Science Vs - True Love: Is Monogamy Unnatural?

Episode Date: September 30, 2021

[REBROADCAST] Are humans built for monogamy? Or is the idea of having one partner forever just a myth forced on us by tired old love songs? We revisit the science of love in one of our favorite episodes, hearing from Dr. Helen Fisher, Professor Larry Young and Dr. Dieter Lukas. Find the transcript here: https://bit.ly/3meWcuN  This episode was produced by Wendy Zukerman with Heather Rogers, Kaitlyn Sawrey, Ben Kuebrich, Shruti Ravindran and Rose Reid. Editing by Annie Rose Strasser and Blythe Terrell. Extra editorial help from Alex Blumberg. Production assistance from Stevie Lane. Fact checking by Ben Kuebrich, Taylor White and Rose Rimler. Music production and original music written by Bobby Lord. Special thanks to Joseph Lavelle Wilson, Austin Mitchell and to Professor Karen L Kramer, Professor Garth Fletcher, Dr. Alexander G. Ophir, Professor David Barash, and Richard Bethlehem. Learn more about your ad choices. Visit podcastchoices.com/adchoices

Hi, I'm Wendy Zuckerman and you're listening to Science Versus from Gimlet. This is the show that pits facts against fairy tales. Today on the show, true love. Are we really supposed to be monogamous for life? To find that one true love to spend the rest of our lives with? So at this moment right now, on a scale of one to ten, how much do you guys love each other? I love them a ten.

Oh, yeah? Yeah. You've got to say ten. Up to ten. I was going to say nine-five, but I think it's a ten. This is Gail and Matt Reid. They've been a couple for almost 50 years. They met at college and still remember

those first moments when they got together. I remember that we were walking in the rain in the field behind where the chapels were and he went up to the, it was like a podium outside. And so I stood up at the lectern and I began to recite something from the beginning of one of the Doors albums. But the wonderful thing was she didn't know I was quoting an album, so she thought I was being original, which is really fabulous. Tell it, brother. When I was back in seminary school, a fellow put forth the proposition that you can petition the Lord with prayer. Petition the Lord with prayer.

You cannot petition the Lord with prayer. So I must have been flirting. Probably so. Gail and Matt believe that true love is possible. So I must have been flirting. Probably so. Gail and Matt believe that true love is possible. One person for life, happily ever after. You know, what happens in the love songs. But not everyone believes in this idea of true love.

There are one true love skeptics out there. Monogamy is ridiculous and people aren't any good at it. We're not wired for it. We didn't evolve to be. It's unnatural. I feel like monogamy is not natural. Look at every animal on the planet besides like penguins and seahorses. You know what I'm saying? We're really setting ourselves up to fail unless we find this one true love. I know many people who have terrible, terrible relationships, and for them, the notion of monogamy seems absurd.

A survey out this year of more than 3,000 Americans found that one in nine of them said they'd engaged in polyamory at some point in their lives. And even more had wanted to give it a go. Plus, in the US, about half of first marriages end in divorce before their 20th anniversary. So clearly, lots of people are reconsidering this idea of one person for life.

Today on our show, we're revisiting one of our favourite episodes to find out who's right here. The true love believers or the skeptics. And to answer this question, we're going to do it a little bit differently from our regular show. We're going to consult advice columnists and relationship bloggers. Just kidding. We're obviously not going to do that. We're going to look at the science, talk to the nerds, just like we always do. All right. so on this show, we are going to investigate, one, that bolt of lightning,

what happens in the brain when we fall in love, and two, are we hardwired to being monogamous or is cheating written in our DNA? When it comes to true love, there's a lot of... So I must have been flirting. But then there's a lot of... So I must have been flirting. But then, there's science. Science vs. True Love is coming up just after the break. Bumble knows it's hard to start conversations.

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And don't forget to subscribe wherever you tune in. Welcome back. So to figure out the science of true love, let's start with that feeling you get when you're newly in love. Matt Reid remembers when that bolt of lightning hit him. This is the story he told us. Gail really needed this book that she'd left over at his place. And it was like a winter night and there was actually like snow on the ground. It might have even still been like snowing slightly. And I went over to your room and got the book and jogged down there with it.

You did? And gave you the book. And I remember consciously thinking, I'm going to make her fall in love with me. Really? And now you've forgotten. I completely forgot. So, Gail, do you remember when you fell in love with Matt? I just remember knowing, like feeling in the spring that I loved him.

