For most people, birth marks a clear dividing line in human life. A baby grows in its mother for about nine months before coming into the world as a separate individual, when the umbilical cord is cut, and we usually consider the mother and child two independent biological systems. The truth is far more interesting.
Research has found that during pregnancy, cells are exchanged between the mother and the fetus. Fetal cells can enter the mother’s body, and maternal cells can cross the placenta and enter the developing child. Although some of these cells disappear, others can remain long after pregnancy ends.
Studies have found that maternal cells can be present in children for many years, and even decades, after birth. In one study, maternal microchimerism was identified in people as late as age 49, among them being those who were healthy. On the other hand, cells picked up from the fetus during pregnancy can also stay in the mother’s body for many years.
Scientific phenomenon
The scientific term for this phenomenon is microchimerism; maternal microchimerism is when cells from the mother remain in her child.
I find this interesting in my role as a therapist, but we must be careful not to imply that the science proves anything beyond what it actually does. No evidence suggests these cells contain a mother’s memories, personality, or emotions, and their presence does not mean a mother remains in control of her child’s biology.
The research shows that the biological division between mother and child is less clear-cut than we once thought, and pregnancy can leave a cellular legacy long after the two bodies have become separate individuals.
What is maternal microchimerism?
The term chimaera originates in Greek mythology, where it referred to an animal made up of parts from different animals; in modern biology, chimerism refers to genetically different cells within a single organism, and when such cells are present in small amounts, the condition is known as microchimerism. This can occur naturally during pregnancy.
The placenta acts as a highly sophisticated interface between the mother and the developing baby, but it is not impermeable, since cells can pass through it in both directions. Studies have found maternal cells in the fetal tissues during pregnancy, as well as fetal cells entering the mother’s circulation.
Some of the transferred cells seem to survive for remarkably long periods
A study in the Journal of Clinical Investigation found that maternal microchimerism can persist in offspring who are immunologically healthy right up to adulthood. The researchers identified maternal genetic material in people whose average age was 28, with ages ranging from nine to 49.
So decades after our birth, we might still have a small number of cells that originated in our mothers.
Although these numbers are very small compared with the huge number of our own cells, their persistence raises interesting questions about what they are doing and why they have stayed.
Your mother’s cells may still be inside you
One of the most remarkable features of maternal microchimerism is that it lasts a long time.
Researchers have found maternal cells in the developing fetus, and later studies have demonstrated that maternal cells or DNA can still be detected in the offspring well into adulthood.
This makes clearer the basic account we usually give ourselves about birth. Biological separation does occur, but it is not as complete as cutting the umbilical cord implies.
It is wrong to exaggerate what this implies; your mother does not run your body in any way, and the fact that a small number of cells are genetically different does not mean her thoughts, feelings, or personality are alive within you.
This shows that human biology is more complex than a simple distinction between self and other.
Researchers who have studied microchimerism have suggested that our usual conception of the biological self should account for the possibility that small groups of cells from another person can become long-term inhabitants of our bodies.
It’s an amazing idea on its own.
Why do these cells stay?
Once scientists established that microchimeric cells could persist, it was natural to ask what, if anything, these cells were doing.
At present, there is no full answer.
An area of study is tissue repair. Studies have found that microchimeric cells are associated with various tissues and that some may take part in repair or regeneration. There is also considerable interest in their connection with the immune system.
Pregnancy poses a special immunological problem. Although the mother and the fetus have different genes, under ordinary conditions the maternal immune system does not treat the developing baby as foreign tissue and therefore does not reject it. The immunological changes that make pregnancy possible are complex, and microchimerism seems to be part of that process.
The researchers are therefore looking into whether persistent microchimeric cells might affect immune tolerance, autoimmune disease, inflammatory processes, and tissue repair.
The results are neither clearly positive nor clearly negative. Although microchimerism has been studied in relation to both beneficial and possibly harmful effects, its importance probably varies with the specific cells, tissues, and circumstances.
This is exactly where good science should be comfortable with uncertainty. We know the phenomenon exists and can last for decades; we are still working out what this means for the biological relationship between mother and child.
The biological self is more complicated than we thought
For centuries, medicine has divided the human body into separate systems because this lets us study an immensely complicated organism more easily. Nowadays, neurology, immunology, endocrinology, gastroenterology, cardiology, psychiatry, and psychology each focus on a particular aspect of human functioning. The body does not respect those divisions to any great extent.
The nervous and immune systems communicate. Hormones affect mood and behaviour. The gut microbiome plays a role in metabolic and neurological processes. Chronic stress can affect inflammatory activity, while experience can change patterns of neural functioning.
Microchimerism adds another fascinating layer to this increasingly interconnected scenario.
Human development does not occur in biological isolation; from the very beginning, the fetus is in a complex relationship with another human body, and cells can move in both directions, with a few remaining after pregnancy ends.
In that respect, the biological account of pregnancy does not come to an end at birth.
Then are we actually born with a clear mind?
In this connection, science addresses a question that interests me professionally.
Is any of us truly born with a completely blank sheet of paper? No, and maternal microchimerism is only one minor factor.
When we come into the world, we have our genes, our temperament, the effects of our development in the womb, and a nervous system that began developing long before we were put into our mother’s arms. By the time a baby is born, a great deal of biological development will already have occurred.
What we have to avoid is the idea that traumatic memories of a mother are in some way stored in her cells and then passed on physically to her child. No evidence supports that conclusion.
There are, on the other hand, reasonable and interesting questions about prenatal development, stress physiology, and how the developing nervous system responds to its environment. Such questions fall within developmental neuroscience and biology, not among the more extravagant assertions about cellular or inherited memory.
