Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas - 328 | Mary Roach on Replacing Parts of Our Bodies

Episode Date: September 15, 2025

Like any machine, bodies occasionally break down, and it's natural to go in search of a replacement part. Ancient societies featured simple prosthetics for teeth, noses, and limbs, while modern medicine pursues more advanced ways of replacing internal organs and microbiomes. But what is striking is not just the impressive ingenuity of our attempts to replicate human anatomy, but the surprising level of difficulty involved in doing it well. I talk with author Mary Roach about the many ways in which humans have chosen to replace bits of themselves, as told in her recent book Replaceable You: Adventures in Human Anatomy. Blog post with transcript: https://www.preposterousuniverse.com/podcast/2025/09/15/328-mary-roach-on-replacing-parts-of-our-bodies/ Support Mindscape on Patreon. Mary Roach received a bachelor's degree in psychology from Wesleyan University. Her books include multiple New York Times bestsellers and have appeared on numerous best-of lists. She was a guest editor in the Best American Science and Nature Writing series, and received the Rushdie Award from the Harvard Secular Society. Web site Wikipedia Bluesky Goodreads profile Amazon author page

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When you need the right person to cut through the chaos, this is a job for Indeed sponsored jobs. And listeners of this show will get a $75 sponsor job credit to help get your job the premium status it deserves at Indeed.com slash podcast. Terms and conditions apply. Need to hire? This is a job for indeed sponsored jobs. Hello, everyone, and welcome to the Mindscape Podcast. I'm your host, Sean Carroll. A few weeks ago, as I'm recording this, there was some kind of global summit.

I'm fuzzy on the details. I didn't really do a lot of research for this intro. But the point is that there was a conversation between Vladimir Putin, who's the president of Russia, and Xi Jinping, who is the leader of China, that was caught on what seems to be a hot mic. In other words, the microphone was turned on, but the speakers didn't actually know that they were being recorded or broadcast, and so they were more candid than they would otherwise be. You might think that they'd be talking about global geopolitics or trade agreements or something like that, or even political philosophy. But no, Putin and Xi were talking about bioengineering and the possibility of immortality, or at least longevity, ultra longevity.

They were saying how advances in biological science were making it possible to replace organs, and if you're could go at this rate, you might end up living for 150 years or even more, subtext being that they would like to live for 150 years or even more. And of course, that's a little contestable, that claim. I mean, there's no contestation to the fact that bioengineering and biology more generally are absolutely leaping ahead by leaps and bounds. We're learning a lot, but there's no actual breakthrough that so far has dramatically increased the upper limit on human lifespans. In fact, this is an issue more generally with sort of the techno-optimist way of thinking about the world. And I say this as someone who is very much attracted to the techno-optimist

way of thinking about the world and to someone who does understand the difference between something being literally incompatible with the laws of physics, in which case you should just give up on it, versus something just being really, really hard, an engineering problem, as we call it. And many biological things are sort of engineering problems. But it's too easy to imagine taking biological things and just making them arbitrarily better. That turns out to be really hard. It's not that it can't be done. We do it.

We're getting better at it. But biology is very, very, very, very complex compared to physics, mechanical engineering, even chemistry, things like that. So today's guest, Mary Roach, is one of our leading and also most entertaining science writers that we have. She's the author of books like Fuzz and Stiff and Bunk and Gulp, as well as Packing for Mars, and her new book is called Replaceable You, Adventures in Human Anatomy. And Mary doesn't have an overarching lesson that she's trying to teach us here, but she goes through a large number of examples, both historically and contemporary science, of how we replace our limbs and our organs and our skin and our hair and things like,

like that with either other biological things or completely mechanical things and how, you know, there's been remarkable improvements in a number of ways, but man, is it still really hard? It's still very, very hard to replace an organ in a way that would just bop you back to the level of health you had before. Even she says, you know, she sort of challenged yourself, what is the simplest thing to possibly imagine replacing? and she came up with a variety of tiers that our tear ducks reproduce, we can't do it. It's not something that we're able to do right now.

So these are things that I'm very happy to think about in a science fictional way and imagine someday we'll get there, and I'm very happy to cheer along the progress that we have going on right now. But a touch of realism is called for in the near term because biology is tough, man. This is one of the lessons that we've seen over the podcast over and over again. So let's go. Mary Roach, welcome to the Mindscape Podcast. Thank you, Sean.

I guess you've written a book called, tell the audience what the title of your book is, so I get the subtitle right and everything. Oh, sure. It's called Replaceable You. Adventures in Human Anatomy is the subtitle. And how long ago, historically, do we know, like when did people start actually replacing body parts

with non-body parts? things? Things really got rolling with noses, it seems, as far back as like 1,500 BC people were actually surgically reconstructing noses. And the reason for that is that there was kind of a surprisingly large demand because nasal mutilation was a popular punishment. And this has gone on various regions of the globe over history where if somebody, if somebody, somebody's done something criminal or offensive or if somebody just wants to punish you, they would hack off the nose, which served both as punishment and a deterrent. Like, because it's right there in your face.

I guess so. So everybody sees, everybody sees it. And like, ooh, yeah. But you can only do it once. You can only, yeah. So if you're a recidivist, you're all set. You're like, you know what? I don't have a nose anyway.

So I guess what the hell. I'm trying to decide if I didn't know. would I think the cutting off the nose or the ear or poking on the eye? Like a nose is very noticeable, but I guess it's not like super damaging if you use it, right? If you lose it. Yeah. So I think, yeah, I think it was more effective as a deterrent than as a punishment. And nevertheless, despite the fact that it was a punishment, they developed the wherewithal to replace the nose somehow.

Yeah. Yeah, it's kind of the very beginnings of plastic surgery. there was a technique and it's still occasionally used today where you take a flap. Flap is a technical term. Take a flap from the forehead or they used to use the cheek as well so you would loosen this flap but keep it attached to its homeland and then flip it over onto the nose and place it there. But it would stay attached to where it's from. So they still had the blood supply while the blood supply was growing in on the nose. And then eventually when the nose, the new nose material had some capillaries and some blood supply, then they would cut off. They'd snip the little isthmus.

