328 | Mary Roach on Replacing Parts of Our Bodies

Summary

Podcast Summary: Sean Carroll's Mindscape, Episode 328

Guest: Mary Roach
Title: Mary Roach on Replacing Parts of Our Bodies
Date: September 15, 2025
Host: Sean Carroll

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Episode Overview

This episode explores the history, science, and challenges of replacing human body parts—ranging from ancient nose prosthetics to the cutting edge of organ transplant, artificial limbs, and even fecal microbiome transfers. Science writer Mary Roach, author of "Replaceable: Adventures in Human Anatomy," joins Sean Carroll for an in-depth, humorous, and sometimes cringe-inducing discussion of what can and can’t be replaced, why biology is much harder to hack than physics, and how our efforts at bodily repair reveal both remarkable ingenuity and fundamental limits.

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Key Discussion Points and Insights

1. The Long History of Body Part Replacement

• Ancient Beginnings:
  • The first known body part replacements were noses, as early as 1500 BCE in Egypt and India, mainly because nasal mutilation was used as a punishment. (06:57–10:20)
  • Techniques then—and even now—include using skin flaps from the forehead or cheek, demonstrating ancient surgical ingenuity.
  • Memorable demonstration: Tycho Brahe's metal nose after a duel, sometimes attached with glue and occasionally falling off. (10:28–12:29)

“[They would] take a flap from the forehead…loosen this flap, but keep it attached…and then flip it over onto the nose…they still had the blood supply while the blood supply was growing in on the nose…”
— Mary Roach [08:19]

• Dentures as Cosmetic Fixes:
  • Early dentures, dating back to the 1700s, were more cosmetic than functional. Some people had all their teeth removed intentionally as a kind of "wedding gift," to make room for better-looking dentures that were, in practice, terrible for eating. (13:09–16:51)
  • George Washington's spring-loaded dentures pushed his upper teeth forward—hence his habitual, tight-lipped portraiture.

2. Why Is Replacing Body Parts So Difficult?

• Complexity of Biology:
  • Even the simplest features—like the tear film in eyes—are incredibly hard to replicate. Roach detailed a researcher's entire career devoted to creating an artificial tear, still unsuccessful. (17:52–20:29)
• Microbiome Transplants as a Rare Success:
  • The fecal microbiome transplant stands out as a relatively simple, effective way of replacing a lost body function, rescuing people with life-threatening infections. (20:29–21:18)

“We can’t even recreate…not even that [tear film]. The only thing I think works best is…a fecal microbiome transplant.”
— Mary Roach [17:52]

3. Prosthetics and Artificial Limbs: Progress and Limits

• Historical and Modern Limbs:
  • From wood and aluminum legs to contemporary osseointegration (direct-bone-anchored limbs), prosthetics now can return some sensation and more natural movement, though infection risk is still a major problem. (23:58–25:30)
  • Contemporary amputees sometimes choose elective amputation for improved quality of life, seeking better function through prosthetics. (25:45–27:15)
• Technological Hurdles:
  • While robotic limbs with neural connections exist, they remain heavy, expensive, mentally taxing, and limited in functional grip and speed. Many users default to their other hand for simple tasks. (29:51–31:50)

“You’re gonna spend like 30 seconds getting your grip right? No, you’re gonna reach over with your other hand and pick it up and eat it.”
— Mary Roach [29:51]

4. Replacing Organs: Artificial, Animal, and Human Donor Parts

• Xenotransplantation:
  • Recent years have seen pig organs (mostly kidneys) transplanted into humans under compassionate use exemptions, sometimes lasting eight months or more. This is still considered a bridge to human transplants. (32:36–34:58, 35:15–37:08)
• Why Pigs?
  • Pigs were chosen due to practical collaborations (Hormel and Mayo), matching organ size, and physiological similarities to humans. (37:08–39:45)
• Immunological and Biological Limits:
  • Major issues: hyperacute immune rejection, pig viruses infecting humans, and even hearts outgrowing their human recipients. (35:15–37:08)

“You can kind of blame it on the Hormel Corporation…”
— Mary Roach [37:14]

