99% Invisible - Replaceable You

Episode Date: September 16, 2025

Mary Roach dives into the strange, funny, and unsettling world of designing new body parts, from pig hearts to prosthetic feet, revealing just how messy replacing ourselves can be.Replaceable You Subscribe to SiriusXM Podcasts+ to listen to new episodes of 99% Invisible ad-free and a whole week early. Start a free trial now on Apple Podcasts or by visiting siriusxm.com/podcastsplus.  Hosted by Simplecast, an AdsWizz company. See pcm.adswizz.com for information about our collection and use of personal data for advertising.

This is 99% Invisible. I'm Roman Mars. I was working at the radio station K-A-L-W in San Francisco in 2003 when a preview copy of the book, Stiff, The Curious Lives of Human Cadhavers, was sent to the station. It immediately became one of my favorite books of all time, full of fun, gruesome, intriguing stories about what happens to our bodies after we die. So, in 2003, I scheduled what turned out to be the very very, first media interview of the author, Mary Roach.

Do you remember that? I remember it so well. I was like, oh, I got it, and I kind of dressed up, even though it's radio. It was like one of the best interviews ever. Over the years, Mary and I have become friends. We even shared an office in Oakland for a while. And over her career, she has continued to come out with some of the best and certainly the funniest science books I've ever read.

Longtime listeners will know that she has been on the show. a few times over the years, but when she announced that her new book was about designing human replacement parts, designing is the key word there, I knew that it was time for us to have a long overdue chat. My name is Mary Roach, and my book is called Replacable You, and the subtitle, which doesn't really tell you that much, is Adventures in Human Anatomy. But what it really is, is this scientific pursuit to find replacement parts for our worn-out diseased and malfunctioning bodies.

That is exactly right. Some of it historical and some of it current. Yeah, just these efforts to swap things out, make things from scratch, grow things from scratch, all those things we want to do and sometimes do, do. I said do, do do. And, you know, what struck me, you know, as I was reading this book and, you know, like we're a design show ostensibly, is that, you know, you know, this is the mother of all design problems. Like, there are really major roadblocks to designing replacement parts for the human body. It is, like, truly difficult.

Could you just talk about why that is? Yeah, I mean, the basic problem here is that you have 200 years, more or less, of medicine and engineering that's trying to compete with millions of years of evolutionary tinkering. And that's tough to do. And the other thing is that just things that seem simple are not in the human body. There's nothing simple. One idea that you present in the book is that we have somewhat worked out how to replace simple organ functions in the body with these big external machines like dialysis for kidney function or a big ECMO machine, which takes over the function of the heart and lungs. But the holy grail for replacement human parts are organic, maybe donated, maybe animal-grown parts that can be surgically implanted into a person whose body is damaged. Why is that last step of integrating replacement parts into the body so difficult?

Yeah, and it comes down, I think, to two very basic features of the human body, and one is the immune system. You know, when you're developing a machine outside the body, the immune system. doesn't give a shit. Yeah. You try to stick that in. And now you've got the immune system. For one, you've also have to deal with clotting. You know, if you've got like a stent in there, you know, anytime the blood's sort of coursing along through the blood vessels, and as long as what it's touching is the wall of a blood vessel, it's fine.

But if it starts, if there's something else there, it's like, ugh, and it starts to form clots. So people with stents and things in the body often have to. be on blood thinners and so there's that going on and then just the body can have a sort of an inflammatory reaction and that can just become a mess and infection that's another thing anytime you open up the body and you put in something from the outside world it's really hard to be 100% sure that you're not letting in bacteria and infection inside the body body is a real bitch. When a hip replacement or a knee replacement goes poorly, it's almost always infection. Yeah. And that's, and that, you know, if you're using a cane, you're not going to have to

worry about infection. I guess that's right. Well, what do you think that impulse is for replacement function to be further and further integrated into the body? Like, for example, when someone is very ill and their heart and lungs can't function. A big ecmo machine will pump the blood out and oxygenated in the machine and then pump the blood back in. And it works amazingly well. Like someone could be on an ecmo machine forever, I suppose. And if someone wanted to live a more normal life where they could walk around and do things, you could go down the path of designing you know, a smaller and smaller ECMO machine. But even the man who invented the ECMO machine decades ago, is now trying to find ways to make donated hearts better and more successful for

