All language subtitles for Historys.Greatest.Mysteries.S06E04.1080p.WEB.h264-EDITH_track3_[eng]

[intense music]

- Tonight, the
search for the Yeti,

a creature of myth
allegedly lurking

amongst the highest peaks

of the mountains
of Eastern Asia.

[intense music continues]

- Tales of the Yeti,

this mythical beast
from the high mountains

of Asia and Siberia,

have existed for
thousands of years.

[intense music continues]

- Traditional
beliefs that the Yeti

is actually protecting
the sacred mountain peaks

and that if humans
encroach on those spaces,

they get killed on sight.

- If the Yeti does exist,

is it a living being or
something else entirely?

[intense music continues]

- This is a species that
should have gone extinct

thousands of years ago.

- No normal animal could survive

at those altitudes indefinitely.

- Now, we'll explore
the top theories

surrounding this
legendary creature.

- This is a tooth that
comes from a creature

that was kind of
like an orangutan,

except that this one
is around 10 feet tall

and potentially weighs
around 1,200 pounds.

- It's hard to say 2,000 years

of eyewitness accounts is
all just mistaken identity.

So really what is
happening here?

- At that high an altitude,

maybe people don't see what
they think they're seeing.

- What exactly is the Yeti,

and could it really exist?

[intense music continues]

[intense music]

April 9th, 2019, the Himalayas.

An Indian army expedition

is on a remote mountain pass

on the border of Nepal and China

when they make a
bizarre discovery,

massive footprints in the snow

that don't match any
known animal on earth.

- The footprints that
they find don't look human

in any way, shape or form.

The footprints measure
about 32 inches long

by 15 inches wide,

which is significantly beyond

what any normal human
footprint should look like.

- They do what any of
us would do nowadays,

which is they tweet it.

They take pictures.

They post them online

from the official Indian
Army Twitter account.

- They send a tweet
to the world saying,

we have found the Yeti,

and the scientific world

and the crypto zoological
world explodes.

[intense music continues]

Tales of the Yeti,

this mythical beast
from the high mountains

of Asia and Siberia,

have existed for
thousands of years,

and what they describe it as

is a large, towering,
fanged, bipedal creature

that is covered from
toe to head in hair,

and it has the features of
both an ape and a human.

[intense music continues]

- [Laurence] The first
recorded sighting

of the Yeti occurs in
the fourth century BCE

- In 326 BCE,

as Alexander is attempting
to conquer the Himalayas,

he hears these stories about
this wild man of the snows,

and so he sends members
of his army out to go

and see if they can
find this beast,

but to no avail.

No monster or no wild
man is ever caught.

[intense music continues]

[horns blaring]

- The origins of the Yeti,

where it actually
begins, is unknown,

but we can go back
to seventh century CE

where if you look
at Tibetan folklore,

they describe a wild, hairy
man of the mountains,

originally known as
the glacier beast.

[intense music continues]

And if you look at
Tibetan religious beliefs,

they see the Yeti as
actually a god of the forest

and all the animals
that live within it.

- There's not
consistent agreement

about the nature
of this creature.

Everyone pretty much
agrees that it exists.

[intense music continues]

Some cultures feature him

as feral, and aggressive,
and dangerous.

And others describe it more

as shy or even mischievous.

[intense music]

There are ideas and
traditional beliefs

that the Yeti is a
spiritual protector,

that it's actually protecting
the sacred mountain peaks,

and that if humans
encroach on those spaces,

they get killed on sight.

[flags flapping]

[intense music]

- [Laurence] The
Yeti first captures

the modern world's imagination

at the turn of the 20th century.

- In 1899, Scottish
explorer Laurence Waddell

publishes his book,
"Among the Himalayas,"

and in it he talks about an
excursion that he's going on

while in the
Himalayan Mountains.

- He recounts a story
of being at 17,000 feet

and coming across
a series of tracks,

and he looks to his guides
and is like, "What is this?"

They say, "This is the wild,
hairy man of the eternal snows."

- In 1921, the explorer
Charles Howard-Bury,

he's up around 20,000 feet,

and he and his guides
also see this same thing,

these giant footprints
in the snow.

So he pulls out his binoculars,

and is scanning the horizon,

and he actually sees something.

He sees off in the
distance against the snow,

this giant lumbering creature.

Now, it's far away.

He can't see a lot
of details of it,

but it's really clearly there,

stark against the snow.

