Original subtitles

NARRATOR: There are nearly 1 billion dogs walking, sniffing, and barking

all over the planet.

In exchange for free meals, they've evolved side-by-side with us

like no other species in the animal kingdom.

MARTY: When you pet a dog, after just a few seconds,

you get this surge of oxytocin which is the hug hormone.

And you get phenylethylamine which is that active ingredient in chocolate.

NARRATOR: Dogs are more than our most loyal companions;

they're superheroes of science.

With over 400 breeds and countless variations,

man's best friend has become the most diverse mammal on land.

So the big question is, how?

(barking, panting).

Every dog, large and small, evolved from just one species.

(howling).

ADAM (off-screen): So the ancestor of the dog was the grey wolf.

And the grey wolf looks a lot like other wild canids.

So it's got prick ears, it's got long sharp incisors, it's got a bushy tail.

NARRATOR: It's a necessary build for surviving nature's harshest conditions.

(howling).

But 15 to 30,000 years ago, humans' discarded scraps transformed less aggressive

wolves from hunters into scavengers.

ADAM: They no longer had to have a shape that was finely tuned

to bringing down large game.

NARRATOR: Physical changes spawned something new:

Canis lupus familiaris, better known as dogs.

They were the first domesticated species on earth.

And their bond with humans has changed both their behavior and shape.

HEIDI: As time goes by we keep selecting for smaller and smaller dogs, and we get this

huge range of dogs that can cover every job imaginable.

ADAM: People started breeding dogs as hunting companions,

as fighting dogs, as companion dogs, as herding dogs.

NARRATOR: The advent of kennel clubs in England in 1873

put them on the evolutionary fast track.

ADAM: That's when breed standards were made, and that's really

accelerated the diversification of all the different,

shapes and sizes and behaviors and forms of dogs today.

LINDA: We shape the dogs, and how they ultimately appear, by our choices.

NARRATOR: From noses to tails, coats to paws, their shape has changed their entire history.

Every part of a dog's body has a tale to tell, from the bottom to the top.

The canines' ancestors have ears wired for sound.

Acute hearing is vital to hunt down even the tiniest rustle of prey from afar.

But modern dogs have different priorities.

ADAM (off-screen): After dogs became domesticated, their ears diversified.

And they don't need to hunt big game anymore.

They're scavenging for people and whatever looks cute and can give them

a good expression is what their meal ticket was.

NARRATOR: Alternative ear styles have different benefits.

The button ear, on burrowing dogs like the Jack Russell terrier, folds over itself to

cover and protect the ear canal from the dirt.

Newfoundlands are a working water dog.

Their drop ears cover their ear opening to prevent water from entering the ear canal.

Rose-shaped ears are slicked back and aerodynamic,

a requirement for any breed with a need for speed,

like greyhounds.

There are many things canine ears can do, but number one is hearing.

Dogs hear four times as well as humans, with a range of frequencies twice as large.

Even the tiny ones hear better than us, sometimes way better.

So when your house is in danger, your best defense

may just be a mere six inches tall.

♪ ♪

It's hard to believe Chihuahuas have anything in common

with their grey wolf ancestor.

But actually, they have at least two: their prick shaped ears.

DEBBYE: It is a cone shape, there's a lot of surface area, and it concentrates the sound,

sends it straight down to their eardrum.

NARRATOR: Chihuahuas likely originated over 1,000 years ago, and to this day,

their sense of hearing is one of the best of any breed.

DEBBYE (off-screen): Because Chihuahuas are such a small breed,

it makes them vulnerable to attack and to predators.

So their hearing really is self-defense.

They can hear a threat coming long before it gets to them, gives them a chance to escape.

NARRATOR: 18 muscles power gigantic ears that turn like satellite receivers.

DEBBYE: You will literally see one ear turn toward the direction of the sound so that

they can pinpoint what it is they're focusing their attention on.

NARRATOR: When something doesn't sound right, they will let you know.

ADAM: Chihuahuas are your sort of classic guard alert dog

and they will bark at the first sign of danger.

DEBBYE: So they will bark incessantly.

And that bark also protects them, because if they can alert their owner,

their pet parent, they know they're gonna be safe.

