Title:

Replaceable You

Author:

Mary Roach

Category:

Non-fiction

Rating:

Date Reviewed:

August 16, 2026

eplaceable You is about our efforts to create human body parts to replace our failing organs. It is a survey of the latest research in all sorts of medical endeavors. Some sound more promising than others. The book begins with a brief history of false teeth. It turns out that dentures are not very useful for chewing - people with dentures would eat in their rooms, using a tool called a masticator that would "pre-chew" their food so that they could swallow it. Then they would sit at the dinner table but not eat anything. They had to keep their mouth tightly shut due to the propensity of the spring-loaded teeth to shoot out of their mouth. This is why George Washington always has his mouth grimly locked tight in all of his portraits. Dentures were apparently common even in the 1940s, 1950s and 1960s. People would have their remaining teeth pulled and switch to false teeth rather than go through the bother of having them extracted one at a time as each one rotted away. I do remember Poligrip commercials on TV when I was a kid. A survey of denture wearers said that 53% of them had gotten their dentures when less than 45 years old. Of course, fluoride in the water supply didn't become standard until the 1960s, which might have something to do with all of those bad teeth.

Some of the topics covered are attempts to create artificial skin (to help burn victims), or to grow organs in pigs that could be transplanted into humans. This cross-species procedure is called xenotransplantation. The hope is that hearts, pancreas, kidneys, liver, etc, could be grown in a pig and then moved into a human. Gene-editing techniques would allow the pig's organ to closely match the human recipient so that the immune system would not reject it. (China has a huge shortage of organ donors, but an abundance of pigs. Roach describes a 26 story pig farm in China, and I don't think she was joking.)

There are chapters on constructing replacement vaginas, penises, hips, prosthetic limbs, corneas. I was fascinated by the promise of the stem cell research. In 2006, Dr Shinya Yamanaka discovered a procedure to take ordinary red blood cells and reverse them back into stem cells. Once you have a patient's stem cells, the hope is to induce them to grow into replacement cells, such as new neurons to cure Parkinsons, or new pancreas cells to cure diabetes. In the far future, perhaps the stem cells could be induced to grow a new replacement organ, but that is well beyond present capabilities.

Replaceable You has plenty of astonishing information, but reading the following paragraphs amazed me the most of all (the scientists are trying to discover ways to lengthen the amount of time a heart can be detached from the body; this will allow for more time to do heart transplants) :

"For reasons that remain a mystery, a heart needs a brain. When person is declared brain-dead, their heart - along with their other organs - begins to fail after around twelve hours, even if the body is being oxygenated on a ventilator. The blood vessels lose tone, the capillaries start to leak, and within forty-eight hours its all over.

If a head-injury or illness were to leave a pregnant person brain-dead, on a ventilator, their organs would keep functioning for the duration of the pregnancy. But once the baby is delivered, the familiar cascade of organ failure would begin. The baby's brain appears to be producing something that sustains the organs of the mother.

The reverse scenario also holds. "Very rarely," Bartlett continues, "a fetus develops without a brain." The "acephalic" baby's organs will continue to function as long as it is inside the mother's womb. "As soon as the fetus is delivered, it dies." Bartlett says. "You need one brain or the other." He reasons that there's a necessary hormone, or possibly several, produced inside the hypothalamus, inside the midbrain. "The hypothalamus consists of hundreds of clusters of hormone-producing cells. We know what four or five of them do, but not the rest."

At the end of Replaceable You, Roach inserts a note that said that the book went to press in 2025, just as the Trump administration was gutting the NIH. Much of the research described in the book was funded by NIH grants, so it is possible that many of the amazing things that scientists and doctors were working on all got tossed out the window. It is hard to imagine a better example of "penny-wise but pound foolish".