And what materials would they use to replace the actual nose? The skin, the cheek. But like, would they put like bone? Oh, oh, bone. Ivory. You know, I don't know what the actual cartilage replacement would. and maybe they just mounted up the flesh, kind of like molded to the flesh. This is not, this is the first time, but I'm sure not the only time that I'm going to be shuddering while we're having this conversation.

It feels a little icky. That's a good question. Did they, did they use anything for the cartilage part? It seemed like they were just kind of molding, like using the flesh as like sculpting clay. That actually seems pretty advanced, like, you know, knowing that you needed blood and the whole bit. I know. Yeah. I was very impressed.

And I was speaking yesterday to a transplant surgeon who said, yeah, we still do that. I did that last week on a pediatric case. And where in the world was this going on? Well, lots of places. But it started out in Egypt and India were the two places. If you go way back, those were the, and yeah, it was called the Indian method. But I think in Egypt that was done as well. So it's...

The Egyptians, of course, were expert mummifiers, so maybe they knew a lot about reconstruction for that reason. Yeah, it could... Yeah, yeah, yeah, it could be. And, of course, I'm an astronomy major from way back, so I know the story of Tico Brahe, but maybe you could tell the audience that one. Yeah, and you even got his name right.

There you go. A lot of people say Tico. Tico Brai. Yeah, Tico, well, I... Yeah, I like Tico, because... Yeah, he lost a significant chunk of his nose in a duel. And so he had a fairly lightweight for metal. There's whole papers disputing whether it was brass, an amalgam of brass and pewter or whatever.

It's unclear exactly what the metal was. And he would carry around a little box of adhesive, some kind of glue to stick it on. And according to one biographer, it would occasionally. drop off the middle of a... I've seen pictures or portraits, I guess. Do you think that those portraits are, you know, faked a little bit to make it look like a more natural nose? Or was it very obvious? No, I think it was pretty nicely done.

It was kind of painted. I mean, there were... The metal noses and the celluloid noses that were made way back when they were often painted. And in one case, there was two different paint colors, one for evening and one for daytime. Oh, my goodness. Okay. Which, you know, if you wear foundation, which it looks like you're not. But if you wear foundation, you know, you can adjust the beauty mirror. What's that called? The makeup mirror, according to daytime, indoors or outdoors light.

So fairly sophisticated nosemaking. My favorite, however, was from 1894, Frank Tetimore. an army surgeon devised. This was one of the early plastic noses and it was suspended from a pair of glasses without it didn't the person didn't need. That makes sense. Didn't necessarily need glasses but so the nose would be suspended and then to hide the line between the artificial nose and the upper lip there was a mustache. So it was essentially the earliest groucho marks glasses ever made. For men that works well. Yes. Right. I never thought of that for the ladies. I'm not sure they did.

But I love the stories just because it humanizes the past, right? Like these people cared about how they looked. Just like we do now, they were doing plastic surgery, makeup. They didn't want to be embarrassed going out in public. Yeah, yeah. And that was true. I read a bunch about early dentures. And dentures are surprisingly, they go back to the 1700s and they were quite elaborate, but they just, they didn't work well at all for chewing. So it was like a wig for the mouth. It was a cosmetic thing that you, and somebody described in a Victorian era that people would use what was called a masticator. So they'd kind of mush, they'd grind.

It looked like a handheld proof. tree pruners and you kind of had a little attachment that was sort of blades and a mushing thing and you'd mush up the food so before you would eat it. So people would, at a Victorian dinner party, the host might masticate in private and then put in the very uncomfortable and not useful for eating teeth and then go out to the table and not really eat. Right. Okay. Yeah. So. And here in the United States, of course, the father of our country, George Washington, was one of these people. George Washington, yeah, there's correspondence of George Washington with various of his dentists. George Washington had this type of denture that was held in place. This was before polygrip. There weren't adhesives. The dentures, the uppers and lowers were spring-loaded,

so there's this very stiff spring pressing the upper up against the upper palate and vice versa to the lower. But it also, the spring had a tendency, at least in George Washington's case, to push the upper denture forward out of the mouth. So when you see those portraits of George Washington, he kind of, you know, kind of looks, first of all, he looks really glum. And he also looks like, so he's kind of like, yeah, he's kind of like holding in his teeth with his upper lip, you know, kind of just holding it in place. Yeah, it was, he was in battle with him. own teeth. And you say you write in the book about how not that long ago, historically, tooth maintenance technology was sufficiently bad that people would intentionally just have their

teeth removed so they could replace them with dentures, which were kind of better looking at the time. Yeah, yeah. This was something I'd heard about a long time ago, maybe on QI or something, you a matrimonial dentures somebody mentioned and I was like come on like that that giving somebody the gift of having their teeth all pulled would be a wedding gift this was this was something that was done like here you go you'll look better yeah this is it won't be as expensive you get them all out at once and I was like I'm not buying that but I went I found a it was something on Reddit where somebody said I don't really buy this is this true a thousand I'm not making that number of 1,000 people wrote in saying my grandmother or my granddad

had this done at a young age, teenage, 20s, 30s, all the teeth pulled. Paul McCartney's dad on fresh air. He mentioned the story, but his dad, when he said, you should have them at 21 will take you in to get them all pulled. Get you some of them newfangled dentures. And so people would do that. And it's kind of sad because at the time, you know, dentures, there were no implants. there are now, you can kind of click dentures into the implant and they stay put pretty well. But back

then, that was not the case. You had like 25% of the chewing efficiency that you would have had if you had your normal teeth. So anyway. Well, this is, so we got some stories on the table so we can start drawing some lessons here. I mean, it seems that one of the lessons of your book is it's hard and maybe even harder than you think to replace body parts artificially. Is that fair saying? That is very fair to say. That it is so challenging. I, at one point when I was working on this book, I thought, is there any bit or piece of the human body that we can really replicate such that the replica is as good or better than what we started out with? And I got very simple. I'm like, okay, tears. Let's do tears. And I found this guy whose entire career has been based on

trying to create an artificial tear. And not specifically the tier that when you cry or when you cut onions, but the tier film, which is a protective and lubricating layer. And the tear film, okay, we spent the duration of two free zooms, what is that, 45 minutes plus 45 minutes, talking about the tear film and the miraculous structure that holds all these layers in place, the glyco-calix and how it helps with retaining moisture and how there's musins that catch the glop and deposit it, you know, that sleeps not in the morning right in the corner of the eye.

