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While we have long known that hereditary genes are responsible for physical attributes and for illnesses or allergies, scientists have discovered that the trauma experienced by one generation can alter genes and those mutations can be passed along to offspring.

Researchers at Mount Sinai hospital and the James J. Peters Veterans Affairs Medical Center, both in New York, studied the genetics of 32 Jewish men and women who had experienced the horrors of persecution during the Nazi regime, either because they had been in a concentration camp, witnessed or experienced torture or were forced into hiding. The children of these individuals, known to have a greater likelihood of stress disorders, were also studied. The researchers then compared their findings to Jewish families who had not been in Europe during that time, and the differences in DNA were noticeable.

The differences had to do with the stress hormone cortisol, which helps the body stabilize after a trauma. Scientific American explains that Holocaust survivors are known to have lower levels of cortisol than their contemporaries, especially survivors with post-traumatic stress disorder (PTSD). Along with low cortisol levels, Holocaust survivors have fewer enzymes that break down the hormone, a response that’s helpful to mitigate the effects of starvation, which many in concentration camps and in hiding experienced. Similarly, the descendants of these individuals also have low levels of cortisol, particularly if their mothers had PTSD. However, this generation was found to have higher than normal levels of the cortisol-busting enzyme, the result of an in-utero process designed to protect the fetus.

Due to this imbalance, descendants of survivors are more vulnerable to PTSD -- which has been previously noted --  and health issues such as obesity and hypertension. Moreover, it seems the next generation would be maladapted to handle starvation themselves.

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Specifically, the researchers looked at a region of a gene that’s not only associated with the regulation of stress hormones but also known to be affected by traumatic experiences. The gene of both the Holocaust survivors and their children showed epigenetic tags -- that is, differences is DNA that result from environmental experiences -- while no tags were found in the control group or their kids.

“The gene changes in the children could only be attributed to Holocaust exposure in the parents,” Rachel Yehuda, who led the research team, told The Guardian. “To our knowledge, this provides the first demonstration of transmission of pre-conception stress effects resulting in epigenetic changes in both the exposed parents and their offspring in humans.”

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The theory that environmental influences like stress and diet can affect the genes of future generations is called epigenetic inheritance. The work of Yehuda and her team is “the clearest example in humans of the transmission of trauma to a child,” The Guardian explains.

Although epigenetic inheritance is considered controversial in the scientific community, the idea that chemical tags from the environment can impact DNA by modifying certain genes that are then passed on has been supported by recent studies. Still unclear, however, is how these tags are passed on. As The Guardian points out, epigenetic tags on reproductive cells are thought to be erased soon after fertilization, but there is research out of Cambridge University that shows how some tags avoid being wiped out.

Yehuda, whose research can be read here, says that the results of the study can teach us “how we adapt to our environment and how we might pass on environmental resilience.”  Still, as Yehuda tells Scientific American, “We are just at the beginning of understanding this.”

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Edition: December 2016

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