The episode features Mary Roach, New York Times bestselling author of books including Stiff, Grunt, Bonk, Gulp, and Packing for Mars, discussing her latest work Replaceable You Adventures in Human Anatomy (Fall 2025). She joins host Neil deGrasse Tyson, co-host Chuck Nice (professional stand-up comedian), and Gary O'Reilly (former soccer pro and announcer) at the Hayden Planetarium.

The conversation explores the history and current state of human body part replacement, from ancient nasal reconstruction dating back to 1500 BC through modern prosthetics, organ transplants, and emerging technologies like 3D bioprinting and genetic engineering.

Roach shares her journalistic approach of targeting "unsuspecting expert researchers" as unpaid tutors, traveling globally to witness cutting-edge medical procedures including visits to China's 26-story pig facilities, bioprinting labs, and a surgeon in Tbilisi performing unconventional reconstructive surgery.

The discussion covers the technical, financial, and ethical challenges of replacement medicine while examining why nature's solutions—like regenerating newt limbs—might offer better answers than current medical technology.

Ancient Origins of Reconstructive Surgery

Humans have been in the replacement parts business since approximately 1500 BC, primarily driven by nasal mutilation as punishment for crimes across cultures including Ireland, Egypt, and the Middle East.

In Nepal, the town of Kirtipur allegedly had its entire male population "denosed" as punishment for disloyalty to local conquerors, illustrating the widespread use of facial mutilation as visible deterrent.

Italian surgeon Gaspari Tagliocozzi developed a groundbreaking technique in the 1500s using skin flaps from the underside of the upper arm to reconstruct noses, requiring patients to hold their arm to their face for weeks using a harness system.

A statue in Bologna depicts Tagliocozzi stepping forward holding a nose, commemorating his pioneering work

This method avoided facial scarring compared to earlier techniques using cheek or forehead flaps

U.S. Army surgeon Frank Tedemore invented a medical version of Groucho Marx glasses in 1894—celluloid plastic noses attached to eyeglasses with mustaches to hide the attachment line.

Syphilis created additional demand for nasal reconstruction as untreated cases caused deterioration of the nasal cartilage bridge, expanding the field of reconstructive surgery.

Modern Prosthetics: Promise and Limitations

Advanced prosthetic legs with microprocessors can sense when users are about to fall and help prevent it, with some using AI to learn individual gait patterns, but they cost approximately $15,000, aren't waterproof, require battery charging, and are heavy.

Insurance typically doesn't cover advanced prosthetics, creating significant financial barriers for amputees who could benefit from the technology.

Prosthetic arms remain far less advanced than legs because "the hand is five fingers that are moving independently, and you've got to track the signals from the brain" - Mary, explaining why most upper-limb amputees simply use their remaining arm.

The Department of Defense funded significant prosthetics research following IED injuries in Iraq and Afghanistan, driving advances in the field particularly for military veterans.

At the Amputee Coalition national gathering, "everybody has a prosthetic leg" but "not so many arms because the arms aren't, you know, because the fingers. that's a problem" - Mary, describing the disparity in adoption rates.

Osseointegration: Screwing Prosthetics Into Bone

Osseointegration technology, developed by Per-Ingvar Brånemark (the same person who invented dental implants), allows prosthetics to screw directly into bone rather than using compression sockets.

Direct bone attachment provides sensation through the bone, allowing users to tell what surface they're walking on and eliminating uncomfortable, sweaty socket compression issues.

Infection remains a significant problem with osseointegration in limbs, unlike dental implants which rarely get infected despite the mouth being "a cesspool of bacteria" because saliva has antibacterial properties.

A market exists for "residual limb antiperspirant" because traditional socket-based prosthetics create sweaty, uncomfortable conditions, particularly on hot days.

Organ Transplants: From Pigs to Humans

Genetically edited pig organs with the alpha-gal protein knocked out are "on a par with putting another human's organ in" for rejection rates, with one patient surviving nine months with a pig kidney while others lasted about two months.

Early pig organ recipients were terminally ill patients who agreed to experimental procedures under compassionate use protocols: "you're going to die soon. So could we give this a whirl?" - Mary.

Chimerism technology theoretically allows creating pigs with human organs by introducing human pluripotent stem cells into pig embryos edited to not grow their own kidneys, though this remains largely experimental.

Mary visited a 26-story pig facility in China with facial recognition technology for pigs, representing ultra-high-tech "piggeries" for pork production that could potentially support organ farming infrastructure.

The facility was so clean that Mary couldn't enter because "I stank" compared to the sterile environment, observing procedures only via video camera.

Rejection Crisis in Composite Tissue Transplants

Face and hand transplants have largely moved away from widespread adoption because "the immune system does not want" composite tissue allotransplants, which contain multiple tissue types that trigger strong rejection responses.

"I remember like 10 years ago, there was just tons of stuff about face transplants, hand transplants... I was like, why do you not hear about that anymore?" - Mary, noting the decline in these procedures.

Bilateral leg transplants were attempted but didn't become standard practice due to immune system complications, with insurance not covering these procedures for most patients.

The complexity of composite tissue—containing skin, muscle, blood vessels, nerves, and other tissue types—makes it exponentially harder for the body to accept compared to single-organ transplants.

