How to Grow a Human: Adventures in How We Are Made and Who We Are

Two summers ago, scientists removed a tiny piece of flesh from Philip Ball’s arm and turned it into a rudimentary “mini-brain.” The skin cells, removed from his body, did not die but were instead transformed into nerve cells that independently arranged themselves into a dense network and communicated with each other, exchanging the raw signals of thought. This was life—but whose?

In his most mind-bending book yet, Ball makes that disconcerting question the focus of a tour through what scie...