Can Trauma Travel Across Generations?
What epigenetics can — and cannot — tell us about inherited stress and trauma
Have you ever experienced an intense fear, anxiety or emotional reaction that seemed strangely disproportionate to your current circumstances?
Perhaps you grew up in a relatively safe environment. You may have loving relationships, financial stability and no obvious reason to feel constantly on guard — yet something inside you still reacts as if danger is close.
Sometimes people ask:
“Where did this come from?”
One possible answer may lie not only in our own life experiences, but also in the experiences of previous generations.
Research in epigenetics has raised a fascinating possibility: some effects of environmental stress can influence biological processes in subsequent generations.
This does not mean that we inherit our ancestors' memories in the same way that we remember our own childhood. It also does not mean that every fear or emotional pattern can be traced to a grandparent.
But animal research has demonstrated something remarkable: an experience in one generation can influence behaviour and biological characteristics in later generations, even when those later generations were never directly exposed to the original experience.
One of the most striking examples comes from a series of experiments conducted by Brian G. Dias and Kerry J. Ressler at Emory University.
THE MOUSE EXPERIMENT THAT CHANGED THE CONVERSATION
In a landmark study published in Nature Neuroscience, Dias and Ressler investigated whether a learned fear response in male mice could influence their offspring.
The researchers used a very specific smell: acetophenone, an odorant with a sweet, cherry-blossom-like scent.
Adult male mice were exposed to the smell and simultaneously given mild foot shocks. Through repeated pairings, the mice learned to associate the odor with an aversive experience.
The researchers then allowed these male mice to mate with females that had not undergone the conditioning.
The offspring — the F1 generation — had never experienced the odor-shock pairing themselves.
Yet when the researchers later exposed them to the same odor, these offspring showed increased behavioral sensitivity to acetophenone compared with control animals.
The effect was also observed in the F2 generation, the grandchildren of the originally conditioned male mice.
This was particularly interesting because the response was odor-specific.
The offspring were not simply more fearful of everything.
They showed increased sensitivity to the particular odor associated with the father's conditioning.
That specificity made the findings especially intriguing.
IT WAS NOT JUST BEHAVIOR
The researchers did not stop with behaviour.
They also examined the neurological system involved in detecting the conditioned odor.
Acetophenone activates a particular odorant receptor known as Olfr151. The researchers found an enhanced neuroanatomical representation of the corresponding olfactory pathway in the offspring.
In other words, the offspring's nervous systems showed structural differences in the system involved in detecting the odor their father had been conditioned to fear.
The researchers also examined sperm DNA.
They found reduced DNA methylation at the Olfr151 gene region in sperm from conditioned male mice, as well as in sperm from F1 males who themselves had never been exposed to the odor.
This provided evidence that the observed effects could involve changes transmitted through the paternal germline rather than simply being learned through ordinary social interaction.
This is where the story becomes particularly fascinating.
The experience was not apparently passed on as a literal memory.
Instead, the researchers found evidence that an environmental experience was associated with biological changes in the germline and with altered behavioural and neural characteristics in subsequent generations.
DID THE MICE REALLY “INHERIT A MEMORY”?
The offspring did not demonstrate a conscious memory of an event that happened to their father.
They had never experienced the electric shock.
They had never learned the association themselves.
What the study demonstrated was increased sensitivity to a specific odor, accompanied by changes in the relevant neural pathway and changes in sperm DNA methylation.
So when we talk about “inherited trauma” or “inherited fear,” it is important not to imagine a literal psychological memory being copied from one brain into another.
The biological reality appears to be much more complex.
WHAT ABOUT SOCIAL LEARNING?
Another obvious explanation would be social transmission.
Perhaps the father somehow taught the offspring to fear the odor.
The experimental design attempted to reduce this possibility.
The conditioned male mice had no direct contact with their offspring. The researchers also used cross-fostering and in-vitro fertilization experiments, providing additional evidence that the effects were associated with parental gametes rather than simply with postnatal social learning.
