Fight, Flight, Survive: What Is Fear and Why Is It Useful?

It’s dark outside. You’re sitting alone at home in silence when suddenly you hear a loud bang in the next room. Your breathing quickens. Your heart starts pounding. Your muscles tense up. A split second later, you realize that a branch from the neighbor’s tree hit the window because of the strong wind. You’re safe. But for a moment, you were scared and reacted as if your life was in danger—your body triggered the “fight or flight” response, which is crucial for the survival of any living creature.

What Is Fear?

Fear is a chain reaction in the brain that starts with a stressful stimulus and ends with the release of chemicals that cause rapid heartbeat, quickened breathing, and fill your muscles with energy (this is also known as the “fight or flight” response). The stimulus can be anything: a spider in the bathroom, an aggressive stranger on the street, a room full of people waiting for your speech, or a sudden loud bang at your window.

More than 100 billion nerve cells in the brain form a complex communication network that is the starting point for everything we feel, think, and do. Some of these messages lead to conscious thoughts and actions, while others trigger automatic responses.

The fear response is almost entirely automatic: we don’t consciously initiate it.

Since brain cells are constantly transmitting information and triggering reactions, dozens of brain regions are directly or indirectly involved in fear. The following parts of the brain play a central role in this process:

• Thalamus – decides where to send incoming sensory data from the eyes, ears, mouth, and skin.
• Sensory cortex – interprets the sensory data received.
• Hippocampus – stores and retrieves conscious memories, processes sets of stimuli to establish context.
• Amygdala – decodes emotions, identifies possible threats, stores fear memories.
• Hypothalamus – activates the “fight or flight” response.

So, the process of creating fear starts with a frightening stimulus and ends with the “fight or flight” response. However, between point A and point B, there are two possible pathways for what happens next, and both processes occur in parallel.

The first pathway is a fast reaction, whose main idea is “better safe than sorry.” Yes, something hit your window, and it could be the wind, but it could also be a burglar trying to break in. It’s much less dangerous to assume it’s a burglar and then calm down when you realize it was just the wind, than to assume it’s the wind and realize too late that someone actually broke into your home. This is what happens first: the brain instantly triggers a quick reaction, making you assume the worst-case scenario, and then the second, slower reaction kicks in to clarify the context. You could say it “asks” clarifying questions. The fast process looks like this:

• The bang at the window is the stimulus. As soon as you hear the sound, your brain sends this sensory data to the thalamus. At this stage, the thalamus doesn’t know if the signals indicate danger or not, but since they might, it forwards the information to the amygdala. The amygdala receives the nerve impulses and takes action to protect you: it tells the hypothalamus to initiate the “fight or flight” response, which could save your life if what you heard really is an intruder.

The slower reaction is much more thoughtful: while the first triggers a fear response just in case, the second considers all the options. The slow process looks like this:

• When your ears hear the sound, they send this information to the thalamus. The thalamus sends it to the sensory cortex, where it’s interpreted for meaning. The sensory cortex identifies several possible interpretations and passes them to the hippocampus to establish context. The hippocampus asks: “Have I seen this particular stimulus before? If so, what did it mean last time? What else could give me a clue?” While you were quietly sitting at home, the hippocampus might have picked up other data, like the sound of strong wind outside. Taking this into account, the hippocampus determines that the bang at the window is most likely caused by the wind. It sends a message to the amygdala that there’s no danger, and the amygdala, in turn, tells the hypothalamus to turn off the “fight or flight” response.

The sensory data about the window—the stimulus—travels both pathways at the same time, but the second reaction takes longer than the first. That’s why we experience a moment of terror before we calm down.

But regardless of which reaction we’re talking about, all roads lead to the hypothalamus: this part of the brain controls the ancient survival response. To trigger the “fight or flight” reaction, the hypothalamus activates two systems: the sympathetic nervous system and the adrenal-cortical system. The sympathetic nervous system uses nerve pathways to initiate reactions in the body, while the adrenal-cortical system uses the bloodstream.