Those are the musins at work and it was, anyway, what all that leads us to is we can't even, we can't even recreate. Not even that. Not even that, yeah. The only thing I think the transplant that I think works the best is one that I addressed in a previous book, which is the fecal microbiome transplant. I think that's a situation where the one that you have has been invaded. You've got, you know, C-DIF running loose in your gut.

And so take someone else's microbiome. And now it's all they're encapsulated. But in the beginning it was just, it actually started out as a veterinary technique. But, you know, going back to when Gulp, when I was working on Gulp, it was like a guy showing up at the medical center with a brown bag saying, not my best work, here you go, though. And that material being put in a blender, an oyster blender, in fact, and mixed with distilled water, I think it was. And then that was introduced into the coloneloscope, which has a kind of a plunger

attachment. And two days later, the guy is having normal bowel movements, which, you know, that was exciting. I mean, people die from C. diff, and this guy in two days, I mean, he was overjoyed. So that's a pretty successful transplant replacement. But we're not replacing healthy normal. We're replacing compromised and invaded. Yeah. I kind of want to ask more about the fecal microbiome.

I mean, what is the role of that? What does that do? What is it? Oh, the fecal microbiome, that's just all the bacteria that you have in your colon that are breaking down what you deliver by eating. So that's incredibly important. And a healthy microbiome does that without causing a lot of gastrointestinal distress. So people with C. diff, that's a bacteria that gets, I don't know how it gets in, but it gets in often in hospital settings.

And it's really hard to eradicate with, I mean, you can antibiotics sometimes do the trick. But when they don't, really hard to get rid of. The fecal microbiome transplant is a pretty amazing thing. Yeah, it is, I guess, a reminder from my perspective, that biology is way more complicated than, I want to say physics, but just mechanics, right? Like a nose is just sitting there, letting the air come in. But in the more complicated biological cases, there's so many moving parts that even now we're not very good at figuring out what they all need to be, to have a, successful replacement. Right, right, right.

That's true. I mean, not even something like hip replacement. Hip replacements, you know, they're at a point where, you know, fewer than 1% of cases, there's a serious infection. But the first one was 1938. And they went through some rough times. There was the big Teflon fiasco where the, you know, it's like a ball and cap. and the cap, they were trying to create the same kind of frictionless movement that exists in the human hip.

And Teflon was a new substance. And there was this guy, John Charnley, who was like, hey, I've heard about this stuff. And it's really great. And the coefficient of friction is really low. And let's try that. And so they started making the cap, you know, the acetabulum, the simulated, you know, cap in the hip where the ball of the femur goes. And it seemed great. Then what happened is it wore down really quickly and the body reacted to it poorly and this horrible cheesy substance.

That's technical term used by John Charlie. Charlie, a cheesy substance. And it was a mess to clean it out and to redo these hips. It was horrible. There was that. Then there was the metal on metal period where little bits of metal debris were setting up kind of an inflammatory reaction. And that was horrible. So it's taken a while to get to the point that we're at.

out now or like every other person in their 80s has a fake hip. I would have thought that that's not an actual statistic. No, I was like, yeah. I would have thought that any chef who is familiar with nonstick cookware could have told him that Teflon does not last very long. You would think, right? You would think. Maybe it wasn't too much back then.

Yeah, I know. I saw a photograph of, you know, of one of these caps. And it was just, you know, it was almost completely worn through, you know, It's just like a mess, yeah. But okay, the hip replacement is an example of what I was going to guess or presume is the other successful genre, which is just limb replacements, right? I mean, they must have had prosthetic limbs of some sort way back in the olden times. Sure, sure, yeah. There were, you know, wooden legs.

There was an aluminum leg that was quite exciting because it was lighter weight. This was in the UK. A lot of the military veterans were excited about the military light leg. Because for a while there was this belief that when you replaced a leg, the prosthetic limb should weigh the same as the remaining leg, which is actually, that's a pretty heavy leg. And so people were dragging around a lot of weight. It was very uncomfortable. It was held up by harness. It was uncomfortable.

So now we're at a point where artificial legs, mostly legs, are starting to be actually screwed into the bone. It's called asio integration. And that's terrific if it works, if you don't get an infection, because now you have sensation of the floor. You can sort of feel the surface that you're walking on. You don't have to check to see if you're stepping on somebody's foot. you can move it just it's just far more like having a natural limb. But it's, you know, it's, you have to close up the skin around it. It's not a complete seal bacteria get in.

So there've been issues with infection. There's a couple of different techniques. Anyway, I would be, if I had an artificial leg, I'd be hopeful that they work the kinks out on that because it sounds like a, a big improvement. And was there any feeling back in the day that like the dentures, we might actually improve ourselves by having an artificial limb? Like maybe you have an arm that could be a hook or a pummel or a hammer or whatever.

I don't think anybody was lusting after a hook. But one of the ways I got interested in this book was I met a woman, And she actually emailed me about something else. And we got to talking, she's a amputee, below the knee amputee. She's an elective amputee. She is someone, she had a healthy foot, that is to say, it had a blood supply. It wasn't wounded, but it was twisted. She'd had spina bifida and it was twisted.

She'd had multiple operations. It just was underperforming. And she would see people with below the knee prosthetic. who were hiking and running and doing all these things that she herself couldn't really do. And she wanted to find a surgeon to cut it off. It took her quite a while to find somebody to cut off, you know, to cut off a, quote-unquote, healthy limb. Because she said they'd say to her, look, this is a healthy foot.