3D Bioprinting: The Wright Brothers Stage

When asked how long before printing transplantable organs, a bioprinting researcher said "we are kind of in the Wright brothers stage" and estimated "about 20 years" with AI potentially accelerating progress.

A researcher successfully printed and installed a single ventricle in a mouse that was "still working" months later, though it lacked valves and the mouse retained its original heart.

The major advantage of 3D printing organs is custom fitting—"a cow valve doesn't fit everybody. Not everybody's a candidate, but now you could" create patient-specific organs - Mary.

Researchers can print heart valves and use cow collagen that human bodies accept, with Mary owning "a little one in a jar" of a 3D printed tri-leaflet valve.

The de-cell/re-cell scaffold approach faces challenges because "the breakdown products, those are molecular, tiny, very tiny, and the stuff you're trying to pump in" - Mary, explaining difficulty directing different cell types to proper locations.

Heart muscle cells must be aligned precisely in a helix shape "because it kind of twists as it pumps," making simple scaffold approaches insufficient for complex organs.

Unconventional Reconstructive Surgery in Tbilisi

Mary traveled to Tbilisi, Georgia after reading about a surgeon who used a patient's middle finger bone for internal rigidity in penis reconstruction following cancer, wrapping it with forearm skin.

The surgeon's office showed Mary photographs including one demonstrating the reconstruction's strength by hanging "a bucket on it, not far off a ceramic water pitcher... white with kind of red and green flowers."

The surgeon never responded to Mary's follow-up attempts to explain why he didn't use standard medical products for erectile dysfunction surgery like malleable implants.

Mary initially imagined "the man's finger taken intact with the nail and everything and just stitched in place and able to kind of move and beckon," though the actual procedure was more conventional.

Fibonacci Sequence in Plastic Surgery

A Mexico City plastic surgeon applies the Fibonacci sequence and golden ratio to Brazilian butt lifts, having published papers on "the perfect calf" and "the perfect buttock proportions."

The golden ratio appears throughout nature in "those shells" and "the design of sunflowers on a sunflower plant," with the surgeon adapting these mathematical principles to aesthetic surgery.

When Mary asked if he used measuring tools, the surgeon said "no, I eyeball it. By now, I can eyeball it" after years of applying Fibonacci principles.

Mary was curious whether the surgeon "discarding Fibonacci for Kardashian" given evolving aesthetic preferences, as the Kardashian aesthetic represented a departure from traditional proportions when she reported the chapter.

Extending Heart Transplant Viability

Traditional heart transplant windows allow only four hours from donor extraction, extendable to 12 hours using modern perfusion systems that provide blood and oxygen supply.

The University of Michigan's Extra Corporeal Life Support Lab developed ECMO (heart-lung machine) technology that oxygenates blood outside the body, used during open heart surgery.

Mobile ECMO units under development could allow emergency personnel to hook up heart attack victims in the field rather than performing CPR, potentially saving more lives.

The critical challenge is the four-minute window before oxygen deprivation creates "the zone of are you saving a life or creating a vegetable" through brain damage.

Head Transplants and Whole Body Replacement

Robert White successfully transplanted monkey heads onto different bodies in 1970, establishing technical feasibility though not practical application.

The theoretical application addresses mismatched conditions: "Alzheimer's, you have a perfectly functioning body and your brain is gone. And ALS, you have a perfectly functioning brain and your body's gone" - Neil.

Neil proposed combining an ALS patient's head with an Alzheimer's patient's body to "get one whole person out of that," illustrating the logical but ethically fraught possibilities.

A surgeon "repeatedly talks about a whole body transplant" as a path toward extended lifespan, though Mary doesn't believe "that's going to come from replacement bits."

In Vitro Gametogenesis and Self-Reproduction

In vitro gametogenesis allows regressing blood cells to pluripotency, then directing them to become eggs (from male cells) or sperm (from female cells), enabling single-parent reproduction.

"You could create another human being with only your own genetic material, which I think Elon Musk is probably really excited about" - Mary, suggesting potential misuse of the technology.

Ethics papers exist addressing in vitro gametogenesis, though Mary notes ethicists are publishing papers rather than necessarily working "in tandem with these efforts."

Current legitimate applications focus on "implanting clusters of cells that might help somebody with Parkinson's or diabetes, and that's pretty cool" rather than reproduction.

Nature's Solutions: Regeneration Over Replacement

Neil deGrasse Tyson argues the ultimate solution may come from studying animals: "newts that can regenerate limbs and tails. Lobsters regenerate claws. They don't need prosthetics. They don't need medical doctors."

Planaria worms can regrow entire heads after decapitation, demonstrating regenerative capabilities built into DNA that humans share with other vertebrates.

Neil proposes the future may involve DNA manipulation to trigger natural regeneration: "you just go in and they twiddle with your DNA and another organ grows."

Neil advocates prioritizing military veterans for regenerative treatments: "at the top of that list, we put military veterans who need the limbs first. Then, everybody else, second in line."

The historical parallel of Manhattan's manure crisis being solved by automobiles rather than horse modification suggests breakthrough solutions often come from unexpected directions rather than direct problem-solving.