And then in the summer, when they both got back to their homes for the holidays. The first summer that we were apart, I would sit in my room and I would play Midnight Train to Georgia, the song by Gladys Knight and the Pips, over and over and over again. And just, you know, cry, you know,

from the sadness of being apart. So what is that obsession, that craving, scientifically speaking? What is being in love doing to your brain? To answer this question, we met Dr Helen Fisher, an anthropologist at Rutgers University, at her apartment in Manhattan. The doorman buzzed us in. Everyone comes here for Dr Fisher.

Helen has spent her career studying romantic love. She pioneered some of the earliest research into scanning the brains of people who are intensely in love. She wanted to see what was happening in their brain when they had that crazy feeling. Before I ever put them into the scanner, I had to make positive that they were madly in love. So I would talk to them for hours, just hours.

And, of course, when you're madly in love, you can talk for hours. You must be so patient. I mean, teenagers are, like, in their early 20s talking about love. Oh, my God. It's fascinating. And the times that they talk about are charming. I mean, I remember one young girl saying, well, we walked home from the 7-Eleven at 3 a.m.

and we had a lemon and he kept tossing it back and forth with me and we were laughing, you know. And somebody else will say, well, you know, we were under the Brooklyn Bridge and we looked up and he said it looked like a cathedral. Okay, okay, okay, okay. So once Helen has established that they are disgustingly in love, she then asks each participant to bring two photos to her.

One of their lover, the other of someone neutral. Somebody at the laundromat. Your distant cousin who you see once a year and just don't know at all. She pops them in the brain scanner. So I will flash on the computer and they will see a huge picture of their sweetheart three inches from them, so close you could kiss them. Helen alternates between showing them the photo of their sweetheart

and then the neutral face. And when the brain scanner is snapping these images of what's happening in their brain, she'll then compare them to see what parts of the brain litter when they were looking at their honeys. They all showed in common activity in a tiny little factory near the base of the brain called the ventral tegmental area. And it lies right next to the brain regions that orchestrate hunger and thirst. That tiny factory in the brain that Helen is talking about pumps out a particular chemical called dopamine,

which plays a big role in the reward system. This drives us to seek out food and water. It's this chemical that also ramps up when we have sex and take drugs like cocaine. In fact, one group of researchers wrote that when they look at the brain on cocaine, it's, quote, remarkably similar, end quote, to someone in love. And to Helen, this all means that we kind of start seeing our beloved in a totally new light.

Everything about them becomes special. You know, the house they live in, the car they drive is different from every other car in the parking lot, the movies they see, the books they read, everything about them becomes special. Bottom line is that basic feeling of romantic love is generated in brain regions linked with wanting, with craving, with obsession, with focus and motivation. You're a huge romantic. I guess I am, yeah, sure. Because with the study, because you interviewed a lot of people

to make sure who was madly in love. Absolutely. And I was wondering whether maybe that was selecting for a particular type of person that falls in love in a very particular way. I wouldn't be surprised. There's always going to be human variation. I've never met two people who were alike in my whole life,

and I'm an identical twin. That's as far as science has gotten. No question about it that I was selecting for a person who was powerfully in love. I needed to have the full-blown experience. So it's possible that not everyone falls in love this hard. Plus, interpreting how brain scans relate to feelings is notoriously difficult.

And Helen's first study only had 17 people in it. But her findings have since been replicated in other groups, including in a study of gay men and women, which showed that their dopamine factories also lit up when they were looking at pictures of their beloved. So it's starting to look like there are chemicals in our brain that switch up when we're in love. But can these chemicals keep us together for life?

That is, is our brain hardwired for monogamy? To find out, we need to look at more monogamous couples and see what's happening in their brain. But the monogamous couples that we're looking at now are furry. Oh, here they are! Inside a little plastic container is a cute couple nesting. The couples are chubby little rodents. They're called prairie

voles. They're about the size of mice and basically look like cute rats. These guys are actually quite vicious towards humans. And the scientist who studies them is Larry Young. He's a professor of neuroscience at Emory University in Atlanta. And Larry tells us that these little puffballs are in it for the long haul. They're monogamous. Yeah, these guys have been together for a while. Larry says in the wilds, once these prairie voles have sex, it's basically a done deal. He mates with her and they find a nest together. After just 24 hours of living together with a mate, prairie voles will then hang out with their partners, in some cases, for life. And if one of the voles dies, they'll rarely pick another. One paper described the enduring nature of this fluff

