Computers seem to be replacing humans across many industries, and we're all getting very nervous. ... But if you want some reason for optimism, visit your local supermarket. ... In a recent research paper called "Dancing With Robots," the economists Frank Levy and Richard Murnane point out that computers replace human workers only when machines meet two key conditions. First, the information necessary to carry out the task must be put in a form that computers can understand, and second, the job must be routine enough that it can be expressed in a series of rules. ... Supermarket checkout machines meet the second of these conditions, but they fail on the first. They lack proper information to do the job a human would do. To put it another way: They can't tell shiitakes from Shinola. Instead of identifying your produce, the machine asks you, the customer, to type in a code for every leafy green in your cart. Many times you'll have to look up the code in an on-screen directory. If a human checker asked you to remind him what that bunch of the oblong yellow fruit in your basket was, you'd ask to see his boss. ... This deficiency extends far beyond the checkout lane.