MARTY: So these incredible ears are just like radar to pick up sound.

You don't need an alarm system in your house if you have a Chihuahua.

You will never have an intruder, you will never have a neighborhood dog

sneak through the yard, but you'll probably never have a total night's sleep either.

NARRATOR: Chihuahuas have some of the best hearing around,

but which dogs can't hear at all?

On their birthday, all of them.

Puppies come out of the womb without the sense of hearing.

MARTY: Their ear canals are actually kind of swollen shut.

Usually it takes anywhere from two to three weeks before they can start to hear.

NARRATOR: Dogs have a short gestation period, just two months,

which means some body parts need to mature after birth.

(sirens).

When a crime breaks out and a fugitive is on the loose,

there's one member of the task force who's all ears.

(barking).

Bloodhounds sport two of the longest drop-ears of any breed,

with an average of eight to ten inches each.

Surprisingly, the large size doesn't aid in hearing.

In fact, it's detrimental to it!

But the ears are prized assets when it comes to the job of tracking.

DEBBYE: Believe it or not, their ears help them with their smell.

NARRATOR: Here's the evidence...

Exhibit A: long droopy ears block sounds from entering the ear canal.

DEBBYE: These big long drooped ears actually sort of close off distractions

and allow them to focus on the smell.

NARRATOR: Exhibit B: their ears scratch the trail's surface.

DEBBYE (off-screen): Those long earsdragging along the ground helps rustle up and disturb

the scent that's in the ground to help them track a specific scent.

NARRATOR: Exhibit C: their ears help decipher the evidence.

DEBBYE (off-screen): The shape and theplacement of these long droopyears can literally form a

cone around them, so when they put their head down it concentrates the smell

in the immediate area where their snout is.

NARRATOR: Scents then get wafted up towards the most powerful doggy nose on earth.

DEBBYE: They have up to 300 million olfactory cells, the nerves that help them smell,

which is 60 times the olfactory cells that a human being has.

MARTY (off-screen): You might have somebody that had walked through here 12 hours ago

that is multiple miles away and they still can smell their scent.

NARRATOR: So if someone goes missing, you're in good hands, or paws,

when a bloodhound and his big droopy ears are on the case.

Canine quiz!

Which pooch currently holds the record for longest dog ears?

NARRATOR: Canine quiz!

Which pooch currently holds the record for longest ears on a living dog?

The longest canine ears on the planet belong to a coonhound named Harbor.

Coonhounds likely descended from bloodhounds and foxhounds,

but Harbor's record-breakers stand alone.

His left ear measures 12 and a quarter inches while his right one is even longer:

an outstanding 13 and a half.

There's a unique shape behind every canine, so what's the backstory on their behinds?

When picturing our four-legged friends,

a wagging appendage comes to mind,

and it does a lot more than thump.

DEBBYE: You actually can tell a lot about a dog breed,

and what they are bred to do, by their tail.

NARRATOR: The tail is made up of six to 23 highly mobile vertebrae.

Originally long and fluffy, its main purpose was for balance.

But as the tail took on more jobs, it evolved into a vast array of shapes and sizes.

DEBBYE: There are long ones, there are short stubby ones,

there are feathered ones, there are curly-Q ones.

And all of them play a role in the function of that dog's breed.

NARRATOR: Genetic mutations and behavior adaptations led to a range of tail styles.

Humans breed for the ones that perform best at specific tasks.

Whippets have long, slender tails that improve their agility and help them make

turns while traveling at high speeds.

Some Pembroke Welsh corgis are born without much of a tail at all.

A one gene switch and they grow just a bobtail on their behind.

Huskies use their tails for temperature control.

DEBBYE: The tail on a Husky is literally a big furry puff, and the husky can curl up in

that subarctic weather and cover his face and keep his nose warm.

NARRATOR: And there's one breed that owes much of its well-being

to the very tip of its tail.

(horn blowing).

Raising a white flag normally means you've given up.

But for this pup's tail, it's a victory.

DEBBYE: Beagles date back to the 1500s.

English hunters bred them to be a companion, a partner to the hunter out in the woods.