transplants. How did that preference for finding solutions that were more and more organic, more and more natural, strike you as you were doing your research? Yeah, there's definitely a bias for wholeness and for normalness, and I'm using quotes around normal. Yeah, yeah. What is normal? But, you know, we all know it when we see it. And you go out and the world wheeling a portable ecmo machine and first of all it's going into your body and yeah okay they can probably finesse it so it's less dramatic but it's kind of like these two vampiric if that's an adjective opening you know in the in the neck you know so and and uh you're you're canulated in other words it's like it's going one tube is going into the other if you trip and fall you're

gonna decanulate and that's like blood's burning everywhere you got like you know a couple minutes and you're dead well yeah going fast forward i don't know 30 years maybe yeah this could be done in one of the in like a little pouch that you wear in a fanny pack i don't know but it's still not you yeah and it's still you'd just rather have something inside you you you know you'd rather be able to pass as just human and there's such a bias for it that it's really hard for people with underperforming limbs, feet, say. You know, I spent some time with a woman who, it took her a long time, but she succeeded in getting her own foot amputated

even though it was healthy. It was healthy, it was viable, but it was underperforming. It was twisted. But it was clear to her watching people with a prosthetic foot, especially below the knee, pretty simple thing to replace, really, in terms of prosthetics. And she'd see those people running and hiking and just sort of living life the way most people do. And she couldn't do any of that.

And yet surgeons were like, nope, not taken off this foot, perfectly healthy foot. And, yeah, as in oxygenated, you know, nothing's dead on it. But it didn't work, you know. And there was a guy who had foot drop, which is, you know, when you're walking, you need to pick your toes up. and then put them down and you do it automatically but some people have nerve with Parkinson's I think too

so you end up kind of shuffling and he didn't want to do that he's like give me a prosthetic foot and so he shot himself in the foot and that way they couldn't say you have a perfectly healthy foot here like you have a mangled mess we will take it off

yeah we've mentioned the fact that a lot of the integration of replacement parts is particularly difficult Could you name some examples of where it's actually kind of worked well? Sure. I would say a couple of success stories. And one of them I don't actually talk about in this book. I talked about it in Gulp.

And that's the fecal microbiome transplant, which is to take somebody else's gut bacteria and put it in your own. Just replace the microbiome. and that works really well, particularly with people who have an infection with C. diff, C. difficil, which is a really serious gut infection that kills, I don't have the numbers, but it's kind of astounding. So you, in back in the day, before they sort of isolated the bacteria and put them in a capsule, you're talking about some guy coming in with a brown paper bag and handing it over going, yeah, not my best effort, but that you take that. It's like shit. You put it. it in a blender, an oyster blender, actually, and you, the guy's taking some antibiotics to get kind of a clean slate. You use a colonoscope, which has a spurting function, and you just put it up there. And within two days, I mean, the patient that I saw two days later, he's having what they say

on the Bristol stool scale, number three, I think, smooth and soft like a sausage or snake. And it's like, it was on Saturday night. He'd had the surgery like Thursday, and on Saturday night, that's what he sent to the physician. I mean, that's not everybody's idea of a great Saturday night, but that, for him, was the best Saturday night ever. And that's a simple, just take it out and put it in. I mean, now it's done with expensive capsules, yada, yada. But that works. The other one that is really pretty amazing is intraocular lenses,

for cataracts. I definitely want to talk about this. My wife has had terrible vision her entire life, recently had cataract surgery and had lens replaced. And it is life-changing for her. Yeah. Yeah. It's so much so that there are people in their 20s

who are extremely near-sighted. And for whatever reason, contacts aren't comfortable. They don't want to do LASIC. They're asking to just have the lens popped out in a new one put in. Like they don't have cataracts, but they don't have cataracts. They don't have cataracts. It's just they want, they want that miraculous vision that you get with these lenses. So a cataract, it's kind of confusing because people think it's a separate thing from the lens. But the lens, as you age, it gets cloudy and dark and hard. And it's, the whole lens is referred to as the cataract. And they take the whole thing out and put in a new, clear, lovely man-made, lens that has been but you know that didn't happen overnight you know back in the 60s that was like a you were in the hospital for eight days it was a big incision with stitches people would lie in bed with

