This reads like something out of a science fiction novel. But its true. New studies are now showing that trauma may be passed down in our genes through molecular memory and epigenetic changes. Ok now let me say that in English that everyone understands. It seems that traumatic experiences endured by our mother and father may also be reverberated or passed down in the genes so that it affects future generations. The idea is that trauma can leave a “chemical signature”, on a person’s genes, which then is passed down to subsequent generations. There is not a mutation present here. It alters the EXPRESSION of the gene by turning it on or off and this affects the subsequent functioning protein that the gene is coding for. Again, this is not genetic. It is epigenetic.
So trauma can possibly change the expression of our genes, but how does that appear in real life and how does this impact us and our children? That remains to be seen and future, large scale studies are needed. But lets take a closer look at what we do know so far.
There are a few animal studies that corroborate trans-generational trauma (trauma that can be passed down from generation to generation) and the scientific community is aiming to validate this in humans as well.
In one study, researchers at Emory University found that fear could be passed through generations in mice. Male mice were trained to fear the smell of cherry blossoms by pairing the smell with an unpleasant electric shock. The mice quickly learned to fear the cherry blossom smell alone. The offspring of these mice ended up having the same fear to the cherry blossom smell, despite never having encountered them on their own. Even the offspring of their offspring displayed the fear! “The researchers propose that DNA methylation — a reversible chemical modification to DNA that typically blocks transcription of a gene without altering its sequence — explains the inherited effect. In the fearful mice, the “smell” gene of sperm cells had fewer methylation marks, which seemed to affect their behavior. (1)
In another study lead by University of Maryland researcher Dr, Tracy Bale, researchers raised male mice pups in what would be considered a traumatic environment, which included leaving the lights on at night, restraining them, or tilting their cage for extended periods of time. This upbringing changes the subsequent behavior of those male mice’s genes in a way that alters how they manage surges of stress hormones. Researchers found their offspring were more numb to the affects of stress hormones. How does this happen? The sperm of the stressed mice end up producing more of a certain molecule called microRNA and this may affect the stress response and mental health of their offspring.
Researchers revealed that an uptick in stress hormones at the initial insult, known as glucocorticoids, triggers changes to proteins around DNA within cells lining tubules of the epididymis, a duct through which sperm passes on its way from the testes. These changes ultimately end up producing more microRNA that are released and encourage the sperm to mature. According to Dr Bale, the microRNA vesicles influence the sperm right before ejaculation and can effectively carry meaningful changes to the final product. (2)
“[The vesicles] interact with the sperm and then the sperm carry those differences to the egg at fertilization,” said Bale, adding that microRNAs in the sperm appear to affect single-stranded genetic material stored in the egg, affecting development and resulting in offspring that are less reactive to stress.”
AND these results are reproducible.
In another study in roundworms, scientists show memories were passed down 14 generations! The European Molecular Biology Organisation (EMBO) in Spain took genetically engineered nematode worms that carry a gene mutated for a fluorescent protein. When activated, this gene made the worms glow under ultraviolet light. Then, they switched things up for the nematodes by changing the temperature of their containers. When the team kept nematodes fairly cool, they measured low activity of the transgene – which meant the worms glowed less brightly.
But by moving the worms to a warmer climate, they suddenly lit up brightly again like Christmas trees, which meant the fluorescence gene had become much more active. This time when the worms were moved back to the cooler environment to see what would happen, they surprisingly continued to glow brightly. This suggests they were retaining some sort of “environmental memory” of the warmer climate. What’s even more shocking is that the memory was passed onto the offspring for 7 generations, none of whom had experienced the warmer climate personally. This is a great example of epigenetic change over time.
There are many more animal studies but some have been debunked while others are at the very least, questioned by the medical community. But what we do know is this–at least in animal studies, the current environment of the father at the time of conception seems to affect the hormonal systems and behaviors of their offspring and possible generations thereafter.
What do we have for human studies and trans-generational memory?