When he asks his guides,

"Okay, so what am
I seeing here?"

they also have an
answer for him.

"The wild man of the snows."

They call it the Meetoh Kangmi.

[intense music]

- When Howard-Bury
is later interviewed

by a journalist about his
experience in the Himalayas,

he mentions Meetoh Kangmi.

The reporter mistakenly
substitutes the word Meetoh,

which means wild, with
mech, which is filthy.

So little journalistic
embellishment.

Little playing around
with some language.

And because of this,

the Yeti now gains
a brand new title

and becomes known henceforth
as The Abominable Snowman.

[intense music continues]

- The idea that there is

some undiscovered,
giant, bipedal creature

living in the mountains
of Asia and Siberia,

well, that just stokes the fires

of the scientific community,

and it basically begins
this wonderful charge

into the mountains
to discover this.

[intense music continues]

And who's gonna
discover it first?

- In 1951, you've got
two British explorers,

Eric Shipton and
Dr. Michael Ward,

who make their way to
the Himalayan Mountains,

and they are again, a
part of an exploration.

As they're ascending
these mountains,

they also come across these
footprints in the snow.

[intense music]

- The footprints are
really intriguing

because it's a very
low, bulbous big toe,

almost more like a
thumb than a toe,

and then three or
four additional toes

that seem kind of hooked,

spaced out differently.

Unmistakably a foot, and
seemingly not human at all.

- In their letters
home, Shipton and Ward

are describing these footprints,

and they're stating that
there's no possible way

that any animal or any human

could have created these
footprints in the Himalayas.

So they conclude

that these footprints do
indeed belong to the Yeti.

[intense music continues]

- About a decade
later, Dr. Ward in 1961

is at a base camp at
about 19,000 feet,

and he meets this Nepalese man.

- He shows up in
just a wool coat

with no shoes and no gloves.

[intense music continues]

Now, he spends the next
14 days without a tent,

and the temperatures were
in the single digits,

and then at night
getting even colder.

And the most amazing
part about it

is that he didn't get frostbite,

- But that's not the only thing.

His feet do not look like a
typical human foot might look.

The skin is thick.

The toes are
misshapen and bulbous.

[intense music continues]

- Ward is starting
to think, well,

if he's not really
affected by the snow,

and he's also walking
around barefoot,

is it possible he's creating

these odd footprints
in the snow?

[intense music continues]

Over time, Ward has spoken

to a lot of Himalayan
residents of the area,

and he's come to realize
that it's not just one man

that's walking around barefoot,

but a number of people living
in this Himalayan region

are doing the exact same thing,

walking around barefoot.

[mysterious music]

- So later on,

Dr. Ward really delves
into this theory.

He actually puts out this theory

of cold-induced vasodilation

so that instead of the
blood vessels in the feet

and the extremities
immediately constricting

and causing frostbite
as they typically would,

they dilate and constrict,
dilate and constrict,

which allows people to
be barefooted in the snow

in these temperatures for
extended periods of time.

[mysterious music continues]

- [Laurence] Ward also proposes
that these foot deformities

are more common in certain
areas of the Himalayas.

[mysterious music continues]

- According to Ward's theory,

we have these remote villages,
no doctors, no clinics,

and these genetic defects.

And so it would make
sense that these people

that are born with these things

that can't get operated on

just have to deal with it.

In these extremely
remote regions,

the villages are very tiny,

and so with just tens of people,

you would imagine that
these genetic defects

with a small gene pool and
possibly some inbreeding

would be passed on from
generation to generation.

- And that would help
explain why these sightings

have been so consistently
reported over time.

It's not one person.

It's an entire lineage of people

with feet shaped this way

walking barefoot over the snow.

- Additionally, people
in the Himalayan region

look at wearing shoes
as incredibly formal,

which is something that they
don't necessarily want to do.

On top of that, if you're
somebody that has a foot

with all of these
deformities on it,

wearing shoes is gonna be
incredibly uncomfortable.

- When we put these
things together,

the shape of people's feet,

the fact that it
would be hereditary,

the fact that they have
this almost superpower

to walk barefoot over the snow,

we get a really
plausible explanation

for photos like Eric Shipton's.

[intense music]

- Ward's theory offers
a compelling answer

to what could be
making these tracks,

but what about the large,

hulking, bipedal creatures
that people are seeing?

It does not explain that at all.