NARRATOR: They're bursting with energy and speed,

possess a powerful sense of smell, and have a low build

that's perfect for tracking down rabbits and larger hare.

DEBBYE: Beagles literally use their whole body to hunt and they're even colored to

blend in with their environment so the prey doesn't see them coming.

LINDA: If they get on a scent, they will chase it down and

they won't look up for miles and miles,

sometimes going, "Where am I?"

NARRATOR: There's one big disadvantage to these hunting machines.

They're so good at camouflage that even hunters lose track of them!

LINDA (off-screen): When you have apack of dogs traveling aheadof you in the distance,

with their noses down, chasing a large rabbit,

you want to be able to see where they're going.

NARRATOR: Losing your pooch is a red flag, so beagles raised a white one.

DEBBYE: Some of the dogs had a white tip on their tail which made it easier to spot the dog

and so breeders began to breed for this white tip

so that hunters would know where their dog was.

NARRATOR: This feature is now the golden standard for the breed,

ensuring that beagles will complete the hunt and come out on top.

ROBERT: While the tail doesn't talk, its actions speak louder than words.

NARRATOR: Pay close attention to the position of your pup's tail and you'll notice that

it's a unique communication device.

ROBERT: A dog wagging its tail more to the right means that they're happy and a tail

wagging more to the left means that a dog is agitated.

NARRATOR: But make sure to look up and down, too.

A stiffly raised tail can mean they're on high alert and standing their ground,

or that they're very excited.

And a tail between the legs means the pup is frightened.

One of the most popular canines on land has a tail specially crafted for sea.

Labs are the most beloved breed in America.

ADAM: They're loyal, they're affectionate, they're trainable.

You know, they're cute.

MARTY: This dog is the Wal-Mart greeter that lives in your house.

They are happy all the time.

NARRATOR: Their story began over 200 years ago in maritime Canada, when fishermen looked

for a dog that could jump into the frigid waters to fetch fish and nets.

Newfoundlands worked, sort of, but these massive dogs retrieved more than just fish;

they'd come back seeping with icy cold water.

By mixing various working breeds, fishermen concocted the lab's ancestor,

the St. John's water dog, which went extinct in the 20th century.

MARTY: The St. John water dog was a specific breed, and it had rugged bodies,

they go through a lot of heavy surf, very strong swimmers.

NARRATOR: Like a modern lab, St. John's had a lot of qualities that help fishermen:

water-repellent coats, a soft mouth perfect for retrieving, and perhaps most importantly,

a sleek tail modeled after one of the best swimmers out there, otters.

LINDA (off-screen): Its very wide base that comes back and narrows to a tip,

which helped them to steer in the water.

MARTY: That tail acts like a rudder.

So they can turn very quickly.

NARRATOR: When a swimming pooch turns his tail, the current applied against it

makes his entire body turn.

And efficient maneuvering makes fetching fish a total breeze!

By the 1800's, hunters started using the St. John's water dog on land.

They mixed the dog with various European breeds and a super mutt was born,

now known as the pure-bred Labrador retriever.

LINDA: Labrador retrievers were quickly adopted by many, many people because

it had so many desirable characteristics.

NARRATOR: Land or sea, their loyal demeanor, and hard-working attitude

make labs ideal pets.

Just be careful of that otter-tail indoors.

LINDA: It's extremely muscular and you need to be very careful with the dog in the

house because it will clear a coffee table.

NARRATOR: Canine quiz!

Which pooch has the longest tail?

And how long is it?

NARRATOR: Which pooch has the longest tail?

And how long is it?

Finnegan, an Irish wolfhound from Calgary, Canada

holds the canine record for longest tail.

Bred large to hunt wolves and Irish elks,

Irish wolfhounds are the tallest breed there is,

and Finnegan's tail truly stands above the rest.

It measures a whopping 28.46 inches.

For thousands of years, the size of dogs evolved to match their environments.

At the same time, humans have selected for height, weight and shape.

From the tiny teacup Yorkie to the gargantuan Great Dane,

canines now come in more sizes than any other mammal on land.

ADAM: So the smallest dogs and the largest dogs are 100 times different

in how much they weigh.

