Untangling The History Of Dog Domestication

[MUSIC PLAYING] FLORA LICHTMAN: Hey, I’m Flora Lichtman. And you’re listening to Science Friday.

[CHEERING, APPLAUSE]

SPEAKER 1: For Best in Show at the 149th Annual Westminster Kennel Club Dog Show, I choose the giant schnauzer.

[CHEERING, APPLAUSE]

SPEAKER 2: Oh, Monty! He did it. Three years, and he finally wins Best in Show.

FLORA LICHTMAN: It is the best time of the year. The Westminster Kennel Club Dog Show has come again. It starts tomorrow. Monty won last year, if you’re not in the know. More than 200 kinds of canines are going to trot around New York arenas competing for top dog. And you might wonder, where did all these breeds come from? The story that’s often told is that dog diversity really took off with the Victorians in the 1800s, but new research is unleashing a different tale.

Here to muddy the waters is Dr. Carly Ameen, author of a recent study in science on the diversification of dogs and a bioarcheologist and lecturer at the University of Exeter in the UK. OK, Carly, do I have this right that this has been the prevailing narrative that we largely have the Victorians to thank for breeds?

CARLY AMEEN: Yeah, absolutely. There’s lots of really interesting work about our relationship with domestic animals, so dogs being some of the ones that are closest to our hearts. But as archeologists, there’s just things we’re interested, how long these relationships have lasted for. But there’s definitely an aversion by archeologists to talk about things like breed, because we really feel like it’s a very modern phenomenon. It’s a modern way of thinking about the world, what we think of as a breed today.

And if you talk to dog breeders, what they’ll tell you a breed today is a really specific set of characteristics that have to do with not just the shape and the size and the coat color, but the stature and the distance between their eyes and ears and the length of their nose and the way they stand and hold their tail. So these are standards. And that, 100% the Victorians begin that, right? These are the first kennel clubs that we see coming across Europe.

So the UK has one of the oldest kennel clubs in the world, and they start to write down, this is what makes a boxer, this is what makes a beagle– all these different types of characteristics. And then they start to intentionally try to continue to replicate that exact form over successive generations. And what we were actually really surprised about finding in our work, when we’re looking at 50,000 years of dogs and wolves, was how much diversity there was in the past, before the Victorians got to writing it down and trying to make it happen.

FLORA LICHTMAN: Tell me about your study. You analyzed hundreds of dog skulls, ancient dog skulls. Where were they from? From what time periods?

CARLY AMEEN: Yep, so we looked at over 600 dog skulls or canid skulls. So dogs and wolves belong to this bigger group that we call canids. And we were looking at archeological materials going back about 50,000 years. And dogs are important to human societies, not just today, but from an archeological point of view as well, because they’re our first domestic animal. So we make–

FLORA LICHTMAN: Our first domestic animal.

CARLY AMEEN: Yeah, so they predate all of our livestock. They actually predate agriculture as well. So before humans settled down to farming wheat and having pigs and cows living alongside them, they’ve already had dogs for thousands of years. And this makes dogs really important to archeologists and to people like me who study really long-term human animal relationships. Because they represent the first time that humans look outside their own species group and say, hey, let’s make a partnership here.

FLORA LICHTMAN: I want to get back to that in a second, but let’s talk about the diversity that you found in some of these skulls. What did you see when you looked at them?

CARLY AMEEN: So the first thing that we were really trying to do was understand if we could identify a dog. So when do you stop seeing wolf shapes and start seeing dogs? Because part of what we don’t know about the story of dog domestication is when and where this happened. So this is why we have this big, broad window, 50,000 years. Because we’re still not exactly sure when this happened. So we have to take this big look through deep time so that we can try to pinpoint.

FLORA LICHTMAN: But we know it has happened by, what, 15,000 years ago?