I can't cut it off. She goes, yeah, but I can't walk on it. And it took her a while to find somebody willing to do that. I mean, it's, you know, I guess if you're, you're a surgeon, there is a kind of a worry. It is there's a finality to lopping off a foot. Kind of can't, not going to get it back. And I guess a fear of what if the patient now has some kind of chronic phantom pain,

phantom limb pain, you know, what, it's just easier to go ahead and do another surgery and hope for the best. There are some runners who are amputees, right? You can get replacements that allow you to run fast. Yeah. The limit of my knowledge right there. You can get replacing. for hockey, for pool.

They're called terminal attachments. So it's a different kind of. You put on a like a rock climbing attachment or a kayaking attachment or a ping pong attachment. Sometimes the piece of equipment is sort of built in. There was a prosthetist who built a mop foot for his wife, which is kind of weirdly sexist. That kind of is, yes. For his wife, is the sealing deal. Yes. Yeah, exactly. Yeah, so, but interesting, you know, I talked to Ezra Freck, who's a, he's a Paralympian. He won a couple of golds in the recent Paralympic games. And it was funny when I met him. I didn't know who he was. I was talking to his dad, who does a lot of work with recent amputees, try to get them back into sports.

And Ezra came up and Ezra has an amputation at the thigh and then he's got, I think it's, anyway, I said to him, can you run? Like, this is, this guy is an unbelievable. He's like a high jump medalist, a sprinter, you know, and I stupidly said, can you run? Yeah, but so yeah, there are definitely their attachments for running. I also said stupidly, like I brought up that business about Oscar Pistorius and did he have an advantage because he had that blade because people often think, oh, that's like techno doping. And Ezra said, well, first of all, he didn't win, like I had said, he didn't win. He placed whatever. And he said, it's the first time somebody with an amputation has had. has made it that far.

Nobody has since. If it were an advantage, we'd be seeing amputees in the Olympics all the time. But anyway, it was an interesting day there at the amputee coalition conference. You've already mentioned the weight issue in the limbs. What other kinds of improvements have there been? Can we hook up nerves in our body

to manipulate the limbs at all? Well, what this tends, that kind of stuff happens in developing. There's a lot of effort now to develop arms, lower arms and hands with articulating fingers so that you can grip things. And so it's, you know, when you think that to your, you think I want to close my hand, you have that thought. You're sending an impulse. And the impulse, if you amplify that impulse and it can. computer kind of translates that, then you, you know, you can move the hand. The ones that I'm, that as far as I know, they're kind of toggling through different grips. It's not, it, it's slow. You know, it's, I mean, the, I read an essay by Britt Young who writes a lot about this. And she pointed out that it, first of all, they're very heavy. Those kind of bionic-looking limbs. They're very heavy. They need to be charged.

They're very expensive and can be exhausting mentally to use. It's not the same as just, you know, me reaching over and picking up my glass like that. I was walking around the amputee coalition with this woman who had the foot amputation, and we passed a booth. I only saw one booth for arms that whole day. And it was that, you know, that classic shot of the kind of Arnold Schwarz. Schwarzenegger bionic-looking limb and it's holding a raspberry. And she laughed.

She goes, are you going to spend like 30 seconds of getting your grip right? No, you're going to reach over with your other hand and pick it up and eat it. So it's that kind of thing. Not to say, I mean, eventually, I would imagine eventually these things will become lighter, faster, more practical, cheaper. but they're not there yet. It does seem that even for robots, it's difficult to get them to like pick up an egg or whatever, all this fine scale stuff.

You know, my favorite kind of, I don't watch a lot of videos on YouTube, but my favorite are the soccer playing robots to fall over. But they're getting better, like you said. I wouldn't want to play against them 20 years ago. I know. I don't want them to get better because they're really entertaining when they fall over each other. So, okay, so but mostly, yeah, so these are the obvious ones.

You lose a nose, you lose a limb. How good are we getting at replicating, like, functions of organs in the body? Obviously, there's artificial hearts. That's probably the biggest success story, I guess. Right. Well, in terms of transplantation, a xenot transplantation has been a pretty cool thing to follow this past couple of years. It's just now seems to be getting to the point.

where patients with, say, a pig kidney, it's mostly kidneys, are making it longer than two months. There was a whole slew of pig hearts and pig hearts and pig kidneys going in to patients who lived about two months. Wow. But there's a man now, Tim Andrews, I think it's going on eight months. And eGenesis has is just starting a trial with, I don't know how many patients getting pig kidneys, a dozen, maybe. Anyway, so it's, and Tim Andrews is in much better shape that the early recipients were getting these organs under compassionate use exemption because these organs have to be FDA approved. Yeah. And they're not yet.

But these were folks who were so close to being deceased that it was felt that, you know, this might. They're not going to make it anyway. So let's give them a chance and let's advance the research. So they were pretty sick. So those are the folks who were lasting two months. Tim Andrews is in better shape. So that's promising. You know, eight months is, you know,

it could be enough time for a patient to make their way up the donor list, you know, and become eligible for, then, for a human organ. So it's right now thought of kind of as a bridge, you know, a stopgap. Do we understand very well what puts that time limit on it? Is it just that, I mean, obviously, at the cellular level, pigs and human beings are different. But is that translatable into a specific reason why it doesn't stick? There have been different reasons. There have been a couple cases of viruses, pig viruses, that actually affect humans.

And so there were some zoonoses, as they say, causing a problem. A pig virus. There was another case where the heart started growing, outgrowing the space that it was in. And that was causing a problem. Kind of like the Grinch, remember the end of the Grinch where his heart grows two sizes. But in the Grinch, it's a happy thing. But in this case, it was a problem. So, and, you know, there's still a tremendous difference between, even if you, you're basically

knocking out this alpha-gal protein, which is a surface protein that makes the body kind of go like, red alarm, this is not normal and attack it. Like, it's called a hyper-acute reaction, and it kills the thing, turns black, starts turning black right away, just like out of there. The body does not want this. So knock that out. Now you're at a level where, you're, you're at a level where. the same kind of immunosuppression that you would give a patient who's receiving a human organ.