And five times different in how tall they are.

NARRATOR: It used to be that all dogs could interbreed.

These days, massive size discrepancy makes mating much less likely.

HEIDI: Chihuahuas and Great Danes, people would look at those two breeds and think,

this actually has to be a completely different species at this point.

NARRATOR: Why do some breeds stop at mere inches while others grow into giants?

HEIDI: One of the really wonderful things about dogs is how they've been able to

adapt to all of our different lifestyles.

ADAM (off-screen): So all dogs big and small have the same 39 pair of chromosomes.

But there's about a dozen genes controlling body size that really drive most of the

differences between small dogs and big dogs.

NARRATOR: All dogs have 99.5% of their DNA in common,

which means that only half of a percent difference in DNA

is responsible for one dog becoming a Great Dane,

and another a Chihuahua.

ADAM: One of the most important genes is called "insulin growth factor one"

that explains about 40% of the variation in body size across modern breeds.

NARRATOR: Measuring just six to nine inches tall,

Pekingese are so tiny they can fit in a sleeve,

which is exactly where they were placed in ancient China.

DEBBYE: Legend has it that if someone attacked them the dog could pop out and

surprise the intruder and bite them.

NARRATOR: Dachshunds have extraordinarily long torsos, so their heads can go deep

into holes while their back-half stays safely above ground.

And for some dogs, bigger is better.

Great Danes are one of the tallest breeds in the world, typically clocking in at a

whopping 28 inches or more at the shoulders for females and over 30 for males.

DEBBYE: Great Danes are exactly what their breed name calls them.

They are a great big dog.

They have huge skeletons,

they can stand as high as seven feet tall if up on their back legs.

Big heads, big muzzles and of course those long lanky feet.

NARRATOR: Believed to be a cross between

big English mastiffs and mighty Irish wolfhounds,

Great Danes have always been giants.

In medieval Germany, they were bred to hunt wild boar.

LINDA: They would chase these giant boar through the forest.

DEBBYE: They were really a very ferocious, very aggressive dog.

NARRATOR: But as hunters bred them larger and larger into the 1800's,

people took notice of their eye-catching size,

and they became a sort of canine celebrity.

LINDA: Landed gentry started using them more and more as estate dogs.

As impressive beasts that would wander their estates and they were kept in the homes

and often lived up on the furniture, closely alongside the humans.

NARRATOR: They were so beloved, that in 1876 they became the national dog of

Germany, which, over time, had an interesting impact on their temperament.

DEBBYE: They were no longer bred to be fighters; they became a pet.

NARRATOR: By breeding only the friendliest Great Danes together,

these guys lost their aggression, but not their stature.

DEBBYE (off-screen): And really theyare gentle giants now.

They're just the world's largest couch potato.

(barking).

NARRATOR: While a Great Dane can hardly fit on our furniture,

the smaller "toy" breeds were specifically engineered for it.

So when you see a tiny toy breed sitting pretty like it's their job,

know that in ancient China, it actually was!

DEBBYE: Toy breeds were developed purely to be companions.

They were literally bred to keep the emperor's feet or hands warm.

NARRATOR: Sometimes it takes a little dog to complete a big task.

And few pups pack more punch per pound than this powerhouse pet.

This lovably stocky, low to the ground, breed's distinct shape helped them excel in a

rather crude sport in England back in the 17th century.

MARTY: There used to be a sport called bull baiting where bulls were actually

chained up and then dogs would attack them.

NARRATOR: While it sounds cringe-worthy, animal baiting had a purpose.

LINDA: Back then, the common belief was that the meat got

tenderized by this stressful experience.

So these bulldogs would chase around these bulls

who would fight in the community center there,

and attract all the potential customers,

and they would then get a premium price

for these stressed animals' meat.

NARRATOR: The bulldog's unique build is surprisingly

the perfect shape for terrorizing a massive bull.

DEBBYE: And so they have these short legs so that they could literally get low to the

ground and even sneak under the belly of the bull so the bull couldn't see them coming.

NARRATOR: When a bull looked down to see what was bothering it,

it was in for an unpleasant surprise.

