Are Raccoons On The Road To Domestication?

FLORA LICHTMAN: I’m Flora Lichtman. And you’re listening to Science Friday. First, there was pizza rat, then Central Park’s celebrity coyote. And finally, I give to you, drunk raccoon.

SPEAKER: A now infamous raccoon. Video obtained by NBC News shows the critter inside a Virginia liquor store, a trash panda splayed out next to a trash can and toilet, like that one person that maybe had one too many at the holiday party.

FLORA LICHTMAN: And there might be more to this ridiculous story than amazing memes. This raccoon points with its tiny little adorable hands to a possible larger trend. A new study shows that raccoons are showing signs of being domesticated. Today, we are talking about that and what it means to be a wild animal in a world dominated by one animal in particular– us. Here to discuss are Raffaela Lesch, a biologist studying raccoons at the University of Arkansas at Little Rock, and Pam Yeh, an evolutionary biologist studying birds, among other creatures, at UCLA. Welcome to you both to Science Friday.

RAFFAELA LESCH: Hi, thank you for having us.

PAMELA YEH: Yeah, thank you so much.

FLORA LICHTMAN: Raffaela, let’s start with that raccoon that lived its best life in the Virginia liquor store.

RAFFAELA LESCH: Yeah.

FLORA LICHTMAN: When you saw that story as someone who studies raccoon domestication, what did you think?

RAFFAELA LESCH: So actually, I got an email. A news agency was asking me for comment on that, and I was like, I’m not sure what to say, other than I’m pretty sure it was fairly drunk. But [LAUGHS] yeah, that was, honestly, perfect timing for our study. It almost seemed like we paid off that raccoon to break into a liquor store right after our paper came out. Yeah.

FLORA LICHTMAN: I mean, OK, so what are the signs that raccoons are getting domesticated?

RAFFAELA LESCH: Yeah, so I got to preface this by saying that there’s– basically, we found one trait that could be associated with the domestication phenotype. We can’t clearly say that they really are on the pathway to domestication, but we can kind of use that as an indication of them potentially being on the pathway of domestication.

So what we found was that urban raccoons have shorter snouts than raccoons that live in the countryside. And this reduction in snout length is a trait that we very commonly see in domesticated animals. And it’s part of what we call the domestication syndrome. So a whole collection of traits that we very much associate with an animal being domesticated, like floppy ears, curly tails, white patches, smaller brains, and shorter snouts.

FLORA LICHTMAN: Smaller brains?

RAFFAELA LESCH: Yeah. Yeah, which it doesn’t automatically mean that they’re dumber. Because there was a study we published on cat brains, and domesticated cats have smaller brains than wild cats. And I had–

FLORA LICHTMAN: Yeah, watch out. We have really a lot of Team Cat people at Science Friday.

RAFFAELA LESCH: Yeah, yeah, yeah. Exactly.

FLORA LICHTMAN: Yeah.

RAFFAELA LESCH: So I just want to say, we never said domesticated cats are dumber. Because it was just about pure brain volume. It doesn’t have to mean anything in regards to intelligence, necessarily. But all of those things are traits we associate with domesticated animals.

FLORA LICHTMAN: But why does snout size, why should that correlate with whether an animal is domesticated?

RAFFAELA LESCH: So there’s one hypothesis, and I’m going to walk you through this hypothesis. But keep in mind we’re still arguing whether this is the thing or not, whether it’s true or not. But the main thought that we have is all these traits that we see in domestication syndrome potentially could be explained by a mechanistic pathway in the early development.

So if you think about the journey of domesticated animal, at the very beginning stages, they have to adapt to living in close proximity to humans. So they undergo a fairly strong selection pressure for friendly and tolerant behavior. Because usually, animals, when they live close to us, if you’re too aggressive, then you usually get eliminated from the breeding population. So animals that are tolerant and can make best use of that human environment can reproduce more. So over time, you have this what we call selection pressure for tameness.

And this hypothesis, the neural crest domestication syndrome hypothesis, suggests that the selection for tameness alters the migration and proliferation of neural crest cells. Those are cells that are very important in development and provide a lot of ancestral cells for different organ systems. So that has the potential to explain all of these traits that we observe across the phylogenetic tree of domesticated animals.

FLORA LICHTMAN: Wait, let me see if I understand. So if you start behaving tamely, somehow, that is linked to an embryonic development stage that also changes the size of your nose?

RAFFAELA LESCH: So it’s kind of. It’s really like a– think about it as like really a multi-generation thing. So that’s not something that happens super fast, but would be a very slow process where, basically, over many generations, these traits basically get reinforced and then show up as this domestication syndrome.

FLORA LICHTMAN: Pam, how do we define domestication?