You know, there's still immunosuppression. But I talk, you know, I spent some time in China for this chapter and this researcher who's been working on xenot transplantation for 30 years. I said, you know, could you eventually edit the pigs to the point where these were the kind of match that didn't even require immunosuppression. And he's like, no, no. But he said, you know, but what you could do, you could sort of tweak it so that the organ was secreting a localized immunosuppression.

So you didn't have to give systemic immunosuppressions. So he had all these ideas, and he was very hopeful for the future of pig organs in humans. Is there a good reason why it's pigs in particular that we use to replace human organs? Oh, that's a fine question. looked into that. You can kind of blame it on the Hormel Corporation. Because I was curious, like, why pigs? Why, for medical and surgical experimentation?

It's been pigs for a long time. And pigs are, pigs, pigs are big and loud, though. There was this great quote by Pavlov, who preferred dogs. said all pigs are hysterical, like you bring them in, and they're squealing really loud. I've seen this in a lab setting. Now, pig is a big animal, and they're very loud anyway. So back in the, God, 40s and 50s, it was a collaboration between the Mayo Foundation, which is the research arm of the Mayo Clinic, and the Hormel Institute, which is the research arm

of pork. those two got got together and bred pigs smaller they bred them smaller so that they'd be easier to have around the lab

the organs would match hours they also did all of this experimentation on comparing the coronary arteries of pigs to humans to see how close are they

and pigs are in fact someone described them pigs as a caricature of an obese human because they get coronary artery disease. They don't get a lot of exercise. This is domesticated pigs. They eat garbage.

So they're kind of perfect for that work. And they were like every kind of, they went into every possible application. There was a, I remember seeing a paper on orthodonture. and were pigs useful for studying orthodontia? They put, somebody put braces on a pig, braces on a pig. Anyway, so poor pigs. They, you know, that, it just, that pushed everything down that road. And once that started, and things began to be known about pig coronary arteries and pig kidney

function and pig liver function and pig teeth, you know, a lot was known. And so it became kind of the go-to animal. Well, yeah, I guess the point is that once you start down that road, you know a lot more about the pig than you do about other options. So if you're a person who's going to get something put in them, let's go with something we know something about. Yeah, that's right. And they are, you know, similar size and fairly, in some cases, fairly similar functions as the Hormel Institute helped us learn. And what is the process like for just figuring out whether these crazy ideas of replacing a human interior organ with an animal's interior organ has any chance of working? Like, what does it like to be the first person to get a liver from a different kind of animal?

Is it basically like it happens with people who are near death anyway, or is it something more expansive? Yeah, yeah, that tends to be the first one. I didn't, I'm sorry, I didn't, I didn't speak to the first, Mr. Bennett, I believe his name was, who, the guy who got the first pig heart, I believe it was, but I spoke to the surgeon, Dr. Mohoedine, I'm probably mispronouncing it, Mojahideen, anyway, and he said that Mr. Bennett said, had a concern, although not all that serious, he said, well, am I. going to be going oink oink after this? Like this could,

you know, that concern that sometimes people who get a new heart have this belief, this sense that they have changed in a way, that they have taken on characteristics of the person who donated the organ. Well, the heart is sort of in literary ways of thinking about the human anatomy. It's the seed of something. And yeah, we know it's just a pump blood, but it means something to the person who has it.

It does, yeah. You don't hear that from people getting kidneys, that they feel like they've taken on traits of the donor. And I guess, yeah, for like hearts and lungs and whatever, a couple months, that's a sobering fact. But for smaller things, I get the impression that, you know, you can replace the valve in a heart with a pig valve, and that would last longer.

Is that right? Yes, absolutely. Yeah, yeah. I mean, eventually, they need to be replaced, but the pig valves last, I don't know, a decade is it? I'm just throwing that out there. I knew someone who had a pig valve, yeah. And it's, yeah, go ahead, go ahead. But we also just do purely mechanical ones. I mean, what's the, what's, do you know the tradeoffs between saying, okay, you need a new body part, heart or just a valve? Do you want the pig heart,

or do you want the completely artificial one? I don't I don't I don't think I mean again I think that the artificial heart is again a stopgap you know you don't meet people who have a artificial heart for very long I don't think I didn't I didn't report on artificial hearts but the sense that I got was that they were a temporary measure while somebody awaits a heart from a from a donor yeah are we the this is not exactly what you were talking about in the book, but how good are we just replacing human parts with human parts? Is the technology for human organ donation pretty good these days? Yeah, there's a couple things going on.

They're pretty cool. I spent some time at the University of Michigan has a lab called the Extra Corporial Life Support Lab, and it's all about devices that do. the job of parts of the body outside the body extra corporeally. And yeah. So when I was there, when I was visiting, they were trying to, they were working toward creating or working toward figuring out how can we keep these hearts that we have taken out

of someone's body for transplantation. How can we extend the shelf life? Because right now, you know, if you just put them on ice in a cooler and you send them off, got, you know, four, six hours, something like that. There are profusion machines that will sort of oxygenate the heart in a kind of, it's called a heart in a box. That'll take you to, I don't know, eight or 12 hours. What they were trying to do is figure out how can we extend that to 24 or 48 hours, because that would allow you to test that organ, see how well it's functioning. So, because right, And now there's an age cutoff and a lot of hearts get dumped because they're too old, but they may be working well.

Maybe the person was a marathon runner, but there's a cutoff. So if you could test the heart and see how well it works and have that be the criterion by which you decide, does this go into another person, you could also work on it. You could fix it. Yeah, I don't know, put in a scent. Clean it up. Yeah, exactly. Kind of like a, you know, reconditioned iPad or whatever. those ones that I always think I should get and I don't.