boar bond as extraordinary. And you could just see how in love they were by looking into their eyes. No, you couldn't. They're just rodents. They just have beady little eyes. But they work you. Anyway, Larry let us out of the lab. Bye, little guys. And back to his office, where he told us about a similar but very different little animal. There's another species of vole, which is what really got me excited,

that looks exactly the same, but they prefer to be alone. Yeah, there's another kind of vole called a meadow vole. But this little animal likes to hook up with whoever, and it's all about free love for these guys. And they don't bond at all. For them, they mate, they have sex, but nothing happens. No bond is formed. Larry showed me a photo of the two voles side by side and they look exactly the same to me. Cuddly fat rodents. They're alike in so many ways, except one is monogamous and the other isn't. And as soon as Larry knew about these two species, he knew that he wanted to study them

to see what was going on in their brains. I thought as a scientist, you know, this is a cool system to be able to look in the brains and the genes to try to figure out what's different biologically between those guys that form these bonds and the ones that don't. To start his investigation, Barry cut up their brains and started analyzing them. And he found one big difference between these two species of voles. And it all had to do with a receptor in their brain that latches onto a chemical called oxytocin. Oxytocin is sometimes called the cuddle chemical

and it's associated with feelings of love. And Larry found that in the monogamous voles, there are a whole bunch of these oxytocin receptors in a particular area of their brain. And you can see the prairie voles have lots of oxytocin receptors there. But the free love voles, they didn't have those oxytocin receptors in that area. You can imagine that when this animal mates and there's lots of oxytocin release, you're completely having a different effect on the brain.

So we said, wow, could this be what's responsible for the prairie vole for being monogamous? He tested this idea by taking a group of these monogamous voles and then using a chemical to block that special oxytocin receptor. And that meant, ultimately, that oxytocin wouldn't work in that spot in their brain. So we stuck the tiny needle down into this area and infused just one microliter of this oxytocin receptor blocker. And then we just let them mate. They gave another bunch of monogamous voles a placebo injection in that same spot in their brain. So that meant their oxytocin receptors were working just like

normal. We could see very clearly that the animals that mated that got the placebo, they all wanted to be over with their partner. What were they doing? They kind of cuddle. We call it huddling, kind of sit next to each other, very motionless, and maybe groom each other. What is groom? What are they doing when they groom?

So they groom, it's just sort of licking, and you're like with their fingers sort of grooming through the hair. Larry's currently doing like a little, I guess it would be my impersonation of a rat, but I guess that's your impersonation of a vole. Yes. All right, so the voles who got the placebo, they were still being all cutesy and hanging out with their partner

and fixing their hair and stuff. But the animals that, where we blocked their receptors and we tested them the next day, they could care less. That is, they didn't give their partner extra attention. No special huddling, no special grooming. It didn't matter to them that they had mated with this other animal the night before, two nights before. They treated them like a stranger. They treated them like a stranger. You unmonogamized voles. Exactly.

And knowing this led me to ask Larry one obvious question. Do you think it's amazing that vole and love have the same letters in them? Yeah, that's pretty cool. All right. So there was another obvious question for Larry. What does this mean for you and me? Are we humans like the free love voles or the monogamous ones? Well, Larry told us that there are studies showing that oxytocin in humans

can affect how we interact with our partners. And as for those oxytocin receptors, they are found in that special spot in the brains of humans as well. But still. I want to make one thing very clear. Vol bonding is not the same as human love. When we love someone, you know, we can use our elaborate cerebral cortex to think about how wonderful our partner is, what we can do in the future, all kinds of, it's much more complicated. But underneath that, there's something, there's this gut feeling that we want to be with that person. And I think that's what

voles experience. They don't experience all the cognitive complexities that we do, but they just have this gut urge to be with their partner. And I think that oxytocin is sort of creating that gut urge. All right. So here's where we're at. Oxytocin receptors have an important role to play in driving voles to stay together for life. And we humans also have that special pattern of receptors in our brain.

But humans have a big, complicated brain. So it's not clear how far these receptors and these chemicals are motivating us to couple up and stay together for life. Because as anyone who's ever been in a relationship can tell you, our big human brains, they definitely complicate things. It's not all about gut urges for us. Sometimes other things just get in the way of true love. Here's Gail and Matt again. He started giving me s**t all of a sudden about lowering the toilet seat and I thought I was just going to kill him over it.