• Valves vs. Whole Organs:
  • Replacement of heart valves with pig derivatives is common and can last for about a decade, while entirely artificial hearts or valves serve mainly as interim measures until donor organs are available. (41:48–43:02)
• Special Mention: The Lens of the Eye:
  • Cataract surgery is a triumph—artificial lenses restore or even improve vision with minimal downtime. Some patients now choose lens implants over LASIK for vision correction. (43:43–51:06)
• Skin Grafts and Regeneration:
  • Skin grafting is routine for burns, sometimes using animal skin temporarily. Culture and spray-on skin offer hope for patients with little healthy skin left, though these are still in development. (54:02–57:50)
  • Regeneration in humans is limited; livers can regrow, but other limbs cannot—contrasting with animals like salamanders. (58:00–59:47)

5. Unsuccessful or Challenging Replacements

• Hair Transplants:
  • Creating functioning hair follicles from stem cells or pluripotent cells remains experimentally elusive. Hair transplants are “a lifetime commitment” and earlier artificial hair solutions (like “doll hair”) were both impractical and unsightly. (60:44–64:32)
• Genital Reconstruction:
  • Most procedures use prosthetics or tissue grafts, but Roach visited a surgeon in Georgia using a patient’s own middle finger as the basis for a reconstructed penis—a "first human baculum." There is no internationally agreed-upon gold standard for such surgeries. (64:48–68:41)

“He chose instead to use for rigidity the man's own middle finger…”
— Mary Roach [65:09]

6. Where Is This All Going?

• Bioprinting & The Future:
  • Experts estimate 3D printing or growing custom body parts might be common in two to three decades; science progresses both slowly and astonishingly fast. (69:35–70:23)
• Mary Roach’s Take on Techno-Optimism:
  • Be hopeful for advances, but don’t underestimate the complexity and biological limits—progress will be incremental rather than revolutionary in the short term. (03:49–05:45, 69:35–70:23)

“For science, that is soon. Two to three decades…but so much is happening with AI and stem cell research, and there’s…both really slow and incredibly fast.”
— Mary Roach [69:35]

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Notable Quotes & Moments

• Sean Carroll (on science optimism):

  “It’s not that [it] can’t be done…biology is very, very complex compared to physics, mechanical engineering, even chemistry.” [04:36]

• Mary Roach (on dentures):

  “It was like a wig for the mouth. It was a cosmetic thing…people would, at a Victorian dinner party…grind [their food] in private and…go out to the table and not really eat.” [13:09]

• Mary Roach (on trying to replace tears):

  “We can't even recreate…not even that.” [17:52]

• Sean Carroll (on pig hearts):

  “So it’s right now thought of kind of as a bridge, a stopgap.” [34:16]

• Mary Roach (on seeing a beating heart for the first time):

  “It is just squirming around like a stoat in a burrow…It’s really active.” [47:31]

• Mary Roach (on basic science):

  “It's so important…understanding of animals and lizards…If you can sort of tease that apart…maybe there’s a way to mimic that or prompt that in humans. So…it's not [a waste].” [59:10]

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Timelines and Notable Timestamps

• [06:57] – History of nose replacements and ancient plastic surgery
• [13:09] – The cosmetic role of dentures in the 18th–19th centuries
• [17:52] – Why replacing even basic body functions (like tears) is hard
• [20:29] – The surprising success of fecal microbiome transplants
• [23:58] – Evolution of artificial limbs and osseointegration
• [32:36] – Xenotransplantation: recent progress using pig organs
• [37:08] – Why pigs are used for organ transplantation
• [43:43] – Eye lens replacements as a surgical success story
• [54:02] – Advances in skin grafts and cultured skin technologies
• [60:44] – Hair replacement science and its limitations
• [64:48] – Unique and experimental approaches to genital reconstruction
• [69:35] – Predicting the future: 3D bioprinting and synthesis

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Conclusion & Tone

The conversation is rich with history, science, bizarre anecdotes, and the unique humor only Mary Roach brings. Both she and Sean Carroll blend fascination, realism, and scientific curiosity—reminding listeners that biology’s intricacies are stubborn, progress is non-linear, and some questions (“Why can’t we regrow fingers?”) might just be for “God” or future generations to answer. Listeners gain a thorough understanding of how far humanity has come—and how far we still have to go—in the quest to repair our own bodies.

Transcript

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[Sean Carroll]

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 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, 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 be done. We do it. We're getting better at it. But biology is 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 Bonk and Gulp, as well as Packing for Mars. And her new book is called Replaceable 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 in contemporary science, of how we replace our limbs and our organs and our skin and our hair and things 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 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 herself what is the simplest thing to possibly imagine replacing? And. And she came up with a variety of tears that our tear ducts reproduce. We can't do it. It's. 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.