Yeah, so, you know, they were testing, you know, if we change, if we alter the flow, the blood flow through this heart, because right now they pump a lot through because they want, you know, the thinking being more oxygen is better. So, you know, it's a high flow rate, but that damages the valves pretty quickly. They start to get leaky. Things start to deteriorate. So they were testing a lower flow rate that day. And it was really cool because there's this heart and it's attached to this gizmo. You know, first they remove it from a pig that has been, of course, completely sedated. And they take it in the other room and here's this first, but amazing thing.

First, you have to stop it. Like a heart will keep on beating for up to 10 minutes outside of body. Okay. You maybe you knew that. I did not know. That, yeah. Even the research fellow who was doing the work sent me a video later of a heart. Because he had said, yeah, like sometimes I have to take a sample for pathology and it's still beating.

The heart is still beating. And I'm trying to take a very thin slice and it's very annoying for me. It's very annoying for me. He sent me an image. A little video of a heart on a blue surgical cloth separated from a body. And it's been cut in half kind of like a deli roll, and it's still beating. It's still beating. It's just the weirdest thing.

Anyway, hearts. I guess this just shows my ignorance. I had assumed that those heartbeats were triggered by signals from our central nervous system. Well, they have an internal kind of electrical system. Yeah, okay. And I used to know the term for that. It is in my book. And like so much, look, these are flashcards.

This is me trying to remember what's in my book. Let's give the audience a reason to buy the book. That's okay. Yes, that word, the term is in there. It'll probably occur to me in about three minutes and I'll blurt it out, derailing whatever we're saying. I mean, I guess I'm occasionally really amazed that our organs last so many decades, at all. You know, we're much better designed than most machines are, right?

Yeah, no, I know. You see, you know, I remember the first time I saw a heart beating. It was an organ recovery. So this person was brain dead, like legally dead, but being oxygenated on a ventilator. And they open up the body cavity to take out the heart. And you see this thing and it is just squirming around like a stout in a burrow, just like it's really active. It's just you know, you feel your heartbeat and it's sort of a gentle, kind of gentle, I don't know, mild. Yeah, calm, mellow. And you see this thing and it's just like, I don't know, I can't, I can't put words to it. But, and it does that for, you know, my mother-in-law is 101.

That thing's been going for 101 years with no sign of slowing down. It's unbelievable. It's just, it's just crazy. I remember seeing at, it was a bioprint. lab and they were showing me their cardiomyocytes heart muscle cells and it's just a layer of cells and they're all beating in tandem they're not it they're not a part of a heart they're just they're they're they're all like it's like a stadium wave they're all doing their thing just like and it's sometimes the researcher said sometimes they get going so so so kind of vehemently that they

they catch air like they come right up off the bottom of the slide It's unbelievable. Like they apparently, one cell will open up a little, you know, kind of like start communicating with the cell next to it and then the next one. And soon they're all just like beating in tandem. They're dedicated to the task. I got to admire it a little bit. They really are. You mentioned briefly a cutoff for organ donations.

Is that like a universal number or is it depend on the organ? Probably depends on the organ. I'm not sure. I just want to know. Am I past the limit? Am I, my organs all sort of useless by now? I don't think so. No, I don't think so.

No, I think you're good to go. And just briefly, I guess, what else we're good at in terms of replacing organs besides hearts? We got livers. Oh, we're really good at the lens of the eye. That's important. I mean, that's a, you know, people are now getting both of them done at once. You go in and a couple hours later, you come home and now you can see, clearer, better. And depending on what kind of lenses you get, you have a little bit of accommodation.

We haven't figured out yet how to mimic the incredible autofocus of the human eye where you go from reading to distance. As a teenager, in my age, not so much. But that is yet to come. There's been a bunch of techniques and multiple lenses and fluids and people sticking various things in there, trying to mimic accommodation. But just a simple single-focused lens is pretty amazing how quickly that can be done. And it goes in. It's got a little plunger, almost like a tampon. You know, tampon.

You've heard books about these things. a planet. And so the lens goes in and it's folded up like a hard taco shell. And then when it's in it unfolds. And so the incision can be much smaller. You don't need a, you need stitches back in the early days of cataract surgery. So this is, yeah, I was going to say, this is for cataracts. It's not just because, you know, my eyesight is failing.

It's a little bit more serious than that. Well, it's gotten, the technique has gotten so reliable and so safe that there are folks who are simply myopes. They're near-sided like me, and I can barely read the big E. And they are getting a lens, rather than get LASIC, they are getting a lens implanted.

So there's not that, yeah. That's the one surgery that I've had to change my body in some way. I did have LASIC, and it's a... Oh, you did. I did, yeah. Oh, I mean, I'm a huge fan of doing it well. Yeah.

They can't fix, like you say, the autofocus, They can't fix it so that you can do, they can't fix both near sighted and far sightness at the same time. So they do your two eyes slightly differently. Oh, yeah. One is good at close and one is good at far. And the brain figures it out. It's sort of completely natural.

Yeah, yeah. I had that with my contacts for a while. I had one, a slightly stronger prescription, yeah. But the downside is that you smell your eyes burning while they're firing lasers into them, and it's a little disconcerting. Oh, really? Wow. Yeah, does that smell like burning flesh? Because I've been in, I've been in surgical procedures where that smell, you know, I'm kind of like, does that, does that smell good? I don't know. Like burning flesh.

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to tell you whether that is true or not, but it smells like something is burning. They offer you a pill if you want to be calm, right, if you don't want to face up to your eyeballs being lasered. But. And did you get a lot of halos and kind of aberrations? It's for me, night vision. Yeah, I mean, fortunately, I was living in L.A. at the time, and they had very, very good, you know, surgeons at this sort.

So, no, like that first day, your eyes feel all weird. The next morning you wake up and it's fine. That's it. Wow. Are you very near-sighted like me? I was pretty darn near-sighted. Yeah. Yeah.

