What does it say about the human condition

that when you enter this world crying,

the doctor's like,

the baby's emotionally devastated to be here, check.

Humans are the only animals

that produce tears due to emotion.

Elephants, for example, produce tears,

but mostly due to irritation.

In fact, the lobocraspis griseifusa moth

will irritate an elephant's eye

so it produces tears that it can drink.

Imagine asking a kid what their favorite animal was

and they were like, Oh you know,

the moth that irritates elephant's eyes

in order to drink their tears.

I'd be like, okay, this kid, he's got issues.

You on the other hand could produce tears from a loss,

joy, self-pity, laughter or when the tone switches

in a "That's So Raven" episode.

And tis wild, but the chemical makeup of your tears

changes based on your emotions.

So why are human tears so unique?

Tears of endogenous depression are different

than tears from acute grief.

If you remove the tears from crying people's faces,

it's hard for you to tell if they're crying from sadness

or laughing from pure joy.

Scientists have a hard time studying tears,

especially emotional ones.

A lot of these studies involve humans as lab rats,

watching sad movies and studying their crying behavior.

Or there are morbid studies.

For example, the one on brain dead people,

where they found they produce tears

when their organs are removed

and will slightly open their eyes

when their nipple is twisted.

For this next study,

could you twist that brain dead person's nipple, please?

(laughing) Do not kill the messenger.

I did not twist those nipples a scientist did.

Oh, they opened their eyes slightly, fascinating.

Due to recent scientific insight

we know a lot more about why we emotionally cry.

Back in 17th century America for example,

it was thought that a marriage was doomed

if the bride did not profusely weep at the wedding.

This was to prove the bride wasn't a witch,

as witches were known to cry

only three tears from the left eye.

Therefore obviously the bride was crying from both eyes

it meant that the bride was not working with Satan.

Think of all the groomzillas who were like,

she's ruining my perfect day,

she's not crying from both eyes.

Thine is a witch

honestly straight weddings are like, so over the top.

To know why you as a human cry,

you have to think back millions of years

to when your ancestors evolved out of the water.

Yep. Your great, great, great

times a million million grandparent

looked like some sort of insect-y shell

amphibian arthropod millipede sort of thing, maybe.

And by leaving the water to live on land,

all of these land dwelling animals from then on

needed a lacrimal apparatus to produce tears

that kept the eyes wet while on land.

But you, my friend are special

because you have three types of tears.

The first is basal tears, which is made up of three layers.

A mucus layer that touches the eyeball,

an aqueous layer, which moisturizes

and protects against invasive bacteria,

and the final oily layer

that stops the other layers from evaporating

and keeps the surface of the eyes smooth.

So your vision is clear.

The second is reflex tears,

which is unique to all land dwelling animals.

In fact, all animals, except for snakes and amphibians,

have a peripheral sensory system

that consists of nerve endings in the eye

that when stimulated by mechanical, thermal, chemical,

or pain stimulus release tears.

It should be known that you don't have a storage of tears

in your eye, ready to come out when you cry,

the tears are created due to a sensory in your body

that triggers the response.

Humans, that means me, that means you are special.

We are the only animals with emotional tears,

also known as psychogenic tears.

Which are controlled by the prefrontal cortex

and the anterior portion of the limbic lobe of the brain.

Some scientists think that we cry

because as a child,

crying was the only way that we were able

to get a response from our parents.

As babies, we don't have the words to express our feelings,

so crying is what we do, and it works.

Known as the acoustic umbilical cord.

Crying serves to connect the infant to the caregiver

as an adaptive strategy.

Developmental psychologists believe

that crying enhances infant survival

by eliciting care and protection from caregivers.

In lactating, females infant crying can cause a rise

in breast temperature and a milk let down reflex.

But the crying starts to decrease

at a time of for brain development in the baby.

When the baby is 24 months old

concurrent with rapid development of spoken language,

crying seems to fall off.

Because of this research,

some scientists posit that we cry

when we don't have the words to explain how we're feeling.

Which I can relate to.

I feel like when I cry, it's usually in moments

where I don't have the words to express

what I'm feeling.

Much like when I was a kid, crying for my mom's attention,

when I couldn't speak English.

It feels like now when I cry it's when emotions are so big

I don't really know how to explain them.

Whether they're happy or sad.

And crying, it's showstopping.

If you cry at a party,

people are going to pay attention to you.

I have a hard time

when the attention is on me in public settings,

so I really like to cry alone while watching a movie.

In fact, once my mom almost kicked me out of a movie theater

because I was crying so loud during "Ever After"

that the people in the audience were like, please be quiet.

We can't even focus on the movie.

Emotional tears are really cool.

But it turns out that the chemical makeup of tears

from emotion are different than the tears from irritation.

A study found that the protein concentration

of emotional tears was 24% greater

than that of an irritant,

and the higher protein tears fall more slowly on the face.

Some scientists think

that emotional tears evolve to have more proteins in them

causing them to fall slower

and give more time for our fellow humans to react

to the response and give us an emotional boost.

In fact, using eye tracking,

a new study found that humans focus way more

on faces with tears and are more aroused by them.

The visual image of a tear falling down a cheek

sets off a response in us to help and be interested.

This all leads to the predictions

that human emotional crying

is a way to get other people to look at you.

The higher protein concentration of emotional tears

makes them fall more slowly,

so people will pay attention and look after you.

There is no gender difference

in crying frequency in infants,

but there is a big shift when we get to adulthood.

In a sample of 286 women and 45 men

between the ages of 18 to 75,

it was found an average

of 5.3 crying episodes per month for the women.

And 1.4 crying episodes per month for the men.

For the women,

most of the cries had to do with a sad film or TV show.

In fact, studies show that from 11 to 16 years of age,

boys cry more from physical pain.

Whereas girls cry more for empathetic reasons,

especially during movies again, or TV shows.

This led some other studies to posit

that women are more empathetic to the crying of others

and found they're more likely

to stop and help someone crying on the street.

For both genders, there's a great decrease in crying

between the ages of 10 to 17

with boys having the biggest decrease.

They aren't able to know for sure

if this is the societal context of big boys don't cry

or if it's actually a hormonal shift,

'cause this is around the age of puberty

when there'd be an increase in testosterone in boys.

There are no studies on crying

for gender non-conforming people.

These are all theories based on complex science,

but there's no specific scientific consensus

as to why adults emotionally cry.

We have made incredible scientific progress

but it's really hard to study emotional crying.

Because think back to the last time you cried,

it truly does feel like every cry is unique.

And every cry is different

because it involves complex biochemistry,

endocrinology, social contexts, cognition

all slamming together to create this moment

that you either embrace or you push away.

I think crying emotionally is fascinating,

because it really shows how complicated we are.

We can't figure out why we do this,

but it's one of our most visceral experiences.

For me personally, when I'm crying emotionally,

sometimes it's when I feel the most alive.

And the fact that we are the only animals

on the planet that do this is fascinating to me.

It's a true testament to how smart and brilliant

and sentience we are as beings.

And we actually might be the only animals in the universe

that do this.

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