[Mary Roach]

Thank you, Sean.

[Sean Carroll]

I guess there's. You've written a book called Tell the audience what the title of your book is. So I get the subtitle right and everything.

[Mary Roach]

Oh, sure. It's called Replaceable, you, Adventures in Human Anatomy is the subtitle.

[Sean Carroll]

And how long ago, historically do we know, like, when did people start actually replacing body parts with non body part things?

[Mary Roach]

Things really got rolling with noses. It seems as far back as like 1500 BCE 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 in various regions of the globe over history, where if 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.

[Sean Carroll]

I guess so.

[Mary Roach]

So everybody sees, everybody sees it. And I go, yeah, but you can.

[Sean Carroll]

Only do it once.

[Mary Roach]

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.

[Sean Carroll]

So I guess what the hell I'm trying to decide. If I didn't know, would I, you know, think the cutting off the nose or the ear or poking on the eye, like a nose is, is very noticeable. But I guess it's not like super damaging if you use it. Right. If you lose it.

[Mary Roach]

Yeah. So I think, yeah, I think it was more effective as a deterrent than as a punishment, you know.

[Sean Carroll]

And nevertheless, despite the fact that it was a punishment, they developed the wherewithal to Replace the nose somehow?

[Mary Roach]

Yeah. Yes, kind of. The. 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. When the nose. The new nose material had some capillaries and some blood supply, then they would cut off, they'd snip the. The little isthmus.

[Sean Carroll]

And what materials would they use to replace the actual nose?

[Mary Roach]

The. The. The skin, the cheek.

[Sean Carroll]

But, like, they put, like, bone.

[Mary Roach]

Oh, oh, oh, bone.

[Sean Carroll]

Ivory.

[Mary Roach]

You know, I don't know what the actual cartilage replacement was. Maybe they just mounded up the flesh, kind of like molded to the flesh.

[Sean Carroll]

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.

[Mary Roach]

That's a good question. Did they. Yeah. Did they use anything for the cartilage part? It seemed like they were just kind of molding. Like using the flesh is like sculpting clay.

[Sean Carroll]

And that actually seems pretty like, you know, knowing that you needed blood and the whole bit.

[Mary Roach]

I know. Yeah, I was. I was very impressed. Yeah. And. And I was speaking yesterday to a transplant surgeon who said, yeah, we. We. We still do that. I did that last week on a pediatric case.

[Sean Carroll]

And where in the world was this going on?

[Mary Roach]

Well, lots of places, but it started in. 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. But I think in Egypt that was done as well. So it's.

[Sean Carroll]

The Egyptians, of course, were expert mummifiers, so maybe they knew a lot about reconstruction for that reason.

[Mary Roach]

Yeah, yeah, yeah, it could be.

[Sean Carroll]

And of course, I'm a astronomy major from way back, so I know the story of Tycho Brahe, but maybe you could tell the audience that one.

[Mary Roach]

Yeah, and you even got his name right.

[Sean Carroll]

There you go.

[Mary Roach]

A lot of. A lot of people say Tycho Tico Bright. Yeah, Tico. Well, I, Yeah, I. I like Tico because, yeah, he lost a significant chunk of his nose in a duel. And so he. He had a lightweight. 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. 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 in the middle of.

[Sean Carroll]

A. I've seen pictures or portrait 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?

[Mary Roach]

No, I think there was. I think it was pretty nicely done. It was kind of painted that. I mean, there were the metal noses and the celluloid noises, noses that were made way back when they were often painted. And in one case, there was a. Two different paint colors, one for evening and one for daytime, which, you know, if you wear foundation, which it looks like you're not, but if you wear foundation, you know, you. You can adjust the beauty mirror. What's that called? The makeup mirror, according to daytime indoors or outdoors light. So fairly sophisticated nose making. There was an. My favorite, however, was from 1894. Frank Tedemor, an army surgeon, devised. This was one of the early plastic noses. And it was suspended from a pair of glasses without, you know, didn't. The person. Didn't need.

[Sean Carroll]

That makes sense.

[Mary Roach]

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 Marx glasses ever made for men.

[Sean Carroll]

That works well.

[Mary Roach]

Yes. Right. I never thought of that for the ladies. I'm not sure they did.

[Sean Carroll]

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.

[Mary Roach]

Yeah, yeah. And that was true. You know, 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. It was like a wig for the mouth. It was a cosmetic thing that you and somebody described in the Victoria era, Victorian era, that people would use what was called a masticator. So they'd kind of mush. They'd grind. It looked like handheld pruners, 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. And then put in the very uncomfortable and not useful for eating teeth, and then go out to the table and not really eat.

