[INTRO ♫].

Everyone is afraid of something. Maybe you're afraid of spiders, or heights, or dogs, or the dark.

And traditionally, we've thought that's because you learned to be afraid. Probably because you had a bad run-in with something at some point. But there's a different idea out there that's been getting more attention lately: the idea that fears aren't just learned... they also can be inherited.

The idea isn't new. Almost 150 years ago, Charles Darwin wrote about his toddler's fear of large zoo animals, which had never hurt the kid in his life. In fact, Darwin noted that many children's fears have nothing to do with their experiences.

So instead, he thought they had to be inherited, and that they were most likely related to real dangers in our evolutionary past. It sounds like a wild idea. Like, how do you inherit something as abstract as fear?

But over the last fifty years, researchers have been studying just how much fears have to do with inheritance and genetics. And their results have been kind of surprising. In this work, they've put a lot of effort into understanding one extreme kind of fear, called a phobia.

Phobias are an intense fear of an object or situation. And while you might throw around that word colloquially, psychologists define phobias as a type of anxiety disorder that typically lasts at least six months. Some common phobias include spiders, getting shots, or public speaking.

And sure, for most of us, these are unpleasant things. But for people with phobias, the fear can be so severe that it interferes with their ability to function. Like, a person with a phobia of dogs can have a hard time just walking down the street.

Phobias aren't uncommon, either. It's estimated that up to 15 percent of people will have one at some point in their life. Until 2002, scientists have generally thought that phobias were learned.

In other words, people developed them as a reaction to something bad happening. But that year, the authors of a literature review proposed that there was another pathway for developing phobias: genetics. Like, the idea is you could be afraid of something you've never come across in your life… just because someone in your past had a bad experience with it.

Which...is a totally bizarre thing to think about. To get a sense of how much genes influence fear, scientists have begun looking at identical twins. Since identical twins have virtually identical DNA, researchers can figure out how heritable a fear is by comparing how often specific phobias appear in identical twins as opposed to other siblings or offspring.

Because even though twins often have lots of similar experiences, they probably don't share the types of experiences that cause phobias—like getting bitten by a dog or falling out of a tree. One 1998 study of 659 pairs of identical and fraternal twins in Australia looked at how many had a fear of blood. The study found that genetics accounted for 71 percent of the variation among those people.

Meaning genetic factors play a pretty big role in determining whether a person has some specific fear. A 2016 study also found that fear of dental work was over 30 percent heritable. So, if you dread going to the dentist, it really might not be your dentist's fault.

Overall, first-degree relatives of people with phobias are more likely to have similar phobias than people with no family history. So, it's pretty clear that phobias are heritable! Which is wild.

But your chances of actually inheriting one seems to vary depending on the phobia itself. Some of that likely has to do with differences in evolutionary pressure. For instance, fear of various animals could have evolved for different reasons.

Like, it makes sense that some people have phobias of dogs or animals that could potentially attack them. But people have phobias of all kinds of other animals. For instance, lots of us are grossed out by things like maggots and slugs, which are pretty unlikely to attack humans.

These phobias seem to have more to do with disgust, which probably evolved to help humans avoid pathogens. So, since these fears evolved through different routes, they likely involve different genes—and that may be part of what makes different fears more or less heritable. The thing is, it's hard to figure out exactly which genes are playing a role, since several different parts of the genome are involved.

So one approach scientists use is called linkage analysis. This method looks at genetic data from extended families where a specific phobia pops up over and over again, and it picks out patterns of genes that tend to be inherited together. If family members who have the phobia also tend to have certain groups of genes, it's likely that the gene that causes the phobia is somewhere in there.

So far, researchers have made some progress in finding the gene regions related to phobias. But they're also pretty sure that phobias are related to other anxiety and panic disorders, which makes it tricky to tease things apart. After all, when phobias run in a family, anxiety disorders often do, too.

The good news is, even though we don't totally understand phobias, we still have pretty good ways of treating them. People who seek help for phobias often use cognitive behavioral therapy, which involves talking through fears and gradually exposing themselves to their phobia. Brain imaging suggests that this kind of therapy disrupts the brain circuits that process fear.

And it's usually pretty effective for treating phobias— no matter whether yours has more to do with nature or nurture. Meanwhile, scientists are still working on understanding these extreme fears. Some are trying to record phobic people's symptoms in as much detail as possible, so they can connect more of the dots between genetic differences and specific fears.

Along the way, they'll also help us understand how our fears connect us not only to our immediate environment but also to our ancestors and our past. Thanks for watching this episode of SciShow Psych! And if you have a fear—one you were born with or one you learned— you can watch this video next to find out how science can help you conquer your fears. [OUTRO ♫].