Studies on the survivors of the Holocaust, the Rwandan Genocide, World War II, the Vietnam War, and the Civil War all suggest that the trauma of war can have multigenerational impacts on crisis survivors and their descendants. Perhaps the strongest evidence comes from the Dutch Hunger Winter of 1944 to 1945. 

Toward the end of World War II, major cities in the Netherlands faced a five-month food shortage. Daily rations in parts of the Nazi-occupied country were limited to less than 400 calories per day. Researchers, including Roseboom, have since traced the hospital records of thousands of people born around the time of the famine, as well as their children and grandchildren. The landmark studies that emerged from that research have established that the health effects of war are far from over after the ceasefire. 

For starters, people who experienced the Dutch famine in the womb had an increased risk of obesity, breast cancer, and mortality once they became adults decades later. They also had higher rates of cardiovascular disease, smaller brain volumes, and were more responsive to stress.

What’s more, their children—the grandchildren of the people who were pregnant during the famine—were also affected. Even two generations after the famine ended, some newborns whose ancestors were malnourished had smaller body length and more fatty tissue; as children, their parents reported that they had more health issues; and as adults, some had higher body weight and BMI. These intergenerational effects have since been bolstered by research on other famines, like the Great Chinese Famine, which has shown that the children of survivors also have weakened cognitive ability, worse socioeconomic outcomes, and greater susceptibility to infectious diseases like tuberculosis.

“The health effects, the participation on the labor market—those are studies that have been replicated in situations in China, in Biafra, in Ukraine,” said Roseboom. “I feel much more confident that this is something that is biological, that is happening across settings.” 

Precisely how the multigenerational effects of war and famine get transmitted is not yet clear. Most likely, there are several pathways. For instance, trauma could alter parenting, which could, in turn, affect a child’s behavior. Additionally, trauma can be passed on through biology. For example, when a pregnant person is stressed, the defenses in the placenta that normally shield a fetus from its parent’s stress hormones falter. “Marinating” a fetus in a parent’s stress hormones could hinder organ development and affect the baby’s health for the rest of its life, Roseboom said. 

Trauma can even affect future generations before they are conceived. Some scientists believe this occurs through mechanisms called epigenetics, the molecular processes that alter how genes work without changing the DNA itself. These include, for example, DNA methylation, a process in which chemical flags placed along the genome turn genes on or off. Survivors of the Holocaust have DNA methylation changes on a gene associated with stress regulation, and the survivors’ children do, too, suggesting that epigenetics might be heritable (though this remains controversial).

As of now, epigenetic inheritance of trauma remains a hypothesis, and a rather tenuous one in humans. “I think [the evidence] is weak,” said Hasan Khatib, who studies genetics and epigenetics at the University of Wisconsin–Madison. That’s because it is ethically and logistically challenging to study humans. To prove that epigenetic changes are inherited, researchers need to perform controlled experiments that track three to four generations of people—a high, perhaps impossible, bar to reach, Khatib said. 

Still, Khatib thinks that it’s feasible, perhaps even likely, that humans inherit trauma through epigenetics. That’s because a growing body of research has shown that it happens in nonhuman animals. 

His lab, for example, published a paper in 2022 on sheep, which he said is the first solid evidence of epigenetic inheritance in mammals. By feeding pairs of sheep brothers different foods, Khatib’s team showed that diet changes cause epigenetic modifications, which then alter the sheep’s physical traits—in this case, testicle size and muscle growth. The sheep’s sons had those same epigenetic and physical changes, and their grandsons did, too, despite not being directly exposed to the diet change themselves. 

That landmark finding is consistent with prior lab animal studies, including in other mammals like mice. The fact that human observational studies hint that this might be happening in people, too, is enough to raise concerns for Khatib.

“If it’s happening in these animals, then most likely, it’s happening in humans,” Khatib said. “I think this is the most important message of these animal models: that yes, it’s possible that in mammalian species we can inherit trauma and famine.” 

Roseboom is less concerned about the precise mechanisms of intergenerational trauma than she is about minimizing it. Much of her work these days is to protect future generations and ensure they have the best possible environments to develop into their full potential. That includes working with a group of concerned medical experts to improve humanitarian aid in Gaza, as well as providing input during the consultation phase of the newly adopted U.N. Declaration on Future Generations. 

“Creating an environment in which every human being gets a chance to develop to its full potential is something that no one could be against,” Roseboom said.