Exposure to violence alters human genetics for future generations

In 1982, the Syrian government laid siege to the city of Hama, an attack that resulted in horrific violence and the deaths of tens of thousands of people and left deep, genetic trauma scars on the lives of survivors.

Decades later, as the country erupted into civil war, the memory of that massacre fueled the resistance against the ruling Assad family.

But beyond its political and social repercussions, the violence may have left a lasting impact in an unexpected place: the DNA of future generations.

Scientists from the University of Florida have found that the grandchildren of women who were pregnant during the Hama siege show genetic marks of that traumatic event – even though they never lived through it themselves.

Passed down through their mothers, these genetic imprints provide some of the first evidence that stress from violence in humans can leave biological signatures that persist across generations.

Violence and genetic trauma

“The idea that trauma and violence can have repercussions into future generations should help people be more empathetic, help policymakers pay more attention to the problem of violence,” said Connie Mulligan, Ph.D., professor of Anthropology at the University of Florida and senior author of the new study.

“It could even help explain some of the seemingly unbreakable intergenerational cycles of abuse and poverty and trauma that we see around the world, including in the U.S.”

Scientists have long known that while life experiences don’t change our genetic code, they can influence how genes function. This process, known as epigenetics, allows our cells to modify genes by adding small chemical markers.

These changes can affect how genes are expressed, often as an adaptive response to stress or environmental factors. Until now, this phenomenon had only been observed in animals.

Mulligan and her team set out to explore whether the same thing could happen in humans. They focused on families who had lived through different waves of violence in Syria, and analyzed three generations of Syrian immigrants in Jordan.

Tracing trauma across generations

To conduct the study, Mulligan collaborated with Rana Dajani, Ph.D., a molecular biologist at Hashemite University in Jordan, and anthropologist Catherine Panter-Brick, Ph.D., of Yale University.

The team examined Syrian families with different experiences of violence. Some had survived the Hama massacre before fleeing to Jordan.

Others had endured the more recent Syrian civil war. A third group had left Syria before 1980, providing a crucial control group that had not been exposed to war.

Dajani, who is the daughter of refugees herself, worked closely with the Syrian immigrant community to gain their trust.

The team collected cheek swabs from 138 people across 48 families, spanning three generations.

“The families want their story told. They want their experiences heard,” Mulligan shared. “I think we worked with every single family who was eligible to participate in the study.”

Back in Florida, Mulligan’s lab analyzed the DNA samples to look for epigenetic markers that might be associated with exposure to violence.

Genetic footprint of violence

The researchers discovered that grandchildren of Hama survivors carried 14 specific genetic modifications that were not found in families who had not experienced the massacre.

These changes suggest that exposure to extreme stress can trigger biological responses that persist for generations.

The study also found 21 genetic modifications in people who had directly lived through violence in Syria.

Another key finding was that individuals exposed to violence while still in their mothers’ wombs showed signs of accelerated epigenetic aging. This kind of biological aging may increase susceptibility to age-related diseases.

Most of these epigenetic changes followed a similar pattern, reinforcing the idea that trauma leaves a genetic signature.

“We think our work is relevant to many forms of violence, not just refugees. Domestic violence, sexual violence, gun violence: all the different kinds of violence we have in the U.S.,” Mulligan said.

“We should study it. We should take it more seriously.”

What this means for the future

It’s still unclear what these epigenetic changes mean for the long-term health of the individuals carrying them.

Some studies suggest that stress-induced genetic modifications may be linked to conditions like diabetes or obesity.

One well-known study on Dutch famine survivors from World War II found that their children carried epigenetic changes associated with increased body weight.

Though more research is needed, these findings could help scientists understand how trauma shapes not just individuals but entire family lineages.

It could also inform policies and interventions aimed at breaking cycles of violence and trauma.

The strength of survivors

While the research highlights the biological scars of war, it also reveals something just as powerful – the resilience of the families who lived through it.

Despite carrying these genetic imprints, they continue to build new lives, raise families, and preserve their culture.

“In the midst of all this violence we can still celebrate their extraordinary resilience. They are living fulfilling, productive lives, having kids, carrying on traditions. They have persevered,” Mulligan said. “That resilience and perseverance is quite possibly a uniquely human trait.”

The full study was published in the journal Scientific Reports.

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