• It is unlikely that you are entirely an extrovert or an introvert.
  • It’s more likely you are somewhere in the middle, but many of us associate with one side more than the other.
  • Scientific evidence has shown how extroverts and introverts differ in behavior and biology.
  • The way you are is written in your DNA, so it’s unlikely you can change it.

At some point in your life, you’ve probably been described as an extrovert or an introvert. It’s true that many of us place ourselves in one of those two categories – or somewhere in the middle if you’re an ambivert.

These labels were coined in the 1920s by the psychologist Carl Jung. He said the differences between these personality types are essentially down to energy. Extroverted people often receive energy by social interactions, while introverts need time alone to recharge.

But nobody is entirely one or the other; introverts enjoy social occasions, too, and extroverts will enjoy reading a book somewhere quiet from time to time. What is clear is that some people are more on one end of the scale than the other.

Linda Blair, a clinical psychologist, told Business Insider that your level of introversion or extroversion is in your DNA. In other words, you can’t change it.

"It has to do with what's called the need for arousal," she said. "This is not sexual arousal, but it's a need to be stimulated before you act - before you can do what you want to do."

Introverts have a lot of the chemical that makes them feel stimulated; extroverts don't have so much. This is why introverts tend to avoid crowded places or deadlines - things that are likely to put extra pressure on them - because they already have pressure within themselves.

Extroverts don't have enough of this arousal chemical. So to complete things or have a good time, they need to feel like they are ready for action, and seek out places where there's pressure.

"It has nothing to do with confidence; it has to do with pressure and arousal," Blair said. "How extroverted or introverted you are is something you need to wear. You need to work with it, live with it, and use it to your advantage."

German psychologist Hans Eysenck came up with this biological explanation for introverts and extroverts a few decades ago. It essentially means that if an introvert is in a loud restaurant or a crowded office, they will easily get overstimulated and overwhelmed. An extrovert requires these highly stimulating environments to get them to do anything.

Another theory says that it's all about reward systems, discussed in a paper from 1970. It suggests that extrovert brains are more sensitive to rewards, like making someone laugh in a social interaction. Introverts don't seek out these rewards.

Other studies have shown how extroverts pay more attention to human faces than introverts, and how introverts have a higher level of brain function in regions associated with learning, vigilance, and motor control.

There are many ways the brains of introverts and extroverts have been shown to be different. There are also studies that show differences in behavior. For example, extroverts talk more abstractly and introverts more concretely, and extroverts have an advantage with speaking and and reading a new language, while introverts are better at listening to it.

Also, extroverts are more likely to take risks and wear more decorative clothing.

As Blair said, this doesn't necessarily mean extroverts are happier or even more confident. It's simply a different way of living. After all, two people can go to a party and stay there for entirely different motivations.

"To show confidence doesn't mean you have to go out and mix with crowds," she said. "To show confidence, it may be that you choose to be alone. Psychology is all about not what you do but why."