Shane Campbell-Staton: This is my best friend Tatanka.

I love this guy.

He's not just like family, he is family.

What we have feels pretty special, but it's certainly not unique.

Male singer: ♪ Yo!

Yo!

♪ Shane: Consider this-- if you take a plane, bus, boat, or helicopter to any part of the world that has humans, you'll find dogs living alongside us.

And, let's face it, we're pretty much everywhere.

To live in our world, dogs have had to reinvent themselves time and time again.

DMX: ♪ Where the hood ♪ ♪ Where the hood, where the hood at?

♪ ♪ Have that ... in the cut, where the wood at?

♪ ♪ Oh, them ... actin' up?

Where the wolves at?

♪ ♪ You better bust that if you gon' pull that ♪ Shane: Shaggy, short-haired, hairless, and dreadlocked.

Tiny, sensible, and massive.

Short legs, long legs.

Ears of every shape and size, and a kaleidoscope of colors.

Idealized forms crafted over generations.

But dogs aren't the only ones transformed by this relationship.

By making themselves indispensable, they've changed our lives and our society itself.

So this isn't just a story about our human footprint on dogs.

It's a story about their pawprint on the world.

Welcome to the age of humans, where one species can change everything, and what we do reveals who we truly are.

This is "Human Footprint."

[Choir vocalizes] [Dog panting] Shane: Dogs have been a part of our society for longer than any other animal or plant species on Earth.

Our alliance began when humans and wolves learned to live with one another, and each species became something different than it was before.

In the millennia that followed, we've shaped entire ways of life around the descendants of those ancient wolves.

Dogs guard our families, hunt our food, herd our livestock.

They learn our languages, commandeer our couches, explore space, and rescue us in more ways than one.

But it's a two-way street.

Joining this alliance has given dogs an advantage, too.

Worldwide, just 250,000 wolves survive in the wild.

Meanwhile, up to a million of their domestic descendants are born every day.

As the world's dog population approaches a billion, their impact on our lives and our planet has never been greater.

So in the age of humans, what does it mean to be a dog?

And what lessons can dogs teach us about ourselves?

Today, most of our dogs need us more than we need them, but not here.

North of the Arctic Circle, an ancient alliance with dogs still means the difference between life and death.

Man: One day we saw these wolves, and they were faster.

They had better smell than us, you know, they could hear better than us, so we're like, "Oh, why don't we befriend this animal?"

[Dogs barking] Thousands of years later, they're still by our side.

[Barking continues] And without them, my people wouldn't survive.

They're part of who we are, dogs.

Shh.

♪ Shane: The sled dog is an animal created and relied upon by us.

Countless generations of evolution have transformed them into the perfect Arctic ally and one of the fastest long-distance runners on the planet.

These dogs belong to my guide, Devon Manik.

He's a normal 21-year old.

Loves listening to music, cruising the web, you know, when he's not out in the bone-chilling cold, doing what it takes to survive here.

[Dogs barking] [Choir vocalizing in native language] Shane: Look at those adorable, bloody little faces.

Devon: Heh heh!

They're no pet dog, eh?

Ha ha!

Do they prefer, like, raw meat over kibble?

If I feed them kibble, they'll start losing weight.

OK. Meat is what keeps them going.

I feed them whatever I hunt, so they eat the whole animal.

What do you imagine it was like for the first people that, like, colonized this place without dogs?

A lot of work.

Ha ha!

Yeah?

Shane, voice-over: A lot of work because there's just not a lot to eat up here, and what little there is, doesn't give up easy.

Woman: So, if you're ever lost in the Arctic, make sure you have muktuk.

It has all the vitamins you need so you won't get scurvy.

[People chuckle] Shane, voice-over: Mavis is Devon's mom and an expert in all the delicacies the Arctic has to offer.

Shane: What is this?

Whale skin.

It's very oily and...oceany.

Oily and oceany.

[Chuckles] I like that.

I like that.

So you could take that piece.

OK, just-- Yeah.

Is it oily and oceany?

Wow.

[Chuckles] It is both oily and oceany.

Yeah, that was a great description.

[Chuckles] Belugas are cute and all, but--heh!-- they taste really good, too.

Ha ha!

Raffy: ♪ You're just a little white whale on the go ♪ How old were you when you started hunting?

I got my first seal when I was 8.

Shane: Wow!

Shane, voice-over: For thousands of years, whether it's across the sea ice or on land, dogs have been an essential part of any hunting expedition here, so what I was about to eat is only here because of that human-canine alliance.

Mavis: Frozen musk ox meat from the leg.

Well, meat is very high in our diet.

Makes up, like, 95% of it.

Shane, voice-over: Between Devon's family's diet and the diets of his dogs, meat is life, and it takes that partnership to bring it to the table for both species.

Devon: That looks so good.

Try it raw.

Just tr--OK. Oh, just pop it in there, huh?

[Chuckles] Good?

OK.

It's like... beef that's been on a treadmill for a while.

[Mavis and Devon chuckle] Do you want more?

Am I killin' you?

No, this is great!

[Laughs] Mavis: He's gonna be sweatin' tonight if you keep feeding him.

I'm a big boy, so I sweat anyway.