[intense music continues]

[intense music]

- [Laurence] The Yeti
is commonly described

as a tall, menacing creature

covered head to toe
and shaggy hair,

but it's possible many
witnesses over the generations

have fallen prey to a
case of mistaken identity.

- When it comes to eyewitness
accounts of the Yeti,

most of these
eyewitnesses spy the Yeti

from a pretty far distance,

or if they do come across
any sort of evidence,

like stray hairs for example,

these are stray hairs that
could potentially belong

to any number of creature.

- There's a really great
example of it from 1832,

this explorer B.H. Hodgson.

He's in the Himalayas.

He has a bunch of
native guides with him,

and they all report seeing
this kind of creature,

tall, hairy, bipedal,
off in the distance.

[suspenseful music]

- And as they
approached the creature,

it shot off into the woods.

And he was like, "What the
heck could that possibly be?

It has to be the Yeti."

- And so after he
published this account,

he actually backtracked

and said, "Must have
been an orangutan."

[suspenseful music continues]

You've gotta wonder
why would an orangutan,

who typically lives in Sumatra

3,500 miles to the south
in a tropical jungle

be doing up in the Himalayas?

The only feasible excuse
would be a traveling circus.

But why would a circus be
trying to summit Everest?

- It's possible that
he picked an orangutan

maybe because that was
the only type of creature

known to him at the
time that would resemble

what he potentially saw in the
snows during his excursion.

- There's really a
lack of hard evidence,

so researchers who want to
take this question seriously

know that they need
something more.

They need something like DNA.

- In 2012, a professor at
Oxford named Bryan Sykes

sends out this public appeal

to everyone around
the world, basically,

send me your Yeti samples.

And he gets like 57 samples.

[suspenseful music continues]

- About half of them,
30 of them are viable,

and he begins testing them.

And he finds what
we might expect,

a large number of
very normal animals,

horses, and dogs, and bears.

- [Laurence] But
there are two samples

that really stand out.

[intense music]

- One of those samples
comes from a hunter

that shot this giant beast 40
years prior in the Himalayas,

and the other sample

comes from this
high-altitude area in Bhutan.

- Both of these
samples, upon analysis,

reveal that they closely match

a known species, Ursus
maritimus, the polar bear.

[intense music continues]

Sykes, speculating
on this, suggests

that maybe what
we're seeing here

is some sort of descendant

of an earlier
polar bear species.

[intense music continues]

- Now, there are some
researchers who speculate

that perhaps the polar bear

that is being found in
these genetic samples

might actually be a subspecies

of polar bear called
Ursus maritimus tyrannus.

Ursus tyrannus was a
monster of a species.

On its hind legs, it
stood as tall as 12 feet

and could weigh over a ton.

Now, Ursus tyrannus went
extinct about 40,000 years ago,

but some speculate
that it is possible

that maybe Ursus tyrannus bred

with other local
bears in the region

over a number of years

and created a new species.

- So polar bears actually
have a lot of characteristics

that make them a pretty
good contender for the Yeti.

For one, they are
perfectly adapted

to incredibly cold climates.

So these are creatures that
are meant to live in conditions

that human beings
cannot survive within,

and they're also
really solitary.

- They will usually roam
for hundreds of miles

by themselves in search of food.

So it is possible that if
you have this solitary figure

roaming these snowy
environs on its own,

seemingly unfazed by anything,

it is possible that that
particular species of bear

could be mistaken for
the Yeti from a distance.

- The fact that bears
walk around on four feet

would have people believe,

well, there's no way to
confuse that with a Yeti,

but if you think
about bear prints,

the front paw actually combines
with that back paw print,

which would form a
large single print,

which could look like a
bipedal Yeti footprint.

[intense music continues]

- [Laurence] But when the two
key samples from the study

are subsequently retested,
there's an issue.

- Two separate
molecular biologists

take a look at
Sykes' as results,

and they contest
that the samples

that he was looking
at to extract DNA from

were actually damaged.

[intense music continues]

- DNA is a fragile thing.

And so if these samples
had not been kept

at the right temperature

with the right humidity,

they break down very quickly,

and after further examination,

the molecular biologists believe

that these DNA samples
actually match more closely

the Himalayan brown bear,

which is much smaller
than a polar bear.

- But Sykes himself, he
stands by his interpretation

of this possible descendant
of Ursus tyrannus.

Either way, a descendant
of Ursus tyrannus

or a local bear,

we still have a plausible
explanation for the Yeti.

