In the 1970s TV show called Six Million Dollar Man, a test pilot is in a horrible accident. The show's famous line goes, "We can rebuild him. We have the technology."

Now, in the 2025 book, Replaceable You , science writer Mary Roach explores how people have collectively lived up to the task of rebuilding human bodies when they fail, as well as all the ways we may not quite be there yet.

Roach looks at everything from pig organs to hair follicles to try to answer the question, how replaceable are you?

Interested in more science behind the human body? Check out our episodes on synthetic cells and the first pig kidney transplant . Email us your question at shortwave@npr.org .

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