The debate between nature and nurture is almost as old as the chicken versus the egg.

What is more likely to influence how we

actually develop a personality and how we behave?

Is it the genes that we're born with? or, Are we taught and molded by our parents,

our school teachers, and our culture?

Behaviorist and humanist perspectives take on the nurture side of the debate.

They believe that you can become anyone you want

to with the right environment and the right stimuli.

But let's talk about the nature side,

the biological perspective of personality gives us more questions and answers

to think about as we reflect on our own personalities.

So, first off, I need to talk about something called evolutionary psychology.

Some of the earliest and most famous examples of the biological

perspective is ideas that were brought forth by Charles Darwin.

Darwin was the father of evolutionary psychology.

Now, his theories of evolution suggested that species evolve over time,

small adaptations happen throughout time that turn into species evolving.

He said that members of the same species with stronger traits were

more likely to reproduce and pass those traits onto the offspring.

Now,

evolution doesn't just favor physical traits like taller

people or people who are faster at swimming.

This theory actually suggests that our personality comes from

an environment that favored certain traits over time.

For example, in places where it's really hot,

people have more melanin in places where it's really cold,

people usually have less melanin.

Now, if the environment can change our physical biology,

who's to say that it can't change our cognitive biology and our personality?

So let's talk a little bit about the genes and the brain.

So where do biologists find our traits?

Well, they would say they find them in our genes and our genetics in our brain.

To test this theory, psychologists have studied identical twins.

Now, identical twins always have the same genes, the same genetic makeup,

but those who are separated at birth will be grown in two different environments.

So when scientists look at their similarities and differences,

they can get a really good idea on what is

actually nature and what is actually nurture from the environment.

So using these identical twin studies,

we can actually start to narrow down what

percentage of traits may be due to genetics.

If a trait can be passed down through a gene, we call it heritable.

You might have heard this word before.

Heritability is a variance between multiple people that

can be accounted for by genetic differences.

Now, basically that is a lot of words to say that with research,

we can tell how much of someone's behavior is really from

their genes and how much of it is from their environment.

In short, we can tell if something is nature or nurture.

Now,

some of our personality traits are influenced by

genes and some of them are actually not.

For example, according to the identical twin personality research,

some of these traits have been correlated to be influenced by genetics.

For example, social closeness is only 15

percent due to your genetics.

So a lot more of it has to do with the

environment that you were raised in. Achievement orientation is 38%.

Traditionalism is 59% which means it's about half and half nature and

nurture and imagination being 74% is mostly due to your genes.

One example of a gene that can influence a trait is the dopamine four receptor gene.

Now,

this gene has actually been connected with the trait

of thrill seeking and people enjoying something called novelty.

Now, novelty basically means new and fun and exciting ideas.

So there's a perfect example that a gene can actually cause a personality trait.

Although even though that term isn't right,

we don't say that they caused a trait and I'll explain that in the rest of this video.

Take the Jim twins as a real life example, that traits can be passed via genes.

Jim Lewis and Jim Springer were identical twins at birth.

They were separated though. They finally connected at the age of

39 and they quickly made headlines for their very similar lives.

This is actually kind of weird.

Both were the same height,

basically the same weight and they had very similar habits.

What's even weirder is that both of these twins

had both been married twice, and the women that they married had the same first names;

their first wife's name was Linda, and the second wife's name was Betty.

Now, they also drove the same car.

Now you might be wondering how crazy are these similarities? It's unpredictable.

Well, not everything about the Jim twins was similar,

they wore different hairstyles and they chose different professions.

But the story of the Jim twins and other studies of identical twins

show that our genes may be very closely correlated with our personality traits

and the decisions that we make. Other studies show just how important our

brain chemistry is to our reactions and how we actually assess our environment.

Different parts of the brain, so called, go off whenever we make decisions.

So the stronger that these responses are,

the more likely a person is to hold certain personality traits.

For example, as I'll talk about in future videos,

people who are highly neurotic also have stronger responses and their amygdala,

the part of the brain that is responsible for reacting to fear.

So, biological theorists of personality,

they believe that by changing the size of your amygdala, theoretically,

we could change how neurotic you are—that, is if you

can actually control the size of a particular brain section.

Now, the physical structure of the brain may also be linked to personality traits.

Studies from Cambridge University revealed a positive correlation between

openness and more folding in the prefrontal cortices.

So next, I'd like to talk about changes in brain chemistry.

So as we move on,

it is really easy to write off the nature theory as something that you cannot change.

Many people believe that if you're born with an aggressive temperament,

you really can't do much to change your

genes and your tendencies to actually be aggressive.

However, that's not, not exactly true.

Our brains have the potential to change

and actually cause our personality to change.

One famous example of this is the case of that of Phineas Gauge.

Phineas Gauge was a railroad worker in the eighteen forties.

Well, while working, he actually suffered a serious accident,

an explosion sent a tamping iron straight into his head

and it damaged a very large part of his brain.

He actually, I think should have been dead, but he survived.

He somehow survived the horrific accident but not without consequences.

They sent him to the hospital and got him fixed up. When Gauge

came back to work after his accident...

I don't know about you,

but I would not go back to work if something like that happened to me.

Well, anyways, his co-workers noticed some serious changes in his personality.

He wasn't as friendly and he was more prone to using profane language.

He was a changed man.

And his case is a prime example of

how a brain injury can severely affect personality,

which is great evidence for the biological model.

So other things like drugs, poor physical health,

and even smartphones have the ability to actually change

our brain chemistry and thus potentially affect our personality.

So due to the principle of neuroplasticity,

which means that we can essentially rewire our brain,

we can also come to the conclusion that

we can change our brain chemistry and ultimately,

we can change our personality.

So as I wrap this video up,

I'd like to offer a little bit more of

my thoughts on the nature versus nurture debate.

Lessons from the biological perspective of personality and behaviorism,

both offer convincing arguments that nature or nurture influence personality.

So, which side is the winner?

Now, I personally believe that nature and nurture are like ingredients in a cake.

You see to make a cake, you need flour,

you need eggs, and baking soda, and maybe a

few other ingredients to actually make a cake.

But do we say that flour causes a cake?

Not really, we need a little bit of both flour and eggs and those other ingredients.

And only after we make a whole bunch of cakes,

can we actually start to see what happens

when we add or subtract different ingredients?

So flour doesn't cause a cake. Genes don't cause personality.

However, each part is an important section of the whole.

We can connect certain tendencies to act

certain way to different parts of the brain.

When Phineas Gauge's personality changed literally overnight,

for example,

psychologists could pinpoint what parts of his

missing brain had influenced certain traits.

However,

other personality traits are influenced greater

by our environment and our culture.

So if we're taught to value agreeableness and we grew

up in an environment where being agreeable is easily,

we're probably going to be more likely to find ways to be agreeable.

So our personality is influenced by nature or nurture. I personally say both.

If you guys enjoyed this video,

feel free to watch some of other videos in the personality series.

I've worked really hard on them.

Now, if you want to learn more about your own personality,

you can go ahead and check out my free

three in one personality quiz in the description below.

I actually hired a web developer to create it.

It combines three of the major personality quizzes into one

test that you can take in under 10 minutes.

And I've also done some research and I'm going

to try to predict some things about you,

like your political stances, your relationship style, and even your health.

So you can go ahead and check that out in the description below.

I hope you guys enjoy this video and most of all, I hope you learned something.

Thank you for watching.