[Mavis chuckles] No, it-- it's like, when you eat the meat, it's like you have a-- a furnace inside you, and you get so hot, like, you panic.

Feels like you don't know-- like you're going to explode.

I'm a little bit concerned now.

Ha ha!

Yeah.

Yeah, you get so hot... OK. but it's from the inside.

I mean, that's got to be a good way to be when the winter comes around, though, I imagine.

Mm-hmm.

[Festive hip-hop music playing] ♪ Devon: Thanks, Mama.

Mavis: You're welcome.

Shane: Thank you so much.

I have the best mom in the world.

Ha ha!

Mm.

Wild carrots.

Ha ha!

She picked them just right across the street.

[Chuckles] Better leave your mom alone.

Yeah!

Ha ha ha!

Choke on your musk ox.

Ha ha ha!

Shane, voice-over.

: Devon's community has first-hand experience of life without dogs, but not by choice.

Male broadcaster: It's the tail end of the brief summer, so-called, that they get on Cornwallis Island, 75 degrees north.

They've named the place Resolute.

Shane: In the 1950s, the Canadian government established a permanent settlement here to secure their claim to the land.

Devon: So they relocated families from northern Quebec all the way up here.

[Film projector whirring] And they were Inuit, but where they live, there's trees growing.

So, coming all the way up here, where there's barely any vegetation, it was really hard for them to live up here.

Mavis: They were promised so much, and when they got here, they were living in canvas tents over the winter.

Then the RCMP killed all the sled dogs.

[Shouting, gunshots, dogs yelping] Shane: The RCMP, or Royal Canadian Mounted Police, killed hundreds of sled dogs, keeping the newly relocated Inuit from hunting or traveling outside of town.

Devon: Since they evolved with us, the dogs need us to survive, we need them to survive.

And they were, like, so close to being extinct, so close.

Shane: Without dogs, the people's livelihoods and their culture itself began to erode.

It's a very dark history, how Resolute became, but in the last about 10 years, maybe, they've had, like, a revival of the sled dogs.

When did you start using a sled dog team?

I was 16.

I had one dog.

My mom got me a dog, actually.

We're in a high polar bear environment.

Shane: Mm-hmm.

So all I thought was, you know, they were just chasing my little boy.

[Laughs] Shane: And--oh, wow.

And I used to take him out of town, and he had a sled and he would pull us home.

My mom would tie me to the bed before she'd let me do something like that.

Devon gradually grew his team from one dog to 16.

Most of them are Inuit sled dogs, the OG of the Arctic.

Devon: It's a very old dog breed from about a thousand years ago.

They came along with the Inuit, from Siberia to Alaska, all the way up to here.

[Dogs barking] Shane, voice-over: But after the near extinction of the Inuit sled dog, there weren't many elders in Resolute to teach Devon how to hunt the old way, so he turned to Gen Z's most trusted source of information.

Devon, voice-over: I used to watch videos on YouTube of Greenland mushers.

You know, I'd try to do how they did it.

You learned how to-- Mavis: Ha ha!

how to run a sled dog team from YouTube?

Ha ha ha!

Well, not entirely, but it was a part of it, yeah.

I learned how to bake, like, cinnamon rolls on YouTube once.

Ha ha ha!

What can I expect out on this-- on this hunt?

[Dogs barking] Devon: At first, it'll be chaos.

[Barking continues] ♪ Shane: I have legitimately never seen and definitely never heard anything like this before.

[Dogs barking] God, these boys are ready to go.

Devon, voice-over: Yeah, adult fights get pretty nasty.

If I don't stop them, they'll try to kill each other.

[Barking continues] It's, uh, game time out here.

[Indistinct shouting] All right, put it there.

Yeah, you might as well not even come out here if you're not going to put the bear skin on it.

[Devon laughs] Two more left.

I put one on, and the last one, you get on the sled.

OK. [Dogs yelping] ♪ Devon: Just hold on for dear life when you're going.

♪ They should start slowing down once we get onto the flat ice.

Shane, voice-over: Over millennia, only the strongest, most cold-tolerant dogs survived these brutal conditions.

They evolved into a creature the planet had never seen.

♪ A team of sled dogs can pull a heavy load across hundreds of miles of snow and ice in a week, all while finding prey and protecting hunters from polar bears.

[High-pitched tone] With these dogs at our sides, humans unlocked life above the Arctic Circle.

[Snow crunching] Devon: I'm usually hunting alone, just me and the dogs.

[Whip cracks] They don't care about anything else.

They just want to pull.

We can't survive without each other.

We're heading out-- it's called Resolute Passage, so it's between here and Griffith Island, and we're gonna just-- gonna follow some cracks, go out wherever the seals are.

Shane, voice-over: Even in this featureless, white landscape, Devon and the dogs knew where the seals would be.

Devon: See a seal way out there.

We're gonna grab the gun and we're gonna stalk it.

On foot?

Yeah.

What do you need me to do?

Aha!

Watch.

Heh!

Here to watch?

Yeah.

OK.

But you can follow me.

How close will you try to get to the seal?

A hundred to 200 yards.

♪ [Whispers] Look, I'll be back.

♪ God, it's cold out here.

[Wind howling] ♪ Shane: Yeah.

I mean, I think he's about to take a shot.

