Untangling The History Of Dog Domestication

A new study suggests dogs began to diversify about 11,000 years earlier than we thought. Plus, a long-running experiment to domesticate foxes.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Ira Flatow?

  Science Friday is supported by MathWorks, creator of MATLAB and Simulink software for technical computing and model-based design. MathWorks, accelerating the pace of discovery in engineering and science. Learn more at mathworks.com.

• 0:19Flora Lichtman?

  Hey, I'm Flora Lichtman, and you're listening to Science Friday.

• 0:24Speaker 02

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

• 0:35Speaker 03

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

• 0:42Flora 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 Amin, author of a recent study in science on the diversification of dogs, and a bioarchaeologist and lecturer at the University of Exeter in the UK. Okay, Carly, do I have this right, that this has been the prevailing narrative,

• 1:26Flora Lichtman?

  that we largely have the Victorians to thank for breeds?

• 1:30Speaker 04

  Yeah, absolutely. And 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 archaeologists, this is things we're interested, how long these relationships have lasted for. But there's definitely an aversion by archaeologists 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.

• 2:13Speaker 04

  These are, so these are standards and that a hundred percent is 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.

• 2:51Flora Lichtman?

  Tell me about your study. You analyzed hundreds of dog skulls, right? Ancient dog skulls. Where were they from? From what time periods?

• 3:00Speaker 04

  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 archaeological materials going back about 50,000 years. And dogs are important to human societies, not just today, but from an archaeological point of view as well. Because they're our first domestic animal.

• 3:22Flora Lichtman?

  Our first domestic animal.

• 3:24Speaker 04

  Yeah, so they predate all of our livestock. They actually predate agriculture as well. So before humans kind of settle 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 archaeologists 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.

• 3:53Flora 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?

• 4:01Speaker 04

  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.

• 4:29Flora Lichtman?

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

• 4:33Speaker 04

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

• 5:06Flora Lichtman?

  And what about the diversity of those skulls?

• 5:09Speaker 04

  Within the dogs themselves?

• 5:11Flora Lichtman?

  Yeah.

• 5:11Speaker 04

  Yeah, so there's lots of diversity. And that was, again, what I think became the, 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 archaeological record. But we do see a huge range in, in sizes of, from really small ones to really big ones and shape, and changes in, in the proportions of the nose to the, the size of the skull.

• 5:54Speaker 04

  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.

• 6:04Flora Lichtman?

  Do we know where dog domestication took place?

• 6:08Speaker 04

  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 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.

• 6:38Flora Lichtman?

  Is this like a hot debate in your world? Like, do people fight over this?

• 6:42Speaker 04

  I wouldn't say they fight, but it is something that people have been working on for a long time. Dogs have this, again, they're the first domestic species, so there's a little bit of kind of scientific prestige around figuring out when and where they come from, because you have this kind of 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.

• 7:23Speaker 04

  Because wolves live all over the world already, it makes that 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 kind of climate and environmental change, wolf populations have really restricted. And some, 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.

• 8:05Speaker 04

  And so we're having to play a little bit of detective work to piece that back together.

• 8:09Flora 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?

• 8:18Speaker 04

  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 like 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, right? And they'll alert you. And these are roles that are really familiar to us today, right? 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.

• 9:03Speaker 04

  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, you know, 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.

• 9:31Flora Lichtman?

  Will you watch the Westminster Dog Show?

• 9:34Speaker 04

  As long as the time change isn't too tricky. Give it a go.

• 9:37Flora Lichtman?

  What breed? What dog are you rooting for?

• 9:41Speaker 04

  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.

• 9:57Flora Lichtman?

  They're cute. Come on, they're cute. Dr. Carly Amin is a bioarchaeologist and lecturer at the University of Exeter in the UK. Carly, thanks for joining me today.

• 10:05Speaker 04

  Thanks for having me.

• 10:11Flora 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.

• 10:26Speaker 05

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• 11:11Speaker 05

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• 11:52Speaker 05

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• 12:09Flora 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.

• 12:43Speaker 06

  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.

• 13:17Flora Lichtman?

  Wait, 10 generations?

• 13:19Speaker 06

  Yeah, really, really fast.

• 13:21Flora Lichtman?

  Yeah.

• 13:21Speaker 06

  Yeah.

• 13:22Flora Lichtman?

  Was that a surprise?

• 13:23Speaker 06

  I mean, it seems pretty surprising to me. Yeah.

• 13:27Flora Lichtman?

  So after 10 generations, how tame are they? Like, should I be imagining, like, you know, dogs or cats? Do they play fetch? Do they sit on your lap? Like, what are they like?

• 13:40Speaker 06

  Yeah, so I've met these foxes. They are, they're not exactly like dogs. So now we're, you know, 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 kind of make interesting noises, sort of almost like a purring noise when you scratch them.

• 14:02Flora Lichtman?

  Behind the ears, on the belly? I really want the details.

• 14:07Speaker 06

  Kind of on the butt. Like, 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.

• 14:30Flora Lichtman?

  What about their brains? Do their brains change when they get tamer?

• 14:35Speaker 06

  Yeah, so this is something that's been really interesting to me. So domestication seems like it's at its heart about behavior, right? Like becoming adapted to being around humans, being comfortable, being in captivity, sort of being complacent enough to be handled by people in a way that's safe. So this is about sort of 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,

• 15:14Speaker 06

  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 sort of like higher level cognition. Yeah, so it's surprising in a way because these tame and aggressive foxes, they have sort of like opposite behavioral changes. But yet we're seeing this parallel change in the part of the brain that is probably controlling that behavior.

• 15:53Flora Lichtman?

  Is it because you're, in both cases, they're selecting for a behavior that makes them sort of more sensitive to these social interactions with humans?

• 16:04Speaker 06

  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 sort of 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.

• 16:25Flora Lichtman?

  What are the differences?

• 16:27Speaker 06

  We don't know yet. We're looking.

• 16:30Flora Lichtman?

  You're looking for them.

• 16:32Speaker 06

  Yeah, right. Check back in a year or so, maybe we'll know.

• 16:34Flora Lichtman?

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

• 16:42Speaker 06

  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.

• 17:10Flora Lichtman?

  Hmm. What about our brains? Do we see this in our brains?

• 17:15Speaker 06

  Yeah, that's a great question. So compared to other apes, humans do have expansion of cortex. So 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 like maybe humans are somehow self-domesticated.

• 17:34Flora Lichtman?

  Wait, wait, why? Say more about this.

• 17:38Speaker 06

  You're right. Yeah. So this is an idea that's been around like 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 sort of be around individuals that you don't know without getting defensive. So maybe during the formation of early human societies, we were also sort of enforcing those types of behaviors.

• 18:18Flora Lichtman?

  Like tamer, tamer humans had more babies?

• 18:22Speaker 06

  Yeah, that, that is the idea. To me, this seems like this is a question about brain evolution, right? 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 so far, that hasn't been done, so we don't really know.

• 18:44Flora Lichtman?

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

• 18:48Speaker 06

  Oh, that's, I don't think I could pick one. I mean, for having one in my house, absolutely dog. But foxes are really fascinating and adorable as well.

• 18:59Flora Lichtman?

  Wait, why wouldn't you want one in your house?

• 19:01Speaker 06

  They pee everywhere.

• 19:06Flora Lichtman?

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

• 19:12Speaker 06

  Thank you so much for having me.

• 19:14Flora 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.

• 19:39Flora Lichtman?

  That was the best. That's the best ending we've had in a while. So thank you.

• 19:43Speaker 06

  Yeah, like, we literally had to pee-proof our lab, like, it was quite the... Yep.