Have you ever yawned

because somebody else yawned?

You aren't especially tired,

yet suddenly your mouth opens wide

and a big yawn

comes out.

This phenomenon is known as contagious yawning.

And while scientists still don't fully understand

why it happens,

there are many hypotheses currently being researched.

Let's take a look at a few

of the most prevalent ones,

beginning with two physiological hypotheses

before moving to a psychological one.

Our first physiological hypothesis

states that contagious yawning

is triggered by a specific stimulus,

an initial yawn.

This is called fixed action pattern.

Think of fixed action pattern like a reflex.

Your yawn makes me yawn.

Similar to a domino effect,

one person's yawn triggers a yawn

in a person nearby that has observed the act.

Once this reflex is triggered,

it must run its course.

Have you ever tried to stop a yawn

once it has begun?

Basically impossible!

Another physiological hypothesis

is known as non-conscious mimicry,

or the chameleon effect.

This occurs when you imitate someone's behavior

without knowing it,

a subtle and unintentional copycat maneuver.

People tend to mimic each other's postures.

If you are seated across from someone

that has their legs crossed,

you might cross your own legs.

This hypothesis suggests

that we yawn when we see someone else yawn

because we are unconsciously copying

his or her behavior.

Scientists believe that this chameleon effect

is possible because of a special set of neurons

known as mirror neurons.

Mirror neurons are a type of brain cell

that responds equally when we perform an action

as when we see someone else

perform the same action.

These neurons are important

for learning and self-awareness.

For example, watching someone do something physical,

like knitting

or putting on lipstick,

can help you do those same actions more accurately.

Neuroimaging studies using fMRI,

functional magnetic resonance imaging,

shows that when we seem someone yawn

or even hear their yawn,

a specific area of the brain

housing these mirror neurons

tends to light up,

which, in turn, causes us to respond

with the same action: a yawn.

Our psychological hypothesis also involves

the work of these mirror neurons.

We will call it the empathy yawn.

Empathy is the ability to understand

what someone else is feeling

and partake in their emotion,

a crucial ability for social animals like us.

Recently, neuroscientists have found

that a subset of mirror neurons

allows us to empathize with others' feelings

at a deeper level.

Scientists discovered

this empathetic response to yawning

while testing the first hypothesis we mentioned,

fixed action pattern.

This study was set up to show

that dogs would enact a yawn reflex

at the mere sound of a human yawn.

While their study showed this to be true,

they found something else interesting.

Dogs yawned more frequently at familiar yawns,

such as from their owner's,

than at unfamiliar yawns from strangers.

Following this research,

other studies on humans and primates

have also shown that contagious yawning

occurs more frequently among friends than strangers.

In fact, contagious yawning starts occurring

when we are about four or five years old,

at the point when children

develop the ability to identify others' emotions properly.

Still, while newer scientific studies aim

to prove that contagious yawning

is based on this capacity for empathy,

more research is needed

to shed light on what exactly is going on.

It's possible that the answer lies

in another hypothesis all together.

The next time you get caught in a yawn,

take a second to think about what just happened.

Were you thinking about a yawn?

Did someone near you yawn?

Was that person a stranger or someone close?

And are you yawning right now?