[Heavy breathing] [Heart beating] ♪ [Gunshot echoes] [Wind howling] ♪ I couldn't get a clear shot.

There was too many snow drifts in the way.

Want to go for a swim?

No, no, hell no.

[Both laugh] Devon: If the seals are gone, they're gone.

We move on!

It's frustrating.

If I don't get a seal, I can't feed my dogs.

Shane, voice-over: This time of year, the sun doesn't set, but Devon knows when to call it a day.

It's after midnight, definitely time to make camp on the ice.

So this is how you secure dogs if you don't have an ice screw.

You just...chisel out two holes in the ice and you make them meet.

Shane: Is there anything I can do to help?

Look out for bears for me.

Oh, OK. [Chuckles] Yeah, that'll hold.

[Chuckles] Shane, voice-over: Then, sure enough, an off-white object appeared on the horizon.

How do you feel about being hunted by polar bear?

Oh, my God, that is actually a polar bear.

Wow!

♪ It's just like I remember from the Coca-Cola commercials.

[Chuckles] ♪ Does this make you nervous at all?

Naw.

But if you were out here without the dogs, would you be nervous?

Yeah.

Heh heh!

[Laughing] What's he doing?

I'm looking at him and he's looking at me.

♪ Like, I wish I could... go back and, like, talk to 13-year-old me and tell myself what was coming.

I'd flip out.

I'm flippin' out now.

Easily the coolest wildlife I've ever actually seen in the wild.

Once he figures out what we are, he'll probably move on.

[Dogs barking] Unless he's starving.

Ha ha ha ha!

These guys love hunting bears, so they're really great alarms.

Maybe he caught a whiff of the dogs.

I hope.

Heh heh!

[Barking continues] Shane, voice-over: Devon's dogs are unlike anything I've seen before.

Humans transformed them into workhorses that haul massive loads over vast distances in the harshest environment on the planet, but they transformed us, too.

By opening up the Arctic, these dogs became the foundation of a unique culture found nowhere else.

[Snow crunching underfoot] Seeing sled dogs at work, it's tempting to think that it's dogs' physical prowess that makes them such perfect partners.

But through our species' history, the bond we share is actually less about brawn than it is about brains.

♪ [Birds chirping] Shane: Do you think that dogs are better at understanding us than we are at understanding them?

I think that's probably pretty safe to say.

I don't think they understand much of our spoken language, but when it comes to our bodies, our movements, our intention that we communicate through our behavior, I think they're really good at that.

Shane, voice-over: This is Brian Hare.

Brian gave up his prospects as a pro-baseball player-- no joke-- [Bat clangs] to study the minds of animals, especially dogs, but his batting average still ain't bad.

Brian: Dogs have these communicative abilities with us that had such a big impact on dog evolution.

Shane, voice-over: Before he got into dogs, Brian was all about chimps.

Back then, everyone thought that chimps, our closest animal relatives, could help us understand the evolutionary roots of our intelligence.

Neil Armstrong: ...for mankind.

Making the transition to dogs, that's a pretty big jump.

So I was working with young children, and we were comparing young children, how they learn to think, to chimpanzees.

Around 9 to 12 months, kids start understanding gestures.

If I point over there, you might look and say, "Oh, OK," you see, and we're kind of on the same page.

And so the idea is, that's the beginning of culture.

So we were looking at chimpanzees and asking, "Can they follow pointing like young kids can?"

And no, they're actually terrible, as smart as they are.

Really?

Yes.

They cannot do that.

Oh, they really struggle.

Shane: That's really surprising to me.

Yeah, I've spent weeks of my life in front of chimpanzees just trying to help them.

Ha ha!

The mentor I was working with basically said, "Well, we think this is unique to humans."

Mm-hmm.

And I was like, "Well, wait a second, unique?"

When I was a kid, I used to play fetch, and the dog would lose the ball, and I would point to where the ball was, and he would run off where I pointed.

My dog just stares at me passive-aggressively... Ha ha!

until I pay attention to him.

So he kind of just, like, peers at you, yeah.

"I know you see me standing here."

Yeah.

"I know you think you're busy."

Yeah.

"But you're not..." Exactly.

"'cause I need to go out."

Ha ha ha ha!

What we found was that even young puppies are really good at using our gestures.

Within a few weeks of life, this really special thing develops very rapidly in dogs that allows them to communicate with humans.

Shane, voice-over: After that, Brian's research went in a whole new and much cuter direction.

[Puppies barking] [Toy squeaks] [Person whistles] Shane: I run a lab, I don't get to do this, and I'm kinda pissed about it, tell you the truth.

Ha ha ha!

What is it like to have the best job in the entire world?

It's like my birthday every day.

Ha ha!

I just wake up in the morning and I'm like, "Aw, I can't wait to see you guys!"

Shane, voice-over: This is Vanessa Woods.

She and Brian wrote the book on dogs' unique cognitive abilities, and today, they also run the Duke Puppy Kindergarten, which is basically a preschool for service dogs.

♪ [Puppies yelping and barking] Vanessa: They are 12 to 13 weeks old right now, so they're all teething and, um, yeah, pretty much going crazy.

Oh!

Shane, voice-over: Being a service dog is no joke, by the way; you got to score big on the doggie equivalent of the SAT.

