The Sum of All Fears

Mother comforting child. Sarah Wilmer/Gallery Stock

Fear can make you cry, make you shake, make you run. It can make you do craven, cowardly things or stupidly brave things. It can shake you to your core and even alter your biology. Something really terrifying might scare you and your grandchildren.

In a study published recently in Nature Neuroscience, researchers exposed female mice to the scent of cherry blossom while simultaneously subjecting them to a stimulus that induced anxiety. This treatment continued until the mice had a reflexive fear-response to the smell of cherry-blossom.

Two generations of mice born to females who had this conditioned response showed a heightened sensitivity to the cherry-blossom scent - despite having never smelled it before.

The authors of the study, Kerry Ressler and Brian Dias, of Emory University, concluded that the mother's fear of the cherry-blossom scent caused genetic alterations that were passed on to her progeny. In other words, fear is a heritable trait.

This effect doesn't involve altering genes, per se. Instead, the trauma affects the nervous system of the parent, and that change is passed down to the next generation.

This new study bolsters previous research suggesting that fear alters our nervous system and behavior, and it can be passed on to offspring. An older study looked at mothers who were pregnant during the 9/11 attacks in New York City and found that of that group, those who developed post-traumatic stress disorder gave birth to children with abnormally low cortisol levels - a symptom associated with PTSD. Low cortisol levels have also been detected in the adult children of Holocaust survivors with PTSD.

Fear and anxiety disorders, like numerous other mental disorders, can also be an unfortunate genetic trait shared by family members. A 1986 study in Archives of General Psychiatry found that relatives of people who had agoraphobia or a panic disorder were at a higher risk of having a panic disorder themselves.

Although his study indicates that fear can be inherited, Dias noted that it is not always passed along, nor must it be heeded. "You can have these individuals go through life with absolutely no issue whatsoever," Dias observed. "This idea that things are predetermined based on what happened to ancestors is completely false. The system is plastic enough to respond to even more environmental change and be protected. It goes both ways."

The malleable nature of these heritable genetic changes means that it is possible to pull the plug on them. Certain psychotherapies can extinguish the response Dias's mice had toward the cherry-blossom scent, for example, and buffer future generations from a traumatic response to what most of us think of as a sweet smell.