[Sean Carroll]

Right, okay.

[Mary Roach]

Yeah.

[Sean Carroll]

And here in the United States, of course, the father of our country, George Washington, was one of these people.

[Mary Roach]

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 he's kind of like, 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 his own teeth.

[Sean Carroll]

And, and you, you say, you write in the book about how not that long ago, historically, tooth maintenance technology was sufficiently bad that people would in intentionally just have their teeth removed so they could replace them with dentures which were kind of better looking at the time.

[Mary Roach]

Yeah, yeah. This was something I'd heard about a long time ago, maybe, maybe on QI or something, matrimonial dentures. Somebody mentioned. And I was like, come on. Like that. Giving somebody the gift of having their teeth all pulled would be a wedding gift. 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 found 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 a thousand. 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 about 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 new fangled dentures. And so people would do that. And it's kind of sad because at the time, dentures, there were no implants. Like, 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.

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[Sean Carroll]

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 to say?

[Mary Roach]

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 tear that when you cry or when you cut onions, but the tear 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 glycocalyx, and how it helps with retaining moisture and how there's mucins that catch the glop and deposit it. You know that sleep snot in the morning right in the corner of the eye. Those are the mucins 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. 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 C. Diff 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 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 oster blender, in fact, and mixed with distilled water, I think it was. And then that was introduced into the colon with a colonoscope, which has a kind of a plunger attachment. And two days later, the guys 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. I mean, we're not replacing healthy, normal. We're replacing compromised and invaded. Yeah.

[Sean Carroll]

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?

[Mary Roach]

Oh, the fecal microbiome that says 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.

[Sean Carroll]

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.

[Mary Roach]

Right, right, right. That's true. I mean, even something like a 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. There was the big Teflon fiasco where the, you know, it's like a ball and cap and the cap. They were trying to, you know, 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. And 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. And 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 out now where like every other person in their 80s has a fake hip.

[Sean Carroll]

I would have thought that that's not.

[Mary Roach]

That'S not an actual statistic.

[Sean Carroll]

No, that's like.

[Mary Roach]

Yeah.

[Sean Carroll]

I would have thought that any chef that who was familiar with non stick cookware could have told him that Teflon does not last very long.

[Mary Roach]

You would think, right?

[Sean Carroll]

You would think it wasn't too much.

[Mary Roach]

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. Just like a mess. Yeah.

[Sean Carroll]

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.

[Mary Roach]

Sure, sure. Yeah. There, there were, you know, wooden legs. There was, there was. There was an aluminum leg that was quite exciting because it was lighter weight. This was in. In the uk, a lot of the military veterans were excited about the military light leg because there, for a while there was this belief that when you replaced a leg, the prosthetic limb should weigh the same as the norm as the. 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 osseointegration. 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, you have to close up the skin around it. It's not a complete seal. Bacteria get in. So there have 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.

[Sean Carroll]

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.

[Mary Roach]

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. She actually emailed me about something else, and we got to talking. She's an amputee, below the knee amputee. She's an elective amputee. So 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 prosthetics 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 so it took her a while to find somebody willing to do that. I mean, it's. You know, I guess if you're a surgeon, there is a kind of a worry. It is. There's a finality to lopping off a foot kind of not gonna 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.

[Sean Carroll]

There are some runners who are amputees, right. You can get replacements that allow you to run fast.

[Mary Roach]

Yes.

[Sean Carroll]

The limit of my knowledge, right there.

[Mary Roach]

You can get replacements 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.

[Sean Carroll]

It kind of is, yes. For his wife sealing the deal.

[Mary Roach]

Yes. Yeah, exactly. Yeah. So, but interesting. You know, I talked to Ezra Freck, who was 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. 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 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 made it that far. Nobody has since. If it were an advantage, we'd be seeing amputees in the Olympics all the time. So. But. But anyway, interesting. It was an interesting day there at the Amputee Coalition Conference.

[Sean Carroll]

You've already mentioned the weight issue in the limbs. How. What other kinds of improvements have there been? Like, can we hook up nerves in our body to manipulate the limbs at all?