So we put them through a series of cognitive tests to find out which dogs are gonna make it.

Shane, voice-over: These tests are some of the same ones Brian was doing, without success, on the chimps.

Shane: So walk me through one of these tests.

Yeah, the one we use most often is just really simple.

So you hide food, but then you just point and you see if the puppy will use your pointing gesture to find the food.

That's it.

OK. Yeah, it's not rocket science.

Vanessa: Puppy has to know that your gesture is not just a finger movement.

It's an intention behind that... something that we call cooperative communication.

These puppies can understand it at 8 weeks.

♪ Shane, voice-over: Seems pretty simple, right?

No tricks involved; you're literally giving them the answer.

But chimps, they don't understand that you're trying to help.

Vanessa: This is actually a really sophisticated cognitive ability.

We don't really see it in any other animals, even great apes, our closest living relatives.

From an evolutionary perspective, these guys come from wolves.

Mm-hmm.

How are wolves at performing this test?

They're terrible.

They're awful at this.

They cannot use a human gesture to find food.

That's just not the way they think, but with dogs, they were able to cross that species divide and communicate with us and understand with us in a way that really no other species can.

Shane, voice-over: It's part of what makes dogs so appealing, and it's a critical skill for a future service dog.

We are trying to get more service dogs graduated, and it's really fun to guess who is gonna make it.

Just between you and me, of these 3... Of these 3... do you think one is most promising?

Nestle's gonna make it.

Nestle!

Touch.

Did you see that?

Bam.

Shane, voice-over: If Nestle and his less-gifted but equally cute classmates graduate to become service dogs, they'll reach the pinnacle of the dog-human partnership... but service dogs ain't the only high-achieving canines on the block.

[Dogs bark] This is canine freestyle, a competitive sport where dogs and humans dance.

Following gestures to find food is one thing, but in freestyle, each partner observes and interprets the other's body language to move in perfect harmony.

In a short, semi-improvised routine, thousands of years of evolution boil down to 3 to 5 minutes of intense inter-species connection.

Meet Trish Koontz and her canine partner, Boone.

They're two of the best.

[Barks] ♪ Why do you like freestyle so much?

Oh, gosh.

Because of this connection thing, we're equal partners.

Dogs have a tremendous capacity for creativity.

We allow dogs to really, fully invent movement, and that's where we get our movement vocabulary.

This is gonna be our phrase for today... Shane, voice-over: Trish teaches a class in canine freestyle at the Durham Kennel Club.

And when you move from here towards the spectators, that's the most powerful movement you can do.

["Come Back in One Piece" playing] [Barks] DMX: ♪ Baby, I am what I am, I'm gon' be who I be ♪ Uh!

♪ Everything from chasin' a cat to ... on a tree ♪ Uh-huh.

♪ Let me see what I gotta see, do what I gotta do ♪ ♪ Dog for life, but keep it true ♪ Shane, voice-over: Freestyle truly is a dance.

With the flick of a wrist, the point of a finger, the subtle lift of the chin, the dogs move exactly as instructed.

No other species can communicate with us so effortlessly.

Shane: What are the cues that you think he is keying in on?

First is always body language with dogs... OK. 100%.

It's more powerful than anything.

I just lift my chin, he's, like--backs up, that subtle.

Shane, voice-over: At the end of the class, Trish let me try it out with Boone.

Even though Boone and I had just met, I moved my body and hands the way Trish taught me, and he understood exactly what I wanted.

Trish: Whoo!

[Clapping] Wow.

Ha ha!

Shane, voice-over: But how did this unique relationship get started when wolves first became part of our lives?

Ha ha ha!

Beastmaster.

Shane, voice-over: Because I'm no anthropologist, but I don't think cavemen were out there dog-dancing with wolves.

The most intuitive answer is that we chose to bring dogs into our lives.

So I've always wondered, about, you know, 10,000 years ago... Mm-hmm.

someone was like, "Hey, guys, you remember those furry things that ate John the other day?"

Ha ha ha!

"What if we made them our best friends?"

Right, right.

Right?

And that was the whole process.

Right.

That's usually the story people tell, right?

People woke up in the morning and said, "Hey, you know what?

Let's invent dogs."

I actually favor a hypothesis where wolves chose humans, and not that humans decided to create dogs.

Shane, voice-over: Brian thinks that as humans spread around the world, the ancient wolf ancestors of today's house pets faced a dilemma.

15,000 years ago, there was no agriculture.

That means you're directly competing with wolves.

If you're a wolf, you have the choice; you can keep doing what you've been doing or you could be like, "You know what, let's just go near the humans..." Mm-hmm.

"and let's just eat out of their latrine and their garbage."

OK.

There was natural selection to be attracted to people, so that's the big idea, is that wolves that were attracted to us had an advantage.

Shane, voice-over: Living around humans, wolves got easy meals, as long as they didn't bite the hands that fed them.

I don't think people would put up with that.

The wolves become friendlier, and it kicked off what we call self-domestication.

OK. Shane, voice-over: According to Brian, a key piece of evidence for self-domestication comes not from dogs or wolves, but from another close relative-- foxes.

It's an amazing story.

So, after World War II, Russia was farming foxes for fur coats.