CARLY AMEEN: Yes, exactly. So what we start to see is by about 10,000 to 11,000 years ago, wolves have these lovely, gracile, long, and slender skulls and that stuff we see in the Pleistocene 50,000 years ago. And modern wolves today have this– there’s diversity within that group, but they’re long and streamlined. And then suddenly, about 11,000 years ago, we see this boxy widening of the braincase and shortening of the nose, this compactness of the skull that you don’t see in the wild wolves.

FLORA LICHTMAN: And what about the diversity of those skulls?

CARLY AMEEN: Within the dogs themselves?

FLORA LICHTMAN: Yeah.

CARLY AMEEN: Yeah, so there’s lots of diversity. And that was, again, what, I think, became the kind of talking point of the study, but was not something we were necessarily looking for when we first got started, was how diverse the skulls got from really early on. So from about 10,000 years ago, we start to see a huge range in sizes and shapes represented by the skulls. We don’t see the most extreme shapes we have today. So really, really short snouts like the French bulldog or the pug, that’s not something that, as of yet, we’ve detected in the archeological record.

But we do see a huge range in sizes from really small ones to really big ones and changes in the proportions of the nose to the size of the skull. And what we found, actually, was that by the Neolithic, so by about 8,000 to 9,000 years ago, the amount of variation in dog skulls is already half of what we see today.

FLORA LICHTMAN: Do we know where dog domestication took place?

CARLY AMEEN: [LAUGHS] Eurasia is about as close as we can get, so not North America. The gray wolf is the descendant of all modern dogs. At its height, it was the most widely distributed mammal in the Northern Hemisphere. It lives everywhere from Saudi Arabia to the Arctic. So we can tell from the genetic work that it was Eurasian gray wolves that have led to our modern dogs, so not the wolves that were living in the Americas. But besides that, we haven’t quite got the where down either.

FLORA LICHTMAN: Is this a hot debate in your world? Do people fight over this?

CARLY AMEEN: I wouldn’t say they fight, but it is something that people have been working on for a long time. Again, they’re the first domestic species, so there’s a little bit of scientific prestige around figuring out when and where they come from. Because you have this first domestic animal attached to it. They’re also, again, really interesting.

Other ways we’ve figured out the origins in time and place of our other domestic species is because their native ranges were really restricted. So the minute you start to see goats outside of Turkey, you’re like, well, how did they get there? People had to have brought them there, because there are no native goats to Britain. So when you start to see goats appearing in Neolithic Britain, we know that that’s part of their relationship with humans.

Because wolves live all over the world already, it makes those questions much harder to figure out because we can’t just use the appearance of them in different places as indication of their relationship with humans. And also, because we’ve spent the last hundreds of years really persecuting wolves, whether that’s intentionally culling them to reduce their populations or inadvertently due to changes in human settlement patterns and broader climate and environmental change, wolf populations have really restricted.

And while the wolf itself is not extinct, some local populations of wolves have gone completely extinct. So we’ve lost a huge amount of genetic information about what that Pleistocene wolf population that gave rise to dogs would have been. And so we’re having to play a little bit of detective work to piece that back together.

FLORA LICHTMAN: So do we have theories about– dogs are our first domesticated animal. How did it happen? Why did we let dogs into our lives?

CARLY AMEEN: So this is one of the things that we still don’t really have a good handle on. You would traditionally think about domestic farm animals for food. We need food. We want food closer to us. We want it easier. So we create that intensity of that relationship. And dogs don’t have that obvious pathway. But what dogs do have is this huge amount of jobs that they do.

So in the past, we know they’re used as hunting companions, as pulling sleds to move things around, especially before we have horses and other types of vehicles. They’re used as guard dogs. They’ll bark, and they’ll alert you. And these are roles that are really familiar to us today. We think of dogs as our pets, and that’s what maybe 80% of dog owners around the world– just have a dog that they have for companionship.