[Mary Roach]

Well, what. This tents. That kind of stuff happens in developing. There's a lot of effort now to develop articulate arms, lower arms and hands with articulating fingers so that you can grip things. And so it's, you know, when you think 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 a 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, I read an essay by Brit Young, who writes a lot about this, and she pointed out that 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 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, for arms that whole day. And it was that, you know, that classic shot of the kind of Arnold Schwarzenegger bionic looking limb and it's holding a raspberry. And she, she laughed, she goes, are you gonna spend like 30 seconds getting your grip right? No, you're gonna reach over with your other hand and pick it up and eat it. Right? 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.

[Sean Carroll]

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.

[Mary Roach]

You know, my, my favorite kind of. I don't watch a lot of videos on YouTube, but my favorite are the, you know, the soccer playing robots. Oh, yes, that fall over.

[Sean Carroll]

But they're getting better. Like you said, like, I wouldn't want to play against them 20 years ago.

[Mary Roach]

I know, I know. I don't want them to get better because they're really entertaining when they fall over each other.

[Sean Carroll]

So. Okay, so. But mostly, yeah, so these are the obvious ones. You lose a nose, you lose it, 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.

[Mary Roach]

Right. Well, in terms of transplantation, a xenotransplantation 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 kidneys going in to patients who lived about two months. But there's a man now, Tim Andrews, I think it's going on eight months and E Genesis is just starting a trial with I don't know how many patients getting pig kidneys. A dozen maybe. Anyway. And Tim Andrews is in much better shape. The early recipients were getting these organs under compassionate use exemption because these organs would have to be FDA approved and they're not yet. But these were folks who were so close to being deceased that it was felt that 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 are lasting two months. Tim Andrews is better shape. So that's promising. You know, eight months is that could be enough time for a patient to make their way up the donor list 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.

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[Sean Carroll]

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?

[Mary Roach]

There have been different reasons. There have been a couple cases of viruses, pig viruses that actually affect humans. So there were some zoonoses, as they say, causing a problem, a pig virus. There was another case where the heart, 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 problematic. So, and you know, there's Still a tremendous difference between. Even if you. You're basically, they're 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 a. It's called a hyperacute 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 they've knocked that out. Now you're at a level where the same kind of immunosuppression that you would give a patient who's receiving a human organ, there's still immunosuppression. But I talking, you know, I spent some time in China for this chapter, and this researcher who's been working on xenotransplantation for 30 years, I said, 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. 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 immunosuppression. So he had all these ideas, and he was very hopeful for the future of pig organs in humans.

[Sean Carroll]

Is there a good reason why it's pigs in particular that we use to replace human organs?

[Mary Roach]

Oh, that's a fine question. And I 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. He said, all pigs are hysterical. Like, you bring them in and they're squealing really loud. I've seen this in a lab setting. A pig is a big animal and they're very loud. Anyway, so the. Back in the 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 together and bred pigs smaller. They bred them smaller so that they'd be easier to have around the lab. The organs would match ours. They also did all of this experimentation on comparing the, like, the coronary arteries of pigs to humans, like, trying to see, like, how close are they and pigs are. In fact, some. Someone described them pigs as a caricature of an obese human because they get. They get coronary artery disease. They don't get a lot of exercise. This is, you know, domesticated pigs. They eat garbage. So they're kind of. 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 orthodontia and were pigs useful for studying orthodontia? Somebody put braces on a pig. Braces on a pig. Anyway, so poor pigs. 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, they. A lot was known. And so it became kind of the go to animal.

[Sean Carroll]

Well, and 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.

[Mary Roach]

Right.

[Sean Carroll]

Who's going to get something put in them? Let's go with something we know something about.

[Mary Roach]

Yeah, that's right. That's right. And they are, you know, similar, similar size and fairly, in some cases, fairly similar functions, as the Hormel Institute helped us learn.

[Sean Carroll]

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 is 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?

[Mary Roach]

Yeah, yeah, that tends to be the first one. I'm sorry, 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. Mohiuddin, I'm probably mispronouncing it Mohiuddin. Anyway, and he said that Mr. Bennett said had a concern, although not all that serious. He said, am I going to be going oink, oink after this? Like this, you know, that concern that sometimes people who get a new heart have this belief, the sense that they have changed in a way that they have taken on characteristics of the person who donated the organ.

[Sean Carroll]

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.

[Mary Roach]

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.

[Sean Carroll]

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?

[Mary Roach]

That. Yes, absolutely. Yeah. Yeah. I mean, eventually they need to be replaced, but the pig valve. Yeah, 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.

