you might show your teeth, change your breathing,

become weak and achy in some places, and maybe even cry?

In other words, why do we do this bizarre thing that is laughter?

When you laugh, your abdominal muscles contract rapidly.

This alters your breathing patterns,

increasing the pressure in your chest cavity, and pushing air out,

which might audibly emerge as a snort, wheeze, or vocalization.

Because you're exerting your abdominal muscles much more

than you usually would while talking,

they may start to hurt.

Laughter also inhibits your reflexes and muscle control,

causing sensations like leg weakness.

So, where does this funny phenomenon come from?

Because there's no archaeological record of laughter,

it's impossible to say exactly how and why it evolved,

but scientists have some theories.

Importantly, humans are not the only animals today

that do something like laughter.

Using ultrasonic recorders,

researchers in the late 90s realized that rats were basically giggling

while being tickled.

Scientists have since compiled evidence of at least 65 species—

mostly mammals, but also some birds— that vocalize during social play.

Some, unsurprisingly, are our closest relatives.

By recording and analyzing the sounds primates make

while playing and being tickled,

researchers grew more convinced that the ancient ancestor of all great apes

did something like laughter.

And, because other apes make laughter-like sounds during rough-and-tumble play,

they think laughter may have originally developed to clearly signal

friendly, non-aggressive intent.

But of course, humans don't just laugh when we're wrestling,

but also when we're amused, and even surprised, confused, or nervous.

Some scientists think laughter took on expanded functions

after humans split from other great apes

and developed large social groups and more complex language abilities.

They hypothesize that laughter gradually became something we could use

not just during play but within speech to convey subtle meanings

and a range of contexts to show our emotions.

This is thought to be one of the reasons that laughter is contagious:

it's like an invitation to share in someone's emotional state.

Just hearing clips of laughter can activate key regions in your brain,

triggering you to smile or laugh yourself.

And, when participants in one study watched a funny video,

they laughed significantly longer and more often

when another person was present—

even though they reported feeling the same level of amusement.

Human laughter is also generally louder

than the play vocalizations of most animals.

Some scientists speculate that this is because our laughter functions

not only as a signal between individuals, but a broadcast to everyone around.

Studies found that observers across the world and as young as 5 months old

could reliably tell the difference between close friends and acquaintances

just from brief clips of them laughing.

Similarly, we can tell whether a laugh is real or fake based just on the sound.

Fake, or volitional, laughter is produced

in entirely different networks in the brain,

relying on speech-like pathways.

Meanwhile, spontaneous laughter arises from older networks

that other animals also use for their vocalizations.

And laughter is not just socially important;

it's also thought to be good for us.

When we laugh, our brains release feel-good neurotransmitters

like endorphins,

and decrease levels of stress hormones like cortisol.

Some research even suggests that people who laugh more

can cope with stress more effectively and have better cardiovascular health.

Laughter is a universal human behavior.

Babies can laugh before they can speak.

Whether it's the best medicine depends on your ailment.

But as something that makes life more tolerable,

strengthens bonds, and potentially improves aspects of your health,

you can't go wrong with a good laugh.

Unless you have a broken rib or something.

Then it's no laughing matter.

Certainly nothing to crack up about.