The researchers therefore concluded that the findings supported inheritance through the parental germline.
This is an important part of the study because it moves the discussion beyond the familiar idea of:
“Children learn their parents' fears by watching them.”
They can.
But biological inheritance may provide another pathway through which parental experiences can influence offspring.
TWO WAYS THE PAST MAY REACH THE NEXT GENERATION
When we talk about intergenerational trauma, it is useful to think about at least two broad pathways.
1. Biological pathways
Environmental experiences can affect biological processes.
Epigenetics is one area researchers are investigating.
The term epigenetics refers to biological mechanisms that influence how genes are expressed without changing the underlying DNA sequence itself.
One such mechanism is DNA methylation, which can influence whether particular genes are more or less active.
In the mouse experiments described above, paternal fear conditioning was associated with altered DNA methylation at specific odorant-receptor gene regions in sperm.
The important point is that this does not mean the DNA sequence itself was rewritten.
It means that the regulation of gene activity can be influenced by biological processes associated with environmental experience.
And in this particular animal model, those changes were associated with differences observed in subsequent generations.
2. Social, relational and developmental pathways
There is another pathway that is much easier to observe in humans.
Parents influence their children through relationships.
A parent who has experienced trauma may become highly protective.
Another may become emotionally distant.
Another may constantly anticipate danger.
A parent who grew up with scarcity may struggle to tolerate an empty refrigerator.
Someone who experienced violence may react strongly when their child takes a risk.
Someone who grew up without emotional support may have difficulty recognising or responding to their child's emotional needs.
Children learn from these patterns.
They learn what danger looks like.
They learn what relationships feel like.
They learn how emotions are handled.
They learn whether the world is generally safe or unpredictable.
These processes do not require any genetic or epigenetic mechanism.
They can happen through attachment, modelling, family dynamics, stress, communication and the environment in which a child develops.
This is one reason why researchers studying intergenerational trauma do not reduce the phenomenon to epigenetics alone. Human development involves biological, psychological, relational and environmental influences interacting with one another.
SO IS TRAUMA ACTUALLY INHERITED?
The answer depends on what we mean by “inherited.”
Animal research provides compelling evidence that certain environmental experiences can produce effects in subsequent generations, including through mechanisms involving the germline.
The Dias and Ressler experiments are one important example.
But human beings are considerably more complicated.
We cannot simply take an experiment performed in mice and assume that the same mechanism explains a particular emotional pattern in a human being.
Human studies face major methodological challenges.
For example, researchers have to distinguish between:
genetic inheritance,
possible epigenetic mechanisms,
conditions during pregnancy,
maternal stress,
early childhood environment,
attachment and caregiving,
family behaviour,
socioeconomic circumstances,
cultural influences,
learned behaviour,
and the individual's own later experiences.
These factors can interact throughout development.
A review by Rachel Yehuda and Amy Lehrner concluded that the strongest evidence for transmissible effects has come from animal models, while human research remains much more difficult to interpret. They specifically note that it is not currently possible to attribute intergenerational effects in humans to a single biological or other mechanism.
A later scoping review likewise found substantial interest and evidence concerning biological embedding and epigenetic mechanisms, while emphasising that the human evidence remains an evolving field of research.
So the scientifically responsible position is not:
“Trauma is definitely inherited through epigenetics.”
Nor is it:
“Epigenetics has nothing to do with intergenerational trauma.”
The evidence is more interesting than either extreme.
CAN THESE BIOLOGICAL EFFECTS CHANGE?
This is perhaps one of the most hopeful parts of the research.
In a follow-up study, Dias and colleagues investigated whether the effects observed in the original mouse model could be reversed.
Male mice were first conditioned to fear particular odors.
Some of these animals then underwent extinction training, in which they were repeatedly exposed to the odor without the associated shock.
The researchers found that offspring of the extinguished animals no longer showed the previously observed behavioral sensitivity to the conditioned odor. The enhanced representation of the corresponding olfactory receptors was also absent.
The researchers additionally observed changes in sperm DNA methylation associated with the extinction procedure.
