Are you smarter than your great-grandmom? If IQ really measures intelligence, the answer is probably a resounding “yes.”  IQ tests are “normed”: Your score reflects how you did compared with other people, like being graded on a curve. But the test designers, who set the average in a given year at 100, have to keep “renorming” the tests, adding harder questions. That’s because absolute performance on IQ tests—the actual number of questions people get right—has greatly improved over the last 100 years. It’s called the Flynn effect, after James Flynn, a social scientist at New Zealand’s University of Otago who first noticed it in the 1980s.  How robust is the Flynn effect, and why has it happened? In the journal Perspectives in Psychological Science, Jakob Pietschnig and Martin Voracek at the University of Vienna report a new “meta-analysis.” They combined data from 271 studies, done from 1909 to 2013, testing almost four million people from 31 countries on six continents. Most of the test questions remain the same over time, so the scientists could look at how much people improved from decade to decade.  They found that the Flynn effect is real—and large. The absolute scores consistently improved for children and adults, for developed and developing countries. People scored about three points more every decade, so the average score is 30 points higher than it was 100 years ago.  The speed of the rise in scores varied in an interesting way. The pace jumped in the 1920s and slowed down during World War II. The scores shot up again in the postwar boom and then slowed down again in the ’70s. They’re still rising, but even more slowly. Adult scores climbed more than children’s.  Why? There are a lot of possible explanations, and Drs. Pietschnig and Voracek analyze how well different theories fit their data. Genes couldn’t change that swiftly, but better nutrition and health probably played a role. Still, that can’t explain why the change affected adults’ scores more than children’s. Economic prosperity helped, too—IQ increases correlate significantly with higher gross domestic product.  The fact that more people go to school for longer likely played the most important role—more education also correlates with IQ increases. That could explain why adults, who have more schooling, benefited most. Still, the Flynn effect has a strong impact on young children. Education, just by itself, doesn’t seem to account for the whole effect.  The best explanation probably depends on some combination of factors. Dr. Flynn himself argues for a “social multiplier” theory. An initially small change can set off a benign circle that leads to big effects. Slightly better education, health, income or nutrition might make a child do better at school and appreciate learning more. That would motivate her to read more books and try to go to college, which would make her even smarter and more eager for education, and so on.  “Life history” is another promising theory. A longer period of childhood correlates with better learning abilities across many species. But childhood is expensive: Someone has to take care of those helpless children. More resources, nutrition or health allow for a longer childhood, while more stress makes childhood shorter. Education itself really amounts to a way of extending the childhood learning period.  But are you really smarter than your great-grandmom? IQ tests measure the kind of intelligence that makes you do well at school. If we had tests for the kind of intelligence that lets you run a farm, raise eight children and make perfect biscuits on a smoky wood stove, your great-grandmom might look a lot smarter than you do.  The thing that really makes humans so smart, throughout our history, may be that we can invent new kinds of intelligence to suit our changing environments.
New research confirms world-wide tests showing IQs have risen for more than a century. Alison Gopnik on the reasons why.