DEBBYE: The old breeds used to open their mouth wide enough to get a big chunk of the

bull's snout, and hold on for dear life.

NARRATOR: In 1835, the passing of an animal cruelty act put an end to bull baiting.

LINDA (off-screen): They lost their function and consequently a group of gentry who really

loved the bulldogs decided to try to save them.

NARRATOR: And we selectively bred these fighters to become flat-faced pets.

MARTY (off-screen): They started getting even more exaggerated features.

Push the nose in, push the nose in further, push the nose in further.

Shorten the legs, so more of that kind of stance where big upper chest,

tiny little lower body, big pushed-in face.

They could never fight today.

DEBBYE: The bulldog of today can't fight anything,

might fight for your spot on the couch,

or for their next dinner, but that's about the extent of it.

NARRATOR: Canine quiz!

Can you name the tallest dog? How tall is he?

NARRATOR: Can you name the tallest dog?

An almighty Great Dane named Zeus holds the Guinness record for tallest dog.

This righteous pup measures a whopping 44 inches tall from his paws to his shoulders,

a whole foot more than the average Great Dane!

There's a famous saying, "It's not what you wear, it's how you wear it."

And for a dog, style is everything.

Canines wear some of the most sensational coats on earth.

But the source of their beauty comes from within.

HEIDI: We found out that there are three main genes that can be altered and create

six different types of dog coats.

NARRATOR: From bristly short to elegantly long,

the variation is truly astonishing.

DEBBYE: The coat on a dog is so much more important than beauty.

The coat on the dog helps them perform a function.

NARRATOR: Wiry coats, as seen on border terriers,

work as a coarse protective layer to shield from the elements.

Originally native to the cold and windy high altitudes of Afghanistan,

Afghan hounds have extravagant, long-haired coats

that serve as tip-to-toe temperature protection.

Komondors, originally a herding breed, sport dreadlock-like corded coats

to help them blend in with sheep, and shield their bodies from the bites of predators.

Poodles are famous for a distinctively clipped, some might say poofy, coat.

But it's not just for show.

DEBBYE: Those puffs on their head and over their hips and on their legs actually help

keep the joints warm.

ROBERT: The Dalmatian is actually born white and develops spots over time.

NARRATOR: Dalmatians' spots serve no evolutionary purpose, aside from looking awesome.

Then there's a breed whose coat creases, crinkles and wrinkles.

MARTY: When you think of this breed, I think of why they created Botox.

NARRATOR: But the wrinkles on a shar-pei have nothing to do with growing old.

LINDA: They have way too much of a molecule called hyaluronan,

which is a very gel-like substance in the skin,

and they have a mutation that makes them make as much

as ten times what they should have.

HEIDI: The hyaluronan builds up in the skin and creates

sort of space for more skin to grow.

And that's where all the folds come from.

NARRATOR: The original shar-peis were not quite as wrinkly as some seen today.

But their genetic mutation has become drastically

more noticeable throughout their 2,000-year history.

LINDA: People found the wrinkles so cute and so snuggly and so adorable,

breeders selected for dogs that had more and more wrinkles

that were maintained into adulthood.

NARRATOR: The wrinkles aren't just for show;

ancient Chinese dog fighters utilized them as a built-in defense.

HEIDI (off-screen): If he had been bitten, that excess skin was supposed to give the dog the

ability to turn around and still be able to get the dog that had attacked him.

NARRATOR: It also means opponents chomp on a mouthful of wrinkles

instead of the meat underneath.

Fortunately, bigger and badder dogs came along and

shar-peis were no longer forced to fight.

But they couldn't rest easy for long.

The Communist Party opposed the ownership of dogs in the 1950's.

And so many shar-peis were slaughtered that by 1978, there were only 60 left,

and they were declared the rarest breed in the world.

Passionate shar-pei enthusiasts ultimately straightened out this breed's

population problem, but the same can't be said for their extra wrinkles.

As many as one in ten humans are allergic to dogs.

Contrary to popular belief, it's not always their coat that causes reactions.

DEBBYE: People are allergic to a specific protein in the saliva of the dog.

So when a dog licks their coat or their skin, they deposit that saliva on their hair and

that's what makes people sneeze.

