We know that stressful experiences can have negative biological repercussions — not just for the people who experience the stress, but also for their children. Now, there's some evidence that this transfer of stress effects might not just be due to a simple case of PTSD changing the way you raise/treat your kids. In a study that's inspired both deep skepticism and jaw-dropping awe (both with good reason) scientists were able to train male mice to fear a specific smell — and then observe that same fear/stress response to the smell in the mice's children and grandchildren. This, despite the fact that the younger generations never had contact with their trained fathers. These results are crazy enough that you shouldn't take them as gospel. But they are hella interesting and will definitely lead to a lot more research as other scientists attempt to replicate them.