Generational Trauma and Your Genes

The human body is a master of memory. Its ability to carry information through time, and even pass it on to future generations, is a unique one. From an evolutionary perspective, the way we remember and learn from extremely stressful situations is particularly important. However, the scars of traumatic events are more than just skin deep—they affect the molecular makeup of cells, right down to their DNA. Environmental and emotional stressors leave marks on the chemical coating of chromosomes in order to control the expression of genes needed for immediate survival. These changes above the DNA level can then be passed on to future generations. While this may seem like a claim of Lamarckian proportions, the inheritance of stress has been seen in animal experiments, and many scientists believe that this phenomenon is also relevant in humans. Incredibly, the descendants of those who lived through traumatic historical events tend to show the symptoms of their ancestors’ mental turmoil.

The theory that suggests how trauma is passed down from one generation to the next is called the transgenerational transmission of trauma (TTT). TTT proposes that traumatic environments can lead to a predisposition for post-traumatic stress disorder (PTSD) in future generations, since more than 30% of the variance associated with PTSD has a heritable component. One of the first epigentic studies about transmission of trauma was performed on the children of Holocaust survivors. Many of them reported having vivid and terrifying dreams, being unable to cope with daily stress, and falling easily into depressive episodes. Although they themselves had not lived through the horrors of World War II, they seemed to be predisposed to anxiety and depression. They showed distinct signs of being traumatized, especially when compared to their peers and other members of their generation who could be considered “normal” or “healthy.” For these children, inheriting the subconscious mind of a parent who had survived the Holocaust was detrimental to their development in a way that they could never have anticipated.

Calculating exactly how epigenetics—the study of heritable changes in gene expression, rather than in the genetic code—works in humans is complicated. Experimental data is difficult to measure in human subjects because of challenges in tracking and predicting such variables across multiple generations. Model systems are set up using other mammals, as transmission of trauma is not limited to humans. In one study, male rats were conditioned to be fearful of a specific smell, as each time they were exposed to this smell they would endure a short electrical shock. The conditioned rats showed a change in DNA methylation, specifically of the M71 receptor, which is involved in sensing the odorant molecule acetophenone, a molecule used heavily in resins and fragrances. Surprisingly, the resulting changes in DNA methylation were seen not only in the brains of the conditioned rats, but in their sperm as well. Therefore, when they were mated with control females, the offspring in the next generation showed the same changes in the methylation of DNA, and similar fearful behaviors to the odors that their parents were conditioned to be fearful of. Similar results were found when in vitro fertilization was used to implant the experimental sperm in control females, further implying a biological, but non-DNA based, inheritance of the stress from the initial generation of rats. The very same concept can be applied to generations of human beings. The models set up in rats and other mammals provide insight into the way that epigenetics works to pass on the effects of trauma in humans.

The applications of transmission of trauma can often be seen in racial and ethnic minorities. The Native American population, in particular, struggles under the weight of historical trauma, from colonization to the pressures of modern day reservation life. Through the loss of land, language, and culture, as well as disproportionally suffering from abuse and discrimination, the Native American population has faced chronic stressors that overstimulate stress response pathways built into the neural and endocrine systems. As a result, we observe increased DNA methylation of endocrine regulator genes and serotonergic genes, as well as decreased DNA methylation of inflammatory genes in the Native American population. These changes in gene expression lead to many health disparities, including increased rates of psychiatric disorders, drug and alcohol dependence, cardiovascular disease, and obesity. It also leads to a relatively shorter life expectancy. Because the trauma being inflicted on the Native population continues to this day, the effects it has on their epigenetics will continue to play a large part in affecting the physical and mental health of future generations.

The impact of the idea of transgenerational transmission of trauma is immense and far-reaching. It suggests that historical events such as colonization and slavery, through the lasting epigenetic scars they’ve left on minority groups, have played a role in establishing the socioeconomic differences and other health disparities we see in those same marginalized groups today. While the causes of these observed effects are undoubtedly partially social, more and more experts today agree that the epigenetic effects from past trauma have also played an important role in shaping the life views, coping abilities, and overall adaptability of the descendants of marginalized populations. Groups and communities who have been pillaged, exploited, or otherwise disenfranchised are still recovering from these tragic events. A prime example is the “comfort women” of the Japanese Imperial Army during World War II, who were subject to rape and torture, the effects of which are still seen to this day in their descendants and are attributed to epigenetics. On an individual level, a stressor as basic as poverty can result in ingrained, multigenerational damage. When marginalized populations, even in the U.S. and here in our local community, are consistently exposed to disease, poor environmental conditions, unsafe home and work lives, and food insecurity, these factors compound on top of each other and can lead to a host of epigenetic changes, leaving descendants worse off and with less capacity to deal with the same stressors previous generations were exposed to. The result? Generation after generation of unalleviated trauma.

We must remember that the health disparities of those who have faced historical trauma can be passed on to their descendants and will continue to alter the way their body functions, generations after the initial stressor. Our environment, built in part by these historical events, shapes our physical and mental health, and epigenetics can help us understand how the common experiences of marginalized people will continue to affect them and their children. Quicker than ever before, we are learning that the social and economic repercussions of historical wrongs are written into the molecules that build us. Developments in epigenetic research will shed light on these mechanisms, and are eagerly anticipated not only by the victims of today, but also by the children of tomorrow.