[Sean Carroll]

But we also just do purely mechanical ones. I mean, what's the. What's. Do you know, the trade offs 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?

[Mary Roach]

I don't. I don't. I don't think again. I think that the artificial heart is, again, a stopgap. You don't meet people who have a artificial heart for very long, I don't think. 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 donor.

[Sean Carroll]

Yeah, this is not exactly what you were talking about in the book, but how good are we at just replacing human parts with human parts? Like, is the technology for human organ donation pretty good these days?

[Mary Roach]

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 Extracorporeal Life Support Lab. And it's all about devices that do the job of parts of the body outside the body, extracorporeally 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, you've got, you know, four, six hours, something like that. There are perfusion machines that will sort of oxygenate the heart in 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. You could, I don't know, put in a stent, clean it up. Yeah, exactly. Kind of like a reconditioned iPad or whatever. The East. Those ones that I always think I should get and I don't. Yeah. So 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.

[Sean Carroll]

Okay.

[Mary Roach]

You maybe you knew that.

[Sean Carroll]

No, that.

[Mary Roach]

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 they 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. Just the weirdest thing. Anyway, hearts.

[Sean Carroll]

I guess this just shows my ignorance. I had assumed that those heartbeats were triggered by signals from our central nervous system.

[Mary Roach]

Well, they have an internal kind of electrical system.

[Sean Carroll]

Yeah. Okay.

[Mary Roach]

And I, I, 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.

[Sean Carroll]

Let's give the audience a reason to buy the book. That's okay.

[Mary Roach]

Yes. That word, the term is in there. It'll. It'll probably occur to me and about three minutes, and I'll Blurt it out, derailing, whatever we're saying.

[Sean Carroll]

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?

[Mary Roach]

Yeah, no, I know. You see, you know, I remember the first time I saw a heart beating. It was a. 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 stoat in a burrow. Just like it's really active. It's just, it's, you know, you feel your heartbeat and it's sort of a gentle, kind of gentle, I don't know, mild.

[Sean Carroll]

Yeah. Calm, mellow motion.

[Mary Roach]

And you see this thing and it's just like. I don't know, 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 crazy. I remember seeing at it was a bioprinting 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, 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 then sometimes, the researcher said sometimes they get going so, so kind of vehemently that they, they catch air. Like they come right up off the bottom of the slot. It's unbelievable. Like that, like they. Apparently one cell will open up a little, you know, kind of like start communicating next to it and then the next one. And soon they're all just like beating in tandem.

[Sean Carroll]

They're dedicated to the task. I got to admire it a little bit.

[Mary Roach]

They are, they really. Are you.

[Sean Carroll]

You mentioned briefly a cutoff for organ donations. Is that a universal number or does it depend on the organ?

[Mary Roach]

Probably depends on the organ. I'm not sure.

[Sean Carroll]

But I just want to know am I past the limit? Am I my organs all sort of useless by now?

[Mary Roach]

I don't think so. No, I don't think so. No. I think you're good to go.

[Sean Carroll]

And just briefly, I guess what else are we good at in terms of replacing organs besides hearts? We got livers.

[Mary Roach]

Oh, we are really good at the lens of the eye, I mean, that's. People are now getting both of them done at once. You go in and couple hours later you come home. And now. 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 at 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 focus lens is pretty. It's pretty amazing how quickly that can be done. And it's, you know, it goes in, it's got a little plunger almost like a tampon. You know, tampon.

[Sean Carroll]

You've written books about these things.

[Mary Roach]

And it. So the lens goes in and it's like. Fold it 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.

[Sean Carroll]

So this is. Yeah, I was going to say this is for cataracts. It's not just because my eyesight is failing. It's a little bit more serious than that.

[Mary Roach]

Well, it's gotten. The technique has gotten so reliable and so safe that there are folks who are simply myopes. You know, they're. They're nearsighted like me. I can barely read the big E. And. And they are getting a lens. Rather than get Lasik, they are getting a lens implanted. So there's not that.

[Sean Carroll]

Yeah, that's the one surgery that I've had to change my body in some way. I did have Lasik and it's.

[Mary Roach]

Oh, you did?

[Sean Carroll]

I did, yeah. Oh, I mean, I. I'm a huge fan of. Of doing it well. And they can't fix, like you say, the autofocus. They can't fix it. So that you can do, you know, they can't fix both nearsighted and far sightings at the same time. So they do your two eyes slightly differently?

[Mary Roach]

Oh, yeah.

