Some suspect the change has something to do with the evolution in how foods are grown and produced, like the crossbreeding of wheat or the use of antibiotics in cattle.

NPR: Study: Food, Skin Allergies Increasing In Children

Speaking for the industry, Stuart Ingis, general counsel for the Digital Advertising Alliance, said the decision to adopt do-not-track is an "evolution" of the industry's approach.

WSJ: Web Companies Agree to Support 'Do Not Track' System

So what do these trends tell us about the demographic evolution of our major metropolitan areas?

FORBES: America's Fastest- and Slowest-Growing Cities