Replaceable You: The new era of body-part replacement moves from sci-fi to clinics

Mary Roach's Replaceable You: Adventures in Human Anatomy surveys how the line between science fiction and the operating room is narrowing. The book argues we are living in an era of discoveries that feel wondrous, improbable, and surreal, as researchers pursue lab-grown parts, animal donors, and novel techniques that may extend and improve life.

In the heart of Roach's reporting is a shift in transplant technology. In some laboratories, surgeons are using heart-in-a-box machines that keep donor hearts beating far longer than before, extending viability from four hours to as much as twelve. Longer windows translate to more transplants and more people given a second chance. The donor animal most often used for comparison is the pig, whose heart and anatomical structure resemble a human's closely enough to be a tractable option for future xenotransplantation. In 2022, surgeons at the University of Maryland transplanted a pig heart into a human patient who lived for about two months, and other teams have implanted pig kidneys into brain-dead patients with some success.

If early results hold, experts predict xenotransplants could become far more common within the next decade. Some clinicians imagine a future in which each patient has their own genetically matched organ set, a personal herd of spare parts edited to reduce rejection. The notion of a barnyard of replacement parts echoes the science-fiction resonance of The Six Million Dollar Man, a theme that Roach notes is increasingly plausible in the clinic.

Beyond hearts, researchers are turning to other animals for substitutes. A Boston plastic surgeon who treats burn victims has experimented with cod skin as a graft material. It seals wounds, reduces infection, and can promote faster healing, sometimes at a cost advantage over synthetic dressings. The incentive structure is pragmatic: insurers will even reimburse more for cod skin than for cheaper options, a detail that Roach attributes to the economics of hospital care. In the operating room, the lexicon of repair can sound almost comic: a dermatome is likened to a medical-grade cheese slicer, and a perfusion cart resembles a salad spinner for organs. Yet the stakes are human lives.

One of the most striking anecdotes Roach recounts is from a plastic surgeon in the country of Georgia, Iva Kuzanov. He has performed finger-to-penis reconstructions by transplanting a patient’s own finger bones and rerouting the urethra to fashion a functional core. He describes cases in which a patient, after surgery, could urinate standing up, a result that was described by a wife who welcomed the return of normal life. If the technology grows more common, such procedures may be sparing for people with complex injuries or deformities and could touch on broader discussions about gender and anatomy.

The frontier Roach surveys also encompasses future promises: 3D-printed organs that could one day replace waiting lists, robotic prosthetics that respond to brain signals and outpace natural flesh, and lab-grown hair follicles that might reverse baldness. None of these are routine yet, but each represents a step toward a future in which replacement becomes as ordinary as repair. The tone is tempered by Roach's insistence that progress does not march in a straight line; she writes that advances typically lurch forward, then stall, then leap again.

The core idea of Replaceable You is not that medicine will turn people into superheroes, but that careful, pragmatic fixes can restore function, dignity, and years of life that might otherwise be lost. The miracles, in Roach's telling, are the everyday gains—faster transplant windows, infections kept in check by novel graft materials, and new urethral reconstructions—that allow people to live fuller lives, laugh, and share meals with their loved ones.