PAMELA YEH: Oh, that’s a good question. We have these wild animals, and their closeness with humans, in terms of their proximity, starts to change their behaviors, change their morphology, change their genes. Because their selection for the ones that happen to be tamer, the ones that happen to have the traits that humans find appealing or find useful– Raffaela, you might have a better– [LAUGHS]

RAFFAELA LESCH: I was really interested to hear your take on it. Because the definition of domestication, that’s actually a really, really difficult question. There’s a bunch of new research that came out where we basically argue back and forth. And that’s kind of like the fun, the sweet spot of science, when you have these back-and-forth arguments of what is domestication, how do you define it.

Because of course, you have the aspects of us actively selecting and breeding, but then you also have aspects of, really, these very beginning stages where animals get used to a human environment, and that doesn’t necessarily have to end up in a domesticated product. And I think there’s more of a spectrum, really, of where do animals end up on that spectrum.

But yeah, the definition is actually really kind of tricky. And just in the last 12 months, there have been a bunch of papers that came out arguing back and forth on how we define these things. Because some definitions, for example, would consider, I think, bedbugs to be domesticated– and I hope I remember this correctly– but house sparrows to not be domesticated. So it is really tricky to find a definition that encompasses this kind of fairly complex interaction and setup of what it means to live in close proximity to humans.

FLORA LICHTMAN: Pam, you had a recent study on the songbird, the dark-eyed junco. So introduce us to them and what their life is like in terms of the ones that you study.

PAMELA YEH: Yeah. So the dark-eyed junco is a small passerine. It’s an unstreaked sparrow. And they’re found, actually, in many places in the US. So they’re a very common species. But they’re typically found at altitude in the mountains, in forest habitat. About maybe 50 years or so, they colonized an urban area in Southern California, which is the campus of UC San Diego.

And so it’s been almost 30 years now since I started studying those guys as a graduate student, because they were here. And my advisor said, there’s something interesting going on. You’re going to find interesting evolution because this is such a different environment. Or we should at least look, you know? And–

FLORA LICHTMAN: From where they live in the wild.

PAMELA YEH: From where they live in the wild. They’re very, very different. And of course, when you get into this type of field, you want to go to the Himalayas. You want to go to Antarctica. You want to go far away. And I was not excited at first about [LAUGHS] this. But they have turned out to be such an interesting species and an amazing set of population. And they have colonized San Diego, but then they’ve colonized other Southern California urban areas over the last few decades.

And so now we have multiple, as far as we can tell, fairly separate urban populations with minimal gene flow. And so that allows us to ask some questions about generalizations we can make about urban evolution. Like, are each of these populations evolving in the same way? Are they evolving in different ways? What are the important selection pressures?

FLORA LICHTMAN: OK, so you studied these birds during the lockdown. What did you find?

PAMELA YEH: We found that the birds that were born in the years where we didn’t have a lot of people on campus actually had longer, skinnier beaks than the ones that were either born before the pandemic or born 2022, ’23, ’24, afterwards. It turns out that the ones that were born during the 2020 and 2021 campus closures had beaks that looked more like the wildland beaks that were longer and skinnier, more slender.

FLORA LICHTMAN: Why would that be?

PAMELA YEH: That is a very good question. And we think it has to do with the food on campus. We have a lot of students on campus– people, faculty, staff. And everyone is eating, and there’s trash overflowing in the trash can sometimes. And we leave crumbs everywhere. And I think that there was strong selection pressure during normal times for birds that had shorter beaks. They probably were able to get at more of that food.

FLORA LICHTMAN: Short beaks are good for trash and scraps.

PAMELA YEH: We think so. [LAUGHS] We think so. I think that they’re good for kind of a generalist being able to grab at the foods that we produce. We don’t know for sure. So I think that would be an important thing to test.

But that seems to be the case, that they can handle more of the odd-sized and variable-shaped foods a little bit more easily. Whereas during the pandemic, when there was way less food on campus, birds were– juncos are typically granivores. They eat a lot of seeds, and they feed their offspring insects. And so you often see them digging in lawns and in vegetation, looking for insects or getting the seeds. And we think that those long, slender beaks do better with insects and grains.

RAFFAELA LESCH: Pam, can I ask you a question? Sorry, Flora, I don’t mean to interrupt, but this is super interesting. Do you think that this could also be a plastic response to what the birds are exposed to early on?

PAMELA YEH: Yeah, that’s a good question. And so that’s why we have to be a little hesitant when we say rapid evolution as a result of the pandemic, because it could be a plastic trait. It could be–

FLORA LICHTMAN: When you say a plastic trait, you mean that it’s basically a trait that is adaptable based on the environment that they’re in, right?

PAMELA YEH: Exactly.

FLORA LICHTMAN: It can change during their life.

PAMELA YEH: Exactly, exactly, exactly. And so we can’t fully rule that out. But we know in general, for birds, there are genes that are related to all these beak traits. And so we think that this is one of those things that doesn’t change that much. But I think it’s something we probably need to– it would be nice to look into more.