sandbags holding their head in place uh there it didn't often go well they would not let people get it till they were a lot older because they they wanted to wait till your vision is so bad that you're going to be grateful for even a small improvement yeah but now it's uh um yeah people are happier with it than they were before. Yeah. And in the book, you actually travel to Mongolia to folks that are encouraging cataract surgery to folks who live out in the plains and therefore have, I guess, sort of damaged eyes from the sun in particular in trying to sort of encourage them to, that this procedure

is like better now and they should consider it. Yeah, yeah. I mean, that was one of the comments that the surgeon, it was Orbis International, that does this work. And he said it's, you know, part of the hesitation people have is because they hear about it from their friends and family when it doesn't go well. And so part of what Orbus does is trained. They're training surgeons. They're doing a small incision surgery and it's something you can do with very minimal equipment and a huge improvement. You don't need stitches. And so that, you know, word spreads, like, oh, that actually works because there was a patient there who's like,

you know, through a translator said, I had heart surgery a few years ago, and I didn't hesitate on that, but I put off having this cataract operation for a long time because it, you know, it just, it didn't always go well, but these days it's pretty amazing. Yeah, yeah. And one of the things that was so remarkable is knowing that before they actually knew how to put good lenses in, if the cataracts was bad enough, they would just take out the lens and use glasses to be the lens at that point. And it was, it's so much of an improvement just to have the cloudy lens out of the way. Yeah. And way way back, you know, in the 1700s, I mean, couching, it was called couching, comes from the French to lie down, secouche. And so they

would just stick a probe. And then we just like sit down here and I have this probe, but I'm going to stick it in your eye. And they would push, they get the, like push the lens down to the bottom of the eyeball and hold it there. There was one 12th century medical manual that recommended holding it there for four or five our fathers. And you would definitely want somebody saying four or five are fathers if they've got a pointy object in your eye holding down your lens. But then, yeah, suddenly light can come through and hit the retina and you're not able to focus on things. You need super thick glasses, but you can now see. You're not blind because some of those cataract, if you let a cataract go long enough, you're, you're functionally blind, you know.

Yeah. So your books are super funny and every other sort of, you know, paragraph is a joke. And there's occasionally, there's, you know, like a joke that is so inappropriate, it makes me laugh, that's so inappropriate that I exclaim out loud. I'll go, Mary Roach. And sometimes I'll go, Mary Francis Roach, I'll, like, invent a middle name for you. Mary Abigail Roach. Did you actually say a phlebotomist glory hole or something? Thank you for noticing that one.

I mean, I was just, I was first of all fascinated by the fact that the early blood banks that, you know, that people were so squeamish about blood that they'd sit down at this, there'd be a wall with holes cut in it and they'd stick their arm through. They'd never have to see the phlebotomist who's drawing the blood. They'd never have to see their own blood coming out in a tube. I was like, oh, my God, it's the lobotomy glory. Is that inappropriate? I don't know. Well, there's, there's, I exclaimed out loud in invoking your middle name, your fake, your fake middle name many, many times just going like, oh my goodness, Mary.

My goodness, Mary. Mary. Anastasia Roach. How could you say such a thing? You sound like my mother. Mary Catherine Roach. That part of the book is so delightful. I was wondering, like, how you.

You know, I know you as just a funny person, it is interesting to me that you write the funniest books I've read. And also they are rigorous factual explorations of things. Is this a natural thing for you? Is this a thing that you're interested in this and this is who you are and so for this? Or is there an aspect to this where you think this is the way to explore this type of thing? Yeah. I think it's the former. I think science in the human body are endlessly interesting. and strange, and I've always been surprised by the things that I learn when I sit down with somebody who knows this stuff, because I didn't pay any attention in high school to science at all. I took the gut science, you know, not the advanced, what is it, the AP science. Apparently that was a better teacher. Anyway, I just didn't pay any attention. I thought science was boring. But, you know, fast forward to when I started writing, and I You know, I was writing for Discover Magazine because they'd asked me to.