[Sean Carroll]

One is good at close and one is good at far, and the brain figures it out. It's sort of completely natural.

[Mary Roach]

Yeah, yeah. I had that with my contacts for a while. I had one. A slightly stronger prescription. Yeah.

[Sean Carroll]

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?

[Mary Roach]

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?

[Sean Carroll]

I am personally not sufficiently acquainted with the smell of burning flesh to tell you whether that is true or not. But it smells like something is burning that they, they offer you a pill if you want to, like, be calm. Right. If you don't want to, don't want to face up to the. Your eyeballs being lasered. But.

[Mary Roach]

And did you get a lot of halos and kind of aberrations? It's for me, night vision.

[Sean Carroll]

Yeah. I mean, fortunately, I was living in LA at the time and they have very, very good, you know, surgeons of this sort. So. No, like that first day your eyes feel all weird. The next morning you wake up and it's fine, Fine. That's it.

[Mary Roach]

Wow. Are you very nearsighted like me?

[Sean Carroll]

I was pretty darn nearsighted. Yeah.

[Mary Roach]

Yeah, yeah, yeah. Okay.

[Sean Carroll]

And it's like, that was like 10 years ago. I'm sure I'm gonna, you know, it's gonna fade away. It's not quite as good as it was, but a lot better than putting contacts every morning.

[Mary Roach]

Yeah, I just, I hate reading glasses, so I, I like to be able to take off my contacts and read. I just have to hold the book like three inches from my face. But, but I like, you know, I have kind of, of microscopic vision.

[Sean Carroll]

Anyway, Anyway.

[Mary Roach]

Anyway. Yeah, anyway.

[Sean Carroll]

Just going through the list of fun things that we are replacing these, 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 that is a big. Is a well known thing. Right?

[Mary Roach]

Yeah. Yes. Skin grafts. Skin is a skin grafting for severe burns. It's an interesting area in that there was a period of time 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 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. 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 sloughs off. Or the surgeon, in the case of cadaver skin or whatever has been put on, they'll peel it off and they want to. They want it to bleed. They want it. It that freshen is the term 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.

[Sean Carroll]

So from one part of your body to another one.

[Mary Roach]

Yeah, yeah, exactly. But with a really serious burn, sometimes there's not much real estate left, you know, and it's. And then they'll end up using the same. Using it like a patch on the leg, 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. There are some great new developments. Like there's something called cea, cultured epithelial autographed. 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 meshed to kind of feed it through. Sort of looks like a pasta maker. So it's it. 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, Cutis, 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. It was. 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, Cutis, and they were like escorting the new skin back and going to install it in this. In this little boy. Again, a compassionate care exemption.

[Sean Carroll]

So and will that.

[Mary Roach]

So. Yeah.

[Sean Carroll]

Will that new skin have the same properties ideally as the old skin? Will it will have the sense of touch?

[Mary Roach]

Sure. It should. Sure. Yeah. It should. Yeah.

[Sean Carroll]

How surprised should we be that the human body is not better at just regrowing things? The thing, you know, we last forever, but if you lose a finger, we don't have the ability to just, you know, the body can't regrow it. Some animals can, I guess. Right.

[Mary Roach]

I know. Our livers, we can regrow. Our liver, we can regrow. Yeah. I mean, you can regrow skin. I mean, if a 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. 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, but first and second degree, second degree burn, the, the body is pretty good about regenerating, but. Yeah. Why, why can't we regrow everything? I don't know, ask. Ask God.

[Sean Carroll]

God has a sense of humor here. But I mean, there must be some mad scientists out there who are trying.

[Mary Roach]

I'm sure that there are people studying salamanders or whatever creatures. And that's why I think 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.

[Sean Carroll]

Yeah.

[Mary Roach]

No, it's not.

[Sean Carroll]

I don't know if you've ever run into Michael Levin at Tufts. He was a former Mindscape 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. Like there's things. You try to move an organ from one place to another and the body just moves it back.

[Mary Roach]

Yeah, yeah, yeah, yeah. That's interesting. But you can also, you can also install things in a body in a different place and it works just fine. You can take, you know, islet cells, you don't have to put them by the pancreas. You can stick the islet cells under the skin. You can, you know, which was great. Because it's easier to access. You don't have to go in for surgery. So 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 at the, on the pancreas.

[Sean Carroll]

And yet, like, we're still not very good at hair, right? We can't, you know, people go bald and we don't know how to really fix it.