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FLORA LICHTMAN: Don’t go away. Because when we come back, Raffaela, I want to hear when I can expect to have a pet raccoon–

RAFFAELA LESCH: Sounds good.

FLORA LICHTMAN: –and whether I can look forward to a raccoondoodle, a raccoon frise, an English cockraccoon.

[LAUGHTER]

PAMELA YEH: I love it.

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FLORA LICHTMAN: We’re back. I’m talking with biologist Raffaela Lesch and Pamela Yeh about urban wildlife and how these creatures are becoming a little less wild. So Raffaela, we know with dog domestication that phase I with wolves was sort of wolves eating our scraps. And I guess, these days, a lot of animals [LAUGHS] are living beside us– rats, bears, possums. Is there something else about an animal that makes it prone to domestication?

RAFFAELA LESCH: Yeah, so you’re asking all the big questions, which is really good. So we have some thoughts on what might increase the probability of an animal falling down that hole of domestication pathway. So they have to have a social system that has enough complexity in it that would benefit a coexistence between these animals and us.

Also, the animals have to be animals that are not super dangerous to us humans. So bears, for example, would most likely never end up on the pathway to domestication, simply because they are too dangerous to really create this environment of a human environment and all of that. So there’s certain limitations–

FLORA LICHTMAN: But wolves were dangerous to us, right?

RAFFAELA LESCH: Well, I mean, mm, wild wolves are really kind of like– they try to stay away from humans. So I guess, they could be dangerous if you really pushed the wolf to its limits. But they’re not really out to get humans. That’s not really–

FLORA LICHTMAN: Eat us.

RAFFAELA LESCH: Yeah, exactly. Yeah, we’re not on the menu. Of course, nutrition, dietary background could make a huge difference. One thought, for example, that we had is that animals that are able to exploit the human trash that we have laying around, because they have somewhat of a match with their dietary background, would have an easier time being domesticated.

So if we look at dogs, for example, they have the ability to digest starch a lot more than wolves do. So they clearly adapted to going through our trash and eating whatever bread and carbohydrates we throw away. So animals that are able to thrive on what we throw away potentially have an easier time going down that pathway.

But now, if you think about cats, they don’t really do carbohydrates to the same degree that dogs can. There, you have an argument that the trash that we have attracts rodents. So cats might have exploited the rodents on the trash. So we were thinking that– or the initial thought behind looking at raccoons was, well, we know they’re there. We know that every single trash can or every single dumpster on campus houses raccoons. [LAUGHS] So it was kind of interesting to look and see if there was a pattern that would hold across the entirety of the United States.

FLORA LICHTMAN: Raffaela, how long till I have a raccoon sleeping at the foot of my bed?

RAFFAELA LESCH: Oh, yeah, that– and see, this is where the bad news comes in. I’m so sorry. [LAUGHS] I wish time travel was a thing. Because it definitely would not be in the human lifetime. So if they are on a pathway to domestication, it would most likely be similar to other animals, like thousands of years. So, many, many generations before we end up with a version of this animal that could be considered domesticated.

And there’s also another thought that we have where we want to confirm our finding. And that is because it ties in so nicely with what Pam said earlier about dietary impacts on morphology and anatomy. So we just looked at this change in snout from a perspective of a domestication framework.

But we also need to consider that, potentially, there could be a difference in dietary background in all of these populations. And we have to test out and rule out that that’s not a signal that we’re picking up. I don’t think it is. But that’s the joy of science. It doesn’t matter what I think. We’re going to need data for that. [LAUGHS]

FLORA LICHTMAN: And this is a tiny bit philosophical, but do you both have feelings about wild animals becoming more dependent on people?

PAMELA YEH: Yeah, I think sometimes people think about humans as one thing. And then there’s nature, and there’s us. But we’re really very much a part of the ecosystem. And the animals affect us, and we affect other animals. So we really need to be aware if we want to think about how we want to change things or how we are trying not to change things.

RAFFAELA LESCH: The fact that our cities keep encroaching, we keep encroaching into wildlife and true wild environments, if we do that, it’s almost inevitable that animals will adapt to us. At the end, we’re also like ecosystem engineers. So wherever we go, we change things. And I think that has to be a very conscious thing that we have to consider as humans. How do we deal with that?

FLORA LICHTMAN: Pam, Raffaela, thank you so much for talking to me today.

RAFFAELA LESCH: Thank you.

PAMELA YEH: Thank you so much. Thanks for having us.

FLORA LICHTMAN: Raffaela Lesch is an assistant professor of biology at the University of Arkansas at Little Rock. And Pam Yeh is an assistant professor of Ecology and Evolutionary Biology at UCLA. This episode was produced by Kathleen Davis and Dee Peterschmidt. Thank you for listening. And if you have an urban wildlife encounter that you want to share, or tell me what wild animal is on your domestication wishlist, I’d love to hear from you. 8774-SCIFRI. I’m Flora Lichtman. See you next time.

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