And I went, oh, holy shit, science. It's kind of cool. The human body. It's like another planet. I think it's interesting. But I think that it stems from my insecurity. I'm always picturing, and the humor that is, I'm picturing someone reading thinking, like I did. Oh, science, this is kind of boring.

I don't think I want to read this book. So I'm like just running as fast as I can, dancing as fast as I can, make it interesting. Stay with me. I'm not going to be boring. It's not going to be a slog like science was for me in high school. I want you to stay here with me. So that's, I think, a large part of it. Also, it's just more fun for me to write that way. I kind of, I entertain myself that way. And if it's not entertaining for me, forget about it. It has to be fun for me. when we come back Mary tells us about her dreams of having flowing locks of hair on her leg

more after the break we're back with Mary Roach so in your books I think I first recognize this in your second book Bonk where you have sex with your husband and an MRI and have people take pictures of it

like the insides of your bodies but you're weekly game for things. It's a huge part of what makes your books so fun. Can you talk about the things that you participated in for this book? Sure. I have to point out, though, that was, in fact, ultrasound, which is so much more embarrassing. At least with an MRI, you have some privacy. Ultrasound, there's a dude in a white coat holding an ultrasound wand to my belly, and Ed is behind me, and that is a really embarrassing afternoon. So, moving on. Yeah, for this, let's see, for this book, yeah, I spent some time in an old Emerson Iron Lung, a holdover from the polio era back before there was a vaccine.

You know, not everybody who got polio had to be in an iron lung, but if you had a bad enough case of paralytic polio, your diaphragm and your rib muscles were out of commission. so you can't breathe. So, and I wanted to get at, like, what does that feel like to have a machine breathe for you? And actually breathe like you because an iron lung, unlike the ventilators in the ICU today, which are positive pressure ventilation, it's like your lung is a party balloon. It's being blown in there. Whereas negative pressure, which is an iron lung, it's done by vacuum. Like you pull out the air out of the tube and then,

the lung, the rib cage expands, and that pulls in the air. Anyway, so I found a guy who's had a iron lung. His wife had died about a year before, and somebody told me, because I was asking around. And so there's this guy, Mark Randolph, who lived in Kansas City, said yes, you can come to Kansas City and try out my deceased wife's iron lung. Now that I'm saying it, it sounds like a really weird thing to ask somebody. But as you say, I'm game. And he was game. And so I got there and they are like two people who he'd recruited to help because it's not simple. It's similar to an MRI in that there's a bed that rolls out and then rolls back in. But then you have to get your head through that opening. And it's like this weird.

Your head's coming through. And there's people are kind of holding the head like it's like they're obstetricians giving birth to you through this hole. It's very, very weird. So I did that. I did that. Like this is something that his wife sort of went through every single night for hours and hours at a time. But how long did you last in the iron? Yeah, about nine minutes.

Because I had planned to, I wanted to spend the night in it. But one thing about it in order to have. to create a vacuum it has to be a seal has to be tight you can't have any air leaks that means that the collar around your neck has to be tight

uncomfortably tight and so it was this weird also he had it turned way up because that's what Mona his late wife had needed so but I didn't need that so I got in there

so it was this weird thing where I was breathing like deeply and luxuriantly like but at the same time feeling like I was being strangled so it was this weird combination of like you're breathing in a more relaxed way than you ever have and yet you feel as though you're being strangled and I asked Jane the woman who had sort of set me up

and I said for Mona what was it what was it like how could she stand it and she said well it was a situation like this she had chronic pulmonary disease so it was a struggle for her to breathe She said, at the end of the day, she was so happy to get in it. She'd been breathing all day, struggling, never quite feeling like she was getting enough air. So she was always happy to get in it at the end of the night and so happy to get out of it in the morning. Yeah. So like that.