It's the stupidest thing. Do you remember that? Not the seat, the lid. The lid. The lid. She was telling me to lower the seat. And I said, you know, what really makes sense is to lower the lid. Why is there a...

Okay, do you see what kind of minutiae bull**** this is? So my point was that if there's a lid, the only reason to have the lid is to close it. I couldn't believe we were even discussing it. I didn't bring it up. You said lower the seat. No, no, no. No, you brought it up.

You told me it was very important to you that from now on, I lower the lid. And you were mad at me. And I just thought, go f*** yourself, Matt, with the lid. Don't I do enough? I clean the toilet. I do this. I do that. What kind of simpleton obsesses over the toilet lid or, or really come on, Matt. It's stupid. Okay. I need to answer what kind of simpleton I am?

Yes, you do. It's a simpleton thing. I don't have to answer that. You see what I've lived with all these years. You've asked me to fold t-shirts a certain way. You want them folded the way they came from, f***ing Hanes, without the cardboard, without the plastic, but they gotta be

folded a certain way. Unlike most people who just throw their s*** in their drawer and it looks like crap. But I'm just saying, if I can fold a t-shirt in a way that makes you and your mother happy, you can close the toilet seat. I do. I do do it. I do it. And it's not that big a deal.

No. And just because you fold t-shirts like a simpleton doesn't make me love you less. I put flowers in the bathroom. I like flowers in the house. I buy flowers. I buy flowers. It's nice. Mostly for him. She keeps them around for me.

I do. So how does it get to a point in a relationship where it can be so annoying when someone asks you to put the lid down? It's hard to know, Wendy. It's really hard to know. So it can be pretty tricky to stay with one person for life, especially when they leave the toilet seat up. Or was it the lid?

The lid. Coming up after the break, we look at the case that monogamy is unnatural and that we were never meant to mate with one person for life. Plus, we'll tell you the story of Matt's relationship with another woman called Gail. Yeah, not his wife. It's Gail number two. You stupid piece of s**t. Welcome back. So we've talked about how the chemicals in our brain potentially drive us to couple up. Now, it's time to look at true love from the skeptic's position. That is, that we're not built to spend our lives with one person.

All right, to dive into this, let's start with this question. Did we evolve to be monogamous for life? Now, to find that out, we really need to know how our ancestors were bonking hundreds of thousands or even millions of years ago. And one way of doing that is by thinking through the theory of evolution. According to Aldowan, the whole idea of evolution is about survival over generations and generations. So the most successful individuals should have traits that drive them to have the most kids, because more kids means more chances that one of those kids will survive to then have more kids of their own.

Now, by this logic, you would think that monogamy would not be a successful trait, right? Because surely having sex wherever you can get it, rather than tying yourself down to one mate, would be the better way to go. And this is why, when it comes to monogamy, a lot of scientists are asking, Why the heck are they doing that? Scientists like Dieter. Hi, yes, my name is Dieter Lukas. Dieter is an evolutionary biologist. He's now at the Max Planck Institute of Evolutionary Anthropology in Germany. And several years ago, he took a close look at our family tree.

And he found that only around 9% of mammals are monogamous. So in the group that we belong to, the mammals, it's actually quite rare. So the majority of mammals have sex and then separate, leaving females to take care of the kids on their own and the males to keep on breeding. But there are a lot of other ways that mammals do it. Let's zoom in on primates, our close cousins. There's polyandry, that is one female with many male partners. It's very rare, but you do see it in tamarins. There's also polygyny, that's where you have one male and many females, like in gorillas.

Then there's our closest relatives, chimps and bonobos, who seem to practise free love with males and females both sleeping around. And finally, there's monogamy. One female, one male. And you see this in gibbons. Dita tells us that it's believed that our earliest ancestors were probably polygynasts. That is, where you have one male to several females.

And you see that when we spot polygyny in other animals, the males tend to be much larger than the females. Like there's one male who's big, who can fight off other males and keep his harem of females. And when we look at our ancestor, who lived three million years ago, Australopithecus afarensis, some estimate that the female was maybe about two-thirds the height of the male. Here's Dieter. The early ancestors, after we split from our common ancestor with the chimpanzee,

that there was still quite a bit of difference in body size between men and women, that men were quite a bit larger than women, and that it actually declined then over the millions of years. From about 2 million years ago, those body size differences shrunk and shrunk. Which brings us to today. Based on CDC data, today men are on average 8% taller and 15% heavier than females. So bigger, but not by much. Which takes us back to our question. Have modern humans evolved to be polygynous or monogamous or something else?

