• The final major biological difference is the level of background noise that is inside the introvert’s or extrovert’s mind. To put it plainly, introverts have perpetual static and chatter in their mind, which makes them more liable to overwhelm, analysis, rumination, and retreating to solitude. Hans Eysenck proved a corollary of this with his lemon juice test, in which he found that introverts were generally easier to arouse and become alert.
• All of these differences make it seem like introverts are somewhat less predisposed to survival than extroverts. But the opposite is true; zoological studies have found that there are generally two groups in a society, rovers and sitters, and both are needed because they complement each other. Rovers are extroverts—thrill-seekers and out and about. Sitters are introverts—planners, analyzers, and operating in the background. That is to say, introverts keep themselves and the people around them safer than they might be otherwise.
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Hans Eysenck, the researcher that coined the term ambivert, also found that the brains of different personality types had different baseline levels of cortical arousal—the degree to which our minds are in motion and being stimulated, the level of static perpetually present.
High cortical arousal is perhaps best illustrated by imagining your brain activity when you are unable to sleep.
Sometimes this is positive, and other times it is negative.
Think of the brain like a power generator.
Some are more active than others, which means they run at a higher level for no reason.
Suppose a power generator runs at a level of 500 watts while on standby, while another power generator runs at a level of 50 watts while on standby.
What accounts for this difference?
It’s unclear, and there is no clear reason other than the fact that these power generators are designed according to different blueprints.top functioning at a level of:
Eysenck found that the brain of an introvert has a higher level of baseline arousal; it’s constantly busy and never turns off.
For them, this is negative.
The introvert is the power generator that runs at a background level of 500 watts, which means it is always active, alert, and analyzing.o much closer to the limit of:
In fact, it has to be careful of how much stimulation it gets, otherwise it just might shut down from external interference and overloading the circuits.
For the introvert, this can be too much social interaction, conversation, or the presence of people in general. Extroverts, on the other hand, can handle being surrounded by people and loud noises.
They’re only starting at 50 watts, after all.
They don’t need time to unplug and recharge alone after social interactions.
Instead, they are only minimally stimulated, so they are actively seeking out highly stimulating environments to raise their arousal levels.
Moreover, it takes a larger number of stimuli because of their blunted reaction to dopamine.
Make no mistake:
it’s not necessarily a positive aspect for the brain of an introvert to have a greater baseline level of arousal.
It doesn’t mean they are constantly at a higher level of cognitive performance.
Would you say that someone who is more easily stressed out is lucky and should be characterized as smarter?
No—you would see it for what it is: a trait that has both negative and positive connotations.
This also doesn’t mean extroverts aren’t aware of their surroundings and capable of constant thought.
What does this difference in baseline arousal mean for us?
Sometimes, we just can’t help how we are wired.
Introverts have to pace themselves a bit more and make sure to keep their average usage rate lower because they are starting from a different point than extroverts are.
As always, alone time is one of the best tools for regulating their levels of arousal and ensuring they don’t become overwhelming.
Extroverts have more leeway in social situations, which leads them to enjoy those situations more.
The reticular activating system (RAS) acts in a way that confirms Eysenck’s findings in a major way.
The RAS is responsible for regulating your levels of alertness and arousal.
Assuming all humans need some type of arousal in their day, it explains why extroverts tend to act out or look for conversation with other people.
On the other hand, introverts have a high level of activity in the RAS.
They don’t require any other stimulation to keep them going.
Studies have also found that the RAS can measure your baseline levels of arousal and even predict how much of an introvert or extrovert you would perceive yourself to be.
If you have an active RAS, you are likely to respond in a greater way to external stimuli.
That sounds curiously like the description of the introvert we have talked about multiple times in this book.
Eysenck devised what was imaginatively called the lemon juice test.
The theory was that if someone’s RAS was more sensitive and had a higher amount of activity, lemon juice squirted onto someone’s tongue would produce more saliva than someone who had a less sensitive RAS. In other words, the more saliva someone produces, the more likely they are an introvert because of an increased level of arousal and reaction to external stimuli.
As Eysenck predicted, the introverts in the studies produced 50% more saliva than the extroverts.
Introverts might just have a higher sensitivity to everything that comes their way.
The fact that something as small as drops of lemon juice can trigger massively different levels of reaction demonstrates the significance of baseline levels of arousal.
A drop of lemon juice is nothing compared to a wild, raging party and meeting 20 new people.
This puts the introvert in a totally different and more sympathetic light.
What the extrovert might barely feel, the introvert might feel at a magnification of ×100.
Just think of the introvert and extrovert at a party.
A simple conversation is going to have a bigger impact on the introvert because of their increased level of baseline arousal.
It functions on the same principle as the lemon juice.
Extroverts require a much larger stimulus to react and therefore would require far more lemon juice to produce the same amount of saliva.
Another helpful analogy is to compare extroverts to a steel wall and introverts to a glass window.
Obviously, it is going to take less impact to break the glass window, and thus, introverts are more sensitive because of their inherent build.
How Did Introverts Survive Evolution?
In our fast-paced, competitive society, it’s easy to imagine that the social fragility of introverts is a fatal character flaw.
These biological differences can lead to a vision of an early hominid that was fearful, easily spooked, and generally a pushover.
This translates into the modern day as well.
Here’s the thinking:
extroverts get all the toys because they’re able to interact with other people more successfully and are more aggressive about getting what they want.
Introverts, on the other hand, are perceived as being shy and less likely to enjoy the advantages of the world because they don’t always mix with others.
Growing tired of social interaction is so undesirable as a trait that pharmaceutical companies produce drugs for people to conquer it.
This thinking might cause those of us who muse about Darwinism and survival of the fittest to wonder, “If introverts are resistant or unable to be assertive about getting the spoils, how did they make it this far on earth?
They should have been swallowed up by T. Rex long ago!” But science suggests that not only did introverts’ tendencies not get them killed, but they may have helped them survive.
Biologists who specialize in evolutionary theory divide the animal kingdom into two categories: “rovers” and “sitters.” These labels correspond to an animal’s tendencies in regard to moving about in the world.
Rovers are the bold ones.
They’re eager to examine the immediate landscape and explore the outer edges of their environment.
Rovers are the ones who go out and kill for food and bring it back to their households.
They’re the type-As in their circles or groups.
They go seize what they want.
Sitters, on the other hand, are in no hurry to venture out of their caves.
They patiently wait until there’s really nothing going on outside before they leave.
They’re content to sit at home and let the rovers bring home take-out food.
Sitters couldn’t care less if they don’t jump all over the savannah, participate in hunting, or get a spot on Animal Planet.
Let the rovers get the spotlight.
So in our rush to toss out labels in the animal kingdom, we’d call the rovers more likely to be bold about entering society and therefore more likely to survive and adapt than the reclusive, overcautious sitters.
But here’s the thing:
rovers are also the first in line to get savagely eaten.
Sure, they may be bold and unafraid to walk freely in the wild.
But that leaves them open to predators who have been hiding in the background, patiently waiting for some poor roving sucker to cross their line of vision.
When that happens, the rover is history.
Meanwhile, as the rover is being turned into a main-course meal with a side vegetable, the sitter is relaxation in their home, safe, sound, and not somebody else’s dinner.
Hopefully it’s not too hard to see how this relationship translates into human extroverts and introverts.
Extroverts have more fun (or at least look like they are), are friendlier, and take more risks, whereas introverts act out of an abundance of caution.
They don’t jump into new situations head-first.
They may appear to be sticks in the mud because they’re not aggressive about socializing.
This keeps them safe and secure and out of harm’s way.