But dogs still have lots of jobs. They’re still out on farms working with people. They’re still pulling sleds in parts of the Arctic. And they even have jobs that we couldn’t have imagined 10,000 years ago, helping to detect drugs in airports and helping people cross the street and with vision impairment. So they’re hugely useful across a huge range of society. And that’s something that we see today, but also certainly would have been true in the past. But it makes it really hard to say why, because they have so many different uses.

FLORA LICHTMAN: Will you watch the Westminster Dog Show?

CARLY AMEEN: As long as the time change isn’t too tricky, I’ll give it a go.

FLORA LICHTMAN: What breed– what dog are you rooting for?

CARLY AMEEN: Oh, well, I’ve always had a place in my heart for the English bulldog, which is dogs that we’ve had in my house. And so, yeah, I have to go for them, even though I think from a breed perspective, maybe we could do a little bit more to make them a bit healthier. But they do have a personal place in my heart.

FLORA LICHTMAN: They’re cute. Come on.

CARLY AMEEN: Yes.

FLORA LICHTMAN: They’re cute.

[CHUCKLING]

Dr. Carly Ameen is a bioarcheologist and lecturer at the University of Exeter in the UK. Carly, thanks for joining me today.

CARLY AMEEN: Thanks for having me.

[MUSIC PLAYING]

FLORA LICHTMAN: We have to take a quick break, but don’t go away. Because coming up, we’re talking about this famous experiment to tame silver foxes, and I’m talking about the wild animal kind. Stick around.

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FLORA LICHTMAN: Back in the ’50s, a pair of Russian scientists started investigating domestication. And their idea– stay with me– was to take wild foxes and selectively breed them to try to tame them. And here’s the wild thing– it worked. With each generation, the foxes became closer to something that resembles a pet. Dr. Erin Hecht, an evolutionary biologist at Harvard, has studied these foxes and what they tell us about domesticated brains. Erin, welcome, and tell us a little bit about this experiment.

ERIN HECHT: Yeah, thank you so much for having me. So as you mentioned, this was an experiment to see what happens when you apply selection pressure, specifically to behavior. So they bred together the foxes that would allow humans to get closer to them before running away, so the foxes that would let a human that was unfamiliar to them get the closest before trying to flee. And within the span of about 10 generations, they had foxes that were acting significantly differently from their predecessor foxes.

FLORA LICHTMAN: Wait, 10 generations?

ERIN HECHT: Yeah. Really, really fast.

FLORA LICHTMAN: Yeah. Was that a surprise?

ERIN HECHT: Yeah, I mean, it seems pretty surprising to me. Yeah. [LAUGHS]

FLORA LICHTMAN: And so after 10 generations, how tame are they? Should I be imagining dogs or cats? Do they play fetch? Do they sit on your lap? What are they like?

ERIN HECHT: Yeah, so I’ve met these foxes. They’re not exactly like dogs. So now we’re 60-plus generations in. And so these are much, much different than the earliest generations of foxes. They’re not exactly like dogs, but they are definitely very friendly. And they like to be scratched. They make interesting noises, sort of almost like a purring noise when you scratch them.

FLORA LICHTMAN: Behind the ears? On the belly? I really want the details.

ERIN HECHT: Kind of on the butt. But yeah, they like a really good butt scratch. They like to cuddle. They’re interested in people. They like New people. They like pets. They like toys. And they’re also just really chill. So most animals, including many domestic dogs, get kind of freaked out in novel situations. And these tame foxes have a pretty mellowed-out stress response.

FLORA LICHTMAN: What about their brains? Do their brains change when they get tamer?

ERIN HECHT: Yeah, so this is something that’s been really interesting to me. So domestication seems like it’s, at its heart, about behavior, like becoming adapted to being around humans, being comfortable being in captivity, being complacent enough to be handled by people in a way that’s safe. So this is about tameness. Behavior comes from the brain, so we should be looking at their brains. But there really hasn’t been much neuroscience research on domestication since about the 1980s.

