The Inheritance of Fear

Fearful MouseRecent research reveals some surprising new insights into what can be inherited. It turns out that fear, or at least fearful behavior, can be passed down by the control of gene expression. This is a very different matter than transmitting a behavior or attitude to the next generation through teaching or observation. Rather than being learned, the fear is transmitted epigenetically.

In a study published in 2014, researchers used electric shock to condition mice to be fearful of the scent of acetophenone (a benign, fruity odor that would not normally trigger fear). The mice exhibited fearful behavior (trembling, cowering) in the presence of the smell, even once the electric shock had been withdrawn, showing that their fear was now a learned behavior.

What was remarkable about this experiment was not the learned fear, but the fact that the fear response was passed on to their offspring for at least two generations. The children and grandchildren of these mice, although they had never been shocked, showed similar trembling and cowering when they smelled acetophenone.

Although one might suspect that this could be transmitted by changes in maternal behavior if the mother was fearful, this was not the case; the fear response was passed down even by male mice.

Not only was the behavioral response passed down, but both the parent mice and their descendants showed changes in their brain structures related to the receptors for acetophenone, and in the area of the brain involved in processing fear. This inheritance was mediated by epigenetic factors (the marking of which genes are turned on or off).

This greatly broadens our understanding of what can be inherited, and what we can pass down to our children. If epigenetic inheritance happens in a similar way in humans, this means that our fears are not just our own baggage, but can burden our descendants as well.


For further reading:

Dias, B. and K. Ressler. (2014). Parental olfactory experience influences behavior and neural structure in subsequent generations. Nature Neuroscience 17, 89–96 (2014) doi:10.1038/nn.3594

Smythies, J., L. Edelstein and V. Ramachandran. (2014). Molecular mechanisms for the inheritance of acquired characteristics – exosomes, microRNA shuttling, fear and stress: Lamarck resurrected? Frontiers in Genetics. 5: Article 133. 3pp. doi:10.3389/fgene.2014.00133.

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