NARRATOR: There's no such thing as a completely hypoallergenic dog.

But some pups, like wheaten terriers,

have coats that naturally carry fewer allergens than others.

So if you really want your allergies to calm down,

wash off your pooch!

Dressing fashionably in weather extremes is tough.

But one breed's coat undeniably stays in style throughout all four seasons.

The husky is a heroic breed group we've been relying on for over 1,000 years.

Ever since they lived as nomads with the Chukchi tribe, huskies have helped humans by

transporting food, medicine, goods and even people.

And with just a glance, it's easy to see they have a lot in common with their ancestors.

ADAM: So Siberian huskies are domesticated dogs that have regained a lot of the

characteristics that wolves had.

In fact, we think there was probably a little bit of wolf blood that got

added back in when they were making the breed.

Like wolves, they've got prick ears, they've got a nice bushy tail.

NARRATOR: And one more, hairy thing, a thick double coat.

To sled in frigid temperatures of negative 75 degrees,

yet avoid a meltdown when the mercury rises,

the husky coat has a few tricks up its sleeve.

Their two layer coat changes with the weather.

In the winter, an inner layer insulates by trapping in body heat,

and an outside protective layer

keeps the frigid cold air even further away.

But in summer, it's a whole new ball game.

Huskies go through a process called "blowing coat,"

which is another way of saying they shed.

And shed.

And shed some more, until their winter coat is left blowing in the wind.

Yet holding onto their outer-coat actually helps them beat the heat.

DEBBYE: The outside protects them from the UV rays of the sun

so they don't get sunburned.

NARRATOR: As long they stay in temperatures below 65,

huskies will keep their cool while working hard,

delivering whatever we need, whenever we need it.

In addition to sledding, huskies make great service dogs and family pets.

And just know, that they tend to get attached.

MARTY: If you want to wear your pet to work I suggest getting one.

NARRATOR: Canine quiz!

We've learned that huskies have two coats, but can you name any bald breeds?

NARRATOR: Canine quiz!

There are a few canines whose only suit is their birthday one.

Can you name any bald breeds?

This distinction goes to the Chinese crested and Mexican hairless.

In ancient times, the body heat radiating off a hairless dog's bare body

was used to aid ailments like headaches and stomach aches

by placing these breeds directly on aching joints.

From digging buried bones to chasing just about everything,

it's the particular shapes of these four parts that put pooches in motion.

The specific shape and build of a canine's quarters impacts their abilities and skills.

HEIDI (off-screen): Short legs in dogs are good for digging.

But the long legs are especially good for running.

And this doesn't always go along with their body size.

For instance, a basset hound is actually a very large dog with very short legs.

NARRATOR: For this breed, coming up short pays off big,

a low build gets their nose closer to the ground

to help them track scents with greater ease.

A gene-mutation prevents their legs from reaching full heights,

and corgis have it, too.

DEBBYE: They were built to nip at the heels of cattle

and that's how they helped herd them.

HEIDI: When the cow tries to kick back at the herding dog, he usually misses the corgi

because he's underneath the kick.

NARRATOR: And then there's deep diversity in doggie paws.

MARTY: Well there's a lot of difference in paws for dogs.

Like some dogs in the northern climates,

they have to have stuff that has very good traction.

NARRATOR: When climbing up an icy hill,

large broad pads help grip and clutch the ground.

Webbed paws on a Labrador retriever help them swim.

But perhaps no dog does more with what little he's got than this lengthy hound.

Call 'em what you want: hot dogs, wiener dogs, weenie dogs, or frankfurters.

This little legged breed does have an official name.

Dachshunds can't shake off the distinction of having

teeny tiny legs paired with a long body.

MARTY: I like to call 'em two dogs long and a half a dog tall.

NARRATOR: But there's a method to the evolutionary madness.

HEIDI: So the bone deformity in short-legged dog, it's really a form of dwarfism.

Oftentimes the legs are a little bit bowed and that's basically because

they stop growing in length early on.

NARRATOR: Developed in medieval Germany over the course of hundreds of years,

dachshunds' tiny legs make them one of the best burrowing breeds around.