So we started looking at the brains of these foxes, and we found something sort of surprising, which is that the brains of both the tame and aggressive foxes changed in a partially similar way. So they both had expansion in several brain regions, most prominently the prefrontal cortex, which is a part of the brain towards the front which is involved in social cognition and higher level cognition. Yeah, so it’s surprising, in a way, because these tame and aggressive foxes, they have opposite behavioral changes. But yet, we’re seeing this parallel change in the part of the brain that is probably controlling that behavior.

FLORA LICHTMAN: Is it because in both cases, they’re selecting for a behavior that makes them more sensitive to these social interactions with humans?

ERIN HECHT: Yeah, I think that’s a plausible possibility. So we’re looking into that more. We’re trying to see if there may be differences in cell types or gene expression that might explain what appears to be a similar change at the macro level. But really, if you go down to the micro level, there’s different things going on.

FLORA LICHTMAN: What are the differences?

ERIN HECHT: We don’t know yet. We’re looking.

FLORA LICHTMAN: Oh.

[LAUGHTER]

ERIN HECHT: Yeah. Check back in–

FLORA LICHTMAN: You’re looking for them.

ERIN HECHT: Yeah, right. Check back in a year or so. Maybe we’ll–

FLORA LICHTMAN: I can’t wait. I’m fascinated by this. I mean, do we see these brain changes in other domesticated animals?

ERIN HECHT: Yeah, we see changes in different lineages of dogs. So in these modern breeds that are more selected for cooperative work, like hunting and herding and guarding, we see expansion of cortex, which is the outer covering of the brain that’s involved in cognition and complex behavior. So that is expanded in these modern breeds, like border collies, German shepherds, golden retrievers, Labrador retrievers, and so forth.

FLORA LICHTMAN: What about our brains? Do we see this in our brains?

ERIN HECHT: Yeah, that’s a great question. So compared to other apes, humans do have expansion of cortex. And compared to other mammals in general, humans have expansion of cortex. There’s this idea that’s been around for a long time that maybe humans are somehow self-domesticated.

FLORA LICHTMAN: Wait, wait. Wait, say more about this.

ERIN HECHT: You’re right. Yeah, so this is an idea that’s been around at least since the time of Darwin. So this idea is that during the course of human evolution, maybe we applied selection pressures to ourselves that are similar to the selection pressures that we apply to animals as we domesticate them, so increased social tolerance, reduced aggression, increased cooperation, ability to be around individuals that you don’t know without getting defensive. So maybe during the formation of early human societies, we were also enforcing those types of behaviors.

FLORA LICHTMAN: Like, tamer humans had more babies?

ERIN HECHT: Yeah, that is the idea. To me, this seems like this is a question about brain evolution. Like, we have a question about behavior. Behavior comes from the brain. So we should figure out what that pattern is in other animals when we apply those selection pressures to them, and then see if that pattern exists in humans. So far, that hasn’t been done. So we don’t really know.

FLORA LICHTMAN: After working on this, are you more of a dog person or a fox person?

ERIN HECHT: Oh, I don’t think I could pick one. I mean, for having one in my house, absolutely, dog. [LAUGHS] But foxes are really fascinating and adorable as well.

FLORA LICHTMAN: Wait, why wouldn’t you want one in your house?

ERIN HECHT: They pee everywhere.

[LAUGHTER]

FLORA LICHTMAN: Dr. Erin Hecht is an evolutionary biologist at Harvard University. Erin, thanks for joining me today.

ERIN HECHT: Thank you so much for having me.

FLORA LICHTMAN: This episode was produced by me, Flora Lichtman, a dog person and a cat person– now maybe a fox person, too– and Rasha Aridi, a diehard cat person who was forced into producing this. Good luck to the terriers this weekend, and only the terriers. Catch you next time. I’m Flora Lichtman.

[MUSIC PLAYING]

FLORA LICHTMAN: That’s the best ending we’ve had in a while. So thank you.

ERIN HECHT: Yeah, we literally had to pee-proof our lab. It was quite the– yeah.

[LAUGHTER]

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