They concluded that extinction-based behavioural strategies could reverse influences of parental stress in the offspring and in the parental germline — at least within this experimental mouse model.
This is a remarkable finding and what the research does demonstrate is that biological effects associated with an environmental experience are not necessarily fixed forever in this animal model.
That opens an important scientific question:
How much of what is biologically shaped by experience can remain flexible throughout life?
WHAT DOES THIS MEAN FOR HUMANS?
Imagine, for example, a family in which previous generations experienced severe famine.
A grandmother who lived through prolonged food scarcity might become extremely anxious whenever food supplies appear low.
Her daughter grows up around this anxiety.
She learns that an empty refrigerator means danger.
She becomes highly controlling around food.
Her own child grows up with a very different material reality — there is plenty of food — but still experiences anxiety whenever the refrigerator becomes empty.
Where does that reaction come from?
There may be many possible explanations.
It could be learned behaviour.
It could be family communication.
It could be attachment and developmental experience.
It could be the individual's own experiences.
There could potentially also be biological contributions.
But we cannot look at that person's reaction and conclude:
“Your grandmother's famine trauma has been epigenetically stored in your genes.”
That would go beyond the evidence.
The example is useful as a way of thinking about the interaction between generations — not as a demonstrated clinical mechanism.
WHAT EPIGENETICS DOES — AND DOES NOT — MEAN
One of the biggest misunderstandings about epigenetics is the idea that our genes are simply destiny.
They are not.
Epigenetic mechanisms are dynamic biological processes involved in regulating gene expression.
But “epigenetic” does not mean:
“Your genes have been permanently programmed.”
And it certainly does not mean:
“Your ancestors' trauma is permanently written into your DNA.”
The science is considerably more nuanced.
The human evidence also does not currently allow us to look at an individual and identify a specific anxiety, addiction, relationship pattern or fear and confidently say:
“This was inherited epigenetically from your ancestors.”
That would require evidence we generally do not have.
What we can say is that researchers are actively investigating how experiences across generations may become biologically embedded, and animal models provide compelling evidence that environmental experiences can sometimes influence subsequent generations through mechanisms involving the germline.
WHAT ABOUT TRAUMA HEALING?
This brings us to an important distinction.
There is a growing body of psychological and somatic work exploring how people can change their relationship with stress, fear, emotional patterns and bodily responses.
Psychotherapy can help people process traumatic experiences.
Somatic approaches can help people become more aware of bodily sensations, defensive responses and emotional states.
Mindfulness practices can develop greater awareness of thoughts, sensations and reactions.
Breathwork can provide an experiential way of exploring breathing, bodily sensations, arousal, attention and emotional experience.
These practices may be meaningful parts of someone's personal process.
But we should be careful about claiming that they “reset inherited trauma in the genes.”
The current evidence does not allow that conclusion.
A more grounded way of looking at it is this:
We may not be able to change what happened before us. But we can influence what happens in us now — and what we pass forward through our relationships, behaviour and environment.
FROM AUTOMATIC PATTERNS TO AWARENESS
This is where the idea of intergenerational trauma becomes personally relevant.
Perhaps you notice that you become extremely anxious when someone you love does not answer your message.
Perhaps you become controlling when someone close to you takes a risk.
Perhaps conflict immediately activates anger.
Perhaps you shut down when emotions become intense.
Perhaps you feel responsible for everyone around you.
Perhaps you constantly expect something bad to happen, even when your life is objectively safe.
Understanding where these patterns may come from can be useful.
A genogram, for example, can help reveal repeating patterns across generations — relationships, losses, addictions, illness, migration, conflict, emotional cut-off and other significant family events.
The goal is not to find someone to blame.
It is to become curious.
What did previous generations have to adapt to?
What strategies helped them survive?
What did they have to suppress?
What was never spoken about?
What patterns continued into the next generation?
And perhaps most importantly:
Which of those patterns still serve me today?
THE BODY CAN BECOME PART OF THE CONVERSATION
Understanding a pattern intellectually is one thing.
