues, then abortion could in fact provide a rejuvenating boost." (pg. 39)
I felt the urge to put the book down at this point and adjust my own discomfort with the implications of such a conclusion. I tried to will myself to continue reading, excusing the suggestive comment that "abortion could in fact provide a rejuvenating boost" as just another example of a science writer's messy handling of the lines between scientific observation and ethics and morality, but it was too much of a bother for me to make the effort to see if the author could provide any additional insight or commentary to make up for it in the next chapter. It became a stick in my craw, one I have neither the time nor the patience to remove for such a short read. I figure I can find an equally engaging book, or even dissect the scientific literature itself, on microchimerism that isn't so ethically fraught. This book will reside on my Did Not Finish shelf.
No, the one specific part that caught me off guard and made me wince, if not recoil in disgust, was near the front of the book, where the author recalls a secretive conversation with Lee Nelson. Barneoud writes of the conversation:
"'An abortion in the early stages of pregnancy might be expected to lead to a greater proportion of stem cells of fetal origin than a full-term birth. They may even have a greater potential for regeneration.'"
The author then follows up with:
"If these cells persist and repair tissues, then abortion could in fact provide a rejuvenating boost." (pg. 39)
I felt the urge to put the book down at this point and adjust my own discomfort with the implications of such a conclusion. I tried to will myself to continue reading, excusing the suggestive comment that "abortion could in fact provide a rejuvenating boost" as just another example of a science writer's messy handling of the lines between scientific observation and ethics and morality, but it was too much of a bother for me to make the effort to see if the author could provide any additional insight or commentary to make up for it in the next chapter. It became a stick in my craw, one I have neither the time nor the patience to remove for such a short read. I figure I can find an equally engaging book, or even dissect the scientific literature itself, on microchimerism that isn't so ethically fraught. This book will reside on my Did Not Finish shelf.
May 16, 2026
A fascinating little book about microchimerism which is the phenomenon where cells from other people live inside your body, sometimes for decades. Lise Barneoud walks you through the discovery of this field and then takes you through a series of remarkable cases that show just how strange and porous our biology really is. Fetal cells that migrate into a mother and help repair her injuries. Cells from older siblings found in younger children. The idea that women who have had multiple partners may carry a mosaic of foreign cells that interact with their immune system in ways we are only beginning to understand.
The book leans heavily on cherry picked cases which is both its strength and its weakness. The cases are genuinely mind blowing and she tells them well but you do walk away wondering how representative they really are. The firefly gene experiment with mice was one of those moments where you just sit back and think about how wild biology is.
What stuck with me most is the philosophical undercurrent. The concept of a singular unified self is something we take for granted and this book quietly dismantles it. You are not just you. You carry bits of your mother, possibly your siblings, possibly others. That is either deeply comforting or deeply unsettling depending on your mood.
Very short book, I finished it in about four hours as an audiobook. If this genre interests you at all it is absolutely worth your time. A great entry point for curious non specialists and probably a goldmine of dissertation ideas for biology PhD students.
The book leans heavily on cherry picked cases which is both its strength and its weakness. The cases are genuinely mind blowing and she tells them well but you do walk away wondering how representative they really are. The firefly gene experiment with mice was one of those moments where you just sit back and think about how wild biology is.
What stuck with me most is the philosophical undercurrent. The concept of a singular unified self is something we take for granted and this book quietly dismantles it. You are not just you. You carry bits of your mother, possibly your siblings, possibly others. That is either deeply comforting or deeply unsettling depending on your mood.
Very short book, I finished it in about four hours as an audiobook. If this genre interests you at all it is absolutely worth your time. A great entry point for curious non specialists and probably a goldmine of dissertation ideas for biology PhD students.
May 19, 2026
Another book that inspired "girl are you fr?" Feelings in me. Having read 'I Contain Multitudes' last year, this builds on that revelation. Once again, science challenges our dogma of us being a singular self, damn. First microbes and now human cells. Damn. It is really interesting to think of the immune system as a gardener of sorts, a balancer rather than a BORDER CONTROL 1000
I thought about the TV show Murray a lot... Aw man... I hate that DNA tests aren't absolute. That poor woman.
MAN, I gotta have surgery in a month. I would love someone to scan my polyp for different DNAs...!!
Admittedly, I didn't love the way the author wrote the prose- I can't put a finger on why, but it was not super captivating to me. I loved the subject matter and efforts they went through, talking to researchers and getting quotes. Very good
I thought about the TV show Murray a lot... Aw man... I hate that DNA tests aren't absolute. That poor woman.
MAN, I gotta have surgery in a month. I would love someone to scan my polyp for different DNAs...!!
Admittedly, I didn't love the way the author wrote the prose- I can't put a finger on why, but it was not super captivating to me. I loved the subject matter and efforts they went through, talking to researchers and getting quotes. Very good
September 4, 2026
Fascinating and poetic nonfiction book about microchimerism aka all the human cells in your body that aren't actually yours. Cells of fetal origin can be found in every organ of a mother’s body and can differentiate into any kind of cell. But it isn't just mother's who have microchimerism. Your mother exchange cells with you while you are in the womb and some of those cells aren't even hers, but her mother's or the fetal cells of your older siblings that are still circulating. There's evidence that those cells can help heal us (pregnant women recover from heart damage faster than non-pregnant women). There's evidence that those cells can harm us (autoimmune disorders).