One example of memory passed down in humans was a study done over a decade ago. It showed that children exposed in utero to famine conditions in Dutch countryside had a higher predisposition to obesity and glucose intolerance. The offspring of those who survived the famine all ended up having a similar chemical signature on their DNA. It’s pretty mind-blowing that our genes “remembered” that trauma of starvation and therefore, could possibly predispose us to difficulty losing weight as a protective mechanism. This one study single-handedly kicked off interest in epigenetics.
Moreover, the studies on mice concerning stress seem to be somewhat accurate for humans too. Remember how some of the studies in mice showed gene changes through differences in methylation? Many of the studies reviewed on humans found that the glucocorticoid receptor (NR3C1) gene (the gene which makes stress hormones) is associated with methylation changes, just like some of the mice studies. For instance, maternal exposure to intimate partner violence during pregnancy was associated with increased NR3C1 DNA methylation in teenage children . Maternal exposure to war violence or rape during pregnancy was associated with increased methylation in the NR3C1 promoter region in newborns (4). But we still are not sure how this translates into the expression of the physical body as an adult.
A study in 2018 published in Brain Sciences “found an accumulating amount of evidence of an enduring effect of trauma exposure to be passed to offspring trans-generationally via the epigenetic inheritance mechanism of DNA methylation alterations and has the capacity to change the expression of genes and the metabolome” (5)
However, there are very few studies on humans that show epigenetic changes that are passed on through generations.
A 2014 study showed that sons (but not daughters) of fathers who began smoking before the age of 11, when they began to produce sperm, were more obese than those whose fathers started smoking later, after their sperm had already formed.(6)
But the results continue to be divided.
In a study in the Proceedings of the National Academy of Sciences (7) by researchers from the National Bureau of Economic Research in 2018, it was found that the sons of Union Army soldiers who endured grueling conditions as prisoners of war were more than 1.2 times more likely to die young than the sons of soldiers who were not prisoners. Said differently, severe paternal hardship as a prisoner of war (POW) led to high mortality among sons, but not daughters, born after the war who survived to the age of 45. What is most interesting is that this trauma to the offspring linked to paternal POW can be countered by adequate maternal nutrition during the second trimester. This is all most consistent with epigenetic explanations.
Studies have also elucidated that severe post-traumatic stress disorder or PTSD and trauma may be passed through generation after generation. Some studies have claimed that holocaust survivors have children who respond to stress differently (less stress response to cortisol). However, critics believe that these headlines are being sensationalized without adequate science to back up the findings
So as it remains currently, although there is great promise and hype, there has only been small breakthroughs in paracrine, microRNA and epigenetic alterations linked to maternal and paternal trauma exposure, PTSD and trans-generational inheritance. Studies have not yet conclusively demonstrated epigenetic transmission of trauma effects in humans, although I have to admit, I’m pretty excited. I mean, studies are showing that sperm can CHANGE their packaging based on their current environment right before they fertilize an egg! From my standpoint, there’s a fairly good chance that our ancestors’ behaviors and experiences may shape who we are today in ways we could’ve never imagined.
Think of the relevance this holds for certain minorities around the world.
1. & Ressler, K. J. Nature Neurosci. http://dx.doi.org/10.1038/nn.3594 (2013).
3. Radtke K.M., Ruf M., Gunter H.M., Dohrmann K., Schauer M., Meyer A., Elbert T. Transgenerational impact of intimate partner violence on methylation in the promoter of the glucocorticoid receptor. Transl. Psychiatry. 2011;1:e21. doi: 10.1038/tp.2011.21. [PMC free article] [PubMed] [CrossRef] [Google Scholar]
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6. Northstone, Kate: Golding, Jean; Smith, George; Miller, Laura L; Pembrey, Marcus. Prepubertal start of father’s smoking and increased body fat in his sons: further characterisation of paternal transgenerational responses. European Journal of Human Genetics volume 22, pages 1382–1386 (2014)
7. Intergenerational transmission of paternal trauma among US Civil War ex-POWs.