It seems obvious that we are affected by the histories of our parents and grandparents. After all, everything about our early lives is determined by the people who care for us.
But scientists thought that history didn’t change the genetic makeups we inherit. Now, as we learn more about how genes are expressed, that basic idea is changing.
Compelling evidence of trauma passing through generations has come from a research team at New York’s Mount Sinai hospital led by Rachel Yehuda. The team studied the genes of 32 Jewish men and women who had either been interned in a Nazi concentration camp, witnessed or experienced torture, or had to hide during the Second World War.
It’s true that DNA doesn’t change because of experience. But chemical tags, called “epigenetic tags,” attach themselves to our DNA, switching genes on and off. Environmental influences — such as smoking, diet, and extreme stress — affect those tags, which, the new research suggests, can be passed on to children. The team found the same tags on a stress-related gene between the parents and their children. In a control group of Jewish parents who didn’t experience this kind of trauma and their children, the tags didn’t match.
There are other examples that suggest this process: Girls born to Dutch women who were pregnant during a severe famine at the end of the Second World War turned out to be more at risk for schizophrenia. In another study, researchers found evidence that when males smoke before puberty, years later their adolescent sons are more likely to be obese.
Scientists had thought that the tags disappeared after fertilization. But research by Azim Surani at Cambridge University and colleagues found that some tags slip through. How long the tagging sticks remains unclear.
In mice, scientists have shown that children and even some grandchildren can inherit a specific fear. Scientists at Emory University in Atlanta exposed male mice to the smell of cherry blossoms alongside a small electric shock. The mice eventually shuddered at the smell even if they weren’t shocked. In the next two generations, pups also shuddered at the smell of cherry blossom when they encountered it for the first time — without any shocks. The pups turned out to have more cherry blossom smell receptors in their brains. As predicted, the pups of control-group mice trained to fear other smells, or no smells, didn’t fear the cherry blossoms.
September 18, 2015
Christopher Nystuen, MD, MBA