Can Post Traumatic Stress Disorder be passed from mother to child? Evidence is growing that the anxiety and mood disorders of PTSD can indeed be passed on from mothers to their offspring. In other words, the environment in which a child is raised - including the environment in the womb - can affect that child's stress response, hard-wiring it for life.

This idea challenges one of the cornerstones of biology - that inheritance is controlled solely by genes. Welcome to the field of "epigenetics" (meaning literally "beyond the genes"), the mechanism by which chemical switches control how the genes actually work, turning them on or off as appropriate and moderating how strongly they act.

Science writer Sue Armstrong explores the phenomenon as it relates to stress with researchers on the front line in Edinburgh and New York, and with the people who are the focus of their studies - survivors of the Holocaust and the collapse of the World Trade Center on 9/11 and their families. She asks what prospects our greater understanding of the physical impact of mental trauma holds for better treatment of PTSD, and whether there are lessons here for addressing the needs of people caught up in the traumatic events of today.

Producer: Ruth Evans

A Ruth Evans production for BBC Radio 4.