-“To be oneself is above all to be made by others and of others” -Edgardo Carosella and Thomas Pradeu
-You don’t have to be a mother to be inhabited by others
-All of us harbor an ordinary micro-monstrosity
-“To be oneself is above all to be made by others and of others” -Edgardo Carosella and Thomas Pradeu
-You don’t have to be a mother to be inhabited by others
-All of us harbor an ordinary micro-monstrosity
September 27, 2025
Hidden Guests was a surprising, engaging read about how we interpret biological evidence, the philosophy of self, and the patchwork ecosystem that makes up the human body.
As someone with a science background, I thoroughly enjoyed reading all the different cases of microchimerism and having my knowledge challenged. Still, all readers, science background or not, will easily engage with this book. The writing and research was concise, it was cohesive and flowed well, and the overall ideas of self and immunity were incredibly thought-provoking.
(4.5/5)
*This ARC was provided by Greystone Books
As someone with a science background, I thoroughly enjoyed reading all the different cases of microchimerism and having my knowledge challenged. Still, all readers, science background or not, will easily engage with this book. The writing and research was concise, it was cohesive and flowed well, and the overall ideas of self and immunity were incredibly thought-provoking.
(4.5/5)
*This ARC was provided by Greystone Books
November 28, 2025
I relish books that leave me with more questions than answers after reading them. This book presents a challenging concept, attempting to demonstrate that there isn’t a singular “me” but rather an “us” due to the various ways cells are exchanged between individuals, such as mother-child interchanges, transfusions, transplants, or even the simple exchange of sexual fluids between partners!
It’s captivating and leaves you pondering the broader implications of human interactions.
Are these exchanges entirely harmless? Do foreign cells contribute to or exacerbate conditions like cancer and heart disease? Are there other forms of exchange within the microchimerism realm?
It’s captivating and leaves you pondering the broader implications of human interactions.
Are these exchanges entirely harmless? Do foreign cells contribute to or exacerbate conditions like cancer and heart disease? Are there other forms of exchange within the microchimerism realm?
June 20, 2025
I enjoyed this book. The science of microchimerism can be very complex but I thought that the author did a great job of maintaining a conversational tone while minimizing jargon. I also thought that the explanations were clear and well-laid out. Also great were the intriguing stories of people affected by microchimerism and the wide-ranging discussions about self versus nonself and the related ethical issues. This is a fascinating book. Thank you to Edelweiss and Greystone Books for the digital review copy.
April 29, 2026
One more case of a good book leading to another. I recently read Carl Zimmer’s She Has Her Mother's Laugh: What Heredity Is, Is Not, and May Become, which touched on the topics of chimerism and microchimerism. Microchimerism occurs when cells with a different DNA profile integrate into another individual. I wanted to know more and a quick search led me to this book. Since microchimerism is a new field of study this isn’t filled with answers but it does cover the recent advances that have been made in researching it and it also speculates about the social and philosophical implications it presents.
September 11, 2026
4.5 stars // Accessible and relatively short, this was a fascinating foray into microchimerism and its implications. Chapter Five, The Other in Me, was especially interesting.
Trophoblasts, pregnancy, vanished twins, confounding DNA tests + evidence, transplants, autoimmune disease, and more.
Epilogue, page 137 -
Can we still speak of self and non-self when the two are so closely intertwined? Our "I" is a "we". [...] a subtle co-construction with the other human and nonhuman cells that enrich us.
CW: animal testing
Trophoblasts, pregnancy, vanished twins, confounding DNA tests + evidence, transplants, autoimmune disease, and more.
Epilogue, page 137 -
Can we still speak of self and non-self when the two are so closely intertwined? Our "I" is a "we". [...] a subtle co-construction with the other human and nonhuman cells that enrich us.
CW: animal testing
January 6, 2026
OMG You absolutely need to check out this book! It will blow your mind. Mothers and fetuses (and twins in útero) exchange cells which can go Anywhere in mother’s body, including heart and brain, and assume function of thise cells. In addition, they are attracted to sites of inflammation to help heal.
January 27, 2026
This is a concise, elegant, and intellectually provocative exploration of microchimerism, the presence of genetically distinct cells within the human body. Blending cutting-edge science with compelling human stories, Barnéoud challenges the deeply rooted notion of a singular, autonomous biological self, showing instead that human identity is far more porous and relational than we assume.
February 16, 2026
This book completely changed the way I think about my own body. Barnéoud doesn’t overhype the science or make wild promises. Instead, she walks through the research carefully, acknowledges what we still don’t know, and shows how much of this field is still evolving. It feels responsible and grounded, which I respect a lot.
February 19, 2026
I give it a 3.75. The writing is clear, scientific basis is good, but in some places it gets a bit fanciful and oversteps the science and heads into conjecture. For the general public, the basics of microchimerism are well presented. It is very well stated that while correlations with microchimerism are evident, they do not mean causation.
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