Can trauma, stress, and even nightmares be passed down from generation to generation?

Scientists say yes. A number of research finds that those who have been traumatized around the time of conception can pass on a DNA code to their offspring that results in a higher vulnerability to stress in their molecules, neurons, cells, and genes. Furthermore, this gene expression—a chemical coating upon the chromosomes—is strong enough to be passed on to a third generation, which means grandchildren have "a kind of biological memory" of what their grandparents experienced, according to studies.