The ultimate cause is the Industrial Revolution. It affects our society in innumerable ways. The intermediate causes are things like smaller family size. If you have a better ratio of adults to children in the home, than an adult vocabulary predominates rather than a child vocabulary. Family size fell in the last century throughout the Western world. Formal schooling is terribly important; it helps you think in the way that IQ testers like. In 1910, schools were focused on kids memorizing things about the real world. Today, they are entirely about relationships. There is also the fact that so many more of us are pursuing cognitively demanding professions. Compared to even 1950, the number of people who are doing technical, managerial or professional jobs has risen enormously. The fact that our leisure has switched away from merely recovery from work towards cognitively taxing pleasures, like playing video games, has also been important.
What goes on in the person’s mind in the test room that allows them to do better on the test? One of the fundamental things is the switch from “utilitarian spectacles” to “scientific spectacles.” The fact that we wear scientific spectacles doesn’t mean that we actually know a lot about science. What I mean is, in 1900 in America, if you asked a child, what do dogs and rabbits have in common, they would say, “Well, you use dogs to hunt rabbits.” This is not the answer that the IQ tests want. They want you to classify. Today, a child would be likely to say, “They are both animals.” They picked up the habit of classification and use the vocabulary of science. They classify the world as a prerequisite to understanding it.
Do IQ gains mean we are more intelligent than our ancestors?
What is important is how our minds differ from those of people 100 years ago, not whether we label it “smarter” or “more intelligent.” I prefer to say our brains are more modern.
Our brains at autopsy are probably different. We have discovered that the brain is like a muscle. A weightlifter has very different muscles than a swimmer. Similarly, we exercise different portions of our brains in a way our ancestors didn’t. They might have had better memories than we do, so they would have a larger hippocampus [a part of the brain that forms, processes and stores memory]. But, we would have exercised certain areas in the prefrontal lobes more than they did. So, those things would be enlarged.
The other important factor is we have learned to use logic to attack the hypothetical. We have an ability to deal with a much wider range of problems than our ancestors would. For example, if you were a businessperson, you would be much more inventive. You would be more imaginative. We are better at executive functions, or at making business decisions. We are also better at moral reasoning.
In your research, you have found that there is a growing gap between the vocabularies of adults and their children. How big is this gap?
You look between 1953 and 2006 on the adult Wechsler IQ test, and its vocabulary subtest, and the gains have been 17.4 points. The gains for schoolchildren during a similar period have been only 4 points. That is a spreading difference of 13 IQ points. That’s huge.
In 1950, something like 12 percent of Americans had experienced at least some tertiary, or post-high school, education; today it is up to 52 percent. More people go into cognitively and verbally demanding professions, like law, school teaching, counseling, psychology and journalism. This has had an effect on adult vocabulary.