Bear species are known
to walk on two hind legs,

so we could still be seeing
where these prints come from.

[intense music continues]

- [Laurence] The Himalayan
mountain range stretches

for more than 1,500 miles

across five countries.

Any one of these countries

could hold the answer

that finally solves

the mystery of the Yeti.

But some researchers believe

that the most compelling
clues come from China.

- As far back as around 300 BCE

one of the original accounts
is a Chinese dictionary

that mentions one
of these wild men

that have like the
face of a human

and the body of a beast.

- In the 16th century,
during the Ming Dynasty,

a naturalist named Li Shizen
describes different types

of wild men that exist
all around China.

- Now, you have to
understand that China

is an incredibly large country,

and all the different
mountainous regions

all start to yield
their own kind of legend

about the wild men.

[intense music]

Over the years, these Chinese
legends begin to coalesce

and form one story,
one mythology,

one legend, one bit of folklore.

And this legendary creature
now becomes known as the Yeren.

- One of the most well-known
stories is that these wild men,

if you come across one,

they will be so filled with joy

at coming upon you that
they will bear hug you

and pass out from excitement,

and you'll fall to
the ground with 'em

'cause they're so strong,
you can't get away.

And then when it
wakes up, it eats you.

[intense music continues]

- However, there
are some researchers

who speculate that the Yeren

might not entirely be based
in myth and in folklore,

and that, in fact,
it might be based

off of a species that
existed on the planet,

in reality, a long,
long time ago.

[intense music continues]

- The name Yeren comes from the
Shennongjia region of China,

where in 1555, a local
newspaper reported

that wild men were
living in the forest

just outside of town,

and they were coming into town

and stealing people's dogs
and chickens to eat them.

- It would be really easy
to dismiss these stories

as being a relic of the past,

an old wives' tale,

but sightings persist.

- In 1976, six officials

from the Chinese
Regional Forest Committee

are walking along in the woods,

and they come across
these wild men.

And they get within
a few yards of them,

and they describe them

as being tall, fully
covered in hair,

and having facial features

that are a mix of
humans and ape.

[suspenseful music]

- In 2007, some tourists

that are in this
Shennongjia region

say they saw these
two large figures

that are covered in hair,

and as they tried to approach,

those individuals
ran into the forest.

They go back, they
get forest rangers,

and together they go back
to figure out exactly

where these creatures went,

and they find broken
branches, some footprints,

and even half-eaten fruit.

[birds chirping]

- It's hard to say

that 2,000 years of
eyewitness accounts

is all just mistaken identity.

So really what is
happening here?

[suspenseful music continues]

[birds chirping]

[intense music]

- [Laurence] One theory that
still intrigues researchers

to this day first
emerges back in 1935,

thanks to a Dutch anthropologist

with an interest
in the Far East.

- Ralph Von Koenigswald is in
Hong Kong on a research trip,

and during the day he
stumbles into a medicine shop.

And while he is in there,

he sees, in a jar, a giant molar

labeled "Dragon's Tooth."

- The reason they're
selling this tooth

is because it's purported

that if you grind up this tooth

and you ingest it,

it's supposed to give
you magical powers.

But Von Koenigswald
looks at that tooth

and he says, "I know this tooth.

I know where this comes from.

This is a primate tooth."

So he buys the tooth.

He takes it back.

Does research on it.

- And through his research,

he identifies it as an
early hominid species

from the human family tree.

According to him,

this particular species
would've been far back enough

in the human family tree

that it would've been
completely covered in hair

except for its
face and its hands,

kind of like a chimpanzee,

except this chimpanzee would've
been about 10 feet tall

and weighed upwards
of 1,200 pounds.

- [Laurence] Based on the
primate's immense size,

the species is named
Gigantopithecus.

- Fossil discoveries over the
last eight or nine decades

show that Gigantopithecus
lived in the area

that is China and Tibet
over 2 million years ago.

Most scientists agree

that Gigantopithecus went
extinct about 250,000 years ago,

but there are those
of us that believe,

because of the
remoteness of the region

and their ability to adapt,

they have actually thrived in
the high-altitude environments

of China, Tibet,
Bhutan, and Siberia.

- In the 1950s, a
British zoologist,

he looks at Shipton's
photographs,

and he creates a plaster
mold of what he thinks

that footprint
would've looked like.

- After he examines
this plaster cast,

he determines this could not
have been made by a bear.

