We all assume we know what life is, but the more scientists learn about brains, zygotes, and pandemic viruses, the more complex the issue becomes. The question hangs over some of society's most charged conflicts, including whether a fertilized egg is a living person, and when a person is considered legally dead. As the author of She Has Her Mother's Laugh points out, chemists are creating droplets that can sense their environment and multiply. Have they made life in the lab? Charting our fascination with such Frankenstein monsters, Carl Zimmer finds a wide array of answers.