For most of the twentieth century, scientists thought inheritance was simple. You get a string of DNA from your parents. That string sets your traits. And whatever your parents lived through does not get passed to you through biology. The genome was seen as a fixed blueprint, and your surroundings could only bring out what was already written there. That picture started to crack in the 1990s. Over the last thirty years, a field called epigenetics has taken it apart. Epigenetics studies changes in how genes get used that can be passed down without changing the DNA itself. Think of it as a layer of chemical switches sitting on top of your genes, deciding which genes turn on or off in which cells. Those switches respond strongly to what you experience. And a growing pile of evidence says these experience-driven switches can be handed down to the next generation.
The first strong human evidence for inherited trauma came from Rachel Yehuda, who runs the Traumatic Stress Studies Division at the Icahn School of Medicine at Mount Sinai. She studied Holocaust survivors and their grown children. The children of survivors had clearly different cortisol levels and stress-system (HPA axis) regulation than other Jewish people of the same generation whose parents had not lived through the Holocaust. And these children had never gone through the trauma themselves. A 2016 study in Biological Psychiatry found specific chemical marks on the FKBP5 gene, which helps control the stress response, that were statistically linked to a parent's Holocaust exposure in both the parents and the children. The body's trauma-shaped stress wiring appeared to have been passed down biologically in a single generation.
Yehuda studied trauma passed down the generations. Michael Meaney, at McGill University, showed another side of this: how much early care from a mother shapes a baby's stress system. His team watched rat pups raised by mothers who licked and groomed them a lot versus a little. The pups who got lots of care had different chemical marks on the glucocorticoid receptor gene (NR3C1). For the rest of their lives they had a steadier stress response, less anxiety, and sharper thinking than the pups who got little care. The key point: this was epigenetic, not genetic. When pups were switched to foster mothers with a different style, the effect switched too. It was not caused by any difference in their genes.
This matters a lot for understanding what we inherit. The care your great-grandmother got as a baby has a believable biological path to how your own stress response works today. It travels down through each generation of mothers and children, carrying the imprint of how well each was cared for. And how well someone could care for their children was itself shaped by safety, by whether there was enough food, and by community support. So the weight of trauma you carry may not be yours at all. It may be the piled-up cost of every caregiving failure, every war, every famine, every forced separation that happened before you were born. Your nervous system is running programs written long before you arrived.