Human fears fall within two broad categories: prepared and learned. In other words, we are hardwired to have some fears while others must be learned through personal experience.

Many fears are primarily learned. For instance, a plane flight with horrible turbulence might lead to you having a fear of flying, and a painful dental experience may cause you to fear going to the dentist.

Prepared fears are those that we inherit. Some prepared fears are universal and are of things that generally threatened our survival historically. These include:

• Fear of dangerous animals like snakes, predators, and spiders.
• Fear of contamination and contagion.
• Fear of social status loss.
• Fear of dangerous environmental features like storms or falling from a high place like a cliff.
• Fears of sudden, loud noises and of looming objects (thus our startle response).

What we fear has a genetic component, and different fears can be passed down through generations of a family.

A Startling Mouse Study Shows the Heritability of Fears

Two different studies of mice illustrate the extent to which fears can be passed down genetically.

The first study by researchers at Emory University conditioned mice to avoid the smell of cherry blossoms by giving the mice a mild electric shock along with the smell. The researchers then bred the conditioned mice and found that their pups and even grand pups also feared the cherry blossom aroma. This was the case even if the pups were conceived by in vitro fertilization and raised by a “parent” who did not have an aversion to cherry blossom smell.

Another mouse study came to a similar conclusion. In this second study, researchers placed mice in an open space without any shelter or hiding spots. Some mice were nervous and anxious in the open space, while others behaved normally. When open-space-anxious mice were bred, their offspring were similarly afraid of open spaces, even when raised by fearless foster parents.

Human Phobia Heritability

Like mice, humans can also pass their phobias to their descendants. Over the past few decades, a multitude of studies have focused on the heritability of fears by focusing on adopted children, and identical and fraternal twins reared together or apart.

A 2013 meta-analysis of 13 studies found that the influence of genetics on fears can range between 0 – 71, depending on the type of phobia. In general, fears of animals and of blood, injury, and injections tend to have the highest levels of heritability. So, you can have a family that tends to be scared of snakes and others that can share a fear of needles. Fears that rise to the level of mental illness such as anxiety and phobias have a genetic component as well. For example, agoraphobia has been found to be about 60% inheritable and panic disorder 30% inheritable.

Even fear of going to the dentist can be inherited. An interesting study from 2016 on the fear of dental pain found that genetics explains about 30% of the fear of going to the dentist; the other 70% is rooted in individual dental experience.

The takeaway is that we all have different sensitivity to fears based on our genetics. If you aren’t scared of the dark but your spouse is, realize that there may be a genetic component, and they aren’t just being irrational.