You can ditch your computer and leave your cellphone at home, but you can’t escape your DNA. It belongs uniquely to you—and, increasingly, to the authorities. Countries around the world are collecting genetic material from millions of citizens in the name of fighting crime and terrorism—and, according to critics, heading into uncharted ethical terrain. … The international police agency Interpol listed 54 nations with national police DNA databases in 2009, including Australia, Canada, France, Germany and China. Brazil and India have since announced plans to join the club, and the United Arab Emirates intends to build the world’s first database...