NEW YORK—In a report released Tuesday that has been hailed as equal parts fascinating and perplexing, researchers at Columbia University found that requests to prove one is not a robot have gone up 400,000% over the past 500 years. “During the Elizabethan era, for example, people were rarely asked to prove they were not a robot,” said report author Walter Lockwood, who noted that he and his colleagues were left scratching their heads over the staggering increase in requests that had occurred over the past half millennium. “Sixteenth-century Londoners could be fairly certain that when they were interacting with someone, they were interacting with another 16th-century Londoner. But jump ahead 450 years or so, and human beings suddenly find themselves being asked whether or not they are a robot all the time. The only question is, why?” Lockwood also noted that, across time, the frequency of requests to prove one is not a robot appears to be inversely correlated with requests to prove one is not a witch.