Everyone’s DNA sequence is unique. But for those who wish to maintain their genetic privacy, it may not be unique enough. A new study argues that more than half of Americans could be identified by name if all you had to start with was a sample of their DNA and a few basic facts, such as the region where they live and about how old they might be. It wouldn’t be simple, and it wouldn’t be cheap. But the fact that it has become doable will force all of us to rethink the meaning of privacy in the DNA age,...