Published in 2025, Replaceable You: Adventures in Human Anatomy is a work of popular science by American author Mary Roach. Known for her immersive and humorous explorations of the human body, Roach has penned several New York Times bestsellers, including Stiff: The Curious Lives of Human Cadavers (2003) and Gulp: Adventures on the Alimentary Canal (2013). In Replaceable You, Roach investigates the strange history and cutting-edge science of replacing human body parts, from prosthetic noses and skin grafts to 3D-bioprinted organs. Traveling from surgical theaters in the United States to xenotransplantation labs in China, she questions the popular narrative of seamless scientific progress, focusing on the human stories and ethical quandaries behind the technology. Roach’s work has been recognized with numerous accolades, and she was a finalist for the Royal Society Winton Prize for Science Books. Replaceable You explores themes including Ethics and Risk at the Frontiers, how The Body Outperforms Its Replacements, and how Progress Is Not Linear.

This guide refers to the W. W. Norton & Company 2025 hardcover edition.

Content Warning: The source material and guide feature depictions of transgender discrimination, ableism, animal cruelty, animal death, illness, and death.

Plot Summary

Author Mary Roach begins her exploration of replacement body parts by describing the various primitive solutions to toothlessness that were common before modern dentures were invented. She establishes that her book is an investigation into the human elements of innovation and error in the quest to replace parts of the body. Roach speaks to surgeon Jeremy Goverman, who voices the book’s central tension by stating, “I don’t think you can replace the human body” (6).

The narrative delves into the history of prosthetics, starting with 16th-century astronomer Tycho Brahe, who wore a metal nose after losing his in a duel. The chapter also documents early, unsuccessful attempts at xenografting, the practice of using “free flaps” of skin from animals like chickens and frogs as temporary wound coverings. 

Roach decides to learn more at the Sumner M. Redstone Burn Center at Massachusetts General Hospital. There, she observes surgeon Jeremy Goverman perform a skin graft on a burn patient. Roach then meets a patient of Goverman’s, Diana Tenny, who survived burns on 90% of her body with the help of over 25 skin graft surgeries. Goverman mentions his work with genetically altered pig skin, prompting Roach to investigate xenotransplantation further by planning a trip to China.

In Chengdu, China, Roach meets with researchers Shaoping Deng and Yi Wang, who explain that a national organ shortage has driven research into animal-to-human transplants. Roach visits a gene-editing lab, ClonOrgan, where pigs are kept, and the researchers tell her about a new idea to grow human organs inside a gene-edited pig.

Roach then visits the Extracorporeal Life Support Lab at the University of Michigan, run by Dr. Robert Bartlett. She observes a research surgery in which a pig’s heart is removed to test methods for keeping donated organs viable for longer periods. Bartlett explains that a major problem in organ donation is that, inexplicably, organs cannot survive long without a human brain. Bartlett hypothesizes that the brain secretes an unknown substance necessary for long-term organ function. 

Next, Roach meets with Dr. Maurice Garcia, director of the Transgender Surgery and Health Program at Cedars-Sinai Medical Center. Garcia explains a surgery he invented that involves creating a neovagina for transgender women using a section of the patient’s colon. He discusses the procedure’s trade-offs and reveals that many of his patients choose the surgery primarily to remove their male anatomy, rather than for its functional benefits with sexual partners. He also criticizes doctors who don’t take transgender patients seriously. Roach also discovers that some surgeons are known for constructing overly large neophalluses for transgender men, at the expense of the patients’ wellbeing. 

Continuing along this train of thought, Roach travels to Tbilisi, Georgia, to find Dr. Iva Kuzanov, a plastic surgeon who performed a penis reconstruction using a patient’s own middle finger. Roach doesn’t speak to the doctor, but his colleagues show her photographs of the operation. Learning about grafts and surgical reconstructions eventually leads Roach to wonder about prosthetic limbs. 

Roach attends the Amputee Coalition National Conference with Judy Berna, a woman who chose to have her foot amputated after a lifetime of pain; her condition stemmed from complications of spina bifida, where scar tissue entangled with her spinal cord, causing her foot to twist as she grew. Roach learns that surgeons are often reluctant to perform such elective amputations. She meets Paralympic athlete Ezra Frech, who publicly advocates for disability awareness. Roach also learns about osseointegration, a novel and under-researched procedure that anchors a prosthesis directly to the bone but carries a high risk of infection.