A Russian geneticist, Dmitry Belyayev, started to select a population of foxes to be friendly.

Shane, voice-over: And this was in Soviet Russia.

Darwinian ideas were not exactly popular, and, in fact, many scientists were murdered for just even trying to study genetics.

In this hostile environment, Dmitry could sort of hide his research by working in Siberia on fox farms.

Mm, wow, so he was slick with it.

Ha ha ha!

Yeah, he was, he was.

He really slid under the radar.

That takes a lot of guts.

Even his own brother was actually murdered.

His brother was a geneticist.

Shane, voice-over: With each generation, Belyayev identified the foxes that were least afraid of people and bred them with each other.

After a couple of decades of breeding, the friendly foxes acted, well, kind of like dogs.

They want to be near you, when they see you, they whimper, they wag their tails like crazy, they jump in your arms.

That's interesting.

Shane, voice-over: This was evolution at warp speed, and the friendly foxes didn't just love people, they began to understand them, too.

And I have gotten to visit and I worked there.

Oh, really?

And got to do research in Siberia with the foxes.

That's amazing.

Yeah.

We played these gesture games with them.

Friendlier foxes are better at reading human gestures, just like dogs.

Mm-hmm.

Shane, voice-over: Belyayev risked his life to do this research, and it paid off.

The Russian fox experiment shows that there's a genetic basis for friendliness.

Once an animal isn't afraid of us, it opens up the door for a deeper level of communication and a new kind of relationship that's been wildly successful.

How many dogs are there now in the world?

Close to one billion?

Meanwhile, wolves, unfortunately, are endangered everywhere where they remain.

So the wolves that woke up in the morning and decided, "You know what, I'm gonna go eat human garbage," they made the right call.

Yeah.

They got friendlier, they won big-time.

Yeah.

Shane, voice-over: Now, millennia have passed since those ancient wolves first stepped out of the woods and into our world.

[Slide projector clicks] But you don't have to dig into the past to understand the lives of these early dogs.

In fact, most of the world's dogs-- 7 out of every 10-- still live this way: not quite wild, but not pets, either.

[Rapid electronic beeping] Today, hundreds of millions of street dogs thrive in cities, towns, and villages around the globe.

♪ And nowhere in the Western Hemisphere has more of them than Mexico.

Here in Mexico City, more than a million ownerless pooches roam the streets.

If you grew up in the US, you might feel a little uncomfortable around street dogs.

We're taught that this isn't the way to live with dogs, but given the numbers, it's our relationship with dogs that's the anomaly.

[Dog barks] [Film projector whirring] [Bicycle bell rings] [Dogs bark] Woman: Generalmente, se mueven en manadas.

Generalmente, este, se van juntando varios perros.

Entonces, van llegando otro y otro y otro a esa misma zona, y, eh, finalmente, se van haciendo compañeros.

Shane, voice-over: Cynthia Martinez is a nonprofit veterinarian who cares for stray dogs, but she doesn't have to go into the office to see her patients.

Here in the streets, reading humans and their intentions can help a dog find a free meal or avoid a beating.

It's probably in this context, living in our shadows, that dogs first learned to understand us.

Shane: I have a very large Great Dane who is pretty pampered, I--I admit.

If he were to end up here on the streets, how do you think he would need to change in order to successfully survive?

Necesitaría... valentía, carácter.

Este, sacar lo más de su instinto.

No confiar tanto en los humanos eso sería.

Actually, it sounds very similar to the lessons that I learned growing up in the 'hood in South Carolina, actually.

[Dogs howling] ♪ Shane, voice-over: The city is its own kind of ecosystem, and these dogs are well-adapted to it.

After all, they've been sharing the streets with us for thousands of years.

In this working-class neighborhood, they still do.

[Dogs barking] ♪ [Siren] ♪ But across town... [Chime dings] things look different.

♪ [Dogs barking] Mexico City's wealthier neighborhoods look a lot more like cities in Europe or the US, at least where the dogs are concerned.

But why?

♪ Shane: Hey, Chris.

What's up, man?

Hi, Shane.

I'm really interested in trying to understand how we got here, like, to this specific relationship with dogs.

Shane, voice-over: This is Chris Pearson, a historian in Liverpool who studies humans' complicated relationship with animals.

He's written a book about how dogs shaped modern cities, and vice versa.

Chris: Imagine you were a street dog in New York in 1800s.

You could go where you wanted to.

You could hang out with different types of dogs, different types of humans.

Shane, voice-over: Until the 19th century, cities in the US and Europe were full of street dogs.

Even in the wealthy neighborhoods, it was normal.

Things began to change as dog breeding and recreational hunting came into fashion among the upper class.

At the same time, a wave of immigrants moved into European and American cities.

Elites began to see the old way of living with dogs on the street as distasteful, but it was more about disdain for certain groups of people than dogs.

Chris: Often, elites in a city, they would marginalize people-- poor people, people of color-- as kind of almost, like, animalistic, and the way in which they lived with animals was sort of seen as evidence of that.

Shane, voice-over: People in power used every opportunity to wipe out street dogs as a way to enforce their way of living, which they perceived as more civilized.

Chris: In 1848, there was what newspapers called the "Great War Against Dogs," which was when, basically, there was a rabies scare.