Yeah. Okay. And it's like, that was like 10 years ago. I'm sure when, you know, it's going to fade away. It's not quite as good as it was, but a lot better than putting contacts every morning. Yeah, I just, I hate reading glasses, so I like to be able to take off my contacts and read. I just, and I have to hold the book like three inches from my face, but I like, you know, I have kind of microscopic vision. Anyway.

Anyway, yeah. Anyway. Just going through the list of fun things that we are replacing, these body parts that we're replacing. Like you mentioned the skin moved around with the nose right at the start, but replacing skin is also something. Yeah. It's a big, is a well-known thing, right? Yeah, yeah. Skin grafts.

Skin is a skin grafting for severe burns. It's an interesting area in that there were the, there was a period of time where, when animals were recruited for this. Often chickens and frogs, I think partly because the chicken has that loose skin under the flaps, and it's sort of like easy to kind of take it off and install it. So it's a lot of popular press stories about people being part frog and part human. But in fact, with a serious third-degree burn,

one of the most dangerous things is that your immune system is suppressed for a while. And so infection, people often, if they're going to die early on, it's from infection, from sepsis. But the other side of that is that the body is very nonchalant about taking on a piece of frog skin or chicken skin or puppy skin or whatever it is. And it will kind of, for a few weeks, it'll kind of take and it'll sit there and it's a very good covering. Eventually the body rejects it.

It sluffs off. or the surgeon in the case of cadaver skin or whatever's been put on, they'll peel it off and they want to, they want it to bleed. They want it. Freshen is the term. Okay. Because now they're going to install the permanent graft, which is the patient's own skin. So ultimately, you want skin from, so that you don't have to use immunosuppression. So from one part of your body to another one?

Yeah, yeah, exactly. but with a really serious burn sometimes there's not much real estate left. Right. You know, and then they'll end up using the same, using it like a patch on the legs, say, and then waiting for that to heal and then using again, it's using it again. It's a long process. It's a, yeah, there are some great new developments like there's something called CEEA cultured epithelial autograph. And this is where you take the patient's own skin, and it's sent off

site, and the patient's skin cells are grown out into a very, very thin patch. So you're creating a graft of their own skin, which is helpful if the patient doesn't have a lot of unburned real estate to work with. There's also spray on skin similarly. That's like, you know, you could sometimes the cadaver skin is mesh to kind of feed it through sort of looks like a pasta maker. So it creates this mesh. So you can stretch it out and cover the wound. And then the spray on skin would be used to fill in the little holes in the mesh. So I think a company QDIS is working on full thickness skin that grown from the patients.

That is not yet approved. It's still in the early stages. But I saw a kid at, I was at Mass General, the Sumner M. Redstone Burn Center. And there was a boy who'd been burned on more than 80% of his body. And he was getting, yeah, he was going to get some of the, they were growing some of his cells. They're sending his biopsy to Switzerland to this company, Cudus. And they were like escorting the new skin back and going to install it. in this little boy.

Again, I compassionate care exemption. And will that new skin have the same properties, ideally, as the old skin? Will it have the sense of touch? Sure. It should, sure. Yeah, it should. Yeah. How surprised should we be that the human body is not better at just regrowing things?

You know, we last forever, but if you lose a finger, we, we, we, we, we. don't have the ability to just, you know, the body can't regrow it. Some animals can, I guess, right? I know. Our livers, we can regrow our liver. We can regrow, yeah, I mean, you can regrow skin. I mean, if first and second degree burn fills itself in from below, you know, just kind of like eventually grows a new layer. Third degree is tough because that, you lose that ability. And so the body tries to close up the hole by contracting, like a drawstring effect. Yeah. And then you have those terrible disfiguring, you know, the jaw pulled down to the collarbone or an eye that won't close, that kind of thing.

But first and second degree burn, the body is pretty good about regenerating. But yeah, why can't we regrow everything? I don't know. Ask God. God has a sense of humor here. But, I mean, there must be some med scientist out there who are trying. to read i'm sure that there there are people studying you know salamanders or whatever creatures and that's why that's why i think it's so it's so important basic science basic

understanding of animals and lizards and creatures that have these different abilities if you can sort of tease that apart and see what's going on maybe there's a way to mimic that or prompt that in humans. And so that's the kind of thing where people go like, they're doing a study on this salamander. What a waste of money? It's like, no.

No, it's not. I don't know if you've ever run into Michael Levin at Tufts. He was a former Minescape guest, and he's studying exactly these things. Like, how do different animals at all different levels sort of encode the plan into, not just their DNA, but, you know, all over, like, there's things.

You try to move an order. again from one place to another and the body moves it back. Yeah, yeah, yeah, yeah. That's interesting. But you can also install things in a body in a different place, and it works just fine. You can take, you know, eyelid cells. You don't have to put them by the pancreas. You can stick the eyelid cells under the skin, which was great because it's easier to access.

You don't have to go in for surgery. So if you, you know, if you're talking about however you've either grown them or they're transplanted or whatever. Some people are looking at, they're parking them all over the body. They don't have to, they don't have to be on the pancreas. And yet, like, we're still not very good at hair, right? We can't, you know, people go bold and we don't know how to really fix it. I know. Yeah, you can get a hair transplant, but man, that is an all-day job. That you can transplant two kidneys in the time it takes to do a hair transplant. Wow.

Okay. Yeah, because you got to go, first of all, you got to, like, pull them all out, and then you got to stick them all in. And that's a, it's like one follicular unit at a time. So that's a lot of, it's a lot of work. And then, you know, you've got this row, you know, bringing your hair line down, but then you keep losing hair, and now you've got the bare strand behind. So you've got to go back and get more.

And eventually, you run out because the side. sides and back are starting to get sparse. Well, I was going to say, like, how successful is it? When you get a hair transplant, does it last forever? Or is it one of these things, just like everything else, where the body starts rejecting it? No, I think, no, hair, it's your own stuff. So, yeah, and I think it works quite well. I mean, ask Elon.