MARTY (off-screen): There's several advantages of dachshunds having these really short legs.

They're really low to the ground, so they're really good trackers.

NARRATOR: And when they find their prey, they don't let go,

even when they're underground.

HEIDI (off-screen): It's very easy for them to dive into the holes of badgers or rabbits,

for hunting purposes, to get in there, you know, attack the prey and pull it back out.

NARRATOR: Their tiny legs allow them to fearlessly explore narrow holes without

getting stuck, and they go deep.

MARTY: It's a dog that might have its, its nose in one zip code and its tail in another.

NARRATOR: Just keep track of where they wind up.

HEIDI: Dachshunds are also excellent at hanging out underneath counters in the

kitchen and picking up scraps without anybody noticing that they're there.

NARRATOR: Dogs walk on their toes, while humans walk on their heels,

but there is something we both have in common:

a love of pampering.

A paw massage puts pups at ease while also promoting better circulation.

If their pads are cracked or dry, ask a veterinarian for special doggy moisturizer

to help soothe them out.

Zipping around at speeds of 65 miles per hour,

cheetahs are the fastest animal on land.

But there's a dog not too far behind.

Portrayed on cave art, and dating back to as early as 8000 B.C.,

greyhounds are one of the most ancient breeds in the world

and they haven't slowed down as the years piled up.

Greyhounds aren't just the fastest breed;

they're one of the fastest species on earth.

LINDA: They are truly the most specialized running dog we have created.

In six strides they can get to 43 miles per hour.

NARRATOR: They're the most prized breed for hunting speedy prey

like deer, foxes, and hare.

And they've covered a lot of ground,

greyhounds can be traced to nearly every continent in the world.

Every inch of their body is built for speed.

DEBBYE (off-screen): Greyhounds are sort of the super model of the dog breeds,

because they have no body fat.

So you can see every strong muscle through their skin.

They are literally the sleek, aerodynamic, narrow bullet of a dog.

NARRATOR: And when they hit the ground running, they go hard.

DEBBYE: They have a webbed foot which allows them to really pound the ground when

they make a strike.

And then they have these really thick pads to take that amount of impact.

NARRATOR: But that's not the only thing that helps the legs go fast.

DEBBYE: The way a greyhound runs, they literally go airborne.

NARRATOR: Because even their spine is built for cruising.

DEBBYE: They have these long spindly vertebrae,

and they are articulated or joined together in a way

that they can stretch them slightly open so they can get the

maximum amount of reach and literally fly through the air.

NARRATOR: Their spine enables a unique running method

known as the double-suspension gallop,

making them go airborne twice per run cycle.

Once when their back legs kick off the ground

and again when their front legs make the leap.

The only downside to their anatomy is when they shut off their motor.

LINDA: Greyhounds really can't sit properly because

they can't get those pelvic bones down to the ground,

so you'll see them in kind of awkward gawky states

when they're trying to sit.

NARRATOR: Fortunately, when you're this fast,

you don't have to excel at sitting.

Canine quiz!

There are four distinct claws on a pooch's paw,

but what's the name of the obscured fifth one off to the side?

NARRATOR: Canine quiz!

Dogs have four distinct claws on their paw,

but what's the name of the fifth one off to the side?

The mini-digit on the inside of a pooches' front leg is called the dewclaw.

Similar to a human thumb, it helps some dogs grip and hold onto to precious items.

While every dog is delightfully different,

there's one particular part that varies the most.

MARTY: Their head is like somebody had a lot of fun.

There's the pug that looked like it ran 60 miles an hour into a wall.

And then there's the ones where their nose and the back of their head

are in two different zip codes.

NARRATOR: The facial region of every dog consists of 36 bones,

but its specific shape determines

which job a breed is best suited for.

HEIDI: There are three basic head types in the dog.

What we call brachycephalic, or short faced.

And that is what you see in pugs and bulldogs.

There's mesocephalic, which is mid-sized face.

And that's sort of your standard Labrador retriever or pointing dog.

And then you have dolichocephalic, which is a very long face.

And that's what you would see in sighthounds like a greyhound or a borzoi.