It had to be made by a
very large bipedal hominid,

and he determines that it is
likely the Gigantopithecus.

- [Laurence] Other researchers
soon voice their support

for the Gigantopithecus theory.

- 1977, American anthropologist
Grover Krantz believes

that the Gigantopithecus
could have survived

in a small tribe in the
remote areas of the Himalayas,

and, therefore,
could be the basis

for what the modern Yeti is.

- [Laurence] It's possible
there are even more layers

to the origin story of
this ancient primate.

- Researchers and scientists

have found very,
very few fossils

when it comes to
Gigantopithecuss,

and because of that,
it's very hard to suggest

that there's a tribe
of Gigantopithecus

that hangs out in the mountains

and evolved into a new species

that became the
basis for the Yeti.

- Until we have something
like a complete skeleton,

it will remain in the
realm of speculation.

Further research into
the Yeti legend suggests

that perhaps Yeti is
an even closer relative

to humans than we had
previously thought.

[intense music]

- For centuries
researchers attempting

to solve the mystery of the Yeti

have relied on inconclusive

or circumstantial evidence
to try to build their case.

Despite some compelling
pervasive oral history,

the hard proof has
not come easily.

But in 2011, a Russian scientist

announced an intriguing
discovery in Siberia

that could completely
change the narrative.

- Dr. Igor Burtsev claims to
have found footprints in a cave

in the Kemerovo
region of Siberia,

which is just north of Mongolia,

footprints that he says
belong to the Yeti.

[suspenseful music]

- In the cave, researchers
not only find the footprints,

but they find what
could be bedding

laid out as if something
was staying there.

And in the bedding they
find these long gray hairs.

DNA tests on the hairs confirm

that it is not from Homo sapien,

but it is from another
hominid species,

one that is closely
related to Homo sapien.

[suspenseful music continues]

- Burtsev concludes
that the gray hairs

that were found in that cave

actually belong to Neanderthals

that are still living in these
mountain ranges in Russia.

[suspenseful music continues]

- Burtsev is not the only person

to tie the Yeti to Neanderthal.

This is something that's been
around for a little while

in the Russian academic world.

- [Laurence] Burtsev
believes a number

of recent Yeti sightings in
Siberia support this claim.

- In September 2012, there's
actually three sightings

in the Kemerovo
Mountains of Siberia.

In fact, one of the
biggest was a fisherman.

He's cruising along and he sees

what he thinks are just

a couple bears at the
shoreline drinking water,

but as he gets closer,

they actually stand up

and run off into the forest.

[suspenseful music continues]

- To date, the most
compelling evidence we have

comes from a short video

that was taken in
February of 2013.

Some boys are playing along

the Ur River in the
Kemerovo region,

and they see this
large bipedal hominid

walking through the trees

carrying what looks like

to be offspring or young.

And as they're excitedly
filming this, very shakily,

the creature turns
and looks at them,

and they lose it.

They lose it, and they run.

- [Laurence] But were
these various encounters

actually with Neanderthals
or something else?

- Neanderthals are a
very distinct species

that showed up around
400,000 years ago

in the area of the world
that's now known as Eurasia.

There was a period of time
for about 30 to 50,000 years

where Neanderthals and
Homo sapiens did coexist.

- The difference
between Neanderthal

and humans are that we
are very thin, our builds,

where they were very robust

and built for cold climates.

They had thick bones,
a big rib cage.

They have elongated skulls,

large, wide noses,
and like a thick brow.

[suspenseful music continues]

The scientific
community believes

that Neanderthals went
extinct about 40,000 years ago

due to the fact that
they were competing

with humans for resources.

- However, there are some
researchers that do suggest

that Neanderthals
didn't go extinct

and that they
continue to live on

in very isolated
regions of the planet.

- It makes sense if you're a
Yeti living in northern Russia,

that you could basically
stay out of view of humans

because it's extremely
remote, extremely cold,

and there's very few humans.

It's a place where these
Yetis or Neanderthals

would actually be able
to exist peacefully.

[fire crackling]

- If the majority
of Neanderthals

went extinct 40,000 years ago,

save for maybe this small group,

that means that there have
been 1,000 generations

of Neanderthals interbreeding
with each other,

and as they interbreed
with each other,

those more brutish
physical features

become that much
more pronounced.

[tense music]

You start to develop
a kind of hominid

that is even hairier,
maybe even stockier,

maybe even bigger,
more barrel-chested.