I don't know. It looks okay. You can afford it. Yeah, it's just that it's a lifetime commitment because you're, as the hair, as the hair line continues to recede, you need to keep, you need to keep having it done. Or you could do, I don't think it's even possible to get this done in Turkey anymore, but in the 70s, there was artificial hair transplantations, essentially like doll hair that was being installed with a little surgical crochet hook, kind of, I mean, not a good solution. No, no, you know, because you can't

really style doll hair and it won't go gray. You start to go gray and it's still, red or whatever but and they got infected and anyway but yeah we're learning it's a but it's just an example to me of like how even the easiest things are a little challenging well yeah yeah i spent time at a biotech startup that they were trying to um create follicles so taking somebody's blood regressing it to pluripotency right so you've got these cells that you can then instruct to what you want them to become. So they were regressing blood cells to pluripotency. So then they're instructing them to become the building blocks of follicles.

These two types of cells, keratinocytes and dermal papillus cells, which kind of do this amazing thing where they get together and they form kind of a primitive follicle, right? And the follicle, it did start creating hair material. but it wasn't growing up out of the skin. It was just sort of a black blob right under the skin. And they called it disorganized hair. So it wasn't the kind of thing you'd show investors and go, look, look, we've grown hair blobs under the skin of this mouse. So they came in.

And then they're like, okay, we've got to give it a little tube so it could come up out of the skin. So they created these little, it was like a Barbie comb, these little rows of tubes that they were going to implant, kind of like a rice. kind of thing. But the tubes ended up being thicker than the skin of the mouse. And they were too delicate to implant, like in the way that anybody would ever be able to do. So then they tried putting the two types of cells on a piece of very thin thread that the thread would be implanted.

This took years. And finally they ran out of money and now they're out of business. And I went to them thinking, okay, follicle. How hard could that be? Yeah, really hard is the answer. Really hard. Well, I have to give you a chance to talk about, you have different chapters in the book where you mentioned,

you know, for both men and women, attempts to regrow or replace our unmentionable bits that, of course, are going to be very, very important to someone. How successful is that? Well, I reported on two very specific types of procedures. One of them is unorthodox. It's not done anywhere outside of Tbilisi in former Soviet Georgia, as far as I know. I was curious about it.

Yes. I mean, any opportunity to head off to somewhere I haven't been. But this is a surgeon who, in reconstructing, it was a man who had had cancer. And the reconstruction of this man's penis was not done in a conventional way, which would involve often flesh from under the form or some hairless part of the body and then surgical implants that you buy from whatever prosthetic company. One per rectile chamber. And he chose instead to use for rigidity the man's own middle finger. Which was still attached to the, I mean.

So, and I envisioned the finger being taken and installed. you know, as is with a nail and everything and able to move and beckon. But, which seemed pretty cool, sort of. But no, he was doing, he was wrapping it in a graft taken from the person's forearm, the underside of the forearm. And so it went, but it did have the function of, it bent. There was, you know, that middle knuckle. The penis could be bent upward.

I saw a slide. I never met this guy. He didn't answer my emails in Russian and Georgian and English. So I just showed up. And fortunately, his office manager is like, come with me. We will go in his office. He's on vacation. I will show you slides.

So I saw. I did see an image of the penis kind of bent at the midsection with a ceramic water pitcher hanging off of it. I don't, you know, I wasn't ever really clear on what I said, is that, is that similar to, because there are malleable penile implants that, and they, you know, it's sort of a gumby thing. You can put it in position upward or you can bend it down out of the way. And she said, yes, so he can wear trousers. So it was a more of a fold it out of the way. So it's not poking straight out. Because this is now going to have bones in it, unlike the typical penis. I know. Yeah. Okay. Just to be sure I understood the process.

Yes, it is. Yes. Yes. It's going to have bones in it. So it would be the very first human baculum. But this is, okay, it sounds like from this particular story that there is no, like, agreed upon successful procedure for these circumstances. Oh, no. No, there is a standard procedure for, well, for erectile dysfunction.

You kind of take these implants, which look like, you know, the width of pencil. and you stick one in each erectile chamber, and they're inflatable. There's a little pump in the scrotum that you squeeze when you want rigidity. So you squeeze that, pump it up, and then you can let the air out. Or there's the malleable, the Gumby Lim kind, where you can, you know, bend it up or bend it down. So, but that's for erectile dysfunction. For reconstruction, I would, you know, you would have the same kind of using, skin from another part of the body, and then there'd be something in there for rigidity.

I would think the same kind of implant that's used in erectile dysfunction. But I don't know. He's the only surgeon. Who's doing that? Who says romance is dead? I think this is good to know. The guy, yeah, yeah, the office manager said that he was in his 60s and she was in her 30s. And he said, she's very happy.

Okay, good. Good. That's the testimony you need. All right. So, you know, we're nearing the end of the podcast. We can be a little bit more expansive. I mean, I know you said very clearly in the book that you're not trying to predict the future. You're trying to explain what is going on now.

But maybe a little predicting of the future is okay. I mean, we are getting much better at synthetic biology, at designer genes, things like that. I mean, do you think that replacing human organs is going to say? see a leap forward that is pretty dramatic pretty soon, or is it just one of those things where it's so hard we should expect progress to be very incremental? No, I think, well, it depends on how you define very soon. Spending time at that bioprinting lab, Adam Feinberg's lab at Carnegie Mellon, he kept saying, this is going to happen really soon.

And then it turned out what he meant by really soon was two to three decades. So for science, that is soon. That's soon. Two to three decades. But, you know, so much is happening with AI and with stem cell research. And there's, it's both really slow and incredibly fast. Do you know what I mean? Yeah.

Yeah. So. And the dream is that someday we'll just 3D print a new limb or pancreas or whatever. Right. Yeah. Or grow it from scratch. Grow it from scratch. Okay. So there'll be room in a couple decades for your writing new book about this. No, you write this one. Maybe. We'll see about that. But Mary Roach, thanks very much for being on the Mindscape podcast. Oh, my pleasure. Thanks, Sean.