NARRATOR: Flat-faced breeds, like boxers look absolutely adorable,

but the compact build comes with a price:

there's less space in their muzzle to circulate air,

which makes them prone to overheating.

Salukis elongated snouts and eye sockets set farther back

are great for spotting small prey in the distance.

MARTY: So it's almost like a gun sight with two little long binoculars looking down there.

NARRATOR: And some canines' heads help us spot prey.

The appropriately named "pointer" uses his noggin to alert hunters.

MARTY: So the game's creeping, the pointer's creeping and finally they both stop.

And they're just staring at each other.

So for the hunter, they can tell by the direction of the head

exactly where the game is.

NARRATOR: But when it comes to being level-headed, one dog has them all beat.

Looking one part egg and one part alien, the bull terrier's odd shaped head

is one of the most unique-looking on the planet.

MARTY: Talk about a distinctive look, there's no other skull looks like it.

NARRATOR: Even their triangular-eyes differentiate them

from the rest of the breeds.

But the shape of their heads didn't always make us scratch ours.

ROBERT: The bull terrier is known for its egg-shaped head

but it didn't always look that way.

NARRATOR: Its original appearance was better suited for being a bad egg.

ROBERT: The bull terrier was originally bred in England in the 1830s.

It was designed to be the ultimate fighting dog

by crossing the tenacity of a terrier with the brute force of a bulldog.

NARRATOR: A new breed called a "bull and terrier" was born.

With ferocious energy and enough muscle to back it up,

they were a sight to see in the ring.

Not long after the bull and terriers' creation, dog fighting was outlawed

and this super-dog was left without a function.

So the purpose of this pooch became to make us smile.

We selectively bred their snout to become more pronounced,

until it nearly took over their entire face.

MARTY: It's just like their whole head is their nose.

NARRATOR: The bull terrier became the dog that makes you do a double take.

Dogs often tilt their heads to the side when we speak.

It turns out it might not just be to hear us better.

One theory suggests that the change in perspective helps them see our entire expression

without their muzzles blocking the view.

It's also entirely possible that they're just being cute.

You've probably heard that a bark can be worse than a bite.

But for one breed, their bite is as bad as it gets.

Rottweilers have a bad rap for being brutal.

The issue stems from their heads.

ROBERT: Rottweilers have massive skulls which house

some of the strongest jaw muscles around.

NARRATOR: Their bite isn't quite as powerful as a great white's.

But the Rotty's 300-pound bite force is nothing to scoff at.

DEBBYE: Once they bite down it's almost impossible to force them to let go.

NARRATOR: So how was this big head used to their advantage?

ROBERT: A Rottweiler's heritage can actually be

traced back to the Roman Empire.

When Rome was busy conquering Europe, they brought their cattle driving dogs with them.

NARRATOR: Their natural strength was a good fit

for moving cattle over long distances,

and their intimidating bite not only ensured cattle wouldn't get stolen,

but that even small valuables were safe and sound.

ROBERT: Their owners would actually hide money in the collars because no thief

would think to ever put their hand there.

NARRATOR: But when the Industrial Revolution came around,

we began moving cattle by rail

and Rotties, and their big heads, were out of a job.

LINDA: But there were so many people who truly loved these dogs

that started looking for new jobs for them.

NARRATOR: Luckily, there was employment for a dog with a menacing mug.

LINDA (off-screen): And they became developed as guard dogs,

they had important roles in the military,

and they continued to have a function

which allowed the breed to be perpetuated.

NARRATOR: Despite their intimidating demeanor, they do make a great family pet.

Because deep down inside, if you train them right,

most Rotties are just big-headed goofballs.

Dogs have undergone an overwhelming amount of change throughout history,

and there are no signs that their rate of evolution will slow down anytime soon.

ADAM: It's safe to say anywhere humans are gonna go, they're gonna take dogs with them.

NARRATOR: As our lifestyles and needs evolve, so too, will the shapes of canines.

HEIDI: There will be more breeds because our lives change,

and then we create sort of a slightly new dog

that's gonna fit into our new life.

NARRATOR: Any shape or any size,

they will forever be man's best friend.

Captioned by Cotter Captioning Services.