You also, when you were researching hair replacement and hair shaft replacement, you proposed the idea of them harvesting a part of your hair and implanting it onto your leg. Yes. And I had a reason for that. I had a good reason, Roman. I wanted to demonstrate for myself. And going forward, maybe people who came to a book event, I wanted to demonstrate donor dominance. And that is, and with a hair transplant, if somebody has male pattern baldness, okay, they've got hair grown on the sides and the back, because hair there isn't affected by testosterone. It doesn't care. But the hair on the top, is sensitive to it. So if you take hair from the back and you put it up top, donor dominance, the donor site rules. So the hair stays. So I wanted to take some head hair because I was actually donating some follicular units for some research down the road at a stem cell place. I said, while you're there, can you take a couple units and transplant them to my leg? Because I just thought it would be cool to have like a few strands of long flowing hair on my calf. Just, you know, not a lot, maybe three or four.

And I could show people. I could talk about donor dominance and I could roll up my pant leg and go, look, look here. This is what I'm talking about. And sadly, they didn't take. And that's what the surgeon was, he's kind of skeptical. He's like, you know, the leg is a much weaker. There's not as much blood supply to the cat. compared with the scalp.

So I don't know if that's going to work. But I made them try it anyway. The woman who, Galena, the woman who does most of the transplanting, she was so not interested in it. He didn't want to tell her. He's like, Galena is done taking the follicle. She goes, okay, you're all set. And the doctor, Dr. Shafu, he goes,

um, Galena, she was talking about wanting to take this. so home hairs and putting him on her leg and yeah anyway we convinced her but it but it didn't take in the end no I'm so disappointed I mean this interaction you know makes me think of another thing which is you know often you are writing about stuff that is pretty sensitive you know stuff to do with our bodies medical stuff that maybe someone might be hesitant to talk to you for for whatever reason and sometimes if you find someone who won't talk to you that's based here in the United States, you'll, like, fly to Russia to find someone to talk with you. I will do that, yes.

And more and more I've noticed that you're probably reaching folks who know your work, and they welcome you even though what they do is pretty sensitive. And in the book, Replaceable You, you talk about this organization called Core, and you kind of have to convince them that your domestication of their work would actually be really helpful to their mission. Could you talk about your role in pulling back the curtain on things that seem? scary or gruesome? The example that you gave has to do

it was tissue donation and that is as opposed to organ donation. You can also donate tissue which is bone, skin, tendon, ligaments and when I wrote stiff I wanted to cover

that but no one at these places would get back to me or return my calls. And I understand why people are hesitant to have someone come in because I've seen it. You know, and I described it kind of like a Francis Bacon painting. For me, it's just kind of amazing to see.

And I could say that the way they take skin from the back, so no one will see there. And from the lower, they don't take anything from the face. They take things from the legs. And it's done. And then they kind of stitch it back up. It's like opening up a tamale almost, pulling the stuff out. they're putting the skin back and stitching it up. And it's, I guess, in a way, you know, it is kind of a gruesome thing to see,

but no more so than witnessing some kinds of surgery. You know, ultimately it's surgery. And unlike surgery, that this patient, in quotes, doesn't feel any pain. There's no downside. You know what I mean? It's all benefit. They don't care. They're just doing something good.

and it doesn't matter what it looks like in someone's imagination. So I kind of just want, I find that if you can demystify this and just say, yeah, it sounds kind of gruesome. This is what it's like. And my hope is always that I'm not putting people off. Either organ donation or tissue donation, you can end up helping, I think it's 75 people with one person's tissue. You know, the bones are used for little spacers and spine.

surgery, the skin is used as sort of biodressing for people who have had serious burns and there's all kinds of reconstruction that can be done with this tissue. So it's a really good thing to do. And I

completely understand why they're called OPEO's organ procurement organizations. I get why they're wary of somebody coming in because if you chose to you could make it sound really bad. I'm like, oh, now they're pulling out this, he's holding this guy leg and there's blood here and I'm like yeah you could make it sound bad if you wanted to but I

I just feel like if you act like you have something to hide people think you have something to hide how is working on this book changed the way you think about yourself and your own body like are you like would you would you get a pig organ put in your body would you know like how does it I don't know how does it change your oh yeah I mean how cool it would be cool I know I'd be like if If you can save my life by throwing a pig heart in there and it's going to actually work for a while, maybe long enough at least for me to get a human transplant, absolutely. And what a cool thing to be able to say at a cocktail party. I've got a pig heart in there.

