American Scientist

REPLACEABLE YOU: Adventures in Human Anatomy. Mary Roach. 288 pp. W. W. Norton & Co., 2025. $28.99.

If you’ve ever wondered whether a sheep could donate skin to a human, or whether a colon could moonlight as a vagina, Mary Roach has answers for you. From cadavers (Stiff) to digestion (Gulp), sex (Bonk), and the afterlife (Spook), her books have made complex biology accessible and engaging for a wide audience. In her latest, Replaceable You: Adventures in Human Anatomy, Roach slices into the world of anatomical substitution with her signature scalpel-sharp wit and a bedside manner that’s equal parts curious and compassionate.

Replaceable You isn’t just a book about body parts, though: It’s also a book about the people who lose said parts, the surgeons who reimagine the parts, and the scientists who dare to ask wild questions, such as whether a human pancreas can be grown in a pig. Roach’s journey through the operating rooms, transplant labs, and burn units of the world is a tour de force of medical ingenuity and ethical introspection. She doesn’t just dissect the science; she probes the soul of it.

One example is Roach’s exploration of intestinal vaginoplasty, a surgical procedure that uses part of the ascending colon to build a vaginal canal in gender-affirming surgery. Roach sits down with urologist Maurice Garcia over pasta and Chianti to discuss the surgical repurposing of the colon. Roach sets the scene:

I’ve reserved table 12, a cozy corner two-top where most other patrons can’t see or hear you, and the banquette is just long enough for two people to squeeze in side by side. It’s the table for canoodlers, or people having an unrestrained conversation about surgically fashioning a vagina out of the colon. The banquette is good, because later my date, Maurice Garcia, will be coming to sit beside me with his iPad, so he can show me a video of the surgery carried out across the street at Cedars-Sinai Medical Center. Dinner and a movie.

Yet beneath the humor lies a profound respect for the trans women seeking anatomical affirmation and for the surgeons striving to make it happen. The patients detailed in the book are not merely case studies or bodies; they are people with stories.

Throughout the book, Roach is unafraid to ask the awkward questions: Can a finger become a penis? (Yes, it happens in Georgia—the country, not the state.) Is it ethical to grow human organs in pigs? Roach explores the ethical minefield: What if a pig engineered to grow a human organ also ends up with enough human brain cells to foster self-awareness? At what point would different moral standards apply? She delves into ethics surrounding the use of death row prisoners as organ donors in China and the importance of patient autonomy in gender-affirming surgery. Each scenario raises questions that science alone can’t answer.

What makes Replaceable You so compelling isn’t just the remarkable science, but the humanity that Roach uncovers throughout. She introduces us to burn survivors like Diana Tenney, whose story of resilience and recovery is as moving as any medical miracle. Diana survived third-degree burns over 90 percent of her body, endured more than 25 surgeries, and in the process became an advocate and inspiration for burn survivors. Her journey, and her relationship with her husband Jerry, is a testament to the power of support. By telling Diana’s story, Roach reminds us that behind every transplant, every prosthetic, every printed organ there’s a person hoping to reclaim a piece of themselves.

Roach also excels at making complex science accessible and even entertaining. Her chapter on skin grafts to treat burn victims includes a comparison to shawarma slicing:

The skin here is about to be allografted . . . [The doctor] prepares the site with a longish blade called the Goulian (pronounced, with some aptness, ghoul-ian). Strips of flesh are pared with a quick, truncated back-and-forth motion. Where have I seen that, I think. A moment later, it pops to mind: shawarma shop.

And on ECMO patients—people on life support using a process called extracorporeal membrane oxygenation that can provide oxygen to circulating blood when the heart and lungs cannot—she notes that a patient “can do it without ever taking a breath. If they felt like it, they could watch Netflix with their head underwater.” It’s anatomy with a wink, but never at the expense of empathy.

Roach reminds us that behind every transplant, every prosthetic, every printed organ, there’s a person hoping to reclaim a piece of themselves.

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Despite her witty writing, Roach also explores serious issues. Ethics are the connective tissue of this book and woven throughout the chapters. She doesn’t shy away from the moral murkiness of xenotransplantation, chimerism, or the historical use of death row prisoners as organ donors. In the context of gender-affirming surgery, she highlights the importance of listening to patients and respecting their decisions, especially in a field where innovation and identity intersect.

Replaceable You is a love letter to the adaptability of the human body. It’s a celebration of the surgeons who see possibility in scar tissue, the researchers who dream in stem cells, and the patients who endure with grace and grit. Whether you’re a biologist, a bioethicist, or just someone who’s ever stubbed a toe and then wondered why toes stick out so much anyway, this book will leave you marveling at the meat machine we call home. It’s a reminder that regenerative medicine and the science behind it isn’t just about fixing what’s broken; it’s about understanding what it means to be whole.