A nervous system can develop and adapt without the baby having to use language or possess conscious autobiographical memory; the systems relating to arousal, regulation, and responses to the environment emerge from the very beginning of life.
That is not the same as saying that a baby is aware of its mother’s experiences.
Cellular inheritance is not the same as emotional memory
I believe this distinction matters because various interesting but independent fields of science can easily be grouped together, and then it may appear that they are making a claim they aren’t.
The fact is that a small number of cells which come from the mother can remain in her children. Since genetics shows that we receive biological information from our parents, epigenetics looks at changes in the way genes are regulated and the complex interaction between biology and the environment, while developmental neuroscience studies how the developing brain and nervous system are shaped over time.
While these areas do overlap, they cannot be used in place of one another. The presence of maternal cells in an adult does not prove that trauma has been inherited. The fact that early experience affects nervous system development does not imply that memories are passed on from mother to child. Findings relating to epigenetics do not suggest that people are permanently programmed by what happened to previous generations.
It is important to recognise that interesting scientific findings can very easily slip into the realm of psychological determinism if the language becomes loose.
I am much more interested in what the evidence actually allows us to say.
Human development begins in relationship. Biology, environment, and experience interact from the earliest stages of life; some influences are genetic, some cellular, some physiological, and, increasingly after birth, some relational and psychological.
We are not blank slates, but neither are we prisoners of what came before us.
What, then, does any of this mean therapeutically?
This matters to me as a therapist because people frequently arrive in therapy with affective reactions they cannot explain.
They may know intellectually that they are safe while experiencing a powerful bodily sense that they are not. They may respond to intimacy, conflict, rejection, criticism or uncertainty in ways that seem disproportionate to what is actually happening in the present.
When this happens, we may be tempted to search for one definitive explanation. Perhaps it was childhood, attachment, trauma, genetics or something inherited from previous generations.
Human beings are rarely that simple. Our emotional responses emerge from an accumulation of temperament, biology, experience, learning and relationships. Therapy does not require us to discover one perfect origin story before change becomes possible.
This is particularly relevant to my work with deeply established emotional patterns. Whether an unwanted response developed very early or much later in life, the key therapeutic question is whether it still operates automatically in the present and whether it can be updated.
This is one reason I am interested in memory reconsolidation and therapeutic approaches that work with established emotional learning. It is also where I may draw on the Orpheus Decoupling Process from Orpheus Mind Technologies, where I work as a Strategic Consultant. Orpheus is designed to work with unwanted emotional reflexes and beliefs that continue automatically, even when somebody consciously knows that they would prefer to feel or respond differently.
None of this requires us to claim that trauma is hidden inside somebody else’s cells.
The therapeutic question is much more practical. What is happening now, what is keeping the response active, and what might allow that response to change?
Perhaps connection is the more interesting story
Maternal microchimerism does not prove that mothers leave their memories behind in their children, nor does it tell us that our emotional lives are fixed before birth.
What it does tell us is that pregnancy leaves a biological legacy considerably more intricate than most of us once imagined.
A small population of cells originating in the mother can remain within her offspring long after birth. In the opposite direction, cells originating from a pregnancy can persist within the mother’s body too.
There is something remarkable about that without needing to turn it into mysticism.
Perhaps the question is therefore not whether we are born “clear” in some absolute sense. We plainly arrive with a biological and developmental history already underway.
The more useful question is what that history means and, just as importantly, what it does not mean.
We carry genetic material from our parents. Our prenatal environment contributes to development. Our experiences after birth keep shaping us, and throughout life the human brain and nervous system retain capacities for learning and change.
What came before us influences us without necessarily condemning us to repeat it.
For me, that is considerably more interesting than the suggestion that a mother’s memories are somehow hidden inside her child’s cells.
The science of maternal microchimerism tells us something more perceptible and, in its own way, more extraordinary. Long after two bodies have become separate lives, traces of their earliest biological connection can remain.
We are only beginning to understand what that means.
References
Maloney, S., Smith, A., Furst, D. E., Myerson, D., Rupert, K., Evans, P. C. & Nelson, J. L. (1999). Microchimerism of maternal origin persists into adult life. Journal of Clinical Investigation, 104(1), 41–47. doi:10.1172/JCI6611.
Jonsson, A. M., Uzunel, M., Götherström, C., Papadogiannakis, N., & Westgren, M. (2008). Maternal microchimerism in human fetal tissues. American Journal of Obstetrics and Gynaecology, 198(3), 325.e1–325.e6. doi:10.1016/j.ajog.2007.09.047.
Nelson, J. L. (2012). The otherness of self: Microchimerism in health and disease. Trends in Immunology, 33(8), 421–427. doi:10.1016/j.it.2012.03.002.
Kinder, J. M., Stelzer, I. A., Arck, P. C. & Way, S. S. (2017). Immunological implications of pregnancy-induced microchimerism. Nature Reviews Immunology, 17, 483–494. doi:10.1038/nri.2017.38.
Khosrotehrani, K. & Bianchi, D. W. (2005). Multi-lineage potential of fetal cells in maternal tissue: A legacy in reverse. Journal of Cell Science, 118(8), 1559–1563. doi:10.1242/jcs.02332.
Boddy, A. M., Fortunato, A., Wilson Sayres, M., & Aktipis, A. (2015). Fetal microchimerism and maternal health: A review and evolutionary analysis of cooperation and conflict beyond the womb. BioEssays, 37(10), 1106–1118. doi:10.1002/bies.201500059.
Groundbreaking science suggests mothers leave living cells behind, raising fascinating questions about biology, development and human connection.
