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A Washington Post-ABC News poll last month revealed that nearly 3 in 4 Americans are worried about a war.

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Despite President Trump's vow that North Korea's continued threats against the United States would be “met with fire and fury and, frankly, power, the likes of which this world has never seen before,” those fears are real.

But why are we so scared?

We, as humans, were hard-wired to err on the side of caution, said Shmuel Lissek, founding director of the ANGST Laboratory at the University of Minnesota.

Evolutionarily speaking, he said, organisms that were overly cautious in the face of low-probability threats were more likely to survive and pass on their genes — and humans inherited those genes.

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“So when there's a very small-probability threat that is of very high intensity, we tend to worry instead of not worry,” Lissek told The Washington Post.

The following Q&A with Lissek has been edited for length and clarity.

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THE POST: Why do people fear war, especially when it is unlikely?

LISSEK: With North Korea, I actually don't know how realistic the fears are. But the fear system evolved to alarm us of survival threats. It's that same alarm system that activates when we're late for a meeting or when we're playing Pac-Man and we're about to get gobbled by the ghost, so it may account for some of why we over-respond to minor threats. Because the system that is responding — the fear system — is the same system that evolved to warn us of survival threats.

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THE POST: What is the No. 1 fear most people have? Why do we fear it?

LISSEK: Because we live in such social worlds, I'd have to say the number-one most common fear is socially related — fear of social evaluation. But aside from that, the fear of death is high up there.

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THE POST: How exactly does the human brain process fear?

LISSEK: The visual stimulus is processed through the light that hits the retina. That is transduced into neural signals and goes to the thalamus, the sensory gateway to the brain, where incoming sensory information is processed in a quick and dirty way. That information then can go right to the amygdala, which is an almond-shaped brain structure deep in the brain that can produce the fear response.

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So — you're walking in a forest. You look down and you see a squiggly line, and you immediately jump back. Initially, you thought it might be a snake, but with further assessment you see it's just a stick and you calm down. In that example, the thalamus is processing that very early visual information, and all it sees is a squiggly line; it can't give you a higher-resolution perception of the image. So at that point, you don't know what it is, but you have a reflex to jump back because it resembles a snake. That's the quick-and-dirty route between the thalamus and the amygdala. But when you look at it more closely and it's a stick — that's the thalamus communicating with the visual cortex, where you get a more finely grained representation of the visual stimulus. The cortex then turns off the amygdala activation.

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THE POST: What is the difference between fear and anxiety?

LISSEK: Fear is defined as an event-related response — you're afraid of something specific. Anxiety is more of a sustained aversive response.

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An example would be in an experiment; if every time you see a blue square you get shocked, you learn to fear the blue square. And that's called fear, and that's tightly linked to the amygdala.

But you also learn to fear the experimental room where the shock occurred. And that's called anxiety, contextual anxiety, because you basically learn to fear the experimental context where you experienced the shock.

So the fear of a North Korean attack would initially start off as fear. It's fear of a discrete threat — the threat of North Korean nuclear threat. It could turn into anxiety if it becomes long-lived.

THE POST: Can you talk about the power that fear has over people? For instance, are people more likely to make certain decisions when they are scared — and is that a response that world leaders, militaries and even terrorists rely on?

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LISSEK: Fear leads you to rely on the easy response as opposed to a more difficult response. You're more likely to sort of fall back on quick and easy information to guide your decisions.

That's one reason in the military, they really focus on training. What the person is supposed to do is really overlearn until it becomes sort of second nature, so that when the person is in a fearful situation, the fear will promote them doing this overlearned behavior. It doesn't take a lot of thinking because they've practiced it so many times.

Fear facilitates overlearned behaviors, or prepotent responses — responses that come easier to the person. But fear also compromises the ability to process things that are not fear-relevant.