Well, academics actually don't agree and there's this big debate going on. So do we have any idea as to when humans began being monogamous? So don't quite know at what stage monogamy really first started in humans. There's huge debates. For those who think that humans are still polygynasts, they point to the fact that men are still larger than women on average. But the other camp of researchers say we shouldn't be putting too much stock into this size difference theory.

They argue that if animals are around the same size, like humans are today, then you actually can't tell much about whether a species is polygamous or monogamous based on size. Both sides can yak on about this for days. Team monogamy can point to the fact that there are these lovely chemicals like dopamine and oxytocin in our brains, and they say that suggests we did evolve to bond with one other person.

While team polygyny will look at the rates of male violence, or even beards, to suggest that men are still competing for a harem of women. All in all though, Dieter? Hi, yes. He warns us that it can be really hard to know what to make of some of this evidence. Partly because it's informed by our current notions of how men and women are supposed to behave. So I mean, we always think that science is so objective and science can tell us the truth. But of course, the questions we ask are already informed by what we want to know. And if we wanted to know whether males use aggression to fight over females, we can find evidence for that.

And if we never asked whether females use aggression to fight with each other, we just didn't see it. So there is, I think, this bias in what has been studied that is now changing, where people are realizing, no, the situation is much more balanced among the sexes, that really is helping us to get a better picture of the behavior. And Dieter ultimately says that when it comes to this question of whether humans evolved to be monogamous... I currently can't think of any way how we could ever know without a time machine. So until we get a time machine.

So until we get our time machine, Dieter kind of throws his hands into the air. I don't even know how to classify humans within this whole system. They don't fit with this pattern of it's easy to say, okay, they're monogamous or not. But here's the thing. Even the most romantic of evolutionary biologists, those who say that we are monogamous, don't necessarily think that we evolved to have a one true love for life. In fact, when scientists say the word monogamy, that often means that animals are just staying with a partner for a breeding season, or two or three, before heading off into

the sunset with a new love. It's a mating system called serial monogamy. Here's Larry, our vole whisperer. When we say monogamous as biologists, we're differentiating them from the most of the other species that don't form any kind of bond with their partners, right? So most mammal species, they mate, and then there's nothing. So there's a sexual attraction, but nothing else. So we're differentiating humans and prairie voles and a few other species in the sense that when there's, after the mating, they actually like each other, and they want to be with each other. So if we humans did evolve to be monogamous, even if just for a breeding season or two. Does it mean that we're

not going to cheat? Remember those voles who stay together for life? Well, not all monogamous voles couple up at all. And even when they do, they sometimes cheat. Yeah, even voles have the occasional side piece. Here's Larry. Even though they bond for life, that doesn't mean they're never going to have an affair. Mm-hmm. A group of scientists ran genetic tests on the babies of paired up, loved up voles and found that 20% of the litters were sired by someone other than their supposed dad. Which means the mum was having a bit of fun on the side.

If you look in nature and you take a nest, and she'll have a number of babies, say four to five babies, most of the times those babies are all, they belong to the male who is her partner. But oftentimes they do not. And we see cheating all over the so-called monogamous animal kingdom. It's estimated that around 90% of bird species are monogamous, but the eggs they're hatching together sometimes come from another birdie daddy. And what about us humans? Well, even for our true

lovers, Gail and Matt, even they've struggled with a bit of eye-wondering. Who was the Gail? Her name was Gail also. The marathoner? Yes. Yeah. Enter the story of Gail number two. Another Gail.

Matt met her while he was training for a marathon. And that was like the most important thing that he was doing. And I remember one Sunday in particular when the kids had the chicken pox, he was training for his marathon and then he went and had bagels and coffee and I was just livid. When I went out for bagels and coffee, it was me. Whoa, whoa, whoa, wait, wait, wait. So while the kids have chicken pox, you're getting bagels with Gail number two. Yes.

It all escalated to the point where Gail was convinced that Matt was having an affair. And then to top it all off, there was this dinner arranged for the marathon runners. Matt said to me, spouses weren't invited. So I called and they said, oh, of course spouses can come, you stupid piece of shit. So why did you say that spouses couldn't come? I know, I don't make shit up. Somebody must have told me because I never have ever done

anything that excluded Gail in my life. Because this woman was really hot for him and he was probably enjoying it. And I don't blame him. Because, you know, it's not easy to have small children and, you know, your wife is bitchy. Did you have a crush on Gail too? No. Yeah, you did. Did you enjoy flirting with Gail too?

