In the 1980s, psychologist James Flynn discovered that, over the past century, our average IQ has increased dramatically. The difference, in fact, is so stark that the phenomenon garnered its own name: the Flynn effect.

In today’s talk, Why our IQ levels are higher than our grandparents’, given at TED2013, Flynn explains that if you scored people a century ago against today’s norms, they’d have an IQ of 70, while if you score us against their norms, we’d have an average IQ of 130. In the years since his original discovery, Flynn has investigated just what this evolution is all about. Hint: our ancestors weren’t on the verge of mental retardation, nor are we all intellectually gifted.

Flynn argues that the effect comes down to three types of thinking we currently practice that we didn’t a century ago: “classification, using logic on abstractions, taking the hypothetical seriously,” as he puts it. In other words, kids are tested in school on their ability not just to recite facts, but to apply logic to abstract scenarios. These types of thinking are also demanded by our jobs, as cognitively demanding professions have risen in popularity and importance. “Some of the habits of mind that we have developed over the twentieth century have paid off in unexpected areas,” he says.