When the hypothalamus tells the sympathetic nervous system to turn on, the overall effect is that the body speeds up, tenses, and becomes very alert, releasing adrenaline and noradrenaline. If there’s a burglar at the window, you’ll need to act fast. At the same time, the hypothalamus releases corticotropin-releasing hormone (CRH) into the pituitary gland, activating the adrenal-cortical system. The pituitary gland (the main endocrine gland) secretes ACTH (adrenocorticotropic hormone). ACTH travels through the bloodstream and eventually reaches the adrenal cortex, where it triggers the release of about 30 different hormones that prepare the body to fight the threat.

The sudden rush of adrenaline, norepinephrine, and dozens of other hormones causes physiological changes in the body, including:

• increased heart rate and blood pressure;
• dilated pupils so the eyes can take in as much light as possible;
• narrowing of blood vessels in the skin to direct more blood to major muscle groups (this is why people sometimes get chills when they’re scared);
• increased blood glucose levels;
• muscle tension, as muscles get energy from adrenaline and glucose (hence goosebumps: tiny muscles attached to each hair tense up, making the hairs stand on end);
• relaxation of smooth muscles to allow more oxygen into the lungs;
• shutting down nonessential systems (like digestion and the immune system) to give more energy to emergency functions;
• trouble focusing on small tasks (the brain is focused solely on the big picture of what’s happening).

All these physical reactions are designed to help us survive a dangerous situation and prepare us either to run away or to fight for our lives. Fear is an instinct that every animal possesses.

Why Do We Feel Fear?

If we weren’t afraid, we wouldn’t live long: we’d walk right into traffic or pick up poisonous snakes. The purpose of fear in humans—and in all animals—is to promote survival. Over the course of human evolution, people who were afraid of the right things survived to pass on their genes, so the trait of fear and the response to it were selected by evolution as useful.

Why do people make a particular facial expression when they’re scared? Charles Darwin said it’s the result of instinctive muscle tension caused by an evolved fear response. To prove his point, he went to the reptile house at the London Zoo. Trying to stay completely calm, he stood as close as possible to the glass, and a viper lunged at him from the other side. Every time it got too close, Darwin flinched and jumped back.

Most of us no longer fight for our lives in the wild, but fear is far from an outdated instinct. Today, it serves the same purpose as it did in the past, when we might have run into a wild animal while foraging. The modern decision not to take a shortcut through a deserted yard at night is based on rational fear that promotes survival. Only the stimuli have changed, but today we’re in just as much danger as we were hundreds of years ago, and our fear protects us just as it did back then.

In addition to instinct, humans have other factors related to fear. For example, people have the “gift of anticipation”: we expect terrible things that might happen, things we’ve heard about, read about, or seen on TV. Most of us have never experienced a plane crash, but that doesn’t stop us from being afraid while sitting on a plane. The anticipation of a frightening stimulus can trigger the same reaction as actually experiencing it—this is also an evolutionary advantage. People who, feeling rain, expected lightning and stayed in the cave had a better chance of not being struck by thousands of volts of electricity.

Common Fears

Some studies show that people may be genetically predisposed to fear certain dangerous things, such as spiders, snakes, and rats—animals that once posed a real threat to humans because they were poisonous or carried diseases.

But while there may be “universal fears,” there are also fears specific to individuals, communities, regions, or even cultures. Someone who grew up in a city is probably more afraid of being robbed than someone who spent most of their life in a village, and people living in earthquake-prone areas are understandably afraid of earthquakes. What we fear says a lot about our life experience. There’s even a phobia called taijin kyofusho, considered a “culturally specific phobia in Japan”—it’s the “fear of offending others through excessive modesty or displays of respect.” The complex social rituals that are part of life in Japan have led to a fear unique to the Japanese.

How to Cope with Fear

Feeling fear from time to time is a normal part of life, but living with chronic fear can be physically and emotionally draining. Living with a constantly weakened immune response and high blood pressure leads to illness, and avoiding everyday activities because of fear doesn’t make life fulfilling.

Uncertainty is a key component of fear, so if there’s something you’re afraid to try because it seems scary or difficult, start small and work step by step. Gradual exposure to the frightening object makes it more manageable. It also helps to find someone who isn’t afraid and spend time with them. Take someone with you when you try to overcome your fear—it’ll be much easier. Finally, talk about it (sharing your fear out loud can make it less scary) and don’t be afraid to seek help. Fear is a complex emotion, and if you’re having trouble overcoming it on your own, reach out to a professional who can help.