- The same qualities
that could contribute

to why a Neanderthal
species would be able

to survive in these climates

could also explain the sightings
of a Yeti creature today.

[tense music continues]

- The fact that the Yeti seems

to vanish almost immediately
once humans come upon them.

Neanderthal would be
very adept at hiding,

especially if they know in
their collective history

that humans are the reason

there's only a
small handful left.

Like the Himalayas, Siberia
is incredibly remote.

The possibility of a
intelligent species

staying hidden makes sense.

- You would need
definitive evidence

before you can say that this
theory actually holds water.

But it's an interesting idea.

[tense music continues]

- [Laurence] Researchers
attempting to identify the Yeti

often focus on an unknown
animal or a lost species,

but some investigators contend

that what people
think they're seeing

is actually a kind of mirage.

- We can't say for certain

that there are a lot
of Yetis out there,

but there are absolutely
a lot of sightings.

[intense music]

So what are people seeing?

We ask that question

and try to answer it through
the archaeological record,

through the fossil record,

but we could also answer that
question with psychology.

[intense music continues]

- In 1998, famed
mountaineer Reinhold Messner

decided that he was going to
write a book about the Yeti

and get down to what
is the Yeti really?

- Reinhold Messner
was the first person

to do a solo ascent
of Mount Everest.

He was also one of
the first people

to do it without any
supplemental oxygen.

He is someone who knows

what he's doing in
mountain climbing.

- He interviewed as
many people as he could,

sherpas, Bhutanese,
Nepalese, everyone.

And what he came up with

was he believes people
are not actually seeing

a flesh-and-bone animal.

What they're
actually experiencing

is something called pareidolia.

[suspenseful music]

- A phenomenon
called pareidolia,

which essentially is the
human brain finding patterns

and seeing structures and
connections among designs

that aren't actually there.

For example, why individuals
have seen the Virgin Mary

in a piece of toast,

or we see figures in the clouds.

- When you go way
back in deep time

when, you know, we had
things to worry about,

like a saber tooth cat,
every second counts.

And so that puts our mind
into like a defensive trick.

And so the pareidolia
is basically

your mind trying to give
you an extra split second

to get outta the way of danger.

But a lot of times it's
just a false alarm.

- [Laurence] But that isn't

the only psychological
phenomenon

that could explain the Yeti.

[suspenseful music continues]

- Another possible
optical illusion

that they could be experiencing

when having a Yeti
encounter are shadow people.

[suspenseful music continues]

And shadow people are your
mind playing tricks on you.

- A shadow person is
literally you perceiving

that a shadow is a
threatening humanoid

or a threatening entity.

Example of this is you wake
up in the middle of the night,

and you look at the
foot of your bed,

and you see this dark figure.

[suspenseful music continues]

You shake it off a little bit,

and then that shadow
person is now vanished.

[suspenseful music continues]

- What's interesting about that

is it depends on
your belief systems.

People who believe in the
paranormal or supernatural

are far more
susceptible to seeing

or experiencing shadow people.

- However, not all shadow people

are figments of the imagination.

There is another phenomenon

that is known as
Brocken spectre,

and you look in the distance,

and you do see a menacing
shadow, a menacing figure.

But Brocken spectre occurs
when you're standing,

and the sun is behind you,

and it's essentially projecting
your shadow in front of you.

- If the wind is blowing,

if that mist is moving at all,

the shadow might appear to
move in ways totally unrelated

to the person whose body
is casting that shadow.

In really high elevations,

especially where the
air is really thin,

the Brocken spectre
becomes even more common.

There's more opportunity for
the right angle of the sun

and more opportunity
for a substance

or a surface on which
the shadow can be cast.

It's not hard to imagine

that people seeing
this apparition

might attribute some sort

of supernatural
significance to it.

- Eric Shipton himself,

the British mountaineer
who found the 1951 prints,

he experienced a Brocken spectre

while climbing
Mount Kenya in 1929,

and he describes it as
seeing the shadowy figure

with this beautiful rainbow
light cast around it.

What's easier to believe,

that people are seeing
a giant relic hominid

wandering the mountains

or their minds are simply
playing tricks on them?

- Scientists speculate there is

yet another possible explanation

for the sightings of
Yetis at these altitudes,

and it is less a question
of a psychological stress

and more a question
of physical stress.

[intense music]

- [Laurence] Over the centuries,

the vast majority
of Yeti sightings

have occurred high
in the mountains,

and some researchers suspect
there's a reason why.