Experiencing it in the body is another.
Sometimes we know perfectly well that we are safe, yet our body reacts as though we are not.
The heart accelerates.
The breath changes.
Muscles tighten.
Attention narrows.
We become restless, defensive or withdrawn.
Or we shut down completely.
These reactions can become automatic.
This is one reason approaches that include body awareness can be valuable.
Instead of asking only:
“Why am I like this?”
we can also begin asking:
“What is happening in me right now?”
“What does my body do when this situation occurs?”
“What am I protecting myself from?”
“What happens when I stay present with the sensation instead of immediately reacting to it?”
That does not require believing that trauma is literally “stored in the body” as a substance waiting to be released.
It simply recognises that psychological experiences and bodily responses are deeply interconnected.
WE ARE NOT ONLY WHAT WE INHERITED
Perhaps the most important message is this:
Our history matters. But history is not the same thing as destiny.
We are influenced by biology.
We are influenced by development.
We are influenced by our parents.
We are influenced by culture.
We are influenced by relationships.
We are influenced by our own experiences.
And potentially, as emerging research suggests, some effects of previous generations may become biologically embedded.
But influence is not the same as inevitability.
The research does not give us a simple formula that says:
grandparent's trauma → parent's biology → your fear.
Human beings are far more complex than that.
And that complexity is also where possibility lives.
WHAT WE PASS FORWARD
Every generation receives something from the generations before it.
Some of it may be biological.
Some of it is relational.
Some of it is cultural.
Some of it is conscious.
Much of it may be completely unconscious.
We inherit stories.
We inherit habits.
We inherit ways of relating.
We inherit beliefs about safety, love, money, conflict, success and ourselves.
And perhaps some biological consequences of our ancestors' experiences may also influence us.
But we are not only receivers.
We are also transmitters.
What we do with our own patterns becomes part of the environment in which the next generation develops.
When we become aware of an automatic reaction, we have an opportunity to respond differently.
When we learn to tolerate an emotion instead of immediately passing it on, something changes.
When we repair a relationship instead of repeating an old pattern, something changes.
When we learn to recognise what our body is communicating instead of being controlled by every automatic reaction, something changes.
And when we become curious about where our patterns came from without turning the past into a life sentence, something changes.
THE PAST MAY INFLUENCE THE STARTING POINT
The science of intergenerational trauma and epigenetics is still developing.
Animal research has provided some remarkable evidence that environmental experiences can influence subsequent generations through biological mechanisms, including changes associated with the germline.
Human research is more complex and remains an active area of investigation.
We should therefore be careful with simple promises and simple explanations.
But we also don't need to dismiss the question.
The possibility that experiences can leave biological traces that influence future generations is scientifically fascinating.
And the possibility that some of these effects may remain flexible is equally important.
Perhaps the most useful question is therefore not:
“Am I carrying my ancestors' trauma?”
but:
“What patterns have reached me — and what will I choose to pass forward?”
We cannot change where our story began.
But we can become more conscious of the patterns we are carrying.
And sometimes, that is where a different future begins.
REFERENCES & FURTHER READING
Dias, B. G., & Ressler, K. J. (2014). Parental olfactory experience influences behavior and neural structure in subsequent generations. Nature Neuroscience, 17, 89–96. DOI: 10.1038/nn.3594.
Aoued, H. S., et al. (2019). Reversing Behavioral, Neuroanatomical, and Germline Influences of Intergenerational Stress. Biological Psychiatry, 85(3), 248–256. DOI: 10.1016/j.biopsych.2018.07.028.
Yehuda, R., & Lehrner, A. (2018). Intergenerational transmission of trauma effects: putative role of epigenetic mechanisms. World Psychiatry, 17(3), 243–257. DOI: 10.1002/wps.20568.
Zhou, Y., & Ryan, J. (2023). Biological Embedding of Early-Life Adversity and a Scoping Review of the Evidence for Intergenerational Epigenetic Transmission of Stress and Trauma in Humans.