Later, Roach observes orthopedic surgeon Dr. Alexander Sah perform multiple hip replacements. She learns about the pros and cons of materials that have been used to replace hips. Roach recounts the work of John Charnley, who pioneered modern hip replacement with his introduction of low-friction polyethylene. She also investigates the historical use of ivory for hip implants by Burmese surgeon Dr. San Baw, which eventually fails because ivory proves too conducive to bacterial growth. Microbiologist Dr. Paul Stoodley tells Roach about the persistent problem of bacterial infections in surgeries.

Roach then speaks to anesthesiologist Dr. Jordan Newmark, who explains how high-stakes his job is. Because patients under general anesthesia are paralyzed and can’t breathe on their own, the anesthesiologist has only minutes after the patient is sedated to insert a breathing tube before oxygen deprivation occurs. At a Stanford medical simulation center, Roach attempts to intubate a training manikin and experiences firsthand the difficulty of navigating the complexities of the human airway.

This leads Roach to explore the iron lung, a large steel box that encases the entire bodies of patients who are unable to move their diaphragms due to diseases like polio. The device functions as a negative-pressure ventilator that mimics natural respiration. To understand the experience, she arranges to spend a night inside one. The experience is profoundly uncomfortable, and she lasts only a few minutes. She then speaks with Dr. Norma Braun, a pulmonary specialist who advocates for modern, wearable negative-pressure devices as a safer alternative to the positive-pressure ventilators common today.

Switching her focus to cataract surgeries, Roach travels to rural Mongolia with the nonprofit Orbis International. The organization operates a nomadic hospital, traveling to remote parts of the country to perform cataract surgeries for those who don’t otherwise have access. In a rustic hospital, Roach watches Dr. Enkhzul Damdin perform manual small-incision cataract surgery, a low-tech but effective procedure.  Roach witnesses the emotional moment when the patient has her bandages removed and can see clearly for the first time.

Next, Roach investigates the stigma surrounding ostomy surgery, which creates an external opening, or stoma, in a person’s stomach or intestine through which to expel waste. At a 5K ostomy awareness run, she meets patients who describe how the procedure gave them their lives back after suffering from inflammatory bowel disease. The narrative then shifts to the search for an artificial anal sphincter, a solution for fecal incontinence that would eliminate the need for an ostomy, but she finds that no device has proven successful in the long term. One project that seemed promising was an attempt to grow sphincters in a lab from stem cells. 

Roach visits the Carnegie Mellon lab of Dr. Adam Feinberg, a leading researcher in 3D bioprinting. Feinberg demonstrates his patented technique, which prints soft biological materials inside a petri dish full of gel. Roach observes the printing of liver and heart muscle tissues, learning about the challenges of replicating complex cellular architecture. She concludes that printing a fully functional, implantable human organ is still likely more than a decade away.

The only organ that regenerative medicine can successfully replicate is the hair follicle. Roach visits  Dr. Richard Chaffoo at Stemson Therapeutics, a company that is working to grow new hair follicles from induced pluripotent stem cells, which are adult cells regressed to an embryonic-like state. 

Roach travels to Mexico City to meet Dr. José Luis Daza-Flores, a plastic surgeon. At his clinic, she observes a liposculpture, a procedure in which fat is suctioned from one part of the body and transferred to another. Roach and the doctor talk about why liposculpture works better than implants, and discuss the social influences that persuade women to get plastic surgery.

In the final narrative chapter, Roach spends a night at the Center for Organ Recovery & Education (CORE) in Pittsburgh to observe a tissue recovery from a deceased donor. She follows the entire process, from the risk-assessment interview with the donor’s family to the recovery of various organs. She is struck by the respectful and highly professional nature of the work.

In her concluding thoughts, Roach reflects that even the body’s simplest parts are far too complex for science to replicate perfectly, which underscores the body’s own inherent brilliance. She concludes that while replacement parts will continue to improve, they will likely never equal the originals. An Epilogue provides updates on the people and research featured in the book, noting that federal funding cuts threaten some of the projects, Stemson Therapeutics has closed, and xenotransplantation has had mixed results.