[Mary Roach]

I, I, I know, yeah. Hair, 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. You know, that's a, okay. Yeah, because you got to go, you, first of all, you got, you gotta like pull them all out and then you gotta stick them all in. And that's a, it's tight. 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 hairline down, but then you keep losing hair and now you've got the, the bare strand behind, so you got to go back and get more and eventually you run out because the sides and back are starting to get sparse.

[Sean Carroll]

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?

[Mary Roach]

No, I think no hair, it's your own, it's your own stuff. So. Yeah, no, I think it works quite well. I mean, ask Elon. I don't know.

[Sean Carroll]

It looks okay.

[Mary Roach]

You got it. It, yeah. It's just that it's a, it's a, a lifetime commitment because you're the, as the hairline 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 because. No, no, you, 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.

[Sean Carroll]

It's evident. It's just an example to me of like how even the easiest things are a little challenging.

[Mary Roach]

Well, yeah, yeah. I spent time at a biotech startup that they were trying to 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 papillae 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, look, we've grown hair blobs under the skin of this mouse. So they came in, then they. 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 paddy kind of thing. But the tubes ended up being thicker than the skin of the mouse. They were. And they were too. 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. I went to them thinking, okay, follicle, how hard could that be? Yeah, really hard is the answer. Really hard.

[Sean Carroll]

Well, I have to give you a chance to talk about. You have different chapters in the book where you mentioned, 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. How successful is that?

[Mary Roach]

Well, I. I reported on two very specific types of procedures. One of them. One of them is unorthodox. It's not. It's not done anywhere outside of Tbilisi in former Soviet Georgia, as far as I know. I was curious.

[Sean Carroll]

You get the it? Yeah.

[Mary Roach]

Yes. I mean, any opportunity to head off to somewhere I haven't been. But this was 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 forearm or some hairless part of the body and then surgical implants that you buy from whatever prosthetic company, you know, one per erectile chamber. And he chose instead to use for rigidity the man's own middle finger, which.

[Sean Carroll]

Was still attached to the. I mean, so.

[Mary Roach]

And I, I envisioned the finger being taken and installed, you know, as is with a nail and everything and able to move and beckon and. But. Which seemed pretty cool, sort of. But no, he was wrapping it in a graft taken from the person's forearm, the underside of the forearm, but it did have the function of it bent. There was 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 with the mid bent at the midsection with a ceramic water pitcher hanging off of it. I don't.

[Sean Carroll]

I know.

[Mary Roach]

You know, I wasn't ever really clear on what that I said. Is that, Is that similar to. Because there are malleable penile implants that. And, 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.

[Sean Carroll]

Because this is now going to have bones in it, unlike the typical penis.

[Mary Roach]

I know. Yeah.

[Sean Carroll]

Okay. Just. Just to be sure I understood the process.

[Mary Roach]

Yes, it is. Yes, yes, it's. It's going to have bones in it. So it would be the very first human baculum.

[Sean Carroll]

But this is. Okay, it sounds like from this particular story that there is no, like, agreed upon successful procedure for these circumstances.

[Mary Roach]

Oh, no, there, there, no, there, there is a standard procedure for, well, it. For erectile dysfunction. You kind of take these implants which look like, you know, they're the width of pencils, 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, you squeeze that, pump it up, and then you can, you know, let the air out or there's the malleable, the gumby limb kind where you can, you know, bend it up or bend it down. So, but that's erectile. For erectile dysfunction, for reconstruction, I would, you know, there 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. He's the only surgeon who's doing.

[Sean Carroll]

Who says romance is dead. I think this is good to know the guy.

[Mary Roach]

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.

[Sean Carroll]

Okay, good, good. That's the testimony you need. All right, so 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 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 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?

[Mary Roach]

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 so much is happening with. With. With AI and with stem cell research, and there's. It's both really slow and incredibly fast. Do you know what I mean?

[Sean Carroll]

Yeah.

[Mary Roach]

Yeah. So.

[Sean Carroll]

And the dream is someday we'll just 3D print a new limb or pancreas or whatever, right?

[Mary Roach]

Yeah. Or grow it from scratch.

[Sean Carroll]

Grow it from scratch. Okay. So there'll be room in a couple decades for you to write a new book about this.

[Mary Roach]

No, you write this one.

[Sean Carroll]

Maybe we'll see about that. All right. But, Mary Roach, thanks very much for being on the Mindscape podcast.

[Mary Roach]

Oh, my pleasure. Thanks, Sean. Sam.