Yes, I did. I'm sure I did. I liked to flirt. But I liked to keep my distance. I didn't get scared if somebody actually, like, responded to being flirted with. I'm sure I did. I like to keep my distance. You know, I don't get scared if somebody actually, like, responded to being forwarded. I believe that is true. So have either of you ever cheated?

No. I've never cheated. I've never cheated. No. No, I've never cheated. I never. She's told me she hasn't, and I have to believe her. Okay. So Gail and Matt say they haven't cheated. I never, she's told me she hasn't and I have to believe her. Okay, so Gail and Matt say they haven't cheated, but that's definitely not true for many couples out there. In fact,

one review paper wrote that, quote, infidelity is relatively widespread, end quote. Also widespread. So, for example, according to a US survey from 2016, around one in every six people admitted to having an extramarital affair in their lifetime. Those are just the people who admitted it in a survey. So, bottom line, infidelity is found throughout the animal kingdom, and there's just no escaping it. But when we do look at the animal kingdom, and there's just no escaping it. But when we do look at the animal kingdom in search of what is natural, there's one final point to consider,

and it's this. There are always individuals that break the mold. So remember that genetic study of the monogamous voles with the mums who had cheated on their partners? Well, in that study, two females didn't actually bond with their male partners. Instead, they coupled up with each other to raise the kids. Point is, this is science, and it's complicated. And even the voles, our poster child animal for monogamy, even they are complicated in their own way. So, when it comes to science versus true love, does it stack up? One, what happens in the brain when we fall in love? Under a scanner, the brain in love looks different to the regular old brain.

And chemicals that play a powerful role in our drive to have sex and eat and take drugs, they also seem to get pumped out when we're in love. Two, are we hardwired to be monogamous? Well, we know that voles and humans have chemical receptors in a part of their brain that could play an important role in making us couple up. But when it comes to our evolutionary history, it's not clear whether for most of our ancestry we were polygynous or monogamous or something else.

And the thing is, when you're looking for guidance on how to live your life, understanding our evolution only gets us so far. The fact that millions of years ago some pre-humans might have been living in a harem, or that all sorts of animals cheat, even the voles. That doesn't mean that you should or shouldn't be monogamous in your own life,

or even that a true love fairy tale ending can't happen for you. Bottom line is, don't let Darwin tell you how to live your life. He's dead. He's Dr. Helen Fisher. Now, I mean, we're not puppets on a string of DNA. All kinds of people say, oh, God, that girl is cute. You know, if I weren't married, I'd go for her in an instant. And they choose not to. Because, I mean, you know, we can, we make decisions in our lives. We've got a big cortex to do that. But it's remarkable how many people do fall into, at some point in their life, an adulterous relationship.

And then one way or another, they solve it. Given that it's all messy and choose-your-own-adventure-like, I asked our couple, Gail and Matt. Any advice? Well, no, I just, I don't really understand, you know, how one does this because, you know, we were just so lucky to find each other and then more or less figured out that we had found each other. And I think there's a lot of luck to that. I really do. I love you, honey. Oh, I love you.

And I always have. And I always will. I will always love you, too. That science versus truth. The trifecta is when I shop, I cook, and I clean. And I say, oh, I got the trifecta. And she looks at me, and instead of saying, thank you, honey, instead that she gets that little fire in her eye. Because I do it all the time, but I never shove it down your throat.

You don't do it as often as I do. That's science versus true love. This episode was produced by me, Wendy Zuckerman, with Heather Rogers, Caitlin Sorey, Ben Kebrick, Shruti Ravindran and Rose Reid. We're edited by Annie Rose Strasser and Blythe Terrell. Extra editorial help from Alex Bloomberg. Production assistance from Stevie Lane. Backchecking by Ben Kebrick, Taylor White and Rose Rimla. Music production and original music written by Bobby Lord.

A special thanks to Joseph Lavelle-, Austin Mitchell, and to all the researchers we spoke to for this episode, including Dr. Karen L. Kramer, Professor Garth Fletcher, Dr. Alexander G. Ophir, Professor David Barash, and Richard Bethlehem. I'm Wendy Zuckerman. Back to you soon.