- Humans have evolved

to live pretty much
right at sea level.

And so when we go higher

and higher up in elevation,

we lose that
concentration of oxygen.

- When you have people
that are climbing mountains

like Mount Everest
or Mount Kilimanjaro,

they usually will make
base camp at around

anywhere from 17 to 19,000 feet,

and they'll stay
there for a few weeks

just to acclimate themselves
to that higher altitude

so that as they go higher,
they don't get sick.

- But if we ascend to high
altitudes too quickly,

that is when our bodies
will begin to fail us.

You can see taste, touch,

and fully experience something

that is completely a
figment of your imagination.

[intense music]

- Altitude sickness is no joke.

It can actually lead to death.

Symptoms of it are things
like headaches, nausea,

dizziness, disorientation,

and also hallucinations.

- [Laurence] Hallucinations,
which could explain

the long history of Yeti
encounters in the Himalayas.

- Hallucinations are
sensory experiences

entirely generated
from within the brain.

So it's important to note

that hallucinations
aren't just imaginary.

It feels, looks,
sounds, smells real.

[intense music continues]

When someone experiences
a hallucination,

it's like a psychosis.

There's no distinguishing
between reality and fantasy.

- Someone suffering
from altitude sickness

may not even be aware
that it's happening to him

because the symptoms can come
on very slowly and subtly.

One second, you're there
and you're feeling great

and the next second you are
talking to an imaginary person.

- There is an example of this

that takes place in 2008.

It's a mountaineer by
the name of Jeremy Windsor.

Jeremy Windsor is attempting
to climb Mount Everest,

and as he gets
higher and higher,

he suddenly has this companion
that's climbing with him

by the name of Jimmy.

- And Jimmy sort of
keeps pace with him.

He sees him kind of out
of the corner of his eye,

over his right shoulder.

They encourage each other

as they're struggling
to make it to the top.

- When he gets back to base camp

and starts to explain
his friend Jimmy,

it becomes very apparent,
not only to his companions,

but to him, that Jimmy
was a complete figment

of his imagination.

- Hallucinations often vanish
as quickly as they appear,

which could explain why
people are seeing the Yeti,

because the Yeti seems

to vanish right when you
get a good look at it.

- [Laurence]
Researchers also believe

that our hallucinations
can be influenced

by deep-seated cultural
and personal beliefs.

- Hallucinations happen.

We know that.

It's a human biological,
physiological experience,

but how we interpret
those hallucinations

owes a lot to culture.

Folklorists actually call this

the cultural source hypothesis

when it comes to explaining
a supernatural belief

that someone has.

[expansive music]

- If you're in the Himalayas,

and you've been hearing
about stories of the Yeti,

your subconscious might
actually drum up a Yeti

for you to hallucinate

as you're making your
way up this mountain.

- We know that at
about 8,000 feet,

the vast majority of people
do not feel any symptoms

of altitude sickness.

When you get to
10,000 feet, however,

about 75% of the
human population

does start to
experience evidence

of this altitude sickness,
including hallucinations.

- So with the majority
of Yeti sightings

happening at above 10,000 feet,

it's reasonable to say

that these sightings
might just be

a symptom of altitude sickness.

- [Laurence] But not
everyone is convinced

this mythic creature
is purely made up.

- It's hard to actually
refute the fact

that we have the same,

if not just similar experiences
over thousands of years.

So it makes it very difficult
to just discount it all

as some sort of hallucination

versus something that
actually might exist.

The fact that we don't
have any concrete clues

over thousands of years

lets the skeptics
basically weigh in

and say, "Doesn't exist."

But biologists discovered
the Coelacanth,

thinking it was extinct

tens of thousands of years ago.

- It is also perfectly plausible
that no single explanation

for the Yeti is the
entire explanation.

Human beings and science are
also continuing to evolve.

So it's very plausible that the
conclusive piece of evidence

that is needed to definitively
prove the existence

of the Yeti is just
around the corner.

[intense music]

- There's something
uniquely compelling

about a wild, hairy humanoid

prowling in the cold shadows

in the highest peaks
of the Far East.

It's a campfire tale that
still inspires wonder

and dread to this day.

Is it a real life relic,

a trick of the mind,
or something else?

The physical evidence
may not be there,

but the intrigue lives on.

I'm Laurence Fishburne.

Thank you for watching
"History's Greatest Mysteries."

[intense music fades out]