Researchers have known since WWII that trauma symptoms could be passed down from generation to generation. This is not to say that they are genetically passed from one generation to another, but that behavior patterns that develop in families as a result of one or more members being traumatized can be handed down for at least two generations. Studies of survivors of the WWII holocaust showed that the symptoms were handed down as far as their grandchildren.
I myself have observed this in my clients. I don't think I will ever forget the year in which I had three middle aged women on my caseload who all appeared to be suffering from "shell shock", yet they had experienced no identifiable trauma. It was not until I talked to the mother of one client who also appeared "shell shocked" that I began to ask different questions and receive very interesting answers. The mother of this client was English and had lived through the bombings by the German army. One parent of the second client was French and had lived through the invasion by the Germans. The father of the third client was an American WWII veteran who suffered severe "shell shock". Suddenly, it all made sense, to both myself and the clients. When I started to suggest my suspicions that their symptoms were not their own, but something they learned from their parents I could see the light go on.