They produced loads and loads of material-- propaganda, if you like-- that these were, like, dangerous, disorderly, dirty dogs who had to be wiped out.

Dogs who weren't leashed or muzzled, they would be killed.

[Thudding sounds] Sometimes you'd have policemen, like, shooting dogs in the street.

[Gunshots] In London, they were poisoned, and in New York, they were drowned in the East River.

Shane, voice-over: The sudden decline in street dogs had an unexpected effect on one big New York City industry.

Chris: So, by the early 20th century, the streets were cleaner.

[Slide projector clicks] Before that, dog mess was part of the urban economy, so people go around picking up dog mess, taking it to tanneries, and it was used to treat leather.

Ha!

People used-- people used dog dookie to tan leather?

Yeah, yeah, yeah.

Now, this is a very important question.

Are any of the leather goods that I'm buying now being treated with dog dookie?

Is that a leather cap you've got on?

[Chuckles] Shane, voice-over: Poop jokes aside, the elite crackdown on dogs wasn't just limiting where dogs could be, it was actually re-defining what dogs were allowed to be.

We've radically transformed the lives of dogs.

We control how they move.

We control how they're bred.

We control heavily what they eat.

You know, it's a huge, huge change.

We don't have street dogs anymore.

Shane, voice-over: This transition changed our relationship with dogs, but it also reinforced how cities are divided by class and race.

You can see it in Mexico City, where the transition is still underway.

Rich parts, you see purebreds on leashes; poor parts, street dogs on every corner.

But just because they live on the street doesn't mean all these dogs are on their own.

Take, for example, my boy Güero.

Man: ♪ What's up?

♪ Man 2, distorted: ♪ What's up?

♪ Both: ♪ Boyeez!

♪ [Dog yelps] Shane, voice-over: Christina Muñoz is another vet who works with street dogs, and she recently took Güero into her home.

♪ [Horn honks, Güero barks] Shane: So how did you decide that you wanted Güero to come home with you?

Porque siempre lo veía en la calle, y, eh, ahorita lo ve muy repuesto, pero en realidad, era un perro superdelgado.

De comer.

Y nos empezó a seguir y a seguir.

Master manipulator.

I like that.

Heh heh!

Yeah, you!

Shane, voice-over: Güero isn't exactly a pet, but he's not entirely a street dog, either.

He's just found one more way to be a dog, and he's definitely not alone.

Millions of dogs around the world live like he does.

Güero has a home base and even a roof over his head, but he also leans on a wider community of humans for life's essentials; a community that includes Christina, but also the ice cream lady on the corner and others that only Güero knows about.

♪ Shane: Now, do you consider yourself Güero's owner?

Yo creo que el 80% sí.

Justo, mi mamá dice que Güero agarra la casa del hotel porque viene a desayunar, comer y cenar.

Y tiene su cuarto, pero se la vive de vago en la calle todo el día.

You can take the dog out the street, but you can't take the street out the dog?

Sí, es como algunas personas, el barrio los respalda.

OK. Ha!

Shane, voice-over: Our cities and towns may be changing, but dogs always seem to find a way to fit in.

Even high above Mexico City, you can hear them in the streets below, doing what they've always done, surviving in a world full of humans.

I think it's easy to look at the street dogs and see the tragedy of it.

But, you know, like, actually seeing the dogs, being able to interact with them on the street, like, seeing individual lives, I think there's something a little bit deeper there that...you know, I think is somewhat hopeful and something that I can relate to in a really odd way.

[Dogs barking] These animals, they don't get a lot, but they make use of what they do get, and you live the life that you can live.

♪ [Dog yelps] Now, in the interest of fairness, I also had to spend some time with the pups that do have it all... [Dogs bark, train whistle blows] because they're part of this story, too, and they're giving back to us in a way you'd never expect.

♪ Woman: I grew up in a family that bred and showed dogs.

Shane: OK. My parents were involved in bearded collies... OK. and I was the trainer, handler, groomer.

Oh, wow.

Ha ha!

I became all of that, and so I grew up in that world.

Shane, voice-over: This is Gail Bisher, and if you can't tell, she's really into dogs.

♪ Gail is a legend in the world of dog breeding and dog shows.

Gail: I really like the competition, and as a young person, I competed, and for me, I grew up in the Midwest, so going to New York City, as a teen, it was...

Very exciting.

It was very exciting.

Yeah.

Ha ha!

Shane, voice-over: By the time she was 12, Gail was training and competing with award-winning dogs, and today, she's the communications director for the most famous dog show in the world, the Westminster Kennel Club Dog Show.

This is Simon, the English Cocker... OK. and Bella the Vizsla.

Hi.

Yeah, just all in the business, you get in there.

Ha ha!

What's going on?

OK. Ha ha!

Yes.

Come here, Simon.

One thing that people don't realize is that dog ownership and breeding has really shaped human history.

If you could have a dog that had certain traits to make it a good hunting companion, that's something that then could help you survive.

Shane, voice-over: Yeah, that checks out.

As humans spread across the world, dogs came with us, crossing the land bridge into the Americas, and even traveling by boat to the Pacific Islands and Australia.

Along the way, we discovered that dogs could be useful for all kinds of things, like hunting, herding, and protection.