I don't know. I always have trouble coming up with interesting small talk. Oh, I find that very hard to believe, Mary. If I could say, you know what, I've got to. I have a friend, Clark, who has a third. kidney. And he would sort of bring that up at parties. And I was all kind of jealous. Man, I wish I had a third kidney. I wish I had third kidney. I mean, I could lie, I suppose. Too honest. But while we're on the subject, what is the deal with pigs? Like, they're kind of the

go-to for human replacement parts, you know, like as an organism. Like, what is it about pigs that makes them good for this? I'm glad you asked. Because I have a whole section on that. And you can blame Hormel. Hormel back in the, oh, I think it might start in the 40s, 40s, 50s era. I'm terrible with dates. But the Mayo Foundation, which is the research arm of the Mayo Clinic, and the Hormel Institute, which is the research arm of pork, they work together to miniaturize pigs in order to create a lab animal that would have organs of approximately the same size.

eyes, but that also wouldn't be so loud and rambunctious as a full-grown pig. That's a large, loud animal to have running around a lab or anywhere in a facility, research facility. So they started breeding them smaller and breeding them for the purpose of studying various surgical procedures. The other thing with pig hearts, pigs are, this one researcher described them as almost a caricature of an obese human because they get atherosclerosis,

they have heart problems, pigs that are being raised on farms don't get a lot of exercise and they eat garbage. So they're a very apt animal to use for studying heart disease. But the other thing going on here is, I mean, obviously a primate

might be a better fit, I mean, better, closer match, but there are ethical issues and also zoonoses, like diseases can transfer more readily between two primates than between a... I mean, it's still an issue with pigs, but less so. So there was all of that going on. Yeah, yeah. So they're close, but not too close.

And there's also, like, agricultural research can push things forward when medical research is not, like, always funded to the best of our ability. Yeah, right. Yeah. And I think, I'm sure on some level, the hormal people were like, Oh, another way to sell pigs. Lab animals. Exactly. I have to say, I did not speak to anybody from the Hormel Institute,

as I don't think they exist anymore. But anyway, they published a whole lot of papers. About pigs. Yeah, the whole miniaturization of the pig project went on for some time. Did you come away from all this research thinking that maybe in our quest to have normal function for our worn-out damaged bodies, we over-emphasize this idea of this integrated whole, like a quote-unquote normal body, and maybe we should be more open to a like a variety of solutions. Yeah, yeah.

I think that it would be great if people were drawn to whatever works best without being hung up by what does it look like and how much will I, how will I not look like everyone else? But, you know, part of that is like if it's in, the other side of that is if it's inside you and it's incorporated in you, you don't have to think about it. You don't see it. You don't have to change its batteries. You don't have to, it becomes part of you and you can just live your life normally. So it's not just that bias for wholeness. It's also wanting to just be able to go through your life without thinking about that part. You know, we are happiest when we are unaware of all our parts and what they're doing. We just want them to do their thing and be invisible. So, you know, anytime you externalize a piece of yourself, it's always there, you know? Yeah, yeah. Well, the book is so good.

Your books are so good. I enjoy talking to you so much. So thank you for doing this. I really appreciate it. Thank you so much for doing this. It was fabulous. 99% Invisible was produced this week by Jacob Medina Gleason and edited by Chris for Johnson. Mixed by Martine Gonzalez, music by Swan Rieau.

Kathy, too, is our executive producer. Kirk Colestead is the digital director. Delaney Hall is our senior editor. The rest of the team includes Chris Barubei, Jason DeLeon, Emmett Fitzgerald, Vivian Lay, Lashemadon, Joe Rosenberg, Kelly Prime, and me, Roman Mars. The 99% of his logo was created by Stefan Lawrence. We are part of the Sirius XM podcast family, now headquartered six blocks north in the Pandora building. In beautiful, uptown, Oakland, California.

You can find us on all the usual social media sites as well as our own Discord server. There's a link to that, as well as every past episode, including many, many with Mary Roach at 99PI.org. Thank you.