Gail: People really selectively bred dogs for specific purposes, and a lot of times, today's pet owner doesn't make that connection.

Shane, voice-over: By the time the Egyptian pyramids were built, dogs had already been shaped into a handful of distinct breeds, each one specialized for a specific task.

If you've ever seen these dogs really do what they're bred to do, it's an incredible sight.

Hmm.

♪ Male broadcaster: He's fast and elusive, intelligent and willing.

Loyalty and devotion to his job are commonplace.

Gail: This creature, in their world, in their, "This is my best me, this is what I do."

Shane, voice-over: But these ancient breeds are just a tiny fraction of what dog diversity has become in the last 150 years.

Shane: I've never been to Westminster.

Is Westminster essentially the Super Bowl of dog showing?

It is serious competition.

OK.

It is serious competition when you're in the ring.

Diana Ross: ♪ I'm ♪ ♪ Coming ♪ ♪ Out ♪ Shane, voice-over: OK, I have died and gone to heaven.

Bouviers, Bulldogs, Spanish Water Dogs, Dachshunds and Chihuahuas, Borzois, Chinese Crested, Basenjis, Pugs, Scottish Deerhounds, and Toy Poodles.

Ma$e: ♪ Now, who's hot, who not?

♪ ♪ Tell me who rock, who sell out in the stores?

♪ ♪ You tell me who flopped, who copped the blue drop?

♪ ♪ Whose jewels got rocks, who's mostly Dolce down... ♪ Shane, voice-over: And these are no ordinary dogs.

These are the best of the best.

For more than a century, the world's most remarkable purebred dogs have descended on New York each year to go for glory in the Olympics of canine competitions.

Gail: All right, you got to be ready.

This is it.

We have 49 states represented... Shane: Wow.

and we have 9 other countries represented this year.

Shane, voice-over: While some duke it out at agility and obedience, the main attraction at Westminster is the conformation competition-- basically a breed-specific beauty pageant-- and these dogs look fresh.

First of all, I have never seen so many dogs that made me feel ugly.

Ha ha!

Female singer: ♪ I don't know what they want ♪ ♪ From me, it's like... ♪ Shane: For every Coonhound and Komondor, every Pharaoh Hound and Corgi, every Cocker Spaniel and Greyhound, the title of "Best in Breed" is the Holy Grail.

Shane: And from a judge's eye, like, how do you define, like, what makes a champion?

Gail: It's the written standard.

So every breed has a written description of what they're supposed to be, what their structure is; bone structure and coat, eye shape, everything, right?

That written standard is what the judges study and are judging the dogs by.

Shane: OK. ♪ Shane, voice-over: In the 19th century, as elites cracked down on free-roaming dogs in major cities, owning and breeding dogs became part of high society.

Breed standards provided a way to keep the lines pure and determine who was in and who was out.

Gail: The Kennel Clubs, really, our job is to help-- is to celebrate these breeds, A, which we love to do, but it's also about just maintaining those historic breeds that have been around for us for a long time.

Shane, voice-over: A carefully curated pedigree can help make a champion, but meticulous breeding has also had a profound effect on the genetics of dogs.

Man: I have been every year for the past 5 years.

Shane, voice-over: This is Adam Boyko, a dog geneticist at Cornell University.

When he arrives for Westminster Week, he arrives in style.

Shane: What is so interesting about these events for you?

Dogs are the most diverse land mammal on earth.

There's a 50-fold difference in body size between a Chihuahua and a Great Dane.

Shane, voice-over: Dog breeders are methodical.

Every generation, they weed out dogs with traits that deviate from the breed standard.

The goal is to create a particular look, and the only way to accomplish that is to remove the genetic variation that makes some dogs within a breed look different.

The result is that dogs of the same breed don't just look the same, their genomes are almost identical, too, and that makes purebred dogs pretty useful if you're a geneticist.

You want a population where the individuals are similar.

This is why scientists spend so long studying mice, right?

'Cause you can have these inbred strains of mice that are all essentially identical to each other.

Shane, voice-over: Just like laboratory mice, the genes of dogs within a breed are so similar that any differences become easy to spot.

♪ And finding those differences helps researchers discover which genes encode which traits.

Shane: Tell me about these dogs.

Adam: Rhodesian Ridgebacks.

This breed was a land race breed in Africa, so this is used as a guardian.

Shane, voice-over: In southern Africa, guarding sheep can mean defending them from lions, so, yeah, these dogs don't mess around.

[Crowd cheering] Shane, voice-over: They're named for the distinctive ridge of fur that grows against the grain on their back.

But a few Ridgebacks, about one in every 200, don't have that signature ridge.

Scientists compared the DNA of Ridgebacks with and without ridges, and, sure enough, found one consistent difference between them.

Adam: That ridge is actually a chromosomal duplication that's 133 kilobases long that's on chromosome 18.

Huh.

And so dogs that have at least one copy of that duplication wind up having this ridge.

OK. Shane, voice-over: Using this technique, scientists studying dogs have discovered the genes that encode dozens of traits.

Mutations in 3 genes determine whether a dog's coat is short or long, straight or curly, and smooth or wiry.

A mutation in another gene, and you lose hair altogether.

One genetic change means the difference between erect and floppy ears, while another produces the stumpy legs of Corgis, Dachshunds, and Basset Hounds.

And just a handful of mutations can shrink a Rottweiler down to the size of a Beagle.

But studying dogs' DNA isn't just helping us find the genes that make each breed distinctive.

[Man cheers] Adam: What are the genes that predispose people and other animals to cancer?

Shane, voice-over: Human populations have a ton of genetic diversity, so figuring out which of our genes does what is really hard.

Thanks to the genetic quirks of dog breeding, though, it's doggy DNA to the rescue, because it turns out that our furry friends can tell us an awful lot about us, too.

[Whistling and applause] ♪ Shane: When did you notice that Chance was, like, beginning to have some issues?

Man: So we noticed he was limping first, and we couldn't quite figure out why, and then one day, we just were feeling his paws just to figure out what was going on, and we felt the lump.

Sit, Chance.

Good boy.

Good.

Shane, voice-over: Cheryl London is a veterinarian who studies cancer in dogs.

Man: He seemed, you know, he's always eager to eat.

Cheryl: OK, well, I'm gonna take a quick look at him.

OK.

Working with animals that have cancer, I mean, these are pets that are a part of somebody's family, can be tough.

Man: Yeah, it was a tough process for us.

We were more concerned about him, obviously... Yeah.

didn't want him sufferin'.

Cheryl, voice-over: I think, for many people, they elect to enroll in clinical trials because they know it may not necessarily benefit their dog, but it could benefit somebody else's dog or somebody else's child.

Shane: Everybody lookin' at you, bud, and you're the star.

Shane, voice-over: Chance suffers from osteosarcoma, a form of bone cancer.

It's a devastating disease, both in dogs and in children.

In dogs, it occurs at about 10,000 to 50,000 cases per year.

In kids, they only see about a thousand, so we see way more of it in dogs than we do in kids.

In both the dogs and in kids, outcomes haven't improved in the last 3 decades, meaning that we've sort of hit a plateau in terms of treatment.

♪ Shane, voice-over: From the veterinary hospital, Cheryl sends Chance's blood sample to the Broad Institute.

Woman: We got a blood sample and we'd separate it, we'd extract the DNA, using those fancy magnetic... Shane, voice-over: Elinor Karlsson is a geneticist, an artist, and, much to my surprise, not a dog person.

[Cat meowing] ♪ Elinor: I've learned how to appreciate dogs... Shane: OK. so I think dogs are fantastic.

Nothing against dogs, but that wasn't-- Yeah.

Do you own a dog?

I don't own a dog.

So they're not that fantastic.

No.

But they're-- Cats are a lot better.

Shh!

So I met a dog this morning named Chance.

Chance had his blood extracted.

Chance has cancer, and he's got cancer in a particular place in his body.

When I was a graduate student, we got started on a project looking at osteosarcoma, bone cancer in dogs.

And so, with dogs, we have these particular breeds, like the Greyhound, where a lot of them were getting bone cancer.

And so we had a study where we sequenced DNA from a bunch of Greyhounds that had bone cancer and dogs that didn't.

Shane, voice-over: Because osteosarcoma was more common in some breeds than others, researchers suspected it had a genetic basis.

By comparing the DNA of dogs that had the disease to dogs that didn't, all within a breed, Elinor and her team were able to identify some of the genes causing osteosarcoma.

Elinor: If you're trying to find the changes that are responsible for a disease like bone cancer, there's a lot fewer changes for you to consider because, for the most part, they're quite similar to each other.

The dogs within a breed are all related to each other.

When you're looking for differences, it makes it a lot easier when mostly everything else is the same.

Exactly.

Shane, voice-over: It turns out that many of the genes that affect osteosarcoma in dogs also affect the disease in humans.

Elinor and other researchers have now found a number of mutations that may contribute to cancer in both species.

Elinor: They're developing cancer just as a natural part of aging, exactly the same way that people do.

Shane, voice-over: We share so much with dogs, maybe it shouldn't be a surprise that the same genetic mutations can make us sick.

According to Elinor, finding the causes of disease is just the beginning.

What do you think dogs tell us about ourselves as a species?

Well, I think one of the biggest things it tells us is that humans are not nearly as special as we like to think we are.

But my mom said that I'm super-special.

You individually... OK. you're, like, the most special.

OK. We're actually using the same drugs to treat dogs and people right now.

Mm-hmm.

We can actually use all of that information from the veterinary world to inform human medicine.

OK. Shane, voice-over: The kinship we feel with our dogs, it's more than skin-deep.

We care for them because we love them, but when we help them, we help ourselves, too.

Dogs are special.

It's just one of those unspoken truths, and their history reveals why.

While they adapted to live in our world, we shaped them into a perfect partner.

It's a true collaboration, millennia in the making.

They help us thrive in the most inhospitable environments on Earth and change the way we live in more comfortable ones.

They watch our bodies to read our minds.

They earn a place in our communities, on the streets, or in our homes.

They dazzle us with their diversity, and like all great friends, they teach us things about ourselves that we would never discover without them.

They can do it all, because in the Age of Humans, where dogs outnumber wolves 3,000 to one, there's no wrong way to be a dog.

♪ ♪ Human Footprint is available with PBS Passport and on Amazon Prime Video.

♪